Soft Tendril-Inspired Grippers: Shape Morphing of Programmable Polymer–Paper Bilayer Composites

Abstract

Nastic movements in plants that occur in response to environmental stimuli have inspired many man-made shape-morphing systems. Tendril is an exemplification serving as a parasitic grasping component for the climbing plants by transforming from a straight shape into a coiled configuration via the asymmetric contraction of internal stratiform plant tissues. Inspired by tendrils, this study using a three-dimensional (3D) printing approach developed a class of soft grippers with preprogrammed deformations being capable of imitating the general motions of plant tendrils, including bending, spiral, and helical distortions for grasping. These grippers initially in flat configurations were tailored from a polymer-paper bilayer composite sheet fabricated via 3D printing a polymer on the paper substrate with different patterns. The rough and porous paper surface provides a printed polymer that is well-adhered to the paper substrate which in turn serves as a passive strain-limiting layer. During printing, the melted polymer filament is stretched, enabling the internal strain to be stored in the printed polymer as memory, and then it can be thermally released, which will be concurrently resisted by the paper layer, resulting in various transformations based on the different printed geometries. These obtained transformations were then used for designing grippers to grasp objects with corresponding motions. Furthermore, a fully equipped robotic tendril with three segments was reproduced, where one segment was used for grasping the object and the other two segments were used for forming a tendril-like twistless spring-like structure. This study further helps in the development of soft robots using active polymer materials for engineered systems.

3D Printing of Hydrogel Architectures with Complex and Controllable Shape Deformation

“…Over the past decades, the bilayer hydrogels or shape memory polymers, which are consisted of two layers with different responsive properties, have captured wide attentions. These bilayer devices showed inhomogeneous swelling or shrinking behaviors in different directions, and thus exhibited complex shape deformations triggered by stimuli . Moreover, the autonomous response of these bilayer devices in specific environments displays a smart behavior .…”

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

“…The tuneable molecular architecture of LCNs prior to polymerization allows for programmed actuation such as bending, twisting or rolling. Multi‐modal shape morphing such as helical winding and unwinding within single liquid crystal (LC) actuators has been realized by employing different cutting directions, dual‐layer actuators with contrasting orientation directions, alignment control through directional printing or patterning . However, in these examples, the covalent crosslinked nature of the network prevents recyclable shape programming.…”

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

“…[8][9][10][11] The tuneable molecular architecture of LCNs prior to polymerization allows for programmed actuation such as bending, twisting or rolling. Multi-modal shape morphing such as helical winding and unwinding within single liquid crystal (LC) actuators has been realized by employing different cutting directions, [12,13] dual-layer actuators with contrasting orientation directions, [14] alignment control through directional printing [15] or patterning. [16][17][18][19] However, in these examples, the covalent crosslinked nature of the network prevents recyclable shape programming.…”