US20040266902A1 - Crosslinking of polyethylene for low wear using radiation and thermal treatments - Google Patents

Crosslinking of polyethylene for low wear using radiation and thermal treatments Download PDF

Info

Publication number
US20040266902A1
US20040266902A1 US10/858,528 US85852804A US2004266902A1 US 20040266902 A1 US20040266902 A1 US 20040266902A1 US 85852804 A US85852804 A US 85852804A US 2004266902 A1 US2004266902 A1 US 2004266902A1
Authority
US
United States
Prior art keywords
joint
joint prosthesis
bearing component
mrad
wear
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US10/858,528
Inventor
Fu-Wen Shen
Harry McKellop
Ronald Salovey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Family has litigation
First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=27360900&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=US20040266902(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Priority claimed from US09/214,586 external-priority patent/US6228900B1/en
Application filed by Individual filed Critical Individual
Priority to US10/858,528 priority Critical patent/US20040266902A1/en
Publication of US20040266902A1 publication Critical patent/US20040266902A1/en
Priority to US11/982,071 priority patent/US20080133021A1/en
Abandoned legal-status Critical Current

Links

Images

Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2/30767Special external or bone-contacting surface, e.g. coating for improving bone ingrowth
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2/46Special tools or methods for implanting or extracting artificial joints, accessories, bone grafts or substitutes, or particular adaptations therefor
    • A61F2/468Testing instruments for artificial joints
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61LMETHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L27/00Materials for grafts or prostheses or for coating grafts or prostheses
    • A61L27/14Macromolecular materials
    • A61L27/16Macromolecular materials obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C71/00After-treatment of articles without altering their shape; Apparatus therefor
    • B29C71/02Thermal after-treatment
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C71/00After-treatment of articles without altering their shape; Apparatus therefor
    • B29C71/04After-treatment of articles without altering their shape; Apparatus therefor by wave energy or particle radiation, e.g. for curing or vulcanising preformed articles
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00Processes of treating or compounding macromolecular substances
    • C08J3/28Treatment by wave energy or particle radiation
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J7/00Chemical treatment or coating of shaped articles made of macromolecular substances
    • C08J7/08Heat treatment
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J7/00Chemical treatment or coating of shaped articles made of macromolecular substances
    • C08J7/12Chemical modification
    • C08J7/123Treatment by wave energy or particle radiation
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2/3094Designing or manufacturing processes
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2/32Joints for the hip
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2/32Joints for the hip
    • A61F2/34Acetabular cups
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2002/30001Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
    • A61F2002/30003Material related properties of the prosthesis or of a coating on the prosthesis
    • A61F2002/3006Properties of materials and coating materials
    • A61F2002/30084Materials having a crystalline structure
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2/32Joints for the hip
    • A61F2/34Acetabular cups
    • A61F2002/3412Acetabular cups with pins or protrusions, e.g. non-sharp pins or protrusions projecting from a shell surface
    • A61F2002/3414Polar protrusion, e.g. for centering two concentric shells
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2/32Joints for the hip
    • A61F2/34Acetabular cups
    • A61F2002/3429Acetabular cups with an integral peripheral collar or flange, e.g. oriented away from the shell centre line
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2/32Joints for the hip
    • A61F2/36Femoral heads ; Femoral endoprostheses
    • A61F2/3609Femoral heads or necks; Connections of endoprosthetic heads or necks to endoprosthetic femoral shafts
    • A61F2002/3611Heads or epiphyseal parts of femur
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C35/00Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/02Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
    • B29C35/08Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
    • B29C35/0805Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
    • B29C2035/085Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using gamma-ray
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C71/00After-treatment of articles without altering their shape; Apparatus therefor
    • B29C71/02Thermal after-treatment
    • B29C2071/022Annealing
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C43/00Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C43/00Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
    • B29C43/02Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles
    • B29C43/16Forging
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29KINDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2023/00Use of polyalkenes or derivatives thereof as moulding material
    • B29K2023/04Polymers of ethylene
    • B29K2023/06PE, i.e. polyethylene
    • B29K2023/0658PE, i.e. polyethylene characterised by its molecular weight
    • B29K2023/0675HMWPE, i.e. high molecular weight polyethylene
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29KINDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2023/00Use of polyalkenes or derivatives thereof as moulding material
    • B29K2023/04Polymers of ethylene
    • B29K2023/06PE, i.e. polyethylene
    • B29K2023/0658PE, i.e. polyethylene characterised by its molecular weight
    • B29K2023/0683UHMWPE, i.e. ultra high molecular weight polyethylene
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29KINDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2995/00Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
    • B29K2995/0037Other properties
    • B29K2995/0087Wear resistance
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29KINDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2995/00Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
    • B29K2995/0037Other properties
    • B29K2995/0089Impact strength or toughness
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29LINDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2031/00Other particular articles
    • B29L2031/753Medical equipment; Accessories therefor
    • B29L2031/7532Artificial members, protheses
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2323/00Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2323/02Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2323/04Homopolymers or copolymers of ethene
    • C08J2323/06Polyethene
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S525/00Synthetic resins or natural rubbers -- part of the class 520 series
    • Y10S525/937Utility as body contact e.g. implant, contact lens or I.U.D.

Definitions

  • Ultrahigh molecular weight polyethylene (hereinafter referred to as “UHMWPE”) is commonly used to make prosthetic joints such as artificial hip joints.
  • UHMWPE Ultrahigh molecular weight polyethylene
  • tissue necrosis and interface osteolysis in response to UHMWPE wear debris, are primary contributors to the long-term loosening failure of prosthetic joints.
  • wear of acetabular cups of UHMWPE in artificial hip joints introduces many microscopic wear particles into the surrounding tissues. The reaction to these particles includes inflammation and deterioration of the tissues, particularly the bone to which the prosthesis is anchored. Eventually, the prosthesis becomes pain-fully loose and must be replaced.
  • the present invention comprises two aspects:
  • the first aspect of the invention presents a method for increasing the wear resistance of a polymer by crosslinking the polymer, followed by thermally treating the crosslinked polymer.
  • the thermal treatments are remelting or annealing.
  • the polymer is crosslinked by gamma irradiation in the solid state prior to being modified to a desired final form or shape of the final product.
  • the surface layer of the crosslinked and thermally treated polymer which is the most oxidized and least crosslinked part of the polymer, is removed, e.g., in the process of machining the final product out of the irradiated bar and thermally treated bar or block.
  • the radiation dose is also preferably adjusted so that the optimal dose occurs within the solid polymer bar or block at the level of the bearing surface of the final product.
  • the polymers made from this method methods for making products (e.g., in vivo implants) from these polymers; and the products (e.g.,in vivo implants) made from these polymers.
  • the second aspect of the invention provides a systematic method for determining an optimal balance among wear resistance and other physical and/or chemical properties that are deemed important to the long-term performance of an implant in vivo, and applying this optimal balance to determine the appropriate crosslinking and thermal treatment conditions for processing a polymer.
  • a flowchart is provided as a non-limiting illustration of the method for determining the optimal balance.
  • methods for treating polymers which apply the above appropriate crosslinking and thermal treatment conditions; the polymers produced by these methods; methods for making products (e.g., in vivo implants) from these polymers; and the products (e.g.,in vivo implants) made from these polymers.
  • FIG. 1 presents the degree of crystallinity vs. depth at indicated doses for UHMWPE that was irradiated in a vacuum (i.e., a low-oxygen atmosphere).
  • FIG. 2 presents the gel content vs. depth at indicated doses for UHMWPE that was irradiated in a vacuum (i.e., a low-oxygen atmosphere).
  • FIG. 3 presents the gel content vs. depth at indicated conditions for UHMWPE.
  • FIG. 5 presents the gel content vs. depth at indicated conditions for UHMWPE.
  • FIG. 6 presents the shape of the acetabular cup fabricated from the irradiated UHMWPE.
  • FIG. 7 presents a schematic diagram of the hip joint simulator used in the wear tests.
  • FIG. 8 presents the wear by volume loss of each cup of the four materials. Upper curves: 3.3 Mrad; Lower curves: 28 Mrad.
  • FIG. 9 presents the curves of the average volumetric wear and standard deviations of three cups of each material at each interval.
  • FIG. 10 presents the oxidation profile as a function of depth at various aging times.
  • FIG. 11 presents the oxidation profile as a function of depth at various aging times.
  • FIG. 12 presents the oxidation profile as a function of depth at various aging times.
  • FIG. 13 presents the oxidation profile as a function of depth at various aging times.
  • FIG. 14 presents the oxidation profile as a function of depth for various materials. The specimens were stored in air for 5 months and then aged for 20 days at 80° C.
  • FIG. 15 presents gel content as a function of depth at various aging times.
  • FIG. 16 presents gel content as a function of depth at various aging times.
  • FIG. 17 presents gel content as a function of depth at various aging times.
  • FIG. 18 presents gel content as a function of depth at various aging times.
  • FIG. 19 presents the degree of crystallinity as a function of depth after 30 days' aging.
  • FIG. 20 shows the combined soak-corrected wear for the non-aged and aged cups.
  • FIG. 21 shows the individual wear for cups irradiated at different doses.
  • FIG. 22 shows the average wear rate versus radiation dose of non-remelted and remelted cups.
  • FIGS. 23A and 23B present the flowchart illustrating so the optimization method of the present invention.
  • FIG. 24 graphically shows the oxidation profiles for irradiated and remelted UHMWPE as a function of depth from the UHMWPE bar surface.
  • FIG. 25 graphically shows the tensile strength at yield versus radiation dose of irradiated UHMWPE with or without remelting, and non-irradiated and not remelted UHMWPE.
  • FIG. 26 graphically shows the tensile strength at break versus radiation dose of irradiated UHMWPE with or without remelting, and non-irradiated and not remelted UHMWPE.
  • UHMWPE ultra-high molecular weight polyethylene
  • HMWPE high molecular weight polyethylene
  • the present invention contains two aspects.
  • the first aspect of the invention provides methods for improving the wear resistance of a polymer by crosslinking (preferably the bearing surface of the polymer) and then thermally treating the polymer, and the resulting novel polymer. Preferably, the most oxidized surface of the polymer is also removed.
  • the methods for using the polymeric compositions for making products and the resulting products e.g., in viva implants. Specific examples of this method are presented in the section: “I. First Aspect of the Invention: Polymeric Compositions with Increased Wear Resistance” and “I (A) Further Examples of the First Aspect of the Invention”, below.
  • the method of the invention utilizes irradiation for crosslinking a polymer followed by thermal treatment to decrease the free radicals to produce a preformed polymeric composition.
  • preformed polymeric composition means that the polymeric composition is not in a final desired shape or form (i.e., not a final product).
  • the final product of the preformed polymeric composition is an acetabular cup
  • irradiation and thermal treatment of the polymer could be performed at pre-acetabular cup shape, such as when the preformed polymeric composition is in the form of a solid bar or block.
  • the wear resistance of the polymer is improved by crosslinking.
  • the crosslinking can be achieved by various methods known in the art, for example, by irradiation from a gamma radiation source or from an electron beam, or by photocrosslinking.
  • the preferred method for crosslinking the polymer is by gamma irradiation.
  • the polymer is preferably crosslinked in the form of an extruded bar or molded block.
  • the crosslinked polymer is subjected to thermal treatment such as by remelting (i.e., heated above the melting temperature of the crosslinked polymer) or annealing (i.e., heated at below the melting temperature of the crosslinked polymer) to produce the preformed polymeric composition.
  • thermal treatment such as by remelting (i.e., heated above the melting temperature of the crosslinked polymer) or annealing (i.e., heated at below the melting temperature of the crosslinked polymer) to produce the preformed polymeric composition.
  • the outer layer of the resulting preformed polymeric composition which is generally the most oxidized and least crosslinked and, thus, least wear resistant, is removed.
  • the bearing surface of the preformed polymeric composition may be fashioned from inside, e.g., by machining away the surface of the irradiated and thermally treated composition before or during fashioning into the final product, e.g., into an implant. Bearing surfaces are surfaces which are in moving contact with another, e.g., in a sliding, pivoting, or rotating relationship to one another.
  • the polymers are generally polyester, poly(methylmethacrylate), nylon, polycarbonates, and polyhydrocarbons such as polyethylene, and polypropylene.
  • High molecular weight (HMW) and ultra-high molecular weight (UHMW) polymers are preferred, such as HMW polyethylene (HMWPE), UHMW polyethylene (UHMWPE), and UHMW polypropylene.
  • HMW polymers have molecular weights ranging from about 10 5 grams per mole to just below 10 6 .
  • UHMW polymers have molecular weights equal to or higher than 10 6 grams per mole, preferably from 10 6 to about 10 7 .
  • the polymers are generally between about 400,000 grams per mole to about 10,000,000 and are preferably polyolefinic materials.
  • the preferred polymers are those that are wear resistant and have exceptional chemical resistance.
  • UHMWPE is the most preferred polymer as it is known for these properties and is currently widely used to make acetabular cups for total hip prostheses and components of other joint replacements.
  • UHMWPE examples of UHMWPE are those having molecular weight ranging from about 1 to 8 ⁇ 10 6 grams per mole, examples of which are: GUR 4150 or 4050 (Hoechst-Celanese Corporation, League City, Tex.) with a weight average molecular weight of 5 to 6 ⁇ 10 6 grams per mole; GUR 4130 with a weight average molecular weight of 3 to 4 ⁇ 10 6 ; GUR 4120 or 4020 with a weight average molecular weight of 3 to 4 ⁇ 10 6 ; RCH 1000 (Hoechst-Celanese Corp.)with a weight average of molecular weight of 4 ⁇ 10 6 and HiFax 1900 of 2 to 4 ⁇ 10 6 (HiMont, Elkton, Md.). Historically, companies which make implants have used polyethylenes such as HIFAX 1900, GUR 4020, GUR 4120 and GUR 4150 for making acetabular cups.
  • GUR 4150 or 4050 Hoechst-Celanese Corporation,
  • All polymeric products must be sterilized by a suitable method prior to implanting in the human body.
  • a suitable method for the formed crosslinked and thermally treated polymeric compositions (i.e., the final products) of the present invention, it is preferable that the products be sterilized by a non-radiation based method, such as ethylene oxide or gas plasma, in order not to induce additional crosslinking and/or oxidation of the previously treated preformed polymeric composition.
  • a non-radiation sterilization method has a minor effect on the other important physical characteristics of the product.
  • the method can be used in conjunction with radiation sterilization. If the final products are to be sterilized by an additional dose of radiation, it is preferable to take into account the effect of this additional radiation dose on the wear resistance and other properties of the polymer, in determining the optimum radiation dose used in the initial crosslinking. Furthermore, it is preferable that the radiation sterilization be done while the final product (e.g., in vivo implant) is packed in a suitable low-oxygen atmosphere (e.g., in partial vacuum, in an inert gas such as nitrogen, or with an oxygen scavenger included) in order to minimize oxidation of the surface layer of the final product during and after sterilization by irradiation.
  • a suitable low-oxygen atmosphere e.g., in partial vacuum, in an inert gas such as nitrogen, or with an oxygen scavenger included
  • the dose ranges in this application do not take into account radiation sterilization. If radiation sterilization is used, then the dose ranges may have to be adjusted. Such adjustment can be easily performed using the teachings herein. For example, if after comparing the dose-response curves for wear with those for other important physical or chemical properties, it is determined that the optimal total radiation dose is 8 Mrad, and it is intended to sterilize the polymer with 2.5 Mrad gamma radiation (the minimum industrial standard sterilization dose), then the initial radiation dose (before sterilization) should be 5.5 Mrad, such that the total dose (initial plus sterilization doses) will be 8 Mrad. These calculations are approximate, since the total crosslinking achieved will not be exactly equivalent to a single 8 Mrad dose.
  • the degree of crystallinity can be determined using methods known in the art, e.g. by differential scanning calorimetry (DSC), which is generally used to assess the crystallinity and melting behavior of a polymer.
  • DSC differential scanning calorimetry
  • Wide-angle X-ray scattering from the resulting polymer can also be used to further confirm the degree of crystallinity of the polymer, e.g. as described in Spruiell, J. E., & Clark, E. S., in “ Methods of Experimental - Physics ”, L. Marton & C. Marton, Eds., Vol. 16, Part S, Academic Press, New York (1980).
  • Other methods for determining the degree of crystallinity of the resulting polymer may include Fourier Transform Infared Spectroscopy ⁇ Painter, P. C. et al., “The Theory Of Vibrational Spectroscopy And Its Application To Polymeric Materials”, John Wiley and Sons, New York, U.S.A.
  • Another aspect of the invention presents a process for making implants using the preformed polymeric composition of the present invention.
  • the preformed polymeric composition may be shaped, e.g., machined, into the appropriate implants using methods known in the art.
  • the shaping process such as machining, removes the oxidized surface of the composition.
  • the preformed polymeric compositions of the present invention can be used in any situation where a polymer, especially UHMWPE, is called for, but especially in situations where high wear resistance is desired. More particularly, these preformed polymeric compositions are useful for making implants.
  • the preformed polymeric compsition can be used to make the tibial plateau (femoro-tibial articulation), the patellar button (patello-femoral articulation), and trunnion or other bearing components, depending on the design of the artificial knee joint.
  • the preformed polymeric composition can be used to make the talar surface (tibio-talar articulation) and other bearing components.
  • the preformed polymeric composition can be used to make the radio-numeral joint, ulno-humeral joint, and other bearing components.
  • the preformed polymeric composition can be used to make the glenoro-humeral articulation, and other bearing components.
  • the preformed polymeric composition can be used to make intervertebral disk replacement and facet joint replacement.
  • the preformed polymeric composition can also be made into temporo-mandibular joint (jaw) and finger joints.
  • jaw temporo-mandibular joint
  • finger joints The above are by way of example, and are not meant to be limiting.
  • the first aspect of the invention provides preformed polymeric compositions which are wear resistant and useful for making in vivo implants.
  • the irradiation dose is preferably from about 1 to about 100 Mrad, and more preferably, from about 5 to about 25 Mrad, and most preferably from about 5 to about 10 Mrad. This most preferable range is based on achieving what the inventors have determined to be a reasonable balance between improved wear resistance and minimal degradation of other important physical properties.
  • a higher dose than the above stipulated most preferable range e.g., 5 to 10 Mrad
  • the optimum radiation dose is preferably based on the dose received at the level of the bearing surface in the final product. Gamma radiation is preferred.
  • the irradiated polymer is then preferably remelted at or above melting temperature of the irradiated polymer, e.g., in air.
  • the melting temperature of the crosslinked or irradiated polymer is identified from the peak of the melting endotherm as measured by DSC.
  • the remelting temperature is from about the melting temperature of the irradiated polymer to about 100° C. to about 160° C. above the melting temperature of the irradiated polymer; more preferably from about 40° C. to about 80° C. above the melting temperature of the irradiated polymer; and most preferably from about 1° C. to about 60° C. above the melting temperature of the irradiated polymer.
  • the remelting temperature is preferably from about 136° C. to about 300° C., more preferably from about 136° C. to about 250° C., and most preferably from about 136° C. to about 200° C. Specific conditions for remelting are described in EXAMPLES 1 and 2, below.
  • the remelting temperature is inversely proportional to the remelting period.
  • the polymer is preferably remelted over a period from about 1 hour to about 2 days, more preferably from about 1 hour to about 1 day, and most preferably from about 2 hours to about 12 hours.
  • annealing Since, depending on the time and temperature applied, annealing can produce less of an effect than remelting on physical properties such as crystallinity, yield strength and ultimate strength, annealing may be used in place of remelting as a means for reducing the free radicals remaining in the polymer after irradiation crosslinking, in order to maintain these physical properties within limits required by the user.
  • Thermal treatment such as remelting or annealing, removes free radicals and thereby improves long term wear resistance of the polymer.
  • annealing is slower and thus takes longer than remelting, making it likely to be more expensive in industrial applications.
  • the annealing temperature is preferably from about room temperature to below the melting temperature of the irradiated polymer; more preferably from about 90° C. to about 1° C. below the melting temperature of the irradiated polymer; and most preferably from about 60° C. to about 1° C. below the melting temperature of the irradiated polymer.
  • UHMWPE may be annealed at a temperature from about 25° C. to about 135° C., preferably from about 50° C. to about 135° C., and more preferably from about 80° C. to about 135° C.
  • the annealing period is preferably from about 2 hours to about 7 days, and more preferably from about 7 hours to about 5 days, and most preferably from about 10 hours to about 2 days.
  • the appropriate amount of crosslinking may be determined based on the degree of swelling, gel content, or molecular weight between crosslinks after thermal treatment. This alternateative is based on the applicant's findings (detailed below) that acetabular cups made from UHMWPE falling within a preferred range of these physical parameters have reduced or non-detectable wear.
  • the ranges of these physical parameters include one or more of the following: a degree of swelling of between about 1.7 to about 5.3; molecular weight between crosslinks of between about 400 to about 8400 g/mol; and a gel content of between about 95% to about 99%.
  • a preferred polymer or final product has one or more, and preferably all, of the above characteristics.
  • the most oxidized surface of the preformed polymeric composition is removed.
  • the depth profiles of oxidation of the preformed polymeric composition can be determined by methods known in the art, such as FTIR, described above and in EXAMPLES 3 and 6.
  • FTIR FTIR
  • EXAMPLES 3 and 6 EXAMPLES 3 and 6.
  • a minimum of about 0.5 mm to 1.0 mm of the surface of preformed polymeric composition which is exposed to air is removed, e.g. by machining, before or while fashioning the preformed polymeric composition into the final product.
  • the user desires to achieve a minimum wear rate of the in vivo implant made from the UHMWPE and HMWPE, and the other physical or chemical properties are important but of lesser concern.
  • the user may choose to irradiate the UHMWPE and HMWPE bar or block between about 15 Mrad to about 20 Mrad (as shown by FIG. 22).
  • GUR 4150 is representative of UHMWPE and HMWPE. The irradiated UHMWPE or HMWPE bar or block is further remelted or annealed at a temperature and time described in “I. First Aspect of the Invention: Polymeric Compositions with Increased Wear Resistance”, above.
