  Fully soft bistable mechanisms have shown extensive applications ranging from
soft robotics, wearable devices, and medical tools, to energy harvesting.
However, the lack of design and fabrication methods that are easy and
potentially scalable limits their further adoption into mainstream
applications. Here a top-down planar approach is presented by introducing
Kirigami-inspired engineering combined with a pre-stretching process. Using
this method, Kirigami-Pre-stretched Substrate-Kirigami trilayered precursors
are created in a planar manner; upon release, the strain mismatch -- due to the
pre-stretching of substrate -- between layers would induce an out-of-plane
buckling to achieve targeted three dimensional (3D) bistable structures. By
combining experimental characterization, analytical modeling, and finite
element simulation, the effect of the pattern size of Kirigami layers and
pre-stretching on the geometry and stability of resulting 3D composites is
explored. In addition, methods to realize soft bistable structures with
arbitrary shapes and soft composites with multistable configurations are
investigated, which could encourage further applications. Our method is
demonstrated by using bistable soft Kirigami composites to construct two soft
machines: (i) a bistable soft gripper that can gently grasp delicate objects
with different shapes and sizes and (ii) a flytrap-inspired robot that can
autonomously detect and capture objects.
