Snap-Buckling Motivated Controllable Jumping of Thermo-Responsive Hydrogel Bilayers.

Responsive hydrogel actuators have promising applications in diverse fields. Most hydrogel actuators are limited by slow actuation or shape transformations. This work reports on snap-buckling motivated jumping of thermoresponsive hydrogel bilayers. The bilayers are composed of poly(NIPAM- co-DMAPMA)/clay hydrogel with different lower critical solution temperatures in each layer, and thus undergo slow reversible curling/uncurling at temperature changes. The gels are adhesive to numerous materials including aluminum. The adhesion between the gels and an aluminum ratchet is utilized to constrain the thermoresponsive deformation of the bilayers to store elastic energy. When the accumulated elastic energy overwhelms the gel-aluminum adhesion, snap-buckling takes place to abruptly release the accumulated energy, which motivates the bilayer to jump. The jumping direction, start time, height, and distance are controlled by the geometry of the bilayers or the ratchet. This work paves a novel way for the rapid actuation of responsive hydrogels in a controlled manner and may stimulate the development of novel hydrogel devices.