Split-Type Microneedles Loaded with miR-125b-Enriched Extracellular Vesicles: A Sustained Preventive and Therapeutic Platform for Nitrogen Mustard-Induced Skin Injuries.

Nitrogen mustard (NM) induces severe, refractory skin injuries lacking specific available therapeutics. Considering that extracellular vesicles (EVs) show promising effects in wound healing, we developed a split-type microneedle (MN-EVs@miR) loaded with miR-125b-enriched engineered EVs (EVs@miR) to treat NM-induced skin injury. EVs were isolated from human umbilical cord mesenchymal stem cells (hUMSCs), loaded with miR-125b via transfection, and then conjugated to hyaluronic acid methacryloyl (HAMA) hydrogel using acrylic acid-polyethylene glycol-N-hydroxysuccinimide (AC-PEG-NHS) to prepare microneedle tips, with polyvinyl alcohol (PVA) and sodium thiosulfate constituting the substrate. The prepared MN-EVs@miR exhibited sufficient mechanical strength (0.34 N/needle), sustained EVs@miR release over 21 days, and long-term in vivo retention (>21 days) with excellent biocompatibility. In vitro, EVs@miR enhanced cell viability, inhibited apoptosis, regulated inflammation (downregulating TNF-α, IL-1β, and IL-6; upregulating IL-10), and promoted angiogenesis. In vivo, MN-EVs@miR significantly mitigated NM-induced skin blistering and necrosis, with superior wound healing efficacy compared to that of EVs@miR injection and blank MNs. In conclusion, the split-type MN-EVs@miR provides a promising preventive and therapeutic strategy for NM-induced skin injuries with potential battlefield and clinical applications.