A Plant Tendril-Like Soft Robot That Grasps and Anchors by Exploiting its Material Arrangement

Some climbing plants use tendrils as efficient strategies to anchor and support their weights while they move in unstructured environments. In this letter, we mimic the essential functions of tendrils that wrap around the support in a soft state by a spiral winding (coiling) and then lignify or stiffen to strengthen the attachment. We implement a simple hierarchical pre-programmed functionality at the material level using off-the-shelf materials and easy fabrication methods to achieve coiling and stiffening and incorporate an electrical control. The resulting robots hence consist of a bilayer of silicone elastomers that encapsulate a thermoplastic core and a heating element. The bilayer that spontaneously forms a helically coiled configuration in its equilibrium state is controlled by a solid-to-liquid phase transition of the thermoplastic core upon resistive heating. Integrating these mechanisms into a single structure allows mimicking the basic tendril functions. Our realization is a straightforward assembly with electrical control that offers the perspective to be a building block for soft robots that require controllable attachment solutions such as growing artifacts and devices that operate in unstructured environments, e.g., operating in vegetation.