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Calcium supplementation of bioinks reduces shear stress-induced cell damage during bioprinting
(2022)
AbstractDuring bioprinting, cells are suspended in a viscous bioink and extruded under pressure through small diameter printing needles. The combination of high pressure and small needle diameter exposes cells to considerable shear stress, which can lead to cell damage and death. Approaches to monitor and control shear stress-induced cell damage are currently not well established. To visualize the effects of printing-induced shear stress on plasma membrane integrity, we add FM 1-43 to the bioink, a styryl dye that becomes fluorescent when bound to lipid membranes, such as the cellular plasma membrane. Upon plasma membrane disruption, the dye enters the cell and also stains intracellular membranes. Extrusion of alginate-suspended NIH/3T3 cells through a 200 µm printing needle led to an increased FM 1-43 incorporation at high pressure, demonstrating that typical shear stresses during bioprinting can transiently damage the plasma membrane. Cell imaging in a microfluidic channel confirmed that FM 1-43 incorporation is caused by cell strain. Notably, high printing pressure also impaired cell survival in bioprinting experiments. Using cell types of different stiffnesses, we find that shear stress-induced cell strain, FM 1-43 incorporation and cell death were reduced in stiffer compared to softer cell types and demonstrate that cell damage and death correlate with shear stress-induced cell deformation. Importantly, supplementation of the suspension medium with physiological concentrations of CaCl2 greatly reduced shear stress-induced cell damage and death but not cell deformation. As the sudden influx of calcium ions is known to induce rapid cellular vesicle exocytosis and subsequent actin polymerization in the cell cortex, we hypothesize that calcium supplementation facilitates the rapid resealing of plasma membrane damage sites. We recommend that bioinks should be routinely supplemented with physiological concentrations of calcium ions to reduce shear stress-induced cell damage and death during extrusion bioprinting.
Firefly ultra dense networks combine the promising properties of centralized processing
and ultra dense deployment. We consider the uplink of the network, where a large
number of remote radio units, referred to as firefly nodes (FNs), are spatially distributed
over an area. In this coverage area, several mobile devices (MDs) are simultaneously
connected to all FNs via sub-6 GHz radio frequency links. In contrast to the cloud
radio access network (C-RAN) architecture, the FNs in firefly ultra dense networks
forward the MDs’ data through multi-hop millimeter-wave (mmWave) links to one
or multiple root nodes, since the coverage radius of an individual mmWave link is
limited. These root nodes then forward the data over optical fiber links further to
a central unit (CU), where the MDs’ signals are decoded. The amount of data that
is received at each FN is potentially huge, and therefore efficient signal processing is
required at each FN before the received signals can be forwarded to other FNs. Thus,
in this thesis, we propose several linear processing strategies and a nonlinear processing
strategy. First, by deploying linear processing schemes, all received signal streams are
linearly filtered at each FN before being forwarded over an available mmWave link. Our
simulation results show significant performance improvement compared to a baseline
scheme. Furthermore, we propose a nonlinear processing strategy that quantizes the
received signals at each FN. In particular, for the nonlinear forwarding at the FNs, we
formulate an optimization problem for a local design strategy and present an optimal
solution by utilizing strong duality and using the Lagrangian method to transform
the optimization problem into an unconstrained problem via its dual formulation. A
bisection algorithm for finding the optimal dual variables and a closed-form solution
for the primal variables are presented. In addition, based on the cut-set bound, we
develop an upper bound of the achievable sum rate for the considered firefly network.
It is shown that the proposed nonlinear forwarding strategy outperforms several linear
forwarding strategies and approaches the performance upper bound in relevant transmit
power regimes at the expense of higher computational complexity. Our simulation
results reveal that having more root nodes in the topology improves the performance
of linear and nonlinear forwarding but also requires additional optical fiber links to
the CU.
In this research, the effects of fumed silica (FS) on the Ultraviolet (UV)-ink rheological behavior and processing windows were discussed. Objects using different concentrations of FS inks were printed by the modified UV-Direct ink writing (DIW) printer. The function of fumed silica in the ink-based system has been verified, and the processing scope has been expended with a suitable amount of FS combined with the UV light. The results show that the combination of a suitable amount of FS with the UV-DIW system reaches fast and accurate printing with a larger processing window compared to the non-UV system. However, an excessively high concentration of FS will increase the yield stress of the ink, which also increases the requirement of extrusion unit and the die-swelling effects.
