USRE44762E1 - Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same - Google Patents
Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same Download PDFInfo
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- USRE44762E1 USRE44762E1 US13/531,232 US53123296A USRE44762E US RE44762 E1 USRE44762 E1 US RE44762E1 US 53123296 A US53123296 A US 53123296A US RE44762 E USRE44762 E US RE44762E
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- United States
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- block
- molecular weight
- compression
- weight polyethylene
- ultra high
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- Expired - Lifetime
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- 239000004699 Ultra-high molecular weight polyethylene Substances 0.000 title claims abstract description 90
- 229920000785 ultra high molecular weight polyethylene Polymers 0.000 title claims abstract description 90
- 238000000034 method Methods 0.000 title claims description 19
- 239000013078 crystal Substances 0.000 claims abstract description 29
- 238000005299 abrasion Methods 0.000 claims abstract description 18
- 230000006835 compression Effects 0.000 claims description 37
- 238000007906 compression Methods 0.000 claims description 37
- 238000002844 melting Methods 0.000 claims description 28
- 230000008018 melting Effects 0.000 claims description 28
- 238000001816 cooling Methods 0.000 claims description 23
- 238000004132 cross linking Methods 0.000 claims description 12
- 238000002425 crystallisation Methods 0.000 claims description 8
- 230000008025 crystallization Effects 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 8
- 230000001678 irradiating effect Effects 0.000 claims description 6
- -1 polyethylene Polymers 0.000 claims description 6
- 239000004698 Polyethylene Substances 0.000 claims description 4
- 229920010741 Ultra High Molecular Weight Polyethylene (UHMWPE) Polymers 0.000 claims description 4
- 238000005520 cutting process Methods 0.000 claims description 4
- 229920000573 polyethylene Polymers 0.000 claims description 4
- 230000002285 radioactive effect Effects 0.000 claims description 4
- 238000007711 solidification Methods 0.000 claims description 4
- 230000008023 solidification Effects 0.000 claims description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 2
- 239000001301 oxygen Substances 0.000 claims description 2
- 229910052760 oxygen Inorganic materials 0.000 claims description 2
- 230000008569 process Effects 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 17
- 238000002513 implantation Methods 0.000 claims 4
- 210000003127 knee Anatomy 0.000 claims 3
- 241001465754 Metazoa Species 0.000 claims 2
- 230000005855 radiation Effects 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 11
- 210000004394 hip joint Anatomy 0.000 abstract description 4
- 210000000629 knee joint Anatomy 0.000 abstract description 4
- 210000002310 elbow joint Anatomy 0.000 abstract description 3
- 238000002360 preparation method Methods 0.000 description 20
- 238000012360 testing method Methods 0.000 description 18
- 210000001503 joint Anatomy 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 6
- 230000007423 decrease Effects 0.000 description 6
- 230000005251 gamma ray Effects 0.000 description 6
- 230000006872 improvement Effects 0.000 description 5
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 4
- 239000011521 glass Substances 0.000 description 4
- 239000003708 ampul Substances 0.000 description 3
- 230000005489 elastic deformation Effects 0.000 description 3
- 230000004927 fusion Effects 0.000 description 3
- 229920000642 polymer Polymers 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 206010063560 Excessive granulation tissue Diseases 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 208000003076 Osteolysis Diseases 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 238000007385 chemical modification Methods 0.000 description 2
- 210000001126 granulation tissue Anatomy 0.000 description 2
- 238000011068 loading method Methods 0.000 description 2
- 208000029791 lytic metastatic bone lesion Diseases 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229920002994 synthetic fiber Polymers 0.000 description 2
- 239000012209 synthetic fiber Substances 0.000 description 2
- GUTLYIVDDKVIGB-OUBTZVSYSA-N Cobalt-60 Chemical compound [60Co] GUTLYIVDDKVIGB-OUBTZVSYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- 239000004677 Nylon Substances 0.000 description 1
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 206010003246 arthritis Diseases 0.000 description 1
- 238000011882 arthroplasty Methods 0.000 description 1
- 210000001188 articular cartilage Anatomy 0.000 description 1
- 230000037396 body weight Effects 0.000 description 1
- 210000000988 bone and bone Anatomy 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000001684 chronic effect Effects 0.000 description 1
- 238000003776 cleavage reaction Methods 0.000 description 1
- 229910001429 cobalt ion Inorganic materials 0.000 description 1
- XLJKHNWPARRRJB-UHFFFAOYSA-N cobalt(2+) Chemical compound [Co+2] XLJKHNWPARRRJB-UHFFFAOYSA-N 0.000 description 1
- 238000000748 compression moulding Methods 0.000 description 1
- 235000019628 coolness Nutrition 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 201000010099 disease Diseases 0.000 description 1
- 208000037265 diseases, disorders, signs and symptoms Diseases 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 210000001145 finger joint Anatomy 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000007943 implant Substances 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 238000002329 infrared spectrum Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 210000002540 macrophage Anatomy 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000002715 modification method Methods 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229920001778 nylon Polymers 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 239000004417 polycarbonate Substances 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 230000007017 scission Effects 0.000 description 1
- 210000000323 shoulder joint Anatomy 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
- C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L23/04—Homopolymers or copolymers of ethene
- C08L23/06—Polyethene
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS 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
- A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
- A61L27/14—Macromolecular materials
- A61L27/16—Macromolecular materials obtained by reactions only involving carbon-to-carbon unsaturated bonds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
- B29C43/003—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor characterised by the choice of material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
- B29C43/02—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles
- B29C43/16—Forging
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F110/00—Homopolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F110/02—Ethene
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/28—Treatment by wave energy or particle radiation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
- B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
- B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
- B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
- B29C2035/085—Heating 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING 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
- B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
- B29K2023/04—Polymers of ethylene
- B29K2023/06—PE, i.e. polyethylene
- B29K2023/0658—PE, i.e. polyethylene characterised by its molecular weight
- B29K2023/0683—UHMWPE, i.e. ultra high molecular weight polyethylene
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING 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
- B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
- B29K2995/0037—Other properties
- B29K2995/0087—Wear resistance
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING 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
- B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
- B29K2995/0037—Other properties
- B29K2995/0089—Impact strength or toughness
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
- B29L2031/00—Other particular articles
- B29L2031/753—Medical equipment; Accessories therefor
- B29L2031/7532—Artificial members, protheses
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised 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
- C08J2323/04—Homopolymers or copolymers of ethene
- C08J2323/06—Polyethene
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2207/00—Properties characterising the ingredient of the composition
- C08L2207/06—Properties of polyethylene
- C08L2207/068—Ultra high molecular weight polyethylene
Definitions
- the present invention relates to an ultra high molecular weight polyethylene molded article suitable for artificial joints having molecular orientation or crystal orientation and to a method of preparing the same.