  • the user may wish to produce an UHMWPE which is as wear resistant as possible while meeting the tensile strength at break (ultimate), tensile strength at yield, and elongation at break criteria of the standard specified by the American Society for Testing and Materials F-648 standard (hereinafter referred to as “ASTM F648”) for UHMWPE for in vivo use.
  • ASTM F648 American Society for Testing and Materials F-648 standard
  • the information about this standard can be found in a current issue of the Annual Book of ASTM Standards, Medical Devices and Services, “Standard Specification for Ultra-High-Molecular-Weight Polyethylene Powder and Fabricated Form for Surgical Implants”, American Society for Testing and Materials.
  • the method of the second aspect of the present invention (as illustrated by the flowchart) may be used to adjust the crosslinking and thermal treatment parameters to meet any current ASTM F648 criteria.
  • the UHMWPE must have: a tensile strength at break (ultimate) of at least 35 MPa (for Type 1) and 27 MPa (for Type 2) at 23° C. and 5.08 cm/min; a tensile strength-at yield of at least 21 MPa (Type 1) and 19 MPa (for Type 2) at 23° C., and 5.08 cm/min; and elongation at break of at least 300% at 5.08 cm/min.
  • the test conditions are described in ASTM D638, Type IV ( Annual Book of ASTM Standards, American Society for Testing and Materials).
  • the second aspect of the invention uses the findings in this patent application (including those presented in the “EXAMPLES” section, below) to construct a method which allows one skilled in the art, to systematically identify the conditions necessary to routinely produce a polymer with an optimal balance of wear resistance and physical and/or chemical properties, with minimal additional testing and minimal trial and error.
  • the optimizing method can be schematically illustrated in a flowchart. Once the optimal conditions have been determined by this method, the polymer can then be subjected to these conditions for processing.
  • the present invention is based in part, on the discovery that wear rate decreases with increasing radiation dose, and there is a maximum dose above which there is little or no additional improvement in wear, but higher doses might degrade other important physical and/or chemical properties of the polymer, such as yield or ultimate strength, elongation to failure, impact strength or fatigue resistance, as well as increasing the susceptibility to oxidation. Oxidation, in turn, is known to adversely affect one or more of these physical properties, and was shown to occur in the examples below for UHMWPE crosslinked at a dose averaging about 28 Mrad if there had been no thermal treatment. Consequently, a polymer irradiated at a high radiation dose may exhibit improved wear resistance, but its other physical or chemical properties may fall outside of desirable or allowable limits, such as those specified by ASTM F648 for UHMWPE for in vivo use.
  • the method is also based in part on the discovery that, while other important physical properties (such as crystallinity or elongation to break) may be markedly affected by the amount of thermal treatment (e.g., remelting or annealing) applied to the polymer after irradiation crosslinking, the wear resistance is not markedly affected.
  • This latter discovery permits reducing the amount of additional testing required by the user in order to identify the crosslinking dose which will provide the user's desired balance among wear resistance and other physical properties.
  • This method is useful, e.g., in the case where performed polymeric composition made of UHMWPE is used for making in vivo implants, such as acetabular cups.
  • the second aspect of the present invention provides a systematic method for optimizing the balance among wear resistance and other desired physical and/or chemical characteristics of a polymer.
  • the steps in this method are summarized in the non-limiting example of the flowchart of FIGS. 23A and 23B.
  • irradiation is used as an example of a crosslinking method
  • implant is used as an example of the product that is made from the polymer.
  • other crosslinking methods and products may be used.
  • Step 2 The bar is irradiated over a range of doses up to the maximum that is likely to produce a material with the desired wear resistance and physical and/or chemical properties. This irradiation may be done, for example, in the case of gamma radiation by means of a cobalt 60 gamma radiation facility as is presently used for industrial-scale sterilization of implants.
  • Step 3 The irradiated bars are then remelted. Applicants found that remelting of an irradiated polymer would substantially reduce the free radicals produced during irradiation, thus minimizing long-term oxidation and chain scission. By improving the polymeric composition's resistance to long-term oxidation, remelting also improves the polymeric composition's long-term resistance to wear. For further discussion of the subject, see EXAMPLES 2, 3, and 4, below
  • the bar may be contained in a low-oxygen atmosphere during the remelting, this may not be essential since, even if the bar is remelted in ambient air, the resultant oxidation may affect only the surface layer of the polymer (e.g. in the following EXAMPLE section, FIGS. 2, 5, and 24 , show oxidation extending to about 1 mm deep).
  • the oxidized surface layer of the preformed polymeric composition will be removed, e.g., during subsequent machining of the products out of the treated bar.
  • Step 4A The radiation dose is correlated with the wear resistance of the products made from the irradiated remelted polymeric composition, as determined in a wear test that adequately simulates the wear conditions of the products. For example, if the polymeric composition will be made into an implant, then the wear test should preferably adequately simulate the wear conditions of such implants in vivo. The correlation may be arrived at by plotting a dose-response curve for irradiation dose vs. wear.
  • Step 4B Similarly, the radiation dose is correlated with each of the physical and/or chemical properties that may be markedly affected by the radiation dose and that might, in turn, substantially affect the performance of the implant in vivo, both for non-remelted and remelted polymer. Again, the correlation may be arrived at by plotting a dose-response curve for irradiation dose vs. each of these physical and/or chemical properties.
  • the user does not have to do dose vs. properties for each property that might be affected, but only those properties that are considered important for the proper functioning of the implant in vivo. Which of these properties are important for the intended application, and the limiting values of these properties, may vary for different polymeric compositions and for different types of applications (e.g., hip prostheses compared to knee prostheses) and must, therefore, be established by the user before applying the flowchart.
  • Step 5 is the first attempt at optimization.
  • the user may first decide on the desired amount of improvement in the wear resistance, i.e., the maximum wear rate that is permissible for the user's application.
  • the dose-response curve for wear (Step 4A) then shows the minimum radiation dose necessary to provide this amount of improvement in wear resistance.
  • Step 4B provide the values of these properties corresponding to the specific radiation dose identified in Step 4A as being necessary to provide the desired improvement in wear resistance. If each of these other physical or chemical properties are within allowable limits for the crosslinked and remelted polymer, then an optimal method has been identified (Step 6). In other words, the implant can be made by irradiating the solid polymer bar, remelting the bar and machining out the implant; the entire process being conducted such that the resulting implant has received the optimal dose at its bearing surface.
  • the user may first decide on critical values for one or more properties, such as ultimate tensile strength, fatigue strength, etc., and then check the corresponding dose response curves for the remelted polymer for the maximum allowable dose, and then check the wear vs. dose curve to determine whether this dose gives sufficient improvement in wear (i.e., the user does not necessarily have to begin by choosing the desired amount of improvement in wear).
  • critical values for one or more properties such as ultimate tensile strength, fatigue strength, etc.
  • Step 7 Anneal samples of a bar or block which have been irradiated to that dose that was identified in Step 4A as being necessary to provide the required improvement in wear resistance, at various time/temperature combinations, to produce a polymer with the critical properties between those for non-remelted and remelted materials.
  • Step 8 The physical or chemical propert(ies) of interest of the irradiated and annealed samples of the polymer are correlated with annealing times and temperatures.
  • Step 9 Using ultimate tensile strength as an example of the physical characteristic of interest, depending on the resultant curve for annealing time and/or temperature vs. ultimate strength, the radiation dose required to achieve the desired wear resistance identified in Step 4A (above) should produce a polymer with an ultimate strength within allowable limits.
  • Step 11 If an annealing process cannot be identified that maintains the properties within allowable limits, then the user may choose to accept a lower radiation dose (Step 11), i.e., to accept less of an improvement in wear resistance. However, if a lower radiation dose (and, therefore, a greater wear rate) is acceptable, then the corresponding physical and chemical properties should again be checked for the remelted polymer (using the correlation arrived earlier in Step 4B), since these may be within limits at the lower radiation dose.
  • remelting may be used instead of annealing to produce a polymer with the desired improvement in wear resistance (Step 6). If not, then the user should proceed with annealing as before (Steps 7 through 10 or 11) but at this lower radiation dose.
  • the user may wish to progressively reduce the required amount of radiation crosslinking (i.e., to accept still higher wear rate) until a dose is identified for which all of the other properties deemed essential are within the user's required limits.
  • the resultant dose represents the maximum improvement in wear resistance obtainable within the user's criteria.
  • the UHMWPE bar or block is preferably irradiated in Step 2 and remelted in Step 3, in a manner and to a dose and temperature and time as described for UHMWPE in the section, “I. First Aspect of the Invention: Polymeric Compositions with Increased Wear Resistance” and “I (A) Further Examples of the First Aspect of the Invention”, above.
  • step 4A acetabular cups are machined out of the irradiated bar and wear tested under conditions suitably representative of the intended in vivo application (e.g., by the method described in the EXAMPLES section below) to establish a wear vs. radiation dose response curve for the specific polymer.
  • EXAMPLE 5 and FIG. 22 show a wear dose-response curve for gamma irradiated GUR 4150 UHMWPE.
  • Another important aspect of the invention is the discovery that wear resistance of GUR 4150 was not markedly affected by remelting and, therefore, it is also not likely to be markedly affected by annealing time and temperature. Therefore, it is expected that the radiation dose necessary to produce the desired reduction in wear that is determined from the wear dose-response curve for remelted polymer in Step 4A, will also apply to an annealed polymer produced in Step 7. Therfore, while the user needs to do his own tests to establish tensile strength vs dose etc., he can rely on the wear vs dose curve developed for the remelted material, rather than running an additional set of wear curves for each annealing condition.
  • FIG. 22 establishes the range on which the user may focus his wear vs. dose experiments for other grades of UHMW polyethylene, to minimize the testing necessary to identify the optimum dose.
  • GUR 4150 is representative of UHMWPEs, especially those useful for implants, in its physical and chemical properties, and applicants have observed that other UHMWPEs, of different molecular weights and with or without calcium stearate, such as GUR 1020 (calcium stearate free, lower molecular weight grade) behaved similarly to GUR 4150 in their wear resistance after irradiation sterilization in air. McKellop, H. et al., Trans. Society for Biomaterials, Vol. 20, pg. 43 (1997).
  • the findings based on GUR 4150 and the above discussion would be applicable to polymers in general, and to UHMW and HMV polymers, in particular, and especially HMWPE and UHMPE.
  • the radiation, remelting and annealing ranges found for GUR 4150 can be applied to polymers in general, and more preferably to HMW and UHMW polymers, and most preferably to HMWPE and UHMWPE; and these ranges can be used at the very least, as starting points in the flowchart for determining the specific ranges for other polymers, and the data in the “EXAMPLES” section below will facilitate the user in arriving at the proper conditions for GUR 4150, ASTM F648 Type 2 UHMWPE, and UHMWPE and HMWPE in general.
  • a user requires a lower limit on tensile strength at break at 40 MPa, and wishes to produce a material with wear no more than 1 mm 3 per million cycles.
  • the wear vs dose curve (FIG. 22) shows that a dose of about 15 Mrad is required to produce a polyethylene with the desired amount of wear resistance.
  • the tensile strength at fracture vs dose curve shows that the tensile strength at 15 Mrad for a remelted material is about 36 Mpa.
  • annealing can be expected to produce a polymer with a value of tensile strength between the limits indicated by the curves for non-remelted and remelted polymer (FIGS. 25 and 26). As shown on these figures, the tensile strength at 15 Mrad for a non-remelted material is about 46 Mpa, well above the user's limit of 40.
  • a subset of the 8mm thick specimens that had been irradiated in vacuum was remelted in a vacuum oven by heating from room temperature to 145° C. slowly (at about 0.3° C./min.) and maintaining at 145° C. for one hour. After remelting, the specimens were slowly cooled to room temperature.
  • the gel content of each material was analyzed as a function of depth from the surface. 100 ⁇ m thick sections (about 50 mg) were microtomed across the specimen. Extraction of the sol-fraction was performed by boiling in p-xylene for 24 hours, with 0.5 wt % of antioxidant (2,6-di-t-butyl-4-methyl phenol) added to prevent oxidation. For highly oxidized sections from the surface layer, which tended to break up during boiling, the specimens were wrapped in PTFE membrane filter (0.5 ⁇ m pore size) to avoid loss of gel. After extraction, the specimens were de-swollen in acetone and dried at 60° C. in a vacuum oven to constant weight. The gel fraction was determined from the ratio of the weight of the dried-extracted material to that of the dry non-extracted material.
  • irradiation increased the crystallinity of the 8 mm thick specimens of UHMWPE from about 55% to 60-66%, with considerable overlapping for the different doses. Similar changes were observed with the samples that were irradiated in air.
  • the gel content i.e., the extent of crosslinking
  • crosslinking increased markedly moving from the surface into the middle of each specimen, reaching about 92% for the 3.3 Mrad dose.
  • the oxygen present in the vacuum chamber was sufficient to cause the increased oxidation and decreased crosslinking of the surface layer.
  • acetabular cups used in patients must first be sterilized by some acceptable means, the test cups in this study were sterilized prior to wear testing using ethylene oxide at the appropriate dose for clinical implants.
  • Ethylene oxide was chosen instead of additional gamma irradiation (e.g., 2.5-4.0 Mrad) in order to confine the results to the effects of the original 3.3 or 28 Mrad doses used to crosslink the materials.
  • the cups Prior to wear testing, the cups were pre-soaked in distilled water for three weeks to minimize additional fluid absorption during the wear test, thereby making the weight loss method for wear measurement more accurate.
  • the cups were enclosed in polyurethane molds and pressed into stainless steel holders (FIG. 7). Each holder was fitted with an acrylic chamber wall to contain the lubricant.
  • the chambers were mounted on the hip simulator wear machine, with each cup bearing against a ball of cobalt-chromium alloy (conventional hip replacement femoral balls were used, with implant-quality surface finish).
  • the ball-cup pairs were subjected to a physiological cyclic load with a peak load of about 2000 Newtons (Paul, J P., “Forces transmitted by joints in the human body”.
  • Each test station on the simulator contains a self-centering unit 5 , the acetabular cup 6 , a dual axis offset drive block 7 , a test chamber 8 , serum lubricant 9 and a femoral ball 10 .
  • the arrow indicates the direction of the computer controlled simulated physiological load applied to the simulated hip joint.
  • the weight loss was corrected for the effects of fluid absorption (which masks wear) by increasing the apparent weight loss of the wear test cups by the mean weight gain of three control cups of each material that were also immersed in serum and cyclically loaded on a separate frame, but without oscillation.
  • the corrected rate of weight loss was converted to volume loss by dividing by the approximate density of UHMWPE (0.94 gm/cc).
  • the mean weight loss (after soak correction) and the standard deviation was calculated for each of the four types of materials at each weighing interval.
  • the wear rate of each cup was calculated by applying linear regression to the wear data for the entire three million cycles. The mean wear rates and standard deviations also were calculated for each type of material.
  • FIG. 8 shows the soak-corrected wear (volume loss) of three cups of each material as a function of wear cycles.
  • FIG. 9 shows the average wear (volume loss) of three cups of each material as a function of wear cycles.
  • the individual wear rates and the mean values for each type of material are listed in Table 3. The most wear occurred with the cups subjected to 3.3 Mrad without remelting. These averaged 21.1 mm 3 per million cycles.
  • the wear of the cups subjected to 3.3 Mrad with remelting averaged 18.6 mm 3 per million cycles, or 12% lower wear than for the non-remelted 3.3 Mrad cups.
  • the cups subjected to 28 Mrad had much lower wear rates than the 3.3 Mrad cups, and the rates were similar, whether or not the material had been remelted. That is, the average wear rate of the non-remelted 28 Mrad cups was about 1.2% that of the non-remelted 3.3 Mrad controls, and the average wear rate of the remelted 28 Mrad cups was about 1.7% of the same controls.
  • FTIR measurements were performed on the above specimens. Segments about 5 mm wide were cut from each polyethylene specimen and the segments were microtomed into 200 ⁇ m thick slices.
  • the oxidation profiles, as indicated by the carbonyl concentration, were measured using a Mattson Polaris FTIR (model IR 10410) with a Spectra-Tech IR plan microscope. Spectra were collected in 100 ⁇ m steps from the surface to the middle of the specimen, using 64 scans summation at a resolution 16 cm ⁇ 1 with a MCT (Mercury Cadmium Telluride) detector.
  • the carbonyl group concentration was indicated by the ratio of the peak height of the ketone absorption band at 1717 cm ⁇ 1 to the height of the reference band at 2022 cm ⁇ 2 (—CH 2 -vibration).
  • FIGS. 10-13 The oxidation profiles as a function of depth are shown in FIGS. 10-13.
  • FIG. 10 for the 3.3 Mrad, non-remelted material, oxidation increased with increasing aging time.
  • the 3.3 Mrad, remelted material (FIG. 11) showed almost no oxidation for 10 and 20 days aging, but some oxidation for 30 days aging.
  • the oxidation peak at the surface with remelting was about 50% of that at the surface without remelting (FIG. 10).
  • the oxidation showed a greater increase with increasing aging time than the 3.3 Mrad, un-remelted material.
  • the percent of undissolved material is an indirect indication of the amount of crosslinking.
  • the gel content as a function of depth for various conditions are shown in FIGS. 15 to 18 .
  • the gel content i.e., crosslinking
  • the gel content decreased with increasing aging time.
  • the gel content was highest (91%) in the un-aged specimen, and decreased with increasing aging time to less than about 5% in the same region for the 30 day aged specimen.
  • the remelted materials (FIG. 16) showed much less reduction in gel content in the surface regions than the non-remelted materials. That is, comparison of FIG. 17 (28 Mrad, non-remelted) and FIG. 18 (28 Mrad, remelted) showed that the remelted UHMWPE had much higher retention of gel content (i.e., crosslinking).
  • Irradiation of UHMWPE produces crosslinking, chain scission and the formation of free radicals. If oxygen is present, it may react with the free radicals to form oxidized species, leading to additional chain scission (reduction in molecular weight) and an increase in crystallinity. Since polymer crystallites melt and become amorphous above the melting temperature, molecular chain movements and rotations are increased, favoring the recombination of free radicals. The results of the present experiments showed that remelting at 150° C. apparently caused the residual free radicals to decay and/or to recombine to form crosslinks, leading to an increased gel content.
  • remelting is an effective way to extinguish free radicals, making the material less susceptible to long-term oxidation and potentially improving the long-term wear resistance, as evident from the results of the artificial aging experiments, where there was much less oxidation of the remelted materials.
  • oxidative degradation cleaves the molecules and leads to a reduction in gel content. This was evident in the present experiments from the reduced gel content after aging, particularly with the non-remelted materials (FIGS. 15 to 18 ). That is, the distribution of oxidation, as indicated by the profiles measured by FTIR, was inverse to the gel content within the material; the higher the oxidation, the lower the gel content (crosslinking). Since remelting extinguishes free radicals and increases gel content, thereby reducing the susceptibility to oxidation, the remelted materials (3.3 and 28 Mrad) had a much greater gel content after artificial aging than the non-remelted materials.
  • extruded bars of GUR 4150 UHMWPE 3′′ diameter ⁇ 15′′ long, were gamma irradiated in air, three bars at each dose of 4.5, 9.5, 14.5, 20.2 or 24 Mrad (SteriGenics, Inc., Corona, Calif.), at a dose rate of 0.45 Mrad/hour. Additional bars were irradiated in air to 50 or 100 Mrad (SteriGenics Inc., Tustin, Calif.), at a dose rate of 0.67 Mrad/hour. For each radiation dose, two bars were then remelted by heating in an oven in ambient atmosphere from room temperature to 150° C. at about 0.3° C./min, holding at 150° C. for 5 hours and then slowly-cooled to room temperature, with the third bar not being remelted. The irradiated-remelted bars were used to produce acetabular cups for the wear tests.
  • FIG. 21 shows the soak-corrected wear (volume loss) of each material (three cups for 3.3 Mrad from EXAMPLE 2, two cups each for radiation dose from 4.5 to 24.5 Mrad, and one cup each for 50 and 100 Mrad).
  • the individual wear rates, determined by linear regression, and the mean values for each type of material are listed in Table 5.
  • FIG. 22 shows the average wear rate (volume loss from 1 to 5 million) of each type of material, that had been re-melted (denoted in the figure by darkened circles) and that had not been re-melted (denoted in the figure by an open circle), as a function of dose.
  • the materials for physical characterization were the same as the wear tested materials described in EXAMPLE 5.
  • the materials included UHMWPE extruded bars (3′′ in diameter) gamma irradiated to 3.3, 4.5, 9.5, 14.5, 20.2, 24, 50 and 100 Mrad, with or without remelting, and the non-irradiated bars.
  • 8 mm thick disks were cut out of irradiated bars with or without remelting, and sterilized with ethylene oxide.
  • the specimens for DSC and swelling measurements were cut out of the center of the 8 mm thick disks. The DSC measurement for crystallinity and melting temperature with sample weighing about 4 mg was described in EXAMPLE 1.
  • the gel fraction was determined as the ratio of the weight of the dried extracted to the initial dry non-extracted network.
  • the degree of swelling was calculated as the ratio of the weight of the swollen gel to the dried extracted gel.
  • the degree of swelling was used to calculate the network chain density, number-average molecular weight between crosslinks and crosslink density, according to the theory of Flory and Rehner (Shen et al., J. Polym. Sci. Polym. Phys., 34:1063-1077 (1996)).
  • Flory and Rehner Shown et al., J. Polym. Sci. Polym. Phys., 34:1063-1077 (1996).
  • the melting temperature and crystallinity for non-irradiated, and irradiated (with and without remelting) materials are shown in Table 6.
  • the degree of swelling, average molecular weight between crosslinks, crosslink density and gel content are shown in Table 7.
  • the melting temperature and crystallinity increased, ranging from-135.3 to 140.2° C., and about 60 to 71%, respectively, over the dose range studied.
  • Remelting of the irradiated bars resulted in reductions in the melting temperature and crystallinity, ranging from about 131 to 135° C., and about 51 to 53%, respectively.
  • the materials for tensile test are the same as the wear tested materials described in EXAMPLE 5, above.
  • the materials included UHMWPE extruded bars (3′′ in diameter) gamma irradiated to 4,5, 9.5, 14.5, 20.2, and 24 Mrad, with or without remelting, and non-irradiated bars.
  • Five tensile specimens each was machined out of the center of the 3′′ diameter bars according to ASTM F648-96 and D-638 (type IV). Tensile tests were performed using an servo-hydraulic tensile test machine at speed of 2 inches/min.
  • the tensile strength at yield, elongation, and tensile strength (ultimate) at breaks are shown in Table 8.
  • the average tensile properties as a function of radiation dose are shown in FIGS. 25-27.
  • the tensile strength at yield after irradiation was higher than that of non-irradiated material, and slightly increased with radiation dose. Remelting of the irradiated bars resulted in a reduction in tensile strength at yield, and the strength remained almost constant over the dose range studied (FIG. 25).
  • the tensile strength (ultimate) and elongation at break decreased with increasing doses (FIGS. 26-27). Remelting resulted in further reduction in ultimate tensile strength over the dose range. However, remelting had almost no effect on the elongation at break over the same dose range.

