OXIDATION RESISTANT HIGHLY-CROSSLINKED UHMWPE

• US 20110116968A1
• Filed: 05/13/2008
• Published: 05/19/2011
• Est. Priority Date: 05/13/2008
• Status: Active Grant

• Current Assignee: Smith & Nephew Orthopaedics Ag (Smith & Nephew PLC)
• Original Assignee: Smith & Nephew Orthopaedics Ag (Smith & Nephew PLC)
• Inventors: Dirix, Yvo, Schmotzer, Hans, Brunner, Lorenz
• Granted Patent: US 8,586,667 B2
• Time in Patent Office: Days
• US Class Current: 422/22
• CPC Class Codes: C08J 5/10 characterised by the additives used in the polymer mixture
• CPC Class Codes: C08K 5/005 Stabilisers against oxidation, heat, light, ozone
• CPC Class Codes: C08L 23/06 Polyethene
• CPC Class Codes: C08L 2666/02 Organic macromolecular compounds, natural resins, waxes or and bituminous materials

Abstract

The present invention relates to highly cross-linked UHMWPE, which is possessed of an improved oxidation resistance, as well as a method for making the same. The UHMWPE material of the current invention is combined with an anti-oxidant compound or a free-radical scavenger prior to formation. Once the UHMWPE with the added material has been formed and treated with gamma or electron bean irradiation, it shows an improved wear resistance and also a good resistance to oxidation. Such a material, is particularly interesting for the field of making replacement joint implants.

Claims

1. A method for fabricating an oxidation resistant UHMWPE material comprising:

mixing a quantity of an additive material, comprising at least an antioxidant or a radical scavenger with a UHMWPE powder;

moulding the mixture of UHMWPE powder and additive material to create a preform by applying a temperature above the melting point of the UHMWPE powder irradiating the preform in air under ambient atmospheric conditions with radiation comprising at least gamma or electron beam radiation at a dose of between about 2 and about 20 Mrad; and

wherein the irradiated preform with the additive material has an oxidation index after artificial ageing that is the same or lower than that of gamma-sterilized standard UHMWPE material without the additive material.

2. The method according to claim 1, wherein the irradiated preform with the additive material has a free radical content which is greater than the gamma-sterilized standard UHMWPE material without the additive material.

3. The method according to claim 1, wherein the irradiation step of the preform increases the crosslinking in the preform such that the irradiated material has a molecular weight between crosslinks that is lower than that of the gamma-sterilized standard UHMWPE material without the additive material.

4. The method according to claim 3, wherein the molecular weight between crosslinks of the irradiated preform is about 10% to about 60% lower than that of the gamma-sterilized standard UHMWPE material without the additive material.

6. The method according to claim 1, wherein the temperature applied to the mixture of additive and UHMWPE powder is above the melting point of the UHMWPE and below the degradation temperature of the additive material.

7. The method according to claim 1, wherein the additive material comprises at least one of:

the carotenoids, such as β

-carotene and lycopene, the flavonoids such as naringenin, hesperitin, luteolin, the amino acid based compounds such as cystein, glutathione, tyrosine, tryptophan or the materials curcumin, propyl gallate, octyl gallate, dodecyl gallate, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), melatonin, eugenol, coenzyme QlO, and Vitamin E.

9. The method according to claim 1, wherein the amount of additive material mixed with the UHMWPE powder is in the range of about 0.001 to about 0.5 wt %.

10. The method according to claim 1, wherein the amount of additive material mixed with the UHMWPE powder is in the range of about 0.02% to about 0.2 wt %.

11. The method according to claim 1 wherein the radiation is at a dose of about 4 to about 15 Mrad.

12. The method according to claim 1, wherein the maximum oxidation index of the irradiated preform after artificial ageing is below that of the gamma-sterilized standard UHMWPE material without the additive material.

13. The method according to claim 1, wherein the maximum oxidation index of the irradiated preform after artificial ageing is between about 5% and about 75% of the gamma-sterilized standard UHMWPE material without the additive material.

14. The method according to claim 1, wherein the maximum oxidation index of the irradiated preform after artificial ageing is between about 10% and about 50% of the gamma-sterilized standard UHMWPE material without the additive material.

15. The method according to claim 1, wherein the maximum oxidation index of the irradiated preform after artificial ageing is between about 15% and about 30% of the gamma-sterilized standard UHMWPE material without the additive material.

16. The method according to claim 1, wherein the free radical content is measured by ESR, and the free radical content of the irradiated preform is higher than that of the gamma-sterilized standard UHMWPE material without the additive material.

17. The method according to claim 1, wherein the free radical content is measured by ESR, and the free radical content of the irradiated preform is about 110% and about 700% that of the gamma-sterilized standard UHMWPE material without the additive material.

18. The method according to claim 1, wherein the free radical content is measured by ESR, and the free radical content of the irradiated preform is about 120% and about 600% that of the gamma-sterilized standard UHMWPE perform without the additive material.

19. The method according to claim 1, wherein the free radical content is measured by ESR, and the free radical content of the irradiated preform is about 130% and about 500% that of the gamma-sterilized standard UHMWPE material without the additive material.

20. The method according to claim 1, further comprising

shaping the irradiated perform into a shaped implant

packaging the shaped implant

sterilizing the shaped implant, wherein the sterilizing comprises at least one of gamma irradiating the implant at between about 2 and about 4 Mrad, and sterilizing the implant by exposing it to ethylene oxide or a gas plasma in a manner sufficient to sterilize the shaped, packaged implant.

5. (canceled)

8. (canceled)

21-48. -48. (canceled)