Scientists in Edinburgh have developed a new 3D-printing technique that could have a huge impact on manufacturing.

Researchers at Heriot-Watt University in Edinburgh, led by Dr Jose Marques-Hueso from the Institute of Sensors, Signals and Systems, have created a method of 3D printing that uses near-infrared light to create complex structures containing multiple materials and colours.

To do this, they modified an established process called stereolithography, and pushed the boundaries of multi-material integration. Ordinarily, a conventional 3D printer would selectively solidify a liquid resin using a blue or UV laser, going layer by layer to build an object. But this approach makes it difficult to mix materials.

In the new project, scientists used a near-infrared (NIR) light source which could reach much further into the resin vat, and therefore did not need to print in layers. The researchers say the findings could have huge implications for industry – particularly in healthcare and electrical applications.

“The novelty of our method, which has never been done before, is to use the NIR invisibility windows of materials to print at a depth of over 5cm, whereas the conventional technology has a depth limit of around 0.1mm,” says Marques-Hueso. “This means that you can print with one material and later add a second material, solidifying it at any position of the 3D space, and not only on top of the outer surfaces.

“For example, we can print a hollow cube that is mostly sealed on all sides. We can then come back later and print an object, made from an entirely different material, inside this box, because the NIR laser will penetrate through the previous material as if it were invisible, because in fact it is completely transparent at the NIR.”

Dr Adilet Zhakeyev, a researcher at Heriot-Watt University who has worked on the project for nearly three years, adds: “Fused deposition modelling (FDM) technology was already able to intermix materials, but FDM has a low resolution, where the layers are visible, while light-based technologies, such as stereolithography, can provide smooth samples with resolutions under five micrometres.”

One of the key components of the project has been the development of resins containing nanoparticles with a special trait known as ‘optical upconversion’. These nanoparticles absorb the near-infrared photons and transform them into blue photons which then solidify the resin. By distributing these particles through the resin, it can be hardened selectively at the point where the laser is focused, rather than all the way through the material, meaning material deeper within can be solidified.

This new method allows multiple materials with different properties to be printed in one sample, opening up new possibilities such as 3D printing objects inside cavities, restoring broken objects or bioprinting inside a body through the skin. “In the same research project, we had previously developed a resin that can be selectively copper-plated,” says Marques-Hueso. “Combining both technologies, we can now 3D print with two different resins and selectively cover just one of them in copper by using a simple plating solution bath. This way, we can create integrated circuitry in 3D, which is very useful for the electronics industry.”

The other advantage of this technology is that it could be surprisingly cheap. “A clear advantage of this technique is that the full machine can be built for less than £400,” says Marques-Hueso. “Some other advanced technologies that use lasers, such as two-photon polymerisation (2PP), require expensive ultrafast lasers in the order of tens of thousands of pounds, but this is not our case because our specialised materials allow the use of inexpensive lasers.”

He adds: “Now that we have results to support our claims, we hope to partner with businesses and develop this technology further.”

Extracted from IMechE website, read more here

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