Figure 7.

(a) Schematic of the bench-top experiments: two pieces of latex rubber sheets (blue and yellow) were pre-stretched along perpendicular directions and a thicker elastic strip is sandwiched in-between. Upon release, the bonded multilayer composite will deform into one of the following shapes in (b–e). (b) A saddle shape when the composite layer is narrow enough. (c) A saddle shape when the composite layer is thick enough. (d) A stable, nearly cylindrical shape when the composite layer is wide and thin enough. (e) The other stable shape (bending upwards) for the same sheet as in (d). (a–e) Adapted from [79]. (f) The robotic Venus flytrap (VFT) with a pair of lobes (traps), embedded spine (copper roll), IPMC trigger fingers and lead wires for sensing and actuation. (g) Schematics of a robotic VFT in an open and closed configuration (adapted from [77]). (h) Snap-buckling of the doubly curved hydrogel device by swelling of the lobes from solvent in the microfluidic channels. Note the characteristic shape changes and reversal of curvature that occur during actuation of the device. Scale bar, 100 µm. Adapted from [78]. (Online version in colour.)