A tough and adhesive hydrogel assisted by milk protein was proposed, which could adhere to diverse surfaces of various materials.

Conductive hydrogels have attached considerable attention due to their good stretchability, excellent conductivity when they are applied in soft electronics. However, to fabricate a flexible hydrogel sensor with excellent toughness and good self-healing properties remains a challenge. In this work, we assembled a dual physical-crosslinking (DPC) ionic conductive polyacrylamide/ carrageenan double-network (DN) hydrogel. This hydrogel has excellent fracture tensile stress and toughness, and demonstrates rapid self-recovery and self-healing ability due to the unique dual physical-crosslinking structures. Besides, the hydrogel is highly conductive by adding some conductive ions. As a result, the hydrogel-based sensor can stably detect human motions and physiological signals. The work provides novel ideas for the development of flexible sensing devices.

Flexible electronic technology has developed rapidly in recent years, showing broad application prospects in motion monitoring, wearable devices, and personalized medicine. Consequently, the demand for high sensitivity and wide sensing range has gradually increased. Conductive hydrogels have high flexibility, excellent conductivity, and good biocompatibility, making them ideal candidates for fabricating flexible sensors. However, conductive hydrogels exhibit weak mechanical stability, which limits their applications. Therefore, sufficient mechanical properties and fatigue resistance are usually needed to fulfill their application requirements. Herein, the research frontiers of sensors based on mechanically robust conductive hydrogels are reviewed. While published papers always focus on the configuration design and application of sensors and the improvement of sensing performance, research on the network design of hydrogels and their effects on mechanical properties and sensing performance are limited. It is attempted in this review to fill this gap by focusing on the design principles of mechanically enhanced conductive hydrogels and their applications in flexible electronic devices. Herein, hydrogels’ structural designs, toughening mechanisms, mechanical properties, and sensing applications are discussed. The different working mechanisms of flexible sensors composed of tough conductive hydrogels and their applications are also reviewed. Finally, the future development directions and challenges in this field are highlighted.