Aspirin-induced mesenchymal stem cell-derived extracellular vesicles promote osteochondral regeneration by reprogramming macrophages.

Persistent inflammatory responses in osteochondral defects produce a hostile microenvironment that severely compromises endogenous tissue repair mechanisms. The local immune microenvironment needs to be modulated to facilitate tissue regeneration. In this study, an innovative bioactive platform was engineered that combined aspirin-induced bone marrow mesenchymal stem cells (BMSCs)-derived extracellular vesicles (Asp-EVs) and a thermoresponsive hydrogel (mPEP) composed of monofunctional polyhedral oligomeric silsesquioxane (mPOSS), polyethylene glycol (PEG), and polypropylene glycol (PPG). We investigated whether mPEP hydrogel-loaded Asp-EVs can enhance osteochondral regeneration by regulating the inflammatory microenvironment and elucidated the underlying mechanisms involved. According to the findings of in vitro experiments, Asp-EVs significantly improved the growth and migration of BMSCs and promoted M1φ-to-M2φ macrophage polarization. Under inflammatory conditions, Asp-EVs restored the chondrogenesis of BMSCs to levels comparable to those of the control group. In vivo, Asp-EVs delivered via the mPEP hydrogel achieved robust osteochondral regeneration in a rat knee defect model, restoring the hyaline-like cartilage and subchondral bone structure. Asp-EVs activated the PINK1/Parkin-mediated mitophagy pathway, rescuing mitochondrial dysfunction and reprogramming the metabolism of macrophages from glycolysis to oxidative phosphorylation and promoting M2φ polarization. These results suggested that the delivery of Asp-EVs via mPEP hydrogels is a promising strategy for osteochondral regeneration.