In situ implantable and reactive oxygen species responsive hydrogel loaded with minocycline for functional rehabilitation of traumatic brain injury

Traumatic brain injury (TBI) currently lacks an effective clinical drug for treatment. Given the pivotal role of the neuroinflammatory response regulated by microglia in the pathological cascade following TBI, targeting microglial anti-inflammatory polarization with pharmacological agents has emerged as a promising therapeutic strategy. However, challenges remain due to the poor brain-targeting ability and low bioavailability of these drugs. To address this limitation, we developed reactive oxygen species (ROS)-responsive injectable hydrogels loaded with minocycline hydrochloride via the Michael addition reaction between 8-arm acrylated polyethelye glycol (PEGA) and dithiothreitol (DTT). In vitro studies demonstrated that the hydrogel exhibits ROS-responsive release behavior, triggered by the elevated ROS levels that occur during the acute phase of TBI. This allows for rapid minocycline release, effectively modulating local inflammation and exerting neuroprotective effects. Furthermore, the hydrogel's sustainable minocycline release over an extended period, continuously regulating microglial anti-inflammatory polarization and enhancing neuroplasticity during the chronic phase, when ROS levels gradually decline. In vivo experiments, including Western blotting, polymerase chain reaction, immunofluorescence staining, hematoxylin-eosin staining, and behavioral assessments, conclusively demonstrated that minocycline-loaded hydrogels effectively regulate microglial anti-inflammatory polarization, leading to improved neuroplasticity and recovery of neurological function in TBI mice. Additionally, minocycline was found to modulate microglial polarization towards an anti-inflammatory phenotype by downregulating interferon regulatory factor 5 (IRF5) and upregulating interferon regulatory factor 4 (IRF4). Overall, the ROS-responsive hydrogel developed in this study holds great promise as a drug delivery system and may significantly enhance the clinical application of minocycline in TBI rehabilitation.