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Laser pen prints free-standing silver wires the width of a hair

A laser pen that directly prints metallic, free-standing 3D structures, without auxiliary support material, has been developed by researchers at Harvard’s Wyss Institute for Biologically Inspired Engineering and the John A. Paulson School of Engineering and Applied Sciences (SEAS).

The work was reported in the Proceedings of the National Academy of Sciences.

The pen uses an ink of silver nanoparticles to print wires the width of a human hair. The nanoparticles pass through a printing head and are annealed with the laser to harden them. The pen nozzle uses a rotary print stage to enable freeform curvature for printing shapes like spirals. The pen can also make sharp angular turns, all written into thin air.

The team name potential applications for the pen as being electronic and biomedical devices relying on customised metallic architectures.

The research was led by Wyss core faculty member Jennifer Lewis, who is also the Hansjörg Wyss Professor of Biologically Inspired Engineering at SEAS. ‘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,’ she told the Harvard Gazette.

The silver wires exhibit excellent electrical conductivity and the pen has the advantage of being able to print the wires directly on low-cost plastic substrates.

Wyss Institute Postdoctoral Fellow Mark Skylar-Scott told the Harvard Gazette that the most challenging aspect of developing the technique was optimising the nozzle-to-laser separation distance: if the laser beam is too close to the nozzle then heat is conducted upstream, which solidifies the ink and clogs the nozzle.

The team were able to modulate the printing speed and distance between the nozzle and laser to control the annealing process.

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