Shrink Films Get a Grip

Robotics and active materials have forged the path for grasping and manipulating delicate objects of various geometries and sizes. To date, the majority of soft robotic grippers have used hydrogels or elastomers, which can repeatably grasp and manipulate small objects. Many of these grippers achieve their grip (due to shape change) only in the presence of either solvent exposure or external pneumatic pressure. Here, we demonstrate thermoplastic polystyrene sheets that actuate from flat sheets into grippers in response to light exposure and maintain their shape upon removal of the light. Black ink patterned on the sheet converts global light illumination to localized heating that causes the planar sheet to deform into the shape of a gripper. These grippers have significantly improved endurance and strength compared to their hydrogel or elastomeric counterparts as they can support >24 000 times their own mass. These grippers release objects upon additional uniform heating, and each gripper serves as a single use device. We report the significance of sample geometry and ink patterning for controlled, localized heating upon the resulting three-dimensional shape and its impact on precision and strength. Various designs for untethered, stimuli-responsive thermoplastic grippers are presented based on targeted applications such as encapsulation.