Ultra high molecular weight polyethylene (UHMWPE) is the material of choice for use as a bearing surface in the majority of total joint replacements. Polyethylene wear and the osteolysis that occurs secondary to the debris particles continue to be the most important factors limiting the long term success of joint arthroplasties. This study was designed to explore the potential benefits of ion implanted UHMWPE. Our first goal was to “label” UHMWPE by mechanically implanting copper [Cu] through a two-step technique of surface coating with elemental Cu followed immediately by Xenon [Xe+] ion bombardment. This technique modifies only one surface or specific area of a polyethylene specimen. After successfully labeling one surface of a PE specimen, analysis of wear debris particles will allow computation of the relative amounts of particles released from the labeled and unlabelled surfaces. Sixty UHMWPE disks were mounted for implantation in a Z-100 implanter with Xe at a beam energy of approximately 100 keV, and a beam current of 0.65 mA (particle). The entire assembly including the specimens were treated with a 300 angstrom layer of copper applied by plasma vapor deposition followed immediately by a dose of Xe+ ions. Additional experiments void of copper pretreatment allowed for ion modified positive controls of Xe only bombardment to be produced.

During our investigation we found a marked improvement of wear characteristics for the ion modified UHMWPE specimens. Before we could continue with our localization goal it was necessary to determine the extent of this increased wear resistance. Therefore a secondary goal became the development of a protocol for measuring this change in surface behavior. Three wear testing experiments were conducted with a multi-motion pin-on-disk wear simulator. The magnitudes of debris wear were measured at three distinct time intervals for comparison between samples. Group means were analyzed using a one way analysis of variance and a Dunnett post hoc test against control. Between 14,400 and 28,800 cycles, UHMWPE wear was significantly less in the treated samples compared to the control group. Unique to our study is the introduction of copper to the surface of the polyethylene. Our experimental results suggest that Xe ion implantation does improve the wear characteristics, but a marked improvement occurs with a preloaded copper layer and a relative implantation dose between 0.5 and 1.0 x 1017 Xe+ ions/cm².