The effect of grain size on the biocompatibility, cell-materials interface, and mechanical properties of microwave-sintered bioceramics

The effect of decreasing the grain size on the biocompatibility, cellmaterial interface, and mechanical properties of microwave-sintered monophase hydroxyapatite bioceramics was investigated in this study. A nanosized stoichiometric hydroxyapatite powder was isostatically pressed at high pressure and sintered in a microwave furnace in order to obtain fine grained dense bioceramics. The samples sintered at 1200 degrees C, with a density near the theoretical one, were composed of micron-sized grains, while the grain size decreased to 130 nm on decreasing the sintering temperature to 900 degrees C. This decrease in the grain size certainly led to increases in the fracture toughness by much as 54%. An in vitro investigation of biocompatibility with L929 and human MRC-5 fibroblast cells showed noncytotoxic effects for both types of bioceramics, while the relative cell proliferation rate, cell attachment and metabolic activity of the fibroblasts were improved with decreasing of grain size. An initial in vivo investigation of biocompatibility by the primary cutaneous irritation test showed that both materials exhibited no irritation properties. (c) 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A:30593070, 2012.