Ultra high molecular weight polyethylene articles and methods of forming ultra high molecular weight polyethylene articles
The present invention generally provides implantable articles and methods of forming implantable articles from a crosslinked ultrahigh molecular weight polyethylene (“UHMWPE”) blend stabilized with Vitamin E. The crosslinked UHMWPE blend may be prepared by combining the UHMWPE material and vitamin E prior to irradiating the UHMWPE blend with electron beam radiation at a sufficient radiation dose rate to induce crosslinking. The crosslinked UHMWPE blend may be incorporated into a variety of implants, and in particular, into endoprosthetic joint replacements.
1. A method of forming a crosslinked ultrahigh molecular weight polyethylene blend comprising:
combining vitamin E and ultrahigh molecular weight polyethylene to form an ultrahigh molecular weight polyethylene blend prior to consolidation of the ultrahigh molecular weight polyethylene blend, in which the blend comprises the vitamin E in a substantially uniform distribution throughout the ultrahigh molecular weight polyethylene;
consolidating the ultrahigh molecular weight polyethylene blend; and
irradiating the consolidated, ultrahigh molecular weight polyethylene blend with electron-beam radiation at an absorbed dose of at least 60 kiloGrey and a dose rate of at least 1 MegaGrey per hour to form a crosslinked ultrahigh-molecular weight polyethylene blend having a swell ratio of less than 4.
2. The method of claim 1 wherein the absorbed dose is at least about 90 kiloGrey and the dose rate is at least 10 MegaGrey per hour.
3. The method of claim 1 wherein the amount of vitamin E in the blend is between about 0.02 w/w % and about 2.0 w/w %.
4. The method of claim 1 wherein the amount of vitamin E in the blend is between about 0.05 and about 0.4 w/w %.
5. The method of claim 1 further comprising the step of heating the ultrahigh molecular weight polyethylene blend prior to, after, or both prior to and after irradiating.
6. The method of claim 1 further comprising the step of forming the crosslinked ultrahigh-molecular weight polyethylene blend into an implant.
7. The method of claim 6 further comprising the step of sterilizing the implant during or subsequent to irradiating.
8. The method of claim 7 wherein the sterilizing step comprises contacting the implant with electron-beam radiation, gamma radiation, gas plasma or ethylene oxide.
9. The method of claim 6 further comprising the step of packaging the implant.
10. The method of claim 9 wherein the sterilizing step occurs during, after or both during and after packaging the implant.
11. A method of forming a sterilized packaged implant comprising:
combining vitamin E and ultrahigh molecular weight polyethylene to form an ultrahigh molecular weight polyethylene blend prior to consolidation of the ultrahigh molecular weight polyethylene blend, in which the blend comprises the vitamin E in a substantially uniform distribution throughout the ultrahigh molecular weight polyethylene;
consolidating the ultrahigh molecular weight polyethylene blend;
forming an implant from the consolidated ultrahigh molecular weight polyethylene blend packaging the implant; and
irradiating the packaged, implant with electron-beam radiation at an absorbed dose of at least 60 kiloGrey and a dose rate of at least 1 MegaGrey per hour wherein the irradiated implant has a swell ratio of less than 4.
12. The method of claim 11 wherein the implant is packaged in a gas permeable package or a oxygen-deprived barrier package.
13. A method comprising:
mixing ultrahigh molecular weight polyethylene and vitamin E to provide a substantially uniform blend of vitamin E throughout the ultrahigh molecular weight polyethylene;
consolidating the substantially uniform blend of ultrahigh molecular weight polyethylene and vitamin E; and
inducing cross-linking of the consolidated blend by irradiating the consolidated blend with electron-beam radiation at an absorbed dose of at least 60 kiloGrey and a dose rate of at least 15 MegaGrey per hour to provide a cross-linked material.
14. The method of claim 13 , further comprising:
processing the cross-linked material to provide an implant;
packaging the implant; and
sterilizing the packaged implant.
15. The method of claim 14 , in which the sterilizing step comprises exposing the packaged implant to radiation.
16. A method comprising:
a first step comprising combining vitamin E and ultrahigh molecular weight polyethylene powder to form a substantially uniform blend of the vitamin E throughout the ultrahigh molecular weight polyethylene powder; and
a second step following the first step, the second step comprising irradiating the substantially uniform blend with electron-beam radiation at an absorbed dose of at least 60 kiloGrey and a dose rate of at least 15 MegaGrey per hour to form a crosslinked blend.
17. The method of claim 16 , further comprising consolidating the substantially uniform blend of the vitamin E and the ultrahigh molecular weight polyethylene powder after the first step and before the second step.