WO2007068216A1 - Method of modification of ultrahigh-molecular-weight polyethylene for manufacture of joint replacements with increased lifetime - Google Patents

Method of modification of ultrahigh-molecular-weight polyethylene for manufacture of joint replacements with increased lifetime Download PDF

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Publication number
WO2007068216A1
WO2007068216A1 PCT/CZ2006/000089 CZ2006000089W WO2007068216A1 WO 2007068216 A1 WO2007068216 A1 WO 2007068216A1 CZ 2006000089 W CZ2006000089 W CZ 2006000089W WO 2007068216 A1 WO2007068216 A1 WO 2007068216A1
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WO
WIPO (PCT)
Prior art keywords
kgy
ultrahigh
molecular
weight polyethylene
modification
Prior art date
Application number
PCT/CZ2006/000089
Other languages
French (fr)
Inventor
Zdenek Horak
Miroslav Slouf
Zdenek Krulis
Jaroslav Fencl
Original Assignee
Ustav Makromolekularni Chemie Akademie Vedceske Republiky
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.)
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Application filed by Ustav Makromolekularni Chemie Akademie Vedceske Republiky filed Critical Ustav Makromolekularni Chemie Akademie Vedceske Republiky
Publication of WO2007068216A1 publication Critical patent/WO2007068216A1/en

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Classifications

    • 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
    • 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
    • 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
    • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
    • C08J7/12—Chemical modification
    • C08J7/123—Treatment by wave energy or particle radiation
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2312/00—Crosslinking
    • C08L2312/06—Crosslinking by radiation

Definitions

  • the invention concerns the method of modification of ultrahigh-molecular-weight polyethylene for bearing parts of total joint replacements.
  • Ultrahigh-molecular-weight polyethylene (UHMWPE) is used as a material for bearing parts of joint replacements such as the hip joint socket or the patellar part of knee.
  • UHMWPE Ultrahigh-molecular-weight polyethylene
  • 2-6)- 10 6 the polymer exhibits high density of entaglements.
  • the crystallizability of UHMWPE macromolecules is substantially limited compared with standard manufactured types of polyethylene of molecular weight ca 10 5 .
  • the characteristic structure of UHMWPE, where crystalline lamellae are dispersed in amorphous matrix, imparts to the material an appropriate combination of mechanical properties required for long-term articulation of components of the artificial joint. It is first of all low friction, high toughness and fatigue resistance. This is
  • the artificial joint socket is at the same time the weakest point of the total joint replacement.
  • UHMWPE wear occurs.
  • the UHMWPE particles formed can initiate an inflammatory process leading to osteolysis and, ultimately, to total replacement failure.
  • the wear resistance of the joint socket material determines the lifetime of the whole joint replacement.
  • procedures of modification of supermolecular UHMWPE structure have been developed that lead to wear resistance enhancement.
  • the polymer can be crosslinked by the action of high-energy radiation, such as ⁇ -rays or accelerated electrons. The formation of three-dimensional network leads to suppression of wear (US patents 5,879,400; US 6,017,975; US 6,143,232).
  • the modification usually involves also subsequent thermal treatment in vacuum or inert atmosphere in the course of which rearrangement of supermolecular structure and recombination of free radicals occur (US patents 6,184,265; US 6,316,158; US 6,562,540; US 6,566,451). Elimination of radicals is necessary to inhibit long- term UHMWPE degradation because the radical lifetime is up to several years.
  • the modification of UHMWPE according to the invention is performed by irradiation of the polymer in inert atmosphere with ⁇ -rays at a dose rate of 0.25 kGy/h - 10 kGy/h for 4-220 h or with accelerated electrons at dose rates 1200 kGy/h -12000 kGy/h for 12 s - 10 min.
  • a combination of dose rate and exposition time is always established so that the total radiation dose makes 40 kGy — 200 kGy.
  • the exposition time is inversely proportional to the dose rate.
  • a short exposition of the material proves to be sufficient for the formation of a crosslinked structure, limiting, at the same time, undesirable parallel radical reactions leading to scission of the already formed networks.
  • UHMWPE ultrahigh-molecular- weight polyethylene of molecular weight 2-6-10 6 ⁇ -radiation - electromagnetic radiation of wavelength 10 "10 - 10 "12 m.
  • Example 7
  • the method of modification of UHMWPE according to the invention can be utilized in the manufacture of bearing parts of total joint replacements.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Organic Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Epidemiology (AREA)
  • Transplantation (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oral & Maxillofacial Surgery (AREA)
  • Dermatology (AREA)
  • Processes Of Treating Macromolecular Substances (AREA)
  • Treatments Of Macromolecular Shaped Articles (AREA)
  • Materials For Medical Uses (AREA)

