  Soft robots have a myriad of potentials because of their intrinsically
compliant bodies, enabling safe interactions with humans and adaptability to
unpredictable environments. However, most of them have limited actuation
speeds, require complex control systems, and lack sensing capabilities. To
address these challenges, here we geometrically design a class of metacaps
whose rich nonlinear mechanical behaviors can be harnessed to create soft
robots with unprecedented functionalities. Specifically, we demonstrate a
sensor-less metacap gripper that can grasp objects in 3.75 ms upon physical
contact and a pneumatically actuated gripper with tunable actuation behaviors
that have little dependence on the rate of input. Both grippers can be readily
integrated into a robotic platform for practical applications. Furthermore, we
demonstrate that the metacap enables propelling of a swimming robot, exhibiting
amplified swimming speed as well as untethered, electronics-free swimming with
tunable speeds. Our metacaps provide new strategies to design the
next-generation soft robots that require high transient output energy and are
capable of autonomous and electronics-free maneuvering.
