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Strontium- and calcium-releasing, titanium-stabilised phosphate-based glasses with a controlled degradation rate are currently under development for orthopaedic tissue engineering applications. Ca and/or Sr were incorporated at varying concentrations in quaternary phosphate-based glasses, in order to promote osteoinduction. Ti was incorporated at a fixed concentration in order to prolong degradation. Glasses of the general formula (P2O5)–(Na2O)–(TiO2)–(CaO)–(SrO) were prepared via the melt-quench technique. The materials were characterised by energy-dispersive X-ray spectroscopy, X-ray diffraction, 31P magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential thermal analysis and density determination. The dissolution rate in distilled water was determined by measuring mass loss, ion release and pH change over a two-week period. In addition, the cytocompatibility and alkaline phosphatase activity of an osteoblast-like cell line cultured on the surface of glass discs was assessed. The glasses were shown to be amorphous and contained Q1, Q2 and Q3 species. Fourier transform infrared spectroscopy revealed small changes in the glass structure as Ca was substituted with Sr and differential thermal analysis confirmed a decrease in crystallisation temperature with increasing Sr content. Degradation and ion release studies also showed that mass loss was positively correlated with Sr content. These results were attributed to the lower electronegativity of Sr in comparison to Ca favouring the formation of phosphate-based mineral phases. All compositions supported cell proliferation and survival and induced at least 2.3-fold alkaline phosphatase activity relative to the control. Glass containing 17.5 mol% Sr had 3.6-fold greater alkaline phosphatase activity than the control. The gradual release of Ca and Sr supported osteoinduction, indicating their potential suitability in orthopaedic tissue engineering applications.

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Gallium-doped phosphate-based glasses (Ga-PBG) were assessed for their impact on Streptococcus mutans and dental mineralisation, firstly by disc diffusion assays followed by biofilms grown on nitrocellulose filter membrane (NFM) and constant-depth film fermentor (CDFF). Short-time exposure (10 min) effects of Ga-PBG on S. mutans biofilm were compared with that of 0.2% chlorhexidine. The effects of Ga-PBG on bovine enamel (which was investigated under pH-cycling condition) and dentine were analysed using transverse microradiography (TMR), profilometry and inductively coupled plasma optical-emission spectrometry (ICP-OES). The disc diffusion assays showed inhibition zones of 24.5 ± 0.5 mm for Ga-PBG compared with controls (C-PBG). Ga-PBG showed statistically significant growth inhibition of S. mutans biofilms on NFM (p = 0.001) and CDFF (p < 0.046) compared with hydroxyapatite (HA) and C-PBG. The CDFF assay revealed a maximum of 2.11 log colony-forming unit (CFU) reduction at 48 h, but short-time exposure effects were comparable with that of 0.2% chlorhexidine only on older biofilms (maximum of 0.59 vs. 0.69 log CFU reduction at 120 h). TMR analyses of the enamel revealed non-significant mineral loss (p = 0.37) only in the case of Ga-PBG samples compared with controls including sodium fluoride. ICP-OES analyses indicated transient gallium adsorption into dentine by calcium displacement. The results confirmed that gallium inhibited S. mutans growth and appears to have the potential to protect the enamel surface under conditions representative of the oral environment. Further work is needed to establish whether it has an application in daily oral hygiene procedures to prevent or reduce caries.