Abstract

The solution concerns the method of modification of ultrahigh-molecular-weight polyethylene increasing the lifetime of joint replacements characterized in that the polymer is irradiated in inert atmosphere with Ϝ-rays at dose rates 0.25 kGy/h - 10 kGy/h for 4-220 h or with accelerated electrons at dose rates at least 1200 kGy/h - 12000 kGy/h for at least 12 s and 10 min at the maximum, the total irradiation dose ranging from 40 IcGy to maximum 200 kGy and the thus irradiated ultrahigh-molecular-weight polyethylene is subsequently heated at 90- 200 0C for 5 min - 10 h in inert atmosphere and then continually cooled at a maximum rate of 20 °C/min.

Description

Method of modification of ultrahigh-molecular-weight polyethylene for manufacture of joint replacements with increased lifetime
Technical field
5
The invention concerns the method of modification of ultrahigh-molecular-weight polyethylene for bearing parts of total joint replacements.
Background art
Ultrahigh-molecular-weight polyethylene (UHMWPE) is used as a material for bearing parts of joint replacements such as the hip joint socket or the patellar part of knee. As a consequence of extremely long polymer chains of molecular weight (2-6)- 106, the polymer exhibits high density of entaglements. The crystallizability of UHMWPE macromolecules is substantially limited compared with standard manufactured types of polyethylene of molecular weight ca 105. The characteristic structure of UHMWPE, where crystalline lamellae are dispersed in amorphous matrix, imparts to the material an appropriate combination of mechanical properties required for long-term articulation of components of the artificial joint. It is first of all low friction, high toughness and fatigue resistance. This is
) why the material was used for construction of joint replacements (US patents 3,297,641; 3,758,273; 4,655,769).
Despite these properties, the artificial joint socket is at the same time the weakest point of the total joint replacement. In long-term articulation of the socket and ceramic or metallic head, UHMWPE wear occurs. The UHMWPE particles formed can initiate an inflammatory process leading to osteolysis and, ultimately, to total replacement failure. Hence the wear resistance of the joint socket material determines the lifetime of the whole joint replacement. This is why procedures of modification of supermolecular UHMWPE structure have been developed that lead to wear resistance enhancement. It turned out that the polymer can be crosslinked by the action of high-energy radiation, such as γ-rays or accelerated electrons. The formation of three-dimensional network leads to suppression of wear (US patents 5,879,400; US 6,017,975; US 6,143,232). The modification usually involves also subsequent thermal treatment in vacuum or inert atmosphere in the course of which rearrangement of supermolecular structure and recombination of free radicals occur (US patents 6,184,265; US 6,316,158; US 6,562,540; US 6,566,451). Elimination of radicals is necessary to inhibit long- term UHMWPE degradation because the radical lifetime is up to several years.
A common feature of the given procedures is specification of the radiation amount applied in irradiation without regard to exposition time. Surprisingly, in a study of structural changes of UHMWPE during its modification by the action of ionizing radiation, it was found out that the selected mechanical properties (in particular wear resistance) depend not only on radiation dose and thermal treatment conditions, but also show a pronounced dependence on the dose rate of ionizing radiation.
It was verified experimentally that the UHMWPE irradiated with the same radiation dose, but with a different dose rate (different exposition time) exhibits great differences in its supermolecular structure, first and foremost in crosslink density. A short exposition to a high dose rate led to higher wear resistance. The required wear resistance keeping other utility properties of UHMWPE has been attained by an appropriate combination of the ionizing radiation dose with a defined dose rate and subsequent thermal exposition under specific conditions. The hitherto known procedures of UHMWPE modification do not take into consideration the principal effect of the radiation dose rate on its supermolecular structure. .
) Disclosure of the invention
The solution described below is based on the experimental finding that UHMWPE irradiated with the same radiation dose, but a different dose rate (different exposition time) shows great differences in supermolecular structure, first of all in crosslink density. A short exposition to a high dose rate led to higher wear resistance. The required wear resistance maintaining other utility properties of UHMWPE could be achieved by an appropriate combination of radiation dose of ionizing radiation with a specific dose rate and subsequent thermal exposition under specific conditions.
