Gallium – sometimes colloquially referred to as the Terminator metal for its resemblance to the shape-shifting cyborg assassin – is glorious stuff.
Among other weird features, this metal may be solid at room temperature, but it’s so soft that you can cut it with a butter knife. If you hold it in your hand, it’ll exceed its melting point and turn into a shiny mush. Now, as revealed by a brand new paper in Physical Review Letters, scientists have been able to make droplets of it beat with a clear rhythm, a bit like a human heart.
Led by the University of Wollongong, this new paper begins by noting that various techniques can be used to initiate fluid motions in certain liquid metals – such as mercury – but that they often produce “irregular motion” that’s “difficult to deactivate or control.”
The authors then explain that, for the very first time, they have managed to use electrical currents to cause metal drops of gallium to exhibit a “heart beating effect”, one that moves at an identifiable, clearly defined frequency.
Not only does this freaky action represent a rather exciting discovery for the team, but they mention that the application of an electrical current caused the symmetry of the drops to shift. This means that the gallium gets wonky each time it beats, allowing it to be propelled at velocities of around a centimeter (0.39 inches) per second.
Making this discovery wasn’t exactly a walk in the park, mind you.
As elucidated by Forbes, the heated liquid gallium was placed on a circular electrode. It’s dunked in a hydroxide solution, which is then given an electrical field to interact with.
This triggers an electrochemical oxidation reaction, and the gallium droplet begins to oxidize. The resulting gallium oxide possesses less surface tension than its pure elemental form, and that's where the scientific sorcery happens.
Now, surface tension describes, in crude terms, the attractive forces between the molecules at the surface of a material. Less of it means that it can’t hold together in the same way, and it begins to flatten out in a pancake-like shape.
The electrode, which is slightly tilted, causes this flatter droplet to move away from it. This removes it from the electrochemical reaction, which causes it to pop up again into a more spherical shape. This cycle continues at a fairly quick rate, which mimics the action of a beating heart – and it allows the drop to move uphill.
Change the electrical current and change the heartbeat, up to 610 beats per minute. It’s extremely cool stuff. Check out this video by New Scientist demonstrating the wizardry at hand:
It’s extremely early days, of course; this is just a proof-of-principle technique at present. If, however, you can imagine gallium-infused muscles for a moment – perhaps in prosthetics or so-called “soft robots” – it’s not difficult to see how electrical currents could be used more precisely to make them move.
Considering how malleable gallium is, and how frequently it’s already used in electronics, one can see how this won’t remain a sci-fi concept for forever. Besides, as the authors note, plenty of biological species already use “exquisite methods” for using internal fluids to propel themselves around and engage in essential biochemistry.
By contrast, human fluidic technology still relies on “inelegant” mechanical flow systems. Gallium hearts, then, could be our way of catching up with evolutionary biology.
That, or we've just seen the start of the development of the T-1000. A tad unnervingly, the team behind the paper explained that this time-traveling killer served to be the project's initial source of inspiration.
