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Rapid energy‐efficient movements are one of nature's greatest developments. Mechanisms like snap‐buckling allow plants like the Venus flytrap to close the terminal lobes of their leaves at barely perceptible speed. Here, a soft balloon actuator is presented, which is inspired by such mechanical instabilities and creates safe, giant, and fast deformations. The basic design comprises two inflated elastomer membranes pneumatically coupled by a pressurized chamber of suitable volume. The high‐speed actuation of a rubber balloon in a state close to the verge of mechanical instability is remotely triggered by a voltage‐controlled dielectric elastomer membrane. This method spatially separates electrically active and passive parts, and thereby averts electrical breakdown resulting from the drastic thinning of an electroactive membrane during large expansion. Bistable operation with small and large volumes of the rubber balloon is demonstrated, achieving large volume changes of 1398% and a high‐speed area change rate of 2600 cm2 s−1. The presented combination of fast response time with large deformation and safe handling are central aspects for a new generation of soft bio‐inspired robots and can help pave the way for applications ranging from haptic displays to soft grippers and high‐speed sorting machines. A voltage‐triggered soft balloon actuator with an impressive displacement (1398% total volume change) at high speed (2600 cm2 s−1 area change rate) is developed by harnessing the mechanical snap‐through and snap‐back instability of a rubber balloon. The trigger actuator is pneumatically coupled to the high‐speed actuator. This concept promises applications in soft bio‐inspired systems in modern robotics and engineering.

The mechanical principles for fast snapping in the iconic Venus flytrap are not yet fully understood. In this study, we obtained time-resolved strain distributions via three-dimensional digital image correlation (DIC) for the outer and inner trap-lobe surfaces throughout the closing motion. In combination with finite element models, the various possible contributions of the trap tissue layers were investigated with respect to the trap’s movement behavior and the amount of strain required for snapping. Supported by in vivo experiments, we show that full trap turgescence is a mechanical–physiological prerequisite for successful (fast and geometrically correct) snapping, driven by differential tissue changes (swelling, shrinking, or no contribution). These are probably the result of the previous accumulation of internal hydrostatic pressure (prestress), which is released after trap triggering. Our research leads to an in-depth mechanical understanding of a complex plant movement incorporating various actuation principles.

Fast snapping in the carnivorous Venus flytrap (Dionaea muscipula) involves trap lobe bending and abrupt curvature inversion (snap‐buckling), but how do these traps reopen? Here, the trap reopening mechanics in two different D. muscipula clones, producing normal‐sized (N traps, max. ≈3 cm in length) and large traps (L traps, max. ≈4.5 cm in length) are investigated. Time‐lapse experiments reveal that both N and L traps can reopen by smooth and continuous outward lobe bending, but only L traps can undergo smooth bending followed by a much faster snap‐through of the lobes. Additionally, L traps can reopen asynchronously, with one of the lobes moving before the other. This study challenges the current consensus on trap reopening, which describes it as a slow, smooth process driven by hydraulics and cell growth and/or expansion. Based on the results gained via three‐dimensional digital image correlation (3D‐DIC), morphological and mechanical investigations, the differences in trap reopening are proposed to stem from a combination of size and slenderness of individual traps. This study elucidates trap reopening processes in the (in)famous Dionaea snap traps – unique shape‐shifting structures of great interest for plant biomechanics, functional morphology, and applications in biomimetics, i.e., soft robotics. The snap traps of the infamous Venus flytrap have remarkable shape‐shifting capabilities. After fast snapping in an attempt to capture prey, the traps can slowly reopen via two modes of sequential deformation. Whereas normal‐sized traps (N traps) reopen smoothly and continuously via hydraulic processes alone, large and slender traps (L traps) can incorporate an additional reverse snap‐buckling instability during reopening.

Plants are dynamic. They adjust their shape for feeding, defence, and reproduction. Such plant movements are critical for their survival. We present selected examples covering a range of movements from single cell to tissue level and over a range of time scales. We focus on reversible turgor-driven shape changes. Recent insights into the mechanisms of stomata, bladderwort, the waterwheel, and the Venus flytrap are presented. The underlying physical principles (turgor, osmosis, membrane permeability, wall stress, snap buckling, and elastic instability) are highlighted, and advances in our understanding of these processes are summarized.

Venus flytrap ( Dionaea muscipula ) leaves exhibit an exceptionally rapid closing motion that occurs within one second. The rapid closure of outwardly curved leaves is thought to be driven by snap-buckling instability—a rapid transition of an elastic system from one state to another. However, the ability of leaves that do not curve outward to also close suggests that the mechanics of leaf closure are complex and need to be understood using three-dimensional (3D) kinematics. We therefore developed a 3D reconstruction method to quantify the curvatures and displacements of leaf blades using two high-speed cameras. We then reconstructed a 3D surface mesh of the leaf, which revealed that the changes in curvature are spatiotemporally heterogeneous. We inferred the stretching and curvature elastic energies of the reconstructed surface, determining that the mechanical forces associated with in-plane deformation become significant in the peripheral regions of the leaf. This was true among different samples; however, the components of the energy profiles varied for each sample. The novelty of this study is that we could infer the elastic energy and the corresponding mechanical forces during closing motion. Our mechanical inference method will be useful for examining the deformation processes of various curved plant structures.

A growing or compressed thin elastic sheet adhered to a rigid substrate can exhibit a buckling instability, forming an inward hump. Our study shows that the strip morphology depends on the delicate balance between the compression energy and the bending energy. We find that this instability is a first-order phase transition between the adhered solution and the buckled solution whose main control parameter is related to the sheet stretchability. In the nearly unstretchable regime, we provide an analytic expression for the critical threshold. Compressibility is the key assumption which allows us to resolve the apparent paradox of an unbounded pressure exerted on the external wall by a confined flexible loop.

In this study, we developed new bending modules and pneumatic self-excited valves. In a previous study, we developed a planar flexible-deformation mobile robot that combines multiple bending modules. The robot moves by a traveling wave, which is periodically generated by pressurizing air to the bending modules. Further, it can move in every direction by simultaneously combining the two directional traveling waves. However, problems such as air leakage from the bending module that constitutes the moving object and the influence of the moving operation owing to the tubes comprising the flow path were identified. To address these problems, new bending modules have been developed. To address air leak issues, we verified the materials used in the bending modules and developed an injection mechanism. To reduce the number of externally connected tubes, we developed new bending modules that could include multiple internal flow paths. In addition, because the mobile robot moves owing to the generation of traveling waves, it is a low-grade operation. However, this requires multiple solenoid valves and electronic circuits. This is useful if traveling waves can be generated by simply supplying air using a pneumatic self-excited valve. In this study, we developed bending modules with multiple internal channels and a pneumatic self-excited valve that utilizes the snap buckling of leaf springs used in the mobile robot.

Explosion of ping‐pong balls that is caused by the rapid inflation of an elastomer membrane. The illustrated ultrafast actuation is based on a plant‐inspired mechanical instability that occurs in natural rubber and can be remotely triggered, presented in article number 1903391 by Martin Kaltenbrunner and co‐workers. These new types of high‐speed soft actuators have potential applications in object sorting or grasping.