@phdthesis{Wenderoth2024, author = {Wenderoth, Sarah}, title = {Synthesis and characterization of shear stress indicator supraparticles}, doi = {10.25972/OPUS-35281}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-352819}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2024}, abstract = {The detection of smallest mechanical loads plays an increasingly important role in many areas of advancing automation and manufacturing technology, but also in everyday life. In this doctoral thesis, various microparticle systems were developed that are able to indicate mechanical shear stress via simple mechanisms. Using a toolbox approach, these systems can be spray-dried from various nanoscale primary particles (silica and iron oxide) to micrometer-sized units, so-called supraparticles. By varying the different building blocks and in combination with different dyes, a new class of mechanochromic shear stress indicators was developed by constructing hierarchically structured core-shell supraparticles that can indicate mechanical stress via an easily detectable color change. Three different mechanisms can be distinguished. If a signal becomes visible only by a mechanical load, it is a turn-on indicator. In the opposite case, the turn-off indicator, the signal is switched off by a mechanical load. In the third mechanism, the color-change indicator, the color changes as a result of a mechanical load. In principle, these indicators can be used in two different ways. First, they can be incorporated into a coating as an additive. These coatings can be applied to a wide range of products, including food packaging, medical devices, and generally any sensitive surface where mechanical stress, such as scratches, is difficult to detect but can have serious consequences. Second, these shear stress indicators can also be used directly in powder form and for example then applied in 3D-printing or in ball mills. A total of six different shear stress indicators were developed, three of which were used as additives in coatings and three were applied in powder form. Depending on their composition, these indicators were readout by fluorescence, UV-Vis or Magnetic Particle Spectroscopy. The development of these novel shear stress indicator supraparticles were successfully combined molecular chemistry with the world of nano-objects to develop macroscopic systems that can enable smart and communicating materials to indicate mechanical stress in a variety of applications.}, subject = {Nanopartikel}, language = {en} } @phdthesis{Daubinger2024, author = {Daubinger, Philip}, title = {Electrochemical and Mechanical Interplay of State-of-the-Art and Next-Generation Lithium-Ion Batteries}, doi = {10.25972/OPUS-35125}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-351253}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2024}, abstract = {The demand for LIB with enhanced energy densities leads to increased utilization of the space within the confinements of the battery housing or to the use of electrode material with increased intrinsic specific energy densities. Both requirements result in more stress on the battery electrodes and separator during cycling or aging. However, the effect of mechanical strain on the cell's electrochemistry and thus the performance of batteries is rather unexplored compared to the impact of current or temperature, for example. The objective of this thesis was to give a better understanding of the electrochemical and mechanical interplay in current- and next-generation lithium based battery cells. Therefore, the thesis was structured into the investigations on SoA and next-generation LIBs. For SoA LIBs, the investigations of the interplay started at laboratory scale. Here, the expansion of various electrodes and also the impact of mechanical pressure and its distribution on the performance of the cells were studied. The investigations at laboratory scale was followed by an examination of the electrochemical and mechanical interactions on large format commercial LIBs which are used in BEVs. Accordingly, the effect of bracing and its effect on the performance was studied in an aging and post-mortem study. To gain a deeper understanding of the mechanical changes in LIBs, an ultrasonic study was performed for pouch cells. Here, the mechanical changes were further investigated in dependence of SoC and SoH. The effects of the mechanical stress on the performance for next-generation batteries were studied at laboratory scale. In the beginning, the expansion of next-generation anode materials such as silicon and lithium was compared with today's anode materials. Furthermore, the effect of mechanical pressure and electrolyte on the irreversible dilation and performance was investigated for lithium metal cells. Overall, it was shown that pressure has a significant effect on the performance of today's and also future LIBs. The interplay of the electrochemical and mechanical effects inside a LIB has a considerable impact on the lifetime, capacity fading and impedance increase of the batteries.