In the past decade, advances in tissue engineering have allowed researchers to fabricate simple tissues. However, the process of creating these native tissues is a time consuming and inefficient process. A scaffold must first be fabricated then exposed to a sea of cells in the hopes of seeding. Furthermore, even though cells may have attached, more time must be spent in order to allow the cells to migrate to their ideal locations. To deal with this problem, researchers have investigated whether rapid prototyping principals could be adapted to facilitate the cell seeding process by placing cells in their respective locations during scaffold fabrication. The goal for this thesis was to establish the foundation for a cell-compatible printer that, in the future, could fabricate pre-seeded scaffolds. This task included implementing changes to a commercial solenoid-based inkjet system that would allow cells to be loaded into the printer in a sterile fashion. In addition, protocols had to be designed with system limitations in mind. An initial test with the designed system showed a majority of cell viability percentages above 90%. If additional tests confirm this possibility, the system should be further modified to provide cells with a proper culturing environment. Furthermore, additional research would need to be performed in order to determine whether scaffolding materials can be dispensed through the system to fabricate scaffolds.

Bioprinting, defined as depositing cells, extracellular matrices and other biologically relevant materials in user-defined patterns to build tissue constructs de novo or to build upon pre-fabricated scaffolds, is among one of the most promising techniques in tissue engineering. Among the various technologies used for Bioprinting, pressure driven systems are most conducive to preserving cell viability. Herein, we explore the abilities of a novel bioprinter - Digilab, Inc.'s prototype cell printer. The prototype cell printer (Digilab Inc., Holliston, MA) is an automated liquid handling device capable of delivering cell suspension in user-defined patterns onto standard cell culture substrates or custom-designed scaffolds. In this work, the feasibility of using the cell printer to deliver cell suspensions to biological sutures was explored. Cell therapy using stem cells of various types shows promise to aid healing and regeneration in various ailments, including heart failure. Recent evidence suggests that delivering bone-marrow derived mesenchymal stem cells to the infarcted heart reduces infarct size and improves ventricular performance. Current cell delivery systems, however, have critical limitations such as inefficient cell retention, poor survival, and lack of targeted localization. Our laboratories have developed a method to produce discrete fibrin microthreads that can be bundled to form a suture and attached to a needle. These sutures can then be seeded with bone-marrow derived mesenchymal stem cells to deliver these cells to a precise location within the heart wall, both in terms of depth and surface localization. The efficiency of the process of seeding cells onto fibrin thread bundles (sutures) has previously been shown to be 11.8 ± 3.9 %, suggesting that 88% of the cells in suspension are not used. Considering that the proposed cell-therapy model for treatment of myocardial infarction contemplates use of autologous bone-marrow derived stem cells, an improvement in the efficiency of seeding cells onto the fibrin sutures is highly desirable. The feasibility of using Digilab's prototype cell printer to deliver concentrated cell suspension containing human mesenchymal stem cells (hMSCs) directly onto a fibrin thread bundle was explored in this work, in order to determine if this technology could be adapted to seed cells onto such biological sutures. First the effect of the printing process on the viability of hMSCs was assessed by comparing to cells dispensed manually using a hand-held pipette. The viability of hMSCs 24 hours post-dispensing using the cell printer was found to be 90.9 ± 4.0 % and by manual pipetting was 90.6 ± 8.2 % (p = ns). Thereafter a special bioreactor assembly composed of sterilizable Delrin plastic and stainless steel pins was designed to mount fibrin thread bundles onto the deck of the cell printer, to deliver a suspension containing hMSCs on the bundles. Highly targeted delivery of cell suspension directly onto fibrin thread bundles (average diameter 310 µm) was achieved with the bundle suspended in mid-air horizontally parallel to the printer's deck mounted on the bioreactor assembly. To compare seeding efficiency, fibrin thread bundles were simultaneously seeded with hMSCs using either the cell printer or the current method (tube-rotator method) and incubated for 24 hours. Seeded thread bundles were visualized using confocal microscopy and the number of cells per unit length of the bundle was determined for each group. The average seeding efficiency with the tube rotator method was 7.0 ± 0.03 % while the cell printer was 3.46 ± 2.24% (p = ns). In conclusion, the cell printer was found to handle cells as gently as manual pipetting, preserve their viability, with the added abilities to dispense cells in user-defined patterns in an automated manner. With further development, such as localized temperature, gas and humidity control on the cell printer's deck to aid cell survival, the seeding efficiency is likely to improve. The feasibility of using this automated liquid handling technology to deliver cells to biological scaffolds in specified patterns to develop vehicles for cell therapy was shown in this study. Seeding other cell types on other scaffolds along with selectively loading them with growth factors or multiple cell types can also be considered. In sum, the cell printer shows considerable potential to develop novel vehicles for cell therapy. It empowers researchers with a supervision-free, gentle, patterned cell dispensing technique while preserving cell viability and a sterile environment. Looking forward, de novo biofabrication of tissue replicates on a small scale using the cell printer to dispense cells, extracellular matrices, and growth factors in different combinations is a very realistic possibility.

