Highly stretchable and self-adhesive ionically cross-linked double-network conductive hydrogel sensor for electronic skin

Flexible, wearable sensors are attracting considerable interest because of their potential applications for human–machine interfaces, human-activity monitoring, and personal healthcare diagnosis. Hydrogels are promising material candidates for the wearable sensors due to their biocompatibility, high water content, structural similarity to natural soft tissues, and resemblance to extracellular matrix. However, the wearable hydrogel sensors have the limitations of poor adhesion and low electroconductivity. Herein, a healable, adhesive, and conductive wearable hydrogel sensor was designed by incorporating polydopamine decorated carbon nanotubes (PDA-CNTs) and FeCl3 into acrylamide-co-acrylic acid polymer (P(AAm-co-AAc)) matrix, forming a catechol/P(AAm-co-AAc)/Fe3+ double-network hydrogel sensor. The hydrogel sensor displayed good stretchability and high sensitivity with a gauge factor of 44.2 at 700% strain. And it exhibited fast and repeatable self-healing ability (healed completely after 60 s at room temperature without any external assistance). The resistance of the hydrogel showed repeatable and periodic variations during multiple cyclic stretching (1000 cycles), demonstrating good stability of this hydrogel sensor. The PDA-CNT hydrogel also showed strong adhesiveness to various substrates, including glass, metal, and plastic. When adhered onto a human body, the hydrogel was able to accurately monitor various motions, such as the bending of finger, wrist, elbow, and knee. These results showed the hydrogel sensor’s sensitivity and repeatability for detecting human motions. The healable, adhesive, conductive hydrogel is a promising material for wearable sensors to monitor human motion and can be used for personal healthcare diagnosis and therapy.