A new type of 3D printing

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While 3D printing techniques have advanced significantly over the past decade, the technology continues to face a fundamental limitation: objects must be built layer by layer. What if they didn’t have to be?

Dan Congreve, assistant professor of electrical engineering at Stanford and former Rowland Fellow at the Rowland Institute of Harvard University, and his colleagues have developed a way to print 3D objects in a stationary volume of resin. The printed object is fully supported by the thick resin – imagine a figure floating in the center of a block of Jell-O – so it can be added from any angle. This removes the need for the support structures typically required to create complex designs with more standard printing methods. The new 3D printing system, recently published in Nature, could make it easier to print increasingly complex designs while saving time and materials. For more information, see the IDTechEx report on 3D printing equipment 2022-2032: technology and market outlook.

“The ability to do this volumetric printing allows you to print objects that were previously very difficult,” said Congreve. “This is a very exciting opportunity for three-dimensional printing in the future.”

On its surface, the technique looks relatively simple: Researchers focused a laser through a lens and shone it into a gel-like resin that hardens when exposed to blue light. But Congreve and his colleagues couldn’t just use a blue laser – the resin would harden along the length of the beam. Instead, they used red light and cleverly designed nanomaterials dispersed in the resin to create blue light only at the precise focal point of the laser. By moving the laser around the resin container, they were able to create detailed, support-free prints.

Congreve’s lab specializes in converting one wavelength of light to another using a method called triplet fusion upconversion. With the right molecules in close proximity to each other, researchers can create a chain of energy transfers that, for example, transform low-energy red photons into high-energy blue photons.

“I became interested in this upconversion technique in graduate school,” said Congreve. “It has all sorts of interesting applications in solar, bio, and now this 3D printing. Our real specialty is in the nanomaterials themselves – designing them to emit the right wavelength of light, to emit it effectively and to be dispersed in resin.”

Through a series of steps (which included sending some of their materials for a spin in a Vitamix blender), Congreve and his colleagues were able to form the necessary upconversion molecules into distinct nanoscale droplets and coat them in a shell. silica protector. Then they distributed the resulting nanocapsules, each of which is 1000 times smaller than the width of a human hair, throughout the resin.

“Finding out how to make nanocapsules tough was not trivial – a 3D printing resin is actually quite tough,” said Tracy Schloemer, postdoctoral researcher at Congreve’s lab and one of the paper’s lead authors. “And if those nanocapsules start collapsing, your ability to upconvert disappears. All of your stuff spills out and you can’t get those molecular collisions that you need.”

The researchers are currently working on ways to refine their 3D printing technique. They are investigating the possibility of printing multiple dots at the same time, which would significantly speed up the process, as well as printing at higher resolutions and smaller scales.

Congreve is also exploring other possibilities for using upconverting nanocapsules. They can help improve the efficiency of solar panels, for example by converting unusable low-energy light into wavelengths that solar cells can collect. Or they could be used to help researchers more precisely study biological patterns that can be triggered by light or even, in the future, deliver localized treatments.

“You can penetrate tissue with infrared light and then transform that infrared light into high-energy light with this upconversion technique to, for example, cause a chemical reaction,” said Congreve. “Our ability to control materials at the nanoscale gives us a lot of really exciting opportunities to solve complex problems that would otherwise be difficult to tackle.”
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