Effect of lipid absorption on wear and compressive properties of unirradiated and highly crosslinked UHMWPE: An in vitro experimental model

Ultra-high molecular weight polyethylene (UHMWPE or polyethylene) components used in total joint arthroplasty absorb lipids in vivo. However, the effect, if any, of this lipid uptake on both the wear and the mechanical properties of polyethylene is not known. We contrasted the effects of lipid diffusion into the polyethylene on the wear and mechanical properties of unirradiated UHMWPE versus that into highly crosslinked UHMWPE preparation (a 95-kGy irradiated and melted UHMWPE). We doped test samples of both types of polyethylenes with either squalene alone or a 15% (w/v) solution of cholestene/squalene (CH/SQ) solution. The diffusion profiles were quantified using infrared microscopy as a function of depth away from free surfaces; we used the 1620 and 1680cm^-1 absorbances characteristic of CH and SQ, respectively. There were no statistically significant changes in the bi-directional pin-on-disk wear rates of neither type of polyethylene after lipid absorption. On the other hand, compressive modulus and compressive strength of both polyethylenes decreased after doping with either lipid.