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S. Baumgartner, A. Ovsianikov, P. Gruber, M. Markovic, M. Oubaha, B. Duffy, J. Stampfl:
"High-Resolution Laser-Based 3D Printing of Organic-Inorganic Hybrids";
Poster: Polymer Processing Society Conference 2015, Graz; 09-21-2015 - 09-25-2015.

The objective of this study is to investigate the effects of both the formulation of hybrid organic-inorganic sol-gel materials (HOIM) and the fabrication conditions using two-photon polymerization (2PP) on the resolution and structure of 3D miniature systems. HOIM are nanostructured materials that can be prepared by a liquid phase method (sol-gel process), the physical and chemical properties of which can be tailored by the employed precursors.
2PP is a novel CAD/CAM-based 3D printing technology based upon the controlled triggering of chemical reactions of photon absorption. The technological potential of ultra-short-pulsed lasers and high resolution optical devices allows the fabrication of complex structures with sub-micron lateral resolution, unachievable with conventional microfabrication techniques. Due to the small achievable size of the parts, many possible applications in different fields have been demonstrated, including optical devices, sensors and biomedical systems. The 2PP technique provides the possibility of parallel production of a large number of structures with high speed and accuracy. Such custom-made parts containing features at the nanoscale level in combination with biocompatible hybrid materials make this technology particularly attractive for biomedical applications.
Here, 2PP processing of different hybrid photosensitive sol-gel materials prepared employing both organosilane and transition metal complexes (zirconium, tantalum and titanium) in various concentration ratios were tested. The fabrication of these miniature systems is performed with variable power and writing speeds as well as different structure designs. Furthermore the influence of voxel size as well as the direction of hatching is also investigated. The observed deviation between the lateral and axial resolution are implemented in the structures geometry. Finally, investigations of the interaction between the various structures and different cell lines are presented.
It can be shown that the influence of the material compositions on the structuring results is limited. Nevertheless, depending on the hybrid used the structuring parameters need to be adapted. Especially the optimal laser beam power as one of the crucial factors for polymerization varies slightly for the different HOIMs. Particularly, titanium sol-gels need higher laser power to start polymerization. Same goes for the different photoinitiator (PI) concentrations of each material. With lower PI concentration the necessary laser power is increased, due to the increased photo-reactivity of the materials, allowing better control of the resolution. Most impact on the structures´ quality, however, has the combination of laser beam power and writing speed. The laser power needs to be higher for greater writing speeds. The influence of the hatching parameters as well as the voxel size on the final structures can also be shown but would need further investigations to fully assess these phenomena.
Initial trials with living cells show promising results as all material compositions proved to be non-toxic for the tested cell lines, thus demonstrating the potential of these materials for the future development of 3D biocompatible devices.

laser based 3D Printing, Organic-Inorganic Hybrids, Two-photon polymerization, sol-gel materials