New form of 3D printing allows for complex shapes without support struts

The printed object is fully supported by the thick resin, removing the need for the support structures typically required for creating complex designs with more standard printing methods.

The new 3D printing system could also make it easier to print increasingly intricate designs while saving time and material, the researchers believe.

“The ability to do this volumetric printing enables you to print objects that were previously very difficult,” said Dan Congreve, an assistant professor of electrical engineering at Stanford. “It’s a very exciting opportunity for three-dimensional printing going forward.”

The technique uses a focused laser which is shone through a lens into a gelatinous resin that hardens when exposed to blue light.

Rather than using a blue laser, which would harden the resin along the entire length of the beam, they used a red light and some cleverly designed nanomaterials scattered throughout resin to create blue light at only the precise focal point of the laser.

By shifting the laser around the container of resin, they were able to create detailed support-free prints. With the right molecules in close proximity to each other, the researchers were able to create a chain of energy transfers that turned low-energy red photons into high-energy blue ones.

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

Through a series of steps the researchers were able to form the necessary upconversion molecules into distinct nanoscale droplets and coat them in a protective silica shell. Then they distributed the resulting nanocapsules, each of which is 1,000 times smaller than the width of a human hair, throughout the resin.

“Figuring out how to make the nanocapsules robust was not trivial – a 3D-printing resin is actually pretty harsh,” said Tracy Schloemer, a postdoctoral researcher and one of the lead authors on the paper. “And if those nanocapsules start falling apart, your ability to do upconversion goes away. All your contents spill 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 points at the same time, which would speed up the process considerably, as well as printing at higher resolutions and smaller scales.

In January, another team of researchers unveiled a customised 3D-printer that can produce flexible, organic light-emitting diode (OLED) displays.