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

ABSTRACT 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.