Sodium is not essential for high bioactivity of glasses

This study aims to demonstrate that excellent bioactivity of glass can be achieved without the presence of an alkali metal component in glass composition. In vitro bioactivity of two sodium-free glasses based on the quaternary system SiO2-P2O5-CaO-CaF2 with 0 and 4.5 mol% CaF2 content was investigated and compared with the sodium-containing glasses with equivalent amount of CaF2. The formation of apatite after immersion in Tris buffer was followed by Fourier-transform infrared spectroscopy, X-ray diffraction, 31P and 19F solid-state MAS-NMR. The dissolution study was completed by ion release measurements in Tris buffer. The results show that sodium-free bioactive glasses formed apatite at 3 h of immersion in Tris buffer, which is as fast as the corresponding sodium-containing composition. This signifies that sodium is not an essential component in bioactive glasses and it is possible to make equally degradable bioactive glasses with or without sodium. The results presented here also emphasize the central role of the glass compositions design which is based on understanding of structural role of components and/or predicting the network connectivity of glasses.