Printing in Free Space

A new kind of 3-D printer forms wires in midair.

A 3-D printer “draws” a coiled antenna in the air. What allows the printer to work this way is a laser that hardens an “ink” of silver nanoparticles as they emerge from the nozzle.

A 3-D printer “draws” a coiled antenna in the air. What allows the printer to work this way is a laser that hardens an “ink” of silver nanoparticles as they emerge from the nozzle.

Image courtesy of Mark Skylar-Scott

In action, what looks like a sharp glowing pen squeezes out a coil of silver, starting from a base and curling upward into the air. It’s actually a nozzle attached to a 3-D printer, and the coil of silver, made of an ink composed of nanoparticles, is thinner than a strand of hair. A few twisting motions, and the microscopic wire emerges from the nozzle to form sharp angles, a spherical antenna, a butterfly with open wings.

These complex shapes, and their ability to hold up as freestanding structures, represent a big step forward in 3-D metal printing, which in the past has produced curvilinear structures by printing them flat on a supportive base (also called a substrate) and later heating them to solidify the material. That two-step process limited the structures’ complexity. Now a technique pioneered by Harvard researchers at the Wyss Institute for Biologically Inspired Engineering and the Paulson School of Engineering and Applied Sciences opens new possibilities: printed metal will be able to assume more—and more complicated—shapes, for applications ranging from 3-D antennas to electrical interconnects.

The breakthrough innovation is a laser positioned right beside the 3-D printer nozzle, says Mark Skylar-Scott, a Wyss Institute postdoctoral fellow in materials science and electrical engineering and lead author of a May 31 Proceedings of the National Academy of Sciences paper on the research. As the ink—actually silver nanoparticles suspended in a polymer solution—flows out of the nozzle, the metallic wire has the consistency of toothpaste: not liquid, but also not rigid enough to form freely supported, complex 3-D structures.

The laser heats the ink as it emerges from the nozzle, annealing it; the nanoparticles fuse together and the polymer decomposes so that the printed filament becomes a solid yet flexible metal wire able to support its own weight as the printhead, moving in x, y, and z axes, forms it into a number of shapes, including helical springs and those curved butterfly wings.

During the fusing process, the metal achieves an electrical conductivity that nearly matches that of bulk silver. And the laser’s precision and the ability to adjust its temperature “on the fly,” Skylar-Scott says, enables researchers to vary the level of conductivity within a single structure and to heat only the wire, without risking damage to the substrate, which could be made of plastic, rubber, or flexible materials.

Working as he does in the research lab of Wyss professor of biologically inspired engineering Jennifer Lewis, who is his coauthor on the paper, Skylar-Scott sees many potential uses for these complex metal structures: in biomedical devices, wearable and flexible electronics, sensors, displays, small antennae, electromagnetic devices, a coil in a speaker, a transformer to amplify signals. But first, he says, someone will have to further refine the technique. “Right now there are a lot of knobs to tweak,” he says, including the position of the laser, its pulse frequency and direction, and the print speed. “With a bit more work,” adds Lewis, “these parameters can be optimized and automated.”

Read more articles by Lydialyle Gibson

You might also like

This Astronomer is Sounding a Warning on 'Space Junk'

As debris accumulates in low Earth orbit, the danger of destructive collisions continues to rise.

Isaac Kohlberg to Step Down as Head of Harvard Technology Development

Partnerships and licensing office could become more critical as funding cuts loom

How AI Energy Demand Costs Consumers

Utilities shift AI infrastructure costs onto consumers.

Most popular

“Do You Find That Reasonable?” Harvard Undergraduates Discuss a Changing University

A student panel grapples—civilly—with shifting policies and differing opinions.

The Professor Who Quantified Democracy

Erica Chenoweth’s data shows how—and when—authoritarians fall.

Harvard Adopts Reforms as Higher Ed Turmoil Continues

University creates new “interfaith engagement” role; Columbia, Brown settle with the government.

Explore More From Current Issue

A six-foot-tall, five-panel folded screen stands in a field of grass next to the woods. It's painted different shades of green, with some squares cut out that represent digital pixels.

Julia Rooney’s paintings cross the analog-digital divide.

group of students perform on a stage in front of a crowd

In comedy groups, students find ways to be absurd, present, and a little less self-conscious.

Illustration of Donald Trump and Alan Garber wearing boxing gloves, facing off beneath the quote: “The stakes are so high that we have no choice.”

Introducing a guide to the issues, players, and stakes.