Conductive Hydrogels for Invasive Neural Interfaces: From Materials Engineering to Neural Signal Interfacing and Neurorehabilitation

In invasive neural interfaces, mechanical mismatch between traditional rigid electrodes and brain tissue often leads to inflammation and signal attenuation. Conductive hydrogels have emerged as ideal alternative materials due to their tissue-matching modulus, hybrid conductive networks, and wet adhesion properties. In this paper, we provide a narrative review of research progress on conductive hydrogels in invasive neural interfaces: we elucidate electronic, ionic, and hybrid conduction mechanisms; critically compare strategies for modulus matching and interfacial adhesion (such as catechol chemistry and covalent anchoring); and summarize their applications in neural signal recording, electrical/optical modulation, and rehabilitation for spinal cord injury and stroke. Finally, we discuss current challenges regarding long-term stability, wireless integration, and intelligent closed-loop systems and outline future directions involving AI-driven design combined with 3D biomanufacturing.