Abstract
Human-machine interface (HMI) electrodes enable interactions between humans and bioelectronic devices by facilitating electrical stimulation and recording neural activity. However, reconciling the soft, hydrated nature of living human tissues with the rigid, dry properties of synthetic electronic systems is inherently challenging. Overcoming these significant differences, which is critical for developing compatible, effective, and stable interfaces, has become a key research area in materials science and technology. Recently, hydrogels have gained prominence for use in HMI electrodes because these soft, hydrated materials are similar in nature to human tissues and can be tuned through the incorporation of nanofillers. This review examines the functional requirements of HMI electrodes and highlights recent progress in the development of polyphenol-mediated multifunctional hydrogel-based HMI electrodes for bioelectronics. Furthermore, aspects such as mussel-inspired and polyphenol-mediated adhesion, underlying mechanisms, tissue-matching mechanical properties, electrochemical performance, biocompatibility, biofouling resistance, stability under physiological conditions, anti-inflammatory, and antioxidant properties are discussed. Finally, applications in bioelectronics and further perspectives are outlined. Advances in HMI hydrogel electrodes are expected to facilitate the unprecedented integration of biological systems and electronic devices, potentially revolutionizing various biomedical fields and enhancing the capabilities and performance of bioelectronic devices.