Sustained release of hydrogen sulfide from anisotropic ferrofluid hydrogel for the repair of spinal cord injury

Spinal cord injury (SCI) results in massive neuronal death, axonal disruption, and cascading inflammatory response, which causes further damage to impaired neurons. The survived neurons with damaged function fail to form effective neuronal circuits. It is mainly caused by the neuroinflammatory microenvironment at injury sites and regenerated axons without guidance. To address this challenge, a ferrofluid hydrogel (FFH) was prepared with Ferric tetrasulfide (Fe 3 S 4 ), carboxymethyl chitosan, and gold. Its internal structural particles can be oriented in a magnetic field to acquire anisotropy. Moreover, Fe 3 S 4 can release hydrogen sulfide (H 2 S) with anti-inflammatory effects under acidic conditions. Regarding in vitro experiments, 0.01g/ml Fe 3 S 4 FFH significantly reduced the inflammatory factors produced by LPS-induced BV2 cells. Oriented and longer axons of the induced neural stem cells loaded on anisotropic FFH were observed. In vivo experiments showed that FFH reduced the activated microglia/macrophage and the expression of pro-inflammatory factors in SCI rats through the NF-κB pathway. Moreover, it significantly promoted directional axonal regrowth and functional recovery after SCI. Given the critical role of inhibition of neuroinflammation and directional axonal growth, anisotropic Fe 3 S 4 FFH is a promising alternative for the treatment of SCI.