Control of surface free energy in titanium doped phosphate based glasses by co-doping with zinc

To significantly improve the biocompatibility of titanium doped phosphate based glasses, codoping with zinc has been attempted. This study investigated the effect of doping a quaternary 15Na2O:30CaO:5TiO2:50P2O5 glass with zinc oxide (1, 3, and 5 mol %) on bulk, structural, surface, and biological properties; the results were compared with glasses free from ZnO and/or TiO2. ZnO as adjunct to TiO2 was effective in changing density, interchain bond forces, degradation behavior, and ions released from the degrading glasses. Incorporation of both TiO2 and ZnO in T5Z1, T5Z3, and T5Z5 glasses reduced the level of Zn2+ release by two to three orders of magnitude compared with glasses containing ZnO only (Z5). 31P NMR results for T5Z1, T5Z3, and T5Z5 glasses showed the presence of Q3 species suggesting that the TiO2 is acting as a network former, and the phosphate network becomes slightly more connected with increasing ZnO incorporation. Regardless of their relative lower hydrophilicity and surface reactivity compared with the control glass free from TiO2 and ZnO (T0Z0), these glasses have significantly higher surface reactivity compared with Thermanox®. This has been also reflected in the maintenance of >98% viable Osteoblasts, proliferation rate, and expression level of osteoblastic marker genes in a comparable manner to Thermanox® and T5 glasses, particularly T5Z1 and T5Z3 glasses. However, T0Z0 and Z5 glasses showed significantly reduced viability compared to Thermanox®. Therefore, it can be concluded that ZnO doped titanium phosphate glasses, T5Z1 and T5Z3 in particular, can be promising substrates for bone tissue engineering applications