Compositional dependence of bioactivity of glasses in the system CaO-SiO2-Al2O3: itsin vitro evaluation

In order to investigate fundamentally the effect of Al₂O₃ on the bioactivity of glasses and glass-ceramics, the compositional dependence of bioactivity of glasses in the system CaO-SiO₂-Al₂O₃ was studiedin vitro. It is already known that the essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body, and that the surface apatite layer can be reproduced even in an acellular simulated body fluid which has almost equal ion concentrations to those of the human blood plasma. In the present study, bioactivity of the glasses was evaluated by examining apatite formation on their surfaces in the simulated body fluid with thin-film X-ray diffraction, Fourier transform infrared reflection spectroscopy and scanning electron microscopic observation. Only CaO-SiO₂-Al₂O₃ glasses containing Al₂O₃ less than 1.5 mol % formed the surface apatite as well as Al₂O₃-free CaO-SiO₂ glasses, but CaO-SiO₂-Al₂O₃ containing Al₂O₃ more than 1.7 mol % did not form it as well as an SiO₂-free CaO-Al₂O₃ glass. This indicates that only a small amount of addition of Al₂O₃ to glass compositions suppresses the bioactivity of glasses and glass-ceramics by suppressing apatite formation on their surfaces in the body.