The long-term stable monitoring of brain signals, including electroencephalogram (EEG), electrocorticogram (ECoG) and local field potential (LFP), is of great significance for the fundamental research in brain science, artificial intelligence and the diagnosis and treatment of brain-related disorders. Therefore, both non-invasive and invasive brain-machine interfaces based on different materials and structures have been widely studied due to their unique performance. Among these materials, hydrogels have emerged as a promising interface material for brain signal collection systems due to their similar mechanical properties to biological tissues, excellent biocompatibility, strong self-adhesive properties, and exceptional ionic conductive characteristics. This review aims to provide an overview on the recent progress of hydrogel-based brain interfaces in the recording of brain signals with non-invasive and invasive methods. It is expected that this paper will serve as a valuable summary and reference for future research in the hydrogel-based brain interface.

The exploration of multi-dimensional brain activity with high temporal and spatial resolution is of great significance in the diagnosis of neurological disease and the study of brain science. Although the integration of electroencephalogram (EEG) with magnetic resonance imaging (MRI) and computed tomography (CT) provides a potential solution to achieve a brain-functional image with high spatiotemporal resolution, the critical issues of interface stability and magnetic compatibility remain challenging. Therefore, in this research, we proposed a conductive hydrogel EEG electrode with an asymmetrical bilayer structure, which shows the potential to overcome the challenges. Benefiting from the bilayer structure with different moduli, the hydrogel electrode exhibits high biological and mechanical compatibility with the heterogeneous brain-electrode interface. As a result, the impedance can be reduced compared with conventional metal electrodes. In addition, the hydrogel-based ionic conductive electrodes, which are free from metal conductors, are compatible with MRI and CT. Therefore, they can obtain high spatiotemporal resolution multi-dimensional brain information in clinical settings. The research outcome provides a new approach for establishing a platform for early diagnosis of brain diseases and the study of brain science.

Biodegradable magnesium (Mg) implants hold immense potential in orthopedics, yet their rapid degradation, insufficient osseointegration, and immune imbalance remain major barriers to clinical translation. This study developed a sodium phytate (SP) passivation layer and an ethyl cellulose (EC) barrier loaded with oleoylserine (OS) multifunctional coating on Mg implant surfaces. This SP-EC-OS coating achieves spatiotemporal synergistic regulation through a triple mechanism of "chemical passivation, barrier isolation, signal-controlled release." The SP layer enhances interfacial bonding strength and corrosion resistance, the EC layer provides a platform for controlled degradation and sustained release, while the continuous release of OS synergistically modulates cellular behavior with Mg²⁺. In vitro results demonstrated that the Mg-SP-EC-OS significantly enhancing corrosion resistance while its programmable release synchronizes with the bone regeneration cascade. More importantly, the synergistic effect of OS and Mg²⁺ promotes osteoblast differentiation and mineralization, inhibits osteoclast activation, and induces macrophage polarization toward the M2 phenotype, achieving immune regulation-driven bone regeneration. In vivo validation of the femoral defect model in rats has shown that Mg-SP-EC-OS implants induce macrophage polarization toward the M2 phenotype through immune regulation, significantly promote new bone formation, reduce bone-implant interface cavities, and maintain excellent systemic biosafety. This multifunctional coating combines corrosion resistance, immunomodulation, and spatiotemporal osteogenic effects, achieving spatiotemporally controlled degradation aligned with the bone healing process. It provides a viable strategy for developing a new generation of degradable magnesium-based orthopedic implants.