THE INFLUENCE OF PARTICLE MORPHOLOGY ON BIOLOGICAL RESPONSE OF MACROPHAGES
Riku Yoshioka, Yuta Nakashima, Yukio Fujiwara, Yoshihiro Komohara, Motohiro Takeya, Yoshitaka Nakanishi
Kumamoto University, Japan
Several studies reported that ultra-high molecular weight polyethylene (UHMWPE) wear debris that generated from the bearing surface of artificial joints is phagocytosed by macrophages. Macrophages release cytokine that stimulate osteoclasts and the subsequent osteolysis. Artificial joint loosening is caused by the osteolysis. In particular, some reports showed that sub-micron size of the particles had a great effect on biological response of macrophages. There is possibility that the other parameters except for the particle size may regulate the macrophages activation and/or production of cytokines. In this study, polymethylmethacrylate (PMMA) particles with narrow particle size distribution were used instead of UHMWPE. Evaluation parameters to the activation of PMMAs are, particle size, Total volume of particles per cell, total surface area of particles per cell. In particle size, significant decrease of cell viability was observed when relatively large particles were tested (5.6–19.3 µm). Production of proinflammatory cytokines was observed with 5.6- and 9.6-µm particles. In total volume of particles per cell, cell death occurred when added volume exceeded 1×105 µm3 per cell. Proinflammatory cytokines were produced upon stimulation with added volume between 1×105 to 4.5×105 µm3 per cell. In total surface area of particles per cell, cell death was caused when the added surface area per cell exceeded 1×105 µm2 and proinflammatory cytokines were produced with the added surface area per cell between 1×105 to 3×105 µm2. These results suggested that biologically active factors exert their effect through total volume and total surface area of particles rather than through particle size. The results of this study is of use to anyone concerned with the design of artificial joints with greater longevity.