Programmable\nand Bidirectional Bending\nof Soft Actuators Based on Janus Structure with Sticky Tough PAA-Clay\nHydrogel

Abstract

Facile\npreparation, rapid actuating, and versatile actions are great challenges\nin exploring new kinds of hydrogel actuators. In this paper, we presented\na facile sticking method to prepare Janus bilayer and multilayer hydrogel\nactuators that benefited from a special tough and adhesive PAA-clay\nhydrogel. Combining physical and chemical cross-linking reagents,\nwe endowed the PAA gel with both toughness and adhesion. This PAA\ngel was reinforced by further cross-linking with Fe³⁺.\nThese two hydrogels with different cross-linking densities exhibited\ndifferent swelling capabilities and moduli in the media manipulated\nby pH and ionic strength, thus acting as promising candidates for\nsoft actuators. On the basis of these gels, we designed hydrogel actuators\nof rapid response in several minutes and precisely controlled actuating\ndirection by sticking two hydrogel layers together. Elaborate soft\nactuators such as bidirectional bending flytrap, gel hand with grasp,\nopen, and gesturing actions as well as word-writing actuator were\nprepared. This method could be generalized by using other stimuli-responsive\nhydrogels combined with the adhesive PAA gel, which would open a new\nway to programmable and versatile soft actuators.