Quantitative assessment of generic processes to enable 3D-bioprinting of artificial tissue

Medientyp: E-Book

Titel: Quantitative assessment of generic processes to enable 3D-bioprinting of artificial tissue

Beteiligte: Koch, Fritz [Verfasser]; Zengerle, Roland [Akademischer Betreuer]; Zengerle, Roland [Sonstige]; Finkenzeller, Günter [Sonstige]

Körperschaft: Albert-Ludwigs-Universität Freiburg, Institut für Mikrosystemtechnik ; Albert-Ludwigs-Universität Freiburg, Fakultät für Angewandte Wissenschaften

Erschienen: Freiburg: Universität, 2023

Umfang: Online-Ressource

Sprache: Englisch

DOI: 10.6094/UNIFR/236616

Identifikator:

Schlagwörter: Biomaterial ; Biomedizinische Technik ; (local)doctoralThesis

Entstehung:

Hochschulschrift: Dissertation, Universität Freiburg, 2023

Anmerkungen:

Beschreibung: Abstract: Bioprinting is a promising technology in which viable cells are used to fabricate artificial tissues by 3D printing with high accuracy. However, bioprinting equipment and related processes are still limited, especially in producing hybrid constructs. Therefore, in this thesis, novel 3D bioprinting processes were developed and characterized to enable hybrid bioprinting. Two bioprinters were used in this work, based on commercial platforms with three-axis systems. One printer combined syringe extrusion and drop-on-demand printheads with fused deposition modeling (FDM). The other printer was a low-cost open-source bioprinter based on a modified commercial FDM printer. The modifications involved software and hardware changes and the design, construction, and characterization of a second extruder printhead. The printhead was designed to allow the use of different syringe sizes or heating elements by changing adapters. This printer was the first hybrid 3D bioprinter with a total cost of less than 1000 €, enabling cost-effective hybrid 3D bioprinting to produce complex structures. For use within the 3D bioprinting processes, biomaterials from natural hydrogels were formulated and extensively characterized. In combination with mesenchymal stem cells (MSCs), their suitability as bioinks for the production of artificial human bone tissue was investigated. MSCs, a relevant and versatile cell entity for the regeneration of bone tissue, were used to optimize printing process parameters for extrusion-based bioprinting. For this purpose, printing accuracy and cell viability criteria were examined. A generic evaluation method was developed based on topview images of the printed structures to define a suitable printing temperature via the material properties of the bioink. Also, the influence of maximum shear stress during extrusion-based printing on cell viability was studied in detail. Cell viability decreased linearly with increasing maximum shear stress by approximately 4% per thousand pascals for MSCs. This allows predicting the influence of different process parameters, for example, nozzle size and flow rate, on cell viability. Using a hybrid printing design based on primary MSCs and human endothelial cells (HUVEC), constructs were printed to induce the formation of artificial bone in a suitable matrix. In total, 2.1 ⋅ 10^6 MSCs and 0.5 ⋅ 10^6 HUVECs were embedded in the printed constructs with a volume of 10 x 10 x 5 mm^3. Rows of overlapping single droplets of endothelial cells were created using droplet-based bioprinting technologies. Mesenchymal stem cells were deposited by extrusion-based bioprinting with previously optimized printing process parameters. The bioprinted constructs were studied in detail in vitro and examined for their printed shape, viability, and long-term stability. Also, 12 days after subcutaneous implantation of the cell-laden constructs in immunodeficient mice, the formation of blood vessels, mostly capillaries with diameters ≤ 10 μm connected to the vasculature of the animal model, was observed. Furthermore, a calcification of the constructs induced by human MSCs could be demonstrated as evidence of bone formation in vivo. In order to support the mechanical stability of the otherwise relatively soft bioinks, the embedding of filaments of Polycaprolactone (PCL) into the printed constructs was investigated using four hybrid printing designs that were developed and tested for their mechanical stability and compatibility with cell-laden hydrogels. It was found that by embedding 25 % (w/v) PCL into the constructs, the compressive modulus for hybrid constructs can be increased by up to 150 times compared to a pure hydrogel construct. In this context, two printing methods were developed for the generic determination of printing parameters and evaluation of printing results. One method uses the optimization of extrusion-based bioprinting to combine high cell viability and printing accuracy with a single bioink. A second method decouples cell viability and mechanical stability requirements addressed by a single bioink. Therefore, a second biomaterialink that does not contain cells was used to adjust the mechanical properties of the bioprinted constructs. This allowed the design and fabrication of artificial human bone tissues

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