Analysis of released products from oxidized ultra-high molecular weight polyethylene incubated with hydrogen peroxide and salt solutions

The wear of ultra-high molecular weight polyethylene (UHMWPE) implants gene rates polymeric and metallic particulate, which can be phagocytosed by huma n macrophages, The generation of these UHMWPE particles has been attributed to wear mechanisms and oxidation of the material, Many cell/particle studi es have focused specifically on investigating particles of virgin materials themselves (i.e, virgin UHMWPE), while in fact, there is a strong likeliho od that the oxidation processes encountered by the materials will yield par ticles with very different surface chemistries. Therefore, it is conceivabl e that chemical changes in the material would lead to altered cellular resp onses, as measured in the various cell study models. This paper has focused on the characterization of UHMWPE particulates that have been exposed to v arious conditions simulating processing steps and some of the oxidative and hydrolytic agents related to inflammatory responses. These include gamma-i rradiation, thermal treatment and chemical oxidation by H2O2 and saline sol utions. Oxidation of the particles was measured using Fourier transform inf rared spectroscopy (FTIR). Degradation products were isolated from the incu bation solutions using high-performance liquid chromatography (HPLC), UHMWP E particulates underwent extensive oxidation after gamma-irradiation and th ermal treatments. There were marked differences following treatments of fil m samples taken from bar stock and the virgin particle samples. Polymer-rel ated products, containing alkenes, alkanes and hydroxyl groups, were found in the incubation solutions. The study concluded that future work must cons ider both the particulates' surface chemistry and the possibility of solubl e degradation products when assessing UHMWPE/cellular interactions. (C) 200 0 Elsevier Science Ltd. All rights reserved.