Functionalizing Double-Network Hydrogels for Applications in Remote Actuation and in Low-Temperature Strain Sensing.

Multifunctional hydrogels have important applications in various fields such as artificial muscles, wearable devices, soft robotics, and tissue engineering, especially for those with favorable mechanical properties, good low-temperature resistance, and stimuli-responsive capabilities. In the current study, a type of polyacrylamide/sodium alginate/carbon nanotube (PAAm/SA/CNT) double-network (DN) hydrogel was fabricated, which exhibited a high tensile strength of 271.68 ± 6.04 kPa, a favorable conductivity of 1.38 ± 0.17 S·m-1, and a good self-healing ability under heating conditions. In addition, the composite hydrogel exhibited controllable photomechanical deformations under near-infrared irradiation, such as bending, swelling, swimming, and object grasping. To further broaden the applications of the hydrogel in low-temperature environments, calcium chloride (CaCl2) was introduced into such a PAAm/SA/CNT DN hydrogel as an additive. Interestingly, the tensile/compressive strengths as well as elasticity were well-maintained at a temperature as low as -20 °C. In addition, the PAAm/SA/CNT/CaCl2 hydrogel presented excellent conductivity, recoverability, and strain-sensing capability under such extreme conditions. Overall, the investigations conducted in this paper have provided potentially new methods and inspirations for the generation of multifunctional PAAm/SA/CNT/CaCl2 hybrid DN hydrogels toward extended applications.