SHH-functionalized fibrin scaffold improves spinal cord repair in rats and modulates primary neural stem cell behavior in vitro

The sustained delivery of regenerative cues within the injured spinal cord microenvironment represents a promising strategy for promoting spinal cord injury (SCI) repair. In this study, we developed a fibrin-based scaffold functionalized through the polydopamine (PD)-mediated immobilization of sonic hedgehog (SHH), designated FG/PD@SHH, to achieve localized and sustained SHH delivery. The PD modification increased the SHH loading efficiency from 51.2% to 70.6%, increased the immobilization efficiency from 24.7% to 59.5%, and increased the retention of SHH from 246.6 ± 76.1 to 595.0 ± 8.9 ng per scaffold. The FG/SHH scaffold released 95.3% of the SHH within 3 days, whereas the FG/PD@SHH scaffold released 43.9% by Day 3 and 95.1% by Day 14. In vitro, primary NSCs cultured on FG/PD@SHH scaffolds exhibited enhanced cell–scaffold interactions, increased expression of adhesion- and proliferation-associated genes, increased expression of the neuronal markers growth-associated protein 43 (GAP-43) and class III β-tubulin (TUBB3), and reduced expression of glial fibrillary acidic protein (GFAP). The increased expression of proteins related to the canonical SHH pathway indicated that scaffold-presented SHH retained biological activity. In a rat model of complete spinal cord transection, FG/PD@SHH scaffold implantation improved Basso–Beattie–Bresnahan (BBB) locomotor scores from Day 28 onward. At 12 weeks, the lesion cavity area decreased from 59.6 ± 6.5% in the FG group and 45.7 ± 7.1% in the FG/SHH group to 31.6 ± 5.8% in the FG/PD@SHH group. The mean Nissl-positive cell count increased from 6.8 ± 1.1 in the FG group and 11.7 ± 2.3 in the FG/SHH group to 18.7 ± 3.9 in the FG/PD@SHH group. These findings suggest that the FG/PD@SHH scaffold provides sustained SHH delivery and supports neural tissue repair after SCI.