Synthesis, characterization and solubility analysis of amorphous SiO2-CaO-Na2O-P2O5 scaffolds for hard tissue repair

The substitution of TiO2 with network modifiers (sodium, Na+ and calcium, Ca2+) within a bioactive glass series was investigated to synthesize amorphous scaffolds from the SiO2-CaO-Na2O-P2O5 glass system. Three glasses were formulated for this study, a control (BG) and two experimental formulations with 9 wt% TiO2 substituted for CaO (SC-1) and Na2O (SC-2) respectively. X-ray diffraction presented an amorphous pattern for BG and SC-1, with extensive crystallinity present in SC-2. Differential thermal analysis presented a higher Tg for SC-1 (559 °C) and SC-2 (627 °C) compared to BG (531 °C), however a greater distribution of Q-species was evident in SC-1 and SC-2, particularly in the Q1-Q2 regions as evidenced by MAS-NMR. Simulated Body Fluid (SBF) testing presented calcium phosphate (CaP) deposition on BG however no visible CaP layer was observed on the surface of SC-1 and SC-2. Ion release profiles exhibited a much slower Si release rate with respect to time for SC-1 and SC-2, which may be the limiting factor when tested in SBF. The addition of TiO2 to the glass stabilized the pH during SBF testing and significantly increased the hardness compared to the control BG. Scaffold fabrication was conducted with SC-1, and a porous amorphous structure was synthesized at 635 °C.