A chitosan-based composite scaffold as a bioactive strontium-delivery system mediating accelerated bone regeneration

Bone defects caused by trauma, tumor resection, or infection represent significant clinical challenges in orthopaedic practice. Current bone graft materials are often limited by suboptimal osteogenic capacity, donor site morbidity, and insufficient mechanical properties. In this study, we developed a composite bone regeneration scaffold composed of chitosan, silk fibroin fibers, and strontium alginate microspheres (CS/SF@SrAlg) via microfluidic electrospray coupled with fiber fragmentation-recombination techniques. This chitosan-based composite scaffold combines excellent biocompatibility, wide availability, and enhanced mechanical properties. Chemical cross-linking and physical interactions among the components facilitated the formation of a composite system for controlled Sr²⁺ release. The scaffold exhibits a hierarchically porous architecture that promotes cellular infiltration, while the silk fibroin fibers improve mechanical integrity and help maintain an optimal microenvironment. In vitro experiments demonstrated that the scaffold significantly enhanced cell proliferation, migration, and osteogenic mineralization, with a cell proliferation rate of more than 120%. In a rat calvarial defect model, the scaffold markedly promoted angiogenesis and osteogenesis, with 81.8% ± 1.48% bone regeneration coverage observed at 8 weeks post-implantation. Mechanistically, RNA transcriptomics revealed that it promoted osteogenesis through modulation of the key PI3K-Akt signaling pathway. Collectively, the CS/SF@SrAlg scaffold represents a promising biomaterial strategy for bone defect repair with substantial potential for clinical application.