Viscosity and crystallization of bioactive glasses from 45S5 to 13-93

There has been increasing interest in the use of bioactive glasses for soft and hard tissue regeneration due to their excellent ability in supporting angiogenesis and osteogenesis. Silicate 45S5 glass, discovered by Hench in 1969, remains as the "Gold Standard" in this material family. However, the ability to form 45S5 into complex 3D shapes is challenging due to its tendency to crystallize upon sintering. Another silicate 13-93 glass shows better processing characteristics through viscous flow sintering. Our work attempts to provide a comprehensive understanding of the viscosity and crystallization kinetics on these two glasses and two intermediates between them (designated as 48S1T and 50S2T). Viscosity analysis reveals a low liquidus viscosity and a high fragility index for all four compositions, making it necessary to use a traditional sintering process to produce structures of desired, complex shape. Nonisothermal crystallization kinetics study using differential scanning calorimetry indicates that the two intermediates show better thermal stability than the 45S5 glass and approach that of 13-93 glass. A gradual change in physical properties, thermal stability, and phase assemblage was noticed with the composition transitioning from 45S5 to 13-93. Results from this work suggest the promising attributes in both intermediates 48S1T and 50S2T compositions, making them attractive candidates for further studies for wide biomedical applications.