Natural living systems such as wood frogs develop tissues composed of active hydrogels with cryoprotectants to survive in cold environments. Recently, hydrogels have been intensively studied to develop stretchable electronics for wearables and soft robots. However, regular hydrogels are inevitably frozen at the subzero temperature and easily dehydrated, and have weak surface adhesion. Herein, a novel hydrogel-based ionic skin (iSkin) capable of strain sensing is demonstrated with high toughness, high stretchability, excellent ambient stability, superior anti-freezing capability, and strong surface adhesion. The iSkin consists of a piece of ionically and covalently cross-linked tough hydrogel with a thin bioadhesive layer. With the addition of biocompatible cryoprotectant and electrolyte, the iSkin shows good conductivity in wide ranges of relative humidity (15-90%) and temperature (−95-25 °C). In addition, the iSkin can adhere firmly to diverse material surfaces under different conditions, including cloth fabric, skin, and elastomers, in both dry and wet conditions, at subzero temperature, and/or with dynamic movement. The iSkin is demonstrated for applications including strain sensing on both human body and winter coat, human-machine interaction, motion/deformation sensing on a soft gripper and a soft robot at extremely cold conditions. This work provides a new paradigm for developing high-performance artificial skins for wearable sensing and soft robotics.

The rapid development of stretchable electronics and soft robotics requires a sustainable power source that can match their mechanical stretchability in various working environments. Ionic hydrogel-based soft triboelectric nanogenerators (TENGs) show great promise for those application scenarios. However, ionic hydrogel-based TENGs suffer from the freezing issue under subzero temperatures. In this study, a low-cost, highly stretchable, and antifreezing ionic triboelectric nanogenerator (iTENG) is designed to involve a dielectric elastomer and a freeze-tolerant ionic hydrogel as the electrification layer and the electrode, respectively. The iTENG design achieves a unique combination of merits such as robust hydrogel–elastomer bonding, high stretchability (300%), and excellent tolerance of extremely low temperature (down to −53 °C). Because of the reliable interfacial bonding, the iTENG shows a good mechanical durability under different stretching conditions. The iTENG can harvest mechanical energies from various human motions and can also serve as a self-powered wearable sensor in both regular and extremely cold environments. The stretchable iTENG overcomes the strain-induced performance degradation of existing stretchable materials with percolated conductive fillers and the water freezing-induced degradation of conductive ionic hydrogels, providing a feasible design of stretchable and sustainable power sources for stretchable electronics and soft robotics operating in harsh environments.

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