Effect of CaO Content on Textural Properties, Bioactivity, and Cytocompatibility of Sol–Gel-Derived Mesoporous SiO2-CaO-P2O5 Bioactive Glass Nanoparticles

Mesoporous bioactive glass nanospheres are highly porous biomaterials with large specific surface area, which makes them promising platforms for drug delivery and bone regeneration scaffolds due to their controllable release of therapeutic ions and molecules and tunable textural properties via compositional design in the SiO₂–CaO–P₂O₅ system. In this study, three compositions of mesoporous bioactive glass nanospheres in the SiO₂–CaO–P₂O₅ system were synthesized via a CTAB-assisted modified sol–gel method, with CaO varied from 11 to 37 mol%, with a corresponding decrease in SiO₂ while maintaining P₂O₅ at 3 mol%. Nitrogen adsorption–desorption analysis (BET/BJH) confirmed mesoporosity and showed very low hysteresis behavior, with the CaO37 sample exhibiting a specific surface area of 240.62 m 2 /g, a pore volume of 0.424 cm 3 /g, and an average pore size of 2.807 nm. Compared with non-templated sol-gel bioactive glasses (SSA ~ 80–94 m 2 /g; pore volume ≈ 0.006–0.079 cm 3 /g), the CaO37 sample exhibits ~ 156–199% higher specific surface area and more than a fivefold increase in pore volume. SEM/FESEM indicated predominantly spherical nanoparticles, with a tendency toward smaller particle size at higher CaO content. In vitro cytocompatibility tests using L929 fibroblast cells showed no cytotoxic response and revealed favorable cell adhesion and spindle-like morphology. Bioactivity was evaluated by immersion in simulated body fluid (SBF) for 3, 7, and 14 days, and apatite formation was confirmed by SEM and XRD. FTIR analysis revealed CaO-dependent network modification, with reduced Si-O-Si contribution and increased Si-O-Ca (NBO) features (950 cm⁻ 1 ), demonstrating a clear composition–structure–property relationship across the SiO₂–CaO–P₂O₅ series.