In vitro assessment of the bioactivity of borate-based bioactive glasses: how different conditions influence hydroxyapatite formation

Abstract This work aimed to assess the bioactivity of synthesized borate-based glasses and examine how different conditions influence the formation of hydroxyapatite (HAp) as a means of evaluating bioactivity in vitro. The prepared glass compositions based on both B 2 O 3 and P 2 O 5 doped with ZnO, CaO and dolomite. Three glass samples were synthesized by the traditional melt and quench process, with the composition (56-x)B 2 O 3 + 28ZnO + 10CaO + 6P 2 O 5 + x dolomite (x = 0.0, 6.0, and 8.0 wt%). The bioactivity of the glass powders was evaluated by immersing them in a simulated body fluid environment (SBF). We systematically investigated the combined effects of dolomite doping and different SBF solution treatment protocols, including the pH-adjusted protocol, static protocol, and refreshed protocol, along with varying immersion times of 7 and 21 days on HAp formation. The samples were immersed in SBF under three conditions: for 7 days with pH maintained at 7.4 (pH-adjusted protocol), for 21 days without changing the SBF solution (static protocol), and for 21 days with the SBF solution refreshed every 48 h (refreshed protocol). Characterization techniques via X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis.) spectroscopy, scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS) were employed before and after immersion in SBF. The amorphous structure, surface composition, and chemical bonding properties were confirmed by analysis prior to immersion. After immersion, HAp formation was detected on the surfaces of the glass powders and revealed its characteristic morphology. The results confirmed the bioactivity of boron-based glass samples and showed that refreshing the SBF solution condition every 48 h yielded the fastest HAp formation, particularly after 21 days of immersion compared to the other conditions (PH-adjusted and static). Although dolomite was added with the expectation of enhancing HAp formation through its calcium content, the results showed a reduction in HAp formation. Nevertheless, dolomite contributed to lowering the melting point of the oxides during glass preparation, while its magnesium content may offer additional biological benefits. Furthermore, its presence positively influenced the optical properties of the glass. These findings underscore the potential of borate-based glasses as promising bioactive materials for bone tissue engineering, emphasizing the critical role of solution management in optimizing bioactivity for biomedical use.