Multi-field-coupling energy conversion for flexible manipulation of graphene-based soft robots

Soft robots enabling controllable movement in a predicable manner have attracted enormous research interests. However, current researches on soft robots are mainly limited to single actuation mode, and thus complex and multidimensional motility is significantly limited. Here, we propose and demonstrate for the first time a multi-field-coupling energy conversion strategy for flexible manipulation of soft robots, by which 3D-positioning, rotating, levitating, capturing and releasing of a small object by a smart claw are synergistically realized via magnetic, ultrasonic, humidity and light fields. The essence of the strategy is coupling design of the robot compositional materials that can convert energy from different fields into efficient mechanical works. As a typical example, we developed a magnetic-field-assisted gradient assembly method for preparing asymmetric Fe3O4 nanoparticles (NPs) and graphene oxide (GO) composite film. The asymmetric distribution of Fe3O4 NPs in GO leads to an reasonable mechanical stiffness and alters the water adsorption capability of the two sides, which not only imparts multi-responsiveness but also suitably addresses the problem of interlayer detachment in the case of bimorph actuators. The robust soft robots demonstrate good durability, revealing great potential for developing advanced robotic systems that permit direct conversion of multi-field energies to mechanical works.