Inspired by sea cucumbers, engineers have designed miniature robots that quickly and reversibly switch between a liquid and solid states. On top of being able to change shape, the robots are magnetic and can conduct electricity. Researchers put robots through an obstacle course of mobility and shape-shifting tests in a study published Jan. 25 in the journal Nature. Theme.
Where traditional robots are hard and rigid, “soft” robots have the opposite problem; They are flexible but vulnerable, and it is difficult to control their movements. “Giving robots the ability to switch between a liquid and solid state gives them more functionality,” says Chengfeng Pan, an engineer at the Chinese University of Hong Kong who led the study.
The team created a new phase-changing material—dubbed a “solid-liquid magnetic phase transition machine”—by fusing magnetic particles into gallium, a metal with a very low melting point (29.8 degrees Celsius).
“The magnetic particles here have two roles,” says senior author and mechanical engineer Carmel Magdy of Carnegie Mellon University. “One is that they make matter respond to an alternating magnetic field, so you can, through induction, heat matter and cause a phase change. But magnetic particles also give robots mobility and the ability to move in response to a magnetic field.”
This is in contrast to current phase transformation materials that rely on heat guns, electric currents, or other external heat sources to induce a transition from a solid to a liquid. The new material also has a very fluid liquid phase compared to other phase-changed materials, whose “liquid” phases are significantly more viscous.
Before exploring potential applications, the team tested the materials’ motion and strength in a variety of contexts. With the help of a magnetic field, the robots jumped over ditches, scaled walls, and even split in half to cooperatively move other objects before melding back together. In one video, a robot in the shape of a person is reduced to a liquid to squirt through a mesh and then extracted and molded back to its original form.
“Now, we’re pushing this material system in more practical ways to solve some very specific medical and engineering problems,” Pan says.
In the biomedical aspect, the team used robotics to remove a foreign body from a model stomach and deliver drugs on demand into the stomach itself. They also show how the material can act as smart soldering robots for assembling and repairing radio circuits (by squirting into hard-to-reach circuits and acting as solder and conductor) and as a universal mechanical “screw” for assembling parts into solid access spaces (by fusing into a threaded socket and then hardening; no actual tightening is needed.)
“Future work should explore how these robots can be used in a biomedical context,” Majidi says. “What we’re showing are just one-off demonstrations, proofs of concept, but more study will be needed to delve deeper into how this can actually be used for drug delivery or for foreign body removal.”