CaO–SiO2–P2O5–B2O3-Based Bioactive Glass (BGS-7) Macrobeads Incorporated in Hydrogels Aid Bone Regeneration: Evaluation in Rabbit Calvarial and Femoral Defect Models

Bone graft substitutes are extensively investigated for addressing critical-size bone defects; however, their efficacy is limited by inadequate bone regeneration and subpar handling properties. Herein, we compared the bone regenerative capacity of CaO-SiO₂-P₂O₅-B₂O₃-based bioactive glass (BGS-7) macrobeads with that of β-tricalcium phosphate (β-TCP) beads and evaluated their performance when incorporated into hydrogels to improve their handling properties. BGS-7 macrobeads were fabricated via alginate crosslinking and heat treatment, and their physicochemical properties and microstructures were characterized. In a rabbit calvarial defect model, BGS-7 macrobeads, heat-treated at 600 and 800 °C, exhibited superior bone bridging and degradation than size-matched β-TCP macrobeads. To further evaluate their regenerative potential, critical-size defects (6 mm diameter × 10 mm depth) were created in the rabbit femoral condyle. To enhance clinical applicability, BGS-7 beads were incorporated into cellulose-based hydrogels and implanted into the defects. Radiographic and histomorphometric analyses demonstrated that bone formation and stable fixation achieved with hydrogel formulations containing BGS-7 microbeads and Laponite were more pronounced than those with BGS-7 beads alone. The findings suggest that BGS-7 macrobeads, particularly when combined with microbead- and Laponite-containing hydrogels, represent a promising bone graft substitute with improved regenerative and handling properties compared with using BGS-7 beads alone.