A New Twist on 3-D Printing: With Liquid Metal

Though it's been around for nearly 30 years, 3-D printing has only recently started to take off -- and the industry is predicted to reach $3.1 billion worldwide by 2016 and $5.2 billion by 2020.

Most 3-D printers thread spools of plastic filament onto a heated nozzle, which drops liquid plastic onto a surface one layer at a time until an object is formed, according to The New York Times.

But researchers at North Carolina State University in Raleigh have spent  four years researching how to conduct 3-D printing in a new way -- with liquid metals.

The team found that by dispensing an alloy of gallium and indium from a needle,  it’s possible to 3-D print metals at room temperature, which  formed flexible structures that can hold their shape. Such bendable metal structures could be used in antennas, flexible displays, and wire bonds, the researchers suggested.

The alloy used in the research instantly forms a skin upon contact with air, about one nanometer thick, allowing the inside to remain a liquid while the exterior holds the structure in place. This method could replace existing techniques used for such 3-D liquid metal printing, which are usually limited to creating spherical structures, the researchers suggested.

Michael Dickey, assistant professor at the university's Department of Chemical and Biomolecular Engineering, published the research along with lead researcher and undergraduate Collin Ladd, and Ju-Hee So and John Muth.

“The thing that doesn’t catch people right away is the fact that we can make wires,” Dickey said. “To me, the stacking on the droplets is not all that surprising, but the fact that you can make wires is really cool because there’s at least two different ways [wires] fail.”

Wires fail from being stretched or exposed to pressure until they are broken, he said -- and this research allowed the researchers to figure out the conditions under which a flexible, conducive material could be formed.

Though this capability has many implications, Dickey says the material itself is limited in that it can’t simply be used alone.

“They would just collapse if you touched them or shook them, so to really make something useful, you’d have to encapsulate them. But I think a compelling argument could be made for co-printing,” he said, suggesting that some kind of ceramic, plastic, rubber or gel polymer could be integrated into a manufacturing process for a product.

Being more focused on teaching and research than the applications of this invention, Dickey said he’s unsure what the exact products to come from this might be, but he guessed that it’s going to “open up some opportunities.”

Another limiting factor of the invention, Dickey noted, is the high price of the metal used. However, it doesn’t make sense to compare the alloy with other materials used in 3-D printing, such as plastic, because the amount of metal needed to create a wire is very little when compared to the amount of plastic needed to create an entire object. The cost of the metal used in their research demonstrations, for instance, was just a few cents.

In the future, the team wants to look at how much smaller they can make the structures -- something Dickey says they didn’t bother with at all in their initial research.

“There’s nothing in the physics per se that suggest you can’t go smaller,” he said. “In fact, if anything, you might be able to make even more complex structures.” The smallest structures formed by the researchers were about 10 micrometers.

For their research, a custom 3-D printer was constructed. While the metal material used in their research can’t simply be plugged into any 3-D printer, Dickey suggested that some minor customizations, such as changing out the printer’s nozzle, could allow for someone to replicate their project.