Insight into the atomic scale structure of CaF2-CaO-SiO2 glasses using a combination of neutron diffraction, 29Si solid state NMR, high energy X-ray diffraction, FTIR, and XPS

Abstract

Bioactive glasses are important for biomedical and dental applications. The controlled release of key ions, which elicit favourable biological responses, is known to be the first key step in the bioactivity of these materials. Properties such as bioactivity and solubility can be tailored for specific applications. The addition of fluoride ions is particularly interesting for dental applications as it promotes the formation of fluoro-apatite. To date there have been mixed reports in the literature on how fluorine is structurally incorporated into bioactive glasses. To optimize the design and subsequent bioactivity of these glasses, it is important to understand the connections between the glass composition, structure and relevant macroscopic properties such as apatite formation and glass degradation in aqueous media. Using neutron diffraction, high energy X-ray diffraction, 29Si NMR, FTIR and XPS we have investigated the atomic scale structure of mixed calcium oxide/calcium fluoride silicate based bioactive glasses. No evidence of direct Si-F bonding was observed, instead fluorine was found to bond directly to calcium resulting in mixed oxygen/fluoride polyhedra. It was therefore concluded that the addition of fluorine does not depolymerise the silicate network and that the widely used network connectivity models are valid in these oxyfluoride systems.