A novel method of cross-linking ultra-high-molecular-weight polyethylene to improve wear, reduce oxidation, and retain mechanical properties - Recipient of the 1999 HAP Paul Award

Increasing cross-linking has been shown in vitro and in vivo to improve mar kedly the wear resistance of ultra-high-molecular-weight polyethylene (UHMW PE). The reduction in the mechanical properties of polyethylene under certa in methods used to produce cross-linking has been a concern, however. These reductions are known to result from the processes used to increase the cro ss-link density and could affect the device performance ill vivo. We presen t a novel method of increasing the cross-link density of UHMWPE in which UH MWPE is irradiated in air at art elevated temperature with a high-dose-rate electron beam and subsequently is melt-annealed. This treatment improves m arkedly the wear resistance of the polymer as tested in a hip simulator, wh ile maintaining the mechanical properties of the material within national a nd international standards. This method leads to the absence of delectable free radicals in the polymer and, as a result, excellent resistance to oxid ation of the polymer.