- These artificial joints includes an artificial hip joint, an artificial knee joint, an artificial elbow joint, an artificial finger joint, artificial shoulder joint and the like.
- the artificial hip joint and artificial knee joint it is necessary for the artificial hip joint and artificial knee joint to have high mechanical strength because gravity corresponding to several times the patient's body weight is applied to them. Therefore, materials for the artificial joint at present are constituted of a hard material of metal or ceramic and a soft socket of an ultra high molecular weight polyethylene (UHMWPE).
- UHMWPE ultra high molecular weight polyethylene
- the UHMWPE constituting such a socket is superior in abrasion resistance as compared with polymeric materials such as polytetrafluoroethylene and polycarbonate, the UHMWPE is inferior in properties such as low abrasion resistance and stress relaxation to impact load which are inherently possessed by articular cartilage of living body. Also, reaction caused by a foreign matter has been a serious problem wherein macrophages proliferate against wear debris of the UHMWPE socket, i.e. component and an abnormal granulation tissue generated thereby causes resorption of the bone.
- the present inventors tried to obtain a molded article of a low friction and to improve an abrasion resistance by introducing molecular orientation or crystal orientation into a finished product by means of, not a chemical modification method, but a physical modification method.
- the invention relates to an ultra high molecular weight polyethylene (UHMWPE) molded article for artificial joints and to an artificial join comprising the UHMWPE molded article.
- UHMWPE ultra high molecular weight polyethylene
- This UHMWPE molded article having molecular orientation or crystal orientation can be obtained by irradiating a low dose of a high energy ray to a raw UHMWPE molded article to introduce a very small amount of crosslinking points in polymer chains so as to be crosslinked slightly, then by compression-deforming the crosslinked UHMWPE molded article after heating up to its compression-deformable temperature, and by cooling the molded article while keeping the deformed state.
- the UHMWPE molded article having molecular orientation or crystal orientation (hereinafter referred to as “oriented UHMWPE molded article”) of the present invention has a low friction and remarkably improved abrasion resistance. And, the artificial joint comprising the oriented UHMWPE molded article has a smooth lubricity and reduced amount of abrasion loss.
- the oriented UHMWPE molded article of the invention has molecular orientation or crystal orientation within the molded article.
- the meaning of “to have molecular orientation within the molded article” is that polymer chains are oriented perpendicular to the direction of the compression, namely, oriented to the direction of the flow of the molecular chains.
- the meaning of “to have crystal orientation” is that the crystal planes in polyethylene such as ( 200 ) plane and ( 110 ) plane are oriented to the direction parallel to the compression plane, namely, that the crystal planes are oriented. Also, the presence of these orientations can be known by means of biefringence measurements, infrared spectra and X-ray diffraction.
- a coefficient of friction of the molded article decreases and abrasion loss also decreases by endowing with those orientations.
- other functional properties for example, tensile strength and tensile modulus are improved, and also density, thermal properties (melting point, heat of fusion) and the like are improved.
- the oriented UHMWPE molded article can be obtained by irradiating a high energy ray to raw UHMWPE and then heating up and compression-deforming the UHMWPE, followed by cooling and solidifying.
- the raw UHMWPE one having a weight-average molecular weight of 2 to 8 million, preferably 5 to 7 million is used.
- the melting point thereof is approximately 136° to 139° C.
- the raw UHMWPE is used usually in the form of block, and may be used in the form of rod.
- Every kind of high energy rays can be employed as the high energy ray to be irradiated, for example a radioactive ray such as ⁇ -ray or X-ray, an electron beam, a neutron ray and the like.
- ⁇ -ray is superior in views of availability of irradiation apparatus and excellent permeability to materials.
- This irradiation of the high energy ray is carried out to generate crosslinking points in the molecular chains of the UHMWPE and then to produce intermolecular crosslinkage.
- the density of crosslinking is preferably such a very small degree that the crystallization is not prevented with ensuring a large elastic-deformation, for example 0.1 to 10, particularly 1 to 2 crosslinking points per one molecular chain.
- the atmosphere of a vacuum or of an inert gas such as N 2 or argon is preferable.
- the temperature of the atmosphere may be room temperature and also may be a higher temperature of not less than the crystal transition point (80° C.).
- the dose of irradiation is very important. If the dose of irradiation is too high, the density of crosslinking becomes higher, and the bridged structure is destroyed if a large deformation is applied in the subsequent process. And, even if the molten state is made, such a degree of elastic deformation required to obtain the desired molecular orientation or crystal orientation cannot be given. As a result, it is obliged to decrease a degree of the deformation, and it becomes impossible to obtain the molecular orientation or crystal orientation which is necessary for molecular chains in the molded article.
- a preferable dose of irradiation (energy) is the dose to give the above-mentioned density of crosslinking and 0.01 to 5.0 MR, preferably 0.1 to 3 MR in case of radioactive rays.
- the UHMWPE molded article which is crosslinked slightly by irradiating with the high energy ray has an infinite weight-average molecular weight because it is crosslinked, and the melting point thereof changes not so much and is 136° and 139° C.
- this slightly crosslinked UHMWPE molded article is heated up to a compression-deformable temperature.
- the compression-deformable temperature of is a temperature of around or not less than the melting point of the crosslinked UHMWPE, and is concretely from the melting point minus 50° C. to the melting point plus 80° C. It is most suitable to heat up to a temperature of not less than the melting point, particularly preferably 160° to 220° C., further preferably 180° to 200° C. to melt completely.
