Effect of increasing titanium dioxide content on bulk and surface properties of phosphate-based glasses

There is an ingoing need for more effective and less costly bone substitute materials. In a previous study, addition of titanium dioxide (TiO 2) up to 5 mol.% was shown to be effective in controlling glass degradation, and this was reflected in enhanced gene expression and bone-forming capacity of phosphate-based glasses. In the current study, incorporation of the maximum possible amount of TiO 2 has been attempted in order to further improve the biological response of these glasses. This report describes the physical, surface properties and short-term response of an osteoblast cell line (MG63) on phosphate glasses doped with the maximum possible TiO 2 content. The results showed that a maximum of 15 mol.% TiO 2 can be incorporated into the ternary formulations while maintaining their amorphous nature; such incorporation was associated with a significant increase in density and glass transition temperature. On crystallization, X-ray diffraction analysis showed the presence of TiP 2O 7 and NaCa(PO 3) 3 as the main phases for all TiO 2-containing glasses, while β-(CaP 2O 6) was only detected for 10 and 15 mol.% TiO 2 glasses. The degradation rate, however, was significantly reduced by an order of magnitude with incorporation of 10 and 15 mol.% TiO 2, and this was reflected in the released ions. This change in the bulk properties, produced with TiO 2 incorporation, was also associated with a significant change in the hydrophilicity and surface reactivity of these glasses. Even though the addition of TiO 2 reduced the hydrophilicity and the surface free energy of these glasses compared to TiO 2 free composition, TiO 2-containing glasses still have a significantly reactive surface layer compared to Thermanox ®. Generally glasses with 5–15 mol.% TiO 2 supported MG63 cell growth and maintained high cell viability for up to 7 days culture, which is comparable to Thermanox ®. Based on the results obtained form this study, TiO 2-containing phosphate glasses are promising substrates for bone tissue engineering applications.