Bioinspired bistable soft actuators

DEAs have been studied for decades as a potential polymer artificial muscle for its excellent mechanical properties and large electric field-induced strains. The structural design of DEAs enhances the actuator performances and converts the electrically–controlled strain to diverse motions including linear motion, bending, twisting and moving with multiple degree of freedom. Inspired by the Venus Flytrap (VFT), whose bistable leaves and local strain redistribution are crucial to the fast closure speed, we developed cylindrically-curved bistable laminated DEAs, and activated the bistable shape transformation by electrically tuning the strain field. To obtain the bistable structure, two elastomeric films are prestrained biaxially and bonded orthogonally to a stiffer elastic film in the middle. Due to the elastic energy minimization, the originally flat laminate immediately self-equilibrated to two bistable cylindrical shapes, with the curvatures orthogonal to each other. Basic theoretical analyses on the interaction of prestrains and bending curvatures provide guidance to the design of bistable morphing shapes. The prestrains on the DE films not only generate various curved shapes, but also decreases the film thickness and therefore reduces the actuation voltage. Similar to the fast closure of VFT, which is activated by the strain redistribution resulted from the motor cell enlargement, our bistable DEA achieves reversible bistable shape transformation by voltage-induced strain change at the area covered by compliant electrodes.