Stiffness Tunable Magnetic Actuators Based on Shape Memory Polymer/NdFeB Composite for Segmental Controllable Motion

Soft magnetic robots have attracted extensive research interest recently due to their fast-transforming ability and programmability. Although the inherent softness of the matrix materials enables dexterity and safe interactions, the contradiction between the easy shape transformation of the soft matrices and load carrying capacity, as well as the difficulty of independently controllable motion of individual segments, severely limits its design space and application potentials. Herein, we have proposed a strategy to adjust the modulus of shape memory polymer composite embedded with hard magnetic particles by in situ Joule heating of printed circuit, which can reversibly change the stiffness from 4.1 GPa at 25°C to 10.9 MPa at 70°C. The stiffness tunable magnetic robots realize the compatibility of fast reversible shape transformation and high load carrying capacity. Furthermore, multiple separated Joule circuits are designed for the independently controllable motion of individual segments. The simulation of Joule heating and magnetic actuation is used to guide the design of devices. The concept of simultaneously programming magnetic anisotropy and stiffness proposed in this work greatly expands the design space and new applications of magnetic actuators, including soft grippers for heavy loads and bionic hand with independent motion of fingers.