At small scales, shape-programmable magnetic materials have significant potential to achieve mechanical functionalities that are unattainable by traditional miniature machines. Unfortunately, these materials have only been programmed for a small number of specific applications, as previous work can only rely on human intuition to approximate the required magnetization profile and actuating magnetic fields for such materials. We proposed a universal programming methodology that can automatically generate the desired magnetization profile and actuating fields for soft materials to achieve desired time-varying shapes. The universality of the proposed method can, therefore, enable other researchers to fully capitalize the potential of shape-programming technologies, allowing them to create a wide range of novel soft active surfaces and devices that are critical in robotics, material science, and medicine.
By using the above methodology, we then addressed a grand challenge facing the existing small-scale robots: multi-locomotion in complex terrains. Previous miniature robots have very limited mobility because they are unable to negotiate obstacles and changes in texture or material in unstructured environments. In our research, we demonstrate magneto-elastic soft millimeter-scale robots that can swim inside and on the surface of liquids, climb liquid menisci, roll and walk on solid surfaces, jump over obstacles, and crawl within narrow tunnels. These robots can transit reversibly between different liquid and solid terrains, as well as switch between locomotive modes. They can additionally execute pick-and-place and cargo-release tasks. We have also developed theoretical models to explain how the robots move. Besides their great biomedical potentials, these soft small-scale robots could be used to study soft-bodied locomotion produced by small organisms.