}, subject = {Lithium-Ionen-Akkumulator}, language = {en} } @phdthesis{SpaethgebLutz2024, author = {Sp{\"a}th [geb. Lutz], Johanna}, title = {Oberfl{\"a}chenfunktionalisierte Gold- und Silbernanopartikel auf Basis von Thioether-Poly(glycidol) f{\"u}r potenzielle biomedizinische Anwendungen - Auswirkungen auf Stabilit{\"a}t, Proteinkoronabildung und Biodistribution}, doi = {10.25972/OPUS-35066}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-350662}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2024}, abstract = {Based on previous results showing that thioether modification of gold nanoparticles (AuNPs), especially coating with a multivalent system, yielded in excellent colloidal stability, the first aim of this thesis was to prove whether functionalization of silver nanoparticles (AgNPs) with thioether also has a comparable or even enhanced stabilization efficacy compared with the gold standard of coating with thiols and, particularly, whether the multivalency of polymers leads to stable AgNPs conjugates. Herein, AgNPs coated with mono- and multivalent thiol- and thioether polymers were prepared to systematically investigate the adsorption kinetics onto the silver surface as well as the colloidal stability after exposure to different conditions relevant for biomedical application. Although the thioether-polymers showed a slower immobilization onto AgNPs, same or mostly even better stabilization was exhibited than for the thiol analogs. As multivalent thioether-poly(glycidol) (PG) is already proven as a promising candidate for AuNP modification and stabilization, the second aim of this thesis was to examine the stealth behavior of thioether-PG, side-chain functionalized with various hydrophobic (alkyl and cholesteryl) units, to gain a deeper understanding of AuNP surface functionalization in terms of protein adsorption and their subsequent cellular uptake by human monocyte-derived macrophages. For this purpose, citrate-stabilized AuNPs were modified with the amphiphilic polymers by ligand exchange reaction, followed by incubation in human serum. The various surface amphiphilicities affected protein adsorption to a certain extent, with less hydrophobic particle layers leading to a more inhibited protein binding. Especially AuNPs functionalized with PG carrying the longest alkyl chain showed differences in the protein corona composition compared to the other polymer-coated NPs. In addition, PGylation, and especially prior serum incubation, of the NPs exhibited reduced macrophage internalization. As the use of mammals for in vivo experiments faces various challenges including increasing regulatory hurdles and costs, the third aim of this thesis was to validate larvae of the domestic silkworm Bombyx mori as an alternative invertebrate model for preliminary in vivo research, using AuNPs with various surface chemistry (one PEG-based modification and three PG-coatings with slightly hydrophobic functionalization, as well as positively and negatively charges) for studying their biodistribution and elimination. 6 h and 24 h after intra-hemolymph injection the Au content in different organ compartments was measured with ICP-MS, showing that positively charged particles appeared to be eliminated most rapidly through the midgut, while AuNPs modified with PEG, alkyl-functionalized PG and negatively charged PG exhibited long-term bioavailability in the silkworm body.}, subject = {Nanopartikel}, language = {en} } @phdthesis{Nadernezhad2024, author = {Nadernezhad, Ali}, title = {Engineering approaches in biofabrication of vascularized structures}, doi = {10.25972/OPUS-34589}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-345892}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2024}, abstract = {Biofabrication technologies must address numerous parameters and conditions to reconstruct tissue complexity in vitro. A critical challenge is vascularization, especially for large constructs exceeding diffusion limits. This requires the creation of artificial vascular structures, a task demanding the convergence and integration of multiple engineering approaches. This doctoral dissertation aims to achieve two primary objectives: firstly, to implement and refine engineering methods for creating artificial microvascular structures using Melt Electrowriting (MEW)-assisted sacrificial templating, and secondly, to deepen the understanding of the critical factors influencing the printability of bioink formulations in 3D extrusion bioprinting. In the first part of this dissertation, two innovative sacrificial templating techniques using MEW are explored. Utilizing a carbohydrate glass as a fugitive material, a pioneering advancement in the processing of sugars with MEW with a resolution under 100 microns was made. Furthermore, by introducing the "print-and-fuse" strategy as a groundbreaking method, biomimetic