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Gegenstand der vorliegenden Arbeit ist die ortsaufgelöste Untersuchung der Schichtdicke und der elektrischen Eigenschaften von Funktionsschichten in gedruckten Polymersolarzellen. Die massendrucktechnische Realisierung der großflächigen Polymersolarzellen mit dem Schichtaufbau Zink/ZnO/P3HT:PCBM/PEDOT:PSS erfolgt im Tief- und Siebdruckverfahren auf einem papierbasierten Bedruckstoff. Die gedruckten Funktionsschichten werden mit verschieden optischen und elektrischen Messverfahren charakterisiert und die Eignung der Verfahren wird diskutiert. Abschließend wird die gesamte Polymersolarzelle mit einer Kombination aus spektraler und elektrischer Messung positionsgenau untersucht. Dadurch kann ein Zusammenhang zwischen den Solarzelleneigenschaften und den ortsaufgelösten Messwerten aufgezeigt werden. / The aim of this work is the space-resolved investigation of the layer thickness and the electrical properties of functional layers in printed polymer solar cells. The realization of the large-area polymer solar cells with a layer structure of zinc/ZnO/P3HT:PCBM/PEDOT:PSS occurs by gravure and screen printing on a paper-based substrate. The printed functional layers are characterized by different optical and electrical measurement methods and the suitability of these methods is discussed. Finally, the complete polymer solar cell is examined dependent on a position by using a combination of spectral and electrical measurement techniques. With this analysis a correlation between the solar cell characteristics and the space-resolved measurements can be shown.

L'ingénierie tissulaire est reconnue comme une méthode potentielle pour réparer ou régénérer les tissus endommagés. Malgré de grandes avancées dans l'ingénierie tissulaire, la réussite de la construction de tissus complexes avec des réseaux vascularisés reste un défi. Dans les modèles d'angiogenèse actuels, les cellules endothéliales sont ensemencées au hasard, n'offrant pas de structure organisée. La technologie de bioimpression par laser offre une résolution d'impression précise. Par cette technique, les structures microvasculaires peuvent être construites pour la fabrication d'organes complexes, ou pour modéliser la progression de la maladie ou les modèles de réponse aux médicaments. Dans cette étude, des techniques de bio-impression au laser ont été utilisées pour étudier le guidage de l'angiogenèse in vitro. Deux techniques basées sur le laser, le transfert direct induit par laser (LIFT) et le transfert latéral induit par laser (LIST) sont utilisées. Comparée à LIFT, la technologie LIST offrait des conditions idéales pour l'impression cellulaire telles que la concentration cellulaire requise pour la formation du tubes endothéliaux et l'uniformité du motif désiré. Nous avons réalisé le modelage de la formation de structures de type capillaire dans des motifs organisés via l'impression LIST. Les constructions de type capillaire formées présentent des motifs uniformes. Les structures formées ont été analysées par microscopie confocale et reconstruction d'images 3D. Bien que le développement de la lumière endothéliale soit incomplet, la technique développée possède le potentiel d'atteindre une stabilisation et un développement de la lumière si l'on recrute un deuxième type de cellule tel que les fibroblastes ou les péricytes. / Tissue engineering has been well acknowledged as a potential method to repair or regenerate damaged tissues in the human body, fulfilling the limitations and shortage in autologous and organ transplantations. Despite great advances in engineering tissues with simple geometry and low requirement for oxygen and blood supply such as cartilage, skin and cornea, success in constructing 3D complex tissues with vascularized networks remains a major challenge. Angiogenesis plays an important role in vascular development in vivo. In current angiogenesis models, endothelial cells are seeded randomly not offering precise and desired patterning. Laser-based bioprinting technology offers precise and high cell printing resolution. By using laser-based bioprinting technology, microvascular structures can be constructed as a platform for complex organ fabrication, disease progression and drug response models. In this study, laser-based bioprinting techniques are employed to study angiogenesis guidance in vitro by patterning endothelial cells. Two laser-based techniques, Laser-Induced Forward Transfer (LIFT) and Laser-Induced Side Transfer (LIST) are used as patterning tools. Compared to LIFT, LIST technology provided ideal conditions for cell printing such as required cell concentration for endothelial tube formation and pattern uniformity. In this study, we achieved the guidance of capillary-like structure formation in desired patterns via LIST printing. The formed capillary-like constructs featured precise patterns and uniformity. The structures were analyzed by confocal microscopy, 3D image reconstruction and frozen section procedure. Though lumen development was incomplete, it possesses the potential to attain further stabilization and lumen development if recruiting a second cell type such as fibroblast or pericyte.