A 3D printing method that can create soft materials that undergo elaborate, rapid and reversible transformations when a magnetic field is applied is reported in Nature this week. The technique can program materials to perform various useful movements, including rolling, jumping and grasping objects.

Soft materials, which change shape in response to stimuli such as heat, light or magnetic fields, have potential in many applications from flexible electronics and soft robotics to biomedical challenges such as drug delivery and tissue engineering. For medical applications, where materials would operate in closed spaces and need to be controlled remotely, magnetic fields offer a promising activation stimulus. However, current fabrication methods permit only simple shape changes.

Xuanhe Zhao and colleagues present a technique for printing soft, magnetically activated materials that transform within a fraction of a second. The fabrication process embeds ferromagnetic microparticles within a silicone rubber matrix. By controlling the alignment of the microparticles by magnetizing the printer nozzle, the authors are able to program different regions of the printed materials to undergo specific transformations in a magnetic field. For example, the materials can switch between different, static shapes or morph dynamically in response to changing magnetic fields. Being elastic, the materials revert to their original pattern when the magnetic field is removed.

The authors demonstrate their technique by printing a six-legged soft robot. By applying different magnetic fields, the robot can be made to crawl along, roll over, carry medicines in the form of pills and even catch and release a falling object. A second design can be made to leap 12 centimetres horizontally by first applying a magnetic field in one direction to collapse the structure, then the other to release it.

Please note that there will be an accompanying Nature Video about this research, which is now on the Nature Research press site.