Laser-fried nanosilver pen paints wires in mid-air (VIDEO)

Harvard engineers have developed a device, which can print silver wires thinner than hair in mid-air. It uses laser to weld together nano-scale silver particles fed by an ink nozzle to create intricate 3D patterns in mid-air.

The device works similar to a 3D-pen, although its movement is guided by a computer. A rotating printing stage allows for curved shapes to be produced.

"I am truly excited by this latest advance from our lab, which allows one to 3D print and anneal flexible metal electrodes and complex architectures 'on-the-fly’," said Jennifer Lewis, lead researcher of the project as reported online in the Proceedings of the National Academy of Sciences.

The most challenging part of the project was to optimize the distance between the nanoparticle ink nozzle and the 100-micrometer spot, where infrared laser anneals it into a strong wire, said study author Mark Skylar-Scott of Harvard's Wyss Institute for Biologically Inspired Engineering.

"If the laser gets too close to the nozzle during printing, heat is conducted upstream which clogs the nozzle with solidified ink," said Skylar-Scott. "To address this, we devised a heat transfer model to account for temperature distribution along a given silver wire pattern, allowing us to modulate the printing speed and distance between the nozzle and laser to elegantly control the laser annealing process 'on the fly’."

The method allows fast printing of electroconductive structures like antennas, biomedical devices and sensors.

The research is based on the team’s previous work, which was to create the silver ink. Previously, however, it had to be annealed in a furnace, Skylar-Scott told IEEE Spectrum. Lewis previously used silver nanoparticle spray to print wires on the outside of a small hemispherical dome.

The team’s next focus would be on using new materials, particularly ceramics and semiconductor materials, to work with their technique.