A semi-interpenetrating network ionic composite hydrogel with low modulus, fast self-recoverability and high conductivity as flexible sensor

•A novel hydrogel is developed based on the idea of semi-interpenetrating network.•The hydrogels exhibit high tensile stress and toughness.•The hydrogels display low modulus, fast self-recoverability and high conductivity.•The hydrogel has a high sensitive in monitoring human motions. There is a growing demand for hydrogel-based sensors due to their biomimetic structures and properties, as well as biocompatibility. However, it is still a challenge to fabricate hydrogel sensor with integration of good mechanical properties and high conductivity. Herein, a tough and conductive hydrogel is developed with semi-interpenetrating network formed by incorporating carboxymethyl chitosan and sodium chloride into polyacrylamide network. The hydrogels have high tensile strength, elongation and toughness, but low modulus comparable to human skin. In addition, the hydrogels exhibit fast self-recovery and satisfactory self-healing capabilities. Owing to the existence of sodium chloride, the hydrogel also has high conductivity, good water retention property and anti-freezing ability. When used as a strain sensor, it demonstrates a broad strain window and shows a high sensitivity in monitoring human motions. This work provides a facile method in fabricating multifunctional ionic conductive hydrogel for applications in wearable electronics and soft robotics.