A 3D-printer that uses crossed light beams to set its ink

A team of Australian researchers have developed an ink that could be used in a brand-new, potentially much faster 3D-printing concept.

Under the technology, a laser’s light beam lances through ink, exciting the atoms in its path. Some of the molecules change shape as they’re touched by the light but they don’t react with anything – yet. A second light beam, in a different colour, hits the ink at another angle, causing contortions in a different set of molecules.

Where these light beams intersect, the two excited molecules react with each other and become solid.

This is the idea driving the new 3D-printing technique.

“Normally, in a 3D printer the inkjet moves around in two dimensions, slowly printing one 2D layer before moving up to print another layer on top,” says Dr Sarah Walden, a researcher at Queensland University of Technology’s Centre for Materials Science.

“But using this technology, you could have a whole two-dimensional sheet activated, and print the entire sheet at once.”

This technology is on the cusp of being taken to market – but there are a few things holding it back.

“These two-colour printers are just being developed now. There’s one commercial one on the market,” says Walden.

At the moment it’s hard to find substances which respond to specific shades of light – and react with each other. This is where Walden and her colleagues’ research comes in.

“We’re making inks that could be used in that type of printing and we think it could really speed up the rate at which we 3D-print materials,” says Walden.

The team has just published a paper in Nature Communications describing one of these inks.

“We’ve tried a lot of things that didn’t work, as you do in research. It was great to finally find a system that behaves,” says Walden.

The system works by manipulating two substances: one a type of chemical called an azobenzene, and the other a type of ketene. These two chemicals don’t react with each other in typical conditions. But when the molecules are exposed to light (red or green light in the azobenzene’s case, UV light in the ketene’s case) each changes shape into a form that makes them react with one another to form a solid compound.

This trick means that, absent both shades of light, nothing happens to the substance – meaning it can be used in subsequent manufacturing processes.

“We use the colours of light to basically turn them into their reactive forms,” summarises Walden.

“But if they don’t find a reaction partner, they just go back to their nonreactive forms. So, when we turn the light off, there won’t be any reactions happening subsequently.”

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Read more: Making light of molecule manufacture

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The researchers initially tested the process with a tuneable laser in the QUT labs, but then were able to replicate it with commercially available light-emitting diodes (LEDs).

Walden says that, so far, the technology has been used to make hand-held, proof-of-concept objects.

“We’ve made little materials in our lab, so we know that this two-colour process works,” she says.

The interdisciplinary team wants to find other chemicals which can respond to light and each other like this.

“You can start to think of biocompatible-type materials with visible light – but that’s well down the track,” says Walden.