Polysaccharide hydrogel-reinforced nanofibrous composite promotes annulus fibrosus regeneration by regulating mitochondrial antioxidant and metabolic functions

Nucleotomy, a surgical procedure employed to address nucleus pulposus (NP) herniation, frequently results in defects within the annulus fibrosus (AF). Owing to the inherently limited self-repair ability of AF tissue, untreated lesions may precipitate reherniation of the NP, thereby accelerating the degeneration of the intervertebral disc. In this study, we introduce a novel composite scaffold comprising hydrogel-reinforced electrospun nanofibers, engineered to mimic the heterogeneous microarchitecture of the native AF matrix while offering improved mechanical support. A mesh-like polycaprolactone (PCL)/gelatin methacryloyl (GelMA) hybrid electrospun nanofibrous membrane was designed to replicate the AF outer region, while a hydrogel mixture of fucoidan methacryloyl (FuMA) and GelMA was sprayed to the membrane surface to emulate the inner region. The integrated FuMA/GelMA hydrogel and PCL/GelMA nanofiber layer enhanced the proliferation of AF cells and markedly improved the synthesis of AF matrix components. Importantly, even under oxidative stress induced by hydrogen peroxide, this hydrogel-reinforced nanofibrous composite effectively maintained the mitochondrial functions of AF cells, thereby supporting their energy metabolism and matrix anabolism. Further molecular experiments unraveled that this composite protected AF cells from oxidative damage through activation of the NRF2-mediated antioxidant enzymes, such as heme oxygenase 1. In a rat caudal disc box defect model, the implantation of a hydrogel-reinforced nanofibrous composite promoted the regeneration of AF tissue, preserved the hydration of NP tissue, and inhibited intervertebral disc degeneration. This approach represents a promising strategy for the repair of nucleotomy-induced AF damage, thereby offering potential therapeutic benefits for patients experiencing intervertebral disc degeneration.