Two photon polymerisation (2PP)
Two-photon polymerisation (2PP) is a technique to fabricate three dimensional structures with resolutions down to 100nm (see St. Stephan’s cathedral and Tower Bridge). An fs-pulsed laser (usually emitting at 800nm) is focussed in the volume of a photopolymerisable formulation. Polymerisation only occurs in the focal point, where the intensity of the absorbed light is highest. This technique is the first AMT capable of fabricating true 3D structures without the necessity of layer-by-layer manufacturing. In contrast to common approaches, potentially time-consuming preparations of the working surface can be discarded. Furthermore, massive overhangs can be produced without the need of supporting material (see Japanese sumo).
High speed 2PP fabrication
The bottleneck of the 2PP 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), we 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.
One of the big benefits of 2PP is the possibility to use infrared light for inducing photopolymerization. Since infrared light does not harm living tissue, 2PP facilitates to perform photopolymerization in the presence of living cells or organisms. By using appropriate biophotopolymers 3D-structures can be printed around living tissue, as indicated by this video, where a cellular scaffold is structured around a nematode.