Bioactive borate glass-hydroxyapatite composites: Influence of the sintering temperature on structural properties and in vitro bioactivity

Recent research efforts have focused on combining hydroxyapatite (HA) with various bioactive glasses to create composite materials for biomedical applications. This research aimed to develop a new group of hydroxyapatite/borate glass composites and to investigate the influence of sintering temperature in the structural properties and in vitro bioactivity. The composites were synthesized using two concentrations (25/75 wt% and 50/50 wt% - bioactive glass/hydroxyapatite) and two sintering temperatures (530 and 1000 °C). The composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), in vitro bioactivity tests in simulated body fluid (SBF), and pH measurements. XRD and FT-IR analyses were performed before and after immersion in SBF solution. Before immersion in SBF, the composites, heat-treated at 530 °C, do not present additional phase formation. However, at 1000 °C, the composites present an NaCaPO₄ additional phase, due to the hydroxyapatite decomposition. XRD and FT-IR results, after immersion in SBF, confirmed the interaction between the ions from the composite and the ions present in the SBF solution. Composite 50BG_530 showed a silver chloride phase, indicating a potential antibacterial activity. 25BG_1000 presented an increase in the crystallinity of the HA phase, as a function of soaking time. Composite 50BG_1000 showed a decrease of NaCaPO₄ phase and an increase of HA's phase, improving the in vitro bioactivity. Based in these results, all composites presented good potential to be applied in bone regeneration.