Abstract

The present invention discloses methods for enhancing the wear-resistance of polymers, the resulting polymers, and in vivo implants made from such polymers. One aspect of this invention presents a method whereby a polymer is irradiated, preferably with gamma radiation, then thermally treated, such as by remelting of annealing. The resulting polymeric composition preferably has its most oxidized surface layer removed. Another aspect of the invention presents a general method for optimizing the wear resistance and desirable physical and/or chemical properties of a polymer by crosslinking and thermally treating it. The resulting polymeric compositions is wear-resistant and may be fabricated into an in vivo implant.

Description

  • This is a continuation of co-pending U.S. patent application Ser. No. 09/795,229, filed on Feb. 26, 2001, entitled “CROSSLINKING OF POLYETHYLENE FOR LOW WEAR USING RADIATION AND THERMAL TREATMENTS”, which is a continuation of application Ser. No. 09/214,586, filed on Jan. 6, 1999, and issued as U.S. Pat. No. 6,228,900, on May 8, 2001, which is the national phase filing of Patent Cooperation Treaty application number PCT/US97/11947, filed on Jul. 8, 1997, which is based on U.S. provisional applications: Ser. No. 60/017,852 filed on Jul. 9, 1996; Ser. No. 60/025,712 filed on Sep. 10, 1996; and Ser. No. 60/044,390, filed on Apr. 29, 1997. The entire contents of the parent applications are expressly incorporated by reference.[0001]
  • TECHNICAL FIELD OF THE INVENTION
  • The present invention relates to polymers. It discloses methods for enhancing the wear-resistance of polymers by crosslinking and thermally treating them. The polymers disclosed herein are useful for making implants, for example, as components of artificial joints such as acetabular cups. [0002]
  • BACKGROUND OF THE INVENTION
  • Ultrahigh molecular weight polyethylene (hereinafter referred to as “UHMWPE”) is commonly used to make prosthetic joints such as artificial hip joints. In recent years, it has become increasingly apparent that tissue necrosis and interface osteolysis, in response to UHMWPE wear debris, are primary contributors to the long-term loosening failure of prosthetic joints. For example, wear of acetabular cups of UHMWPE in artificial hip joints introduces many microscopic wear particles into the surrounding tissues. The reaction to these particles includes inflammation and deterioration of the tissues, particularly the bone to which the prosthesis is anchored. Eventually, the prosthesis becomes pain-fully loose and must be replaced. [0003]
  • Improving the wear resistance of the UHMWPE socket and, thereby, reducing the rate of production of wear debris would extend the useful life of artificial joints and permit them to be used successfully in younger patients. Consequently, numerous modifications in physical properties of UHMWPE have been proposed to improve its wear resistance. [0004]
  • UHMWPE components are known to undergo a spontaneous, post-fabrication increase in crystallinity and changes in other physical properties. {See e.g., Rimnac, C. M., et al., [0005] J. Bone & Joint Surgery, 76-A(7):1052-1056 (1994)}. These changes occur even in scored (non-implanted) cups after sterilization with gamma radiation, which initiates an ongoing process of chain scission, crosslinking, and oxidation or peroxidation involving the free radicals formed by the irradiation. These degradative changes may be accelerated by oxidative attack from the joint fluid and cyclic stresses applied during use.
  • In an attempt to improve wear resistance, DePuy-DuPont Orthopaedics fabricated acetabular cups from conventionally extruded bar stock that previously had been subjected to heating and hydrostatic pressure that reduced fusion defects and increased the crystallinity, density, stiffness, hardness, yield strength, and increased the resistance to creep, oxidation and fatigue. Alternatively, silane cross-linked UHMWPE (XLP) has also been used to make acetabular cups for total hip replacements in goats. In this case, the number of in vivo debris particles appeared to be greater for XLP than conventional UHMWPE cup implants {Ferris, B. D., [0006] J. Exp. Path., 71:367-373 (1990)}.
  • Other modifications of UHMWPE have included: (a) reinforcement with carbon fibers; and (b) post-processing treatments such as solid phase compression molding. Indeed, carbon fiber reinforced polyethylene and a heat-pressed polyethylene have shown relatively poor wear resistance when used as the tibial components of total knee prosthesis. {See e.g., Rimnac, C. M., et al., [0007] Trans. Orthopaedic Research Society, 17:330 (1992)}.
  • Recently, several companies have modified the method of radiation sterilization to improve the wear resistance of UHMWPE components. This has typically involved packaging the polyethylene cups either in an inert gas (e.g., Howmedica, Inc.), in a partial vacuum (e.g., Johnson & Johnson, Inc.) or with an oxygen scavenger (e.g., Sulzer Orthopaedics, Inc.). [0008]
  • SUMMARY OF THE INVENTION
  • The present invention comprises two aspects: [0009]
  • The first aspect of the invention presents a method for increasing the wear resistance of a polymer by crosslinking the polymer, followed by thermally treating the crosslinked polymer. Non-limiting examples of the thermal treatments are remelting or annealing. Preferably, the polymer is crosslinked by gamma irradiation in the solid state prior to being modified to a desired final form or shape of the final product. In the preferred embodiment, the surface layer of the crosslinked and thermally treated polymer, which is the most oxidized and least crosslinked part of the polymer, is removed, e.g., in the process of machining the final product out of the irradiated bar and thermally treated bar or block. The radiation dose is also preferably adjusted so that the optimal dose occurs within the solid polymer bar or block at the level of the bearing surface of the final product. Also presented are the polymers made from this method; methods for making products (e.g., in vivo implants) from these polymers; and the products (e.g.,in vivo implants) made from these polymers. [0010]
  • The second aspect of the invention provides a systematic method for determining an optimal balance among wear resistance and other physical and/or chemical properties that are deemed important to the long-term performance of an implant in vivo, and applying this optimal balance to determine the appropriate crosslinking and thermal treatment conditions for processing a polymer. A flowchart is provided as a non-limiting illustration of the method for determining the optimal balance. Also provided are methods for treating polymers which apply the above appropriate crosslinking and thermal treatment conditions; the polymers produced by these methods; methods for making products (e.g., in vivo implants) from these polymers; and the products (e.g.,in vivo implants) made from these polymers.[0011]
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 presents the degree of crystallinity vs. depth at indicated doses for UHMWPE that was irradiated in a vacuum (i.e., a low-oxygen atmosphere). [0012]
  • FIG. 2 presents the gel content vs. depth at indicated doses for UHMWPE that was irradiated in a vacuum (i.e., a low-oxygen atmosphere). [0013]
  • FIG. 3 presents the gel content vs. depth at indicated conditions for UHMWPE. [0014]
  • FIG. 4 presents the degree of crystallinity vs. depth at indicated conditions for UHMWPE. [0015]
  • FIG. 5 presents the gel content vs. depth at indicated conditions for UHMWPE. [0016]
  • FIG. 6 presents the shape of the acetabular cup fabricated from the irradiated UHMWPE. [0017]
  • FIG. 7 presents a schematic diagram of the hip joint simulator used in the wear tests. [0018]
  • FIG. 8 presents the wear by volume loss of each cup of the four materials. Upper curves: 3.3 Mrad; Lower curves: 28 Mrad. [0019]
  • FIG. 9 presents the curves of the average volumetric wear and standard deviations of three cups of each material at each interval. [0020]
  • FIG. 10 presents the oxidation profile as a function of depth at various aging times. [0021]
  • FIG. 11 presents the oxidation profile as a function of depth at various aging times. [0022]
  • FIG. 12 presents the oxidation profile as a function of depth at various aging times. [0023]
  • FIG. 13 presents the oxidation profile as a function of depth at various aging times. [0024]
  • FIG. 14 presents the oxidation profile as a function of depth for various materials. The specimens were stored in air for 5 months and then aged for 20 days at 80° C. [0025]
  • FIG. 15 presents gel content as a function of depth at various aging times. [0026]
  • FIG. 16 presents gel content as a function of depth at various aging times. [0027]
  • FIG. 17 presents gel content as a function of depth at various aging times. [0028]
  • FIG. 18 presents gel content as a function of depth at various aging times. [0029]
  • FIG. 19 presents the degree of crystallinity as a function of depth after 30 days' aging. [0030]
  • FIG. 20 shows the combined soak-corrected wear for the non-aged and aged cups. [0031]
  • FIG. 21 shows the individual wear for cups irradiated at different doses. [0032]
  • FIG. 22 shows the average wear rate versus radiation dose of non-remelted and remelted cups. [0033]
  • FIGS. 23A and 23B present the flowchart illustrating so the optimization method of the present invention. [0034]
  • FIG. 24 graphically shows the oxidation profiles for irradiated and remelted UHMWPE as a function of depth from the UHMWPE bar surface. [0035]
  • FIG. 25 graphically shows the tensile strength at yield versus radiation dose of irradiated UHMWPE with or without remelting, and non-irradiated and not remelted UHMWPE. [0036]
  • FIG. 26 graphically shows the tensile strength at break versus radiation dose of irradiated UHMWPE with or without remelting, and non-irradiated and not remelted UHMWPE. [0037]
  • FIG. 27 graphically shows the elongation at break versus radiation dose of irradiated UHMWPE with or without remelting, and non-irradiated and not remelted UHMWPE.[0038]
  • DETAILED DESCRIPTION OF THE INVENTION
  • Abbreviations used in this application are as follows: [0039]
  • UHMW—ultra-high molecular weight [0040]
  • UHMWPE—ultra-high molecular weight polyethylene [0041]
  • HMW—high molecular weight [0042]
  • HMWPE—high molecular weight polyethylene [0043]
  • The present invention contains two aspects. The first aspect of the invention provides methods for improving the wear resistance of a polymer by crosslinking (preferably the bearing surface of the polymer) and then thermally treating the polymer, and the resulting novel polymer. Preferably, the most oxidized surface of the polymer is also removed. Also presented are the methods for using the polymeric compositions for making products and the resulting products, e.g., in viva implants. Specific examples of this method are presented in the section: “I. First Aspect of the Invention: Polymeric Compositions with Increased Wear Resistance” and “I (A) Further Examples of the First Aspect of the Invention”, below. [0044]
  • The method of the invention utilizes irradiation for crosslinking a polymer followed by thermal treatment to decrease the free radicals to produce a preformed polymeric composition. The term “preformed polymeric composition” means that the polymeric composition is not in a final desired shape or form (i.e., not a final product). For example, where the final product of the preformed polymeric composition is an acetabular cup, irradiation and thermal treatment of the polymer could be performed at pre-acetabular cup shape, such as when the preformed polymeric composition is in the form of a solid bar or block. [0045]
  • A second aspect of the invention provides a systematic method (an example of which is illustrated in the flowchart, below) for determining the optimal parameters for the above mentioned crosslinking and thermal treatment. This second aspect provides a method for determining the maximum possible improvement in wear resistance, consistent with keeping the other physical and/or chemical propert(ies) within the user's desired limits, with the least amount of trial and error testing. Once the optimal parameters (i.e., crosslinking conditions such as radiation dose when radiation is used to crosslink the polymer, and thermal treatment parameters) are determined by this method, the polymer will then be processed according to the optimal parameters. Thus, this protocol renders the development of a preformed polymeric composition with particular chemical/mechanical characteristics routine without resort to undue experimentation. Also presented are the methods for using the preformed polymeric composition for making products, and the products, e.g., in vivo implants. [0046]
  • In the present invention, the wear resistance of the polymer is improved by crosslinking. The crosslinking can be achieved by various methods known in the art, for example, by irradiation from a gamma radiation source or from an electron beam, or by photocrosslinking. The preferred method for crosslinking the polymer is by gamma irradiation. The polymer is preferably crosslinked in the form of an extruded bar or molded block. [0047]
  • In the preferred method, the crosslinked polymer is subjected to thermal treatment such as by remelting (i.e., heated above the melting temperature of the crosslinked polymer) or annealing (i.e., heated at below the melting temperature of the crosslinked polymer) to produce the preformed polymeric composition. [0048]
  • In the preferred embodiment of both the first and second aspects of the invention, the outer layer of the resulting preformed polymeric composition, which is generally the most oxidized and least crosslinked and, thus, least wear resistant, is removed. For example, the bearing surface of the preformed polymeric composition may be fashioned from inside, e.g., by machining away the surface of the irradiated and thermally treated composition before or during fashioning into the final product, e.g., into an implant. Bearing surfaces are surfaces which are in moving contact with another, e.g., in a sliding, pivoting, or rotating relationship to one another. [0049]
  • Choices of Polymers [0050]
  • The polymers are generally polyester, poly(methylmethacrylate), nylon, polycarbonates, and polyhydrocarbons such as polyethylene, and polypropylene. High molecular weight (HMW) and ultra-high molecular weight (UHMW) polymers are preferred, such as HMW polyethylene (HMWPE), UHMW polyethylene (UHMWPE), and UHMW polypropylene. HMW polymers have molecular weights ranging from about 10[0051] 5 grams per mole to just below 106. UHMW polymers have molecular weights equal to or higher than 106 grams per mole, preferably from 106 to about 107. The polymers are generally between about 400,000 grams per mole to about 10,000,000 and are preferably polyolefinic materials.
  • For implants, the preferred polymers are those that are wear resistant and have exceptional chemical resistance. UHMWPE is the most preferred polymer as it is known for these properties and is currently widely used to make acetabular cups for total hip prostheses and components of other joint replacements. Examples of UHMWPE are those having molecular weight ranging from about 1 to 8×10[0052] 6 grams per mole, examples of which are: GUR 4150 or 4050 (Hoechst-Celanese Corporation, League City, Tex.) with a weight average molecular weight of 5 to 6×106 grams per mole; GUR 4130 with a weight average molecular weight of 3 to 4×106; GUR 4120 or 4020 with a weight average molecular weight of 3 to 4×106; RCH 1000 (Hoechst-Celanese Corp.)with a weight average of molecular weight of 4×106 and HiFax 1900 of 2 to 4×106 (HiMont, Elkton, Md.). Historically, companies which make implants have used polyethylenes such as HIFAX 1900, GUR 4020, GUR 4120 and GUR 4150 for making acetabular cups.
  • Sterilization Methods [0053]
  • All polymeric products must be sterilized by a suitable method prior to implanting in the human body. For the formed crosslinked and thermally treated polymeric compositions (i.e., the final products) of the present invention, it is preferable that the products be sterilized by a non-radiation based method, such as ethylene oxide or gas plasma, in order not to induce additional crosslinking and/or oxidation of the previously treated preformed polymeric composition. Compared to radiation sterilization, a non-radiation sterilization method has a minor effect on the other important physical characteristics of the product. [0054]
  • Nevertheless, the method can be used in conjunction with radiation sterilization. If the final products are to be sterilized by an additional dose of radiation, it is preferable to take into account the effect of this additional radiation dose on the wear resistance and other properties of the polymer, in determining the optimum radiation dose used in the initial crosslinking. Furthermore, it is preferable that the radiation sterilization be done while the final product (e.g., in vivo implant) is packed in a suitable low-oxygen atmosphere (e.g., in partial vacuum, in an inert gas such as nitrogen, or with an oxygen scavenger included) in order to minimize oxidation of the surface layer of the final product during and after sterilization by irradiation. [0055]
  • The dose ranges in this application do not take into account radiation sterilization. If radiation sterilization is used, then the dose ranges may have to be adjusted. Such adjustment can be easily performed using the teachings herein. For example, if after comparing the dose-response curves for wear with those for other important physical or chemical properties, it is determined that the optimal total radiation dose is 8 Mrad, and it is intended to sterilize the polymer with 2.5 Mrad gamma radiation (the minimum industrial standard sterilization dose), then the initial radiation dose (before sterilization) should be 5.5 Mrad, such that the total dose (initial plus sterilization doses) will be 8 Mrad. These calculations are approximate, since the total crosslinking achieved will not be exactly equivalent to a single 8 Mrad dose. [0056]
  • Nevertheless, the applicants have discovered that a high level of crosslinking in the surface layer of a polymer markedly reduces the degradative effects of surface oxidation, i.e., that would otherwise occur if a non-pre-crosslinked polymer were irradiated in the presence of oxygen (for example, see FIG. 3). [0057]
  • Methods for Characterizing the Polymers [0058]
  • The degree of crystallinity can be determined using methods known in the art, e.g. by differential scanning calorimetry (DSC), which is generally used to assess the crystallinity and melting behavior of a polymer. Wang, X. & Salovey, R., [0059] J. Arc. Polymer Sci., 34:593-599 (1987).
  • Wide-angle X-ray scattering from the resulting polymer can also be used to further confirm the degree of crystallinity of the polymer, e.g. as described in Spruiell, J. E., & Clark, E. S., in “[0060] Methods of Experimental-Physics”, L. Marton & C. Marton, Eds., Vol. 16, Part S, Academic Press, New York (1980). Other methods for determining the degree of crystallinity of the resulting polymer may include Fourier Transform Infared Spectroscopy {Painter, P. C. et al., “The Theory Of Vibrational Spectroscopy And Its Application To Polymeric Materials”, John Wiley and Sons, New York, U.S.A. (1982)} and density measurement (ASTM D1505-68). Measurements of the gel content and swelling are generally used to characterize crosslink distributions in polymers, the procedure is described in Ding, Z. Y., et al., J. Polymer Sci., Polymer Chem., 29:1035-38 (1990). FTIR can also be used to assess the depth profiles of oxidation as well as other chemical changes such as unsaturation {Nagy, E. V., & Li, S., “A Fourier transform infrared technique for the evaluation of polyethylene orthopaedic bearing materials”, Trans. Soc. for Biomaterials, 13:109 (1990); Shinde, A. & Salovey, R., J. Polymer Sci., Polym. Phys. Ed., 23:1681-1689 (1985)}.
  • Use of Crosslinked Polymers for Implants [0061]
  • Another aspect of the invention presents a process for making implants using the preformed polymeric composition of the present invention. The preformed polymeric composition may be shaped, e.g., machined, into the appropriate implants using methods known in the art. Preferably, the shaping process, such as machining, removes the oxidized surface of the composition. [0062]
  • Preformed Polymeric Compositions [0063]
  • The preformed polymeric compositions of the present invention can be used in any situation where a polymer, especially UHMWPE, is called for, but especially in situations where high wear resistance is desired. More particularly, these preformed polymeric compositions are useful for making implants. [0064]
  • Implants Made of Crosslinked Polymers [0065]
  • An important aspect of this invention presents implants that are made with the above preformed polymeric compositions or according to the methods presented herein. In particular, the implants are produced from preformed polymeric composition are UHMW polymers crosslinked by gamma radiation followed by remelting or annealing, removing the oxidized surface layer and then fabricating into a final shape. The preformed polymeric composition of the present invention can be used to make implants for various parts of the body, such as components of a joint in the body. For example, in the hip joints, the preformed polymeric composition can be used to make the acetabular cup, or the insert or liner of the cup, or trunnion bearings (e.g. between the modular head and the stem). In the knee joint, the preformed polymeric compsition can be used to make the tibial plateau (femoro-tibial articulation), the patellar button (patello-femoral articulation), and trunnion or other bearing components, depending on the design of the artificial knee joint. In the ankle joint, the preformed polymeric composition can be used to make the talar surface (tibio-talar articulation) and other bearing components. In the elbow joint, the preformed polymeric composition can be used to make the radio-numeral joint, ulno-humeral joint, and other bearing components. In the shoulder joint, the preformed polymeric composition can be used to make the glenoro-humeral articulation, and other bearing components. In the spine, the preformed polymeric composition can be used to make intervertebral disk replacement and facet joint replacement. The preformed polymeric composition can also be made into temporo-mandibular joint (jaw) and finger joints. The above are by way of example, and are not meant to be limiting. [0066]
  • The following discusses the first and second aspects of the invention in more detail. [0067]
  • I. First Aspect of the Invention: Polymeric Compositions with Increased Wear Resistance [0068]
  • The first aspect of the invention provides preformed polymeric compositions which are wear resistant and useful for making in vivo implants. In this aspect, for polymers in general, and more preferably UHMW and HMW polymers, and most preferably UHMWPE and HMWPE, the irradiation dose is preferably from about 1 to about 100 Mrad, and more preferably, from about 5 to about 25 Mrad, and most preferably from about 5 to about 10 Mrad. This most preferable range is based on achieving what the inventors have determined to be a reasonable balance between improved wear resistance and minimal degradation of other important physical properties. [0069]
  • In vivo implants of the present invention, i.e., irradiated within the above dose ranges are expected to function in vivo without mechanical failure. The UHMWPE acetabular cups used by Oonishi et al. [in [0070] Radiat. Phys. Chem., 39: 495-504 (1992)] were irradiated to 100 Mrad and functioned in vivo without reported mechanical failure after as long as 26 years of clinical use. Furthermore, it is surprising that, as shown in the EXAMPLES, acetabular cups from the preformed polymeric composition prepared according to the present invention, but irradiated to much less than 100 Mrad, exhibited much higher wear resistance than reported by Oonishi et al.
  • On the other hand, if a user is primarily concerned with reducing wear, and other physical properties are of secondary concern, then a higher dose than the above stipulated most preferable range (e.g., 5 to 10 Mrad) may be appropriate, or vice versa (as illustrated in the detailed examples in the following section). The optimum radiation dose is preferably based on the dose received at the level of the bearing surface in the final product. Gamma radiation is preferred. [0071]
  • The irradiated polymer is then preferably remelted at or above melting temperature of the irradiated polymer, e.g., in air. As used herein, the melting temperature of the crosslinked or irradiated polymer is identified from the peak of the melting endotherm as measured by DSC. Preferably, the remelting temperature is from about the melting temperature of the irradiated polymer to about 100° C. to about 160° C. above the melting temperature of the irradiated polymer; more preferably from about 40° C. to about 80° C. above the melting temperature of the irradiated polymer; and most preferably from about 1° C. to about 60° C. above the melting temperature of the irradiated polymer. For example, in the case of UHMWPE, the remelting temperature is preferably from about 136° C. to about 300° C., more preferably from about 136° C. to about 250° C., and most preferably from about 136° C. to about 200° C. Specific conditions for remelting are described in EXAMPLES 1 and 2, below. [0072]
  • Generally, in practice, the remelting temperature is inversely proportional to the remelting period. The polymer is preferably remelted over a period from about 1 hour to about 2 days, more preferably from about 1 hour to about 1 day, and most preferably from about 2 hours to about 12 hours. [0073]
  • Since, depending on the time and temperature applied, annealing can produce less of an effect than remelting on physical properties such as crystallinity, yield strength and ultimate strength, annealing may be used in place of remelting as a means for reducing the free radicals remaining in the polymer after irradiation crosslinking, in order to maintain these physical properties within limits required by the user. Thermal treatment, such as remelting or annealing, removes free radicals and thereby improves long term wear resistance of the polymer. On the other hand, annealing is slower and thus takes longer than remelting, making it likely to be more expensive in industrial applications. [0074]
  • The annealing temperature is preferably from about room temperature to below the melting temperature of the irradiated polymer; more preferably from about 90° C. to about 1° C. below the melting temperature of the irradiated polymer; and most preferably from about 60° C. to about 1° C. below the melting temperature of the irradiated polymer. For example, UHMWPE may be annealed at a temperature from about 25° C. to about 135° C., preferably from about 50° C. to about 135° C., and more preferably from about 80° C. to about 135° C. The annealing period is preferably from about 2 hours to about 7 days, and more preferably from about 7 hours to about 5 days, and most preferably from about 10 hours to about 2 days. Instead of using the above range of radiation dose as a criterion, the appropriate amount of crosslinking may be determined based on the degree of swelling, gel content, or molecular weight between crosslinks after thermal treatment. This altenative is based on the applicant's findings (detailed below) that acetabular cups made from UHMWPE falling within a preferred range of these physical parameters have reduced or non-detectable wear. The ranges of these physical parameters include one or more of the following: a degree of swelling of between about 1.7 to about 5.3; molecular weight between crosslinks of between about 400 to about 8400 g/mol; and a gel content of between about 95% to about 99%. A preferred polymer or final product has one or more, and preferably all, of the above characteristics. These parameters can also be used as starting points in the second aspect of the invention (as illustrated by the flowchart, discussed below) for determining the desired radiation dose to balance the improvement in wear resistance with other desired physical or chemical properties, such as polymer strength or stiffness. [0075]
  • After crosslinking and thermal treatment, preferably, the most oxidized surface of the preformed polymeric composition is removed. The depth profiles of oxidation of the preformed polymeric composition can be determined by methods known in the art, such as FTIR, described above and in EXAMPLES 3 and 6. In general, to remove the most oxidized surface, preferably a minimum of about 0.5 mm to 1.0 mm of the surface of preformed polymeric composition which is exposed to air is removed, e.g. by machining, before or while fashioning the preformed polymeric composition into the final product. [0076]
  • I. (A) Further Examples of the First Aspect of the Invention [0077]
  • As noted above, the most preferable range of dose for crosslinking radiation (i.e., from 5 to 10 Mad) was based on achieving what the inventors have determined to be a reasonable balance between improved wear resistance and minimal degradation of other important physical properties. The following examples illustrate applications of the present invention with altenative criteria for the optimal dose. These examples use in vivo implants as non-limiting examples of the products, and UHMWPE or HMWPE bar or block as a non-limiting example of a starting material. [0078]
  • In the first example, the user desires to achieve a minimum wear rate of the in vivo implant made from the UHMWPE and HMWPE, and the other physical or chemical properties are important but of lesser concern. In such a case, the user may choose to irradiate the UHMWPE and HMWPE bar or block between about 15 Mrad to about 20 Mrad (as shown by FIG. 22). As discussed in the section “II (b) Application of the Flowchart”, below, GUR 4150 is representative of UHMWPE and HMWPE. The irradiated UHMWPE or HMWPE bar or block is further remelted or annealed at a temperature and time described in “I. First Aspect of the Invention: Polymeric Compositions with Increased Wear Resistance”, above. [0079]
  • In a second example, the user may wish to produce an UHMWPE which is as wear resistant as possible while meeting the tensile strength at break (ultimate), tensile strength at yield, and elongation at break criteria of the standard specified by the American Society for Testing and Materials F-648 standard (hereinafter referred to as “ASTM F648”) for UHMWPE for in vivo use. The information about this standard can be found in a current issue of the [0080] Annual Book of ASTM Standards, Medical Devices and Services, “Standard Specification for Ultra-High-Molecular-Weight Polyethylene Powder and Fabricated Form for Surgical Implants”, American Society for Testing and Materials. The method of the second aspect of the present invention (as illustrated by the flowchart) may be used to adjust the crosslinking and thermal treatment parameters to meet any current ASTM F648 criteria.
  • For example, to meet the 1996 ASTM F648 (F648-96) criteria for [0081] Type 1 or 2 UHMWPE, the UHMWPE must have: a tensile strength at break (ultimate) of at least 35 MPa (for Type 1) and 27 MPa (for Type 2) at 23° C. and 5.08 cm/min; a tensile strength-at yield of at least 21 MPa (Type 1) and 19 MPa (for Type 2) at 23° C., and 5.08 cm/min; and elongation at break of at least 300% at 5.08 cm/min. The test conditions are described in ASTM D638, Type IV (Annual Book of ASTM Standards, American Society for Testing and Materials). Alternatively, to meet the 1996 ASTM F648 criteria for Type 3 UHMWPE, the UHMWPE must have: a tensile strength at break (ultimate) of at least 27 MPa at 23° C. and 5.08 cm/min; a tensile strength at yield of at least 19 MPa at 23° C., and 5.08 cm/min; and elongation at break of at least 250% at 5.08 cm/min.
