The effect of sodium content on the bioactivity of glasses used in grit-blasting technique

Objectives: Bioactive glasses are widely used as implant coatings due to their ability to form a chemical bond with bone. Glass composition has an important role in determining the glass bioactivity and osseointegration. Coating the titanium implants with bioactive glasses using grit blast technique depends on their ability to embed physically in the surface. As there is a direct relationship between the sodium concentration in the glasses and their hardness, glasses with variable sodium content were designed to investigate their ability to embed in the titanium surface. The aim of this study is to investigate the effect of increasing sodium content on the bioactivity of the glasses.
Methods: Three glasses in the system of SiO₂-CaO-Na₂O-P₂O₅-CaF₂ were prepared by the melt quench technique where Na₂O is substituted for CaO on molar basis. Each glass powder with particle size less than 38µm was immersed in tris buffer solution and simulated body fluid (SBF) at 37ºC for 3, 6, 9, 24, 72 and 168 hours. The pH changes and apatite formation for all glasses after immersion were investigated. The crystalline phases of the glasses were examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ¹⁹F Nuclear Magnetic Resonance (NMR).
Results: Increasing sodium content in the glasses showed a pronounced rise in the pH level of the two solutions with a slight drop at the 6 hours time point for the SBF. The apatite-like phase started to form within 3 hours of immersion for all glasses in tris buffer solution while in SBF, the formation of apatite clearly occurred after 24 hours immersion. ¹⁹F NMR showed that the glasses form fluorapatite when immersed in these solutions.
Conclusions: This study shows that the variation of sodium content in soda-lime phosphosilicate glasses has no adverse effect on the reactivity and apatite formation of these glasses.