Researchers from the Shenzhen Campus of Sun Yat-sen University, Carnegie Mellon University, the Chinese University of Hong Kong and Zhejiang University have created a new phase-shifting material — dubbed a magnetoactive phase transitional matter (MPTM) — by embedding magnetic neodymium-iron-boron microparticles in gallium, a metal with a very low melting point (29.8 degrees Celsius). The team’s material can reversibly switch between solid and liquid phase by heating with alternating magnetic field or through cooling.
“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,” said Dr. Chengfeng Pan, a researcher at the Chinese University of Hong Kong.
“Giving robots the ability to switch between liquid and solid states endows them with more functionality.”
“The magnetic particles here have two roles,” added Dr. Carmel Majidi, a researcher at 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 team’s new material, MPTM, boasts an extremely fluid liquid phase compared to other phase-changing materials, whose ‘liquid’ phases are considerably more viscous.
Before exploring potential applications, the researchers 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 a video, a robot shaped like a person liquefies to ooze through a grid after which it is extracted and remolded back into its original shape.
Schematic and applications of the liquid-solid phase transition of MPTM. Image credit: Wang et al., doi: 10.1016/j.matt.2022.12.003.
“Now, we’re pushing this material system in more practical ways to solve some very specific medical and engineering problems,” Dr. Pan said.
On the biomedical side, the authors 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; no actual screwing required).
“Future work should further explore how these robots could be used within a biomedical context,” Dr. 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.”
The team’s work appears in the journal Matter.
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Qingyuan Wang et al. Magnetoactive liquid-solid phase transitional matter. Matter, published online January 25, 2023; doi: 10.1016/j.matt.2022.12.003
