Immunomodulatory-osteogenic dual-functional nanofibers augment screw anchorage in osteoporotic bone.

Screw fixation remains the primary clinical strategy for osteoporotic fractures (OPF). However, impaired osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and limited cellular migration often lead by osseointegration failure and screw loosening. Inspired by the architectural concept of "column-interface synergistic load-bearing", we developed a polydopamine-functionalized coaxial electrospun nanofiber scaffold (S-MS-PDA) to address both biological and mechanical fixation challenges at the screw-bone interface. The scaffold's coaxial design enabled the spatiotemporal sequential release of bioactive factors, including SDF-1 and P24, precisely modulating MAPK, JAK-STAT, Wnt, and bone remodeling pathways. This approach promoted BMSCs recruitment and osteogenic differentiation, rapidly establishing an early osteogenic microenvironment. Additionally, polydopamine-mediated interface engineering created a biomimetic transition zone, improving mechanical compatibility between the screw and bone and modulating local inflammation. In a rat osteoporosis model, the S-MS-PDA scaffold significantly reduced interfacial stress concentration and enhanced the bone-implant contact by 3.31 fold. This study presents a novel scaffold system that integrates biological activation with mechanical reinforcement, offering a promising tissue engineering strategy for the internal fixation of osteoporotic fractures.