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Lasers and nanoparticles combine to allow metalic 3D printing in midair

Traditional 3D printing has limits that have negatively impacted its usefulness. For one, almost all 3D printers use plastic as the medium, and that plastic needs to be supported during the printing process. An experimental printer developed by Harvard’s Wyss Institute and the School of Engineering and Applied Sciences (SEAS) uses nanoparticles and lasers to make metallic 3D printing feasible in midair.

The printing medium is a special formulation of silver nanoparticle ink. The ink is fed through a printing nozzle that can move along the x, y, and z axis. The silver ink itself would just drip out of the nozzle and splash on the floor before solidifying. However, the team led by Wyss researcher Jennifer Lewis programmed a laser to follow the nozzle around, exposing the extruded ink to just the right amount of thermal energy to solidify it into a wire thinner than a human hair.

The result shown in the video below is fascinating — the silver wire anneals so quickly after leaving the nozzle that it doesn’t look like liquid ink at all. The team was able to create complex designs and structures like spirals, zig-zags, and even little silver butterflies. The silver ink is highly electrically conductive when solidified, and the team says the system can be used to print flexible circuit boards. All you need is an inexpensive plastic substrate.

Getting this level of detail from the nozzle was a substantial challenge. The nozzle can be programmed to move wherever you want, but the laser needs to follow precisely and expose the ink to the right amount of energy. Too little and the ink won’t solidify, but too much and the silver nanoparticles would clog the nozzle. Keeping the heat consistent at the nozzle actually means the laser can’t just be on at a consistent level. The researchers had to devise a model that takes into account how heat is transferred across a given wire structure. That affects how fast the nozzle moves, the flow of ink, and how much energy is applied by the laser.

You put all that together and you have a machine that can print almost any shape without a bunch of supporting structures that are just going to be trimmed away. The team envisions this sort of technology being used to make flexible electronics, custom sensors, and medical device prototypes. This is just an experimental system right now. The build volume is small and it’s complicated to maintain. But in the future? Who knows?

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