Mar.12, 2012

Researchers all over the world are working on 3D printers today. The Vienna University of Technology has now made a major breakthrough in the 3D printing technology: it is now possible to print three dimensional objects with incredibly fine details using "two-photon lithography".

This photo shows a racing car with about 285 micrometers length - printed at the Vienna University of Technology.

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.

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.

The dramatically increased speed means that much larger objects can now be created in a given period of time - making two-photon-lithography more useful for industry. The 3d printer could also be used to create tailor made construction parts for biomedical technology or nanotechnology. The TU Vienna team is now developing bio-compatible resins for medical applications, creating scaffolds to which living cells can attach themselves.

The bottleneck of the two photon polymerisation technique was the long processing time. To fabricate parts visible without a microscope, several days of structuring was necessary. Usual process speeds of several 100µm/s were reported. TU Vienna could improve the 2PP technique considerably. Using novel photopolymerisable systems (synthesised at the Institute of Applied Synthetic Chemistry) and a new mechanical setup (designed and assembled at the Institute of Materials Science and Technology), they are now able to fabricate at speeds of up to 5m/s.

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.

Photo credit: TU Wien

Source: Vienna University of Technology


Posted in 3D Printers


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