Antioxidant doping of crosslinked polymers to form non-eluting bearing components
View Patent ↗Methods provide a non-eluting antioxidant doped UHMWPE in the form of an implant bearing component. The process includes the steps of: (a) providing a preform; (b) irradiating the preform with γ-irradiation to crosslink the UHMWPE; (c) doping the crosslinked preform by exposing it to an antioxidant composition at a temperature below the melting point of the UHMWPE; (d) removing the doped material from contact with the antioxidant composition; and then (e) annealing by heating the doped material at a temperature above 30° C. and below the melting point of the UHMWPE; followed by (f) making an implant bearing component from the doped material, wherein at least 1 mm but no more than about 15 mm of material are removed to make the component.
1. A method of incorporating a non-eluting amount of α-tocopherol into UHMWPE to make an implant component having a bearing surface, the method comprising:
(a) machining a consolidated UHMWPE or molding nascent UHMWPE powder to make a preform;
(b) irradiating the preform with high energy radiation to a dose of 5 to 20 MRad;
(c) doping the irradiated preform by exposing it to an antioxidant composition comprising α-tocopherol at a temperature greater than 30° C. and below the crystalline melting point of the UHMWPE;
(d) removing the doped preform from exposure to the antioxidant composition; and then
(e) homogenizing the doped preform by heating at a temperature above 30° C. and below the melting point of the UHMWPE; followed by
(f) making the implant component from the doped preform by machining greater than or equal to 1 mm of material but less than or equal to 15 mm from the doped preform to make the implant component, and
(g) packaging and sterilizing the implant component, wherein the vitamin E index throughout the implant is 0.01 or greater, and 0.2 or less.
2. A method according to claim 1 , wherein the high energy radiation is gamma radiation.
3. A method according to claim 1 , wherein the dose of gamma-irradiation is 6.5 MRad or greater.
4. A method according to claim 1 , wherein the doping is carried out at a temperature of 100° C to 130° C.
5. A method according to claim 1 , wherein the homogenizing step is carried out at a temperature of 100° C to 130° C.
6. A method according to claim 1 , wherein the antioxidant comprises greater than or equal to 50% by weight of α-tocopherol.
7. A method according to claim 1 , wherein the antioxidant composition is 100% by weight α-tocopherol.
8. A method according to claim 1 , wherein the implant component is characterized by a vitamin E index at the bearing surface of the component that is less than the saturation limit of vitamin E in the component at body temperature.
9. A method of making a non-eluting oxidation-resistant medical implant component comprising UHMWPE and vitamin E, wherein the vitamin E index throughout the implant is 0.01 or greater, and 0.2 or less, the method comprising:
(a) machining a consolidated UHMWPE article or molding a UHMWPE powder to make a preform;
(b) irradiating the preform with γ-irradiation at a dose of about 1 MRad to about 20 MRad;
(c) doping the irradiated preform by submerging it in vitamin E at a temperature of 100° C to 130° C for at least one hour;
(d) removing the preform from the vitamin E and heating for at least an additional hour at 100° C to 130° C; and then
(e) machining the preform to form the implant component; followed by
(f) sterilizing the implant component by exposing it to γ-irradiation at a dose of 1-4 MRad.
10. A method according to claim 9 , wherein the implant component is characterized by a vitamin E index at the surface of the component that is less than the saturation limit of vitamin E in the component at body temperature.
11. A method according to claim 9 , wherein the vitamin E index throughout and on the surface is less than or equal to 0.15.
12. A method according to claim 9 , wherein the vitamin E index throughout and on the surface is less than or equal to 0.10.
13. A method according to claim 9 , wherein the vitamin E comprises α-tocopherol.
14. A method according to claim 9 , comprising doping the irradiated preform in vitamin E for 1-24 hours and heating for an additional 1-400 hours after removing the preform from the vitamin E.
15. A process for making a non-eluting antioxidant doped UHMWPE bearing component, comprising:
(a) providing a UHMWPE preform;
(b) irradiating the preform at a dose of 5 to 20 MRad of gamma irradiation;
(c) doping the preform with an antioxidant comprising α-tocopherol;
(d) annealing the doped preform below its melting point;
(e) machining the preform to the shape of the bearing component, wherein from 1 to 15 mm of material is removed from the preform to make the component; and
(f) packaging and sterilizing the bearing component, wherein the vitamin E index throughout the implant is 0.01 or greater, and 0.2 or less.
16. A process according to claim 15 , comprising irradiating the preform to a dose of approximately 10 MRad.