Hydrogel-Based Flexible Neural Interfaces for Brain–Computer Interfaces and Neurorehabilitation: A Review

Abstract Hydrogel-based flexible neural interfaces have attracted increasing attention in brain–computer interface (BCI) and neurorehabilitation owing to their softness, conductivity, biocompatibility, adhesion, and tissue adaptability. Compared with conventional metal electrodes, rigid implantable electrodes, and traditional wet/dry EEG electrodes, hydrogels can construct low-impedance, low-damage, and long-term-stable bioelectronic interfaces with the skin, scalp, cerebral cortex, and neural tissues, thereby improving neural signal acquisition quality and wearing comfort. This review systematically summarizes the structural characteristics, conductive mechanisms, mechanical matching, antidrying performance, and biocompatibility of hydrogel materials. It further highlights the design strategies of hydrogel EEG electrodes, ECoG interfaces, implantable microelectrodes, and multifunctional neural interfaces and discusses their roles in BCI signal acquisition, preprocessing, motor intention decoding, and closed-loop control. Hydrogel neural interfaces are expected to be integrated with functional electrical stimulation, exoskeletons, rehabilitation robots, and virtual reality feedback for motor function reconstruction and assistive control in stroke, spinal cord injury, and neurodegenerative diseases. However, challenges remain in long-term stability, signal drift, motion artifacts, biosafety, algorithm generalization, and clinical translation. In the future, the integration of hydrogel-based flexible neural interfaces with artificial intelligence, multimodal sensing, and closed-loop neuromodulation may provide new technical pathways for intelligent and personalized neurorehabilitation.