A 285 µm racecar, printed at the Vienna University of Technology.
Printing three dimensional objects with incredibly fine details is now possible using “two-photon lithography”. With this technology, tiny structures on a nanometer scale can be fabricated. Researchers at the Vienna University of Technology (TU Vienna) have now made a major breakthrough in speeding up this printing technique: The high-precision-3D-printer at TU Vienna is orders of magnitude faster than similar devices. This opens up completely 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.” In two-photon lithography, this is a world record.
This amazing progress was made possible by combining several new ideas. “It was crucial to improve the control mechanism of the mirrors”, says Jan Torgersen (TU Vienna). The mirrors are continuously in motion during the printing process. The acceleration and deceleration-periods have to be tuned very precisely to achieve high-resolution results at a record-breaking speed.
Photoactive Molecules Harden the Resin
3D-printing is not all about mechanics – chemists had a crucial role to play in this project too. “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 Jan 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 (see Video), which saves a lot of time. A team of chemists led by Professor Robert Liska (TU Vienna) developed the suitable initiators for this special resin.
Researchers all over the world are working on 3D printers today – at universities as well as in industry. “Our competitive edge here at the Vienna University of Technology comes from the fact that we have experts from very different fields, working on different parts of the problem, at one single university”, Jürgen Stampfl emphasizes. In materials science, process engineering or the optimization of light sources, there are experts working together and coming up with mutually stimulating ideas.
Because of the dramatically increased speed, much larger objects can now be created in a given period of time. This makes two-photon-lithography an interesting technique for industry. At the 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.