Soft stimuli-responsive grippers and machines with high load-to-weight ratios

Abstract

Soft untethered grippers and machines are emerging fields of research due to their wide range of desirable properties and capabilities over traditional hard robots. Stimuli-responsive hydrogels are naturally soft and untethered (i.e., they respond to a signal from the environment); however, they are not used as grippers due to the weak mechanical properties of the hydrogels. This manuscript describes the fabrication of a general class of stimuli-responsive grippers that are soft and untethered. Each gripper is composed of a stimuli-responsive hydrogel with a hole in the middle for gripping onto objects and a layer of coating around its sides. Importantly, these grippers exert surprisingly large gripping forces relative to their weights—∼10 000, which is the highest reported in the literature for a gripper. This high load-to-weight ratio is unexpected because the stimuli-responsive hydrogel is soft, not tethered to any external supply of energy, and fabricated by simple methods. The approach is general: high load-to-weight ratios were achieved for both pH- and temperature-responsive hydrogels. As soft grippers, they gripped onto objects of different shapes and sizes easily. A class of soft untethered machines can be fabricated by assembling these soft grippers with different modular blocks of stimuli-responsive hydrogels for performing complex operations.