- the compression-deformation can be carried out, however, at a temperature of even around the melting point, for example 100° to 130° C. If completely melted, since the crosslinked UHMWPE is in the state of rubber to possess rubber elasticity, the compression-deformation is easily carried out.
- the compression-deformation is carried out under a pressure of 30 to 200 kgf/cm 2 , usually 50 to 100 kgf/cm 2 , with heating at the above-mentioned temperature in a die suitable for the use or be using a hot press machine. It is sufficient that a degree of the compression is approximately 1 ⁇ 3 to 1/10 of an original thickness in case of a molded article in the form of block.
- the deformation of the crosslinked UHMWPE molded article of the present invention is a rubber elastic deformation because molecular chains are crosslinked slightly, and after the molecular chains are stretched to give the necessary molecular orientation, then cooled as they are and crystallized, the crystal orientation can be obtained.
- non-crosslinked, namely non-irradiated UHMWPE molded article is fluid-deformed when heated and compressed at a temperature of not less than the melting point, and thus molecular orientation or crystal orientation cannot be obtained.
- the UHMWPE molded article having the molecular orientation or crystal orientation obtained by the compression-deformation as described above is cooled and solidified while keeping the deformed state. If the deformed state is set free before solidification, the stretched molecular chains are relaxed in stress to return to the original state because the compression-deformation is conducted in the molten state. That is, the molecular orientation or crystal orientation in the UHMWPE molded article is relaxed in a moment. Therefore, the deformed state must not be set free until solidified.
- the cooling method there are rapid coolings such as water-cooling and air-cooling as well as standing to cool, and the cooling is carried out down to room temperature, preferably to a temperature of around 20° to 40° C. Further, it is preferable to cool at a constant rate under a condition of 10° C./min, preferably 1° C./min to obtain excellent dynamic properties because the cooling rate has a great influence on the crystallinity, particularly on the degree of crystallinity of the produced molded article.
- the completion of the solidification can be confirmed by decrease of a pressure guage (the volume being shrinked after the completion of the crystallization).
- the compression-deformed UHMWPE molded article may be subjected to isothermal crystallization at around 100° to 130° C., preferably 110° to 120° C., for 1 to 20 hours, preferably 5 to 10 hours, with keeping the deformed state, and then cooled to room temperature, preferably to 40° C. and solidified.
- isothermal crystallization the degree of crystallinity becomes higher and the dynamic properties are improved.
- the cooling after the isothermal crystallization is not particularly limited and cooling at a rate of 1° C./min is preferable.
- the melting point of the UHMWPE molded article having the molecular orientation or crystal orientation obtained by the cooling and solidification is 135° to 155° C.
- the compression-deformed molded article which is obtained as described above can also be processed to a socket for artificial joints by cutting and can be molded by means of the compression-deformation mold with a die comprising a convex and concave portions.
- the surface hardness can be further reinforced by introducing metal ions, e.g. titanium, zirconium, iron, molybdenum, aluminium and/or cobalt ion, into the UHMWPE molded article for artificial joints which is obtained by cutting the compression-deformed molded article.
- a block of UHMWPE (thickness 3 cm, width 5 cm, length 5 cm) having a weight-average molecular weight of approximately 6 million and a melting point of 138° C. was put in a glass ampul and the glass was sealed after reducing the inner pressure (10 ⁇ 2 to 10 ⁇ 3 mmHg) under vacuum.
- ⁇ -Ray from cobalt 60 was irradiated at a dose of 0.5 MR to this glass ampul at 25° C.
- the UHMWPE block irradiated by the radioactive ray (melting point: 138° C., weight-average molecular weight: infinite) was taken out from the glass ampul, melted completely at 200° C. by using at hot press, compressed to 1 ⁇ 3, 1/4.5 and 1 ⁇ 6 of the original thickness by applying a pressure of 50 kgf/cm 2 m and then cooled to room temperature through natural cooling with keeping the deformed state.
- Irradiated UHMWPE molded articles were obtained by compression-deforming and cooling naturally similarly in Preparation Example 1 except that a dose of irradiation of ⁇ -ray was changed to 1.0 MR, 1.5 MR or 2.0 MR.
- Each weight-average molecular weights of the 1.0 MR irradiated article, 1.5 MR irradiated article and 2.0 MR irradiated article were infinite, and the melting points thereof were almost constant and were 138° C.
- a test sample having a thickness of 7 mm and a diameter of 7 mm was prepared by cutting from the UHMWPE molded article obtained in each of Preparation Examples 1 to 8 and Comparative Preparation Examples 1 to 3, and wear factor and coefficient of friction were evaluated by measuring a friction force and wear factor as the following.
- the unidirectional-type testing machine is operated by pressing a test sample on a surface of a ceramic disc, which is rotating in the clockwise direction, by means of the arm-type loading method.
- the load can be varied by providing a weight to the one end of the arm.
- the rotation of the disc is transmitted to a bearing by way of a belt according to the rotation of an invertor-controlled motor.
- the testing speed was set to 50 mm/s. Also, all tests were carried out in 50 ml saline for 48 hours and the temperature of the liquid was kept at 25 ⁇ 2° C.
- a friction force was measured by a lever type dynamometer fixed to the arm portion of the testing machine. The friction force was recorded with a pen recorder with the lapse of time. The friction coefficients shown in test results (Table 1) were determined in case of a sliding distance of 8640 m (48 hours after tests begin).
- the wear volume was evaluated by compressing the rotating disc of zirconia at a pressure of 1 MPa and by measuring the decreased thickness of the test sample with a non-contact type capacitance level gauge.
- the test for each test sample was carried out three times under each loading condition, and the coefficient of friction and coefficient of abrasion were calculated in average value.
- the surface of the zirconia disc was made in intentionally roughened to Ra; 0.2 to 0.3, and the wear volume was measured after 48 hours.
- the heat of fusion and melting point were measured at a scan speed of 10° C./min by means of DSC-50 of SHIMADZU CORPORATION. And, the tensile strength and Young's modulus were measured at a tensile rate of 100%/min by means of Autograph S-100 of SHIMADZU CORPORATION.
