Ultra-stretchable and adhesive hydrogel based on double network structure as flexible strain sensor for human motion detection

In recent years, conductive hydrogels were widely applied as flexible strain sensor due to its outstanding stretchability, high flexibility and conductivity. However, most conductive hydrogels would reduce the sensitivity and accuracy of hydrogel-based strain sensor for the lack of self-adhesion. Herein, a highly stretchable and excellent adhesive hydrogel based on chitosan network and ionic liquid crosslinking network was prepared. Chitosan (CS) worked as network skeleton, which could enhance the mechanical properties of hydrogel by participating in the construction of double network structure. Furthermore, dimethylaminoethyl methacrylate maleate (DM-M) as cross-linker, the hydrogel was imparted with high ionic conductivity (0.29 S/m) while it also enhanced the mechanical properties of the hydrogel. The ionic bonding conferred high toughness to the hydrogel for avoiding stress concentration during tensile process. Additionally, the hydrogel could form strong adhesion to a variety of substrate surfaces through electrostatic interaction, hydrogen bond and metal complexation. Meanwhile, the hydrogel remained strong adhesion under different pH, solvent and temperature condition. Therefore, the hydrogel with excellent adhesive property, mechanical properties and high electrical conductivity have been designed as flexible strain sensor, which could detect limb movement and physiological signals with real-time feedback electrical signals. Thus, this highly stretchable, tough and adhesive hydrogel based on double network structure would promote the development of flexible electronic device.