Toward a rational design of bioactive glasses with optimal structural features: Composition-structure correlations unveiled by solid-state NMR and MD simulations

Abstract

The physiological responses of silicate-based bioactive glasses (BGs) are known to depend critically on both the P content (nP) of the glass and its silicate network connectivity (NBOSi). However, while the bioactivity generally displays a nonmonotonic dependence on n P itself, recent work suggest that it is merely the net orthophosphate content that directly links to the bioactivity. We exploit molecular dynamics (MD) simulations combined with 31P and 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy to explore the quantitative relationships between NBOSi, nP, and the silicate and phosphate speciations in a series of Na 2O-CaO-SiO2-P2O5 glasses spanning 2.1 ≤ NBOSi ≤ 2.9 and variable P2O 5 contents up to 6.0 mol %. The fractional population of the orthophosphate groups remains independent of nP at a fixed N BOSi-value, but is reduced slightly as NBOSi increases. Nevertheless, P remains predominantly as readily released orthophosphate ions, whose content may be altered essentially independently of the network connectivity, thereby offering a route to optimize the glass bioactivity. We discuss the observed composition-structure links in relation to known composition-bioactivity correlations, and define how Na 2O-CaO-SiO2-P2O5 compositions exhibiting an optimal bioactivity can be designed by simultaneously altering three key parameters: the silicate network connectivity, the (ortho)phosphate content, and the nNa/nCa molar ratio. © 2013 American Chemical Society.