Shapeshifting robot can turn from a liquid to a solid

Taking inspiration from sea cucumbers — and arguably also from the T-1000 from Terminator 2: Judgement Day — engineers in China and the US have designed miniature robots that can rapidly and reversibly shift between liquid and solid states. On top of being able to shapeshift, the robots are magnetic and can conduct electricity. The researchers put the robots through an obstacle course of mobility and shape-morphing tests in a study published in the journal Matter.

Where traditional robots are hard-bodied and stiff, ‘soft’ robots have the opposite problem: they are flexible but weak, and their movements are difficult to control. Study leader Chengfeng Pan, from The Chinese University of Hong Kong, noted, “Giving robots the ability to switch between liquid and solid states endows them with more functionality” — so the team created the new phase-shifting material, dubbed a magnetoactive solid-liquid phase transitional machine, by embedding magnetic particles in gallium, a metal with a very low melting point (29.8°C).

“The magnetic particles here have two roles,” said senior author Carmel Majidi, from Carnegie Mellon University. “One is that they make the material responsive to an alternating magnetic field, so you can, through induction, heat up the material and cause the phase change. But the magnetic particles also give the robots mobility and the ability to move in response to the magnetic field.”

This is in contrast to existing phase-shifting materials that rely on heat guns, electrical currents or other external heat sources to induce solid-to-liquid transformation. The new material also boasts an extremely fluid liquid phase compared to other phase-changing materials, whose ‘liquid’ phases are considerably more viscous.

Before exploring potential applications, the team tested the material’s mobility and strength in a variety of contexts. With the aid of a magnetic field, the robots jumped over moats, climbed walls and even split in half to cooperatively move other objects around before coalescing back together. In one instance, a robot shaped like a person liquefied to ooze through a cage, after which it was extracted and remoulded back into its original shape.

“Now, we’re pushing this material system in more practical ways to solve some very specific medical and engineering problems,” Pan said.

On the biomedical side, the team used the robots to remove a foreign object from a model stomach and to deliver drugs on demand into the same stomach. They also demonstrated how the material could work as smart soldering robots for wireless circuit assembly and repair (by oozing into hard-to-reach circuits and acting as both solder and conductor) and as a universal mechanical ‘screw’ for assembling parts in hard-to-reach spaces (by melting into the threaded screw socket and then solidifying, with no actual screwing required.)

“Future work should further explore how these robots could be used within a biomedical context,” Majidi said. “What we’re showing are just one-off demonstrations, proofs of concept, but much more study will be required to delve into how this could actually be used for drug delivery or for removing foreign objects.”

Image shows the shapeshifting robot after its escape from a cage. Image courtesy of Wang and Pan et al (screenshotted from a video) under CC BY-SA.