Two-Photon Lithography Prints in Fine Detail

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

Developed by scientists at the Vienna University of Technology, the 3-D printer uses a liquid resin that is hardened by a focused laser beam guided through the resin by scanning mirrors. The result is a solid polymer line a few hundred nanometers wide.

This 285-µm race car was printed at the Vienna University of Technology. (Images: 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 of time.

“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.

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

“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.”

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, which saves 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 creation of biological tissues. The 3-D printer could also be used to create tailor-made construction parts for biomedical technology and nanotechnology.

For more information, visit: www.tuwien.ac.at/EN