Self-powered functional hydrogel bioelectronics: From material design to biomedical applications

<h2>Summary</h2> Hydrogels, prized for tissue-like properties and biointegration, are crucial for sustainable, self-powered wearable/implantable devices. However, adoption is hindered by low energy output, robustness issues, integration complexity, environmental sensitivity, and biosafety concerns. This review synthesizes recent advances in hydrogel-based piezoelectric and triboelectric nanogenerators (PENGs/TENGs). It outlines their fundamental principles and different design architectures. Key synthetic and natural polymer properties are examined, summarizing material/structural innovations to boost energy output while discussing potential trade-offs. Critical hydrogel properties for biomedical use, tunable adhesion, mechanics, self-healing, environmental adaptability, biocompatibility and degradation, and injectability are systematically reviewed, detailing current design strategies. Practical applications explored include wearable energy harvesters, human-computer interfaces, physiological monitoring, and bioelectronic medicine, with discussions of device implementation and clinical translation. Finally, the review covers remaining research gaps and emerging directions in self-powered functional hydrogel bioelectronics, providing insights to advance soft bioelectronics and self-powered wearables.