Multi-responsive, bidirectional, and large deformation bending actuators based on borax cross-linked polyvinyl alcohol derivative hydrogel

This study demonstrates a multi-responsive high-performance bilayered hydrogel actuator (HA) obtained via coating a borax cross-linked N1,N1-diethylethane-1,2-diamine (DEEDA)-modified polyvinyl alcohol (PVA) microgel (PVA–DEEDA–borax) on a polyacrylic acid-coated biaxially oriented polypropylene (BOPP) substrate, and reveals that the amount of borax that is added plays a decisive role in the ultimate performance of the actuator. The HA is able to perform rapid, reversible, and sustainable bidirectional self-rolling deformation actuated by heat- and moisture-triggered swelling/deswelling of PVA–DEEDA–borax gel, transforming into 2D/3D tube, wave and cross shapes through designing the assembly of actuators. The significant difference in the swelling behavior between PVA–DEEDA–borax and BOPP generates enough force to actuate the performance of the hydrogels as soft artificial muscle and self-adapted smart manipulator with capability of lifting masses much heavier than the actuator devices, showing potential applications in small-scale soft robotics.