Heriot-Watt University scientists develop new 3D printing technique

Scientists in Edinburgh at Heriot-Watt University have developed a new 3D printing technique with the potential to impact manufacturing industries. Jose Marques-Hueso, from the Institute of Sensors, Signals, and Systems, and his team have developed a method of 3D-printing that utilizes near-infrared lights to produce complex structures with multiple colors and materials.

This was achieved by scientists who modified stereolithography and pushed the limits of multi-material material integration. A 3D printer uses a UV or blue laser on a resin liquid to selectively solidify it. The limitations in intermixing the materials has proven to be an issue.

Through this project, the scientists use a NIR light source capable of printing at far greater depths into the resin vat – without the need to print in layers. The findings hold tremendous opportunities for industry – particularly those that rely on specialist parts such as in the health and electrical sectors.

“The novelty of our new 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. 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,” said Dr. Marques-Hueso. “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.”

“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 micrometers,” said Dr. Adilet Zhakeyev, a Ph.D. researcher at Heriot-Watt University who has worked on the project for nearly three years.

Heriot-Watt University states that the key element of the project was the development of engineered polymers containing nanoparticles with optical upconversion. They absorb NIR photons which are then converted into blue light, solidifying the resin. This occurrence is ‘non-linear’ – meaning it can obtain the blue photons mostly at the focus of the laser, and not on the way through it. The NIR is able to penetrate the material like it’s transparent. It will solidify the only material inside.

The new 3D printing method allows multiple materials, with different properties, to be printed in the same sample – for example, flexible elastomers and rigid acrylic, which are useful for many businesses, such as shoe production. This technique offers a wide range of possibilities including the 3D printing of objects in cavities, the restoration of damaged objects and even bioprinting on skin.

“In the same research project, we had previously developed a resin that can be selectively copper-plated,” said Dr. 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 costs of this exciting technology are surprising low. According to Dr. Marques-Hueso, “A clear advantage of this technique is that the full machine can be built for less than £400. 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 specialist materials allow the use of inexpensive lasers… Now that we have results to support our claims, we hope to partner with businesses and develop this technology further.”

The project, titled ‘Multimaterial Stereolithography by Crosslinking through Luminescence Excitation‘, has received £280,000 of funding from the Engineering and Physical Sciences Research Council (EPSRC). The findings of the project have been published by Applied Materials Today.