Due to the occurrence of THz-excited vibrational modes in biomacromolecules, the THz frequency range has been identified as particularly suitable for developing and applying new bioanalytical methods. We present a scalable THz metamaterial-based biosensor being utilized for the multifrequency investigation of single- and double-stranded DNA (ssDNA and dsDNA) samples. It is demonstrated that the metamaterial resonance frequency shift by the DNA’s presence depends on frequency. Our experiments with the scalable THz biosensors demonstrate a major change in the degree of the power function for dsDNA by 1.53 ± 0.06 and, in comparison, 0.34 ± 0.11 for ssDNA as a function of metamaterial resonance frequency. Thus, there is a significant advantage for dsDNA detection that can be used for increased sensitivity of biomolecular detection at higher frequencies. This work represents a first step for application-specific biosensors with potential advantages in sensitivity, specificity, and robustness.
Mithilfe des LDS®-Verfahrens kann die Integration elektrischer Systeme in multifunktionale Produkte realisiert werden. In vielen Bereichen, auch in Hochfrequenz (HF)-Anwendungen, bietet das LDS®-Verfahren hohes Nutzenpotenzial hinsichtlich Funktionalität und Integrationsdichte, wodurch ein kompaktes Kommunikationssystem mit genauen Abmessungen sowie mit reduzierter Anzahl an Verbindungsstellen geschaffen werden kann. Hierfür müssen die mittels LDS®-Verfahren hergestellten Bauteile zahlreiche Anforderungen bezüglich ihrer HF-Eigenschaften erfüllen. Passive Intermodulation (PIM) als eine der Leistungsanforderungen ist zu einem wachsenden Anliegen hinsichtlich des Designs und der Fertigung von HF-Bauteilen geworden. Die Evaluierung von PIM an den mittels LDS®-Verfahren hergestellten Mikrostreifenleitungen steht in dieser Arbeit im Fokus.
Eine im Rahmen dieser Dissertation durchgeführte Untersuchung kommt zu dem Ergebnis, dass sowohl der PIM-Pegel als auch die Qualitätsmerkmale von den Laserprozessparametern abhängig sind. Durch die Einstellung der Laserprozessparameter kann der PIM-Pegel beeinflusst werden. Aus den präsentierten Forschungsergebnissen ergibt sich, dass das LDS®-Verfahren für HF-Anwendungen unter Berücksichtigung von PIM einsetzbar ist.
Amorphe Kohlenstoffschichten (a-C:H) finden riesiges Potenzial im Einsatz für trockene Kontaktbedingungen. Die vorliegende Arbeit hat das Ziel, das Design einer industrieüblichen a-C:H-Schicht auf Werkzeugstahl zu modifizieren, um die Verschleißbeständigkeit im trockenen Gleitkontakt zu erhöhen. Der Hintergrund für die vorliegenden Untersuchungen liegt darin, dass ein schmierstofffreier Blechumformprozess durch werkzeugseitiges Beschichten realisiert werden kann. Untersucht bezüglich des Schichtdesigns werden vor allem Haftschicht, Schichtdicke und Abscheidegasatmosphäre. Auf ihren Einflüssen auf die tribologisch relevante Schichtcharakteristik im Vergleich zu dem a-C:H-Referenzschichtsystem liegen die Schwerpunkte. Nach den tribologischen Evaluationen werden die Verschleißspuren mit dem Rasterelektronenmikroskop untersucht und die Verschleißmechanismen der Schichtsysteme werden dabei identifiziert. Schließlich werden die Einflüsse aller untersuchten Faktoren im Schichtdesign auf die Verschleißbeständigkeit unter schmierstofffreien Bedingungen zusammengestellt und ein Prozessfenster daraus abgeleitet.
Wesentlicher Gegenstand der Dissertationsschrift ist die Erforschung eines neuartigen additiven Fertigungsansatzes zur Herstellung elastischer mechatronischer Komponenten. Es wird die Kombination von Variationen und Weiterentwicklungen des Aerosol-Jet-Druck Verfahrens zur Produktion gestapelter Dielektrischer Elastomere beschrieben. Den Rahmen eines prototypischen Anwendungsfalls zur Ableitung der notwendigen und wünschenswerten Eigenschaften solcher flexiblen mechatronischen Systeme und damit letztlich der Anforderungen an ein Fertigungsverfahren bilden nachgiebige und damit anpassungsfähige Robotersysteme. Deren makroskopisch wirksame Kinematiken und Wirkflächen vereinen einen Merkmalskatalog hinsichtlich ihrer grundlegenden Konzepte und ihrer Anforderungen an einen Fertigungsansatz, der zukünftig auch einen Übertrag der gewonnenen Erkenntnisse auf andere Anwendungsdomänen flexibler mechatronischer Systeme erlaubt.
