Professor Dan Congreve and colleagues have made progress in volumetric printing.

Their paper, “Triplet fusion upconversion nanocapsules for volumetric 3D printing,” published in Nature.com describes their new system for 3D printing. The paper’s co-lead authors are Samuel N. Sanders (Harvard) and Stanford postdoc, Tracy H. Schloemer.

The printed object is fully supported by the thick resin – imagine an action figure floating in the center of a block of Jell-O – so it can be added to from any angle. This removes the need for the support structures typically required for creating complex designs with more standard printing methods. The new 3D printing system could make it easier to print increasingly intricate designs while saving time and material.

“The ability to do this volumetric printing enables you to print objects that were previously very difficult,” states Dan. “It’s a very exciting opportunity for three-dimensional printing going forward.”

Printing with light
At its surface, the technique seems relatively straightforward: The researchers focused a laser through a lens and shone it into a gelatinous resin that hardens when exposed to blue light. But Congreve and his colleagues couldn’t simply use a blue laser – the resin would cure along the entire length of the beam. Instead, 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.

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, the researchers can create a chain of energy transfers that, for example, turn low-energy red photons into high-energy blue ones.

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 protective silica shell. Then they distributed the resulting nanocapsules, each of which is 1000 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,” states postdoc and co-lead author, Tracy Schloemer. “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.”

In addition to postdoctoral scholar Tracy Schloemer, and Professor Dan Congreve, co-authors of this research are former visiting researcher Michael Seitz; and EE PhD candidate Arynn Gallegos. Other co-authors, including a co-lead author, are from the Rowland Institute at Harvard University.

• Read their paper, “Triplet fusion upconversion nanocapsules for volumetric 3D printing," Nature.com
• Excerpted from "Stanford engineers develop new kind of 3D printing," Stanford News.