Extracellular biogenic nanoscale mitochondria reprogram the wound microenvironment via ROS scavenging independent of cellular uptake.

Mitochondria are nanoscale organelles essential for cellular metabolism and redox regulation, making them a compelling target for regenerative therapeutics. Analysis of wound-edge tissues from pediatric patients with chronic non-healing ulcers revealed marked metabolic insufficiency and impaired regenerative signaling, underscoring an unmet clinical need for mitochondrial-based interventions. Here, we show that topically applied mesenchymal stem cell-derived mitochondria (MSC-mt), functioning as naturally derived nanoscale organelles, markedly accelerate wound closure in a murine full-thickness skin injury model. MSC-mt enhanced angiogenesis, collagen deposition, and fibroblast survival while reducing oxidative stress and apoptosis. Mechanistically, their cytoprotective effects occur primarily through extracellular scavenging of reactive oxygen species (ROS), independent of cellular internalization. Excessive immobilization of MSC-mt within a thermosensitive hydrogel compromised their efficacy, emphasizing the importance of mitochondrial mobility and microenvironmental access. Under high oxidative stress, internalized MSC-mt activated PINK1-Parkin-mediated mitophagy, indicating a context-dependent intracellular quality-control response. These findings position MSC-mt as a cell-free, organelle-level nano-therapeutic that operates through a dual extracellular-intracellular mechanism and emphasize the importance of delivery strategies that preserve mitochondrial functionality and spatial freedom.