branching microchannels embedded in hydrogel matrices were fabricated, which can then be endothelialized to mirror in vivo vascular conditions. The second part of the dissertation explores extrusion bioprinting. By introducing a simple binary bioink formulation, the correlation between physical properties and printability was showcased. In the next step, employing state-of-the-art machine-learning approaches revealed a deeper understanding of the correlations between bioink properties and printability in an extended library of hydrogel formulations. This dissertation offers in-depth insights into two key biofabrication technologies. Future work could merge these into hybrid methods for the fabrication of vascularized constructs, combining MEW's precision with fine-tuned bioink properties in automated extrusion bioprinting.}, subject = {3D-Druck}, language = {en} } @phdthesis{Emmert2023, author = {Emmert, Martin}, title = {The Influence of Substrate Micro- and Nanotopographies on Essential Cell Functions}, doi = {10.25972/OPUS-32779}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-327796}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {The introduction of novel bioactive materials to manipulate living cell behavior is a crucial topic for biomedical research and tissue engineering. Biomaterials or surface patterns that boost specific cell functions can enable innovative new products in cell culture and diagnostics. This study aims at investigating the interaction of living cells with microstructured, nanostructured and nanoporous material surfaces in order to identify distinct systematics in cell-material interplay. For this purpose, three different studies were carried out and yielded individual effects on different cell functions. Cell migration processes are controlled by sensitive interaction with external cues such as topographic structures of the cell's environment. The first part of this study presents systematically controlled assays to investigate the effects of spatial density and local geometry of micron scale topographic cues on amoeboid migration of Dictyostelium discoideum cells in quasi-3D pillar fields with systematic variation of inter-pillar distance and pillar lattice geometry. We can extract motility parameters in order to elucidate the details of amoeboid migration mechanisms and consolidate them in a two-state contact-controlled motility model, distinguishing directed and random phases. Specifically, we find that directed pillar-to-pillar runs are found preferably in high pillar density regions, and cells in directed motion states sense pillars as attractive topographic stimuli. In contrast, cell motion in random probing states is inhibited by high pillar density, where pillars act as obstacles for cell motion. In a gradient spatial density, these mechanisms lead to topographic guidance of cells, with a general trend towards a regime of inter-pillar spacing close to the cell diameter. In locally anisotropic pillar environments, cell migration is often found to be damped due to competing attraction by different pillars in close proximity and due to lack of other potential stimuli in the vicinity of the cell. Further, we demonstrate topographic cell guidance reflecting the lattice geometry of the quasi-3D environment by distinct preferences in migration direction. We further investigate amoeboid single-cell migration on intrinsically nano-structured, biodegradable silica fibers in comparison to chemically equivalent plain glass surfaces. Cell migration trajectories are classified into directed runs and quasi-random migration by a local mean squared displacement (LMSD) analysis. We find that directed movement on silica fibers is enhanced in a significant manner by the fibers' nanoscale surface-patterns. Further, cell adhesion on the silica fibers is a microtubule-mediated process. Cells lacking microtubules detach from the fibers, but adhere well to glass surfaces. Knock-out mutants of myosin II migrating on the fibers are as active as cells with active myosin II, while the migration of the knock-out mutants is hindered on plain glass. We investigate the influence of the intrinsically nano-patterned surface of nanoporous glass membranes on the behavior of mammalian cells. Three different cell lines and primary human mesenchymal stem cells (hMSCs) proliferate readily on nanoporous glass membranes with mean pore sizes between 10 nm and 124 nm. In both proliferation and mRNA expression experiments, L929 fibroblasts show a distinct trend towards mean pore sizes > 80 nm. For primary hMSCs, excellent proliferation is observed on all nanoporous surfaces. hMSC on samples with 17 nm pore size display increased expression of COL10, COL2A1 and SOX9, especially during the first two weeks of culture. In upside down culture, SK MEL-28 cells on nanoporous glass resist the gravitational force and proliferate well in contrast to cells on flat references. The effect of