Injectable Porous Microspheres Loaded With Biomimetic Preconditioned Bone Marrow Mesenchymal Stem Cell-Derived Exosomes for Vascularized Bone Regeneration

Critical-sized bone defects remain a highly challenging clinical problem due to insufficient intrinsic self-healing capacity. Bone marrow mesenchymal stem cell (BMSC)-derived exosomes have emerged as promising cell-free therapeutic candidates for bone regeneration, owing to their paracrine effects in regulating bone regeneration-related processes. However, enhancing exosome bioactivity via biomimetic preconditioning and developing efficient delivery vectors remain key bottlenecks in this field. Herein, we developed a synergistic bone regenerative system composed of biomimetic preconditioned BMSC-derived exosomes (BioPre-Exos) and injectable porous polydopamine (PDA)-modified gelatin methacryloyl (GelMA) microspheres. The biomimetic preconditioning strategy adopted 3% hypoxia combined with 3D GelMA microsphere culture, mimicking the bone marrow microenvironment to regulate BMSC functions and significantly boost exosome bioactivity. Functional experiments verified that BioPre-Exos robustly promoted BMSC migration, osteogenic differentiation, angiogenesis, and macrophage polarization toward an anti-inflammatory phenotype in vitro. Furthermore, in a rat femoral condyle defect model, the composite system markedly improved neovascularization density and bone volume fraction, thus achieving efficient vascularized bone regeneration. These findings indicate that this cell-free biomimetic synergistic delivery system holds great application potential in the clinical treatment of bone defects.