Effect of UHMWPE particle size, dose, and endotoxin on in vitro macrophage response

Ultra-high molecular weight polyethylene wear debris generated by a prosthetic hip or knee has been linked to osteolysis and the limited lifespan of the implant. However, research results are conflicting with regard to which characteristics of the polyethylene wear debris are most inflammatory. The goal of this study was to determine whether particle size, number, and the presence of endotoxin significantly contribute to increased secretion of pro-inflammatory mediators by macrophages in vitro in response to polyethylene wear debris generated by a hip simulator. The results show that the prevailing inflammatory factor is endotoxin. The macrophages released only minimal levels of TNF-α and IL-6 in response to cleaned polyethylene particles, but these cytokines were released in significantly higher amounts in response to particles spiked with lipopolysaccharide (LPS). The number (up to 500 particles per cell) and size of the particles tested in this study had no significant influence on any of the measured outputs (macrophage viability, TNF-α, IL-6, or PGE₂) unless associated with LPS.