The role of calcium (source & content) on the in vitro behaviour of sol-gel quaternary glass series

To highlight the effect of salt precursors on the final properties, bioactivity and biocompatibility, five quaternary (Si-Ca-P-Na) glass compositions were successfully prepared through two distinct rapid sol-gel routes; one using acetate salt precursors (A) catalysed by nitric acid, and the other using nitrate salts (N) and citric acid as a catalyst. The sols dried rapidly, and stabilised at 550 & 800 °C to be characterised by X-ray diffraction (XRD), Magic angle spinning-Nuclear magnetic resonance (Si MAS-NMR) and Fourier transform infra-red spectroscopy (FTIR). Upon immersion in simulated body fluid (SBF), hydroxyapatite (HAp) formation was initially enhanced by increasing Ca-content up to 40 mol%, but the formation of calcite was favoured with further increments of Ca to 45 and 48 mol%. The A-glasses exhibited lower density and lower network connectivity compared with N-glasses. The chemical surface modifications after 4 h in SBF were more evident for N-glasses in comparison to A-glasses. The biocompatibility is favoured for the samples treated at 800 °C and for the samples of the higher silica contents.