Carbon Nanotube-Encapsulated Liquid Metal Hydrogel Fibers: An Integrated Conductive, Stretchable, and Adhesive Platform for Multifunctional Sensing

Developing multifunctional conductive hydrogel fibers is a growing trend and a challenge for flexible electronics. Here, a promising strategy is reported to develop multifunctional conductive hydrogel fibers for multifunctional sensing. The multifunctional conductive hydrogel fibers are designed and fabricated by in situ copolymerization of carboxyl-group-functionalized carbon nanotube (CNT)-encapsulated liquid metal (LM) and polyacrylamide/sodium alginate (PAM/SA) hydrogel. The resulting PAM/SA/CNTs/LM (PSCL) hydrogel fibers present conductive, self-healing, adhesive, and antifreezing properties. CNT-encapsulated LM endows the PSCL hydrogel fiber with a conducting network with a conductivity of 0.51 S m^-1. PSCL exhibits high stretchability, excellent mechanical properties, good adhesion strength, and a self-healing ability. Based on its multifunctional properties, the PSCL hydrogel fiber strain sensor shows enhanced sensitivity, wide detection range, and strain cycle stability, enabling it to monitor a wide range of human motions, from gross joint movements to subtle physiological activities, such as finger and cheek movements and detection of speech-related physiological signals. The conductivity enables PSCL as a stretchable electrode to construct PSCL-TENG that can drive small devices, such as calculators. Furthermore, the wireless sensing system constructed using freeze-resistant moisturizing PAM/SA/CNTs/LM/ethylene glycol (PSCLE) hydrogel fibers successfully displays the collected human movement signals in real time on a mobile phone. This study provides new insights for developing multifunctional hydrogel fibers for smart wearable sensing devices.