Bioactivity of Na2O-CaO-SiO2 Glasses

Bioactivities of Na₂O-CaO-SiO₂ glasses were evaluated by examining the formation of bonelike apatite, which is responsible for their bonding to living bone, on their surfaces in a simulated body fluid, using thin-film X-ray diffraction and Fourier-transform infrared reflection spectroscopy. It was found that glasses in a wide compositional region in the P₂O₅-free Na₂O-CaO-SiO₂ system can show bioactivity, as those in the P₂O₅-containing system. The rate of apatite formation on the surfaces of glasses varied largely with the composition of the glasses. Under a constant SiO₂ content of 50 mol%, a glass containing equimole of Na₂O and CaO showed the highest rate of the apatite formation. Variation in the rate of apatite formation with the glass composition corresponded well with the rate of increase in the degree of the supersaturation of the simulated body fluid with respect to the apatite due to dissolution of sodium and calcium ions from the glasses. Little difference was observed in the rates of ion dissolution and of apatite formation between P₂O₅-containing Bioglass 45S5-type and a corresponding P₂O₅-free Na₂O-CaO-SiO₂ glass. It is believed that P₂O_s-free Na₂O-CaO-SiO₂ glasses also show bioactivity as high as that of Bioglass.