Untethered gripper-type hydrogel millirobot actuated by electric field and magnetic field

This paper proposes a novel concept of an untethered gripper-type hydrogel millirobot that can be actuated by electric and magnetic fields. The proposed millirobot has two arms consisting of anodic and cathodic electroactive hydrogels, which generate bending motions by the electric field to enable the 'open' and 'close' motion of a gripper. Meanwhile, it can locomote using the magnetic field due to the magnetic nanoparticles (MNPs) contained inside its two arms. Therefore, when the electric and magnetic fields are used in combination, the proposed millirobot can simultaneously perform gripping motion and locomotion. In this study, we first investigated the bending motion characteristics of each electroactive hydrogel when an electric field was applied to both the anodic and the cathodic electroactive hydrogels of the proposed millirobot. Then, by applying an electric field to the untethered gripper-type hydrogel millirobot which combines the two hydrogels in a gripper form, we confirmed that each hydrogel moves in the opposite direction at the same electric field, while the millirobot implements the open and close gripping motions. Moreover, the proposed robot can locomote in the desired direction by applying a magnetic field through an electromagnetic actuation (EMA) system. Finally, it was verified that this robot can demonstrate gripping motion and locomotion simultaneously by the electric and magnetic field integrated system.