Curcumin-encapsulated exosomes in bisphosphonate-modified hydrogel microspheres promote bone repair through macrophage polarization and DNA damage mitigation

Repairing critical-sized bone defects represents a major challenge in clinical therapeutics due to inhibited osteogenic differentiation, harsh bone tissue microenvironment, and abnormal inflammatory response. Mesenchymal stem cell-derived exosomes (MSC-Exos) have demonstrated tremendous regenerative potential in tissue repair. However, the confined therapeutic efficacy, deficient targeting capability, and poor retention rate have rendered MSC-Exos-based cell-free therapies insufficient for clinical bone defect repair. This study prepared curcumin-loaded MSC-Exos (Cur@Exos) based on an endogenous drug delivery approach and encapsulated in bisphosphonate-modified GelMA hydrogel microspheres by microfluidics. The CE@BP-Gel microspheres demonstrated superior biocompatibility and were competent to accelerate biomineralization. The sustained-release Cur@Exos in the composite hydrogel microspheres actively regulated the polarization of RAW264.7 cells toward the regenerative M2 type and inhibited the osteoclastic activity, thereby creating an immune microenvironment suitable for osteogenesis. Meanwhile, the composite hydrogel microspheres can directly support the adhesion, proliferation and osteogenic differentiation of BMSCs and facilitate the migration and angiogenesis of HUVECs. <i>In vivo</i> experiments demonstrated that the CE@BP-Gel microspheres significantly accelerated the repair of critical-sized cranial bone defects in SD rats. The targets and mechanisms of action of CE@BP-Gel in bone immune regulation were investigated based on network pharmacology, molecular dynamics simulation and RNA sequencing. It was found that CE@BP-Gel mitigates DNA damage induced by ROS in inflammatory environments. The encapsulated curcumin enhances DNA damage repair by activating the TDP1 enzyme, consequently reducing the expression of inflammatory factors in macrophages. This study demonstrates a promising therapeutic strategy to design an exosome-based drug delivery system for bone defect repair.