FS 16 Bioprinting of vascularized bone tissue

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1 S52 FS 16 Bioprinting of vascularized bone tissue Petra Kluger Zell- und Tissue Engineering, Fraunhofer IGB c/o Reutlingen University, Stuttgart, Deutschland, Annika Wenz, University of Stuttgart, Germany Reutlingen University, Fraunhofer Institute for Interfacial Engineering and Biotechnology, Stuttgart, Deutschland Iva Tjoeng, Fraunhofer Institute for Interfacial Engineering and Biotechnology, Stuttgart, Deutschland Julia Rogal, Fraunhofer Institute for Interfacial Engineering and Biotechnology, Stuttgart, Deutschland Nicolai Wilk, Fraunhofer Institute for Interfacial Engineering and Biotechnology, Stuttgart, Deutschland Kirsten Borchers, Fraunhofer Institute for Interfacial Engineering and Biotechnology, Stuttgart, Deutschland Petra J. Kluger, Fraunhofer Institute for Interfacial Engineering and Biotechnology, Reutlingen University, Reutlingen, Deutschland Bone tissue is one of the most frequently transplanted tissues. Since procedures like the transplantation of autologous bone bear risks, though, regenerative medicine and tissue engineering reach to face those problems by engineering bone substitutes by using suitable materials and living cells. For the fabrication of bone tissue equivalents, evolving manufacturing techniques like bioprinting can be used. We developed bioinks that can either support the osteogenic differentiation of human adipose-derived stem cells (hascs) and formation of a bone matrix by further addition of hydroxyapatite, or the formation of vascular structures by or human microvascular endothelial cells (ECs). The bioinks were used to build up geometries like 3D grids, cylindrical structures and combination hydrogels of bone and vascularization hydrogels via a microextrusion-based printing system, which were afterwards cultured for up to four weeks under static or dynamic culture conditions in a bioreactor. Evaluation of the hydrogels by mechanical analysis and staining of bone specific proteins like collagen type I, alkaline phosphatase and osteopontin showed formation of a bone matrix. This was also observes after culture under control conditions without the addition of osteogenic supplements, indicating osteoinductive properties of the hydroxyapatite. Co-culture of ASCs and ECs in a suitable hydrogel environment resulted in improved formation of bone matrix and capillary structures compared to the respective monocultures. Additionally, the perfusion culture in a bioreactor allowed the build-up and successful culture of cell-laden hydrogel constructs with a volume of >1 cm 2. In conclusion, we were able to develop bioinks and a printing process which allow the successful build-up of bone tissue equivalents whose bioreactor culture enables the setup of relevant geometries and sizes.

2 S53 FS 17 Alginate di-aldehyde gelatin crosslinked hydrogel (ADA-GEL) for biofabrication approach tailoring of tubular structures for blood vessel supply Florian Ruther, Lehrstuhl für Biomaterialien, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Deutschland, Aldo R. Boccaccini, Lehrstuhl für Biomaterialien, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Deutschland, Thomas Distler, Lehrstuhl für Biomaterialien, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Deutschland, Tobias Zehnder, Lehrstuhl für Biomaterialien, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Deutschland, Rainer Detsch, Lehrstuhl für Biomaterialien, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Deutschland, Naturally occurring biopolymers like alginate and gelatin are extensively studied for many biomedical applications. Alginate is widely used in cell encapsulation and biofabrication due to its rapid ionic gelation with divalent cations, but has a very poor cell-material interaction. Gelatin on the other hand is a biodegradable protein which contains cell binding peptide sequences (RGD sequence). The composition of gelatin is very similar to that of natural type I collagen and therefore highly applied in the field of biofabrication. To overcome the limited mechanical properties of pure gelatin hydrogels and the drawbacks of alginate hydrogels alone, gelatin is covalently crosslinked with alginate di-aldehyde (ADA), which is prepared by partial oxidation of alginate. Thus, ADA-GEL forms a cell friendly hydrogel with tunable degradability and stiffness, which can be used for biofabrication applications such as microencapsulation and three dimensional printing of cells. We could show that 3D environments formed by ADA-GEL can be applied in regenerative medicine and cancer research to mimic native extracellular tissue conditions. To mimic a native tissue successfully, it also requires the neovascularization of these engineered constructs. The human vascular system is a complex network of blood vessels of various sizes and different types of cells. Blood vessels are generally hollow structures, which are composed of a complex assembly of several shell layers. To generate functional vascular systems, two components are therefore critical, the colonizing cells and the scaffold material. The present work focused on plotting vessel-like structures based on ADA-GEL using a bioplotter and a core/shell-needle. The goal was to confirm ADA GEL hydrogel as a promising material for immobilization of cells and for use in bioplotting technology, for fabrication of vessel-like constructs and thus to highlight it as a promising bioink in the field of biofabrication.

