Two-photon lithography prints nano-scale models within minutes.
Researchers at the Vienna University of Technology have developed a process that significantly speeds up the nanometer scale printing of 3D objects using “two-photon lithography”. The high-precision-3D-printer at TU Vienna is orders of magnitude faster than similar devices, opening new areas of application, such as in medicine.
The 3D printer uses a liquid resin, which is hardened at precisely the correct spots by a focused laser beam. The focal point of the laser beam is guided through the resin by movable mirrors and leaves behind a polymerized line of solid polymer, just a few hundred nanometers wide. This high resolution enables the creation of intricately structured sculptures as tiny as a grain of sand.
“Until now, this technique used to be quite slow,” says Professor Jürgen Stampfl from the Institute of Materials Science and Technology at the TU Vienna. “The printing speed used to be measured in millimeters per second; our device can do five meters in one second.”
This world record in two-photon lithography was made possible by combining several new ideas, foremost of which was improving the control mechanism of the mirrors says Jan Torgersen at TU Vienna. During TU Vienna’s printing process, the mirrors are continuously in motion, so the acceleration and deceleration periods have to be tuned very precisely to achieve high-resolution results at a record-breaking speed.
In addition to the mechanics, the chemistry of the resin played a crucial role in the project as well, he says.
“The resin contains molecules, which are activated by the laser light. They induce a chain reaction in other components of the resin, so-called monomers, and turn them into a solid,” says Torgersen. “These initiator molecules are only activated if they absorb two photons of the laser beam at once – and this only happens in the very center of the laser beam, where the intensity is highest.”
In contrast to conventional 3D-printing techniques, solid material can be created anywhere within the liquid resin rather than on top of the previously created layer only. Therefore, the working surface does not have to be specially prepared before the next layer can be produced. A team of chemists led by Professor Robert Liska at TU Vienna developed the suitable initiators for this resin.
Because of the increased speed, much larger objects can now be created and TU Vienna scientists are now developing bio-compatible resins for medical applications. They can be used to create scaffolds to which living cells can attach themselves facilitating the systematic creation of biological tissues. The 3d printer could also be used to create tailor made construction parts for biomedical technology or nanotechnology.
In the video, a race car with dimensions of 330x130x100µm3 is fabricated. The structure consists of 100 layers, each made of an average of 200 polymer lines. It is finished in 4 minutes and resembles the CAD file at a precision of ±1µm.