Injectable hydrogel microspheres encapsulating extracellular vesicles derived from melatonin-stimulated NSCs promote neurogenesis and alleviate inflammation in spinal cord injury

Spinal cord injury (SCI) is a devastating condition that results in sensory and motor dysfunctions below the injury site. Currently, there is no effective treatment. Extracellular vesicles (NEVs) derived from neural stem cells (NSCs) have shown promising potential in exerting neuroprotective effect. However, the limited yield and quality of NEVs restrict their further application. Melatonin, an indolamine hormone that is released from the pineal gland, was used in the present study to enhance the secretion and therapeutic effects of NEVs. Compared with original NEVs, NEVs derived from melatonin-pretreated NSCs (MNEVs) exhibited improved neuroregenerative and anti-inflammatory properties in vitro. Furthermore, to achieve prolonged retention in vivo, MNEVs were encapsulated in GelMA hydrogel microspheres (MNEVs@GM). After encapsulation, MNEVs effectively accumulated at the site of injury over a 28-day period. The injection of MNEVs@GM successfully improved motor function recovery in SCI model mice. Subsequently, MNEVs@GM inhibited the uncontrollable inflammatory response after SCI by increasing M2 macrophage polarization; in addition, MNEVs released from MNEVs@GM exerted neuroprotective effects by promoting axonal regeneration and remyelination. Collectively, these findings reveal a promising cell-free approach for suppressing inflammation and promoting neural regeneration to treat SCI.