MACROPHAGE PHAGOCYTOSIS OF POLYETHYLENE PARTICULATE IN-VITRO

In this study, an in vitro model has been developed to examine the int eractions of macrophages with ultrahigh molecular-weight polyethylene (UHMWPE) and high-density polyethylene (HDPE) particles. Polyethylene particles are the major constituent of the material debris formed as a result of orthopedic implant wear. However, the study of polyethylene particle interactions with cells has been limited. UHMWPE (18-20 mu m ) and HDPE (4-10 mu m) were suspended in soluble collagen type I and s ubsequently solidified on glass coverslips. The particle chemistry was characterized by Fourier transform infra-red spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Mouse cell line macrophages ( IC-21) were established on the collagen-particle substrata and maintai ned for up to 24 h. The response of the cells to the particles was exa mined by light and transmission electron microscopy (LM and TEM), as w ell as by scanning electron microscopy (SEM), and compared to cells on control collagen surfaces without particles. Histological analysis of the samples revealed that the mac macrophages surrounded larger parti cles (18-20 mu m) and the cells appeared to be attached to the surface of the particles, and the smaller particles (4-10 mu m) had been phag ocytosed within 2 h. Inflammatory cytokines (TNF-alpha, IL-1 alpha, IL -1 beta, and IL-6), lysosomal enzymes (beta-galactosidase and hexosami nidase), and prostaglandin E-2 were released into the medium, and IL-1 alpha, IL-1 beta, PGE(2), beta-galactosidase, and hexosaminidase leve ls were significantly increased over collagen control values. The resu lts demonstrate active phagochemotaxis by macrophages for wear particu lates and validate this model as a means of studying the specific in v itro interactions of polyethylene with cells. (C) 1998 John Wiley & So ns, Inc.