Selectively cross-linked polyethylene orthopedic devices

Abstract

An improved prosthetic medical device having improved wear resistance and toughness is provided in the present application. A method is provided to selectively cross-link the polymeric matrix comprising the medical device by employing an interrupting means such as a mask, wire mesh or chopper wheel placed in between the medical device and irradiation source. In addition, the medical device may be translated while being irradiated to further effect the selective cross-linking. The present invention also provides for an injection molding process wherein a prosthetic medical device is formed in a single step, then selectively cross-linked.

Description

CROSS REFERENCE [0001] This is a continuation application of U.S. patent application Ser. No. 10 / 094,789, filed Mar. 11, 2002, which claims the benefit of U.S. patent application Ser. No. 09 / 553,503, filed Apr. 20, 2000, which claims the benefit of Provisional Application No. 60 / 130,322, filed Apr. 21, 1999, the disclosures of which are incorporated herein by reference.FIELD OF THE INVENTION [0002] This invention relates generally to producing prosthetic medical devices. More specifically, the invention provides methods to produce compositions made of polyethylene which have been irradiated in such a manner so that only a selected percentage of the overall composition has been allowed to cross-link. The capability to precisely control the degree and location of cross-linking in a polymer has particular advantages in the orthopedic device arts. BACKGROUND OF THE INVENTION [0003] Many prosthetic medical devices are implanted into load-bearing joints such as knees, hips, etc. As such, ...

AI Technical Summary

Benefits of technology

The present invention provides methods for producing cross-linked polyethylene orthopedic devices with improved wear characteristics. The methods involve selectively controlling the cross-linking of the polymer in specific areas and to a specific degree, using localized and controlled radiation exposure. The invention allows for the fabrication of various types of prosthetic devices with improved properties such as mechanical toughness and wear resistance. The polymeric materials used can be any combination of polyethylenes including high molecular weight polyethylene, ultra high molecular weight polyethylene, and cross-linked polyethylene. The invention also provides masks, shields, or screens to interrupt the radiation beam and allow for controlled cross-linking. The workpiece can be rotated or translated while exposed to the interrupted radiation beam, and the invention also includes methods for forming prosthetic devices by injection molding.

Problems solved by technology

Improving wear resistance without losing strength or causing oxidative degradation is a difficult balance to obtain.

Another difficulty conventionally encountered in the manufacturing process of polymeric components of ball and socket or bearing-type prosthetic medical devices, such as hips, knees, and other load-bearing joints, is that they cannot be formed easily by inexpensive injection molding techniques.

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