A dual-functional engineered exosome-laden hydrogel redirects endogenous neural stem cell fate for spinal cord injury repair.

Spinal cord injury (SCI) repair is severely restricted by a hostile post-injury microenvironment that drives endogenous neural stem cells (eNSCs) toward astroglial scar formation rather than neuronal regeneration. Here, we developed a dual-functional "molecule-carrier-scaffold" strategy that combines engineered exosomes with a sustained-release hydrogel to simultaneously remodel the inflammatory niche and redirect eNSCs fate. Human umbilical cord mesenchymal stem cell-derived exosomes were engineered to display a neurotrophic factor cocktail (GDNF/NT3/IGF1; termed EXO(GNI)) and then incorporated into an injectable, in situ photocrosslinkable hydrogel composed of ionic liquid-modified cellulose nanocrystal-reinforced methacrylated silk fibroin (CNCs/SilMA). The resulting EXO(GNI)@CNCs/SilMA scaffold exhibited a biomimetic porous architecture, spinal cord-compatible mechanical properties, and sustained local release of exosomes during the acute-subacute repair window. In a mouse complete spinal cord transection model, a single implantation of EXO(GNI)@CNCs/SilMA attenuated acute neuroinflammation and promoted endogenous repair. Lineage tracing showed that the majority of lesion-region Tuj1(+) cells were derived from the traced endogenous lineage, and EXO(GNI)@CNCs/SilMA significantly reduced astrocytic differentiation while increasing neuronal and oligodendroglial lineage outputs. Mechanistically, EXO(GNI) acted through a dual route: uptake by macrophages/microglia contributed to inflammatory niche modulation, while direct uptake by eNSCs supported fate instruction. Inhibitor studies further indicated that PI3K-AKT and Wnt/Ca(2+)-CaMKII signaling functioned as parallel pro-differentiation modules, with reduced sustained β-catenin signaling associated with neuronal lineage commitment. These cellular and molecular changes were accompanied by improved motor/sensory recovery and electrophysiological conduction. Collectively, this engineered exosome-loaded hydrogel provides a combinatorial biomaterial platform that reshapes the inhibitory SCI niche and harnesses endogenous neural stem cell-based repair.