Crosslinking has been shown to improve significantly the wear resistance of ultra high molecular weight polyethylene (UHMWPE), both in joint simulator tests and in clinical use. High-energy ion radiation, when used to induce crosslinking in UHMWPE, produces free radicals. In the presence of oxygen, the free radicals have been shown to be responsible for oxidative degradation of polyethylene. A melt-anneal treatment of highly crosslinked UHMWPE substantially eliminates the free radicals to an undetectable low level.
The aim of this study was to determine the effect of accelerated oxidative aging on the mechanical and fracture properties of melt-annealed highly crosslinked UHMWPE. Compression molded GUR 1050 UHMWPE was crosslinked by electron-beam irradiation at 100 ± 10 kGy and was followed by a melt-anneal treatment. Both melt-annealed highly crosslinked and conventional gamma irradiated in nitrogen UHMWPE were exposed to an accelerated oxidative challenge in the laboratory. The tensile mechanical properties and crack growth resistance curves (J-R curves) determined for oxidative aged melt-annealed highly crosslinked UHMWPE were either equivalent or superior to the oxidative aged conventional gamma irradiated UHMWPE. The difference in tensile mechanical properties and J-R curves for non-aged and oxidative aged melt-annealed crosslinked UHMWPE was insignificant, indicating that oxidative aging had no detrimental effect on mechanical and fracture properties of melt-annealed highly crosslinked UHMWPE.