Designing Gripper-like Architectures from Self-folded Bilayers

Motivated by the environmentally responsive actuation mechanisms of non-muscular plants, research efforts have been made toward the development of smart reconfigurable devices that can sense and autonomously respond to their surroundings. Tetherless self-folding microgrippers - extensively used for micro/ nano-manipulation - are examples of such engineered systems as they could be actuated on-demand by external stimuli. Being multilayer in nature, these structures rely on spatially patterned hinges for their morphing behavior, and hence they require extensive fabrication efforts. The goal of this work is to establish a design paradigm so that gripper-like architectures could be realized from simple stimuli-responsive planar bilayers (one layer expanding isotropically due to a stimulus while the other remains passive). Through a combination of finite element modeling and experiment, we investigated the stimulus-responsive behavior of bilayer stars and established the principles to achieve stable axisymmetric gripper-like shapes in a programmable manner. Thus, in addition to proposing a simpler route to achieve microgrippers, our research contributes to the rapidly emerging multidisciplinary field of stimuli-responsive self-assembly.