Die dargestellten Methoden zur Herstellung von flexiblen Elektroden, Silikon-Dielektrika und integrierter Aktoren und Sensoren umfassen zum einen den Multi-Aerosol-Druck von RTV2-Silikonen zur programmierbaren Fertigung von Silikonlagen mit Schichtdicken im Bereich von 10 µm und deren Stapelung zu Volumenkörpern mit mehreren hundert Lagen. Weiterhin werden neuartige Ansätze zum zeiteffizienten Aerosol-Jet-Druck von elastischen Elektrodenstrukturen auf der Basis von reduziertem Graphenoxid vorgestellt. Der deren Herstellung erfolgt mittels eines neuartigen Hybrid-Atomizers, der die pneumatische und die ultraschallbasierte Aerosolerzeugung kombiniert. Daneben wird der Direktdruck von gefüllten Polymermatrizen durch die Kombination von drei Aerosolströmen beschrieben. Mit diesen neuartigen Ansätzen wird die Herstellung von prototypischen elastischen mechatronischen Komponenten in einem integrierten Prozessgerät demonstriert.
Die Verschmelzung der physikalischen und virtuellen Welt prägt die heutigen Lebens- und Arbeitswelten. Neue technische Lösungen meist in Form smarter Produkt-Service-Systeme - sollen individuelle Bedürfnisse und Bedarfe adressieren. Adoptionsprognosen in diesem Kontext erfordern zuverlässige Daten, Informationen und geeignete Analyseinstrumente für die Vorhersage individuellen Verhaltens. Speziell in Vorimplementierungsphasen sind Adoptionsprognosen ein wertvolles Instrument zur Vorhersage künftiger Ereignisse oder Situationen.
Diese Arbeit bietet einen interdisziplinären Einblick in Adoptions- und Akzeptanzprozesse unter Zugrundelegung emotionaler Antizipationen im Sinne der Simulation der zukünftigen Realität menschlicher Entscheidungsprozesse. Die auf Basis eines mehrphasigen Mixed-Methods-Ansatzes gehobenen Erkenntnisse der Arbeit zeigen, dass das thesenbasiert konzipierte und empirisch validierte Affective Adoption Forecasting Framework A²FORE den aktuellen Herausforderungen der Abschätzung individueller Adoptionsentscheidungen vor Markteinführung neuartiger smarter Produkt-Service-Systeme mit besonderem Fokus auf vulnerablen Konsumenten im Gesundheitswesen begegnen kann. A²FORE spiegelt die Nutzbarmachung antizipatorischer Emotionen als Prognoseelement für den Erfolg smarter Produkt-Service-Systeme wider. Dies entspricht der praxisbezogenen Forderung der Entwicklung eines handhabbaren Modells zur Adoptionsprognose auf Basis eines User Acceptance Testings im Rahmen von Vorimplementierungsphasen.
Organic solar cells (OSCs) are characterized by a high degree of flexibility in terms of shape, color, transparency and even recyclability. In addition, the energy consumption for production is low compared to classic PV technology. This makes OSCs perfect candidates for truly sustainable and eco-friendly energy converters of the future. The energy efficiencies of OSC devices have recently received a boost to over 18%, aided by decent interface engineering and are thus moving towards commercialization. Before they are ready for the market, however, universal interface materials must be found which are reliable, inexpensive and scalable, and which increase component efficiency and stability. Consequently, this work focuses on the development of functional and generic interface materials for the production of highly efficient and stable OSCs with simple processing techniques.
In the case of solution-processed tandem OSCs, their reliability and reproducibility often suffer from solvent inter-diffusion occuring during the wet processing of upper sub-cells on the top of less robust intermediate layers. One major aspect of this thesis is the design and application of a fully functional and robust IML to inhibit solvent penetration in solution-processed tandem OSCs. By incorporating of a hydrolysed methoxysilane crosslinker, (3-glycidyloxypropyl)trimethoxysilane (GOPS) into PEDOT:PSS, the robustness of the cross-linked GOPS-treated PEDOT:PSS film is significantly enhanced. By combining this cross-linked film with an ultra-thin PEDOT: PSS:MoO3 and ZnO nanoparicles (NPs), an efficient crosslinked IML is developed without any thermal post-treatment necessity. The reliability and generic application of this IML are fully demonstrated by fabricating inverted homo-tandem OSCs with three different light-harvesting materials processed from different high boilingpoint solvents with improved efficiencies and excellent reproducibility, in comparison to those with the control IML. The robust IML can block the penetration of high boiling-point solvents such as orthodichlorobenzene and chlorobenzene without further treatment and is even suitable for photoabsorber materials that are sensitive to thermal annealing at elevated temperature.
