Ion release, hydroxyapatite conversion, and cytotoxicity of boron-containing bioactive glass scaffolds

We report the development and characterization of boron-releasing highly porous three-dimensional bioactive glass (BG) scaffolds fabricated by the foam replica technique. Three types of bioactive glasses with (wt%) 0.2%, 12.5%, 25% B₂O₃, and related varying SiO₂ contents (wt%): 50%, 37.5%, and 25%, were investigated. The well-known 13-93 (silicate) and 13-93B3 (borate) (in wt% – 56.6% B₂O₃, 5.5% Na₂O, 11.1% K₂O, 4.6% MgO, 18.5% CaO, 3.7% P₂O₅) BGs were used as controls to study the influence of the presence of boron on the mechanical properties, surface reactivity, and cytotoxicity of scaffolds. Surface morphology and surface properties of the BG scaffolds were measured. X-ray diffraction (XRD) analyses showed that the scaffolds of all five compositions were amorphous. The scaffolds with 12.5 wt% B₂O₃ exhibited satisfactory compressive strength in the range of 1–2 MPa. A dissolution study in cell culture medium was carried out, and ion release profiles, and apatite formation of the scaffolds were assessed. The cytotoxicity of the scaffolds was evaluated using a stromal cell line (ST2). Cells were found to attach and spread well on the scaffolds' surfaces. We conclude that borosilicate scaffolds containing 12.5 wt% B₂O₃ provide the best combination of properties, including relatively high mechanical strength, apatite formation, and cytocompatibility, and thus, they are promising candidates for bone tissue engineering.