  • The plots of mechanical properties vs irradiation dose for GUR 4150 (which is representative of [0082] Type 2 UHMWPE) (FIGS. 25-27) show that, for all of the radiation doses between 5 to 25 Mrad, the above ASTM F648 criteria for Types 2 UHMWPE are fulfilled except for the elongation at break, which crosses the 300 limit at about 6 Mrad. Thus, if the ASTM F648 criteria are to be met for Types 2 UHMWPE, the maximum (i.e., the most preferred) gamma radiation dose is about 6 Mrad. As illustrated in the second aspect of the invention (following section), the corresponding curves of wear and other physical properties vs. crosslinking dose could be used to determine the preferred dose range for other Types of UHMWPE or for other polymers in general.
  • II. Second Aspect of the Invention: Method for Optimizing Wear Resistance and Desirable Physical and/or Chemical Characteristics of a Polymeric Composition [0083]
  • The second aspect of the invention uses the findings in this patent application (including those presented in the “EXAMPLES” section, below) to construct a method which allows one skilled in the art, to systematically identify the conditions necessary to routinely produce a polymer with an optimal balance of wear resistance and physical and/or chemical properties, with minimal additional testing and minimal trial and error. In one embodiment of this aspect of the invention, the optimizing method can be schematically illustrated in a flowchart. Once the optimal conditions have been determined by this method, the polymer can then be subjected to these conditions for processing. [0084]
  • The present invention is based in part, on the discovery that wear rate decreases with increasing radiation dose, and there is a maximum dose above which there is little or no additional improvement in wear, but higher doses might degrade other important physical and/or chemical properties of the polymer, such as yield or ultimate strength, elongation to failure, impact strength or fatigue resistance, as well as increasing the susceptibility to oxidation. Oxidation, in turn, is known to adversely affect one or more of these physical properties, and was shown to occur in the examples below for UHMWPE crosslinked at a dose averaging about 28 Mrad if there had been no thermal treatment. Consequently, a polymer irradiated at a high radiation dose may exhibit improved wear resistance, but its other physical or chemical properties may fall outside of desirable or allowable limits, such as those specified by ASTM F648 for UHMWPE for in vivo use. [0085]
  • The method is also based in part on the discovery that, while other important physical properties (such as crystallinity or elongation to break) may be markedly affected by the amount of thermal treatment (e.g., remelting or annealing) applied to the polymer after irradiation crosslinking, the wear resistance is not markedly affected. This latter discovery permits reducing the amount of additional testing required by the user in order to identify the crosslinking dose which will provide the user's desired balance among wear resistance and other physical properties. This method is useful, e.g., in the case where performed polymeric composition made of UHMWPE is used for making in vivo implants, such as acetabular cups. [0086]
  • II(a) Summary of the Steps of the Optimization Method [0087]
  • Thus, the second aspect of the present invention provides a systematic method for optimizing the balance among wear resistance and other desired physical and/or chemical characteristics of a polymer. The steps in this method are summarized in the non-limiting example of the flowchart of FIGS. 23A and 23B. In the flowchart and the following discussion, for ease of discussion, irradiation is used as an example of a crosslinking method, and implant is used as an example of the product that is made from the polymer. However, as discussed elsewhere in this application, other crosslinking methods and products may be used. [0088]
  • Step 1: The process typically begins with the polymer in solid form, such as an extruded bar or block. [0089]
  • Step 2: The bar is irradiated over a range of doses up to the maximum that is likely to produce a material with the desired wear resistance and physical and/or chemical properties. This irradiation may be done, for example, in the case of gamma radiation by means of a [0090] cobalt 60 gamma radiation facility as is presently used for industrial-scale sterilization of implants.
  • Step 3: The irradiated bars are then remelted. Applicants found that remelting of an irradiated polymer would substantially reduce the free radicals produced during irradiation, thus minimizing long-term oxidation and chain scission. By improving the polymeric composition's resistance to long-term oxidation, remelting also improves the polymeric composition's long-term resistance to wear. For further discussion of the subject, see EXAMPLES 2, 3, and 4, below [0091]
  • Although the bar may be contained in a low-oxygen atmosphere during the remelting, this may not be essential since, even if the bar is remelted in ambient air, the resultant oxidation may affect only the surface layer of the polymer (e.g. in the following EXAMPLE section, FIGS. 2, 5, and [0092] 24, show oxidation extending to about 1 mm deep). In the preferred embodiment of the invention, the oxidized surface layer of the preformed polymeric composition will be removed, e.g., during subsequent machining of the products out of the treated bar.
  • [0093] Step 4A The radiation dose is correlated with the wear resistance of the products made from the irradiated remelted polymeric composition, as determined in a wear test that adequately simulates the wear conditions of the products. For example, if the polymeric composition will be made into an implant, then the wear test should preferably adequately simulate the wear conditions of such implants in vivo. The correlation may be arrived at by plotting a dose-response curve for irradiation dose vs. wear.
  • [0094] Step 4B: Similarly, the radiation dose is correlated with each of the physical and/or chemical properties that may be markedly affected by the radiation dose and that might, in turn, substantially affect the performance of the implant in vivo, both for non-remelted and remelted polymer. Again, the correlation may be arrived at by plotting a dose-response curve for irradiation dose vs. each of these physical and/or chemical properties.
  • The user does not have to do dose vs. properties for each property that might be affected, but only those properties that are considered important for the proper functioning of the implant in vivo. Which of these properties are important for the intended application, and the limiting values of these properties, may vary for different polymeric compositions and for different types of applications (e.g., hip prostheses compared to knee prostheses) and must, therefore, be established by the user before applying the flowchart. [0095]
  • [0096] Step 5 is the first attempt at optimization. The user may first decide on the desired amount of improvement in the wear resistance, i.e., the maximum wear rate that is permissible for the user's application. The dose-response curve for wear (Step 4A) then shows the minimum radiation dose necessary to provide this amount of improvement in wear resistance.
  • Similarly, the dose response curves for the other physical or chemical properties deemed critical or important [0097]
  • ([0098] Step 4B) provide the values of these properties corresponding to the specific radiation dose identified in Step 4A as being necessary to provide the desired improvement in wear resistance. If each of these other physical or chemical properties are within allowable limits for the crosslinked and remelted polymer, then an optimal method has been identified (Step 6). In other words, the implant can be made by irradiating the solid polymer bar, remelting the bar and machining out the implant; the entire process being conducted such that the resulting implant has received the optimal dose at its bearing surface.
  • Alternatively, the user may first decide on critical values for one or more properties, such as ultimate tensile strength, fatigue strength, etc., and then check the corresponding dose response curves for the remelted polymer for the maximum allowable dose, and then check the wear vs. dose curve to determine whether this dose gives sufficient improvement in wear (i.e., the user does not necessarily have to begin by choosing the desired amount of improvement in wear). [0099]
  • However, if not enough improvement in wear will be obtained while keeping these other chemical and physical properties within allowable limits, or conversely, if the dose required for the desired wear improvement causes one or more of these properties to be out of allowable limits, then the user can use a lower radiation dose (i.e., accept a higher wear rate) if he wishes to remelt the materials or, alternatively, annealing may be substituted for remelting (Step 7). For a crosslinked material, annealing is less efficient than remelting in removing free radicals, but may cause less of a reduction in other important physical properties. [0100]
  • Whether annealing is a practical option will be apparent from the dose-response curves for the non-remelted and remelted polymers. That is, if the desired value of the property in question falls between the two curves (see for example, FIGS. 25 and 26), then a polymer with the desired limiting value may be produced by an annealing process with an appropriate time/temperature combination. [0101]
  • It is not necessary to generate additional wear dose-response curves for each of the many possible combinations of annealing time and temperature. It is expected that the radiation dose necessary to produce the desired reduction in wear that is determined from the wear dose-response curve for remelted polymer in [0102] Step 4A, will also apply to an annealed polymer produced in Step 7.
  • Step 7: Anneal samples of a bar or block which have been irradiated to that dose that was identified in [0103] Step 4A as being necessary to provide the required improvement in wear resistance, at various time/temperature combinations, to produce a polymer with the critical properties between those for non-remelted and remelted materials.
  • Step 8: The physical or chemical propert(ies) of interest of the irradiated and annealed samples of the polymer are correlated with annealing times and temperatures. [0104]
  • Step 9: Using ultimate tensile strength as an example of the physical characteristic of interest, depending on the resultant curve for annealing time and/or temperature vs. ultimate strength, the radiation dose required to achieve the desired wear resistance identified in [0105] Step 4A (above) should produce a polymer with an ultimate strength within allowable limits.
  • Similar consideration should be given to each of the other important physical and/or chemical properties by generation of individual curves of these properties versus annealing time and/or temperature. If each of these properties is within allowable limits at a particular annealing time and temperature combination, then a suitable method has been identified (Step 10). [0106]
  • If an annealing process cannot be identified that maintains the properties within allowable limits, then the user may choose to accept a lower radiation dose (Step 11), i.e., to accept less of an improvement in wear resistance. However, if a lower radiation dose (and, therefore, a greater wear rate) is acceptable, then the corresponding physical and chemical properties should again be checked for the remelted polymer (using the correlation arrived earlier in [0107] Step 4B), since these may be within limits at the lower radiation dose.
  • If the properties are within limits for the remelted polymer at the lower radiation dose, then remelting may be used instead of annealing to produce a polymer with the desired improvement in wear resistance (Step 6). If not, then the user should proceed with annealing as before (Steps 7 through 10 or 11) but at this lower radiation dose. [0108]
  • The user may wish to progressively reduce the required amount of radiation crosslinking (i.e., to accept still higher wear rate) until a dose is identified for which all of the other properties deemed essential are within the user's required limits. The resultant dose represents the maximum improvement in wear resistance obtainable within the user's criteria. [0109]
  • II(b) Example Applications of the Flowchart [0110]
  • As starting points for the flowchart, the ranges for radiation doses, remelting and annealing temperatures and times described in section “I. First Aspect of the Invention: Polymeric Compositions with Increased Wear Resistance” and “I (A) Further Examples of the First Aspect of the Invention”, above, can be used, with regard to polymers in general, UHMW and HMW polymers in particular, and HMWPE and UHMWPE especially. [0111]
  • For ease of discussion, the following examples illustrate the application of the flowchart using UHMWPE (which also behaves similar to HMWPE) as an example of a polymer and an acetabular cup as an example of an implant. GUR 4150 is representative of such a class of UHMWPE. Similarly, the description uses gamma radiation as an example for crosslinking the polymer. These examples are meant to illustrate and not meant to limit the invention. [0112]
  • The method described by the flowchart is applicable to other polymers, implants or other products made from such polymers, and crosslinking methods (examples of which are described elsewhere in this application), and methods for making an implant or product out of the preformed polymeric composition. [0113]
  • From the data provided by the EXAMPLES (following sections) a number of generalities were discovered that allowed simplification of the use of the flowchart, i.e., to minimize the amount of additional testing that would be required of a user wishing to apply the method to other polymers, or to the GUR4150 of the EXAMPLES but with various optimization criteria. [0114]
  • To establish the critical curve for the reduced in vivo wear (Step 4A), the UHMWPE bar or block is preferably irradiated in [0115] Step 2 and remelted in Step 3, in a manner and to a dose and temperature and time as described for UHMWPE in the section, “I. First Aspect of the Invention: Polymeric Compositions with Increased Wear Resistance” and “I (A) Further Examples of the First Aspect of the Invention”, above.
  • In [0116] step 4A, acetabular cups are machined out of the irradiated bar and wear tested under conditions suitably representative of the intended in vivo application (e.g., by the method described in the EXAMPLES section below) to establish a wear vs. radiation dose response curve for the specific polymer. EXAMPLE 5 and FIG. 22 show a wear dose-response curve for gamma irradiated GUR 4150 UHMWPE.
  • Applicants discovered that it is not necessary to generate additional wear dose-response curves for each of the many possible combinations of annealing time and temperature. This follows from the results of EXAMPLE 2. Since annealing is done at a lower temperature than remelting and, therefore, has a less marked effect on physical properties in general, it can be expected that annealing will have even less of an effect on the wear resistance than remelting. [0117]
  • Another important aspect of the invention is the discovery that wear resistance of GUR 4150 was not markedly affected by remelting and, therefore, it is also not likely to be markedly affected by annealing time and temperature. Therefore, it is expected that the radiation dose necessary to produce the desired reduction in wear that is determined from the wear dose-response curve for remelted polymer in [0118] Step 4A, will also apply to an annealed polymer produced in Step 7. Therfore, while the user needs to do his own tests to establish tensile strength vs dose etc., he can rely on the wear vs dose curve developed for the remelted material, rather than running an additional set of wear curves for each annealing condition. This represents a considerable saving in experimental costs, since the tensile strength tests typically may be completed in a few days (using common tensile test apparatus), but the tests of wear vs dose require months to complete (and require highly specialized equipment and techniques available on only a handful of laboratories in the world).
  • Furthermore, if the user is working with GUR 4150, he can use the dose vs wear curve of FIG. 22 (as well as the plots of other mechanical properties, FIGS. 25-27) without needing to run any wear or tensile tests. Finally, if he is working with another grade of UHMW polyethylene, he can probably use FIG. 22, since other tests have shown that the wear resistances of these materials are very similar to GUR 4150 for a given sterilization treatment. At the least, FIG. 22 establishes the range on which the user may focus his wear vs. dose experiments for other grades of UHMW polyethylene, to minimize the testing necessary to identify the optimum dose. [0119]
  • For other polymers, comparable wear tests at each end of the range of interest for radiation dose could be applied to verify whether remelting or annealing also does not markedly affect their wear resistance. Nevertheless, GUR 4150 is representative of UHMWPEs, especially those useful for implants, in its physical and chemical properties, and applicants have observed that other UHMWPEs, of different molecular weights and with or without calcium stearate, such as GUR 1020 (calcium stearate free, lower molecular weight grade) behaved similarly to GUR 4150 in their wear resistance after irradiation sterilization in air. McKellop, H. et al., [0120] Trans. Society for Biomaterials, Vol. 20, pg. 43 (1997).
  • Further, it has been observed that, although the starting physical properties of HMWPE are different from those of UHMWPE, these differences will be substantially reduced after sufficient crosslinking. For example, they are almost equal after electron beam irradiation treatment to 300 kGy (30 Mrad), for properties like gel content, swelling and strength. Streicher, R. M., [0121] Beta- Gamma 1/89: 34-43, at p. 42, right col., fourth full paragraph. Even the wear properties were the same, after the differences in the molecular arrangement between HMWPE and UHMWPE were offset by the irradiation procedure. Thus, it is predicted that the findings based on GUR 4150 and the above discussion would be applicable to polymers in general, and to UHMW and HMV polymers, in particular, and especially HMWPE and UHMPE. Thus, the radiation, remelting and annealing ranges found for GUR 4150 can be applied to polymers in general, and more preferably to HMW and UHMW polymers, and most preferably to HMWPE and UHMWPE; and these ranges can be used at the very least, as starting points in the flowchart for determining the specific ranges for other polymers, and the data in the “EXAMPLES” section below will facilitate the user in arriving at the proper conditions for GUR 4150, ASTM F648 Type 2 UHMWPE, and UHMWPE and HMWPE in general.
  • The following examples illustrate the use of these generalities in conjunction with the flowchart. In the first example, if the user is working with GUR 4150, or an UHMWPE that satisfies [0122] ASTM F648 Type 2 criteria in general, then, based on FIGS. 25-27, only the elongation will fall below the ASTM limit (i.e., 300%) over the dose range of interest, i.e., 0 to 25 Mrad, and this occurs at about 6 Mrad. Thus, the maximum allowable dose is 6 Mrad and, from the wear vs dose plot (FIG. 22), it can be seen that a 6 Mrad dose will provide a wear rate of about 7 to 8 mm3 per million cycles. This is about a 78% or more reduction over the 33.1 mm3 per million cycles shown for non-remelted polyethene gamma irradiated to 3.1 Mrad in air. If this reduction in wear rate is sufficient for the user's purpose, then his goal is achieved. Note however, that the elongation vs dose plot (FIG. 27) shows virtually the same behavior whether the polyethylene is remelted or not, so if the above 78% reduction is not sufficient for the user's purpose, then the user would have no choice but to increase the radiation dose, as annealing is also not likely to affect the elongation to break, for the reasons discussed above.
  • In a second example, a user requires a lower limit on tensile strength at break at 40 MPa, and wishes to produce a material with wear no more than 1 mm[0123] 3 per million cycles. The wear vs dose curve (FIG. 22) shows that a dose of about 15 Mrad is required to produce a polyethylene with the desired amount of wear resistance. However, the tensile strength at fracture vs dose curve shows that the tensile strength at 15 Mrad for a remelted material is about 36 Mpa. Since this is below the user's acceptable limit of 40 Mpa, he can either use a smaller radiation dose and, therefore, accept a smaller improvement in wear rate (i.e., if he wishes to remelt his material) or he can try annealing instead of remelting since, depending on the time/temperature combination used, annealing can be expected to produce a polymer with a value of tensile strength between the limits indicated by the curves for non-remelted and remelted polymer (FIGS. 25 and 26). As shown on these figures, the tensile strength at 15 Mrad for a non-remelted material is about 46 Mpa, well above the user's limit of 40. So, with minimal trial and error, the user can identify an annealing time and temperature that, when applied to a polyethylene that has been exposed to 15 Mrad radiation, has a tensile strength of the required 40 Mpa. Again, based on the wear test results, the user knows that he does not have to re-do the wear vs dose curve for all of the various annealing treatments he tries, in order to identify the dose necessary to produce the desired improvement in wear resistance.
  • Having described the invention, the following examples are presented to illustrate and support the invention, and are not to be construed as limiting the scope of the invention. [0124]
  • EXAMPLES
  • The nominal dose of radiation applied to implants at a commercial radiation facility typically varies within a range. Therefore, in the following examples, the average gamma radiation doses are given, such as average gamma radiation doses of 3.3, 26.5, and 28 Mrad. The average of 3.3 Mrad was arrived at by averaging the minimum and maximum doses, e.g., a minimum of 3.28 and a maximum of 3.45 Mrad. Similarly, for example, the average of 26.5 was based on averaging a minimum of 25.14 and a maximum of 27.70 Mrad; and the average of 28 was based on averaging a minimum of 26.01 and a maximum of 30.30 Mrad. [0125]
  • Example 1 Effect of Radiation Atmosphere and Dose on the Physical Properties of UHMWPE
  • Experimental Details [0126]
  • Commercial-grade UHMWPE extruded bars (GUR 4150, Poly Hi Solidur), with a weight average molecular weight of 5-6×10[0127] 6, were used as received. The 8 mm thick specimens were cut from the bars and irradiated with gamma-rays at room temperature either in ambient air or in a vacuum chamber at SteriGenics International (Tustin, Calif.) to average doses ranging from 3.3 to 250 Mrad. Radiation was delivered at a dose rate of 0.2 Mrad/hr. For 250 Mrad, the dose rate was 4 Mrad/hr. Cobalt-60 was used as a source of gamma radiation. A subset of the 8mm thick specimens that had been irradiated in vacuum was remelted in a vacuum oven by heating from room temperature to 145° C. slowly (at about 0.3° C./min.) and maintaining at 145° C. for one hour. After remelting, the specimens were slowly cooled to room temperature.
  • The physical properties of the disk specimens before and after irradiation and remelting were characterized by DSC, gel content analysis and FTIR. [0128]
  • Gel Content Analysis [0129]
  • The gel content of each material was analyzed as a function of depth from the surface. 100 μm thick sections (about 50 mg) were microtomed across the specimen. Extraction of the sol-fraction was performed by boiling in p-xylene for 24 hours, with 0.5 wt % of antioxidant (2,6-di-t-butyl-4-methyl phenol) added to prevent oxidation. For highly oxidized sections from the surface layer, which tended to break up during boiling, the specimens were wrapped in PTFE membrane filter (0.5 μm pore size) to avoid loss of gel. After extraction, the specimens were de-swollen in acetone and dried at 60° C. in a vacuum oven to constant weight. The gel fraction was determined from the ratio of the weight of the dried-extracted material to that of the dry non-extracted material. [0130]
  • Differential Scanning Calorimetry (DSC) [0131]
  • For DSC measurements, samples were cored and microtomed into 200 μm thick sections across the depth. Specimens (−4 mg) were heated from 5° C. at 10° C./min in a differential scanning calorimeter (Perkin-Elmer DSC-4) to 170° C. The melting temperature was identified from the peak of the melting endotherm. Indium was used for calibration of the temperature and heat of fusion. The heat of fusion was determined by comparing the area under the melting endotherm to the area of fusion of an indium sample having a known heat of fusion of 28.4 J/g, and divided by 292 J/g, the heat of fusion of an ideal polyethylene crystal, to get the degree of crystallinity. [0132]
  • Results and Discussion [0133]
  • As shown in FIG. 1, irradiation increased the crystallinity of the 8 mm thick specimens of UHMWPE from about 55% to 60-66%, with considerable overlapping for the different doses. Similar changes were observed with the samples that were irradiated in air. The gel content (i.e., the extent of crosslinking) (FIG. 2) also increased with increasing radiation dosage. Importantly, crosslinking increased markedly moving from the surface into the middle of each specimen, reaching about 92% for the 3.3 Mrad dose. Apparently, the oxygen present in the vacuum chamber was sufficient to cause the increased oxidation and decreased crosslinking of the surface layer. Thus, our method, i.e., of irradiating a bar and machining away the surface is more effective and efficient than use of a vacuum or other low oxygen atmosphere in producing a final product with minimal oxidation of the bearing surface. For reference (FIG. 3), chemically crosslinked polyethylene (PE) (1% peroxide, irradiated in air) (Shen, F. W. et al. [0134] J. of Poly. Sci. Part B: Poly Phys 34:1063-1077 (1996)), which exhibits very low wear, has a gel content of about 90% at about 100 microns from the surface, rising to a maximum of nearly 100% in the center.
  • In a second phase of this example, the 8 mm thick disks that had been irradiated in vacuum were remelted by heating to 145° C. for one hour, and slowly cooled. This reduced the peak melting temperature, the degree of crystallinity and the crystal size. For example (FIG. 4), the crystallinity of the 3.3 Mrad specimens was reduced from the range of 60-65% to the range of 50-53% by remelting. [0135]
  • In addition, during remelting, residual free radicals that were formed by the irradiation apparently recombined and increased the total crosslinking (as evident from the increased gel content, FIG. 5). Extinguishing free radicals in this manner, in turn, further reduces the oxidation that would otherwise occur when the cups are stored on the shelf or exposed to body fluids after implantation. [0136]
  • The lower gel content (crosslinking) near the surface (FIG. 3) was due to oxidation of the surface layer at the time of irradiation. Thus, it can be expected that the polymer of the surface layer would have less wear resistance than that in the center of the specimen. In the method presented in this application, this gradient would not be present, since the surface layer would be removed during machining of the final implant from the irradiated bar or block. [0137]
  • The crystallinity and gel content of the irradiated 8 mm thick disks, with and without remelting, are compared in FIGS. 4 and 5, respectively. [0138]
  • Example 2 Wear Testing of Radiation Crosslinked Cups with and without Remelting
  • Experimental Details [0139]
  • Six extruded bars of UHMWPE (GUR 4150), each 3 inches in diameter, were exposed to 3.3 or 28 Mrad of gamma radiation at a dose rate of 0.2 Mrad per hour in ambient air (SteriGenics, Inc., Tustin, Calif.). Two bars for each radiation dose were then remelted by heating in an oven in ambient atmosphere from room temperature to 150° C. at about 0.3° C. per minute and holding at 150° C. for five hours, and then slow-cooling to room temperature. The crystallinity and gel content of these four materials were measured across the cross section of extra samples of each bar using differential scanning calorimetry (DSC) and gel content analysis. The results are summarized in Tables 1 and 2. [0140]
  • Four sets of acetabular cups were machined from bars of each of the four materials at a commercial machining shop (Bradford and Meneghini Manufacturing Co., Santa Fe Springs, Calif.). Each cup had a 2 inch outer diameter (O.D.) and 1.26 inch inner diameter (I.D.), and 1 inch outer radius and 0.633 inch inner radius (FIG. 6). Wear tests were run on two sets of three cups for each radiation dose that had been remelted, and two sets of three cups for each dose that had not been remelted. The bars were intentionally used with larger diameters than the final cups so that the process of machining away the outer 0.5 inches of each bar removed the so most oxidized, most crystalline, least crosslinked surface layer which is about 0.5 to 1.0 mm thick. In this manner, the bearing surface of each cup consisted of material from near the center of the bar, i.e., the most crosslinked, least crystalline, least oxidized region, which is predicted to be the most wear resistant. [0141]
  • Since acetabular cups used in patients must first be sterilized by some acceptable means, the test cups in this study were sterilized prior to wear testing using ethylene oxide at the appropriate dose for clinical implants. Ethylene oxide was chosen instead of additional gamma irradiation (e.g., 2.5-4.0 Mrad) in order to confine the results to the effects of the original 3.3 or 28 Mrad doses used to crosslink the materials. [0142]
  • Prior to wear testing, the cups were pre-soaked in distilled water for three weeks to minimize additional fluid absorption during the wear test, thereby making the weight loss method for wear measurement more accurate. For the wear test, the cups were enclosed in polyurethane molds and pressed into stainless steel holders (FIG. 7). Each holder was fitted with an acrylic chamber wall to contain the lubricant. The chambers were mounted on the hip simulator wear machine, with each cup bearing against a ball of cobalt-chromium alloy (conventional hip replacement femoral balls were used, with implant-quality surface finish). The ball-cup pairs were subjected to a physiological cyclic load with a peak load of about 2000 Newtons (Paul, J P., “Forces transmitted by joints in the human body”. In [0143] Lubrication and Wear in Living and Artificial Human Joints. Proc Instn Mech Engrs 1967;181 Part 3J:8-15) and the cups were oscillated against the balls through a bi-axial 46° arc at 68 cycles per minute. Each test station on the simulator (FIG. 7) contains a self-centering unit 5, the acetabular cup 6, a dual axis offset drive block 7, a test chamber 8, serum lubricant 9 and a femoral ball 10. The arrow indicates the direction of the computer controlled simulated physiological load applied to the simulated hip joint.
  • During the test, the bearing surfaces were kept immersed in bovine blood serum to simulate lubrication in the human body. Sodium azide at 0.2% was added to the serum to retard bacterial degradation, and 20 mM ethylene-diaminetetraacetic acid (EDTA) was added to prevent precipitation of calcium phosphate onto the surface of the balls (McKellop, H. and Lu, B., “Friction and wear of Polyethylene-metal and Polyethylene-ceramic Hip Prostheses on a Joint Simulator, Transactions of the Fourth World Biomaterials Congress, Berlin, April 1992, p. 118). A poly-ethylene skirt covered each test chamber to minimize airborne contaminants. [0144]