- the density and melting point of UHMWPE molded article obtained from the 0.5 MR irraidation test of Preparation Example 3 are higher and the tensile strength and Young's modulus thereof increase, as compared with those of the UHMWPE molded article obtained from the non-irradiation test of Comparative Preparation Example 3.
- the melting point rises from 138.0° to 149.5° C.
- the ultra high molecular weight polyethylene molded article for artificial joints obtained according to the present invention has the molecular orientation or crystal orientation in the molded article, and is low in friction and is superior in abrasion resistance, and therefore is available as a components of artificial joints.
- the ultra high molecular weight polyethylene molded article for artificial joints of the present invention can be used as a component for artificial hip joints (artificial acetabular cup), a component for artificial knee joints (artificial tibial insert) and the socket for artificial elbow joints, and in addition to the medical use, it can be applied as materials for various industries by utilizing the characteristics such as low friction and superior abrasion resistance.
Abstract
An ultra high molecular weight polyethylene molded article for artificial joints has molecular orientation or crystal orientation in the molded article, and is low in friction and is superior in abrasion resistance, and therefore is available as components for artificial joints. Further, the ultra high molecular weight polyethylene molded article for artificial joints can be used as a component for artificial hip joints (artificial acetabular cup), a component for artificial knee joints (artificial tibial insert) and the socket for artificial elbow joints, and in addition to the medical use, it can be applied as materials for various industries by utilizing the characteristics such as low friction and superior abrasion resistance.
Description
More than one reissue application has been filed for the reissue of U.S. Pat. No. 6,168,626. The reissue applications are: Ser. No. 10/141,374 filed May 8, 2002; Ser. No. 10/643,674 filed Aug. 19, 2003, a divisional reissue of Ser. No. 10/141,374; and Ser. No. 11/522,504 filed Sep. 15, 2006, a continuation reissue of (now abandoned) Ser. No. 10/643,673 (which was a divisional reissue of Ser. No. 10/141,374); and the current application, a continuation reissue of Ser. No. 10/643,674.
The present invention relates to an ultra high molecular weight polyethylene molded article suitable for artificial joints having molecular orientation or crystal orientation and to a method of preparing the same.
Thirty years or more have passed since an artificial joint was developed and applied clinically to patients suffering from any diseases of arthritis. Since then, benefits given by the artificial joint have been great in the sense of social welfare because, for example, patients with chronic rheumatism have been able to walk again and to return to public life. On the other hand, however, serious problems have occurred, particularly late appearing complications caused by total joint arthroplasty, a high rate of “loosening” in the implant components, and the necessity of revision of the joint with a surgical operation due to osteolysis around the implanted artificial joint.
These artificial joints includes an artificial hip joint, an artificial knee joint, an artificial elbow joint, an artificial finger joint, artificial shoulder joint and the like. Among those joints, it is necessary for the artificial hip joint and artificial knee joint to have high mechanical strength because gravity corresponding to several times the patient's body weight is applied to them. Therefore, materials for the artificial joint at present are constituted of a hard material of metal or ceramic and a soft socket of an ultra high molecular weight polyethylene (UHMWPE). While the UHMWPE constituting such a socket is superior in abrasion resistance as compared with polymeric materials such as polytetrafluoroethylene and polycarbonate, the UHMWPE is inferior in properties such as low abrasion resistance and stress relaxation to impact load which are inherently possessed by articular cartilage of living body. Also, reaction caused by a foreign matter has been a serious problem wherein macrophages proliferate against wear debris of the UHMWPE socket, i.e. component and an abnormal granulation tissue generated thereby causes resorption of the bone.
After artificial joints were developed, though some improvements in qualities of material and design have been made, for example, a cementless artificial joint and the like with respect to the hard material, there has been no remarkable progress for about thirty years with respect to the soft socket portion except that the UHMWPE was employed. And if the artificial joint is used for a long period of time, numerous wear debris of polyethylene are produced because of friction between the hard material such as metal and the UHMWPE of the socket. By considering the osteolysis due to granulation tissue containing a foreign matter which is caused by the wear debris, further improvement of abrasion resistance is indispensable. As an attempt to reduce the abrasion of UHMWPE, it can be considered to select a material for the hard material and to improve the UHMWPE. Though the irradiation of an ultra high dose of γ-ray was tried for improving the UHMWPE, it was made clear that coefficient of abrasion increases and abrasion loss does not decrease. Also, though the improvement to increase molecular weight of the UHMWPE was made and a weight-average molecular weight of the UHMWPE at present has been increased to approximately 5 to 8 million, it is difficult to make a UHMWPE having a far ultra high molecular weight. Further, considerable improvement in dynamic properties can scarcely be expected even if a UHMWPE having a weight-average molecular weight of 10 million could be synthesized. Thus, it is regarded that any improvement in dynamic properties of the UHMWPE by chemical modification reached its limitation, and it is regarded to be difficult to obtain a UHMWPE molded article having a more excellent abrasion resistance and lower friction.
It is well-known that Carothers of E.I. Du Pont developed, first all over the world, a synthetic fiber, i.e., Nylon, and greatly contributed industrially. As means for improving mechanical properties of this synthetic fiber, uniaxial stretching in the direction of fiber axis is carried out industrially. Also, to improve the strength of the film, biaxial stretching and rolling are carried out industrially. In accordance with these methods, mechanical properties can be increased considerably by giving uniaxial orientation or biaxial orientation to molecules or crystals.
From these points of view, there is an idea that orientation is given to molecules or crystals in the polymer structure to improve the mechanical properties. However, any technologies cannot endow molecules or crystals with orientation in a large molded article in the form of block, and it is not easy to consider enablement of a method.
Then, the present inventors tried to obtain a molded article of a low friction and to improve an abrasion resistance by introducing molecular orientation or crystal orientation into a finished product by means of, not a chemical modification method, but a physical modification method.
