Graphene Oxide/Alginate Hydrogel Fibers with Hierarchically Arranged Helical Structures for Soft Actuator Application

Hierarchically arranged helical structures were constructed in graphene oxide (GO)/alginate hydrogel fibers by combining the wet spinning and confined drying methods. After fixing both ends of the Ca2+-crosslinked GO/alginate hydrogel fibers, multistep twists were utilized to construct hierarchically arranged helical structures during the drying process. The microstructures and tensile mechanical properties of one-, two-, and three-strand hydrogel fibers with hierarchical helical structures were analyzed in detail. The results demonstrated that a combination of high strength (∼2 MPa), high toughness (>5 MJ/m3), and large strain (>700%) could be achieved in the alginate-based hydrogel fibers. The fracture surfaces of the helical hydrogel fibers were studied to reveal the improvement in the mechanical properties. Cyclic tensile tests showed that a hysteresis loop existed in the loading–unloading curves of the helical GO/alginate hydrogel fibers, and a good self-recovery property emerged after resting for a period of time. The actuation performance of the helical GO/alginate fibers in response to water adsorption was also studied in detail. The results showed that the actuation performances could be tuned by the helical structure, and the helical fibers could be applied as a soft actuator.