Soft robot system uses 3D printed built-in magnetic actuators and could find applications in medicine

Engineers at the U.S. Army research laboratory’s Institute for Soldier Nanotechnologies (ISN) at MIT have developed a 3D printing platform that can enable both the modelling and design of complex magnetically actuated devices. The technology is earmarked for producing soft robots that can crawl, roll, jump, or grab, fulfilling tasks such as squinting into cracks in the wall of a cave, jump over a trip wire, or crawl under a vehicle: all tasks which soldiers cannot perform safely.

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This is a time-lapse photo for various designs of developed magnetic active material. Image: MIT Soft Active Materials Lab

The technique uses an elastomeric composite as ink, infused with ferromagnetic microparticles. This material is printed through a nozzle to which a magnetic field is applied. This re-orients the magnetic particles along the field, imparting a patterned magnetic polarity to the filaments that are printed.

Using this, the researchers can programme ferromagnetic domains into complex 3D-printed soft materials to enable “previously inaccessible modes of transformation”. The mechanical actuators formed by these domains are orders of magnitude faster and have much greater power density than existing 3D-printed active materials, the team claims.

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These are the schematics of the printing process and the material composition. The ferromagnetic particles embedded in the composite ink are reoriented by the applied magnetic field prior to printing. Image: US Army

Alex Hsieh of the Army research laboratory explained that the team managed to create a structure that could jump forward 120mm within 0.7 seconds. “This jump was due to a rapid release of elastic and magnetic potential energy stored in that structure,” he said. This achievement was due in part to the materials used by the MIT team, which had unusual properties: when exposed to magnetic actuation, they shrink.

“Such complex shape-morphing structures could have great potential for the army, because they may help create soft robots - robots with pliable limbs similar to natural organisms. Compared to the current generation of rigid robots, soft robots could move much more dexterously on a complex battlefield terrain,” Hsieh said.

Another development is a system to predict how a design will behave. "We have developed a printing platform and a predictive model for others to use. People can design their own structure and domain patterns, validate them with the model, and print them to actuate various functions. By programming complex information of structure, domain, and magnetic field, one can even print intelligent machine such as robots," said MIT Professor Xuanhe Zhao, an investigator at the army's ISN.

The team has also demonstrated movements that have other applications outside defence. One of these is the delivery of pharmaceuticals.