This approach has never been attempted, not only in Japan, but also in other countries. The idea to endow the polyethylene molded article for artificial joints with molecular orientation or crystal orientation is the very creative, and it is sure that this invention, if actually carried out, will be applied to artificial joints all over the world. Also, this invention will be revolutionary in terms of industrial innovation whereby disadvantages which have been problems for the past thirty years are improved.
The invention relates to an ultra high molecular weight polyethylene (UHMWPE) molded article for artificial joints and to an artificial join comprising the UHMWPE molded article.
This UHMWPE molded article having molecular orientation or crystal orientation can be obtained by irradiating a low dose of a high energy ray to a raw UHMWPE molded article to introduce a very small amount of crosslinking points in polymer chains so as to be crosslinked slightly, then by compression-deforming the crosslinked UHMWPE molded article after heating up to its compression-deformable temperature, and by cooling the molded article while keeping the deformed state.
The UHMWPE molded article having molecular orientation or crystal orientation (hereinafter referred to as “oriented UHMWPE molded article”) of the present invention has a low friction and remarkably improved abrasion resistance. And, the artificial joint comprising the oriented UHMWPE molded article has a smooth lubricity and reduced amount of abrasion loss.
The oriented UHMWPE molded article of the invention has molecular orientation or crystal orientation within the molded article. The meaning of “to have molecular orientation within the molded article” is that polymer chains are oriented perpendicular to the direction of the compression, namely, oriented to the direction of the flow of the molecular chains. The meaning of “to have crystal orientation” is that the crystal planes in polyethylene such as (200) plane and (110) plane are oriented to the direction parallel to the compression plane, namely, that the crystal planes are oriented. Also, the presence of these orientations can be known by means of biefringence measurements, infrared spectra and X-ray diffraction. And, a coefficient of friction of the molded article decreases and abrasion loss also decreases by endowing with those orientations. Also, other functional properties, for example, tensile strength and tensile modulus are improved, and also density, thermal properties (melting point, heat of fusion) and the like are improved.
As described above, the oriented UHMWPE molded article can be obtained by irradiating a high energy ray to raw UHMWPE and then heating up and compression-deforming the UHMWPE, followed by cooling and solidifying.
As the raw UHMWPE, one having a weight-average molecular weight of 2 to 8 million, preferably 5 to 7 million is used. The melting point thereof is approximately 136° to 139° C. The raw UHMWPE is used usually in the form of block, and may be used in the form of rod.
Every kind of high energy rays can be employed as the high energy ray to be irradiated, for example a radioactive ray such as γ-ray or X-ray, an electron beam, a neutron ray and the like. Among them, γ-ray is superior in views of availability of irradiation apparatus and excellent permeability to materials. This irradiation of the high energy ray is carried out to generate crosslinking points in the molecular chains of the UHMWPE and then to produce intermolecular crosslinkage. The density of crosslinking is preferably such a very small degree that the crystallization is not prevented with ensuring a large elastic-deformation, for example 0.1 to 10, particularly 1 to 2 crosslinking points per one molecular chain.
With respect to the irradiation atmosphere, if oxygen exists, it is not preferable since a decomposition (cleavage) occurs simultaneously, and therefore the atmosphere of a vacuum or of an inert gas such as N2 or argon is preferable. The temperature of the atmosphere may be room temperature and also may be a higher temperature of not less than the crystal transition point (80° C.).
The dose of irradiation (energy) is very important. If the dose of irradiation is too high, the density of crosslinking becomes higher, and the bridged structure is destroyed if a large deformation is applied in the subsequent process. And, even if the molten state is made, such a degree of elastic deformation required to obtain the desired molecular orientation or crystal orientation cannot be given. As a result, it is obliged to decrease a degree of the deformation, and it becomes impossible to obtain the molecular orientation or crystal orientation which is necessary for molecular chains in the molded article. On the other hand, in case that a dose of irradiation is too low or not irradiation is carried out, molecular chains are fluidized in the manner of viscous fluidity without stretching to be plastic-deformed, resulting in that the molecular orientation or crystal orientation cannot be obtained. A preferable dose of irradiation (energy) is the dose to give the above-mentioned density of crosslinking and 0.01 to 5.0 MR, preferably 0.1 to 3 MR in case of radioactive rays.
The UHMWPE molded article which is crosslinked slightly by irradiating with the high energy ray has an infinite weight-average molecular weight because it is crosslinked, and the melting point thereof changes not so much and is 136° and 139° C.
Then, this slightly crosslinked UHMWPE molded article is heated up to a compression-deformable temperature. The compression-deformable temperature of is a temperature of around or not less than the melting point of the crosslinked UHMWPE, and is concretely from the melting point minus 50° C. to the melting point plus 80° C. It is most suitable to heat up to a temperature of not less than the melting point, particularly preferably 160° to 220° C., further preferably 180° to 200° C. to melt completely. The compression-deformation can be carried out, however, at a temperature of even around the melting point, for example 100° to 130° C. If completely melted, since the crosslinked UHMWPE is in the state of rubber to possess rubber elasticity, the compression-deformation is easily carried out.
The compression-deformation is carried out under a pressure of 30 to 200 kgf/cm2, usually 50 to 100 kgf/cm2, with heating at the above-mentioned temperature in a die suitable for the use or be using a hot press machine. It is sufficient that a degree of the compression is approximately ⅓ to 1/10 of an original thickness in case of a molded article in the form of block. The deformation of the crosslinked UHMWPE molded article of the present invention is a rubber elastic deformation because molecular chains are crosslinked slightly, and after the molecular chains are stretched to give the necessary molecular orientation, then cooled as they are and crystallized, the crystal orientation can be obtained. On the other hand, non-crosslinked, namely non-irradiated UHMWPE molded article is fluid-deformed when heated and compressed at a temperature of not less than the melting point, and thus molecular orientation or crystal orientation cannot be obtained.
Then, the UHMWPE molded article having the molecular orientation or crystal orientation obtained by the compression-deformation as described above is cooled and solidified while keeping the deformed state. If the deformed state is set free before solidification, the stretched molecular chains are relaxed in stress to return to the original state because the compression-deformation is conducted in the molten state. That is, the molecular orientation or crystal orientation in the UHMWPE molded article is relaxed in a moment. Therefore, the deformed state must not be set free until solidified.
