Bearing material of medical implant having reduced wear rate and method for reducing wear rate

Abstract

Disclosed is a bearing material of a medical implant comprising a polymer such as UHMWPE and a surface active agent that is not covalently bonded to the polymer. The surface active agent includes a hydrophilic moiety or segment, such as an ethoxylated moiety, and a hydrophobic moiety or segment, such as an alkanol, alkenol, aromatic alcohol, alkylamine, alkenyl amine, alkyl aromatic alcohol, alkanoic acid, alkenoic acid, or any combination thereof. The bearing material has a reduced wear rate. Also disclosed is a method of reducing the wear rate of a polymeric bearing material of a medical implant when it articulates against a hard counterface in the presence of synovial fluid, the method comprising providing a surface active agent in the synovial fluid in close proximity to the bearing surface, the hard counterface, or both.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 depicts the known wear rate of UHMWPE bearing material against various counterfaces as a function of the concentration of proteins in the serum.

FIG. 2A depicts the weight change of UHMWPE pin as it rubs against cast CoCrMo counterfaces in water and in bovine calf serum plus 1% by weight surface active agent in accordance with an embodiment of the invention. FIG. 2B depicts the weight change of the UHMWPE pins in bovine calf serum only.

FIG. 3 depicts the coefficient of friction between UHMWPE pins and CoCrMo counterfaces as a function of the number of cycles in serum (diamonds), 1% by weight surface active agent (triangles), and serum plus 1% by weight surface active agent (x), in accordance with an embodiment of the invention.

Claims

1. A bearing material of a medical implant comprising a polymer and a surface active agent that is not covalently bonded to the polymer, wherein the bearing material is adopted for articulating against a hard counterface of the medical implant.

2. The bearing material of claim 1, wherein the polymer comprises polyethylene.

3. The bearing material of claim 2, wherein the polyethylene is ultrahigh molecular weight polyethylene (UHMWPE).

4. The bearing material of claim 1, wherein the surface active agent is an anionic, cationic, nonionic, or amphoteric surface active agent.

5. The bearing material of claim 4, wherein the surface active agent is a nonionic surface active agent.

6. The bearing material of claim 5, wherein the nonionic surface active agent comprises an alkoxylated hydrophilic moiety and a hydrophobic moiety.

7. The bearing material of claim 6, wherein the alkoxylated hydrophilic moiety is an ethoxylated moiety.

8. The bearing material of claim 6, wherein the hydrophobic moiety is selected from the group consisting of alkanol, alkenol, aromatic alcohol, alkylamine, alkenyl amine, alkyl aromatic alcohol, alkanoic acid, alkenoic acid, and any combination thereof.

9. The bearing material of claim 7, wherein the nonionic surface active agent is an alkoxylated fatty alcohol.

10. The bearing material of claim 9, wherein the hydrophobic moiety of the alkoxylated fatty alcohol includes a C8-C100 alkyl or alkenyl chain.

11. The bearing material of claim 10, wherein the hydrophobic moiety of the alkoxylated fatty alcohol includes a C10-C50 alkyl or alkenyl chain.

12. The bearing material of claim 11, wherein the hydrophobic moiety of the alkoxylated fatty alcohol includes a C15-C30 alkyl or alkenyl chain.

13. The bearing material of claim 9, wherein the hydrophilic moiety of the alkoxylated fatty alcohol includes from about 3 to about 110 ethylene oxide units.

14. The bearing material of claim 13, wherein the hydrophilic moiety of the alkoxylated fatty alcohol includes from about 10 to about 80 ethylene oxide units.

15. The bearing material of claim 14, wherein the hydrophilic moiety of the alkoxylated fatty alcohol includes from about 20 to about 50 ethylene oxide units.

16. The bearing material of claim 10, wherein the hydrophilic moiety of the alkoxylated fatty alcohol includes from about 3 to about 110 ethylene oxide units.

17. A method of reducing the wear rate of a polymeric bearing material of a medical implant, said bearing material having a bearing surface, said bearing surface articulating against a hard counterface of the medical implant in the presence of synovial fluid, the method comprising providing a surface active agent in the synovial fluid in close proximity to the bearing surface, the hard counterface, or both.

18. The method of claim 17, wherein the bearing material includes a surface active agent that migrates to the interface between the synovial fluid and the bearing surface.

19. The method of claim 17, wherein the hard counterface includes a surface active agent and releases said surface active agent into the synovial fluid in close proximity to the hard counterface.

20. The method of claim 17, wherein the surface active agent is provided by injecting the surface active agent into the synovial fluid.

21. The method of claim 17, wherein the surface active agent is provided such that it elutes from a non-articulating portion of the medical implant.

22. The method of claim 17, which includes reducing the coefficient of friction between the bearing surface and the opposing surface.

23. The bearing material of claim 5, wherein the nonionic surface active agent comprises a block copolymer of hydrophilic and hydrophobic blocks.

24. The bearing material of claim 23, wherein the block copolymer is an A-B, A-B-A, or B-A-B block copolymer, wherein A is a hydrophilic block and B is a hydrophobic block.

25. The bearing material of claim 24, wherein A is polyethylene oxide (PEO) and B is polypropylene oxide (PPO).