The modification of UHMWPE according to the invention is performed by irradiation of the polymer in inert atmosphere with γ-rays at a dose rate of 0.25 kGy/h - 10 kGy/h for 4-220 h or with accelerated electrons at dose rates 1200 kGy/h -12000 kGy/h for 12 s - 10 min. A combination of dose rate and exposition time is always established so that the total radiation dose makes 40 kGy — 200 kGy. The exposition time is inversely proportional to the dose rate. A short exposition of the material proves to be sufficient for the formation of a crosslinked structure, limiting, at the same time, undesirable parallel radical reactions leading to scission of the already formed networks. In the course of heating after irradiation, it is of advantage to shape UHMWPE by pressing to the required shape of final product; in this case it is necessary to heat the material at 135-200 0C.
To retain the achieved desirable properties of UHMWPE modified by the method according to the invention, in particular its high wear resistance, it is not appropriate to sterilize the final product by irradiation but, instead, by other accessible methods, preferably by the action of ethylene oxide or plasma.
The advantages of UHMWPE modification by the procedure according to the invention are elucidated in the following examples.
Used abbreviations and symbols
UHMWPE - ultrahigh-molecular- weight polyethylene of molecular weight 2-6-106 γ-radiation - electromagnetic radiation of wavelength 10"10 - 10"12 m.
Electron rays - electrons accelerated in a potential gradient to energies 105 - 106 eV
) Examples of the invention
Example 1
The modification procedure was applied to UHMWPE of average molecular weight 2-106 processed to an intermediate of plate shape, 5 mm thick. The material was irradiated with γ- rays in a chamber with the central 60Co source in nitrogen atmosphere, with a 50 kGy dose at the dose rate 0.25 kGy/h. After exposition, the irradiated material was immediately put into a press mold preheated to a temperature of 100 0C, then in the mold into a hydraulic press, heated to 150 0C and kept at the temperature for 10 min. Then the mold was cooled to laboratory temperature at a rate of 15 °C/min. After withdrawing the pressed piece from the mold, decisive characteristics of the material were determined. The conditions and results of the determinations are collected in Tables 1 and 2. Example 2
The modification procedure of Example 1 was applied to UHMWPE of average molecular weight MN = 2-106, the material being irradiated with a dose of 50 kGy at the dose rate 2.5 lcGy/h. The conditions and results of the determinations are collected in Tables 1 and 2.
5
Example 3
The modification procedure of Example 2 was applied to UHMWPE of average molecular weight Mv, = 2-106, the material being moreover sterilized with ethylene oxide. After withdrawing the pressed piece from the mold, decisive characteristics of the material were determined. The conditions and results of the determinations are collected in Tables 1 and 2.
Example 4
The modification procedure was applied to UHMWPE of average molecular weight Mw =
2-106 processed to an intermediate of plate shape, 50 mm thick. Immediately after exposition, the material was irradiated with accelerated electrons at 150 0C in air with a dose of 50 kGy at the dose rate 12000 kGy/h. The irradiated material was put into a press mold preheated to a temperature of 150 0C, then in the mold into a hydraulic press, and kept at the temperature for 10 min. The mold was cooled to laboratory temperature at a rate of 15 °C/min. After withdrawing the pressed piece from the mold, decisive characteristics of the material were
) determined. The conditions and results of the determinations are collected in Tables 1 and 2.
Example 5
The modification procedure of Example 4 was applied to UHMWPE of average molecular weight Mw = 2 T O6 , the material being irradiated in a closed chamber filled with nitrogen. The conditions and results of the determinations are collected in Tables 1 and 2.
Example 6
The modification procedure of Example 4 was applied to UHMWPE of average molecular weight My, = 2-106 , the material being irradiated at 150 0C in a closed chamber filled with nitrogen, but not further thermally treated. The conditions and results of the determinations are collected in Tables 1 and 2. Example 7
The modification procedure was applied to UHMWPE of average molecular weight Mw =
2-106 processed to an intermediate of plate shape, 50 mm thick. The material was irradiated with accelerated electrons, at 150 0C in a closed chamber filled with nitrogen, with a dose of 50 kGy at the dose rate 1200 kGy/h. Immediately after exposition, the irradiated material was put into a press mold preheated to a temperature of 150 0C, then in the mold into a hydraulic press, and kept at the temperature for 10 min. The mold was cooled to laboratory temperature at a rate of 15 °C/min. After withdrawing the pressed piece from the mold, decisive structural and mechanical characteristics of the material were determined. The conditions and results of the determinations are collected in Tables 1 and 2.
Industrial applicability
The method of modification of UHMWPE according to the invention can be utilized in the manufacture of bearing parts of total joint replacements.

