Surface Reactions of Mesoporous Bioactive Glasses Monitored by Solid-State NMR: Concentration Effects in Simulated Body Fluid

Abstract

A bone-mineral-mimicking layer of hydroxycarbonate apatite (HCA) forms at the surface of a bioactive glass on its contact with body fluids. We report a solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy study of the surface reactions preceding the HCA formation at three CaO–SiO2–(P2O5) mesoporous bioactive glasses (MBGs) with distinct compositions, surface areas, and mesoporous arrangements, during their immersion in simulated body fluid (SBF) out to 30 days. The evolution of the various populations of coexisting silicate species associated with the bulk and surface portions of the pore-walls were monitored. The MBGs revealed drastically different surface alterations between the scenarios of low (0.6 g/L) and high (20 g/L) MBG concentrations in the SBF: for the low MBG dose, which is expected to be more relevant for in vivo conditions, all MBGs follow a “universal” dissolution mechanism beyond ≈24 h of SBF soaking, regardless of their precise compositions and textural properties. The only esse...