As the cooling method, there are rapid coolings such as water-cooling and air-cooling as well as standing to cool, and the cooling is carried out down to room temperature, preferably to a temperature of around 20° to 40° C. Further, it is preferable to cool at a constant rate under a condition of 10° C./min, preferably 1° C./min to obtain excellent dynamic properties because the cooling rate has a great influence on the crystallinity, particularly on the degree of crystallinity of the produced molded article. The completion of the solidification can be confirmed by decrease of a pressure guage (the volume being shrinked after the completion of the crystallization).
Also, before the cooling, the compression-deformed UHMWPE molded article may be subjected to isothermal crystallization at around 100° to 130° C., preferably 110° to 120° C., for 1 to 20 hours, preferably 5 to 10 hours, with keeping the deformed state, and then cooled to room temperature, preferably to 40° C. and solidified. When carrying out the isothermal crystallization, the degree of crystallinity becomes higher and the dynamic properties are improved. The cooling after the isothermal crystallization is not particularly limited and cooling at a rate of 1° C./min is preferable.
The melting point of the UHMWPE molded article having the molecular orientation or crystal orientation obtained by the cooling and solidification is 135° to 155° C.
The compression-deformed molded article which is obtained as described above can also be processed to a socket for artificial joints by cutting and can be molded by means of the compression-deformation mold with a die comprising a convex and concave portions. The surface hardness can be further reinforced by introducing metal ions, e.g. titanium, zirconium, iron, molybdenum, aluminium and/or cobalt ion, into the UHMWPE molded article for artificial joints which is obtained by cutting the compression-deformed molded article.
Hereinafter, the present invention is explained concretely by referring to Preparation Examples and Examples.
A block of UHMWPE (thickness 3 cm, width 5 cm, length 5 cm) having a weight-average molecular weight of approximately 6 million and a melting point of 138° C. was put in a glass ampul and the glass was sealed after reducing the inner pressure (10−2 to 10−3 mmHg) under vacuum. γ-Ray from cobalt 60 was irradiated at a dose of 0.5 MR to this glass ampul at 25° C. Then, the UHMWPE block irradiated by the radioactive ray (melting point: 138° C., weight-average molecular weight: infinite) was taken out from the glass ampul, melted completely at 200° C. by using at hot press, compressed to ⅓, 1/4.5 and ⅙ of the original thickness by applying a pressure of 50 kgf/cm2m and then cooled to room temperature through natural cooling with keeping the deformed state.
The same raw UHMWPE block as was used in Preparation Examples 1 to 3 was compressed to ⅓, 1/4.5 and ⅙ of the original thickness after melting completely at 200° C. by using a hot press in the same way without irradiation, and cooled naturally to room temperature with keeping the deformed state.
Irradiated UHMWPE molded articles were obtained by compression-deforming and cooling naturally similarly in Preparation Example 1 except that a dose of irradiation of γ-ray was changed to 1.0 MR, 1.5 MR or 2.0 MR. Each weight-average molecular weights of the 1.0 MR irradiated article, 1.5 MR irradiated article and 2.0 MR irradiated article were infinite, and the melting points thereof were almost constant and were 138° C.
An irradiated UHMWPE molded article was obtained similarly in Preparation Example 1 except that after the irradiation of γ-ray (0.5 MR), the temperature was raised to 130° C. and the compression-deformation to ⅓ was carried out under a pressure of 200 kgf/cm3 for 5 minutes.
An irradiated UHMWPE molded article was obtained similarly in Preparation Example 1 except that after the compression molding, isothermal crystallization was carried out for 10 hours at 120° C. and then natural cooling was carried out.
A test sample having a thickness of 7 mm and a diameter of 7 mm was prepared by cutting from the UHMWPE molded article obtained in each of Preparation Examples 1 to 8 and Comparative Preparation Examples 1 to 3, and wear factor and coefficient of friction were evaluated by measuring a friction force and wear factor as the following.
Testing apparatus and testing conditions:
The unidirectional Pin-On-Disc wear and friction testing machine manufactured by Research Center for Biomedical Engineering, Kyoto University, was used for the test.
The unidirectional-type testing machine is operated by pressing a test sample on a surface of a ceramic disc, which is rotating in the clockwise direction, by means of the arm-type loading method. The load can be varied by providing a weight to the one end of the arm. The rotation of the disc is transmitted to a bearing by way of a belt according to the rotation of an invertor-controlled motor. The testing speed was set to 50 mm/s. Also, all tests were carried out in 50 ml saline for 48 hours and the temperature of the liquid was kept at 25±2° C.
Means to measure frictional force and wear volume:
A friction force was measured by a lever type dynamometer fixed to the arm portion of the testing machine. The friction force was recorded with a pen recorder with the lapse of time. The friction coefficients shown in test results (Table 1) were determined in case of a sliding distance of 8640 m (48 hours after tests begin).
The wear volume was evaluated by compressing the rotating disc of zirconia at a pressure of 1 MPa and by measuring the decreased thickness of the test sample with a non-contact type capacitance level gauge.
The test for each test sample was carried out three times under each loading condition, and the coefficient of friction and coefficient of abrasion were calculated in average value. In this case, the surface of the zirconia disc was made in intentionally roughened to Ra; 0.2 to 0.3, and the wear volume was measured after 48 hours.
Wear factor and coefficient of friction were calculated according to the equation of Dowson et al.
- Wear Factor (WF)=Wear volume (mm3)/{Load (N)×Sliding distance (m)}
- Coefficient of friction (CF)=Friction force (N)/Load (N)
The test results are shown in Table 1. With respect to the non-irradiated sample, there is no substantial difference in the wear factor (WF), that is, WF of 15.3×10−7 for the sample having the compression ratio at deformation (original thickness/thickness after compression-deformation) of 3, WF of 16.4×10−7 for the compression ratio of 4.5, and WF of 14.9×10−7 for the compression ratio of 6.
