Soft Three-Dimensional Robots with Hard Two-Dimensional Materials

Abstract

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.

Materials as Machines

“…Similarly, including carbon black in polymeric materials is a facile route to enabling either photothermal or electrothermal responses 404. The incorporation of 2D materials such as graphene and transition metal dichalcogenides into diverse polymer networks that include brush polymers, PDMS elastomers, acrylamide copolymers, pH responsive matrices, as well as the SWNT incorporation into PVA polymer to prepare nanoyarns, have all been applied in compelling actuators that also demonstrate, to an extent, the SME 405,406…”

Bioelectronics‐Related 2D Materials Beyond Graphene: Fundamentals, Properties, and Applications

“…Carbon‐based low‐dimensional materials such as graphene and carbon nanotubes have been used as artificial muscles, showing superior mechanical properties and good electrical conductivity. [ 259,260 ] However, carbon‐based actuators feature certain limitations, the most obvious of which is the byproduct of the thermal effect induced by simple thermally driven actuation.…”

Advances in Stimuli-Responsive Soft Robots with Integrated Hybrid Materials

“…A variety of futuristic applications of stimuli-responsive soft robots have been proposed in the forms of flexible electronics, sensors, biomedical tools, optics, and actuators [1][2][3][4][5][6][7][24][25][26]. Furthermore, hybrid stimuli-responsive soft robots combined with multi-functional nanoparticles, low-dimensional materials, or liquid crystals have also displayed promising applications in flexible electronics, mechanical sensors, smart actuators, and biomedical systems [18][19][20][21][23][24][25][26][27][28]. This section particularly describes advanced applications of hybrid stimuli-responsive soft robots focusing on extensively multi-responsive and multi-functional actuators (e.g., manipulators, grippers, and walkers) and sensors (e.g., wearable electronics, strain sensors, biosensors, and gas sensors).…”