Incorporation of B2O3 in CaO-SiO2-P2O5 bioactive glass system for improving strength of low-temperature co-fired porous glass ceramics

Bioactive glass ceramics (BGCs) have different rates of biodegradation and mechanical properties depending on their chemical compositions and sintering temperatures. The present study was aimed to develop the boron-rich, phosphorus-low CaO–SiO₂–P₂O₅–B₂O₃ bioactive glasses (BG-B_x, X = 0, 10, 20) potentially for improving the mechanical properties of BGCs via low-temperature co-fired process. The B₂O₃-free BG-B₀ shrunk well at ~ 726 °C and melted at over 1050 °C, while the onset shrinking and melting temperatures of the 20 mol% B₂O₃-doped BG-B₂₀ was lowered to ~ 648 °C and ~ 952 °C, respectively. The BG-B₂₀ thermally treated at 850–950 °C was transformed into wollastonite and calcium borate, and crystallization decreased the kinetics but did not inhibit the development of hydroxyapatite on their powder and disc surface when immersed in simulated body fluid. The in vitro degradation in Tris buffer confirmed that the degradation rate markedly increased with increasing boron content in BG-B_x. The compressive strength and flexural strength of the 10% BG-B₂₀-reinforced 45S5 porous BGC sintered at 850 °C was nearly four times than that of 45S5 porous constructs. These studies suggest that the boron-rich, phosphorus-low CaO–SiO₂–P₂O₅–B₂O₃ system is a promising biomaterial and potential low temperature co-fired aid for improving the mechanical and biological properties of porous BGCs.