Another main aspect of this work is the development of scalable and highly efficient p-type Sb:SnO2 (ATO) transport layers as an alternative to the commonly used, but acidic, PEDOT: PSS. The ATO NPs are derived from stable SnO2 electron transport material (ETM) using a simple and practical doping approach. Introducing antimony cations into the SnO2 host during flame spray pyrolysis changes the conduction character of the SnO2 NPs impressively from an n-type to a p-type character, accompanied by a dramatic shift in the work function from 4.01 ± 0.01 eV for pure SnO2 NPs to 5.28 ± 0.01 eV for SnO2 with an optimal Sb content of 20 mol%. This goes along with an increase in electrical conductivity by approx. three orders of magnitude. The doping mechanism was examined in detail by means of Hard x-ray photoelectron spectroscopy, confirming that Sb3+ cations are the dominant substitutions for partial Sn4+ sites in the SnO2 host lattices. Both, the n-type and the 20 mol% p-type SnO2-based layer show excellent charge extraction properties, superior UV resistance, and remarkable generic applicabilities, compatible with various state-of-the-art organic semiconductors for photovoltaics. The excellent SnO2-based interface materials processed by doctor-blading in ambient require no any complex post-treatment. The usage of SnO2-based interface materials lead to a significant reduction of the currently existing interface challenges of OSCs, which are of great concern to the photovoltaic community.
This work investigates the cost-efficient integration of renewable hydrogen into steelworks for the production of methane and methanol as an efficient way to decarbonize the steel industry. Three case studies that utilize a mixture of steelworks off-gases (blast furnace gas, coke oven gas, and basic oxygen furnace gas), which differ on the amount of used off-gases as well as on the end product (methane and/or methanol), are analyzed and evaluated in terms of their economic performance. The most influential cost factors are identified and sensitivity analyses are conducted for different operating and economic parameters. Renewable hydrogen produced by PEM electrolysis is the most expensive component in this scheme and responsible for over 80% of the total costs. Progress in the hydrogen economy (lower electrolyzer capital costs, improved electrolyzer efficiency, and lower electricity prices) is necessary to establish this technology in the future.
This work is dedicated to the crystallization and luminescent properties of a prospective Ca2YMgScSi3O12:Ce (CYMSSG:Ce) micropowder (MP) phosphor converter (pc) for a white light–emitting LED (WLED). The set of MP samples was obtained by conventional solid-phase synthesis using different amounts of B2O3 flux in the 1–5 mole percentage range. The luminescent properties of the CYMSSG:Ce MPs were investigated at different Ce3+ concentrations in the 1–5 atomic percentage range. The formation of several Ce3+ multicenters in the CYMSSG:Ce MPs was detected in the emission and excitation spectra as well as the decay kinetics of the Ce3+ luminescence. The creation of the Ce3+ multicenters in CYMSSG:Ce garnet results from: (i) the substitution by the Ce3+ ions of the heterovalent Ca2+ and Y3+ cations in the dodecahedral position of the garnet host; (ii) the inhomogeneous local environment of the Ce3+ ions when the octahedral positions of the garnet are replaced by heterovalent Mg2+ and Sc3+ cations and the tetrahedral positions are replaced by Si4+ cations. The presence of Ce3+ multicenters significantly enhances the Ce3+ emission band in the red range in comparison with conventional YAG:Ce phosphor. Prototypes of the WLEDs were also created in this work by using CYMSSG:Ce MP films as phosphor converters. Furthermore, the dependence of the photoconversion properties on the layer thickness of the CYMSSG:Ce MP was studied as well. The changes in the MP layer thickness enable the tuning of the white light thons from cold white/daylight to neutral white. The obtained results are encouraging and can be useful for the development of a novel generation of pcs for WLEDs.
The comprehensive use of natural polymers, such as lignin, can accelerate the replacement of mineral oil-based commodities. Promoting the material recovery of the still underutilized technical lignin, polyolefin-lignin blends are a highly promising approach towards sustainable polymeric materials. However, a limiting factor for high-quality applications is the unpleasant odor of technical lignin and resulting blends. The latter, especially, are a target for potential odor reduction, since heat- and shear-force intense processing can intensify the smell. In the present study, the odor optimization of kraft and soda HDPE-lignin blends was implemented by the in-process application of two different processing additives–5% of activated carbon and 0.7% of a stripping agent. Both additives were added directly within the compounding process executed with a twin screw extruder. The odor properties of the produced blends were assessed systematically by a trained human panel performing sensory evaluations of the odor characteristics. Subsequently, causative odor-active molecules were elucidated by means of GC-O and 2D-GC-MS/O while OEDA gave insights into relative odor potencies of single odorants. Out of 70 different odorants detected in the entirety of the sample material, more than 30 sulfur-containing odorants were present in the kraft HDPE-lignin blend, most of them neo-formed due to high melt temperatures during extrusion, leading to strong burnt and sulfurous smells. The addition of activated carbon significantly decreased especially these sulfurous compounds, resulting in 48% of overall odor reduction of the kraft blend (mean intensity ratings of 5.2) in comparison to the untreated blend (10.0). The applied stripping agent, an aqueous solution of polymeric, surface-active substances adsorbed onto a PP carrier, was less powerful in reducing neo-formed sulfur odorants, but led to a decrease in odor of 26% in the case of the soda HDPE-lignin blend (7.4). The identification of single odorants on a molecular level further enabled the elucidation of odor reduction trends within single compound classes. The obtained odor reduction strategies not only promote the deodorization of HDPE-lignin blends, but might be additionally helpful for the odor optimization of other natural-fiber based materials.
