Bionic Soft Multimodal Actuators for Fast, Large Deformation under Ultralow Magnetic Conditions

Very recently, magnetically driven soft actuators have prompted increasing interest due to their programmable deformation, swift response, and remote actuation. However, it is still challenging to trigger strong and fast actuating performances with an extremely weak magnetic field due to the difficult task of in situ programming of magnetic domains and the limited mechanical structures. Here, first a bionic sandwich structure is proposed for designing soft magnetic actuators with a specific threshold value. The crab-like jointed structure of PDMS-embedded NdFeB upper/lower layers is essential for generating the desirable threshold effect, while a flytrap-inspired soft interlayer is further implemented to decrease the driving magnetic field. Theoretical analysis and numerical simulations are implemented to optimize the actuating performances of soft actuators (deformation rate, deformation angle) by modulating the structural parameters. Experimental results show that the biomimetic features yield a promptly switchable bistable state, a superior strong deformation rate of 1.93, and a maximum deformation angle of 25.5 degrees under an ultralow magnetic field of 1 mT. Two demonstrative applications of soft actuators are investigated, including threshold switching and soft grippers, suggesting their broad applications in engineering fields. Remarkably, the magnetic soft grippers associated with the gecko-inspired adhesion surface exhibit an improved and stable grasping ability. This work focuses on designing highly deformable actuators and functions in emerging areas of soft robotics.