  • At intervals of 250,000 cycles, the cups were removed from the machine, rinsed, inspected under light microscopy and replaced in fresh lubricant. At intervals of 500,000 cycles, the cups were removed, cleaned, dried and weighed to indicate the amount of wear. After inspection under light microscopy, the cups were replaced on the wear machine with fresh lubricant and testing was continued to a total of three million cycles. One million cycles is approximately the equivalent of one year's walking activity of a typical patient. [0145]
  • The weight loss was corrected for the effects of fluid absorption (which masks wear) by increasing the apparent weight loss of the wear test cups by the mean weight gain of three control cups of each material that were also immersed in serum and cyclically loaded on a separate frame, but without oscillation. The corrected rate of weight loss was converted to volume loss by dividing by the approximate density of UHMWPE (0.94 gm/cc). The mean weight loss (after soak correction) and the standard deviation was calculated for each of the four types of materials at each weighing interval. The wear rate of each cup was calculated by applying linear regression to the wear data for the entire three million cycles. The mean wear rates and standard deviations also were calculated for each type of material. [0146]
  • Results [0147]
  • FIG. 8 shows the soak-corrected wear (volume loss) of three cups of each material as a function of wear cycles. FIG. 9 shows the average wear (volume loss) of three cups of each material as a function of wear cycles. The individual wear rates and the mean values for each type of material are listed in Table 3. The most wear occurred with the cups subjected to 3.3 Mrad without remelting. These averaged 21.1 mm[0148] 3 per million cycles.
  • The wear of the cups subjected to 3.3 Mrad with remelting averaged 18.6 mm[0149] 3 per million cycles, or 12% lower wear than for the non-remelted 3.3 Mrad cups. The cups subjected to 28 Mrad had much lower wear rates than the 3.3 Mrad cups, and the rates were similar, whether or not the material had been remelted. That is, the average wear rate of the non-remelted 28 Mrad cups was about 1.2% that of the non-remelted 3.3 Mrad controls, and the average wear rate of the remelted 28 Mrad cups was about 1.7% of the same controls.
  • Discussion [0150]
  • The results of the wear test clearly demonstrated the improved wear resistance of the UHMWPE acetabular cups that resulted from exposure to 28 Mrad gamma radiation. Apparently, the crosslinking generated by the higher radiation dose reduced the wear rates to less than a few percent of the control value (3.3 Mrad). The minimum amount of wear debris necessary to induce clinically significant osteolysis and other problems in a specific patient has not been established, and it may vary among patients. Nevertheless, a material which reduces the wear rate to the very low levels exhibited by the 28 Mrad cups in this study would be very likely to provide a large margin of safety over currently used materials. [0151]
  • The wear curves for both of the 28 Mrad specimens (FIGS. 8 & 9) were slightly negative on the first weighing at 0.5 million cycles. This was most likely due to a slight under-correction for fluid absorption (that is, the wear test cups absorbed slightly more water than the soak controls, and the error between the two was greater than the weight loss due to wear, producing a negative wear value). If this assumption is correct, then the overall wear rates for the two 28 Mrad sets were somewhat smaller, and possibly closer together, than the values indicated in Table 3. [0152]
  • Example 3 Artificial Aging of Radiation-Crosslinked UHMWPE
  • Materials [0153]
  • Six UHMWPE (GUR 4150) extruded bars (3″ diameter) were gamma irradiated in air, three bars each at 3.3 or 28 Mrad, at a dose rate of 0.2 Mrad/hour. For each radiation dose, two bars were then remelted by heating in an oven at ambient atmosphere from room temperature to 150° C. at about 0.3° C./min, holding at 150° C. for 5 hours and slowly cooling to room temperature, and the third bar was not remelted. A 13 mm (0.5 inch) layer of the outer diameter of the treated (remelted) and untreated (non-remelted) bars was machined away to remove the most oxidized, least crosslinked surface layer. The bars were used to produce specimens for the artificial aging tests described here and for the wear tests described in EXAMPLE 2. [0154]
  • To examine the effect of artificial aging on these four materials (3.3 and 28 Mrad, remelted and not remelted), 8 mm thick disks were cut from these 2 inch diameter cores and were heated in an oven slowly (˜0.2° C./min) to 80° C. at ambient atmosphere and held at 80° C. for 10, 20 or 30 days. In addition, one acetabular cup for each of the four conditions (3.3 and 28 Mrad, remelted and not remelted) that had been fabricated at the same time as the wear test cups of EXAMPLE 2 and stored in air for about 5 months was cut into four pieces and aged at 80° C. for the same periods. [0155]
  • The gel content analysis and DSC method are as described in EXAMPLE 1, above. [0156]
  • Fourier Transform Infrared Spectroscopy (FTIR) [0157]
  • FTIR measurements were performed on the above specimens. Segments about 5 mm wide were cut from each polyethylene specimen and the segments were microtomed into 200 μm thick slices. The oxidation profiles, as indicated by the carbonyl concentration, were measured using a Mattson Polaris FTIR (model IR 10410) with a Spectra-Tech IR plan microscope. Spectra were collected in 100 μm steps from the surface to the middle of the specimen, using 64 scans summation at a resolution 16 cm[0158] −1 with a MCT (Mercury Cadmium Telluride) detector. The carbonyl group concentration was indicated by the ratio of the peak height of the ketone absorption band at 1717 cm−1 to the height of the reference band at 2022 cm−2 (—CH2-vibration).
  • Results [0159]
  • The oxidation profiles as a function of depth are shown in FIGS. 10-13. As shown in FIG. 10 for the 3.3 Mrad, non-remelted material, oxidation increased with increasing aging time. In contrast, the 3.3 Mrad, remelted material (FIG. 11) showed almost no oxidation for 10 and 20 days aging, but some oxidation for 30 days aging. However, the oxidation peak at the surface with remelting was about 50% of that at the surface without remelting (FIG. 10). For the 28 Mrad, non-remelted UHMWPE (FIG. 12), the oxidation showed a greater increase with increasing aging time than the 3.3 Mrad, un-remelted material. Again, oxidation was much lower with remelting, i.e., the 28 Mrad, remelted UHMWPE (FIG. 13) essentially exhibited no oxidation after 20 days aging (FIG. [0160] 13), and the oxidation peak at the surface after 30 days was only about ⅓ that without remelting (FIG. 12).
  • Similarly, with the acetabular cups stored in air for 5 months and then aged for 20 days at 80° C., the remelted materials (3.3 or 28 Mrad) showed no oxidation (FIG. 14), while the non-remelted cups (3.3 or 28 Mrad) showed substantial oxidation (FIG. 14), especially for 28 Mrad UHMWPE, and with a subsurface oxidation peak in both non-remelted materials. [0161]
  • Since crosslinking of UHMWPE reduces its solubility, the percent of undissolved material (gel content) is an indirect indication of the amount of crosslinking. The gel content as a function of depth for various conditions are shown in FIGS. [0162] 15 to 18. As shown in FIG. 15 for 3.3 Mrad, non-remelted material, the gel content (i.e., crosslinking) decreased with increasing aging time. There was a strong gradient of gel content in the highly oxidized surface regions after 30 days aging, i.e., increasing from a minimum on the surface to a maximum about 2 mm below the surface. Near the surface, the gel content was highest (91%) in the un-aged specimen, and decreased with increasing aging time to less than about 5% in the same region for the 30 day aged specimen. In contrast, the remelted materials (FIG. 16) showed much less reduction in gel content in the surface regions than the non-remelted materials. That is, comparison of FIG. 17 (28 Mrad, non-remelted) and FIG. 18 (28 Mrad, remelted) showed that the remelted UHMWPE had much higher retention of gel content (i.e., crosslinking).
  • The results of the DSC measurements indicated the degree of crystallinity as a function of depth for various materials aged for 30 days at 80° C., as shown in FIG. 19. Near the surface, the degree of crystallinity was 83% for the 28 Mrad, non-remelted material after aging, compared to 65% before aging. The high level of crystallinity and increased brittleness of the surface zone of the aged material often resulted in fragmentation of a layer about 1 mm thick during microtoming. In contrast, the 28 Mrad remelted material showed less increase in crystallinity in the surface regions due to aging, and no brittle zone was observed. Similarly, due to aging, the 3.3 Mrad non-remelted material exhibited an increase in crystallinity from 60% to about 78%, and the surface layer was again brittle, although not as brittle as with the 28 Mrad, non-remelted material. [0163]
  • Discussion [0164]
  • Irradiation of UHMWPE produces crosslinking, chain scission and the formation of free radicals. If oxygen is present, it may react with the free radicals to form oxidized species, leading to additional chain scission (reduction in molecular weight) and an increase in crystallinity. Since polymer crystallites melt and become amorphous above the melting temperature, molecular chain movements and rotations are increased, favoring the recombination of free radicals. The results of the present experiments showed that remelting at 150° C. apparently caused the residual free radicals to decay and/or to recombine to form crosslinks, leading to an increased gel content. Therefore, remelting is an effective way to extinguish free radicals, making the material less susceptible to long-term oxidation and potentially improving the long-term wear resistance, as evident from the results of the artificial aging experiments, where there was much less oxidation of the remelted materials. [0165]
  • For a crosslinked polymer, oxidative degradation cleaves the molecules and leads to a reduction in gel content. This was evident in the present experiments from the reduced gel content after aging, particularly with the non-remelted materials (FIGS. [0166] 15 to 18). That is, the distribution of oxidation, as indicated by the profiles measured by FTIR, was inverse to the gel content within the material; the higher the oxidation, the lower the gel content (crosslinking). Since remelting extinguishes free radicals and increases gel content, thereby reducing the susceptibility to oxidation, the remelted materials (3.3 and 28 Mrad) had a much greater gel content after artificial aging than the non-remelted materials.
  • An appropriate amount of crosslinking of UHMWPE can improve its wear resistance. The high level of crosslinking in the UHMWPE caused by the 28 Mrad gamma irradiation, as evident from the high gel content (EXAMPLE 2), apparently contributed to the much greater wear resistance exhibited by the acetabular cups tested in EXAMPLE 2. In addition, as shown in EXAMPLE 3, remelting of the irradiated UHMWPE markedly reduced the residual free radicals, rendering the material much more resistant to subsequent oxidation and, therefore, resistant to a reduction in crosslinking, which can be of substantial benefit for implants in long-term clinical use. [0167]
  • Example 4 Wear Testing of Irradiated Cups with and without Artificial Aging
  • Materials and Methods [0168]
  • The wear testing of irradiated cups with and without remelting was described in EXAMPLE 2. Effects of artificial aging on the physical properties of irradiated UHMWPE, with and without remelting, were described in EXAMPLE 3. To examine the resistance of crosslinked cups to thermal-induced oxidation, and the effect of such oxidation on the wear of irradiated cups with and without remelting, two acetabular cups for each of the four conditions (3.3 and 28 Mrad, remelted and not remelted) that had been wear tested for 3 million cycles as described in EXAMPLE 2, were heated in an oven slowly (˜0.2° C./min) to 80° C. at ambient atmosphere and held at 80° C. for 20 days, with one acetabular cup for each of the four conditions being stored in ambient air. The oxidation profile after 20-day aging for each condition was shown in FIG. 14, EXAMPLE 3. [0169]
  • Prior to wear testing, the cups were pre-soaked in distilled water for four weeks to minimize additional fluid absorption during the wear test, thereby making the weight loss method for wear measurement more accurate. The details for the wear test were described in EXAMPLE 2. [0170]
  • Results [0171]
  • FIG. 20 shows the combined soak-corrected wear (volume loss) for the cups before aging (3.3 and 28 Mrad, remelted and not remelted) during the first 3 million cycles (same data as EXAMPLE 2) and for the same cups, after two cups of each material had been artificially aged, from 3 to 7 million cycles. The individual wear rates and the mean values for each type of material, calculated by linear regression, are listed in Table 4. [0172]
  • All cups subjected to 3.3 Mrad with remelting showed comparable wear rates, whether or not the material had been remelted or remelted and aged. Wear was negligible for all of the cups subjected to 28 Mrad, whether or not these were remelted, and whether or not they were aged. [0173]
  • Discussion [0174]
  • The results of the wear test clearly demonstrated the improved wear resistance of the UHMWPE acetabular cups that resulted from exposure to 28 Mrad gamma radiation. Apparently, the minor oxidation at the surface (FIG. 14) of the highly crosslinked acetabular cups (28 Mrad, without remelting) induced by the artificial aging, had very limited effect on the wear resistance. Although a substantial oxidation peak occurred about 0.4 mm below the surface, because of the very high wear resistance of the 28 Mrad cups, the total penetration due to wear was too shallow to reach this sub-surface oxidized zone, even after 4 million cycles. [0175]
  • For the non-remelted 3.3 Mrad cups, subsurface oxidation, peaking at about 1 mm below the surface (FIG. 14), occurred after aging in air at 80° C. for 20 days. Since the total depth of penetration of these cups was about 300 microns (at 7 million cycles), the full effect of this subsurface oxidation would not become apparent until a much larger number of wear cycles. [0176]
  • Nevertheless, the sub-surface oxidation in the non-remelted cups (EXAMPLE 3,.particularly for the 28 Mrad specimen) leads to reduced molecular weight, a reduction in crosslinking (as indicated by gel content) and an increased crystallinity and brittleness, all of which can contribute to reductions in mechanical properties such as fatigue strength and, eventually, a reduction in wear resistance. Although remelting had no apparent effect on the wear resistance of the aged cups in the present example, the elimination of free radicals by remelting improves the long-term resistance to oxidation, thereby improving the long-term wear resistance in vivo. [0177]
  • Example 5 Wear Testing of Gamma-Irradiated UHMWPE with Multiple Doses
  • Materials and Methods [0178]
  • In EXAMPLE 2, we demonstrated the improved wear resistance of UHMWPE acetabular cups that resulted from exposure to 28 Mrad gamma radiation, as compared to cups irradiated to 3.3 Mrad. The average wear rate of the 28 Mrad cups was less than 2% of that of the 3.3 Mrad cups (i.e., a dose within the normal 2.5 to 4.0 Mrad range used to sterilize implants). To examine the wear as a function of radiation dose and, thereby, determine an optimum dose for reducing wear, extruded bars of GUR 4150 UHMWPE, 3″ diameter×15″ long, were gamma irradiated in air, three bars at each dose of 4.5, 9.5, 14.5, 20.2 or 24 Mrad (SteriGenics, Inc., Corona, Calif.), at a dose rate of 0.45 Mrad/hour. Additional bars were irradiated in air to 50 or 100 Mrad (SteriGenics Inc., Tustin, Calif.), at a dose rate of 0.67 Mrad/hour. For each radiation dose, two bars were then remelted by heating in an oven in ambient atmosphere from room temperature to 150° C. at about 0.3° C./min, holding at 150° C. for 5 hours and then slowly-cooled to room temperature, with the third bar not being remelted. The irradiated-remelted bars were used to produce acetabular cups for the wear tests. [0179]
  • Seven sets of acetabular cups were machined from the irradiated-remelted bars for each of the seven doses at a commercial machining shop (Bradford and Meneghini Manufacturing Co., Santa Fe Springs, Calif.). Each cup had a 2″ O.D. and 1.26″ I.D., with 1″ outer radius and 0.63″ inner radius (FIG. 6). Wear tests were run on the remelted specimens, using two cups for each radiation dose from 4.5 to 24 Mrad, and one cup each for 50 and 100 Mrad. The bars were intentionally used with larger diameters than the final cups so that the process of machining away the outer layer of each bar, about 0.5 inch thick, effectively removed the most oxidized, most crystalline, least crosslinked surface layer (about 0.5 to 1.0 mm). In this manner the bearing surface of each cup consisted of material from near the center of the bar, i.e., the most crosslinked, least crystalline, least oxidized region, which was expected to be the most wear resistant. [0180]
  • Because acetabular cups used in patients must first be sterilized by some acceptable means, the test cups in this study were sterilized prior to wear testing using ethylene oxide at the appropriate dose for clinical implants. Ethylene oxide was chosen instead of additional gamma irradiation (e.g., 2.5-4.0 Mrad) in order to focus the results on the effects of the radiation doses used to crosslink the materials. Prior to wear testing, the cups were pre-soaked in distilled water for four weeks to minimize additional fluid absorption during the wear test, thereby making the weight loss method for wear measurement more accurate. The details for the wear test method were described in EXAMPLE 2. [0181]
  • Results [0182]
  • FIG. 21 shows the soak-corrected wear (volume loss) of each material (three cups for 3.3 Mrad from EXAMPLE 2, two cups each for radiation dose from 4.5 to 24.5 Mrad, and one cup each for 50 and 100 Mrad). The individual wear rates, determined by linear regression, and the mean values for each type of material are listed in Table 5. At about 2.1 million cycles, there was a temporary overloading of the test cups, due to a malfunction of the computer controller. Although this overload had only a minor effect on the wear rates of the cups, the cup irradiated to 100 Mrad cracked and was, therefore, removed from the test. [0183]
  • FIG. 22 shows the average wear rate (volume loss from 1 to 5 million) of each type of material, that had been re-melted (denoted in the figure by darkened circles) and that had not been re-melted (denoted in the figure by an open circle), as a function of dose. [0184]
  • The wear of the cups subjected to 3.3 or 4.5 Mrad with remelting averaged 17.5 or 9.3 mm[0185] 3 per million cycles, respectively, showing about 13% or 54% lower wear than for the 3.3 Mrad non-remelted cups (20.1 mm3 per million cycles). In contrast, the wear rate of the 9.5 Mrad remelted cups averaged 2.2 mm3 per million cycles, i.e., about 89% lower than for the 3.3 Mrad non-remelted cups. For radiation doses greater than 9.5 Mrad, minimal systematic wear occurred, such that, compared to that with 3.3 Mrad non-re-melted cups, the wear rates were about 94% lower for the 14.5 Mrad remelted cups, and minimal wear (>99% reduction) for the 20.2 Mrad remelted cups.
  • “Negative” wear rates were calculated for the cups given 24 Mrad or greater doses. Apparently, these cups absorbed more water than the soak control cups, and the error between the two was greater than the weight loss due to wear, giving a net gain in weight. [0186]
  • Discussion [0187]
  • The results clearly demonstrated that the wear resistance of UHMWPE acetabular cups were improved substantially with increasing radiation dose over the range of 4.5 to 9.5 Mrad (i.e., with increasing crosslinking), such that wear was too small to accurately quantify for doses exceeding about 20 Mrad. Since, in addition to improving wear resistance, radiation induced crosslinking may degrade other physical properties, such as elongation to failure and fatigue strength, the dose-response curve developed in the present example provides the opportunity to select an optimum dose, i.e., one that provides the desired amount of improvement in wear resistance with a minimum reduction in other physical properties. The procedure for arriving at the choice of dose for a particular in vivo application is described in this application. [0188]
  • UHMWPE acetabular cups that had been compression molded and then exposed to 3.1 Mrad gamma radiation in air but were not thermally treated (i.e., typical of commercially used implants over the past two decades), showed an approximate wear rate of 33.1 mm[0189] 3/million cycle using the procedure of the wear test described in EXAMPLE 2, above. When compared to these conventional UHMWPE acetabular cups, the acetabular cups of the present invention (i.e., irradiated bar stock, remelted and machined into cups) show the following percentage reduction in wear rate: for the 3.3 Mrad remelted acetabular cup from EXAMPLE 2, above (about 47% reduction in wear rate); 4.5 Mrad remelted acetabular cup from EXAMPLE 5, above (about 72% reduction in wear rate); 9.5 Mrad remelted acetabular cup from EXAMPLE 5, above (about 93% reduction in wear rate).
  • Example 6 Physical Characterization of Gamma-Irradiated UHMWPE with or without Remelting
  • Materials and Methods [0190]
  • The materials for physical characterization were the same as the wear tested materials described in EXAMPLE 5. The materials included UHMWPE extruded bars (3″ in diameter) gamma irradiated to 3.3, 4.5, 9.5, 14.5, 20.2, 24, 50 and 100 Mrad, with or without remelting, and the non-irradiated bars. 8 mm thick disks were cut out of irradiated bars with or without remelting, and sterilized with ethylene oxide. The specimens for DSC and swelling measurements were cut out of the center of the 8 mm thick disks. The DSC measurement for crystallinity and melting temperature with sample weighing about 4 mg was described in EXAMPLE 1. For swelling measurements, 1 mm thick sheet weighing about 0.5 gram was cut out of the center of the 8 mm thick disk, and extraction of the sol-fraction was performed in boiling p-xylene for 72 hours, with 0.5 wt % antioxidant (2,6-di-t-butyl-4-methyl phenol) being added to prevent oxidation. After extraction, the gel was transferred to fresh p-xylene and allowed to equilibrate at 120° C. for 2 hours. The swollen gel was then quickly transferred to a weighing bottle, covered and weighed. The data was obtained as the average of five measurements. After measurements, samples were deswollen in acetone and then dried at 60° C. in a vacuum oven to a constant weight. The gel fraction was determined as the ratio of the weight of the dried extracted to the initial dry non-extracted network. The degree of swelling was calculated as the ratio of the weight of the swollen gel to the dried extracted gel. The degree of swelling was used to calculate the network chain density, number-average molecular weight between crosslinks and crosslink density, according to the theory of Flory and Rehner (Shen et al., [0191] J. Polym. Sci. Polym. Phys., 34:1063-1077 (1996)). For examining the oxidation profiles of the extruded bars irradiated and remelted in air, a two hundred micron thick section was microtomed perpendicular to the bar surface and examined by FTIR as a function of depth from the bar surface.
  • Results and Discussion [0192]
  • The melting temperature and crystallinity for non-irradiated, and irradiated (with and without remelting) materials are shown in Table 6. The degree of swelling, average molecular weight between crosslinks, crosslink density and gel content are shown in Table 7. After irradiation, the melting temperature and crystallinity increased, ranging from-135.3 to 140.2° C., and about 60 to 71%, respectively, over the dose range studied. Remelting of the irradiated bars resulted in reductions in the melting temperature and crystallinity, ranging from about 131 to 135° C., and about 51 to 53%, respectively. [0193]
  • As shown in Table 7, with increasing radiation dose, the degree of swelling and average molecular weight between crosslinks decreased, while the crosslink density increased. The gel content, in general, increased with radiation dose, but reached a plateau region at about 9.5 Mrad. With re-melting, the degree of swelling and average molecular weight between crosslinks for bars irradiated up to 9.5 Mrad were significantly reduced, but remained almost unchanged after 9.5 Mrad. The crosslink density increased, after remelting, with dose up to 9.5 Mrad and then remained almost unchanged. The gel content, generally, increased after remelting. [0194]
  • The oxidation profiles for the 9.5 and 24 Mrad materials, after remelting at 150° C. in air for 5 hours, as a function of depth from the bar surface are shown in FIG. 24. The results clearly showed that the oxidation drops tremendously within 1 mm, and the most oxidized layer is about 1 mm deep below the surface, after irradiation and remelting in air. [0195]
  • Example 7 Tensile Properties of Gamma-Irradiated UHMWPE at Various Doses, with or without Remelting
  • Materials and Methods [0196]
  • The materials for tensile test are the same as the wear tested materials described in EXAMPLE 5, above. The materials included UHMWPE extruded bars (3″ in diameter) gamma irradiated to 4,5, 9.5, 14.5, 20.2, and 24 Mrad, with or without remelting, and non-irradiated bars. Five tensile specimens each was machined out of the center of the 3″ diameter bars according to ASTM F648-96 and D-638 (type IV). Tensile tests were performed using an servo-hydraulic tensile test machine at speed of 2 inches/min. [0197]
  • Results and Discussion [0198]
  • The tensile strength at yield, elongation, and tensile strength (ultimate) at breaks are shown in Table 8. The average tensile properties as a function of radiation dose are shown in FIGS. 25-27. The tensile strength at yield after irradiation was higher than that of non-irradiated material, and slightly increased with radiation dose. Remelting of the irradiated bars resulted in a reduction in tensile strength at yield, and the strength remained almost constant over the dose range studied (FIG. 25). The tensile strength (ultimate) and elongation at break decreased with increasing doses (FIGS. 26-27). Remelting resulted in further reduction in ultimate tensile strength over the dose range. However, remelting had almost no effect on the elongation at break over the same dose range. [0199]
  • All publications and patent applications mentioned in this Specification are herein incorporated by reference to the same extent as if each of them had been individually indicated to be incorporated by reference. [0200]
  • Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity and understanding, it will be obvious that various modifications and changes which are within the skill of those skilled in the art are considered to fall within the scope of the appended claims. Future technological advancements which allows for obvious changes in the basic invention herein are also within the claims. [0201]
    TABLE 1
    3.3 Mrad
    Before remelting After remelting
    Distance peak melting degree of peak melting degree of
    from surface temperature crystallinity gel content temperature crystallinity gel content
    (mm) (° C.) (%) (%) (° C.) (%) (%)
    34.8-35 135.3 59.6 91 131.4 52.5 94.7
    35.8-36 135.4 60.2 91 131.5 51.2 94.7
    36.8-37 135.3 60.5 91 131.4 51.9 94.7
    37.8-38 135.3 60 91.1 131.3 52 95
    (center)
  • [0202]
    TABLE 2
    28 Mrad
    Before remelting After remelting
    Distance peak melting degree of peak melting degree of
    from surface temperature crystallinity gel content temperature crystallinity gel content
    (mm) (° C.) (%) (%) (° C.) (%) (%)
    34.8-35 139.8 65.1 95.8 135 52 97.7
    35.8-36 139.8 64.2 95.8 134.8 52.1 97.7
    36.8-37 139.7 64.5 95.8 134.9 52.5 97.7
    37.8-38 139.7 65.3 95.8 134.9 52.7 97.7
    (center)
  • [0203]
    TABLE 3
    Wear Rate Mean Wear
    (mm3/million Rate ± Std
    Cup # Material cycles) Deviation
    N11 3.3 Mrad 20.8 21.1 ± 0.3
    N16 Not 21.2
    N17 remelted 21.4
    R21 3.3 Mrad 17.7 18.6 ± 1.3
    R26 Remelted 20.1
    R27 18.0
    N35  28 Mrad 0.29  0.25 ± 0.03
    N31 Not 0.24
    N32 remelted 0.24
    R48  28 Mrad 0.36  0.36 ± 0.001
    R45 Remelted 0.35
    R49 0.36
  • [0204]
    TABLE 4
    0-3 Million Cycles
    (non-aged) 3-7 Million Cycles
    Wear Rate Mean Wear Wear Rate Mean Wear
    (mm3/million Rate ± Std (mm3/million Rate ± Std
    Cup # Material cycles) Deviation Conditions cycles) Deviation
    N11 3.3 Mrad 20.8 21.1 ± 0.3 non-aged 21.2
    N16 Not 21.2 aged 21.5  21.8 ± 0.5
    N17 remelted 21.4 aged 22.2
    R21 3.3 Mrad 17.7 18.6 ± 1.3 non-aged 17.5
    R26 Remelted 20.1 aged 19.2  19.8 ± 1.0
    R27 18.0 aged 20.5
    N35  28 Mrad 0.29  0.25 ± 0.03 non-aged 0.03
    N31 Not 0.24 aged −0.47 −0.71 ± 0.3
    N32 remelted 0.24 aged −0.93
    R48  28 Mrad 0.36  0.36 ± 0.001 non-aged 0.47
    R45 Remelted 0.35 aged 0.08 −0.06 ± 0.2
    R49 0.36 aged −0.20
  • [0205]
    TABLE 5
    (1-5 million cycles)
    Wear Rate
    (mm3/ Mean Wear Rate ± SD
    Cup # Material million cycles) (mm3/million cycles)
    N11  3.3 Mrad 20.46 20.12 ± 0.7* 
    N16 Not 19.32
    N17 remelted 20.59
    R21  3.3 Mrad Remelted 17.04 17.51 ± 0.48*
    R26 18.0
    R27 17.49
    RA2  4.5 Mrad Remelted 9.93 9.28 ± 0.92
    RA3 8.63
    RB3  9.5 Mrad Remelted 2.39 2.22 ± 0.24
    RB6 2.05
    RC5 14.5 Mrad Remelted 1.26 1.17 ± 0.13
    RC6 1.08
    RD1 20.2 Mrad Remelted 0.26 0.12 ± 0.2 
    RD6 −0.02
    RE3   24 Mrad Remelted −0.49 −0.59 ± 0.13 
    RE4 −0.68
    RF2   50 Mrad Remelted −0.8
    RG1  100 Mrad Remelted −6.88**
  • [0206]
    TABLE 6
    Non-remelted Remelted
    Melting point Crystallinity Melting point Crystallinity
    Samples (° C.) (%) (° C.) (%)
    Non-irrad. 133.8 55
     3.3 Mrad 135.3 ± 0.1 60.1 ± 0.4 131.4 ± 0.1 51.8 ± 0.6
     4.5 Mrad 136.2 ± 0.2 65.8 ± 1.6 131.6 ± 0.2 52.0 ± 1.3
     9.5 Mrad 137.1 ± 0   67.1 ± 2.2 134.8 ± 0.2 53.3 ± 2.1
    14.5 Mrad 137.5 ± 0.2 69.6 ± 1.6 135.0 ± 0.1 53.0 ± 1.5
    20.2 Mrad 137.4 ± 0.1 70.8 ± 2.8 135.3 ± 0.1 52.1 ± 1.8
      24 Mrad 137.9 ± 0.3 68.0 ± 1.3 135.2 ± 0.1 51.7 ± 1.2
      50 Mrad 138.9 ± 0.2 67.0 ± 1.3 135.2 ± 0   52.8 ± 0.2
     100 Mrad 140.2 ± 0.3 66.3 ± 2.7 130.8 ± 0.2 52.3 ± 1.7
  • [0207]
    TABLE 7
    Non-remelted Remelted
    M.W. M.W.
    between Crosslink Gel between Crosslink Gel
    Degree of crosslinks density content Degree of crosslinks density content
    Samples swelling (g/mol) (mol %) (%) swelling (g/mol) (mol %) (%)
     3.3 Mrad 5.29 8400 0.17 94.7 3.21 2500 0.56 98.1
     4.5 Mrad 3.57 3500 0.40 97.8 3.15 2400 0.58 98.4
     9.5 Mrad 2.82 1900 0.74 98.6 2.54 1400 1.0 98.9
    14.5 Mrad 2.35 1100 1.27 98.7 2.36 1100 1.27 99.2
    20.2 Mrad 2.27 1000 1.40 98.8 2.25 1000 1.40 99.2
      24 Mrad 2.17 900 1.56 98.7 2.24 1000 1.40 99.2
      50 Mrad 1.92 600 2.33 98.7 2.17 900 1.56 99.1
     100 Mrad 1.71 400 3.50 98.6 1.71 400 3.50 98.5
  • [0208]
    TABLE 8
    Tensile Strength at Tensile Strength Elongation at
    Materials Yield (MPa) at Break (MPa) Break (%)
    Non-irradiated 23.3 ± 0.11 52.1 ± 4.78  356 ± 23
    Without remelting
     4.5 Mrad 24.9 ± 0.33 46.9 ± 2.91  314 ± 12
     9.5 Mrad 25.3 ± 0.12 47.6 ± 2.76 251 ± 8
    14.5 Mrad 25.7 ± 0.25 46.4 ± 1.20 213 ± 5
    20.2 Mrad 26.2 ± 0.27 40.2 ± 2.72 175 ± 7
      24 Mrad 26.4 ± 0.23 40.0 ± 5.42  164 ± 17
    After remelting
     4.5 Mrad 21.5 ± 0.33 45.6 ± 8.89  309 ± 20
     9.5 Mrad 21.3 ± 0.60 43.2 ± 2.80 252 ± 8
    14.5 Mrad 21.8 ± 0.29 36.8 ± 1.72 206 ± 9
    20.2 Mrad 21.9 ± 0.18 34.3 ± 3.61 185 ± 8
      24 Mrad 21.7 ± 0.25 32.3 ± 2.81  160 ± 19

