Physical properties and biocompatibility effects of doping SiO2 and TiO2 into phosphate-based glass for bone tissue engineering.

Phosphate glass is continuing to gain more attention as potential bone substitutes. The ternary (P2O5-CaO-Na2O) is investigated in terms of both physical properties and biocompatibility by doping different percentages of SiO2 and TiO2. Two groups were prepared; the first has different percentages of TiO2 and SiO2, whereas the second group compositions have 5 mol% TiO2 and 5 mol% SiO2 being added to compensate the network-forming oxide P2O5 and the network-modifying oxide CaO. Density, mass loss, pH, DTA, XRD, and cation release experiments were performed to study the physicochemical properties of the compositions, while MG63 and hMS cells were used within in vitro cell culture to study their biocompatibility. Results showed that an increase in TiO2 content correlated with an increase in glass density, decreased mass loss, increased trend of Tg and Tm values, and Na+ and Ca2+ release in group 1. There was no improvement in the MG63 viability or the ability of hMSCs to differentiate into osteoblasts where TiO2 decreased in favour of SiO2. Furthermore, in group 2, 50P2O5-25CaO was less dense than 45P2O5-30CaO, degraded dramatically less, had lower Tg and Tm values and released less Na+ and Ca(2+). The synergistic effect of doping 5 mol% TiO2 and 5 mol% SiO2 increased the MG63 viability in both compositions and was found 45P2O5-30CaO to have promising results in terms of the ability of hMSCs to differentiate into osteoblasts. To conclude, substituting TiO2 in place of SiO2 improved the physical properties and the biocompatibility of (P2O5-CaO-Na2O) glass system, whereas doping 5 mol% SiO2 and 5 mol% TiO2 together in place of P2O5 and CaO had a synergistic effect in controlling their degradation rate and improving their biological responses.

Strontium- and calcium-containing, titanium-stabilised phosphate-based glasses with prolonged degradation for orthopaedic tissue engineering.

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, (31)P 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 Q(1), Q(2) and Q(3) 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.