3 S54 FS 18 Two-step printability assessment for inks processed with extrusion-based bioprinting Tomasz Jüngst, Abteilung für Funktionswerkstoffe der Medizin und Zahnheilkunde und Bayerisches Polymer Institut, Universitätsklinikum, Naomi Paxton, Abteilung für Funktionswerkstoffe der Medizin und Zahnheilkunde, Universitätsklinikum Thomas Böck, Abteilung für Funktionswerkstoffe der Medizin und Zahnheilkunde, Universitätsklinikum Willi Smolan, Abteilung für Funktionswerkstoffe der Medizin und Zahnheilkunde, Universitätsklinikum Jürgen Groll, Abteilung für Funktionswerkstoffe der Medizin und Zahnheilkunde und Bayerisches Polymer Institut, Universitätsklinikum Biofabrication is a young and active field of research and in one of its facets it aims for the automated production of biologically functional, hierarchical constructs for applications like tissue replacement. One of the key bottlenecks of biofabrication are suitable materials as these so-called inks need to have properties that enable to process them with techniques as 3D Bioprinting. In some cases, even cell laden inks are required to mimic the hierarchy of the tissue that needs to be regenerated. These bioinks impose even more stringent requirements on the materials as they need to combine good printing properties with adequate cytocompatibility. Scientists have set themselves the task to overcome this bottleneck by designing novel inks. To support them, we developed a two-step assessment focusing on ink printability via pressure driven extrusion-based bioprinting. The first step of this printability assessment is a simple screening based on fiber formation and layer stacking properties of material that is manually dispensed from a syringe. The second step requires a rheometer to evaluate the ink s shear thinning and post-printing recovery. Applying a power law model to fit the shear viscosity data helped gaining deeper understanding of the dispensing process by estimating the conditions, like shear-rate, extrusion velocity, shear stress and residence time, present in the nozzle. Further it enabled the calculation of the mean shear rate present in the nozzle during dispensing and this information was used to analyze the recovery tests that shall imitate the dispensing process. Combining the data gained from the fit with printer parameters like pressure range, needle diameter and printing velocity helped gaining deeper understanding for the dispensing process and can be used to effectively design new bioinks. This two-step assessment was demonstrated and validated using different materials including non-printable compositions and represents an easy to reproduce approach.

4 S55 FS 19 3D-printed biomimetic in-vitro-tumor-angiogenesis-model Jan Schöneberg, Zahnärztliche Werkstoffkunde und Biomaterialforschung, Universitätsklinikum RWTH Aachen, Aachen, Deutschland, Benjamin Theek, Helmholtz Institut für Biomedizinische Technik, Lehrstuhl für Experimentelle Molekulare Federica De Lorenzi, Helmholtz Institut für Biomedizinische Technik, Lehrstuhl für Experimentelle Molekulare Andreas Blaeser, Zahnärztliche Werkstoffkunde und Biomaterialforschung, Universitätsklinikum RWTH Aachen, Aachen, Deutschland Fabian Kießling, Helmholtz Institut für Biomedizinische Technik, Lehrstuhl für Experimentelle Molekulare Horst Fischer, Zahnärztliche Werkstoffkunde und Biomaterialforschung, Universitätsklinikum RWTH Aachen, Aachen, Deutschland Tumor-associated angiogenesis, the formation of new blood vessels, is an essential process for the development of tumors, and therefore a suitable target for anti-cancer therapies. Here we present a novel method to produce a three-dimensional in vitro angiogenesis model by using a 3D drop-on-demand bioprinting technique with the aim to provide a more sophisticated, animal-free, in vitro drug screening under the principles of the 3R for a more ethical use of animals in testing. To resemble the natural structure of the vasculature, a dissolvable core made of gelatin is printed into a custom made bioreactor. Next, the gelatin is coated with a fibrin gel, laden with smooth muscle cells (SMCs), mimicking the thin layer of tunica media. The printed channel is surrounded by a fibrin/collagen hydrogel blend containing fibroblasts (tunica adventitia). Finally, the gelatin core is washed out and endothelial cells are introduced into the channel, resembling the tunica intima. The constructs are cultivated under physiological flow conditions and cancer cells are induced in proximity to the channels. Our results confirm that the printed constructs are stable for several weeks with a µm thick continuous endothelium surrounded by an up to 200 µm thick layer of SMCs. The studied materials show high cell compatibility and cell viabilities of more than 80 % directly after the printing process and more than 90 % after four days. The mechanical characteristics of our hydrogels were tested and in line with the characteristics of natural vascular channels. We conclude that the proposed model could be further used as a tunable in vitro test platform to study the tumor-associated angiogenic process with a particular focus on effects of chemotherapy drugs in the future.

5 S56 FS 20 Extrusion based 3D printing for biomedical applications: opportunities and limitations Michael Gelinsky, Zentrum für Transl. Knochen-, Gelenk- und Weichgewebeforschung, TU Dresden, Dresden, Deutschland, Additive Manufacturing (AM) is a currently fast developing research field and first industrial applications can be found in several disciplines. For biomedical engineering, AM is of special interest as specific tools and small devices (e. g. bioreactors for cell cultivation) can be fabricated in a fast and efficient manner. Extrusion based 3D printing (also called 3D plotting or direct writing etc.) enables utilisation of sensitive materials like biopolymer hydrogels, proteins, drugs or even living cells as it is based on deposition of materials which are pasty at room or physiological temperature. In the last couple of years a hughe variety of biomaterials, suitable for 3D plotting, were developed, especially for medical applications. 3D bioprinting describes printing of live cells, suspended in soft hydrogels. This technology allows positioning of more than one cell type with high spatial accuracy within a 3D construct and guarantees high seeding efficiency compared to conventional cell seeding of pre-fabricated scaffolds. Very recently, our group has expanded 3D bioprinting to non-mammalian cells. We could demonstrate initially successful bioprinting with live microalgae ( green bioprinting ) and could show now that also plant cells can be utilised for 3D bioprinting. This opens up totally new possibilities for biotechnological applications like cascade reactions which is currently under investigation. The paper will describe and discuss opportunities and limitations of extrusion based 3D printing in biomedical engineering with respect to suitable biomaterials, novel printing technologies (like multi-channel and core/shell plotting), fabrication of patient-specific constructs and integration of biological components, especially living cells.