In Vitro and In Vivo Evaluation of Toxicity of Structurally Different Diamond-Like Carbon Wear Debris in Joint Replacements

Diamond-like carbon (DLC) wear debris, which is often composed of different types of structures, is generated from DLC-modified artificial joints in the human body, and its biocompatibility evaluation is especially important to prevent wear-debris-induced implant failure. Here, RAW 264.7 macrophages (inflammatory-reaction assay) and primary mouse osteoblasts (osteoblastogenesis assay) were employed to investigate the toxicity of DLC wear particles (DWPs) by evaluation of cell viability and morphology, enzyme-linked immunosorbent assays, and quantitative reverse-transcription polymerase chain reaction (PCR). Relevant histopathological analysis of rat joints was also performed in vivo. We found that DWPs with a relatively high sp(2)/sp(3) ratio (graphite-phase tendency) manifested a higher cytotoxicity and significant inhibition of osteoblastogenesis. DWPs with a relatively low sp(2)/sp(3) ratio (diamond-phase tendency) showed good biocompatibility in vivo. The DWPs exhibiting a low sp(2)/sp(3) ratio demonstrated reduced secretion of TNF-alpha and IL-6, along with increased secretion of TIMP-1, resulting in the downregulation of MMP-2 and MMP-9 and upregulation of interleukin-10 (IL-10), thereby attenuating the inflammatory response. Moreover, coculturing osteoblasts with DWPs exhibiting a low sp(2)/sp(3) ratio resulted in an elevated OPG/RANKL ratio and increased expression of OPG mRNA. Because of the absence of electrostatic repulsion, DWPs with a relatively low sp(2)/sp(3) ratio enhanced bovine serum albumin adsorption, which favored cellular activities. Cytotoxicity assessment of DWPs can help establish an evaluation system for particle-related joint disease and can facilitate the clinical application of DLC-coated prostheses.