Claims (40)

1. A preformed polymeric composition comprising a crosslinked thermally treated polymer.
2-30. (canceled).
31. An implantable bearing component made by the process comprising the steps of:
(a) crosslinking, by irradiation, a preformed polymer in its solid state;
(b) remelting the crosslinked polymer; and
(c) fashioning the implantable bearing component from the crosslinked and remelted polymer, wherein the polymer is selected from the group consisting of: ultra high molecular weight polyethylene (UHMWPE) and high molecular weight polyethylene (HMWPE).
32. The implantable bearing component of claim 31, wherein the polymer is crosslinked by gamma radiation at a dose of from about 1 to about 100 Mrad.
33. The implantable bearing component of claim 32, wherein the gamma radiation dose is from about 4 to about 15 Mrad.
34. The implantable bearing component of claim 33, wherein the gamma radiation dose is from about 4.5 to about 10 Mrad.
35. The implantable bearing component of claim 33, wherein the implantable bearing component is for use in a joint prosthesis.
36. The implantable bearing component of claim 35, wherein the joint prosthesis is selected from the group consisting of: hip, knee, ankle, elbow, jaw, shoulder, finger and spine joint prostheses.
37. The implantable bearing component of claim 36, wherein the joint prosthesis is selected from the group consisting of: hip and knee joint prostheses.
38. The implantable bearing component of claim 33, wherein the implantable bearing component is selected from the group consisting of: an acetabular cup, an insert of an acetabular cup, and a liner of an acetabular cup.
39. A joint prosthesis comprising:
a first member adapted to be secured to a first bone constituting a first portion of a joint;
an articulating surface on the first member;
a second member adapted to be secured to a second bone constituting a second portion of the joint; and
the implantable bearing component of claim 33, said implantable bearing component being adapted for disposition between the second member and the articulating surface, said implantable bearing component being adapted to receive said articulating surface for movement therein.
40. The joint prosthesis of claim 39, wherein the joint prosthesis is selected from the group consisting of: hip, knee, ankle, elbow, jaw, shoulder, finger and spine joint prostheses.
41. The joint prosthesis of claim 40, wherein the joint prosthesis is selected from the group consisting of: hip and knee joint prostheses.
42. The joint prosthesis of claim 39, wherein the joint prosthesis is for use in a hip joint replacement wherein:
(a) the first bone is a femur;
(b) the second bone is a pelvic bone;
(c) the first member is a prosthetic stem;
(d) the second member is a prosthetic acetabular shell;
(e) the articulating surface is a prosthetic femoral head; and
(f) the implantable bearing component is selected from the group consisting of: an acetabular cup liner and an acetabular cup insert.
43. The joint prosthesis of claim 39, wherein said articulating surface and said first member are separate units.
44. A joint prosthesis comprising:
a first member adapted to be secured to a first bone constituting a first portion of the joint;
an articulating surface on the first member;
the implantable bearing component of claim 33 adapted to be secured to a second bone constituting a second portion of the joint, said implantable bearing component being adapted to receive said articulating surface for movement therein.
45. The joint prosthesis of claim 44, wherein the joint prosthesis is selected from the group consisting of: hip, knee, ankle, elbow, jaw, shoulder, finger and spine joint prostheses.
46. The joint prosthesis of claim 45, wherein the joint prosthesis is selected from the group consisting of: hip and knee joint prostheses.
47. The joint prosthesis of claim 44, wherein the joint prosthesis is for use in a hip joint replacement wherein:
(a) the first bone is a femur;
(b) the second bone is a pelvic bone;
(c) the first member is a prosthetic stem;
(d) the implantable bearing component is a prosthetic acetabular cup; and
(e) the articulating surface is a prosthetic femoral head.
48. The joint prosthesis of claim 44, wherein said articulating surface and said first member are separate units.
49. The joint prosthesis of claim 42, wherein said prosthetic femoral head and said prosthetic stem are separate units.
50. The joint prosthesis of claim 47, wherein said prosthetic femoral head and said prosthetic stem are separate units.
51. The implantable bearing component of claim 31, wherein the implantable bearing component is for use in a joint prosthesis.
52. The implantable bearing component of claim 51, wherein the joint prosthesis is selected from the group consisting of: hip, knee, ankle, elbow, jaw, shoulder, finger and spine joint prostheses.
53. The implantable bearing component of claim 52, wherein the joint prosthesis is selected from the group consisting of: hip and knee joint prostheses.
54. The implantable bearing component of claim 31, wherein the implantable bearing component is selected from the group consisting of: an acetabular cup, an insert of an acetabular cup, and a liner of an acetabular cup.
55. A joint prosthesis comprising:
a first member adapted to be secured to a first bone constituting a first portion of a joint;
an articulating surface on the first member;
a second member adapted to be secured to a second bone constituting a second portion of the joint; and
the implantable bearing component of claim 31, said implantable bearing component being adapted for disposition between the second member and the articulating surface, said implantable bearing component being adapted to receive said articulating surface for movement therein.
56. The joint prosthesis of claim 55, wherein the joint prosthesis is selected from the group consisting of: hip, knee, ankle, elbow, jaw, shoulder, finger and spine joint prostheses.
57. The joint prosthesis of claim 56, wherein the joint prosthesis is selected from the group consisting of: hip and knee joint prostheses.
58. The joint prosthesis of claim 55, wherein the joint prosthesis is for use in a hip joint replacement wherein:
(a) the first bone is a femur;
(b) the second bone is a pelvic bone;
(c) the first member is a prosthetic stem;
(d) the second member is a prosthetic acetabular shell;
(e) the articulating surface is a prosthetic femoral head; and
(f) the implantable bearing component is selected from the group consisting of: an acetabular cup liner and an acetabular cup insert.
59. The joint prosthesis of claim 55, wherein said articulating surface and said first member are separate units.
60. A joint prosthesis comprising:
a first member adapted to be secured to a first bone constituting a first portion of the joint;
an articulating surface on the first member;
the implantable bearing component of claim 31 adapted to be secured to a second bone constituting a second portion of the joint, said implantable bearing component being adapted to receive said articulating surface for movement therein.
61. The joint prosthesis of claim 60, wherein the joint prosthesis is selected from the group consisting of: hip, knee, ankle, elbow, jaw, shoulder, finger and spine joint prostheses.
62. The joint prosthesis of claim 61, wherein the joint prosthesis is selected from the group consisting of: hip and knee joint prostheses.
63. The joint prosthesis of claim 60, wherein the joint prosthesis is for use in a hip joint replacement wherein:
(a) the first bone is a femur;
(b) the second bone is a pelvic bone;
(c) the first member is a prosthetic stem;
(d) the implantable bearing component is a prosthetic acetabular cup; and
(e) the articulating surface is a prosthetic femoral head.
64. The joint prosthesis of claim 60, wherein said articulating surface and said first member are separate units
65. The joint prosthesis of claim 58, wherein said prosthetic femoral head and said prosthetic stem are separate units.
66. The joint prosthesis of claim 63, wherein said prosthetic femoral head and said prosthetic stem are separate units.
67. The implantable bearing component of claim 31, wherein the polymer is crosslinked by radiation selected from the group consisting of: gamma radiation, electron beam radiation, and photon radiation.
68. The implantable bearing component of claim 31, wherein the preformed polymer is in the form of a polyethylene bar or polyethylene block.
US10/858,528 1996-07-09 2004-05-30 Crosslinking of polyethylene for low wear using radiation and thermal treatments Abandoned US20040266902A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US10/858,528 US20040266902A1 (en) 1996-07-09 2004-05-30 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US11/982,071 US20080133021A1 (en) 1996-07-09 2007-10-31 Crosslinking of polyethylene for low wear using radiation and thermal treatments

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
US1785296P 1996-07-09 1996-07-09
US2571296P 1996-09-10 1996-09-10
US4439097P 1997-04-29 1997-04-29
US09/214,586 US6228900B1 (en) 1996-07-09 1997-07-08 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US09/795,229 US6800670B2 (en) 1996-07-09 2001-02-26 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US10/858,528 US20040266902A1 (en) 1996-07-09 2004-05-30 Crosslinking of polyethylene for low wear using radiation and thermal treatments

Related Parent Applications (1)

Application Number Title Priority Date Filing Date
US09/795,229 Continuation US6800670B2 (en) 1995-01-20 2001-02-26 Crosslinking of polyethylene for low wear using radiation and thermal treatments

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US11/982,071 Continuation US20080133021A1 (en) 1996-07-09 2007-10-31 Crosslinking of polyethylene for low wear using radiation and thermal treatments

Publications (1)

Publication Number Publication Date
US20040266902A1 true US20040266902A1 (en) 2004-12-30

Family

ID=27360900

Family Applications (6)

Application Number Title Priority Date Filing Date
US09/795,229 Expired - Lifetime US6800670B2 (en) 1995-01-20 2001-02-26 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US10/858,528 Abandoned US20040266902A1 (en) 1996-07-09 2004-05-30 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US10/936,149 Abandoned US20050048096A1 (en) 1995-01-20 2004-09-07 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US11/633,865 Expired - Fee Related US8003709B2 (en) 1996-07-09 2006-12-04 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US11/633,803 Expired - Lifetime US8008365B2 (en) 1996-07-09 2006-12-04 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US11/982,071 Abandoned US20080133021A1 (en) 1996-07-09 2007-10-31 Crosslinking of polyethylene for low wear using radiation and thermal treatments

Family Applications Before (1)

Application Number Title Priority Date Filing Date
US09/795,229 Expired - Lifetime US6800670B2 (en) 1995-01-20 2001-02-26 Crosslinking of polyethylene for low wear using radiation and thermal treatments

Family Applications After (4)

Application Number Title Priority Date Filing Date
US10/936,149 Abandoned US20050048096A1 (en) 1995-01-20 2004-09-07 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US11/633,865 Expired - Fee Related US8003709B2 (en) 1996-07-09 2006-12-04 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US11/633,803 Expired - Lifetime US8008365B2 (en) 1996-07-09 2006-12-04 Crosslinking of polyethylene for low wear using radiation and thermal treatments
US11/982,071 Abandoned US20080133021A1 (en) 1996-07-09 2007-10-31 Crosslinking of polyethylene for low wear using radiation and thermal treatments

Country Status (7)

Country Link
US (6) US6800670B2 (en)
EP (3) EP0935446B1 (en)
JP (2) JP2000514481A (en)
AU (1) AU3655197A (en)
CA (1) CA2260241C (en)
DE (1) DE69737325T2 (en)
WO (1) WO1998001085A1 (en)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050125074A1 (en) * 1995-01-20 2005-06-09 Ronald Salovey Crosslinking of polyethylene for low wear using radiation and thermal treatments
US20070197679A1 (en) * 2006-02-21 2007-08-23 Anuj Bellare Crosslinked polymers
WO2007024689A3 (en) * 2005-08-22 2007-11-08 Gen Hospital Corp Dba Massachu Oxidation resistant homogenized polymeric material
US7344672B2 (en) 2004-10-07 2008-03-18 Biomet Manufacturing Corp. Solid state deformation processing of crosslinked high molecular weight polymeric materials
US20080133018A1 (en) * 1995-01-20 2008-06-05 Ronald Salovey Chemically crosslinked ultrahigh molecular weight polyethylene for artificial human joints
US7780896B2 (en) 2004-10-07 2010-08-24 Biomet Manufacturing Corp. Crosslinked polymeric material with enhanced strength and process for manufacturing
US8003709B2 (en) 1996-07-09 2011-08-23 Orthopaedic Hospital Crosslinking of polyethylene for low wear using radiation and thermal treatments
US8262976B2 (en) 2004-10-07 2012-09-11 Biomet Manufacturing Corp. Solid state deformation processing of crosslinked high molecular weight polymeric materials
US8641959B2 (en) 2007-07-27 2014-02-04 Biomet Manufacturing, Llc Antioxidant doping of crosslinked polymers to form non-eluting bearing components
US9586370B2 (en) 2013-08-15 2017-03-07 Biomet Manufacturing, Llc Method for making ultra high molecular weight polyethylene

Families Citing this family (114)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU693260B2 (en) 1994-09-21 1998-06-25 Bmg Incorporated Ultrahigh-molecular-weight polyethylene molding for artificial joint and process for producing the molding
US5879400A (en) 1996-02-13 1999-03-09 Massachusetts Institute Of Technology Melt-irradiated ultra high molecular weight polyethylene prosthetic devices
US8865788B2 (en) 1996-02-13 2014-10-21 The General Hospital Corporation Radiation and melt treated ultra high molecular weight polyethylene prosthetic devices
US6017975A (en) 1996-10-02 2000-01-25 Saum; Kenneth Ashley Process for medical implant of cross-linked ultrahigh molecular weight polyethylene having improved balance of wear properties and oxidation resistance
EP1028760B1 (en) 1996-10-15 2004-04-14 Orthopaedic Hospital Wear resistant surface-gradient cross-linked polyethylene
US7959652B2 (en) 2005-04-18 2011-06-14 Kyphon Sarl Interspinous process implant having deployable wings and method of implantation
US6068630A (en) 1997-01-02 2000-05-30 St. Francis Medical Technologies, Inc. Spine distraction implant
US7306628B2 (en) 2002-10-29 2007-12-11 St. Francis Medical Technologies Interspinous process apparatus and method with a selectably expandable spacer
US6692679B1 (en) 1998-06-10 2004-02-17 Depuy Orthopaedics, Inc. Cross-linked molded plastic bearings
DE69934440T2 (en) * 1998-06-10 2007-09-27 Depuy Products, Inc., Warsaw Method of producing crosslinked molded plastic bearings
FR2784290B1 (en) * 1998-10-07 2001-02-09 Pierre Kehr METHOD FOR MANUFACTURING A COTYLOIDAL HIP PROSTHESIS IMPLANT
US6245276B1 (en) 1999-06-08 2001-06-12 Depuy Orthopaedics, Inc. Method for molding a cross-linked preform
US6627141B2 (en) 1999-06-08 2003-09-30 Depuy Orthopaedics, Inc. Method for molding a cross-linked preform
US6432349B1 (en) 1999-06-29 2002-08-13 Zimmer, Inc. Process of making an articulating bearing surface
US6143232A (en) * 1999-07-29 2000-11-07 Bristol-Meyers Squibb Company Method of manufacturing an articulating bearing surface for an orthopaedic implant
AU742611B2 (en) * 1999-07-29 2002-01-10 Depuy Orthopaedics, Inc. Gamma irradiated heat treated implant for mechanical strength
EP1072274A1 (en) * 1999-07-29 2001-01-31 Depuy Orthopaedics, Inc. Two step gamma irradiation of polymeric bioimplant
US6184265B1 (en) * 1999-07-29 2001-02-06 Depuy Orthopaedics, Inc. Low temperature pressure stabilization of implant component
US6365089B1 (en) 1999-09-24 2002-04-02 Zimmer, Inc. Method for crosslinking UHMWPE in an orthopaedic implant
SK8232002A3 (en) * 1999-12-17 2003-05-02 Cartificial As Medico Chemical A prosthetic device
US6395799B1 (en) 2000-02-21 2002-05-28 Smith & Nephew, Inc. Electromagnetic and mechanical wave energy treatments of UHMWPE
WO2001080778A1 (en) * 2000-04-27 2001-11-01 The Orthopaedic Hospital Oxidation-resistant and wear-resistant polyethylenes for human joint replacements and methods for making them
ES2286131T3 (en) 2000-07-31 2007-12-01 Massachusetts General Hospital CONSTREATED MONOPOLAR ACETABULAR COMPONENT.
US6818172B2 (en) 2000-09-29 2004-11-16 Depuy Products, Inc. Oriented, cross-linked UHMWPE molding for orthopaedic applications
US6955876B2 (en) * 2000-11-01 2005-10-18 Kane Michael D Compositions and systems for identifying and comparing expressed genes (mRNAs) in eukaryotic organisms
DE10105085C1 (en) 2001-02-05 2002-04-18 Plus Endoprothetik Ag Rotkreuz Production of implant part, e.g. bearing for hip prosthesis, by crosslinking ultra-high molecular weight polyethylene parison with ionizing radiation includes recombination of free radicals with microwaves and/or ultrasound
US6547828B2 (en) 2001-02-23 2003-04-15 Smith & Nephew, Inc. Cross-linked ultra-high molecular weight polyethylene for medical implant use
US7182784B2 (en) 2001-07-18 2007-02-27 Smith & Nephew, Inc. Prosthetic devices employing oxidized zirconium and other abrasion resistant surfaces contacting surfaces of cross-linked polyethylene
US6652586B2 (en) * 2001-07-18 2003-11-25 Smith & Nephew, Inc. Prosthetic devices employing oxidized zirconium and other abrasion resistant surfaces contacting surfaces of cross-linked polyethylene
GB0122117D0 (en) 2001-09-13 2001-10-31 United Ind Operations Ltd Method of crosslinking polyolefins
EP1308255A1 (en) * 2001-10-30 2003-05-07 Dsm N.V. Process for the manufacturing of a shaped part of ultra high molecular weight polyethylene and a fibre made with this process
WO2003049930A1 (en) * 2001-12-12 2003-06-19 Depuy Products, Inc. Orthopaedic device and method for making same
CA2471771C (en) 2002-01-04 2012-01-03 Massachusetts General Hospital A high modulus crosslinked polyethylene with reduced residual free radical concentration prepared below the melt
US7819925B2 (en) 2002-01-28 2010-10-26 Depuy Products, Inc. Composite prosthetic bearing having a crosslinked articulating surface and method for making the same
DE60302760T2 (en) 2002-01-29 2006-08-10 Paul Smith SINTERING ULTRAHOCHMOLECULAR POLYETHYLENE
CA2429930C (en) * 2002-06-06 2008-10-14 Howmedica Osteonics Corp. Sequentially cross-linked polyethylene
US20040048958A1 (en) * 2002-09-06 2004-03-11 Didier David A. High temperature ultra high molecular weight polyethylene
JP2006511255A (en) * 2002-10-11 2006-04-06 カーティフィシャル・アクティーゼルスカブ Medical devices containing biocompatible polymer products with a layered structure
US7799084B2 (en) 2002-10-23 2010-09-21 Mako Surgical Corp. Modular femoral component for a total knee joint replacement for minimally invasive implantation
US8070778B2 (en) 2003-05-22 2011-12-06 Kyphon Sarl Interspinous process implant with slide-in distraction piece and method of implantation
US7931674B2 (en) 2005-03-21 2011-04-26 Kyphon Sarl Interspinous process implant having deployable wing and method of implantation
US8048117B2 (en) 2003-05-22 2011-11-01 Kyphon Sarl Interspinous process implant and method of implantation
US7833246B2 (en) 2002-10-29 2010-11-16 Kyphon SÀRL Interspinous process and sacrum implant and method
US7909853B2 (en) 2004-09-23 2011-03-22 Kyphon Sarl Interspinous process implant including a binder and method of implantation
US7549999B2 (en) 2003-05-22 2009-06-23 Kyphon Sarl Interspinous process distraction implant and method of implantation
JP5122126B2 (en) 2003-01-16 2013-01-16 ザ・ジェネラル・ホスピタル・コーポレイション Method for producing oxidation-resistant polymer material
US7241455B2 (en) * 2003-04-08 2007-07-10 Boston Scientific Scimed, Inc. Implantable or insertable medical devices containing radiation-crosslinked polymer for controlled delivery of a therapeutic agent
US7938861B2 (en) 2003-04-15 2011-05-10 Depuy Products, Inc. Implantable orthopaedic device and method for making the same
US20040254545A1 (en) * 2003-06-16 2004-12-16 Rider Dean Loller Method and apparatus for extending feeding tube longevity
DE602004025030D1 (en) 2003-06-27 2010-02-25 Abs Corp FUSSGELARTARTHROPLASTIE SYSTEM
JP2005237629A (en) * 2004-02-26 2005-09-08 Kyocera Corp Artificial joint and manufacturing method of the same
GB2429164B (en) * 2004-03-11 2008-12-24 Acumed Llc Systems for bone replacement
ATE440622T1 (en) * 2004-07-27 2009-09-15 Cordis Corp METHOD FOR COATING STENTS
US8012209B2 (en) 2004-09-23 2011-09-06 Kyphon Sarl Interspinous process implant including a binder, binder aligner and method of implantation
US7547405B2 (en) 2004-10-07 2009-06-16 Biomet Manufacturing Corp. Solid state deformation processing of crosslinked high molecular weight polymeric materials
DE102004056713B4 (en) * 2004-11-24 2008-04-10 Mathys Ag Bettlach Method for producing prosthesis elements and blanks of prosthesis elements
US8100944B2 (en) 2004-12-13 2012-01-24 Kyphon Sarl Inter-cervical facet implant and method for preserving the tissues surrounding the facet joint
US7601170B2 (en) 2004-12-13 2009-10-13 Kyphon Sarl Inter-cervical facet implant and method
US7335697B2 (en) 2004-12-23 2008-02-26 Depuy Products, Inc. Polymer composition comprising cross-linked polyethylene and methods for making the same
US7435372B2 (en) 2005-03-31 2008-10-14 Zimmer, Inc. Liquid bath annealing of polymers for orthopaedic implants
EP1890864B1 (en) * 2005-06-14 2015-12-30 OMNIlife science, Inc. Crosslinked polyethylene article
US7538379B1 (en) * 2005-06-15 2009-05-26 Actel Corporation Non-volatile two-transistor programmable logic cell and array layout
US20060289098A1 (en) * 2005-06-23 2006-12-28 Balogh George F Tire containing cellular rubber within its tire cavity
ES2509884T3 (en) * 2005-08-18 2014-10-20 Zimmer Gmbh Ultra-high molecular weight polyethylene articles and methods for forming ultra-high molecular weight polyethylene articles
US8343230B2 (en) * 2005-09-22 2013-01-01 Depuy Products, Inc. Orthopaedic bearing material
US20070077268A1 (en) * 2005-09-30 2007-04-05 Depuy Products, Inc. Hydrophobic carrier modified implants for beneficial agent delivery
US7812098B2 (en) * 2006-03-31 2010-10-12 Depuy Products, Inc. Bearing material of medical implant having reduced wear rate and method for reducing wear rate
DK1891987T3 (en) * 2006-08-25 2010-12-13 Depuy Products Inc Carrying material for medical implant
WO2008052574A1 (en) 2006-10-30 2008-05-08 Plus Orthopedics Ag Processes comprising crosslinking polyethylene or using crosslinked polyethylene
US8562616B2 (en) 2007-10-10 2013-10-22 Biomet Manufacturing, Llc Knee joint prosthesis system and method for implantation
US8328873B2 (en) 2007-01-10 2012-12-11 Biomet Manufacturing Corp. Knee joint prosthesis system and method for implantation
US8163028B2 (en) 2007-01-10 2012-04-24 Biomet Manufacturing Corp. Knee joint prosthesis system and method for implantation
US8187280B2 (en) 2007-10-10 2012-05-29 Biomet Manufacturing Corp. Knee joint prosthesis system and method for implantation
EP2104474B1 (en) 2007-01-10 2012-08-29 Biomet Manufacturing Corp. Knee joint prosthesis system
WO2008101116A1 (en) * 2007-02-14 2008-08-21 Brigham And Women's Hospital, Inc. Crosslinked polymers and methods of making the same
US8664290B2 (en) 2007-04-10 2014-03-04 Zimmer, Inc. Antioxidant stabilized crosslinked ultra-high molecular weight polyethylene for medical device applications
AU2008236996B2 (en) * 2007-04-10 2012-11-08 Zimmer, Inc. An antioxidant stabilized crosslinked ultra-high molecular weight polyethylene for medical device applications
US7947081B2 (en) * 2007-07-11 2011-05-24 Linares Medical Devices, Llc Skeletal implant for replacing a human bone
WO2009039171A2 (en) * 2007-09-17 2009-03-26 Linares Medical Devices, Llc Artificial joint support between first and second bones
GB0718821D0 (en) * 2007-09-26 2007-11-07 Benoist Girard Sas Cement spacer for use in prosthetic cup and method of use therein
JP5682914B2 (en) * 2007-11-06 2015-03-11 ディーエスエム アイピー アセッツ ビー.ブイ. Production method of high molecular weight polyethylene
JP2011503253A (en) * 2007-11-06 2011-01-27 ディーエスエム アイピー アセッツ ビー.ブイ. Production method of (ultra) high molecular weight polyethylene
US8979938B2 (en) * 2007-11-08 2015-03-17 Linares Medical Devices, Llc Artificial knee implant including liquid ballast supporting / rotating surfaces and incorporating flexible multi-material and natural lubricant retaining matrix applied to a joint surface
US8828088B2 (en) * 2007-11-08 2014-09-09 Linares Medical Devices, Llc Joint assembly incorporating undercut surface design to entrap accumulating wear debris from plastic joint assembly
US8764837B2 (en) * 2008-03-26 2014-07-01 Linares Medical Devices, Llc Reinforced joint assembly
US9539097B2 (en) 2007-11-08 2017-01-10 Linares Medical Devices, Llc Hip and knee joint assemblies incorporating debris collection architecture between the ball and seat interface
US20100003828A1 (en) * 2007-11-28 2010-01-07 Guowen Ding Methods for adjusting critical dimension uniformity in an etch process with a highly concentrated unsaturated hydrocarbon gas
EP2249887B1 (en) 2008-01-30 2017-06-21 Zimmer, Inc. Othopedic component of low stiffness
US8702801B2 (en) * 2008-02-25 2014-04-22 Linares Medical Devices, Llc Artificial wear resistant plug for mounting to existing joint bone
JP5311457B2 (en) * 2008-06-20 2013-10-09 ナカシマメディカル株式会社 Method of molding sliding member for artificial joint and sliding member for artificial joint molded by this method
DE102008047009B4 (en) * 2008-07-11 2020-08-06 Mathys Ag Bettlach Joint socket with physiological load transfer
RU2011110394A (en) * 2008-08-20 2012-09-27 Е.И.Дюпон де Немур энд Компани (US) METHOD FOR ESTIMATING WEAR RESISTANCE AT HIGH TEMPERATURE
US9745462B2 (en) * 2008-11-20 2017-08-29 Zimmer Gmbh Polyethylene materials
WO2010058822A1 (en) * 2008-11-20 2010-05-27 国立大学法人東京医科歯科大学 Plate denture and process for producing same
US7935740B2 (en) 2008-12-30 2011-05-03 Basell Poliolefine Italia S.R.L. Process for producing high melt strength polypropylene
KR101040567B1 (en) 2009-08-11 2011-06-16 (주)오티스바이오텍 Method for manufacturing UHMWPE liner of artificial hip joint prosthesis
GB0922339D0 (en) 2009-12-21 2010-02-03 Mcminn Derek J W Acetabular cup prothesis and introducer thereof
US9132209B2 (en) 2010-05-07 2015-09-15 Howmedia Osteonics Corp. Surface crosslinked polyethylene
US8926705B2 (en) 2010-05-10 2015-01-06 Linares Medical Devices, Llc Implantable joint assembly featuring debris entrapment chamber subassemblies along with opposing magnetic fields generated between articulating implant components in order to minimize frictional force and associated wear
US8399535B2 (en) 2010-06-10 2013-03-19 Zimmer, Inc. Polymer [[s]] compositions including an antioxidant
US9700651B2 (en) 2012-05-31 2017-07-11 Kyocera Medical Corporation Bearing material and method of producing the same
GB2524668A (en) 2012-09-10 2015-09-30 Acumed Llc Radial head prosthesis with floating articular member
EP3052562B1 (en) 2013-10-01 2017-11-08 Zimmer, Inc. Polymer compositions comprising one or more protected antioxidants
AU2015229947A1 (en) 2014-03-12 2016-10-27 Zimmer, Inc. Melt-stabilized ultra high molecular weight polyethylene and method of making the same
CN107207741B (en) 2014-12-03 2021-05-11 捷迈有限公司 Antioxidant-infused ultra-high molecular weight polyethylene
US9763792B2 (en) 2015-10-01 2017-09-19 Acumed Llc Radial head prosthesis with rotate-to-lock interface
US11697706B2 (en) 2018-04-20 2023-07-11 Adaptive 3D Technologies Sealed isocyanates
US11739177B2 (en) 2018-04-20 2023-08-29 Adaptive 3D Technologies Sealed isocyanates
US11911956B2 (en) 2018-11-21 2024-02-27 Adaptive 3D Technologies Using occluding fluids to augment additive manufacturing processes
MX2021006406A (en) 2018-12-03 2021-08-16 Forta Llc Radiation-treated fibers, methods of treating and applications for use.
DE102021103016A1 (en) * 2021-02-09 2022-08-11 Aesculap Ag Process for the production of a sliding surface element, sliding surface element and knee joint endoprosthesis
WO2023012268A1 (en) 2021-08-04 2023-02-09 Röhm Gmbh Polymer composition based on poly(meth)acrylimide for tribological applications
WO2023139194A1 (en) 2022-01-24 2023-07-27 Röhm Gmbh Polymer foams based on blends of poly(vinylidene fluoride) and poly(meth)acrylimide
WO2023139195A1 (en) 2022-01-24 2023-07-27 Röhm Gmbh Polymer foams based on poly(meth)acrylimide

