INMdok (Leibniz Institute for New Materials)
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Friction force microscopy of tribochemistry and interfacial ageing for the SiOx/Si/Au system
Get PDFFriction force microscopy was performed with oxidized or gold-coated silicon tips sliding on Au(111) or oxidized Si(100) surfaces in ultrahigh vacuum. We measured very low friction forces compared to adhesion forces and found a modulation of lateral forces reflecting the atomic structure of the surfaces. Holding the force-microscopy tip stationary for some time did not lead to an increase in static friction, i.e., no contact ageing was observed for these pairs of tip and surface. Passivating layers from tip or surface were removed in order to allow for contact ageing through the development of chemical bonds in the static contact. After removal of the passivating layers, tribochemical reactions resulted in strong friction forces and tip wear. Friction, wear, and the re-passivation by oxides are discussed based on results for the temporal development of friction forces, on images of the scanned area after friction force microscopy experiments, and on electron microscopy of the tips
Verbundprojekt: Biodegradierbare polymerbasierte Einwegsysteme in der Intensivmedizin; Teilvorhaben INM: antimikrobielle Materialien für Einwegsysteme im medizinischen Bereich : Schlussbericht : Vorhabenbezeichnung: BioPolyMed : Laufzeit des Vorhabens: 01.11.2015-31.10.2018
Get PDFNosokomiale Infektionen mit multiresistenten Erregern sind besonders gefürchtet, da nur wenige oder keine Antibiotika wirksam sind, und Krankenhäuser durch aufwendige hygienische Isolierungsmaßnahmen in ihrer Struktur und Organisation vor Herausforderungen gestellt werden. Zur Verbesserung der Patientensicherheit und Optimierung des Einsatzes zunehmend limitierter finanzieller Mittel kommt der Prävention nosokomialer Infektionen sowie der Eindämmung multiresistenter Erreger eine besondere Bedeutung zu. Ein wichtiges Ziel des Gesamtvorhabens war es, die Voraussetzungen für die Optimierung von Einwegsystemen zu schaffen, um die Übertragung von Erregern von Krankenhausinfektionen, insbesondere von multiresistenten Erregern zu verhindern bzw. zu minimieren, damit ein entscheidender Beitrag zur nachhaltigen Prävention nosokomialer Infektionen geleistet werden kann. [...
A bio-based route to the carbon-5 chemical glutaric acid and to bionylon-6,5 using metabolically engineered Corynebacterium glutamicum
Get PDFIn the present work, we established the bio-based production of glutarate, a carbon-5 dicarboxylic acid with recognized value for commercial plastics and other applications, using metabolically engineered Corynebacterium glutamicum. The mutant C. glutamicum AVA-2 served as a starting point for strain development, because it secreted small amounts of glutarate as a consequence of its engineered 5-aminovalerate pathway. Starting from AVA-2, we overexpressed 5-aminovalerate transaminase (gabT) and glutarate semialdehyde dehydrogenase (gabD) under the control of the constitutive tuf promoter to convert 5-aminovalerate further to glutarate. The created strain GTA-1 formed glutarate as a major product, but still secreted 5-aminovalerate as well. This bottleneck was tackled at the level of 5-aminovalerate re-import. The advanced strain GTA-4 overexpressed the newly discovered 5-aminovalerate importer NCgl0464 and formed glutarate from glucose in a yield of 0.27 mol mol−1. In a fed-batch process, GTA-4 produced more than 90 g L−1 glutarate from glucose and molasses based sugars in a yield of up to 0.70 mol mol−1 and a maximum productivity of 1.8 g L−1 h−1, while 5-aminovalerate was no longer secreted. The bio-based glutaric acid was purified to >99.9% purity. Interfacial polymerization and melt polymerization with hexamethylenediamine yielded bionylon-6,5, a polyamide with a unique struct
Exploring the Potential of Electroplated Chips towards Biomedical Sensing and Diagnostics
Get PDFIn the past decade the significant progress in the cellular stress response was witnessed. Nevertheless, the development of the minimally-invasive and accurate sensing tools for the identification of the increasing number of potentially relevant species in clinical diagnostics, using smaller sample volumes is a major challenge. Herein, the potential of the electroplated nanomaterials towards biomedical sensing and diagnostics is summarized. The key factors affecting the surface functionality, dimensionality, S/N ratio and analytical response of the prepared chips are highlighted. Furthermore, the application of electroplated chips as a fast “read out” platform for profiling of clinical samples was demonstrated
New designs for bioinspired microstructures with adhesion to rough surfaces
