Development of Bioinks for TE
Pneumatic extrusion allows printing of biocompatible materials in a wide viscosity range. However, the minimum feature size is somewhat larger than 100 µm due to the high fluidic resistance of pasty materials inside of narrow nozzles. Piezoelectric printing allows much finer drops but valve less dispensers are usually limited to an upper viscosity of about 10 mPa*s. Piezoelectric valve dispensers basically allow higher viscosities but apply high shear stress to embedded cells leading to a low viability rate.
The Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik is working on „bioinks“, that means printable material systems made from biomolecules of the extracellular matrix (ECM).
The developed material systems are based on water-soluble collagen. The chemical composition can be modified in order to adjust the viscosity in a range from 3….120 mPa*s. These bioinks are therefore printable even through valve less piezoelectric nozzles (Left: GeSiM micro dispenser with reservoir on top on a modified Nano-Plotter).
The variation of the matrix composition allows the adjustment of the following properties:
- Viscosity and gelling properties of the non-linked bioink
- Mechanical properties of the cross-linked hydrogels
- Composition and biological function of the cross-linked hydrogels (ECM)
 Eva Hoch, Thomas Hirth, Günter Tovar, Kirsten Borchers: Chemical tailoring of gelatin to adjust its chemical and physical properties for functional bioprinting. Journal of Materials Chemistry B 1, 41, 5675-5685 (2013).
 Eva Hoch, Christian Schuh, Thomas Hirth, Günter E. M. Tovar, Kirsten Borchers: Stiff gelatin hydrogels can be photo-chemically synthesized from low viscous gelatin solutions using molecularly functionalized gelatin with a high degree of methacrylation; Journal of Materials Science: Materials in Medicine 23, 11, 2607-2617 (2012).
 Sascha Engelhardt, Eva Hoch, Kirsten Borchers, Wolfdietrich Meyer, Hartmut Krüger, Günter E. M. Tovar and Arnold Gillner: Fabrication of 2D protein microstructures and 3D polymer-protein hybrid microstructures by two-photon polymerization. Biofabrication 3, 2, 025003 (2011)
Fraunhofer Institute for Interfacial Engineering and Biotechnology