Non-oxidizing polymeric medical implant

• US 6,372,814 B1
• Filed: 06/28/2000
• Issued: 04/16/2002
• Est. Priority Date: 06/01/1993
• Status: Expired due to Fees

• Current Assignee: Howmedica Osteonics Corp. (Stryker Corporation)
• Original Assignee: Stryker Technologies Corporation
• Inventors: Stark, Casper F., Sun, Deh-Chuan
• Primary Examiner(s): Berman, Susan W.
• Application Number:
  US09/604,868
• Time in Patent Office: 657 Days
• Field of Search: 522/161, 522/157, 522/111, 522/112, 523/105, 523/113, 525/937
• US Class Current: 522/161
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: A61L 2/08 Radiation
• CPC Class Codes: A61L 2/081 Gamma radiation
• CPC Class Codes: A61L 2/082 X-rays
• CPC Class Codes: A61L 2/087 Particle radiation, e.g. electron-beam, alpha or beta radiation
• CPC Class Codes: A61L 27/16 obtained by reactions only involving carbon-to-carbon unsaturated bonds
• CPC Class Codes: A61L 29/041 obtained by reactions only involving carbon-to-carbon unsaturated bonds
• CPC Class Codes: A61L 31/048 obtained by reactions only involving carbon-to-carbon unsaturated bonds A61L31/041 takes precedence
• CPC Class Codes: B29C 2035/085 using gamma-ray
• CPC Class Codes: B29C 35/0805 using electromagnetic radiation
• CPC Class Codes: B29C 43/00 Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor by liberation of internal stresses B29C61/006
• CPC Class Codes: B29C 43/16 Forging
• CPC Class Codes: B29K 2023/0683 UHMWPE, i.e. ultra high molecular weight polyethylene
• CPC Class Codes: B29K 2105/253 Preform
• CPC Class Codes: B29K 2995/0087 Wear resistance
• CPC Class Codes: B29K 2995/0089 Impact strength or toughness
• CPC Class Codes: B29L 2031/7532 Artificial members, protheses
• CPC Class Codes: C08L 23/04 Homopolymers or copolymers of ethene
• CPC Class Codes: C08L 23/06 Polyethene
• CPC Class Codes: Y10S 522/915 involving inert gas, steam, nitrogen gas, or carbon dioxide
• CPC Class Codes: Y10S 525/937 : Utility as body contact e.g. implant, contact lens or I.U.D.
• CPC Class Codes: Y10S 623/901 : Method of manufacturing prosthetic device

Abstract

A medical implant made of polymeric material having an increased oxidation resistance is formed by a method including the steps of placing a resin powder in a sealed container. A substantial portion of the oxygen is removed from the sealed container by either a vacuum, an oxygen absorbent or by flushing with inert gas. The container is then repressurized with a gas such as nitrogen, argon, helium or neon so that long term storage may be possible. On use, the resin is transferred to a forming device which both melts and forms the resin in an oxygen reduced atmosphere to produce a polymeric raw material such as a rod or bar stock. The medical implant is then formed from this raw material annealed and sealed in an airtight package in an oxygen reduced atmosphere. The implant is then radiation sterilized and thereafter annealed in the package for a predetermined time and temperature sufficient to form cross-links between any free radicals in neighboring polymeric chains.

Claims

1. A formed ultra-high molecular weight polyethylene device having a weight average molecular weight greater than 400,000, said material irradiated to create free radicals while sealed by a layer of material whose function is to prevent said material from contact with oxygen in a concentration greater than 1% volume by volume and then heated at a temperature of greater than 25°

C. to create cross-links between free radicals while sealed within said layer for a sufficient time to create a level of cross-linking, wherein the temperature and time are selected to be at least equivalent to heating said irradiated material at 50°

C. for 144 hours as defined by the Arrhennius'"'"' equation (14).

2. The device as set forth in claim 1 wherein the polyethylene material has a solubility of less than 74.7% in solvent.

3. The device as set forth in claim 1 wherein the polyethylene material has an oxidation index of 0.01 or less after oven aging in air at 80°

C.

4. The device as set forth in claim 1 wherein the polyethylene material is heated to a temperature between 25°

C. and the melting point of said polymer.

5. The device as set forth in claim 1 wherein said heating takes place for at least about 4 hours.

6. The device as set forth in claim 1 wherein the layer of material whose function is to prevent said polyethylene material from contact with oxygen is heated while surrounded by an oxygen containing atmosphere.

7. A device comprising an ultra-high molecular weight polyethylene material having a weight average molecular weight greater than 400,000, said material irradiated to create free radicals while out of contact with oxygen in a concentration greater than 1% volume by volume and then heated while out of contact with oxygen in a concentration greater than 1% volume by volume at a temperature of greater than 25°

C. for a sufficient time to create a level of cross-links between free radicals wherein the temperature and time are selected to be at least equivalent to heating said irradiated material at 50°

C. for 144 hours as defined by the Arrhennius'"'"' equation (14).

8. The device as set forth in claim 7 wherein the polyethylene material has a solubility of less than 74.7% in solvent.

9. The device as set forth in claim 7 wherein the polyethylene material has an oxidation index of 0.01 or less after oven aging in air at 80°

C.

10. The device as set forth in claim 7 wherein the polyethylene material is heated to a temperature between 25°

C. and the melting point of said polymer.

11. The device as set forth in claim 7 wherein said heating takes place for at least about 4 hours.

12. The device as set forth in claim 7 where a layer of material is provided to prevent said polyethylene material from coming into contact with oxygen.

13. A device comprising an ultra-high molecular weight polyethylene having a weight average molecular weight greater than 400,000, said polyethylene irradiated to create free radicals while sealed by a layer of material whose function is to prevent said polyethylene from contact with oxygen in a concentration greater than 1% volume by volume and then heated at a temperature of greater than 25°

C. for sufficient time to create cross-links between free radicals while sealed within said layer, wherein said temperature and time are selected to be at least equivalent to heating said irradiated material at 50°

C. for 144 hours as defined by Arrhennius'"'"' equation (14).

14. The device as set forth in claim 13 wherein the polyethylene has a solubility of less than 74.7% in solvent.

15. The device as set forth in claim 13 wherein the polyethylene has an oxidation index of 0.01 or less after oven aging in air at 80°

C.

16. The device as set forth in claim 13 wherein the polyethylene is heated to a temperature between 25°

C. and the melting point thereof.

17. The device as set forth in claim 13 wherein said heating takes place for at least about 4 hours.

18. The device as set forth in claim 13 wherein the layer of material whose function is to prevent said polyethylene material from contact with oxygen is heated while surrounded by an oxygen containing atmosphere.

19. A method for treating ultrahigh molecular weight polyethylene material having a weight average molecular weight greater than 400,000 comprising:

irradiating said material while out of contact with oxygen in a concentration greater than 1% volume by volume to create free radicals; and

annealing said material while out of contact with oxygen in a concentration greater than 1% volume by volume at a temperature greater than 25°

C. for a sufficient time to create cross-links between free radicals, wherein the temperature and time are selected to be at least equivalent to heating said material at 50°

C. for 144 hours as defined by Arrhennius'"'"' equation (14).

20. The method as set forth in claim 19 further including the step of providing an oxygen impermeable barrier around said material prior to irradiating.

21. The method as set forth in claim 20 wherein said material is a finished manufactured article.

22. The method as set forth in claim 19 wherein said time is at least about 4 hours.