Remarkable decrease was observed, however, with respect to the 0.5 MR irradiated sample, i.e. WF if 9.07×10−7 for the compression ratio of 3, WF of 2.78×10−7 for the compression ratio of 4.5, and WF of 5.31×10−8 for the compression ratio of 6.
Characteristics of the UHMWPE molded articles obtained in Preparation Example 3 and Comparative Preparation Example 3 are shown in Table 2.
The heat of fusion and melting point were measured at a scan speed of 10° C./min by means of DSC-50 of SHIMADZU CORPORATION. And, the tensile strength and Young's modulus were measured at a tensile rate of 100%/min by means of Autograph S-100 of SHIMADZU CORPORATION.
As shown in Table 2, the density and melting point of UHMWPE molded article obtained from the 0.5 MR irraidation test of Preparation Example 3 are higher and the tensile strength and Young's modulus thereof increase, as compared with those of the UHMWPE molded article obtained from the non-irradiation test of Comparative Preparation Example 3. Particularly, the melting point rises from 138.0° to 149.5° C.
TABLE 1 | |||||
Dose of | Compression deformation | Wear | Coefficient |
irradiation | Temperature | Compression | factor | of friction | ||
MR | (° C.) | ratio | Cooling | (WF) | (CF) | |
Preparation | ||||||
Example | ||||||
1 | 0.5 | 200 | 3 | standing to cool | 9.07 × 10−7 | 0.11 |
2 | 0.5 | 200 | 4.5 | standing to cool | 2.78 × 10−7 | 0.08 |
3 | 0.5 | 200 | 6 | standing to cool | 5.31 × 10−8 | 0.03 |
4 | 1.0 | 200 | 3 | standing to cool | 7.35 × 10−7 | 0.04 |
5 | 1.5 | 200 | 3 | standing to cool | 4.62 × 10−7 | 0.02 |
6 | 2.0 | 200 | 3 | standing to cool | 8.31 × 10−8 | 0.01 |
7 | 1.0 | 130 | 3 | standing to cool | 9.64 × 10−7 | 0.12 |
8 | 1.0 | 200 | 3 | allowed to cool after | 2.53 × 10−8 | 0.01 |
the isothermal | ||||||
crystallization for | ||||||
10 hours at 120° C. | ||||||
Comparative | ||||||
Preparation | ||||||
Example | ||||||
1 | — | 200 | 3 | standing to cool | 15.3 × 10−7 | 0.14 |
2 | — | 200 | 4.5 | standing to cool | 16.4 × 10−7 | 0.15 |
3 | — | 200 | 6 | standing to cool | 14.9 × 10−7 | 0.12 |
TABLE 2 | |||||
Heat of | Melting | Tensile | Young's | ||
Density | fusion | point | strength | modulus | |
Sample | (g/cm3) | (cal/g) | (° C.) | (kg/cm2) | (kg/cm2) |
Comparative | 0.931 | 31.6 | 138.0 | 0.3 × 103 | 1.36 × 104 |
Preparation | |||||
Example 3 | |||||
Preparation | 0.948 | 39.2 | 149.5 | 1.3 × 103 | 1.95 × 104 |
Example 3 | |||||
The ultra high molecular weight polyethylene molded article for artificial joints obtained according to the present invention has the molecular orientation or crystal orientation in the molded article, and is low in friction and is superior in abrasion resistance, and therefore is available as a components of artificial joints.
Further, the ultra high molecular weight polyethylene molded article for artificial joints of the present invention can be used as a component for artificial hip joints (artificial acetabular cup), a component for artificial knee joints (artificial tibial insert) and the socket for artificial elbow joints, and in addition to the medical use, it can be applied as materials for various industries by utilizing the characteristics such as low friction and superior abrasion resistance.
Claims (34)
1. An ultra high molecular weight polyethylene molded block having a molecular weight not less than 5 million, having been crosslinked slightly and having been compression-deformed in a direction perpendicular to a compression plane, cooled and solidified in a compression-deformed state under pressure so as to have orientation of crystal planes in a direction parallel to the compression plane, and a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane.
2. The molded block of claim 1 , wherein a melting temperature of the ultra high molecular weight polyethylene is in a range of 135 to 155° C.
3. A method for producing an ultra high molecular weight polyethylene molded block having orientation of crystal planes in a direction parallel to a compression plane, comprising slightly crosslinking an ultra high molecular weight polyethylene molded block having a molecular weight not less than 5 million by irradiating the block with a high energy ray and thereby introducing a very small amount of crosslinking points into molecular chains of the block, then heating the crosslinked ultra high molecular weight polyethylene molded block up to a compression deformable temperature, compression-deforming the block by compressing the block in a direction perpendicular to the compression plane so as to deform the block, and then cooling the block while keeping the block in a deformed state under pressure, said block after cooling having a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane.
4. The method of claim 3 , where the high energy ray is a radioactive ray and a dose of the irradiation is in the range of 0.01 to 5.0 MR.
5. The method of claim 3 or 4 , wherein the compression-deformable temperature is in a range of 50° C. lower than a melting temperature of the crosslinked ultra high molecular weight polyethylene to 80° C. higher than the melting temperature.
6. The method of claim 3 , 4 or 5 wherein a weight-average molecular weight of the ultra high molecular weight polyethylene before irradiation is in a range of 2 to 8 million.
7. An ultra molecular weight polyethylene molded block having orientation of crystal planes in a direction parallel to a compression plane, said block produced by slightly crosslinking an ultra high molecular weight polyethylene block having a molecular weight of not less than 5 million by irradiating the block with a high energy ray and thereby introducing a very small amount of crosslinking points into molecular chains of the block, then heating the crosslinked block up to a compression deformable temperature, compression-deforming the block by compressing the block in a direction perpendicular to the compression plane so as to deform the block, and then cooling and solidifying the block while keeping the block in a deformed state under pressure, said block after cooling and solidifying having a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane.
8. Artificial joint for implantation in a joint of an animal, the joint comprising a joint component formed from an ultra high molecular weight polyethylene molded block having a molecular weight of not less than 5 million, having been crosslinked slightly and having been compression-deformed in a direction perpendicular to a compression plane, cooled and solidified in a compression-deformed state under pressure so as to have orientation of crystal planes in a direction parallel to the compression plane, said block having a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane.
