Compositional Dependence of Bioactivity of Glasses in the System CaO-SiO<sub>2</sub>-P<sub>2</sub>O<sub>5</sub>

TLDR

Apatite layer formation on glass surfaces is essential for bone bonding and can be reproduced in simulated body fluid with ion concentrations similar to blood plasma. The study investigates how glass composition in the CaO–SiO₂–P₂O₅ system affects bioactivity by examining apatite formation in simulated body fluid. Apatite formation was detected using thin‑film X‑ray diffraction, Fourier‑transform infrared spectroscopy, and scanning electron microscopy, and the results were interpreted in terms of ion dissolution from the glasses. Glasses based on CaO–SiO₂, whether containing small amounts of P₂O₅ or not, form apatite, whereas CaO–P₂O₅ glasses, with or without SiO₂, do not, showing that CaO–SiO₂ compositions are bioactive contrary to the prevailing view.

Abstract

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. The apatite layer can be reproduced on their surfaces even in an acellular simulated body fluid which has ion concentrations almost equal to those of the human blood plasma. In the present study, in order to investigate the compositional dependence of bioactivity of glasses fundamentally, the apatite formation on the surfaces of glasses in the system CaO-SiO2-P2O5 was examined in the simulated body fluid. Thin-film X-ray diffraction, Fourier transform infrared reflection spectroscopy and scanning electron microscopic observation were used for detecting the apatite formation. It was found that CaO-SiO2 glasses free form P2O5 as well as those containing small amounts of P2O5 form the apatite layer on their surfaces, whereas CaO-P2O5 glasses free from SiO2 as well as those containing SiO2 do not form it. This indicates that bioactive glasses and glass-ceramics are obtained in compositions based on CaO-SiO2 rather than CaO-P2O5, contrary to the general view. These results were interpreted in terms of ions dissolved from glasses.