Citations (90)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2904480A (en) * 1955-06-06 1959-09-15 Grace W R & Co Polyethylene
US2948666A (en) * 1956-11-21 1960-08-09 Gen Electric Irradiation process
US3022543A (en) * 1958-02-07 1962-02-27 Grace W R & Co Method of producing film having improved shrink energy
US3090770A (en) * 1960-04-26 1963-05-21 Grace W R & Co Blended polyethylene compositions of improved clarity and method of making same
US3297641A (en) * 1964-01-17 1967-01-10 Grace W R & Co Process for cross-linking polyethylene
US3330748A (en) * 1955-01-11 1967-07-11 Gen Electric Method and apparatus for irradiating organic polymers with electrons
US3563869A (en) * 1957-11-05 1971-02-16 Grace W R & Co Irradiated polyethylene
US3646155A (en) * 1968-12-20 1972-02-29 Midland Silicones Ltd Cross-linking of a polyolefin with a silane
US3671477A (en) * 1969-03-10 1972-06-20 Campbell Mfg Co Ltd Composition comprising unsaturated elastomer,epoxy resin polycarboxylic acid or anhydride,cross-linking catalyst and filler and golf ball made therefrom
US3758273A (en) * 1970-04-03 1973-09-11 Gillette Co Processes for sterilizing polypropylene objects
US3886056A (en) * 1971-11-01 1975-05-27 Ryozo Kitamaru Process for producing a high melting temperature polyethylene employing irradiation and orienting
US3944536A (en) * 1973-06-18 1976-03-16 E. I. Du Pont De Nemours & Company Exceptionally rigid and tough ultrahigh molecular weight linear polyethylene
US4138382A (en) * 1978-05-01 1979-02-06 Dow Corning Corporation Hydrophilic, water-swellable, crosslinked, copolymer gel and prosthesis employing same
US4281420A (en) * 1979-02-15 1981-08-04 Raab S Bone connective prostheses adapted to maximize strength and durability of prostheses-bone cement interface; and methods of forming same
US4390666A (en) * 1981-08-14 1983-06-28 Asahi Kasei Kogyo Kabushiki Kaisha Polyethylene blend composition
US4518552A (en) * 1983-11-09 1985-05-21 Mitsuboshi Belting Ltd. Method of producing accurately sized material of ultra high molecular weight polyethylene
US4582656A (en) * 1981-08-12 1986-04-15 Hewing Gmbh & Co. Method of producing molded articles from polyolefin molding compositions crosslinked by irradiation
US4587163A (en) * 1984-03-06 1986-05-06 Zachariades Anagnostis E Preparation of ultra high molecular weight polyethylene morphologies of totally fused particles with superior mechanical performance
US4586995A (en) * 1982-09-17 1986-05-06 Phillips Petroleum Company Polymer and irradiation treatment method
US4655769A (en) * 1984-10-24 1987-04-07 Zachariades Anagnostis E Ultra-high-molecular-weight polyethylene products including vascular prosthesis devices and methods relating thereto and employing pseudo-gel states
US4668527A (en) * 1985-03-06 1987-05-26 Osaka University Method for amorphizing a material by means of injection of exotic atoms into a solid with electron beams
US4682656A (en) * 1986-06-20 1987-07-28 Otis Engineering Corporation Completion apparatus and method for gas lift production
US4743493A (en) * 1986-10-06 1988-05-10 Spire Corporation Ion implantation of plastics
US4747990A (en) * 1985-03-12 1988-05-31 Cie Oris Industrie S.A. Process of making a high molecular weight polyolefin part
US4813210A (en) * 1985-09-27 1989-03-21 Nissho Corporation Radiation-sterilized, packaged medical device
US4816517A (en) * 1982-09-29 1989-03-28 Vulkor, Incorporated Crosslinked polymer interdispersions containing polyolefin and method of making
US4820466A (en) * 1985-01-31 1989-04-11 Zachariades Anagnostis E Process for obtaining ultra-high modulus products
US4832965A (en) * 1985-05-17 1989-05-23 Helin Stig Aake Method of making a bottle and packaging a water ration therein
US4891173A (en) * 1987-09-09 1990-01-02 Toa Nenryo Kogyo Kabushiki Kaisha Process for producing a crosslinked and oriented polyethylene film
US4892552A (en) * 1984-03-30 1990-01-09 Ainsworth Robert D Orthopedic device
US4902460A (en) * 1985-11-30 1990-02-20 Mitsui Petrochemical Industries, Ltd. Process for preparation of molecularly oriented, silane-crosslinked ultra-high-molecular-weight polyethylene molded article
US4916198A (en) * 1985-01-31 1990-04-10 Himont Incorporated High melt strength, propylene polymer, process for making it, and use thereof
US4944974A (en) * 1984-10-24 1990-07-31 Zachariades Anagnostis E Composite structures of ultra-high-molecular-weight polymers, such as ultra-high-molecular-weight polyethylene products, and method of producing such structures
US4950151A (en) * 1985-01-31 1990-08-21 Zachariades Anagnostic E Rolling die for producing high modulus products
US5001206A (en) * 1983-12-10 1991-03-19 Stamicarbon B.V. Oriented polyolfins
US5001008A (en) * 1987-07-21 1991-03-19 Mitsui Petrochemical Industries, Ltd. Reinforcing fibrous material
US5014494A (en) * 1988-09-27 1991-05-14 Sherwood Medical Company Method of sterilizing medical articles
US5017627A (en) * 1980-10-09 1991-05-21 National Research Development Corporation Composite material for use in orthopaedics
US5024670A (en) * 1989-10-02 1991-06-18 Depuy, Division Of Boehringer Mannheim Corporation Polymeric bearing component
US5030402A (en) * 1989-03-17 1991-07-09 Zachariades Anagnostis E Process for producing a new class of ultra-high-molecular-weight polyethylene orthopaedic prostheses with enhanced mechanical properties
US5037928A (en) * 1989-10-24 1991-08-06 E. I. Du Pont De Nemours And Company Process of manufacturing ultrahigh molecular weight linear polyethylene shaped articles
US5096654A (en) * 1987-07-24 1992-03-17 The National Research And Development Corporation Solid phase deformation process
US5130378A (en) * 1989-09-02 1992-07-14 Bayer Aktiengesellschaft Copolymers containing secondary amino groups and a process for their production
US5130376A (en) * 1990-04-23 1992-07-14 Hercules Incorporated UHMWPE/styrenic molding compositions with improved flow properties and impact strength
US5133757A (en) * 1990-07-31 1992-07-28 Spire Corporation Ion implantation of plastic orthopaedic implants
US5137688A (en) * 1990-11-29 1992-08-11 General Electric Company Irradiated articles molded from polycarbonate-polyamide blends
US5178812A (en) * 1990-11-28 1993-01-12 E. I. Du Pont De Nemours And Company Method of making composites having improved surface properties
US5180394A (en) * 1989-07-25 1993-01-19 Davidson James A Zirconium oxide and nitride coated prosthesis for wear and corrosion resistance
US5192323A (en) * 1990-11-05 1993-03-09 Zimmer, Inc. Method of surface hardening orthopedic implant devices
US5200439A (en) * 1990-04-13 1993-04-06 Mitsui Toatsu Chemicals, Inc. Method for increasing intrinsic viscosity of syndiotactic polypropylene
US5210130A (en) * 1990-08-07 1993-05-11 E. I. Du Pont De Nemours And Company Homogeneous, high modulus ultrahigh molecular weight polyethylene composites and processes for the preparation thereof
US5236563A (en) * 1990-06-18 1993-08-17 Advanced Surface Technology Inc. Surface-modified bioabsorbables
US5236669A (en) * 1990-09-12 1993-08-17 E. I. Du Pont De Nemours And Company Pressure vessel
US5292584A (en) * 1991-04-11 1994-03-08 E. I. Du Pont De Nemours And Company Ultrahigh molecular weight polyethylene and lightly-filled composites thereof
US5296583A (en) * 1992-07-09 1994-03-22 University Of Michigan Calcification-resistant synthetic biomaterials
US5407623A (en) * 1994-01-06 1995-04-18 Polteco, Inc. Process for obtaining ultra-high modulus line products with enhanced mechanical properties
US5414049A (en) * 1993-06-01 1995-05-09 Howmedica Inc. Non-oxidizing polymeric medical implant
US5435723A (en) * 1993-08-18 1995-07-25 O'brien; Gary R. Endosseous dental implant system
US5439949A (en) * 1991-08-21 1995-08-08 Rexene Corporation Propylene compositions with improved resistance to thermoforming sag
US5480683A (en) * 1988-05-24 1996-01-02 Nitruvid Process for reducing the coefficient of friction and wear between a metal part and an organic polymer-or copolymer-based part and its application to artificial limb-joints and fittings working in marine environments
US5505984A (en) * 1993-01-21 1996-04-09 England; Garry L. Method for forming biocompatible components using an isostatic press
US5508079A (en) * 1994-08-15 1996-04-16 Owens-Corning Fiberglas Technology, Inc. Conformable insulation assembly
US5508319A (en) * 1991-06-21 1996-04-16 Montell North America Inc. High melt strength, ethylene polymer, process for making it, and use thereof
US5515590A (en) * 1994-07-19 1996-05-14 University Of Kentucky Research Foundation Method for reducing the generation of wear particulates from an implant
US5545453A (en) * 1994-08-15 1996-08-13 Owens Corning Fiberglas Technology, Inc. Conformable insulation assembly
US5549698A (en) * 1993-04-22 1996-08-27 Implex Corp. Prosthetic acetabular cup and method of implant
US5549700A (en) * 1993-09-07 1996-08-27 Ortho Development Corporation Segmented prosthetic articulation
US5593719A (en) * 1994-03-29 1997-01-14 Southwest Research Institute Treatments to reduce frictional wear between components made of ultra-high molecular weight polyethylene and metal alloys
US5609643A (en) * 1995-03-13 1997-03-11 Johnson & Johnson Professional, Inc. Knee joint prosthesis
US5609638A (en) * 1994-11-29 1997-03-11 Zimmer, Inc. Reinforced polyethylene for articular surfaces
US5621070A (en) * 1988-12-02 1997-04-15 E. I. Du Pont De Nemours And Company Ultra high molecular weight linear polyethylene processes of manufacture
US5625858A (en) * 1995-01-18 1997-04-29 Canon Kabushiki Kaisha Contact charging member, process for producing same and electrophotographic apparatus using same
US5645882A (en) * 1994-11-16 1997-07-08 Alcon Laboratories, Inc. Cross-linked polyethylene oxide coatings to improve the biocompatibility of implantable medical devices
US5652281A (en) * 1989-12-21 1997-07-29 Montell North America Inc. Graft copolymers of polyolefins and a method of producing same
US5709020A (en) * 1994-07-19 1998-01-20 University Of Kentucky Research Foundation Method for reducing the generation of wear particulates from an implant
US5721334A (en) * 1996-02-16 1998-02-24 Newyork Society For The Ruptured And Crippled Maintaining The Hospital For Special Surgery Process for producing ultra-high molecular weight low modulus polyethylene shaped articles via controlled pressure and temperature and compositions and articles produced therefrom
US5753182A (en) * 1996-02-14 1998-05-19 Biomet, Inc. Method for reducing the number of free radicals present in ultrahigh molecular weight polyethylene orthopedic components
US5798417A (en) * 1996-10-15 1998-08-25 E. I. Du Pont De Nemours And Company (Fluorovinyl ether)-grafted high-surface-area polyolefins and preparation thereof
US5876453A (en) * 1994-11-30 1999-03-02 Implant Innovations, Inc. Implant surface preparation
US5879400A (en) * 1996-02-13 1999-03-09 Massachusetts Institute Of Technology Melt-irradiated ultra high molecular weight polyethylene prosthetic devices
US5879407A (en) * 1997-07-17 1999-03-09 Waggener; Herbert A. Wear resistant ball and socket joint
US6017975A (en) * 1996-10-02 2000-01-25 Saum; Kenneth Ashley Process for medical implant of cross-linked ultrahigh molecular weight polyethylene having improved balance of wear properties and oxidation resistance
US6168626B1 (en) * 1994-09-21 2001-01-02 Bmg Incorporated Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same
US6184265B1 (en) * 1999-07-29 2001-02-06 Depuy Orthopaedics, Inc. Low temperature pressure stabilization of implant component
US6228900B1 (en) * 1996-07-09 2001-05-08 The Orthopaedic Hospital And University Of Southern California Crosslinking of polyethylene for low wear using radiation and thermal treatments
US6245276B1 (en) * 1999-06-08 2001-06-12 Depuy Orthopaedics, Inc. Method for molding a cross-linked preform
US6281264B1 (en) * 1995-01-20 2001-08-28 The Orthopaedic Hospital Chemically crosslinked ultrahigh molecular weight polyethylene for artificial human joints
US6281262B1 (en) * 1998-11-12 2001-08-28 Takiron Co., Ltd. Shape-memory, biodegradable and absorbable material
US20020007219A1 (en) * 1996-02-13 2002-01-17 Merrill Edward W. Radiation and melt treated ultra high molecular weight polyethylene prosthetic devices
US6692679B1 (en) * 1998-06-10 2004-02-17 Depuy Orthopaedics, Inc. Cross-linked molded plastic bearings

