Soft Three-Dimensional Robots with Hard Two-Dimensional Materials.

Inspired by biological organisms, soft engineered robots seek to augment the capabilities of rigid robots by providing safe, compliant, and flexible interfaces for human-machine interactions. Soft robots provide significant advantages in applications ranging from pick-and-place, prostheses, wearables, and surgical and drug-delivery devices. Conventional soft robots are typically composed of elastomers or gels, where changes in material properties such as stiffness or swelling control actuation. However, soft materials have limited electronic and optical performance, mechanical rigidity, and stability against environmental damage. Atomically thin two-dimensional layered materials (2DLMs) such as graphene and transition metal dichalcogenides have excellent electrical, optical, mechanical, and barrier properties and have been used to create ultrathin interconnects, transistors, photovoltaics, photocatalysts, and biosensors. Importantly, although 2DLMs have high in-plane stiffness and rigidity, they have high out-of-plane flexibility and are soft from that point of view. In this Perspective, we discuss the use of 2DLMs either in their continuous monolayer state or as composites with elastomers and hydrogels to create soft three-dimensional (3D) robots, with a focus on origami-inspired approaches. We classify the field, outline major methods, and highlight challenges toward seamless integration of hybrid materials to create multifunctional robots with the characteristics of soft devices.