paclitaxel treatment of MDA MB 321 breast cancer cells is already visible after 48 h on nanoporous membranes and strongly pronounced in comparison to reference samples. The studies presented in this work showed novel and distinct effects of micro- and nanoscale topographies on the behavior of various types of living cells. These examples display how versatile the potential for applications of bioactive materials could become in the next years and decades. And yet this variety of different alterations of cell functions due to topographic cues also shows the crucial part of this field of research: Carving out distinct, robust correlations of external cues and cell behavior is of utmost importance to derive definitive design implications that can lead to scientifically, clinically and commercially successful products.}, language = {en} } @article{KadeBakirciTandonetal.2022, author = {Kade, Juliane C. and Bakirci, Ezgi and Tandon, Biranche and Gorgol, Danila and Mrlik, Miroslav and Luxenhofer, Robert and Dalton, Paul D.}, title = {The Impact of Including Carbonyl Iron Particles on the Melt Electrowriting Process}, series = {Macromolecular Materials and Engineering}, volume = {307}, journal = {Macromolecular Materials and Engineering}, number = {12}, issn = {1438-7492}, doi = {10.1002/mame.202200478}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318482}, year = {2022}, abstract = {Melt electrowriting, a high-resolution additive manufacturing technique, is used in this study to process a magnetic polymer-based blend for the first time. Carbonyl iron (CI) particles homogenously distribute into poly(vinylidene fluoride) (PVDF) melts to result in well-defined, highly porous structures or scaffolds comprised of fibers ranging from 30 to 50 µm in diameter. This study observes that CI particle incorporation is possible up to 30 wt\% without nozzle clogging, albeit that the highest concentration results in heterogeneous fiber morphologies. In contrast, the direct writing of homogeneous PVDF fibers with up to 15 wt\% CI is possible. The fibers can be readily displaced using magnets at concentrations of 1 wt\% and above. Combined with good viability of L929 CC1 cells using Live/Dead imaging on scaffolds for all CI concentrations indicates that these formulations have potential for the usage in stimuli-responsive applications such as 4D printing.}, language = {en} } @article{ChristGlaubittBerberichetal.2022, author = {Christ, Bastian and Glaubitt, Walther and Berberich, Katrin and Weigel, Tobias and Probst, J{\"o}rn and Sextl, Gerhard and Dembski, Sofia}, title = {Sol-gel-derived fibers based on amorphous α-hydroxy-carboxylate-modified titanium(IV) oxide as a 3-dimensional scaffold}, series = {Materials}, volume = {15}, journal = {Materials}, number = {8}, issn = {1996-1944}, doi = {10.3390/ma15082752}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-270694}, year = {2022}, abstract = {The development of novel fibrous biomaterials and further processing of medical devices is still challenging. For instance, titanium(IV) oxide is a well-established biocompatible material, and the synthesis of TiO\(_x\) particles and coatings via the sol-gel process has frequently been published. However, synthesis protocols of sol-gel-derived TiO\(_x\) fibers are hardly known. In this publication, the authors present a synthesis and fabrication of purely sol-gel-derived TiO\(_x\) fiber fleeces starting from the liquid sol-gel precursor titanium ethylate (TEOT). Here, the α-hydroxy-carboxylic acid lactic acid (LA) was used as a chelating ligand to reduce the reactivity towards hydrolysis of TEOT enabling a spinnable sol. The resulting fibers were processed into a non-woven fleece, characterized with FTIR, \(^{13}\)C-MAS-NMR, XRD, and screened with regard to their stability in physiological solution. They revealed an unexpected dependency between the LA content and the dissolution behavior. Finally, in vitro cell culture experiments proved their potential suitability as an open-mesh structured scaffold material, even for challenging applications such as therapeutic medicinal products (ATMPs).}, language = {en} } @article{HaiderAhmadYangetal.2021, author = {Haider, Malik Salman and Ahmad, Taufiq and Yang, Mengshi and Hu, Chen and Hahn, Lukas and Stahlhut, Philipp and Groll, J{\"u}rgen and Luxenhofer, Robert}, title = {Tuning the thermogelation and rheology of poly(2-oxazoline)/poly(2-oxazine)s based thermosensitive hydrogels for 3D bioprinting}, series = {Gels}, volume = {7}, journal = {Gels}, number = {3}, issn = {2310-2861}, doi = {10.3390/gels7030078}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-241781}, year = {2021}, abstract = {As one kind of "smart" material, thermogelling polymers find applications in biofabrication, drug delivery and regenerative medicine. In this work, we report a thermosensitive poly(2-oxazoline)/poly(2-oxazine) based diblock copolymer comprising thermosensitive/moderately hydrophobic poly(2-N-propyl-2-oxazine) (pPrOzi) and thermosensitive/moderately hydrophilic poly(2-ethyl-2-oxazoline) (pEtOx). Hydrogels were only formed when block length exceeded certain length (≈100 repeat units). The tube inversion and rheological tests showed that the material has then a reversible sol-gel transition above 25 wt.