Revealing structure and property relationships in ZrO2-containing phosphosilicate bioactive glasses

Elucidating the intricate structures of novel bioactive glasses is essential for understanding their structure–property relationships, particularly regarding dissolution rate and bioactivity which are key factors in designing glass compositions for biomedical applications. In this study, we investigate the structure and property relations of a series of novel bioactive phosphosilicate glasses through an integrated experimental and computational study by using characterization techniques such as magic angle spinning nuclear magnetic resonance (MAS NMR), neutron diffraction, and molecular dynamics (MD) computer simulations. Our results reveal that zirconia significantly alters the chemical environment surrounding silicon, as evidenced by ²⁹Si NMR, through the formation of Si–O–Zr linkages. This structural modification is further supported by shifts in partial pair distribution function peak positions toward longer distances for P–O and Si–O pairs, as observed in neutron diffraction data for glasses containing 4 mol% ZrO₂. Additionally, apparent depolymerization is observed around silicon, showing a decrease of Si Q⁴ and Q³ species with increasing ZrO₂. Phosphorus predominantly exists as Q⁰ (∼90%) and Q¹ (∼10%) species, showing little sensitivity to zirconia composition variations, as demonstrated by ³¹P NMR. Increasing the P₂O₅ content results in a more disordered and heterogeneous glass network, as neutron diffraction revealed. MD simulations indicate a preferential distribution of isolated orthophosphate units. The structural information from MD was employed to establish a quantitative structure–property relationship analysis with key physical properties, such as Young's modulus and density. These combined results highlight the power of integrating experimental and computational methods to unveil significant composition-driven modifications in short- and medium-range glass structures, ultimately governing the properties of bioactive glasses.