To achieve the greenhouse gas reduction targets formulated in the European Green Deal, energy- and resource-intensive industries such as the steel industry will have to adapt or convert their production. In the long term, new technologies are promising. However, carbon capture storage and utilization solutions could be considered as short-term retrofitting solutions for existing steelworks. In this context, this paper presents a first experimental demonstration of an approach to the utilization of process off-gases generated in a steelworks by producing methane and methanol in hydrogen-intensified syntheses. Specifically, the integration of two methane synthesis reactors and one methanol synthesis reactor into a steel plant is experimentally simulated. An innovative monitoring and control tool, namely, a dispatch controller, simulates the process off-gas production using a digital twin of the steel plant and optimizes its distribution to existing and new consumers. The operating states/modes of the three reactors resulting from the optimization problem to be solved by the dispatch controller are distributed in real time via an online OPC UA connection to the corresponding experimental plants or their operators and applied there in a decentralized manner. The live coupling test showed that operating values for the different systems can be distributed in parallel from the dispatch controller to the test rigs via the established communication structure without loss. The calculation of a suitable control strategy is performed with a time resolution of one minute, taking into account the three reactors and the relevant steelworks components. Two of each of the methane/methanol synthesis reactors were operated error-free at one time for 10 and 7 h, respectively, with datasets provided by the dispatch controller. All three reactor systems were able to react quickly and stably to dynamic changes in the load or feed gas composition. Consistently high conversions and yields were achieved with low by-product formation.
Current assisted reproduction technologies (ART) are insufficient to cover the slice of the population needing to restore fertility, as well as to amplify the reproductive performance of domestic animals or endangered species. The design of dedicated reproductive scaffolds has opened the possibility to better recapitulate the reproductive 3D ovarian environment, thus potentially innovating in vitro folliculogenesis (ivF) techniques. To this aim, the present research has been designed to compare ovine preantral follicles in vitro culture on poly(epsilon-caprolactone) (PCL)-based electrospun scaffolds designed with different topology (Random vs. Patterned fibers) with a previously validated system. The ivF performances were assessed after 14 days under 3D-oil, Two-Step (7 days in 3D-oil and on scaffold), or One-Step PCL protocols (14 days on PCL-scaffold) by assessing morphological and functional outcomes. The results show that Two- and One-Step PCL ivF protocols, when performed on patterned scaffolds, were both able to support follicle growth, antrum formation, and the upregulation of follicle marker genes leading to a greater oocyte meiotic competence than in the 3D-oil system. In conclusion, the One-Step approach could be proposed as a practical and valid strategy to support a synergic follicle-oocyte in vitro development, providing an innovative tool to enhance the availability of matured gametes on an individual basis for ART purposes.
Recently, the industry has been progressing through an exciting technological upheaval era,
heading to the fourth industrial revolution.
1 Everything has been becoming smarter in the fourth
industrial revolution2
, and our life is surrounded by smart electronics: smartphones, smart TVs,
smartwatches, and newly smart factories and smart cities.3-6
In smart devices, the detectors will
be more needed to collect data.7 Estimations remark that the main obstacles to integrating
sensors in smart devices are high prices and sensitivity.8 Printing is a cost-effective and precise
technology to manufacture electronic devices.9 Printed sensors have already been established in
the market, like printed displays and readers in smartwatches, printed near-field communication
(NFC), and radio-frequency identification (RFID) labels.10
This work is focused on printed thin-film detectors through several printing approaches, utilizing
inkjet, slot-die, 3D, and robotic printing. Inkjet printing and slot-die coating are the main interest
of this work due to their unique properties in precise printing with the lowest material waste.
Functional electronic material ink will be filled in the reservoir and printed in the wanted covering
pattern. New printable inorganic/ organic inks have been formulated based on various materials,
such as PbS nanocrystals, CrPS4 flakes, graphene, perovskites, polymers, etc. Their printability
is investigated through their rheological behaviors and “Ohnesorge” number concept. Later, a
homogenous film is obtained from the deposition of multiple droplets next to each other on a
substrate. The film quality is improved by enhancing the wetting properties, controlling particle
migration, and solvent modifications. Finally, this thesis will introduce novel printing approaches
to manufacture thin-film photodetectors, in various light detection ranges, from x-ray to near-infrared regime.