\% concentration. Rheological tests further revealed a gel strength around 3 kPa, high shear thinning property and rapid shear recovery after stress, which are highly desirable properties for extrusion based three-dimensional (3D) (bio) printing. Attributed to the rheology profile, well resolved printability and high stackability (with added laponite) was also possible. (Cryo) scanning electron microscopy exhibited a highly porous, interconnected, 3D network. The sol-state at lower temperatures (in ice bath) facilitated the homogeneous distribution of (fluorescently labelled) human adipose derived stem cells (hADSCs) in the hydrogel matrix. Post-printing live/dead assays revealed that the hADSCs encapsulated within the hydrogel remained viable (≈97\%). This thermoreversible and (bio) printable hydrogel demonstrated promising properties for use in tissue engineering applications.}, language = {en} } @article{RoedelBaumannGrolletal.2018, author = {R{\"o}del, Michaela and Baumann, Katrin and Groll, J{\"u}rgen and Gbureck, Uwe}, title = {Simultaneous structuring and mineralization of silk fibroin scaffolds}, series = {Journal of Tissue Engineering}, volume = {9}, journal = {Journal of Tissue Engineering}, doi = {10.1177/2041731418788509}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226427}, pages = {1-16}, year = {2018}, abstract = {Silk fibroin is commonly used as scaffold material for tissue engineering applications. In combination with a mineralization with different calcium phosphate phases, it can also be applied as material for bone regeneration. Here, we present a study which was performed to produce mineralized silk fibroin scaffolds with controlled macroporosity. In contrast to former studies, our approach focused on a simultaneous gelation and mineralization of silk fibroin by immersion of frozen silk fibroin monoliths in acidic calcium phosphate solutions. This was achieved by thawing frozen silk fibroin monoliths in acidic calcium phosphate solution, leading to the precipitation of monocalcium phosphate within the silk fibroin matrix. In the second approach, a conversion of incorporated -tricalcium phosphate particles into brushite was successfully achieved. Furthermore, a controlled cryostructuring process of silk fibroin scaffolds was carried out leading to the formation of parallel-oriented pores with diameters of 30-50 mu m.}, language = {en} } @phdthesis{Mueller2022, author = {M{\"u}ller, Melanie}, title = {Untersuchung von Grenzfl{\"a}chenreaktionen von kristallisierenden Glasloten bei der F{\"u}gung von Hochtemperaturbrennstoffzellen}, doi = {10.25972/OPUS-29687}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-296871}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2022}, abstract = {F{\"u}r die F{\"u}gung der Interkonnektoren einer Hochtemperaturbrennstoffzelle wurden in der hier vorliegenden Arbeit glaskeramische Lote entwickelt und untersucht. Es konnte ein hochviskoses Glas gefunden werden, das trotz fehlendem Erweichen bei der F{\"u}gung eine stabile, gasdichte und elektrisch isolierende glaskeramische F{\"u}gung ausbildet. Auch w{\"a}hrend des Betriebs kommt es zu keinem Erweichen der F{\"u}gung. Weiter treten keine feststellbaren Reaktionen mit den potentiellen Reaktionspartnern, den Stahlelementen, auf. Es konnte eine Korrelation dieses Reaktionsverhaltens mit dem Kristallisationsverhalten der Glaskeramik gefunden werden. Das Verhalten des Glaslotes wurde {\"u}ber mehrere tausend Stunden unter Betriebsbedingungen beziehungsweise betriebsimulierenden Bedingungen untersucht. Dabei konnte die Kristallisationsentwicklung beschrieben werden. Ein weiterer Aspekt der Arbeit war die Untersuchung des Einflusses der einzelnen Faktoren, denen ein Glaslot w{\"a}hrend seines Einsatzes von der F{\"u}gung bis zum Betrieb ausgesetzt ist, wie die F{\"u}getemperatur, die Viskosit{\"a}t der eingesetzten glasbildenden Schmelze oder die Dualgasatmosph{\"a}re im Betrieb, auf das Gef{\"u}ge und die Diffusion. Hierbei konnte gezeigt werden, dass die F{\"u}getemperatur mit Abstand den gr{\"o}ßten Einfluss auf die Stabilit{\"a}t der Glaslotschicht hat. Diese bedingt nicht nur die Kinetik des Fließens und die Benetzung des Stahls durch das Glas, sondern vor allem, welche Kristallphasen gebildet werden und wie das finale Gef{\"u}ge im Hinblick auf Kristallitgr{\"o}ße und -verteilung aussieht. So kommt es bei h{\"o}heren Temperaturen zu einem gr{\"o}ßeren Restglasphasenanteil und einem geringeren Kristallitanteil, was wiederum die Diffusion der Stahlelemente in die Glaslotschicht beg{\"u}nstigt.}, subject = {Hochtemperaturbrennstoffzelle}, language = {de} }