wear resistance and oxidation resistance of polymer material or a polymer component for bioimplantation are improved by packaging a polymer object in a sealed gas impermeable package substantially free of oxygen , irradiating the package with penetrating radiation to an extent sufficient to effect a desired substantial level of cross - linking within the polymer , and warming the packaged object while maintaining an elevated hydrostatic pressure to cause gases released during irradiation to recombine , stabilizing the material against subsequent oxidative change . the pressure stabilization terminates active sites , substantially eliminating free radicals . when applied to finished parts , the process simultaneously hardens and sterilizes the parts without degrading mechanical properties or dimensions . when applied to bulk material or unfinished parts , the part may be subsequent machined or otherwise finished , and sterilized by any conventional means . the procedure achieves high levels of cross linking without increasing susceptibility to aging or chemical degradation .