Plant-derived adhesive hydrogel with high stretchability and conductivity for wearable electronics

Nowadays, hydrogel-based sensors have drawn great attention owing to the growing demand for wearable devices. However, tailoring the property of the hydrogel sensor through a facile approach remains a great challenge. In this work, inspired by natural plants, a stretchable, adhesive and conductive hydrogel was prepared via the coordination between gallic acid (GA) and Zn2+ and chemical cross-linking. The dynamic crosslinking provided greater structural integrity for the polyvinyl alcohol / polyacrylamide (PVA/PAM) double network, endowing the hydrogel with high mechanical performance (0.25 MPa at 910% tensile strain, and 1.21 MPa at 70% compressive strain). Meanwhile, the presence of GA enabled the hydrogel with excellent repeatable adhesive performance, which greatly solved the problem of signal loss caused by poor adhesion. Moreover, the addition of ZnCl2 enhanced the ionic conductivity and gauge factor of the hydrogel. Besides, the conductive hydrogel exhibited successively stable changes of resistance signals under different external stimuli (5–500% strains and 80–200 mm/min rates) and superior durability (over 500 cycles). The hydrogel-based wearable sensors demonstrated excellent sensing performance in detecting various human motions. The multifunctional PVA/PAM/GA-Zn2+ hydrogel has significant applications in soft robots and healthcare monitoring as the flexible strain sensor.