EV-Functionalized Fish Scale Scaffold Leverages Topographic and Biochemical Cues for Enhanced Bone Regeneration

The repair of critical-size bone defects remains clinically challenging, largely owing to the limited homing and osteogenic capacity of endogenous bone marrow mesenchymal stem cells (BMSCs). To address this, we developed a cell-free strategy that combines a decellularized fish scale (DC-FS) scaffold with stem cell sheet-derived extracellular vesicles (CS-EVs). This design leverages the scale's innate microgrooved topography for directional cell guidance while loading CS-EVs to provide sustained pro-osteogenic cues. The resulting CS-EVs/DC-FS composite retained the intrinsic micro/nanoarchitecture and mineralized composition of the biological scaffold and permitted controlled EVs release. The scaffold promoted directional migration, adhesion, and osteogenic differentiation of BMSCs in vitro, upregulating key markers including RUNX2, OPN, and BMP2. Mechanistically, EV-derived miRNAs, notably miR-146a-5p, were associated with activation of the Sirt1/Wnt/β-catenin signaling pathway. In a rat critical-size calvarial defect model, CS-EVs/DC-FS accelerated bone deposition, improved trabecular microstructure, and enhanced overall regeneration quality. This study establishes a topography-guided and EV-mediated strategy for bone regeneration, offering an integrated nature-derived solution for reconstructing challenging maxillofacial and orthopedic bone defects.