Developing bioactive glasses (BGs) with enhanced therapeutic properties for biomedical applications remains an interesting focus in tissue engineering and regenerative medicine. The chemical composition of a BG has a significant effect on bioactivity and biological properties [1]. Borate BGs, compared to silicate BGs, are a matter of interest due to a higher bioactivity rate and complete dissolution. In the last few years, there has been increasing interest in the incorporation of various elements in the glass network for synthesising bioactive glasses with enhanced biological effects [2]. Selenium has been reported as a therapeutic ion that, when incorporated into the silicate BG structure, shows enhanced bioactivity, antibacterial properties, and selective toxicity for cancerous cells at specific concentrations [3].

In this study,1393-B3 borate BG (54.6 % B2O3, 6 % Na2O, 7.9 % K2O, 7.7 % MgO, 22.1 % CaO, 1.7 % P2O5 in mol%) was synthesized by the melt-quenching method as reported in reference [4]. Selenium was incorporated in 1393-B3 borate BG, producing 1Se, 2Se, and 3Se glasses. According to ICP-OES, the composition of the reference 1393-B3 glass was validated, and SeO2 was incorporated at 0.05 mol %, 0.46 mol %, and 0.50 mol % in 1Se, 2Se, and 3Se structures, respectively. X-ray diffraction (XRD) analysis indicated that all melted glasses were amorphous. Fourier transform infrared spectroscopy (FTIR) data revealed that increasing Se content might generate weaker B-O-B bonds due to the modifier role of Se in the glass. Differential thermal analysis (DTA) revealed an increase in the glass transition temperature (Tg) and the onset of crystallization (Tc) due to a minor improvement in network connectivity following the initial addition of selenium in 1Se. Nevertheless, additional Se in the glass structure in 2Se and 3Se samples decreased Tg and Tc values. The biocompatibility evaluation of all BGs was followed through an indirect WST-8 cell viability assay. MG-63 osteosarcoma cells survived in extracts of 1393-B3, 1Se, and 2Se BGs at 0.1 % concentration after 24 h of exposition to glass extracts, indicating cell viability. The 3Se BGs, which contain almost ~ 10 times more Se than 1Se, showed toxic effects on the cells under the same conditions. The 1393-B3 and 1Se samples indicated more than 90 % viability of the cells at this concentration after 72 h incubation. The ICP-OES analysis revealed that the reduced cell viability observed in 2Se and 3Se may be attributed to the increased release of Se ions, which was found to be 7- and 12-fold higher, respectively, compared to 1Se in cell medium after 72 hours. These findings underscore the potential of Se-doped borate-based glasses for biomedical applications.