The Effect of polyethylene particle chemistry on human monocyte-macrophagefunction in vitro

Osteolysis remains the most important problem in orthopedic implant failure . Wear debris from the implant contains polyethylene (PE) particulate which has been shown to activate monocyte-derived macrophages (MDM). Although th e response of MDM has been shown to be influenced by the size, shape, and c hemical type of PE, the effect of chemically altered PE on MDM has not been studied. In this study, human MDM were seeded onto glass coverslips coated with virgin high density (HD)PE and chemically modified HDPE (impregnated with ppm levels of CoCl2 and oxidized by heat) mixed with type I collagen a nd cultured for 96 h. Light microscopic evaluation demonstrated consistent phagocytosis of the HDPE particulate that was confirmed by scanning electro n and transmission electron microscopy with little evidence of cytotoxicity . Evaluation of pro-inflammatory mediator secretion by MDMs in response to the virgin and chemically modified HDPE revealed significant differences in interleukin (IL)-1, tumor necrosis factor (TNF)-alpha, and IL-6 secretion. A significant elevation of IL-1 secretion was observed after initial expos ure to virgin HDPE particles compared with controls (p = 0.001). IL-1 secre tion was also elevated in the low oxidized particle groups (p = 0.001), whe reas the highly oxidized particles were not different than controls. Secret ion of both IL-6 (p = 0.03) and TNF-alpha (p = 0.007) were significantly el evated by the low oxidized HDPE particles whereas the virgin and highly oxi dized groups showed no difference. The different effects on MDM activation when HDPE surface chemistry was altered, highlight the importance of defini ng the particle properties when studying the role of MDM activation in in v itro systems and extrapolating these observations to the in vivo situation. (C) 2000 John Wiley & Sons, Inc.