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?
“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.”
“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.