Optimizing Bioactive Glass-Nanoparticle-Polymer Blend Scaffolds: A Shift in Bone Regeneration Design

Scaffolds for bone tissue engineering have traditionally been designed to mimic the inorganic-to-organic ratio of mature bone, aiming to recapitulate its mechanical properties. However, early bone repair is not characterized by immediate mechanical strength but rather by materials that highly promote osteogenesis. In this study, we present the fabrication and evaluation of composite scaffolds composed of bioactive glass nanoparticles (BGNPs), silk fibroin, gelatin, and alginate, designed to optimize the ratio of inorganic BGNPs to biological polymers to enhance both biocompatibility and osteogenic potential. Characterization of the scaffolds revealed that the balance between BGNP and polymer content significantly influenced their structural and functional properties. Thermogravimetric analysis (TGA) showed a positive correlation between polymer content and scaffold water retention, while differential TGA(DTG) indicated that BGNPs improved the thermal stability of the polymer matrix. Swelling and biodegradation studies demonstrated that scaffolds with higher polymer content absorbed more water and degraded faster, creating a more dynamic environment conducive to cell activity. Uniaxial compression testing demonstrated that scaffolds with balanced compositions exhibited mechanical properties resembling those of the soft callus. In vitro biocompatibility tests demonstrated that scaffolds with higher polymer content were noncytotoxic, whereas those with excessive BGNPs reduced cell viability. Scaffolds with balanced compositions (Polymer blend: BGNPs = 9:1 and 7:3) showed significantly enhanced cell viability and osteogenicity, as indicated by increased alkaline phosphatase activity. Surprisingly, the optimal ratios resembled those of the soft callus, rather than mature bone. Based on these findings, we propose that scaffold designs should mimic the inorganic-to-organic composition of the soft callus, formed in the early stages of bone repair, as this composition better promotes osteogenesis. Optimizing the BGNP-to-polymer ratio is crucial for creating biomaterials that will achieve long-term clinical success.