The first fully inkjet-printed NIR photoconductor and printed multi-array of NIR photodetectors are
presented in chapter 4.1. Their performance is almost the same and comparable to a PbS
nanocrystal reference detector fabricated by drop-casting on commercial lithographically
prepared electrodes. The detectors show a responsivity of ~1 A/W at the wavelength of an
excitonic peak (~ 1000nm). The specific detectivity obtained here is more than 1E+12 (cm √Hz)/W
ii
at a frequency of 10 Hz. In multi-array detectors, it took 15 seconds to fabricate each
photodetector and the costs were less than 50 cents per detector.
In chapter 4.2, the photodetector's architecture design is developed toward NIR photodiodes. The
slot-die printing is employed to print the NIR photodiode. This printing protocol could be utilized
for the fabrication of NIR imagers.
The first fully inkjet-printed 2D-material photodetector using CrPS4 and graphene flakes is
presented in chapter 4.3. The response spectrum of the device has been measured from 300 to
1000 nm wavelengths with a peak at 735 nm. The detectors showed a responsivity of ~0.2 A/W
at the excitonic peak and the noise current was 50 pA Hz−1/2, and the specific detectivity was more
than 5E+8 jones.
Last but not least, self-powered x-ray photodiodes based on the organic/perovskite thin films are
presented in chapter 4.4. The perovskite X-ray photodiode (based on MAPbI3) was operated at
0V with a sensitivity of 3E-9 C/mGyair cm2
. The perovskite x-ray detector showed comparable
performance to other self-powered X-ray detectors. Also, we made a thin-film PM6:Y6 X-ray
photodiode with a sensitivity of 1E-9 C/mGyair cm2
, operated at 0V
Eine wesentliche Herausforderung bei der Herstellung von Kunststoff-Metall-Hybridbauteilen im Montagespritzguss ist die eingeschränkte Mediendichtheit aufgrund der chemischen Inkompatibilität der beiden Werkstoffe. Der Einsatz strukturierter, metallischer Einleger hat in diesem Zusammenhang ein großes Potential die Dichtheit zu steigern. Im Rahmen dieser Arbeit wird daher die umformtechnische Strukturierung metallischer Einleger im Folgeverbundwerkzeug als hoch effizientes Fertigungsverfahren untersucht. Ziel dieser Arbeit ist ein Verständnis für die Herstellbarkeit strukturierter Einleger aufzubauen und die Prozessgrenzen abzuleiten im Hinblick auf die funktionsgerechte Auslegung. Anhand der Untersuchungen zum Verrunden der Schnittkanten mittels Prägen wurde die Querschnittsfläche des Einlegers als wichtigste Einflussgröße auf die Formfüllung und somit auf die Abbildungsgenauigkeit identifiziert. Bei den Untersuchungen zum Einprägen von Quernuten in die Einlegeroberfläche konnte durch die Gliederung des Werkstoffflusses in axiale und laterale Richtung, ein ganzheitliches Verständnis hinsichtlich der Ausformung der Nuten sowie der Längung und Breitung der Einleger geschaffen werden. Gerade die Breitung wird in diesem Zusammenhang durch die vorherrschenden Fließbehinderungen stark beeinflusst. Abschließend wurden die Untersuchungsergebnisse der umformtechnischen Strukturierung anhand der resultierenden Dichtheit umspritzter Einleger eingeordnet und eine Erhöhung der Dichtwirkung aufgezeigt. Dadurch wird ein Beitrag zur Entwicklung und Fertigung widerstandfähiger elektronischer Systeme geleistet.
Komplexität ist eine der großen Herausforderungen unserer Zeit. Daher müssen Ingenieure besonders in der Entwicklung die stetig steigende Komplexität in diversen Domänen beherrschen, um den Produkt- und damit Unternehmenserfolg zu realisieren. Für die zweckmäßige Modellierung der vielen verschiedenen Elemente und Relationen komplexer Systeme sind domänenübergreifende, integrative und damit holistische Modellierungsansätze erforderlich, welche jeweils kontextbezogen nützliche, mathematische Analyse- sowie Visualisierungsmöglichkeiten erlauben um Entwicklern eine multikriterielle Bewertung bestimmter Handlungsalternativen zu ermöglichen. Derzeit bestehende Ansätze eignen sich hierfür jedoch unter anderem aufgrund methodischer Defizite, ihres hohen Modellierungsaufwands, eingeschränkter Analyse- und Visualisierungsmöglichkeiten oder ihrer geringen Unterstützung bei der multikriteriellen Bewertung nur eingeschränkt.
Daher wird in der vorliegenden Arbeit ein Konzept vorgestellt, mit dem Entwickler beim holistischen Komplexitätsmanagement in der Produktentwicklung unterstützt werden, indem kontextbezogen jeweils geeignete Methoden für die integrierte Modellierung, Analyse, Visualisierung und Bewertung komplexer Systeme für eine zielgerichtete Entscheidungsfindung zur Verfügung gestellt werden. Zur effektiven und effizienten Anwendung der Methodik wird ein IT-Werkzeug präsentiert, das Entwickler bei deren Aufgaben im Rahmen des holistischen Komplexitätsmanagements unterstützt.
In the past few years, portable consumer electronics such as tablets and smartphones have
become compact multi-functional devices. The upcoming and new generations will have
implemented more and more virtual and augmented reality applications which require specialized
in- and output devices such as tracking sensors or motion controllers and headmounted
displays or pico-projectors. Optical sensing and imaging are crucial to many of
these functions. Thus, depending on the application efficient and compact high-power light
sources that emit either in the infrared or the spectral range of visible red to green, to blue
are a key technology that should be available cheaply and in large quantities. There are several
optoelectronic semiconductors that are suitable for such applications. Ideally, the light
source should emit a narrow beam like emission that allows efficient coupling and seamless
integration of high pulsed output power into the system. Common light emitting diodes
(LED) are inexpensive surface emitters whose optical bandwidth and switching dynamics
are determined by spontaneous emission. While high output powers can be achieved by
scaling the surface area, the beam quality stays poor. In contrast, surface emitting lasers
have narrow farfields, but they require complicated lateral mode control. Hence, high output
power requires an array of multiple low power emitters which adds complexity to the
optical integration. In general, lasers are able to provide increased power density and fast
turn-on/off switching times, however, their coherent emission introduces speckle noise to
interferometric sensors and imaging systems. A semiconductor light source that can meet
the required specifications is a superluminescent diode (SLED). Their unique emitter characteristics
comprise laser-like beam properties and broad-band emission similar to LEDs.
Therefore SLEDs are capable of high output power densities but short coherence length
required for visualization or sensing applications. One drawback is that SLEDs are usually
designed as edge emitters and therefore have similarly complicated fabrication process as
laser diodes, which entails wafer cleaving and subsequent coating of facets which requires
handling and testing of individual stripes or bars. Thus, the elaborate fabrication of SLEDs
has been one of the major drawbacks preventing them from becoming more appealing to
larger market segments. In addition, SLED operation requires suppression of lasing – hence
optical feedback at the mirrors is critical. This is achieved by maximizing the light outcoupling
and reducing feedback by designing the losses. Consequently, typical SLEDs are
light sources with relatively low efficiencies.
This thesis deals with the theoretical and experimental investigation of a novel SLEDs design
that is based on surface-emission. Moreover, the new approach is completely processed
on wafer-scale using thin-film technology which thereby allows an inexpensive fabrication
comparable to LEDs. Similar to common edge emitters, the novel SLED design relies on
an amplification of optical modes by an in-plane gain-guided waveguide. However, in order
to achieve surface emission the waveguide is terminated by integrated micro-mirrors that
deflect the amplified spontaneous emission (ASE) via total internal reflection towards the
chip surface. A conventional dry etching process is used to fabricate the mirrors on wafer
level. Furthermore, using thin film technology, the wafer is flipped after etching, bonded
to a new carrier, and the substrate is removed. All other processing steps including outcoupling
surface treatments and final testing are also done on wafer level.
In the first part of the thesis an introduction to the fundamental physics of optoelectronic
semiconductors is presented, providing the theoretical basis of SLEDs especially in comparison
to lasers. In order to simulate the optical output power of the investigated SLED
design, a rate equation-based frequency-resolved model that accounts for non-ideal facet
reflectivities and lasing onset is introduced and first examples are discussed. Additionally,
the model was extended to investigate the theoretical optical switch-off characteristics of
SLEDs. Based on these results, supported by more elaborate FDTD simulations, the investigation
is focused on an analysis of light propagation and out-coupling in the novel
surface-emitter concept. The second part of the thesis is dedicated to the fabrication and
experimental investigation of first surface-emitting InGaAs/AlGaAs SLEDs emitting in the
near IR. The fabricated epitaxy, design and geometry variations are presented along with
the corresponding fabrication workflow with focus on the integrated micro-mirrors and used
dielectric coatings. A direct comparison of as-cleaved edge emitting devices and uncoated
surface emitting chips has been made in order to evaluate the efficiency of surface outcoupling.
In both cases, the etched mirrors show identical output power, demonstrating their
high quality and efficiency. One of the most promising designs uses both ends of the waveguide
as emitting facets which leads to reduced losses and a high out-coupling efficiency.
