How to print metal in mid-air Thursday, 19 May 2016

A team of American engineers has worked out how to use 3D printing to create complex metallic architectures in one step without auxiliary support material.

Jennifer Lewis from Harvard University's Wyss Institute for Biologically Inspired Engineering said they used an ink composed of silver nanoparticles, sending it through a printing nozzle and then annealing it using a precisely programmed laser that applies just the right amount of energy to drive the ink’s solidification.

The printing nozzle moves along x, y, and z axes and is combined with a rotary print stage to enable freeform curvature. In this way, tiny hemispherical shapes, spiral motifs, even a butterfly made of silver wires less than the width of a hair can be printed in free space within seconds.

“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 Lewis.

She said, when compared to conventional 3D printing techniques used to fabricate conductive metallic features, the laser-assisted direct ink writing is not only superior in its ability to produce curvilinear, complex wire patterns in one step, but also in the sense that localised laser heating enables electrically conductive silver wires to be printed directly on low-cost plastic substrates.   

Her colleague Mark Skylar-Scott said the most challenging aspect of honing the technique was optimising the nozzle-to-laser separation distance.

“If the laser gets too close to the nozzle during printing, heat is conducted upstream which clogs the nozzle with solidified ink,” he said.

“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.”

They say the technique opens up potential applications in electronic and biomedical devices that rely on customised metallic architectures.


A spiral is created without any support structure. Photo: Lewis Lab/Wyss Institute at Harvard University