Oxynitride glasses for potential biomedical usage

The low strength of bioglasses have restricted their use to non‐load bearing applications and therefore improvements in mechanical properties are needed. One solution to this challenge is to incorporate nitrogen into the glass silicate network. This paper outlines the effect of nitrogen on properties and structure of two series of glasses: (1) a “bioglass” composition (without P₂O₅) in the Na₂O‐CaO‐SiO₂ system plus Si₃N₄ to give different levels of N and (2) glasses of series (1) with a simple substitution of CaF₂ for CaO. In both cases, the Na:Ca:Si ratio was kept constant so that changes in properties and structure were simply a result of changes in O:N ratio. Properties were all observed to increase linearly with nitrogen content. These increases are consistent with N in the glass structure in 3‐fold coordination with silicon and extra cross‐linking of the glass network. The combination of both nitrogen and fluorine in series (2) glasses gives better mechanical properties at much lower melting temperatures since fluorine reduces Tm, allows higher solubility of nitrogen and does not affect the higher mechanical properties arising from incorporation of nitrogen. The local structure around silicon and nitrogen was investigated by²⁹Si MAS‐NMR spectroscopy which confirms formation of SiO₃N, SiO₂N₂ tetrahedra with extra bridging anions. Bioactivity was assessed and is discussed.