ince the invention of the stereolithography process to produce parts layer by layer via light, additive manufacturing technologies gained an increasing attention. Beside the stereolithography process, new technologies have been invented as Fused Deposition Modelling (FDM), 3D-printing, or the Selcetive Laser Melting. Up-to-date, a broad range of materials can be used to manufacture parts additively. Using these technologies, a fast and flexible production of models, prototypes or functional parts can be achieved.

Rapid prototyping is part of our research, since research projects often require special parts that are not commercially available or prototypes for funcionality validation are necessary for fürther development. We investigate the possibilities of rapid prototyping by using UV-curable polymers for microfluidic devices. Our Connex350™ 3D-printer features a technology called PolyJet Matrix. Using this technology it is possible to print two materials simultaniously leading to a wide range of composites with different mechanical properties. These composites can have elastic, rubber-like materials or can show rigid behavior. Dependent on the mixing ratio, a fine grading on the material properties can be achieved. Another feature of this printer is the ability to print certain areas of one part with different material properties, so printing two-component parts is no problem.

Our second printer is a DLP-based bottum-uo stereolithographic machine called RapidShape HA 90. Due to specially modified optics this printer features a pixel-resolution of 15 microns. With this resolution it is possible to print even small structures such as microfluidic cannels in high quality. Beside the fabrication of complex structures in macro- and micro scale, biocompatibility is a current topic. For some of the used precursors biocompatibility can be achieved by adequate treatment after the curing process. So printing scaffolds for 3D-cell culture is another application for this printer.

Bioprinting is the additive manufacturing of cell-laden biomaterials that offers the possibility to generate 3D cell cultures with a spatial placement of certain cell types into the construct. Using this technique, the manufacturing of in vivo like constructs for e.g. testing of new pharmaceuticals in a pre-clinical stage or complex biological models is possible. In our labs, two Bioprinters of the type "BioScaffolder 3.2" from GeSiM with various tools are available. This includes normal heatable pneumatic extruders, core-shell-extruders or a nanopipette. Also we have the possibility to 3D print plastics with a high temperature extruder.

For bioprinting, a so called bioink is necessary which consists of a hydrogel with encapsulated cells. Suited hydrogels for bioprinting often consists of natural materials as hyaluronic acid, gelatin or alginat. To perform a well controlled 3D print, the rheological properties has to be adjusted. In our lab, we investigated these properties with the oscillatory rheometer MCR 502 and optimized the concentration of our hydrogel components. The extrusion of our bioink based on alginate and gelatin was possible with low pressures causing low shear stress and a high cell viability after printing. Since a long term cultivation of the constructs leads to necrotic areas in the centre due to insufficient nutrient transport, a vascularization is necessary. In our lab, we will use a core-shell extruder to include hollow channels inside the bioconstruct to achieve a homogeneous nutrient supply and long term survival of the cells. For cultivation of 3D cell cultures, a perfusion is superior in contrast to a static cultivation. Therefor we will print bioreactors made of cyclo olefin copolymer and embed it with the complex 3D construct.

After the manufacturing and cultivation process is established, we will use a co-culture whereby HUVECs will be encapsulated into the channels for investigation of angiogenesis process.

Beside our current research, we are highly interested in the development of complex 3D cell culture models and would look forward for new cooperations.