Inhibition of aseptic loosening of artificial joints by graft polymerizaiton of a novel biocompatible polymer MPC

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Despite improvements in techniques and materials, aseptic loosening of artificial hip joints remains as the most serious problem. This study investigated mechanical and biological effects of our original biocompatible phospholipid polymer composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) nano-graft onto artificial surface of polyethylene liner on prevention of aseptic loosening.To examine mechanical effects of MPC grafting of polyethylene liner, we performed hip simulator tests (3.0x10^6cycles) using cross-linked polyethylene (CL-PE) liners with or without nano-graft of MPC onto artificial surface (MPC liner/CL-PE liner) and PE liner. The friction torque was about 90% lower in MPC liners than control liners. Total amounts of wear produced from MPC liner was about 1/4 and 1/40 of those from GL-PE and PE liners, respectively. Three-dimensional morphometric analysis and SEM analysis of MPC liners revealed no or little wear. The effect of MPC grafting was maintained or pronounced … More after the test, because XPS analysis confirmed the remainder of the specific spectra of MPC on the liner surface.To examine biological responses of macrophages and osteoblasts, we prepared MPC nanoparticles (500nm). Using in vitro/vivo murine particle-induced osteolysis model, we examined biological effects of MPC nanoparticles on osteoclastogenesis. When nanoparticles were exposed to cultured mouse macrophages, MPC nanoparticles were hardly phagocytosed by macrophages and did not enhance the concentration of cytokines and PGE_2. Furthermore, the culture medium of macrophages exposed to MPC nanoparticles did not induce RANKL mRNA expression in osteoblasts and osteoclastogenesis from bone marrow cells. In vivo murine osteolysis model, particle-induced bone resorption was hardly observed in mice implanted MPC nanoparticles.Some medical devices grafted MPC onto its surface have been already used under authorization of the FDA. These results demonstrate that MPC polymer grafting decreases wear production and even if wear particles are produced, they are biologically inert, suggesting an epochal improvement of artificial hip joints preventing aseptic loosening. Less