Poly(Vinyl Alcohol)-Carbon Nanotube Self-Adhesive Hydrogels for Wearable Strain Sensors

Wearable conductive hydrogel sensors, which are highly convenient, have attracted attention for their great potential in human motion monitoring and smart healthcare. However, the self-adhesive properties, sensing performance, and stability of traditional hydrogels are not ideal, which seriously hinders their use in monitoring and diagnosing joints throughout the human body. Here, CaCl₂ is used to crosslink PVA to improve its self-adhesive properties, and it is then combined with a CNT conductive network. Next, a cyclic freeze-thaw strategy is utilized to fabricate a wearable PVA-Ca-CNT hydrogel with excellent self-adhesive properties and stability. PVA-Ca-CNT hydrogels can adhere to various substrates, with a maximum self-adhesion strength of 398 kPa and a unit adhesion energy of as high as 305 μJ cm^-2. Furthermore, the CNT three-dimensional network enhances the tensile strength to 110 kPa, with almost no hysteresis. Based on resistance changes, PVA-Ca-CNT hydrogel exhibits a sensitivity of up to 11.11 as a strain sensor as well as a response to strain stimuli within 180 ms. When PVA-Ca-CNT hydrogel is adhered to the surface of human skin, it operates as a sensor for monitoring human movement. Not only can it accurately monitor the movement positions of major joints in the human body, it can also accurately identify tiny movements of the fingers and be used as a finger Morse code output device, which demonstrates the enormous potential of human motion monitoring systems based on self-adhesive hydrogel sensors in practical applications.