Raphael Thys
Scientists have achieved a breakthrough in robotics: a shape-shifting robot that can switch between liquid and metallic states to navigate difficult environments without sacrificing strength.
Because they can be both soft and hard, the tiny sea cucumber-inspired robots can overcome the limitations of robots being just one thing or the other, and therefore have the potential to find greater utility in areas like electronics assembly and even medical applications to offer .
The researchers had the robots navigate obstacle courses, remove objects or put them in a model of the human stomach, and even liquify to escape from a cage before reforming back into their original humanoid form.
“Enabling robots to switch between liquid and solid states gives them more functionality,” says engineer Chengfeng Pan of the Chinese University of Hong Kong in China.
Timelapse showing the robot’s daring prison escape. (Wang et al., object2023)
There are many uses for small robots that can get around in places too small or awkward for humans to do with typical tools, from tricky repair jobs to targeted drug delivery. But hard materials aren’t the best for navigating tight spaces or tight angles, while soft, more flexible robots tend to be weak and more difficult to control.
To find a compromise, a team of researchers led by Pan and his colleague Qingyuan Wang of Sun Yat-sen University in China turned to nature for inspiration. Animals like sea cucumbers can alter the stiffness of their tissues to improve carrying capacity and limit physical damage, while squid can alter the stiffness of their arms for camouflage, object manipulation, and locomotion.
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To create a robot that could do something similar, the researchers needed a non-toxic material that could easily switch between soft and rigid states at ambient temperature. They turned their attention to gallium, a soft metal that has a melting point of 29.76 degrees Celsius (85.57 degrees Fahrenheit) at normal pressure — just a few degrees below the average human body temperature. You can smelt gallium just by holding it in your hand.
The researchers embedded a gallium matrix with magnetic particles, creating what they call a “solid-liquid magnetoactive phase-change machine.”
“The magnetic particles have two roles here,” says mechanical engineer Carmel Majidi of Carnegie Mellon University, one of the lead authors of the team’s work.
“One is that they make the material respond to an alternating magnetic field, so you can inductively heat the material and cause the phase change. But the magnetic particles also give the robots mobility and the ability to move in response to a magnetic field.”
After testing whether the solid-to-liquid transition was reversible (it was), the researchers ran their little robots through a series of tests. The robots could leap small moats, climb over obstacles, and even split up to perform cooperative tasks by moving objects around before rejoining and solidifying again.
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They even melted a small humanoid version – shaped like a Lego figure – to escape a small prison cell, seep through the bars and regroup on the other side in an homage to a scene from the Terminator 2 movie.
Next, the team explored practical applications. They created a model of a human stomach and had the robot gobble up a small object inside and remove it – a useful way, it’s imagined, for pulling out swallowed batteries, for example – and then do the reverse process, launching an object on its way The team hopes it could provide drugs.
For circuit repair, the robots could navigate to and melt circuits to act as conductors and solder; and even act as a fastener, seeping into threaded sockets and solidifying and performing the function of a bolt without anyone having to fasten it in place.
For real applications the phase change machine would have to be optimized a bit. For example, since the melting point of the human body is higher than the melting point of pure gallium, a robot designed for biomedical purposes could have a gallium-based alloy matrix that would increase the melting point while maintaining functionality.
According to the researchers, this has yet to be investigated in detail.
“Future work should further explore how these robots could be used in a biomedical context,” says Majidi.
“What we are showing are just one-off demonstrations, proofs of concept, but many more studies are needed to explore how this might actually be used for drug delivery or foreign body removal.”
The research was published in object.