Nerve Growth Factor-Laden Anisotropic Silk Nanofiber Hydrogels to Regulate Neuronal/Astroglial Differentiation for Scarless Spinal Cord Repair

Scarless spinal cord regeneration remains a challenge due to the complicated microenvironment at lesion sites. In this study, the nerve growth factor (NGF) was immobilized in silk protein nanofiber hydrogels with hierarchical anisotropic microstructures to fabricate bioactive systems that provide multiple physical and biological cues to address spinal cord injury (SCI). The NGF maintained bioactivity inside the hydrogels and regulated the neuronal/astroglial differentiation of neural stem cells. The aligned microstructures facilitated the migration and orientation of cells, which further stimulated angiogenesis and neuron extensions both <i>in vitro</i> and <i>in vivo</i>. In a severe rat long-span hemisection SCI model, these hydrogel matrices reduced scar formation and achieved the scarless repair of the spinal cord and effective recovery of motor functions. Histological analysis confirmed the directional regenerated neuronal tissues, with a similar morphology to that of the normal spinal cord. The <i>in vitro</i> and <i>in vivo</i> results showed promising utility for these NGF-laden silk hydrogels for spinal cord regeneration while also demonstrating the feasibility of cell-free bioactive matrices with multiple cues to regulate endogenous cell responses.