Swelling-induced snap-buckling in a 3D micro hydrogel device,inspired by the insect-trapping action of Venus flytrap, makes it possible to generate astonishingly fast actuation. We demonstrate that elastic energy is effectively stored and quickly released from the device by incorporating elastic instability. Utilizing its rapid actuation speed, the device can even jump by itself upon wetting.
Figure： Microgel jumps upon wetting (see ESI,† Movie 3). Numbers indicate the sequence of the motion. The device is placed on a glass substrate
(1). When a solvent droplet is applied to the left leg
(2). the solvent not only surrounds the leg, it also fills all the microfluidic network in the device by capillary action. Even after solvent surrounding the legs evaporates, embedded microfluidic channels are still filled with solvent, resulting in bending of legs outwards
(3–5). With two legs bent outwards, the device is ready to jump
(6). As the solvent in the channels further evaporates, snap-buckling takes place as the legs snap back to the original shape in de-swelling process. This rapid motion produces enough thrust for jumping. The device jumps out of the view field
(7). and is found outside the initial view field
(8). Cross mark indicates the initial position of the device. Scale bar indicates 1 mm.