Gallium, combined with ferromagnetic neodymium-iron-boron particles, melts at 30.6C (87.08F).
When scientists felt an alternating magnetic field through the material, which was shaped like a miniature Lego figurine, its temperature increased – allowing it to melt.
Now a puddle, the magnetic field was able to move the melted metal man from inside a cage to outside – where it was gathered in a mould, reformed and left to cool down after the magnetic field was turned off.
With its temperature back below 30C (86F) in line with ambient room temperature, the robot regained its strength and original shape within 80 seconds of the magnetic field being switched off.
“The magnetic particles here have two roles,” said Carmel Majidi, senior author and mechanical engineer 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.”
Scientists say previous attempts to make shape-shifting robots have needed heat guns, electrical currents or other external heat sources to control the shift from solid to liquid.
But by enriching gallium with magnetic particles and ensuring you work in a strictly temperature-controlled room, a magnetic field is all that is needed.