3D-printed liquid metal brings stretchable gadgets closer

Image caption,
The structures are free-standing - with liquid metal inside

Stretchable electronics may start appearing in the near future, after researchers created liquid metal structures on a 3D printer.

A team at North Carolina State University used an alloy of two metals - gallium and indium - that are liquid at room temperature but form a "skin" when exposed to air.

When printed, the shapes can be stretched without reverting to blobs.

The technology could be used for micro-circuits and wearable electronics.

The technique is detailed in the journal Advanced Materials.

"The metal forms a very thin layer of oxide and because of it, you can actually shape it into interesting shapes that would not be possible with normal liquids like water," said the lead author, Michael Dickey.

He explained that the printer used a syringe to stack the droplets on top of one another.

The droplets retained their shape without merging into a single big droplet, which allowed the scientists to then shape the metal.

"It's an additive manufacturing technique, so you're basically directly printing the material in 3D space," Dr Dickey said.

"The resulting structures are soft, and if you embed them in, say, rubber, for example, you can create structures that are deformable and stretchable."

Gadget makers could potentially use the technique to make connections between electronic components that would not break if their device was pulled or twisted.

Wearable tech

The work was "potentially revolutionary," said Jason Heikenfeld, professor of electrical engineering at the University of Cincinnati, who was not involved in the research.

"Folks have tried to work with liquid metal for some time - some of us when we were younger would break up a thermometer and you'd see liquid metal - mercury - go all over the place," he said.

"It was evidence that although these materials have a significant upside, in terms of what you can do with them, they are extremely challenging to work with."

Flexible electronics are starting to emerge, with companies such as Samsung, LG and Nokia experimenting with bendy displays for phones and televisions.

But this technology was not stretchable - something you could achieve when you involved liquid metals, said Dr Heikenfeld.

"Stretchable is a whole other game because you're now talking about wearable and conformable," he said.

He added that the recent research also addressed another important issue of using liquid metals - toxicity. Unlike mercury, the gallium and indium alloy was safe, he said.

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