Enhanced wear performance of highly crosslinked UHMWPE for artificial joints

It is well known that osteolysis induced by polyethylene wear debris is the main cause of long-term failure of hip and knee prostheses. We developed a treatment of medical-grade ultra-high molecular-weight polyethylene (UHMWP E) in order to improve its tribologic properties and reduce its wear. Medic al-grade UHMWPE was irradiated with a 200 kGy dose of radiation, thermally stabilized at a temperature close to the melting point, and then sterilized with ethylene oxide. The irradiation treatment was per formed to crosslink the UHMWPE. The thermal stabilization treatment, contributing to the react ion between the free radicals generated by the irradiation process, was cho sen to enhance crosslinking and to prevent oxidation and the shortening of chains. The non-invasive sterilization process with ethylene oxide was chos en to prevent the re-formation of free radicals. The wear performance of th is material was compared to UHMWPE, untreated or treated with different ste rilization techniques, using gamma and beta irradiation. insoluble crosslin ked constituents were measured with an extraction method. Wear was evaluate d using a flat-on-ring wear test machine. While small differences were foun d among the different sterilization processes, 200 kGy-irradiated UHMWPE fo llowed by thermal treatment and sterilization with ethylene oxide had the l east wear and the greatest amount of crosslinking. (C) 2000 John Wiley & So ns, Inc.