Family Cites Families (74)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US552104A (en) * 1895-12-31 And herman ellis
US2946666A (en) * 1957-10-29 1960-07-26 Lewis C Eymann Apparatus for ammoniation of phosphate materials
NL91090C (en) 1957-11-02 1958-12-15
US2948866A (en) 1958-10-24 1960-08-09 Cie Ind Des Telephones Adjustable correcting networks
US3057791A (en) 1959-07-06 1962-10-09 Phillips Petroleum Co Radiation curing of polymers
US3162623A (en) 1961-12-26 1964-12-22 Du Pont Crosslinking of polymers with nitrogen fluorides
DE1241994B (en) 1964-01-31 1967-06-08 Glanzstoff Ag Process for the saturation of double bonds in polyolefins
DE1669649B2 (en) 1966-05-27 1971-05-19 Badische Anilin- & Soda-Fabrik Ag, 6700 Ludwigshafen PROCESS FOR MANUFACTURING FINE PARTICLE, FOAM-SHAPED OLEFINE POLYMERIZATES WITH HIGH HEAT STABILITY
US3832827A (en) * 1967-12-18 1974-09-03 J Lemelson Container forming and filling apparatus
US4055769A (en) * 1972-03-21 1977-10-25 Conrad Sander Method and apparatus for curing, a coating on a substrate
US3944538A (en) 1973-10-02 1976-03-16 Miklos Bodanszky Process and apparatus for the synthesis of peptides not linked to polymers
DE2447627C3 (en) 1974-10-05 1980-06-26 Dr. Rudolf Kuerner Chemische Spezialprodukte Inh. Dr. Rudolf Kuerner, 6380 Bad Homburg Antimicrobial preparation
US4055862A (en) * 1976-01-23 1977-11-01 Zimmer Usa, Inc. Human body implant of graphitic carbon fiber reinforced ultra-high molecular weight polyethylene
AU523866B2 (en) 1978-04-18 1982-08-19 Du Pont Canada Inc. Manufacture of film
US4241463A (en) 1978-10-16 1980-12-30 Precision Cast Specialties, Inc. Prosthetic implant device
DE3069144D1 (en) 1979-06-06 1984-10-18 Nat Res Dev Polymer processing
US4455691A (en) * 1979-10-03 1984-06-26 Minnesota Mining And Manufacturing Company Silicone gel filled prosthesis
JPS58157830A (en) 1982-03-12 1983-09-20 Nitto Electric Ind Co Ltd Preparation of sliding sheet
US4483333A (en) 1982-06-01 1984-11-20 Wrf/Aquaplast Corporation Orthopedic cast
EP0120672B1 (en) 1983-03-23 1989-03-08 Toa Nenryo Kogyo Kabushiki Kaisha Oriented polyethylene film and method of manufacture
DE3312543A1 (en) 1983-04-07 1984-10-11 Bayer Ag, 5090 Leverkusen 2,2-DIMETHYL-3- (2-HALOGEN-VINYL) -CYCLOPROPANCARBONIC ACID ESTER, METHOD FOR THE PRODUCTION THEREOF AND THEIR USE AS A PEST CONTROL
CA1240101A (en) * 1983-05-06 1988-08-09 Michael J. Pappas Multi-component prosthesis with increased wall flexibility facilitating component assembly
GB8332952D0 (en) 1983-12-09 1984-01-18 Ward I M Polymer irradiation
US4539374A (en) 1984-03-21 1985-09-03 E. I. Du Pont De Nemours And Company Polyolefin with improved processing properties
EP0157601B1 (en) 1984-03-30 1991-05-08 National Research Development Corporation Tubular materials
EP0161802B1 (en) 1984-04-13 1990-06-27 National Research Development Corporation Solid phase deformation process
IN164745B (en) 1984-05-11 1989-05-20 Stamicarbon
DE169259T1 (en) 1984-07-25 1986-04-30 Surgical Patent Products Inc. Ltd., Panama VESSEL PROSTHESES FOR DRY STORAGE, METHOD FOR TREATMENT AND THEIR USE IN SURGERY.
US5160472A (en) 1984-10-24 1992-11-03 Zachariades Anagnostis E Method of producing composite structures of ultra-high-molecular-weight polymers, such as ultra-high-molecular-weight polyethylene products
CA1280543C (en) 1985-01-31 1991-02-19 B. Joseph Scheve Polypropylene with free-end long chain branching, process for making it, and use thereof
GB2172744B (en) * 1985-03-23 1989-07-19 Stc Plc Semiconductor devices
US4701288A (en) * 1985-06-05 1987-10-20 Bausch & Lomb Incorporated Method of making articles of dissimilar polymer compositions
US4876049A (en) 1985-11-21 1989-10-24 Nippon Petrochemicals Co., Ltd. Method for preparing molded articles of ultra-high molecular weight polyethylene
US4965846A (en) 1986-08-11 1990-10-23 Baxter International Inc. Pivot pin bearing/seal with loose eyelet especially suited for disposable continuous flow blood filtration system cartridges
US4828827A (en) * 1986-12-12 1989-05-09 Ethicon, Inc. Process for augmenting soft tissue with cross-linked polyvinyl pyrrolidone
US4888369A (en) 1987-01-21 1989-12-19 Himont Incorporated Polypropylene composition resistant to high energy radiation, and radiation sterilized articles therefrom
US5047446A (en) 1988-07-22 1991-09-10 Himont Incorporated Thermal treatment of irradiated propylene polymer material
US5264214A (en) 1988-11-21 1993-11-23 Collagen Corporation Composition for bone repair
GB8827967D0 (en) 1988-11-30 1989-01-05 Ward I M Die-free drawing
ES2087147T3 (en) 1988-12-02 1996-07-16 Du Pont LINEAR POLYETHYLENE OF ULTRAELEVADO MOLECULAR WEIGHT, ARTICLES AND MANUFACTURING PROCEDURES.
BR8907795A (en) 1988-12-02 1991-08-27 Du Pont PROCESS TO PRODUCE MOLDED LINEAR POLYETHYLENE ARTICLES OF ULTRA HIGH MOLECULAR WEIGHT
JP2590015B2 (en) * 1989-02-15 1997-03-12 三田工業株式会社 Toner image developing device
US5160677A (en) 1989-12-15 1992-11-03 United States Surgical Corporation Pressurized powder support for treating processes
US5153039A (en) 1990-03-20 1992-10-06 Paxon Polymer Company, L.P. High density polyethylene article with oxygen barrier properties
US5352732A (en) 1990-08-07 1994-10-04 E. I. Du Pont De Nemours And Company Homogeneous, high modulus ultrahigh molecular weight polyethylene composites and processes for the preparation thereof
US5180484A (en) * 1990-08-27 1993-01-19 Uop Caustic free liquid/liquid process for sweeting a sour hydrocarbon fraction
US5702448A (en) 1990-09-17 1997-12-30 Buechel; Frederick F. Prosthesis with biologically inert wear resistant surface
DE4030564A1 (en) 1990-09-27 1992-04-02 Hoechst Ag GRAFT POLYMER BASED ON ULTRA HIGH MOLECULAR POLYETHYLENE
US5160484A (en) 1990-09-28 1992-11-03 Cranston Print Works Company Paper saturant
US5059196A (en) 1991-03-07 1991-10-22 Dow Corning Wright Corporation Femoral prosthesis holder/driver tool and method of implantation using same
DE4110705C1 (en) * 1991-04-03 1992-10-22 Degussa Ag, 6000 Frankfurt, De
US5972444A (en) 1991-10-15 1999-10-26 The Dow Chemical Company Polyolefin compositions with balanced shrink properties
US5334640A (en) * 1992-04-08 1994-08-02 Clover Consolidated, Ltd. Ionically covalently crosslinked and crosslinkable biocompatible encapsulation compositions and methods
US5236583A (en) 1992-05-20 1993-08-17 Wang Yiu Te High-pressure/vacuum operated apparatus for sewage and mud disposal
US5468842A (en) 1992-06-23 1995-11-21 E. I. Du Pont De Nemours And Company Annealed linear high density polyethylene and preparation thereof
US5238563A (en) * 1992-07-29 1993-08-24 Exxon Research & Engineering Company Multi-element housing
US5253732A (en) * 1993-02-22 1993-10-19 Daniels Danny R Portable folding tree stand
WO1995006148A1 (en) 1993-08-20 1995-03-02 Smith & Nephew Richards, Inc. Self-reinforced ultra-high molecular weight polyethylene composites
US5496312A (en) 1993-10-07 1996-03-05 Valleylab Inc. Impedance and temperature generator control
US5449145A (en) * 1993-10-08 1995-09-12 Surgin Surgical Instrumentation, Inc. Valve device for controlling flows in surgical applications
US5420367A (en) * 1994-09-27 1995-05-30 E. I. Du Pont De Nemours And Company Polymers of vinyl(perfluorocyclopropane)
US20050125074A1 (en) * 1995-01-20 2005-06-09 Ronald Salovey Crosslinking of polyethylene for low wear using radiation and thermal treatments
AU727279B2 (en) 1995-01-20 2000-12-07 Orthopaedic Hospital Chemically crosslinked ultrahigh molecular weight polyethylene for artificial human joints
US5577368A (en) * 1995-04-03 1996-11-26 Johnson & Johnson Professional, Inc. Method for improving wear resistance of polymeric bioimplantable components
JPH11510534A (en) 1995-07-26 1999-09-14 ミネソタ マイニング アンド マニュファクチャリング カンパニー Radiation-crosslinkable thermoplastic composition and preparation of graphic articles using the same
US5674293A (en) 1996-01-19 1997-10-07 Implant Sciences Corp. Coated orthopaedic implant components
CA2243852C (en) 1996-01-22 2006-11-07 The Dow Chemical Company Polyolefin elastomer blends exhibiting improved properties
NZ331107A (en) 1996-02-13 2000-04-28 Gen Hospital Corp Radiation and melt treated ultra high molecular weight polyethylene prosthetic devices
AU3655197A (en) 1996-07-09 1998-02-02 Orthopaedic Hospital Crosslinking of polyethylene for low wear using radiation and thermal treatments
EP1028760B1 (en) 1996-10-15 2004-04-14 Orthopaedic Hospital Wear resistant surface-gradient cross-linked polyethylene
US6245196B1 (en) 1999-02-02 2001-06-12 Praxair Technology, Inc. Method and apparatus for pulp yield enhancement
US6143232A (en) 1999-07-29 2000-11-07 Bristol-Meyers Squibb Company Method of manufacturing an articulating bearing surface for an orthopaedic implant
US6318158B1 (en) 2000-03-01 2001-11-20 Coulter International Corp. Sample preparation and delivery system employing external sonicator
WO2001080778A1 (en) 2000-04-27 2001-11-01 The Orthopaedic Hospital Oxidation-resistant and wear-resistant polyethylenes for human joint replacements and methods for making them

Patent Citations (100)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3330748A (en) * 1955-01-11 1967-07-11 Gen Electric Method and apparatus for irradiating organic polymers with electrons
US2904480A (en) * 1955-06-06 1959-09-15 Grace W R & Co Polyethylene
US2948666A (en) * 1956-11-21 1960-08-09 Gen Electric Irradiation process
US3563869A (en) * 1957-11-05 1971-02-16 Grace W R & Co Irradiated polyethylene
US3022543A (en) * 1958-02-07 1962-02-27 Grace W R & Co Method of producing film having improved shrink energy
US3090770A (en) * 1960-04-26 1963-05-21 Grace W R & Co Blended polyethylene compositions of improved clarity and method of making same
US3297641A (en) * 1964-01-17 1967-01-10 Grace W R & Co Process for cross-linking polyethylene
US3646155A (en) * 1968-12-20 1972-02-29 Midland Silicones Ltd Cross-linking of a polyolefin with a silane
US3671477A (en) * 1969-03-10 1972-06-20 Campbell Mfg Co Ltd Composition comprising unsaturated elastomer,epoxy resin polycarboxylic acid or anhydride,cross-linking catalyst and filler and golf ball made therefrom
US3758273A (en) * 1970-04-03 1973-09-11 Gillette Co Processes for sterilizing polypropylene objects
US3886056A (en) * 1971-11-01 1975-05-27 Ryozo Kitamaru Process for producing a high melting temperature polyethylene employing irradiation and orienting
US3944536A (en) * 1973-06-18 1976-03-16 E. I. Du Pont De Nemours & Company Exceptionally rigid and tough ultrahigh molecular weight linear polyethylene
US4138382A (en) * 1978-05-01 1979-02-06 Dow Corning Corporation Hydrophilic, water-swellable, crosslinked, copolymer gel and prosthesis employing same
US4281420A (en) * 1979-02-15 1981-08-04 Raab S Bone connective prostheses adapted to maximize strength and durability of prostheses-bone cement interface; and methods of forming same
US4336618A (en) * 1979-02-15 1982-06-29 Raab S Bone connective prostheses adapted to maximize strength and durability of prostheses-bone cement interface; and methods of forming same
US5017627A (en) * 1980-10-09 1991-05-21 National Research Development Corporation Composite material for use in orthopaedics
US4582656A (en) * 1981-08-12 1986-04-15 Hewing Gmbh & Co. Method of producing molded articles from polyolefin molding compositions crosslinked by irradiation
US4390666A (en) * 1981-08-14 1983-06-28 Asahi Kasei Kogyo Kabushiki Kaisha Polyethylene blend composition
US4586995A (en) * 1982-09-17 1986-05-06 Phillips Petroleum Company Polymer and irradiation treatment method
US4816517A (en) * 1982-09-29 1989-03-28 Vulkor, Incorporated Crosslinked polymer interdispersions containing polyolefin and method of making
US4518552A (en) * 1983-11-09 1985-05-21 Mitsuboshi Belting Ltd. Method of producing accurately sized material of ultra high molecular weight polyethylene
US5001206A (en) * 1983-12-10 1991-03-19 Stamicarbon B.V. Oriented polyolfins
US4587163B1 (en) * 1984-03-06 1990-04-03 E Zachariades Anagnostis
US4587163A (en) * 1984-03-06 1986-05-06 Zachariades Anagnostis E Preparation of ultra high molecular weight polyethylene morphologies of totally fused particles with superior mechanical performance
US4892552A (en) * 1984-03-30 1990-01-09 Ainsworth Robert D Orthopedic device
US4655769A (en) * 1984-10-24 1987-04-07 Zachariades Anagnostis E Ultra-high-molecular-weight polyethylene products including vascular prosthesis devices and methods relating thereto and employing pseudo-gel states
US4944974A (en) * 1984-10-24 1990-07-31 Zachariades Anagnostis E Composite structures of ultra-high-molecular-weight polymers, such as ultra-high-molecular-weight polyethylene products, and method of producing such structures
US4820466A (en) * 1985-01-31 1989-04-11 Zachariades Anagnostis E Process for obtaining ultra-high modulus products
US4950151A (en) * 1985-01-31 1990-08-21 Zachariades Anagnostic E Rolling die for producing high modulus products
US4916198A (en) * 1985-01-31 1990-04-10 Himont Incorporated High melt strength, propylene polymer, process for making it, and use thereof
US4668527A (en) * 1985-03-06 1987-05-26 Osaka University Method for amorphizing a material by means of injection of exotic atoms into a solid with electron beams
US4747990A (en) * 1985-03-12 1988-05-31 Cie Oris Industrie S.A. Process of making a high molecular weight polyolefin part
US4832965A (en) * 1985-05-17 1989-05-23 Helin Stig Aake Method of making a bottle and packaging a water ration therein
US4813210A (en) * 1985-09-27 1989-03-21 Nissho Corporation Radiation-sterilized, packaged medical device
US4902460A (en) * 1985-11-30 1990-02-20 Mitsui Petrochemical Industries, Ltd. Process for preparation of molecularly oriented, silane-crosslinked ultra-high-molecular-weight polyethylene molded article
US4682656A (en) * 1986-06-20 1987-07-28 Otis Engineering Corporation Completion apparatus and method for gas lift production
US4743493A (en) * 1986-10-06 1988-05-10 Spire Corporation Ion implantation of plastics
US5001008A (en) * 1987-07-21 1991-03-19 Mitsui Petrochemical Industries, Ltd. Reinforcing fibrous material
US5096654A (en) * 1987-07-24 1992-03-17 The National Research And Development Corporation Solid phase deformation process
US4891173A (en) * 1987-09-09 1990-01-02 Toa Nenryo Kogyo Kabushiki Kaisha Process for producing a crosslinked and oriented polyethylene film
US5480683A (en) * 1988-05-24 1996-01-02 Nitruvid Process for reducing the coefficient of friction and wear between a metal part and an organic polymer-or copolymer-based part and its application to artificial limb-joints and fittings working in marine environments
US5014494A (en) * 1988-09-27 1991-05-14 Sherwood Medical Company Method of sterilizing medical articles
US5621070A (en) * 1988-12-02 1997-04-15 E. I. Du Pont De Nemours And Company Ultra high molecular weight linear polyethylene processes of manufacture
US5030402A (en) * 1989-03-17 1991-07-09 Zachariades Anagnostis E Process for producing a new class of ultra-high-molecular-weight polyethylene orthopaedic prostheses with enhanced mechanical properties
US5180394A (en) * 1989-07-25 1993-01-19 Davidson James A Zirconium oxide and nitride coated prosthesis for wear and corrosion resistance
US5130378A (en) * 1989-09-02 1992-07-14 Bayer Aktiengesellschaft Copolymers containing secondary amino groups and a process for their production
US5024670A (en) * 1989-10-02 1991-06-18 Depuy, Division Of Boehringer Mannheim Corporation Polymeric bearing component
US5037928A (en) * 1989-10-24 1991-08-06 E. I. Du Pont De Nemours And Company Process of manufacturing ultrahigh molecular weight linear polyethylene shaped articles
US5652281A (en) * 1989-12-21 1997-07-29 Montell North America Inc. Graft copolymers of polyolefins and a method of producing same
US5200439A (en) * 1990-04-13 1993-04-06 Mitsui Toatsu Chemicals, Inc. Method for increasing intrinsic viscosity of syndiotactic polypropylene
US5130376A (en) * 1990-04-23 1992-07-14 Hercules Incorporated UHMWPE/styrenic molding compositions with improved flow properties and impact strength
US5236563A (en) * 1990-06-18 1993-08-17 Advanced Surface Technology Inc. Surface-modified bioabsorbables
US5133757A (en) * 1990-07-31 1992-07-28 Spire Corporation Ion implantation of plastic orthopaedic implants
US5210130A (en) * 1990-08-07 1993-05-11 E. I. Du Pont De Nemours And Company Homogeneous, high modulus ultrahigh molecular weight polyethylene composites and processes for the preparation thereof
US5236669A (en) * 1990-09-12 1993-08-17 E. I. Du Pont De Nemours And Company Pressure vessel
US5192323A (en) * 1990-11-05 1993-03-09 Zimmer, Inc. Method of surface hardening orthopedic implant devices
US5178812A (en) * 1990-11-28 1993-01-12 E. I. Du Pont De Nemours And Company Method of making composites having improved surface properties
US5137688A (en) * 1990-11-29 1992-08-11 General Electric Company Irradiated articles molded from polycarbonate-polyamide blends
US5292584A (en) * 1991-04-11 1994-03-08 E. I. Du Pont De Nemours And Company Ultrahigh molecular weight polyethylene and lightly-filled composites thereof
US5508319A (en) * 1991-06-21 1996-04-16 Montell North America Inc. High melt strength, ethylene polymer, process for making it, and use thereof
US5439949A (en) * 1991-08-21 1995-08-08 Rexene Corporation Propylene compositions with improved resistance to thermoforming sag
US5296583A (en) * 1992-07-09 1994-03-22 University Of Michigan Calcification-resistant synthetic biomaterials
US5505984A (en) * 1993-01-21 1996-04-09 England; Garry L. Method for forming biocompatible components using an isostatic press
US5549698A (en) * 1993-04-22 1996-08-27 Implex Corp. Prosthetic acetabular cup and method of implant
US6372814B1 (en) * 1993-06-01 2002-04-16 Stryker Technologies Corporation Non-oxidizing polymeric medical implant
US5543471A (en) * 1993-06-01 1996-08-06 Howmedica Inc. Non-oxidizing polymeric medical implant
US5728748A (en) * 1993-06-01 1998-03-17 Howmedica Inc. Non oxidizing polymeric medical implant
US6174934B1 (en) * 1993-06-01 2001-01-16 Stryker Technologies Corporation Non-oxidizing polymeric medical implant
US5414049A (en) * 1993-06-01 1995-05-09 Howmedica Inc. Non-oxidizing polymeric medical implant
US5650485A (en) * 1993-06-01 1997-07-22 Howmedica Inc. Non-oxidizing polymeric medical implant
US5435723A (en) * 1993-08-18 1995-07-25 O'brien; Gary R. Endosseous dental implant system
US5549700A (en) * 1993-09-07 1996-08-27 Ortho Development Corporation Segmented prosthetic articulation
US5407623A (en) * 1994-01-06 1995-04-18 Polteco, Inc. Process for obtaining ultra-high modulus line products with enhanced mechanical properties
US5593719A (en) * 1994-03-29 1997-01-14 Southwest Research Institute Treatments to reduce frictional wear between components made of ultra-high molecular weight polyethylene and metal alloys
US5879388A (en) * 1994-07-19 1999-03-09 The University Of Kentucky Research Foundation Implant pre-treated for reducing the generation of wear particulates
US5515590A (en) * 1994-07-19 1996-05-14 University Of Kentucky Research Foundation Method for reducing the generation of wear particulates from an implant
US5709020A (en) * 1994-07-19 1998-01-20 University Of Kentucky Research Foundation Method for reducing the generation of wear particulates from an implant
US5508079A (en) * 1994-08-15 1996-04-16 Owens-Corning Fiberglas Technology, Inc. Conformable insulation assembly
US5545453A (en) * 1994-08-15 1996-08-13 Owens Corning Fiberglas Technology, Inc. Conformable insulation assembly
US6168626B1 (en) * 1994-09-21 2001-01-02 Bmg Incorporated Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same
US5645882A (en) * 1994-11-16 1997-07-08 Alcon Laboratories, Inc. Cross-linked polyethylene oxide coatings to improve the biocompatibility of implantable medical devices
US5609638A (en) * 1994-11-29 1997-03-11 Zimmer, Inc. Reinforced polyethylene for articular surfaces
US5876453A (en) * 1994-11-30 1999-03-02 Implant Innovations, Inc. Implant surface preparation
US5625858A (en) * 1995-01-18 1997-04-29 Canon Kabushiki Kaisha Contact charging member, process for producing same and electrophotographic apparatus using same
US6281264B1 (en) * 1995-01-20 2001-08-28 The Orthopaedic Hospital Chemically crosslinked ultrahigh molecular weight polyethylene for artificial human joints
US5609643A (en) * 1995-03-13 1997-03-11 Johnson & Johnson Professional, Inc. Knee joint prosthesis
US5879400A (en) * 1996-02-13 1999-03-09 Massachusetts Institute Of Technology Melt-irradiated ultra high molecular weight polyethylene prosthetic devices
US20020007219A1 (en) * 1996-02-13 2002-01-17 Merrill Edward W. Radiation and melt treated ultra high molecular weight polyethylene prosthetic devices
US5753182A (en) * 1996-02-14 1998-05-19 Biomet, Inc. Method for reducing the number of free radicals present in ultrahigh molecular weight polyethylene orthopedic components
US5721334A (en) * 1996-02-16 1998-02-24 Newyork Society For The Ruptured And Crippled Maintaining The Hospital For Special Surgery Process for producing ultra-high molecular weight low modulus polyethylene shaped articles via controlled pressure and temperature and compositions and articles produced therefrom
US6228900B1 (en) * 1996-07-09 2001-05-08 The Orthopaedic Hospital And University Of Southern California Crosslinking of polyethylene for low wear using radiation and thermal treatments
US6242507B1 (en) * 1996-10-02 2001-06-05 Depuy Orthopaedics, Inc. Process for medical implant of cross-linked ultrahigh molecular weight polyethylene having improved balance of wear properties and oxidation resistance
US6017975A (en) * 1996-10-02 2000-01-25 Saum; Kenneth Ashley Process for medical implant of cross-linked ultrahigh molecular weight polyethylene having improved balance of wear properties and oxidation resistance
US6562540B2 (en) * 1996-10-02 2003-05-13 Depuy Orthopaedics, Inc. Process for medical implant of cross-linked ultrahigh molecular weight polyethylene having improved balance of wear properties and oxidation resistance
US5798417A (en) * 1996-10-15 1998-08-25 E. I. Du Pont De Nemours And Company (Fluorovinyl ether)-grafted high-surface-area polyolefins and preparation thereof
US5879407A (en) * 1997-07-17 1999-03-09 Waggener; Herbert A. Wear resistant ball and socket joint
US6692679B1 (en) * 1998-06-10 2004-02-17 Depuy Orthopaedics, Inc. Cross-linked molded plastic bearings
US6281262B1 (en) * 1998-11-12 2001-08-28 Takiron Co., Ltd. Shape-memory, biodegradable and absorbable material
US6245276B1 (en) * 1999-06-08 2001-06-12 Depuy Orthopaedics, Inc. Method for molding a cross-linked preform
US6184265B1 (en) * 1999-07-29 2001-02-06 Depuy Orthopaedics, Inc. Low temperature pressure stabilization of implant component

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080133018A1 (en) * 1995-01-20 2008-06-05 Ronald Salovey Chemically crosslinked ultrahigh molecular weight polyethylene for artificial human joints
US20050125074A1 (en) * 1995-01-20 2005-06-09 Ronald Salovey Crosslinking of polyethylene for low wear using radiation and thermal treatments
US8008365B2 (en) 1996-07-09 2011-08-30 Orthopaedic Hospital Crosslinking of polyethylene for low wear using radiation and thermal treatments
US8003709B2 (en) 1996-07-09 2011-08-23 Orthopaedic Hospital Crosslinking of polyethylene for low wear using radiation and thermal treatments
US7993401B2 (en) 2004-10-07 2011-08-09 Biomet Manufacturing Corp. Solid state deformation processing of crosslinked high molecular weight polymeric materials
US8137608B2 (en) 2004-10-07 2012-03-20 Biomet Manufacturing Corp. Crosslinked polymeric material with enhanced strength and process for manufacturing
US9017590B2 (en) 2004-10-07 2015-04-28 Biomet Manufacturing, Llc Solid state deformation processing of crosslinked high molecular weight polymeric materials
US8398913B2 (en) 2004-10-07 2013-03-19 Biomet Manufacturing Corp. Solid state deformation processing of crosslinked high molecular weight polymeric materials
US7780896B2 (en) 2004-10-07 2010-08-24 Biomet Manufacturing Corp. Crosslinked polymeric material with enhanced strength and process for manufacturing
US7927536B2 (en) 2004-10-07 2011-04-19 Biomet Manufacturing Corp. Solid state deformation processing of crosslinked high molecular weight polymeric materials
US8262976B2 (en) 2004-10-07 2012-09-11 Biomet Manufacturing Corp. Solid state deformation processing of crosslinked high molecular weight polymeric materials
US7344672B2 (en) 2004-10-07 2008-03-18 Biomet Manufacturing Corp. Solid state deformation processing of crosslinked high molecular weight polymeric materials
WO2007024689A3 (en) * 2005-08-22 2007-11-08 Gen Hospital Corp Dba Massachu Oxidation resistant homogenized polymeric material
US8461225B2 (en) 2005-08-22 2013-06-11 The General Hospital Corporation Oxidation resistant homogenized polymeric material
US8889757B2 (en) 2005-08-22 2014-11-18 The General Hospital Corporation Oxidation resistant homogenized polymeric material
US20070197679A1 (en) * 2006-02-21 2007-08-23 Anuj Bellare Crosslinked polymers
WO2007098447A2 (en) * 2006-02-21 2007-08-30 The Brigham And Women's Hospital, Inc. Crosslinked polymers
US7635725B2 (en) 2006-02-21 2009-12-22 The Brigham And Women's Hospital, Inc. Crosslinked polymers
WO2007098447A3 (en) * 2006-02-21 2008-07-10 Brigham & Womens Hospital Crosslinked polymers
US8641959B2 (en) 2007-07-27 2014-02-04 Biomet Manufacturing, Llc Antioxidant doping of crosslinked polymers to form non-eluting bearing components
US9421104B2 (en) 2007-07-27 2016-08-23 Biomet Manufacturing, Llc Antioxidant doping of crosslinked polymers to form non-eluting bearing components
US9586370B2 (en) 2013-08-15 2017-03-07 Biomet Manufacturing, Llc Method for making ultra high molecular weight polyethylene

Also Published As

Publication number Publication date
JP2000514481A (en) 2000-10-31
EP0935446A1 (en) 1999-08-18
EP1795212A3 (en) 2007-09-05
EP0935446A4 (en) 2001-12-19
US8003709B2 (en) 2011-08-23
US20080133021A1 (en) 2008-06-05
EP1795212A2 (en) 2007-06-13
US20070100016A1 (en) 2007-05-03
JP4187712B2 (en) 2008-11-26
DE69737325D1 (en) 2007-03-22
WO1998001085A1 (en) 1998-01-15
US20070100017A1 (en) 2007-05-03
US20020037944A1 (en) 2002-03-28
JP2005161029A (en) 2005-06-23
EP0935446B1 (en) 2007-02-07
EP2319546A1 (en) 2011-05-11
US8008365B2 (en) 2011-08-30
DE69737325T2 (en) 2007-11-22
US20050048096A1 (en) 2005-03-03
CA2260241A1 (en) 1998-01-15
US6800670B2 (en) 2004-10-05
CA2260241C (en) 2010-09-14
AU3655197A (en) 1998-02-02

Similar Documents

Publication Publication Date Title
US8003709B2 (en) Crosslinking of polyethylene for low wear using radiation and thermal treatments
US6228900B1 (en) Crosslinking of polyethylene for low wear using radiation and thermal treatments
WO1998001085A9 (en) Crosslinking of polyethylene for low wear using radiation and thermal treatments
US6494917B1 (en) Wear resistant surface-gradient crosslinked polyethylene
EP0722973B1 (en) Chemically crosslinked ultrahigh molecular weight polyethylene for artificial human joints
US8324291B2 (en) Sequentially cross-linked polyethylene
US20050125074A1 (en) Crosslinking of polyethylene for low wear using radiation and thermal treatments
AU727279B2 (en) Chemically crosslinked ultrahigh molecular weight polyethylene for artificial human joints

Legal Events

Date Code Title Description
STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION