TY - THES A1 - Böhm, Christoph T1 - Loewner equations in multiply connected domains T1 - Loewner Gleichungen für mehrfach zusammenhängende Gebiete N2 - The first goal of this thesis is to generalize Loewner's famous differential equation to multiply connected domains. The resulting differential equations are known as Komatu--Loewner differential equations. We discuss Komatu--Loewner equations for canonical domains (circular slit disks, circular slit annuli and parallel slit half-planes). Additionally, we give a generalisation to several slits and discuss parametrisations that lead to constant coefficients. Moreover, we compare Komatu--Loewner equations with several slits to single slit Loewner equations. Finally we generalise Komatu--Loewner equations to hulls satisfying a local growth property. N2 - Zunächst diskutieren wir eine Verallgemeinerung der radialen und chordalen Loewner Differentialgleichung auf mehrfach zusammenhängende Standardgebiete (Kreisschlitzgebiete, Kreisringschlitzgebiete, parallel Schlitz-Halbebenen). Diese Differentialgleichungen werden Komatu-Loewner Differentialgleichungen bezeichnet. Wir verallgemeinern diese auch auf mehrere Schlitze und zeigen, dass es Parametrisierungen gibt, die zu konstanten Koeffizienten führen. Zusätzlich vergleichen wir Komatu-Loewner Gleichungen für mehrere Schlitze mit Loewner Gleichungen im Einschlitzfall. Schließlich untersuchen wir den Fall von allgemeineren Wachstumsprozessen, die dadurch charakterisiert sind, dass nur ein "lokaler Zuwachs" möglich ist. KW - Biholomorphe Abbildung KW - Differentialgleichung KW - Loewner-Theorie KW - Loewner theory Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129903 ER - TY - THES A1 - Böhm, Christoph T1 - Thermal Stability of the Polyesters PCL and PLGA during Melt Electrowriting T1 - Thermische Stabilität der Polyester PCL und PLGA während des Melt Electrowriting Prozesses N2 - The focus of this thesis was to investigate how PCL and PLGA react to the heat exposure that comes with the MEW process over a defined timespan. To assess the thermal stability of PCL during MEW over 25 d, an automated collection of fibers has been used to determine the CTS on each day of heating for three different temperatures. PCL is exceptionally stable over 25 d at 75 °C, whereas for 85 °C and 95 °C a slight upward trend during the last 10 d could be observed, which is an indication for thermal degradation. Same trend could be observed for diameter of fibers produced at a fixed collector speed. For all temperatures, CTS during the first 5 d decreased due to inhomogeneities of the melt. Physical analysis of the fibers by XRD and mechanical testing showed no significant changes. To investigate the chemical details of the thermal durability, PCL was artificially aged over 25 d at 75 °C, 85 °C and 95 °C. Data from GPC analysis and rheology revealed that PCL is degrading steadily at all three temperatures. Combined with GC-MS analysis, two different mechanisms for degradation could be observed: random chain scission and unzipping. Additional GPC experiment using a mixture of PCL and a fluorescence labelled PCL showed that PCL was undergoing ester interchange reactions, which could explain its thermal stability. PLGA was established successfully as material for MEW. GPC results revealed that PLGA degraded heavily in the one-hour preheating period. To reduce the processing temperature, ATEC was blended with PLGA in three mixtures. This slowed down degradation and a processing window of 6 h could be established. Mechanical testing with fibers produced with PLGA and all three blends was performed. PLGA was very brittle, whereas the blends showed an elastic behavior. This could be explained by ester interchange reactions that formed a loosely crosslinked network with ATEC. N2 - Ziel dieser Arbeit war, die Veränderung von PCL und PLGA während des MEW-Verfahrens bei bestimmten Temperaturen über einen definierten Zeitraum zu untersuchen. Für die Bewertung der thermischen Stabilität von PCL während des MEW-Prozesses über 25 d wurden Fasern in einem vorgegebenen Druckmuster gesammelt, um täglich die CTS für drei verschiedene Temperaturen zu bestimmen. Allgemein war PCL bei 75 °C über 25 d thermisch stabil. Allerdings nahm die CTS bei allen Temperaturen während der ersten 5 d aufgrund von Inhomogenitäten der Schmelze ab. Bei 85 °C und 95 °C wurde in den letzten 10 d ein leichter Anstieg der CTS beobachtet, was auf thermische Degradation hinweist. Dieser Anstieg war ebenfalls im Durchmesser der Fasern zu beobachten, die mit konstanter Kollektorgeschwindigkeit hergestellt wurden. Die physikalische Untersuchung der Fasern mittels XRD und mechanischer Tests ergab keine signifikanten Veränderungen. Um die Chemie der thermischen Beständigkeit zu untersuchen, wurde PCL über 25 d bei 75 °C, 85 °C und 95 °C künstlich gealtert. GPC- und rheologische Analysen zeigten, dass PCL bei allen Temperaturen stetig abbaut. Mit der GC-MS-Analyse konnten zwei Abbaumechanismen beobachtet werden: zufällige Kettenspaltung und Unzipping. GPC-Messungen mit einer Mischung aus PCL und einem fluoreszenzmarkierten PCL zeigten, dass es zu Esteraustauschreaktionen kommt, welche die thermische Stabilität erklären. PLGA wurde erfolgreich als Material für MEW etabliert. Die GPC-Daten zeigten, dass PLGA während der einstündigen Aufheizphase stark abgebaut wurde. Um die Verarbeitungstemperatur zu senken, wurden drei Mischungen mit verschiedenen Verhältnissen von PLGA und ATEC hergestellt. Dadurch verlangsamte sich der Abbau, wodurch ein Verarbeitungsfenster von 6 h erreicht wurde. Mechanische Tests zeigten für PLGA ein sprödes, für die Mischungen ein elastisches Verhalten. Dies kann durch Esteraustauschreaktionen mit ATEC erklärt werden, durch die ein Polymernetzwerk entstehen könnte. KW - Degradation KW - Polylactid-co-Glycolid KW - Polycaprolacton KW - Additive Fertigung KW - polycaprolactone KW - poly(lactic-co-glycolic acid) KW - additive manufacturing KW - degradation KW - Rapid Prototyping KW - PCL KW - PLGA Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-306139 ER - TY - JOUR A1 - Schnabel, Renate B. A1 - Camen, Stephan A1 - Knebel, Fabian A1 - Hagendorff, Andreas A1 - Bavendiek, Udo A1 - Böhm, Michael A1 - Doehner, Wolfram A1 - Endres, Matthias A1 - Gröschel, Klaus A1 - Goette, Andreas A1 - Huttner, Hagen B. A1 - Jensen, Christoph A1 - Kirchhof, Paulus A1 - Korosoglou, Grigorius A1 - Laufs, Ulrich A1 - Liman, Jan A1 - Morbach, Caroline A1 - Navabi, Darius Günther A1 - Neumann-Haefelin, Tobias A1 - Pfeilschifter, Waltraut A1 - Poli, Sven A1 - Rizos, Timolaos A1 - Rolf, Andreas A1 - Röther, Joachim A1 - Schäbitz, Wolf Rüdiger A1 - Steiner, Thorsten A1 - Thomalla, Götz A1 - Wachter, Rolf A1 - Haeusler, Karl Georg T1 - Expert opinion paper on cardiac imaging after ischemic stroke JF - Clinical Research in Cardiology N2 - This expert opinion paper on cardiac imaging after acute ischemic stroke or transient ischemic attack (TIA) includes a statement of the "Heart and Brain" consortium of the German Cardiac Society and the German Stroke Society. The Stroke Unit-Commission of the German Stroke Society and the German Atrial Fibrillation NETwork (AFNET) endorsed this paper. Cardiac imaging is a key component of etiological work-up after stroke. Enhanced echocardiographic tools, constantly improving cardiac computer tomography (CT) as well as cardiac magnetic resonance imaging (MRI) offer comprehensive non- or less-invasive cardiac evaluation at the expense of increased costs and/or radiation exposure. Certain imaging findings usually lead to a change in medical secondary stroke prevention or may influence medical treatment. However, there is no proof from a randomized controlled trial (RCT) that the choice of the imaging method influences the prognosis of stroke patients. Summarizing present knowledge, the German Heart and Brain consortium proposes an interdisciplinary, staged standard diagnostic scheme for the detection of risk factors of cardio-embolic stroke. This expert opinion paper aims to give practical advice to physicians who are involved in stroke care. In line with the nature of an expert opinion paper, labeling of classes of recommendations is not provided, since many statements are based on expert opinion, reported case series, and clinical experience. KW - cardiac imaging KW - echocardiography KW - ischemic stroke KW - transient ischemic attack KW - expert opinion KW - magnetic resonance imaging KW - computed tomography Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-266662 SN - 1861-0692 VL - 110 IS - 7 ER - TY - JOUR A1 - Ryma, Matthias A1 - Tylek, Tina A1 - Liebscher, Julia A1 - Blum, Carina A1 - Fernandez, Robin A1 - Böhm, Christoph A1 - Kastenmüller, Wolfgang A1 - Gasteiger, Georg A1 - Groll, Jürgen T1 - Translation of collagen ultrastructure to biomaterial fabrication for material-independent but highly efficient topographic immunomodulation JF - Advanced materials N2 - Supplement-free induction of cellular differentiation and polarization solely through the topography of materials is an auspicious strategy but has so far significantly lagged behind the efficiency and intensity of media-supplementation-based protocols. Consistent with the idea that 3D structural motifs in the extracellular matrix possess immunomodulatory capacity as part of the natural healing process, it is found in this study that human-monocyte-derived macrophages show a strong M2a-like prohealing polarization when cultured on type I rat-tail collagen fibers but not on collagen I films. Therefore, it is hypothesized that highly aligned nanofibrils also of synthetic polymers, if packed into larger bundles in 3D topographical biomimetic similarity to native collagen I, would induce a localized macrophage polarization. For the automated fabrication of such bundles in a 3D printing manner, the strategy of “melt electrofibrillation” is pioneered by the integration of flow-directed polymer phase separation into melt electrowriting and subsequent selective dissolution of the matrix polymer postprocessing. This process yields nanofiber bundles with a remarkable structural similarity to native collagen I fibers, particularly for medical-grade poly(ε-caprolactone). These biomimetic fibrillar structures indeed induce a pronounced elongation of human-monocyte-derived macrophages and unprecedentedly trigger their M2-like polarization similar in efficacy as interleukin-4 treatment. KW - biofabrication KW - extracellular matrix KW - immunomodulation KW - macrophages KW - melt electrofibrillation KW - melt electrowriting Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256381 VL - 33 IS - 33 ER - TY - JOUR A1 - Böhm, Christoph A1 - Tandon, Biranche A1 - Hrynevich, Andrei A1 - Teßmar, Jörg A1 - Dalton, Paul D. T1 - Processing of Poly(lactic–co–glycolic acid) Microfibers via Melt Electrowriting JF - Macromolecular Chemistry and Physics N2 - Polymers sensitive to thermal degradation include poly(lactic-co-glycolic acid) (PLGA), which is not yet processed via melt electrowriting (MEW). After an initial period of instability where mean fiber diameters increase from 20.56 to 27.37 µm in 3.5 h, processing stabilizes through to 24 h. The jet speed, determined using critical translation speed measurements, also reduces slightly in this 3.5 h period from 500 to 433 mm min\(^{−1}\) but generally remains constant. Acetyl triethyl citrate (ATEC) as an additive decreases the glass transition temperature of PLGA from 49 to 4 °C, and the printed ATEC/PLGA fibers exhibits elastomeric behavior upon handling. Fiber bundles tested in cyclic mechanical testing display increased elasticity with increasing ATEC concentration. The processing temperature of PLGA also reduces from 165 to 143 °C with increase in ATEC concentration. This initial window of unstable direct writing seen with neat PLGA can also be impacted through the addition of 10-wt% ATEC, producing fiber diameters of 14.13 ± 1.69 µm for the first 3.5 h of heating. The investigation shows that the initial changes to the PLGA direct-writing outcomes seen in the first 3.5 h are temporary and that longer times result in a more stable MEW process. KW - poly(lactide-co-glycolide) KW - 3D printing KW - additive manufacturing KW - electrohydrodynamics KW - melt electrospinning writing KW - plasticizers Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318444 VL - 223 IS - 5 ER - TY - JOUR A1 - Böhm, Christoph A1 - Stahlhut, Philipp A1 - Weichhold, Jan A1 - Hrynevich, Andrei A1 - Teßmar, Jörg A1 - Dalton, Paul D. T1 - The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting JF - Small N2 - Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that places unique constraints on the processing of thermally degradable polymers. With a single nozzle, MEW operates at low throughput and in this study, medical-grade poly(ε-caprolactone) (PCL) is heated for 25 d at three different temperatures (75, 85, and 95 °C), collecting daily samples. There is an initial increase in the fiber diameter and decrease in the jet speed over the first 5 d, then the MEW process remains stable for the 75 and 85 °C groups. When the collector speed is fixed to a value at least 10% above the jet speed, the diameter remains constant for 25 d at 75 °C and only increases with time for 85 and 95 °C. Fiber fusion at increased layer height is observed for 85 and 95 °C, while the surface morphology of single fibers remain similar for all temperatures. The properties of the prints are assessed with no observable changes in the degree of crystallinity or the Young's modulus, while the yield strength decreases in later phases only for 95 °C. After the initial 5-d period, the MEW processing of PCL at 75 °C is extraordinarily stable with overall fiber diameters averaging 13.5 ± 1.0 µm over the entire 25-d period. KW - polycaprolactone KW - 3D printing KW - additive manufacturing KW - electrohydrodynamic KW - melt electrospinning writing Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257741 VL - 18 IS - 3 ER -