9. Artificial joint according to claim 8 , the joint for implantation in a joint of a human being.
10. Artificial joint for implantation in a joint of an animal, the joint comprising a joint component formed from an ultra high molecular weight polyethylene molded block having a molecular weight of not less than 5 million, having been crosslinked slightly and having been compression-deformed in a direction perpendicular to a compression plane so as to have orientation of crystal planes in a direction parallel to the compression plane, wherein said block having a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane and the melting temperature of the molded block is in a range of 135 to 155° C.
11. Artificial joint according to claim 10 , the joint for implantation in a joint of a human being.
12. A method for producing an ultra high molecular weight polyethylene (UHMWPE) artificial hip component, UHMWPE artificial knee component, UHMWPE artificial elbow component, UHMWPE artificial finger component, or UHMWPE artificial shoulder component having improved abrasion resistance, comprising:
(a) crosslinking an ultra high molecular weight polyethylene block having a molecular weight not less than 5 million by irradiating the block with a high energy radiation at a level of at least 1 MR;
(b) heating said crosslinked block up to a compression deformable temperature below the melting point of the UHMWPE;
(c) subjecting said heated block to pressure; then
(d) cooling said block; and
(e) processing said cooled block to form said component.
13. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said irradiation is gamma irradiation at a level of from 1 MR to 5 MR.
14. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said heating is in a range of from 50° C. lower than the melting temperature of the crosslinked ultra high molecular weight polyethylene to the melting temperature.
15. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said pressure is applied so as to deform the block.
16. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 15, wherein said deformation is in a direction perpendicular to the plane of compression.
17. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 16, wherein said block is cooled in a compression-deformed state under pressure.
18. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 17, wherein said block has an orientation of crystal planes in a direction parallel to the compression plane.
19. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 16, wherein said block has a thickness, after compression, of at least 5 mm in a direction perpendicular to the compression plane.
20. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 16, wherein said block, prior to compression, has a thickness of at least 3 cm.
21. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 18, wherein said cooled block has a melting point of from 135° C. to 155° C.
22. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said irradiation is conducted in the presence of oxygen.
23. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said irradiation is conducted under a vacuum or in an inert atmosphere.
24. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, additionally comprising processing said block, after cooling, by a process comprising cutting said block to form said component.
25. A method of producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein after said subjecting to pressure step, said block is subjected to isothermal crystallization.
26. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein after said subjecting to pressure step, said block is subjected to isothermal treatment at a temperature of from around 100° C. to 130° C. for a period of from 1 hour to 20 hours.
27. A method of making an artificial joint component having improved abrasion resistance, the artificial joint component being obtained by fabrication from a crosslinked ultra high molecular weight polyethylene (UHMWPE) which is prepared by the method comprising:
a) providing raw UHMWPE in the form of a rod;
b) crosslinking the rod with gamma-irradiation at a dose of at least 1 MR;
c) heating the crosslinked rod to a compression deformable temperature below the melting point of the UHMWPE;
d) subjecting the heated rod to pressure; and
e) cooling and solidifying the rod.
28. A method according to claim 27, wherein the dose of gamma-irradiation is 1 MR to 5 MR.
29. A method according to claim 27, wherein the compression deformable temperature is greater than the melting point minus 50° C.
30. A method according to claim 28, wherein pressure is applied in step d) to deform the rod.
31. A method according to claim 30, wherein the deformed rod is cooled in a compression deformed state.
32. A method of producing a UHMWPE artificial joint component comprising making a crosslinked UHMWPE according to claim 27 and processing the rod after solidification to form the joint component.
33. A method according to claim 32, wherein the joint component is selected from hip, knee, elbow, finger, and shoulder.
34. A method according to claim 32, wherein the joint component is a hip component or a knee component.
Priority Applications (1)
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US13/531,232 USRE44762E1 (en) | 1994-09-21 | 1995-09-18 | Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same |
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JP25456494 | 1994-09-21 | ||
PCT/JP1995/001858 WO1996009330A1 (en) | 1994-09-21 | 1995-09-18 | Ultrahigh-molecular-weight polyethylene molding for artificial joint and process for producing the molding |
US08/640,738 US6168626B1 (en) | 1994-09-21 | 1995-09-18 | Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same |
US13/531,232 USRE44762E1 (en) | 1994-09-21 | 1995-09-18 | Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same |
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US08/640,738 Expired - Lifetime US6168626B1 (en) | 1994-09-21 | 1995-09-18 | Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same |
US13/531,232 Expired - Lifetime USRE44762E1 (en) | 1994-09-21 | 1995-09-18 | Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
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US08/640,738 Expired - Lifetime US6168626B1 (en) | 1994-09-21 | 1995-09-18 | Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same |
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US (2) | US6168626B1 (en) |
EP (1) | EP0729981B1 (en) |
JP (2) | JP3563075B2 (en) |
KR (1) | KR100293587B1 (en) |
CN (2) | CN1123583C (en) |
AU (1) | AU693260B2 (en) |
CA (2) | CA2654851C (en) |
DE (1) | DE69525924T2 (en) |
WO (1) | WO1996009330A1 (en) |
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AU3485595A (en) | 1996-04-09 |
CN1135762A (en) | 1996-11-13 |
CA2177042C (en) | 2009-05-12 |
AU693260B2 (en) | 1998-06-25 |
JP2004027237A (en) | 2004-01-29 |
JP3563075B2 (en) | 2004-09-08 |
KR100293587B1 (en) | 2001-09-17 |
CA2654851C (en) | 2011-01-18 |
CN1123583C (en) | 2003-10-08 |
CN1478812A (en) | 2004-03-03 |
EP0729981A4 (en) | 1999-03-03 |
WO1996009330A1 (en) | 1996-03-28 |
DE69525924D1 (en) | 2002-04-25 |
CA2177042A1 (en) | 1996-03-28 |
EP0729981B1 (en) | 2002-03-20 |
EP0729981A1 (en) | 1996-09-04 |
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