Enhancement of motor functional recovery using immunomodulatory extracellular vesicles-loaded injectable thermosensitive hydrogel post spinal cord injury

Persistence of inflammation during the secondary injury of spinal cord injury (SCI) has been identified as the root cause of poor regenerative capability of spinal cord. M2 microglia derived extracellular vesicles (EVs) have shown therapeutical potential for inflammation alleviation as well as neural regeneration, however their applications in SCI treatment is limited due to issues such as poor accumulation, short retention, and lack of controlled release in lesion tissue. Herein, a novel M2 derived EVs delivery thermosensitive hydrogel system was established harnessing both therapeutic potency of EVs and responsiveness of hydrogel for spinal cord injury. EVs were isolated from IL-4 polarized type2 BV2 cells and incorporated into poly (d, l-lactide)-poly (ethylene glycol)-poly(d,l-lactide) PLEL hydrogel to develop an injectable hydrogel with the properties of thermo-sensitive, anti-inflammation and anti-apoptosis. PLEL thermosensitive hydrogel not only provided sufficient flowability to gain access to injured tissue during injection, but also enabled effective retention and controlled release of delivery cargo once the hydrogel was deployed as the gelation happened quickly at body temperature. In vivo results demonstrated that PLEL/EVs hydrogel successfully improved motor nerve functional recovery post SCI evidenced by elevated BBB scores and reduced scare areas. Mechanistic study revealed that sustained release of EV attenuated the local inflammation via EVs-induced M2 polarization and inhibited the apoptosis of neurons via Bcl-2 pathway, which systematically to protect spinal cord. Therefore, this EVs loaded thermosensitive hydrogel approach provides a microenvironment-responsive and noninvasive route to improve SCI therapy via both anti-inflammatory and neural protective mechanisms.