Restoration of spinal cord biophysical microenvironment for enhancing tissue repair by injury-responsive smart hydrogel

Spinal cord injury (SCI) represents a central nervous system disaster, resulting in the destruction of spinal cord structure and function and the formation of an adverse microenvironment at the SCI site. Various biomaterial-based therapeutic strategies have been developed to repair SCI by bridging spinal cord lesions. However, con-structing a favorable biophysical microenvironment with biomaterials for spinal cord regeneration remains challenging because of the unmatched mechanical and electrical transmission properties with native spinal cords and the supra-or subtherapeutic dose release of biological molecules independent of SCI activity. Herein, we developed a new hydrogel with mechanical properties and conductivities comparable to those of native spinal cords by controlling gelatin and PPy concentrations. To endow the hydrogel with a biological function, gluta-thione (GSH) was conjugated on the hydrogel through gelatin-derived amine groups and GSH-derived sulfhydryl groups to prepare an MMP-responsive hydrogel with a recombinant protein, GST-TIMP-bFGF. The MMP-responsive conductive hydrogel could release bFGF on-demand in response to the SCI microenvironment and provide a favorable biophysical microenvironment with comparable mechanical and electrical properties to native spinal cords. In SCI model rats, the MMP-responsive bionic mechanical and conductive hydrogel could inhibit MMPs levels, promote axon regeneration and angiogenesis, and improve locomotion function recovery after SCI.