These shapeshifters melt and reshape thanks to magnetic fields

Shape-shifting liquid metal robots may not be limited to science fiction anymore.

Mini machines can Switch from solid to liquid and back again to squeeze into tight spaces and perform tasks such as soldering a circuit board, the researchers reported Jan. 25 Thing.

This phase shift property, which can be controlled remotely with a magnetic field, is thanks to gallium metal. The researchers combined the mineral with magnetic particles To guide the movements of the metal with magnets. This new material could help scientists develop soft, flexible robots that can swing through narrow passages and be externally steered.

Scientists have been developing magnetically controlled soft robots for years. Most of the materials that exist for these robots are either made of stretchy but rigid materials, which cannot pass through the narrowest spaces, or magnetic fluidswhich is fluid but unable to hold heavy objects (SN: 7/18/19).

In the new study, the researchers blended both approaches after discovering them Inspiration from nature (SN: 3/3/21). “Sea cucumbers can change their hardness very quickly and reverse them,” says mechanical engineer Carmel Magidi of Carnegie Mellon University in Pittsburgh, for example. “Our challenge as engineers is to simulate this in soft materials systems.”

So the team turned to the metal gallium, which melts at about 30 degrees Celsius — just above room temperature. Instead of attaching a heater to a piece of metal to change its state, the researchers exposed it to a rapidly changing magnetic field to liquefy it. The alternating magnetic field generates electricity inside the gallium, causing it to heat up and melt. The material hardens when allowed to cool to room temperature.

Because the magnetic particles are scattered throughout the gallium, the permanent magnets can pull it around. In the solid state, magnets can move matter at a speed of about 1.5 meters per second. The upgraded gallium can also carry about 10,000 times its own weight.

External magnets can still manipulate the liquid form, causing it to expand, split and fuse. But controlling the movement of the liquid is more challenging, because the particles in gallium can rotate freely and have magnetic poles that are not aligned as a result of melting. Because of their different orientations, the particles move in different directions in response to the magnet.

Majidi and his colleagues tested their strategy in small machines performing different tasks. In a direct demonstration of the film Terminator 2a toy person escaped from a prison cell by melting through the bars and re-solidifying into their original shape using a mold placed just outside the bars.

On the practical side, one machine removed a small ball from a typical human stomach by melting slightly to wrap around the foreign body before exiting the organ. But gallium alone will turn into a solid inside a real human body, since the metal is a liquid at body temperature, about 37 degrees Celsius, a few metals, such as bismuth and tin, will be added to gallium in biomedical applications to raise the melting point of the substance, As the authors say. In another demonstration, the material was liquefied and re-hardened to solder a circuit board.

Although this phase change material is a huge step in the field, questions remain about its biomedical applications, says biomedical engineer Amir Jafari of the University of North Texas at Denton, who was not involved in the work. He says one of the big challenges is precisely controlling the magnetic forces inside the human body that are generated from an external device.

“It’s a compelling tool,” says robotics engineer Nicholas Pera of Harvard University, who was also not involved in the study. But, he adds, scientists who study soft robots are constantly creating new materials.

“The real innovation that’s coming is in combining these different innovative materials.”