Recent advances in conductive hydrogels for soft biointegrated electronics: Materials, properties, and device applications

Conductive hydrogels have paved the way for recent progress in developing soft bioelectronics devices by addressing mechanical mismatches between soft biological tissues and rigid electronic devices. Compared to traditional wearable devices made from rigid materials, soft hydrogel-based sensors offer superior long-term performance and high-quality biosignal monitoring through conformal contact , low impedance, and a moisturised interface. The choice of materials for conductive hydrogels, particularly conductive fillers, is critical for enhancing their biosignal detection quality and facilitating effective electrical stimulation. In this review article, we highlight recent advances in conductive hydrogel development, focusing on the electrical and mechanical properties of hydrogels relative to the types of conductive fillers used (i.e. carbon-based nanomaterials , conducting polymers , metal-based nanomaterials, and liquid metals). We also explore the application of these hydrogels to various wearable sensors for the physical, electrophysiological, and electrochemical monitoring of body movements, vital signs, and bioanalytes, as well as their application to electrical stimulation. Finally, we discuss the challenges that need to be addressed in the future to further advance hydrogel-based bioelectronic development.