Injectable chitosan-based hydrogel via in situ gelation modulates the inflammatory microenvironment and facilitates minimally invasive repair of peripheral nerve injury

Non-transecting peripheral nerve injuries require effective inflammation control, support of axon regeneration, and strategies that minimize additional surgical trauma. Injectable hydrogels are attractive carriers for local therapy, and chitosan is a widely used biocompatible matrix; however, conventional chitosan systems often depend on acidic dissolution and crosslinking or cytotoxic crosslinkers, which may aggravate nerve injury and hinder clinical translation. Here, we develop an injectable chitosan-based hydrogel (IBU-CS-GP) in which ibuprofen is complexed with chitosan for solubility range expansion toward near-neutral pH, thereby permitting genipin-mediated crosslinking under near-physiological pH and resolving the mismatch between chitosan solubility and the optimal pH for genipin. The resulting hydrogel forms a stable depot after perineural injection, enabling minimally invasive in situ gelation and localized drug delivery. We characterize its physicochemical properties, ibuprofen release profile, and biosafety, and evaluate its immunomodulatory and pro-regenerative effects in vitro and in a rat sciatic nerve crush model. In vitro, the IBU-CS-GP hydrogel suppresses macrophage inflammatory activation and reduces pro-inflammatory mediator production, thereby promoting a repair-supportive phenotype; in parallel, it indirectly enhances endothelial and stromal cell activities involved in angiogenesis and matrix remodeling. In vivo, perineural injection results in sustained ibuprofen release, accompanied by accelerated recovery of gait and nerve conduction, better preservation of gastrocnemius muscle mass and architecture, and more organized axon regeneration. These data suggest that the IBU-CS-GP hydrogel is a promising minimally invasive local therapy for non-transecting peripheral nerve injuries, as it enables near-neutral-pH in situ gelation and modulates the post-injury microenvironment.