Cell mechanical microenvironment modulates the secretion phenotype of mesenchymal stem cell-derived exosomes for diabetic wound therapy

Mesenchymal stem cell-derived exosomes represent a promising cell-free therapy for chronic diabetic wounds. However, most existing studies have overlooked the regulatory role of the cell microenvironment, particularly the mechanical cues in the extracellular matrix (ECM) (e.g., matrix viscoelasticity), on exosome biogenesis, as well as the impact of exosomes obtained from theses mechanical microenvironments on the therapeutic efficacy for wound repair. In this study, we engineer two collagen-based hydrogel culture platforms including a photo-crosslinked elastic methacrylated collagen (CMA) and a self-assembled viscoelastic collagen (Col), which exhibit similar fibrous morphologies and elastic moduli but distinct stress-relaxation properties. Bone marrow mesenchymal stem cells (BMSCs) cultured on above matrices produce exosomes (e.g., e-Exos and v-Exos) with markedly different characteristics. Compared to e-Exos, v-Exos display lower particle yield, larger size, and significantly higher protein content per particle, which may be attributed to upregulated Rab27a and downregulated Rab27b, PLD2, SNAP23, and CHMP4b expressions of BMSCs in viscoelastic cell microenvironment. In a streptozotocin-induced diabetic rat model with full-thickness wounds, v-Exos loaded in the PF-127 hydrogel significantly accelerate diabetic wound healing compared to e-Exos, showing enhanced granulation tissue formation, re-epithelialization, and collagen deposition. Particularly, v-Exos reduce TNF-α expression and promote CD163 and CD31 expressions at wound sites, creating a favorable anti-inflammatory environment and facilitating angiogenesis. In vitro studies also confirm that v-Exos effectively promote vascular network formation of endothelial cells and proliferation and migration of fibroblasts compared to e-Exos. Collectively, our findings demonstrate the potential of mechanical preconditioning-driven exosome optimization through matrix viscoelasticity, providing a promising strategy for enhancing the efficacy of exosome-based therapies in diabetic wound healing.