Editorial to Special Issue: Polymeric Hydrogels for Flexible Electronics

Hydrogel electronics have recently attracted extensive research interest for great potential for flexible, wearable, and implantable devices for robotics, human-machine interface, and advanced healthcare. Unlike silicon and metal-based traditional electronics, hydrogel electronics are highly stretchable, flexible, and adaptive to biotissues and organs. Conductive hydrogels coated on medical devices can bridge bioelectronics and biotissues to collect biophysical signals or work as electrodes to provide electrical stimulation. Tough, stretchable, and fatigue-resistant hydrogels are needed to endure cyclic loadings. The sensitivity, linearity, and detection of limit are key parameters for hydrogel sensors. Besides, tolerance against harsh environments usually requires resistance against low or high temperatures without losing the mechanical and sensory performances. The sensory performances depend on not only the intrinsic network structures but also the micro-/nanostructures of hydrogel devices. Delicate network designs are needed to achieve high conductivity, high sensitivity, and linear sensing, while diverse micro-/nanostructures are fabricated to amplify the sensitivity. Polymer hydrogel electronics have emerged as new horizons of flexible, wearable, and implantable devices. However, it is still at a very early stage. Key fundamental issues like the sensing mechanisms and structure-sensory performance relationship need extensive and intensive studies. On the other hand, although numerous potential applications are demonstrated, more endeavors are needed to tackle critical issues for practical applications.