Claims

C L A I M S
1. The method of modification of ultrahigh-molecular- weight polyethylene for manufacture of joint replacements with enhanced lifetime characterized in that the polymer is irradiated in inert atmosphere with γ-rays at the dose rates 0.25 kGy/h - 10 kGy/h for 4-220 h or with accelerated electrons at dose rates at least 1200 kGy/h - 12000 kGy/h for 12 s - 10 min, the total irradiation dose amounting to 40 IcGy - 200 kGy, and the thus irradiated ultrahigh-molecular-weight polyethylene is subsequently heated at 90-200 0C for 5 min — 10 h in inert atmosphere and then is continually cooled at a maximum rate of 20 °C/min.
2. The method of modification of ultrahigh-molecular-weight polyethylene enhancing the lifetime of joint replacements according to Claim 1, characterized in that the irradiated ultrahigh-molecular-weight polyethylene is heated at 135-200 0C and simultaneously press-molded.
PCT/CZ2006/000089 2005-12-13 2006-12-13 Method of modification of ultrahigh-molecular-weight polyethylene for manufacture of joint replacements with increased lifetime WO2007068216A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CZPV2005-768 2005-12-13
CZ20050768A CZ297700B6 (en) 2005-12-13 2005-12-13 Modification method of ultra high-molecular polyethylene for manufacture of joint prostheses with increased service life

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WO2007068216A1 true WO2007068216A1 (en) 2007-06-21

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997029793A1 (en) * 1996-02-13 1997-08-21 Massachusetts Institute Of Technology Radiation and melt treated ultra high molecular weight polyethylene prosthetic devices
WO1998014223A1 (en) * 1996-10-02 1998-04-09 E.I. Du Pont De Nemours And Company Process for medical implant of cross-linked ultrahigh molecular weight polyethylene having improved balance of wear properties and oxidation resistance
US5879400A (en) * 1996-02-13 1999-03-09 Massachusetts Institute Of Technology Melt-irradiated ultra high molecular weight polyethylene prosthetic devices
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
WO2002048259A2 (en) * 2000-12-12 2002-06-20 Massachusetts General Hospital Selective, controlled manipulation of polymers

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6143232A (en) * 1999-07-29 2000-11-07 Bristol-Meyers Squibb Company Method of manufacturing an articulating bearing surface for an orthopaedic implant

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997029793A1 (en) * 1996-02-13 1997-08-21 Massachusetts Institute Of Technology Radiation and melt treated ultra high molecular weight polyethylene prosthetic devices
US5879400A (en) * 1996-02-13 1999-03-09 Massachusetts Institute Of Technology Melt-irradiated ultra high molecular weight polyethylene prosthetic devices
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
WO1998014223A1 (en) * 1996-10-02 1998-04-09 E.I. Du Pont De Nemours And Company Process for medical implant of cross-linked ultrahigh molecular weight polyethylene having improved balance of wear properties and oxidation resistance
WO2002048259A2 (en) * 2000-12-12 2002-06-20 Massachusetts General Hospital Selective, controlled manipulation of polymers

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CZ2005768A3 (en) 2007-03-07
CZ297700B6 (en) 2007-03-07

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