Oxidation resistant homogenized polymeric material
The present invention relates to methods for making oxidation resistant homogenized polymeric materials and medical implants that comprise polymeric materials, for example, ultra-high molecular weight polyethylene (UHMWPE). The invention also provides methods of making antioxidant-doped medical implants, for example, doping of medical devices containing cross-linked UHMWPE with vitamin E by diffusion and annealing the anti-oxidant doped UHMWPE in a super critical fluid, and materials used therein.
1. A method of making an antioxidant-doped homogenized cross-linked consolidated interlocked hybrid polymeric material comprising the steps of:
a) providing a polymeric material in a powder form;
b) doping the polymeric material with an antioxidant without using a supercritical fluid, thereby forming an antioxidant-doped polymeric material;
c) annealing the antioxidant-doped polymeric material from step b) in a supercritical fluid, thereby forming an antioxidant-doped homogenized polymeric material;
d) heating and pressurizing the heated antioxidant-doped homogenized polymeric material under 10-1000 MPa to a counterface of a second material, thereby forming a hybrid material having an interface between the polymeric material and the second material;
e) holding at the pressure and temperature;
f) cooling the heated polymeric material;
g) releasing the pressure, thereby forming an antioxidant-doped homogenized interlocked hybrid material; and
h) irradiating the antioxidant-doped homogenized hybrid material by ionizing radiation, thereby forming an antioxidant-doped homogenized cross-linked interlocked hybrid material.
2. The method according to claim 1 , wherein the annealing is carried out above 30° C. and above 200 psi.
3. The method according to claim 1 , wherein the annealing is carried out at about 120° C. and at about 1700 psi.
4. The method according to claim 1 , wherein the annealing is carried out at above 120° C. and above 1700 psi.
5. The method according to claim 1 , wherein the polymeric material is irradiated at a temperature between about room temperature and about 90° C.
6. The method according to claim 1 , wherein the polymeric material is irradiated at a temperature between about 90° C. and the peak melting point of the polymeric material.
7. The method according to claim 1 , wherein the doping is carried out by soaking the polymeric material in the antioxidant for about an hour or about 16 hours.
8. The method according to claim 1 , wherein the antioxidant is heated to a temperature between the room temperature and about 100° C. and the doping is carried out at a temperature between the room temperature and about 100° C.
9. The method according to claim 1 , wherein the polymeric material is selected from a group consisting of a low-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene (UHMWPE), and a mixture thereof.
10. The method according to claim 1 , wherein the polymeric material is polymeric resin powder, polymeric flakes, polymeric particles, or a mixture thereof.
11. The method according to claim 1 , wherein the irradiation is carried out in air or inert gaseous atmosphere containing between about 1% and about 22% oxygen.
12. The method according to claim 1 , wherein the irradiation is carried out in an inert atmosphere, wherein the inert atmosphere contains gas selected from the group consisting of nitrogen, argon, helium, neon, or a combination thereof.
13. The method according to claim 1 , wherein the radiation dose is between about 25 and about 1000 kGy.
14. The method according to claim 1 , wherein the radiation dose is about 65 kGy, about 75 kGy, or about 100 kGy.
15. The method according to claim 1 , wherein the radiation is a gamma or an electron beam irradiation.
16. The method according to claim 1 , wherein the polymeric material is soaked in a solution of the antioxidant in ethanol.
17. The method according to claim 1 , wherein the supercritical fluid is CO 2 .
18. The method according to claim 1 , wherein the antioxidant is vitamin E.
19. The method according to claim 1 , wherein the polymeric material at step (a) is a blend of a polymeric material and an antioxidant.