In the 1991 James Cameron science fiction film Terminator 2: Judgement Day, the villain was a shape-shifting android called T-1000. Now engineers have designed something similar – a robot that can shift between solid and liquid states, and back again.
The magnetic and electrically conductive robots were put through the ringer by the researchers, who made it manoeuvre through an obstacle course, climb walls, and even escape through the bars of a tiny jail cell – uncannily similar to the Terminator 2 scene where the T-1000 oozes its liquid metal form right through a prison bar door.
But, instead of using this phase-changing ability to try to assassinate the fictional leader of the human rebellion, John Connor, the technology could one day be used for good — improving health care by delivering drugs or removing foreign objects.
The researchers’ design was actually inspired by sea cucumbers, which can reversibly alter the stiffness of their tissues – increasing the amount of force that can be applied to it and preventing physical damage from the environment.
“Giving robots the ability to switch between liquid and solid states endows them with more functionality,” says Dr Chengfeng Pan, an engineer at the Chinese University of Hong Kong who led the study, which has been published in the journal Matter.
Because traditional robots are hard-bodied but stiff, whereas soft robots are flexible but weak and their movements are difficult to control, the team created a new material called “magnetoactive solid-liquid phase transitional machine” or MPTM.
MPTM is made of a rare-earth neodymium (NdFeB) magnetic particles embedded in gallium (Ga) – a metal with a very low melting point of only 29.8°C.
“The magnetic particles here have two roles,” says senior author Carmel Majidi, a Professor in Mechanical Engineering at Carnegie Mellon University in the US.
“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.”
Existing phase-shifting materials rely on heat guns, electrical currents, or other external heat sources to induce a transformation from a solid to liquid state. Then, when they are liquid, are much more viscous than the extremely fluid liquid phase of MPTM.
These unique properties result in a robot that split in half to cooperatively move other objects around before coalescing – all with just the aid of a magnetic field.
“Now, we’re pushing this material system in more practical ways to solve some very specific medical and engineering problems,” says Pan.
The team showed that MPTM could be used as soldering robots for assembling and repairing wireless circuits, demonstrating it could ooze into hard-to-reach circuits and act as both solder and conductor.
It could also be a universal mechanical “screw” for assembling parts in hard-to-reach spaces because MPTM can also melt into a threaded screw socket and then solidify – no actual screwing required.
They were even able to use the material to remove a foreign object from a model stomach and to deliver drugs on-demand into the same stomach.
“Future work should further explore how these robots could be used within a biomedical context,” concludes 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.”