Multifunctional injectable hydrogel promotes functional recovery after stroke by modulating microglial polarization, angiogenesis and neuroplasticity

A precursor solution loaded with BDNF and VEGF is injected into the brain cavity of a stroke mouse induced by the photothrombotic method and then gelated in situ to form a multifunctional hydrogel. An in vitro release test showed that BDNF and VEGF can be sustainably released within three weeks. The multifunctional hydrogel shows the highest cell viability and affinity to brain microvascular endothelial cells (BMECs), whereas primary neurons cultured with it exhibit the best morphology, the highest expression of synaptic plasticity-related proteins and the greatest ability to inhibit apoptosis. This further shows that the encapsulated VEGF and BDNF in the multifunctional hydrogel play roles in angiogenesis and neuroplasticity via the VEGF-VFGPR2 and BDNF-TrkB pathways, respectively. Additionally, they may have a synergistic effect on enhancing angiogenesis and neuroplasticity. Furthermore, the addition of BDNF can modulate the polarization of BV2 cells toward an anti-inflammatory phenotype in vitro. The colocalization of CD31/Ki67 staining showed that treatment with the multifunctional hydrogel can lead to maximum angiogenesis in the peri-infarct zone of stroke mice, whereas IBA-1/iNOS and IBA-1/CD206 staining showed that it modulates the polarization of activated microglia toward an anti-inflammatory phenotype in vivo. Finally, PSD-95/Vglut1 staining showed the best synaptic plasticity after treatment with the multifunctional hydrogel, and ethological observations, including rotarod, foot fault and balance beam tests, demonstrated the best motor recovery of stroke mice. Consequently, the multifunctional hydrogel can significantly promote poststroke rehabilitation by regulating microglial polarization and enhancing angiogenesis and neuroplasticity.