Untethered magneto-thermal flexible actuators for soft robotics

Soft robots are devices that can perform delicate and sensitive movements. Such robots have flexible actuators activated by external triggers. Magnetic soft actuators, triggered by external magnetic fields, can be operated remotely and wirelessly. We present new materials and processes to fabricate 2D and 3D magneto-thermal actuators (MTA) by a printing process. Unlike most earlier reports, our actuators are activated by an alternating magnetic field. The formed bilayer actuators which combine a flexible polymer layer with a magnetic layer can heat up under an alternating magnetic field (AMF) which triggers the actuation and shape morphing. The actuation is based on the difference in the thermal expansion coefficient of the two layers. The achieved curvatures are very large, in the range of 0.08–0.1 mm^-1. The effect of various actuation parameters was studied, providing a good agreement of the experimental results with the modeling predictions. A 2D gripper and a “flower” were activated remotely without wiring or patterning of the magnetic layer. A 3D-printed MTA, obtained by combining stereolithography-based 3D printing with spray deposition, was also developed. Actuators with complex 3D structures formed by 3D printed process, resulting in objects that undergo remotely activated shape morphing, as demonstrated for a drone-like wing, performing a controlled tilting movement. The excellent actuation of these magneto-thermal actuators suggests their promise in soft robotics, for which wireless and remote activation present an unmet need.