Magnetic Putty as a Reconfigurable, Recyclable and Accessible Soft Robotic Material

Magnetically hard materials are widely used to build soft magnetic robots, providing large magnetic force/torque and macrodomain programmability. However, their high magnetic coercivity often presents practical challenges when attempting to reconfigure magnetization patterns, requiring a large magnetic field or heating. This work presents magnetic putty as a robotic material that is easy to shape in 3D and can autonomously self-heal, allowing recovery from mechanical damage and assembly of parts without adhesives. The magnetic putty is a soft composite made of hard-magnetic particles embedded in a viscoelastic silicone putty matrix. The interplay of its mechanical and magnetic properties is explored experimentally. The viscoelastic behavior is influenced by particle magnetization and the application of external magnetic fields. At the same time, its mechanical properties affect its magnetic properties, such as coercivity, remanence, and retention. The magnetic putty combines the benefits of hard- and soft-magnetic materials—high remanence and low coercivity—having large magnetic force under small fields and an easily reconfigurable magnetization profile. We show that the magnetization of magnetic putty can be easily reoriented with maximum magnitude using an external field that is only one tenth of its coercivity. We also describe how its magnetic field-induced stress changes under alternating magnetic fields. We show that, at a low magnetic field frequency and large field magnitude, it becomes an analog frequency doubler. We also demonstrate using magnetic putty as a robotic material to build reconfigurable magnetic setups, shapable magnets with adaptive polarities, recyclable magnetic robots, and growing bioinspired rotating vines. We envision that this easy-to-access material can provide the soft robotics community with a research and educational tool to explore fundamental questions and fast prototype magnetic soft robots.