Two-photon lithography prints in fine detail

Ashley N. Paddock, ashley.paddock@photonics.com

A new 3-D printing technology uses two-photon lithography to rapidly create detailed objects on the nano-scale. The technique, which is orders of magnitude faster than similar devices, opens up new areas of application, such as medicine.

Developed by scientists at Vienna University of Technology, the printer uses a liquid resin that is hardened by a focused laser beam guided through it by scanning mirrors. The result is a solid polymer line a few hundred nanometers wide.

This 285-µm race car was printed at Vienna University of Technology. Images courtesy of TU Vienna.

“Until now, this technique used to be quite slow,” said Jürgen Stampfl, a professor at the Institute of Materials Science and Technology at the university. “The printing speed used to be measured in millimeters per second; our device can do five meters in one second.”

Several new ideas were combined to reach the higher speed, which now makes it possible to create much larger objects in a given period.

“It was crucial to improve the steering mechanism of the mirrors,” said Jan Torgersen. The mirrors are continuously in motion during the printing process; the acceleration and deceleration periods must be tuned very precisely to achieve high-resolution results at a record-breaking speed.

Chemistry also plays a crucial role.

“The resin contains molecules which are activated by the laser light,” Torgersen said. “They induce a chain reaction in other components of the resin, so-called monomers, and turn them into a solid.”

A miniature version of St. Stephen’s Cathedral in Vienna.

These initiator molecules are activated only if they absorb two photons of the laser beam at once, which happens only in the very center of the beam, where the intensity is highest. In contrast to conventional 3-D printing techniques, solid material can be created anywhere within the liquid resin, rather than only on top of the previously created layer. Because of this, the working surface does not have to be specially prepared before the next layer is produced, saving time.

Robert Liska and a team of chemists at the university created the suitable ingredients for this special resin.

The scientists now are developing biocompatible resins for medical applications. They could create scaffolds to which living cells could attach themselves, enabling systematic formation of biological tissues. The 3-D printer also could be used to create tailor-made construction parts for biomedical technology and nanotechnology.