T-1000 is here: Scientists make breakthrough in shape-shifting robots

Scientists have developed a remarkable "shape-shifting" robot made of gallium, enriched with magnetic particles, that can liquify and then revert to its original shape when an alternating magnetic field is applied. 

This groundbreaking development provides the robot with the ability to maneuver through tight spaces and even escape from captivity. Scientists have high hopes that this technology could be employed in medicine to address various challenges, such as foreign object removal from the body. 

A proof of concept study was published in the journal Matter in January 2023, outlining the team's progress in this new frontier of robotics.

Soft-bodied robots, which can deform to move in various ways, have become increasingly popular among scientists over the last few decades. These robots can deform their bodies to move in many ways, for example, swimming, climbing, rolling, and jumping their way to get a job done. 

Even more impressively, some robots have the ability to shape-shift between several distinct configurations. However, they remain solid and thus are unable to pass through gaps that are narrower than their bodies. For example, we would be out of luck if we needed a soft-bodied robot to fit through a hole only a few millimeters wide so that we could tighten a bolt inside a machine without dismantling it.

"Giving robots the ability to switch between liquid and solid states endows them with more functionality. Now, we're pushing this material system in more practical ways to solve some very specific medical and engineering problems."

Chengfeng Pan, engineer at The Chinese University of Hong Kong

For the past few years, scientists have been playing around with liquid-based robots. These robots can fit almost anywhere by squishing down, stretching out, and even splitting into multiple streams and then coming back together. However, a liquid robot's greatest strength is also its greatest weakness: liquids cannot take much pressure without deforming; so while they can get almost anywhere, they are pretty weak, which limits what they can do once they reach the destination.

Therefore an international team of engineers developed a new liquid robot mixing in solid microscopic magnetic particles to get the best of both worlds, they call it a magnetoactive solid-liquid phase transitional machine, or MPTM.  By using magnets to push and pull the magnetic particles, MTPM can shape-shift to perform tasks in the same way some soft robots do. And much like the T1000 from Terminator 2, it can also change from solid to liquid and get back to solid again.

The liquid metal the team used is gallium and at sea level, gallium melts just before its temperature hits 30 degrees celsius. In other words, its melting point is high enough for it to stay solid in your typical room but low enough to melt in the palm of your hand. In order to get gallium to melt whenever they want, the team controls its temperature by exposing it to a magnetic field that keeps flip-flopping the direction it is pointing at.

That causes all the magnetic particles suspended in the gallium to collectively flip flop as well and all that movement creates heat. So while it is exposed to this magnetic field, the temperature inside the robot becomes hot enough for it to melt and stay liquid. Then the team can use magnets to push or pull it wherever they want it to go and in whatever shape it needs to be in. And when they need it to be solid, they just turn the field off and wait for the metal to cool back down as hot things do. 

However, this MPTM is not actually the first solid-to-liquid transitioning material, but past attempts were a lot goopier and the lack of fluidity limited their usefulness. While testing their new kind of liquid metal, robot researchers were able to solder a small LED into a hard-to-reach circuit by having it act as a universal screw.

The robot melted down, filled a threaded hole, and then solidified to hold the two plastic plates together — kind of a single-use robot, but it did get the job done. They also demonstrated MPTM's potential as a medical device in one test where they had it enter a fake stomach in its solid form, liquefy to surround a foreign object, and then solidify to grab hold of the object. Then some magnets outside the stomach guided the whole kit and the foreign object right out.

In another experiment, they had it grab a drug, go to a specific target location in the fake stomach, liquefy to release the drug in that location, and then skedaddle. 

Now, the internal temperature of a live human body is well over the melting point of gallium. So if it ever becomes an actual medical procedure, we would need to use a different metal. Luckily, the team already has their sights set on a gallium alloy that can stay solid inside a human when it needs to.

In the final experiment, there was the prison break. They made a tiny human-shaped MPTM robot and stuck it behind literal bars. It was able to melt down, trickle out of its cell and then retake its human shape — all in less than 10 minutes. MPTM might be used in a range of fields that require specific precise actions in hard-to-reach places, and it is all thanks to magnetism.

"Giving robots the ability to switch between liquid and solid states endows them with more functionality," lead author of the study Chengfeng Pan, an engineer at The Chinese University of Hong Kong, said in a statement. "Now, we're pushing this material system in more practical ways to solve some very specific medical and engineering problems."