Much like the terrifying T-1000 from the movie Terminator 2, this miniature robot can rapidly switch between liquid and solid states and back again.

Its designers, a team based at Carnegie Mellon University in Pennsylvania, demonstrated the robot’s shapeshifting ability by having it melt into a liquid and ooze through the bars of an enclosed cage before reforming into its solid state once outside.

The team created the phase shifting bot – dubbed a ‘magnetoactive solid-liquid phase transitional machine’ – by embedding magnetic particles in gallium, a metal with a very low melting point of 29.8 °C.

A phase change is the process of matter changing to from one state, either solid, liquid, gas or plasma, to another. These changes occur when sufficient energy is supplied to the system, or a sufficient amount is lost from it.

In the case of the bot, it can be heated into liquid form or cooled into solid form by the application of an external magnetic field via the process of induction. The same magnetic field can also be used to move the robot around.

“The magnetic particles here have two roles,” said senior researcher and mechanical engineer Dr Carmel Majidi of 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.”

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Though currently very much in the proof-of-concept stages, the robot could be used in a vast number of biomedical and industrial applications, the team say.

They have already used it to remove a foreign object from a model stomach and as a drug delivery system.

They have also used it to repair circuits by oozing into hard-to-reach areas and acting as solder and as a mechanical screw by melting it into a threaded screw socket and then solidifying it.

“Future work should further explore how these robots could be used within a biomedical context,” said Majidi.

“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.”

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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.