ASE operation can be sustained up to 250mW, and the respective wall-plug efficiency exceeds
15%. As the new surface emitting approach allows light to be emitted from both
ends of the waveguide, the optical out-coupling and wall-plug efficiencies of the first demonstrator
devices are already comparable to those of edge-emitting counterparts. Despite the
fact that the surface emitting SLED has two outcoupling windows at the ends of the waveguide,
after optimizing the micro-mirrors its farfield is comparable to that of a conventional
edge emitting device. The spectral width of the ASE is approximately 10nm. When the
current exceeds 900mA, the device operates in lasing mode due to the residual feedback
of the surface outcoupler into the waveguide. Increased lasing threshold will result from
optimizing the anti-reflective coating. Similarly, by deviating the outcoupling mirror angle
from the 45° as well as curved waveguides feedback can be further reduced. High-power
pulsed operation has also been investigated. Moreover, SLEDs show rise- and fall times
of 3 ns and 2 ns as a result of their faster stimulated emission rates than LEDs. Following
this, the introduced rate equation-based model was calibrated with experiments. Most of
the simulated L-I curves are in excellent agreement to the experiment for various epitaxy
and waveguide designs including single- and double-pass amplifying SLEDs. Moreover,
simulated spectral characteristics were conducted and showed a high degree of similarity
with experimentally obtained spectral features. As the model does not assume ideal facets
with zero reflectivity, it can be used not only to estimate the operation regimes but also
to increase the lasing threshold and ASE output power. Moreover, with arrays of surface
emitting SLEDs the power can be scaled and further control added to the farfield without
requiring any additional processing steps. With a parallel aligned configuration, the ASE
output power per chip could be scaled up to over five times the output power of a single
stripe device. Optimal etching provides a surface-emitting array with a superimposed farfield
that is comparable to a single stripe’s beam profile. In addition, radial symmetrically
aligned surface-emitting SLED arrays resulted in surprisingly narrow far-field distributions
and high output power densities. Thus, the surface-emitting concept allows for a wider
range of arrangements of contacts and waveguides which offers several advantages towards
compact chip and package designs. Finally, the surface-emitter design was transferred to
the visible red emitting AlGaInP/AlInP material system where first experimental results
of red surface-emitting micro-mirror based demonstrators were very promising. In fact,
with a wall-plug efficiency of approximately 6% the performance of red surface-emitting
SLEDs was already comparable to simulations and experimental results of edge emitting
counterparts.
Abstract
The authors present a thermally and dynamically coupled fluid–structure‐interaction (FSI) model of a thermoforming process variant along with simulation results. By purposeful arrangement of the inlet nozzles, the process variant under consideration seeks to improve the deformation behavior of a plastic sheet made of polyvinyl chloride (PVC), ultimately leading to a more uniform wall thickness distribution. In order to capture the complex interaction between deforming sheet and turbulent flow field in the pressure box, the numerical model must realistically reproduce both fluid and solid domain and accurately handle coupling between the simulation participants. Detailed information is provided on modeling aspects of the solid and in particular of the fluid domain. Wall thickness distributions obtained from experiments for two test cases are compared to results generated using varying parametrizations of the simulation model. The results in general are in line with experimental measurements, although some peculiarities in the measured data could not be reproduced. Despite its limitations concerning accuracy and the computational cost, the holistic simulation approach using FSI appears to be a helpful tool for investigating thermoforming due to the detailed resolution of the inflation process in time and space.
Abstract
One of the main challenges in modern tissue engineering is to design biocompatible scaffolds with finely tuned porous architecture and capacity to load bioactive molecules that guide the growth and differentiation of the cells during tissue reconstruction. This work proposes a strategy to design porous alginate scaffolds (PAS) with well‐tuned architecture by leaching of sacrificial vaterite CaCO3 microspheres packed in alginate. Pore size and interconnectivity depend on CaCO3 sphere dimensions and packing as well as alginate concentration. Varying of these parameters, almost hundred percent pore interconnectivity (or, by contrast, a zero pore interconnectivity) can be achieved. Junctions between interconnected pores are about 50–70% of the pore dimensions that provides molecular transport through the PASs potentially ensuring diffusion of nutrition, oxygen and metabolic products when cell seeding. An opportunity to fabricate a multifunctional scaffold is demonstrated by encapsulation of desired macromolecules into the individual pores of a scaffold (is illustrated by dextran loading). Mechanical properties of PASs are found typical for soft and hydrated structures (Young's modulus of 19 ± 15 kPa) which is appropriate for cell seeding. The three cell lines (HeLa, HEK293, and L929) are cultured on different alginate scaffolds to examine cell viability and adhesiveness.