To prevent wear debris-induced
osteolysis and aseptic loosening, cross-linked
ultra-high molecular weight polyethylene's (
UHMWPE) with improved wear resistance have been developed. Hip simulator studies have demonstrated very low wear rates with these new materials leading to their widespread clinical use. However, the biocompatibility of this material is not known. We studied the macrophage response to cross-linked
UHMWPE (XLPE) and compared it to conventional
UHMWPE (CPE) as well as other clinically used orthopaedic materials such as
titanium-
alloy (TiAlV) and
cobalt-chrome
alloy (CoCr). Human peripheral blood monocytes and murine macrophages, as surrogates for cells mediating peri-implant
inflammation, were cultured onto custom designed lipped disks fabricated from the test materials to isolate cells. Culture supernatants were collected at 24 and 48h and analyzed for
cytokines such as IL-1alpha, IL-1beta,
TNF-alpha and
IL-6. Total
RNA was extracted from adherent cells and gene expression was analyzed using qualitative RT-PCR. In both in vitro models, macrophages cultured on cross-linked and conventional
polyethylene released similar levels of
cytokines, which were also similar to levels on control tissue culture dishes. Macrophages cultured on TiAlV and CoCr-
alloy released significantly higher levels of
cytokines. Human monocytes from all donors varied in the magnitude of
cytokines released when cultured on identical surfaces. The variability in individual donor responses to TiAlV and CoCr surfaces may reflect how individuals respond differently to similar stimuli and perhaps reveal a predisposed sensitivity to particular materials.