Get PDFAdhesion to substrates with surface roughness is a research field with many unsolved questions. A more thorough understanding of the underlying principles is important to develop new technologies with potential implications for instance in robotics, industrial automatization and wearable interfaces. Nature is a vast source of inspiration as animals have mastered climbing on various surfaces at high speed with several attachment and detachment events in a short time. In this work, new designs for dry adhesives inspired by natural blueprints are presented. Different strategies were explored to understand and tune adhesion on a range of substrates from smooth glass to polymers with skin-like roughness. Both the material properties and the geometry of the dry adhesives were utilized to improve adhesion strength. Three concepts are presented in this work: (i) composite structures with tunable interface, (ii) soft pressure sensitive adhesive layers, and (iii) funnel-shaped microstructures. This thesis aims for better understanding of the adhesion behavior as a function of several important factors including hold time, substrate material and roughness. The new concepts for bioinspired structures investigated in the present thesis will contribute to the development of performant, reversible adhesives for a variety of applications where surface roughness is involved.Adhäsion an rauen Oberflächen stellt immer noch ein Forschungsfeld mit vielen ungelösten Problemen dar. Um neue Technologien mit Bedeutung für beispielsweise die Robotik, industrielle Automatisierung und körpernahe Sensorik zu entwickeln, bedarf es eines tieferen Verständnisses der zugrunde liegenden Prinzipien. Hier stellt die Natur eine vielfältige Inspirationsquelle dar, da bestimmte Lebewesen in der Lage sind, auf unterschiedlichsten Untergründen zu haften. Im Rahmen dieser Arbeit werden der Natur nachempfundene Modelle und Lösungen zur Haftung vorgestellt. Zum Verständnis der Haftungsmechanismen und zur Optimierung der Hafteigenschaften auf einer Bandbreite von Substraten, von glattem Glas bis hin zu rauen, hautähnlichen Polymeroberflächen, wurden unterschiedliche Herangehensweisen untersucht. Zur Erhöhung der Haftkraft kamen sowohl Variationen in den verwendeten Materialien, als auch in der Geometrie der Haftstrukturen zum Einsatz. Drei Konzepte werden in dieser Arbeit vorgestellt: (i) Kompositstrukturen mit variablen Grenzflächen; (ii) weiche, drucksensitive Schichten und (iii) trichterförmige Mikrostrukturen. Es wird ein besseres Verständnis des Adhäsionsverhaltens in direktem Zusammenhang mit verschiedenen Struktur-, Substrat- und Messparametern angestrebt. Die in dieser Arbeit vorgestellten, neuen Konzepte für bioinspirierte Strukturen sollen zur Entwicklung performanter, reversibler Haftverbindungen für einen breiten Anwendungsbereich auf rauen Oberflächen beitragen.L’adhésion sur des surfaces rugueuses offre beaucoup de questions ouvertes aux chercheurs. Pour développer des technologies pionnières dans les domaines comme la robotique, automatisation industrielle et les capteurs portables, une connaissance plus détaillée des mécanismes gouvernant ce phénomène est nécessaire. La nature est une source d’inspiration vaste avec une multitude d’animaux possédant la capacité d’escalader diverses surfaces à grande vitesse. Cette thèse présente de nouveaux designs d’adhésifs secs inspirés par la nature. Différentes stratégies ont été explorées afin de comprendre et modifier l’adhésion sur des surfaces variées comme le verre poli ou des polymères avec une texture de surface ressemblant celle de la peau. Les propriétés des matériaux et la géométrie des structures ont été utilisées comme paramètres pour maximiser l’adhésion. Cette thèse comprend trois parties : (i) des structures composites avec interface variable, (ii) des films mous sensibles à la pression, et (iii) des structures en forme d’entonnoir. Les paramètres étudiés englobent entre outre le temps d’attente, le matériau du substrat et sa rugosité. Tous les concepts peuvent être raffinés et optimisé envers certaines applications. Les nouveaux concepts de structures inspirés par la nature présentés ci-dedans ont pour but de contribuer au développement d’adhésifs performants et réversibles pour une variété d’applications pour lesquelles la rugosité joue un important rôle
Microenvironments to regulate cellular behavior for neural development and regeneration
Get PDFStrategies for regeneration after injury or during aging require the development of biomaterials able to reconstruct the essential components and properties of natural extracellular microenvironment. A particular feature in neural regeneration is the oriented disposition of neurons within nerves and cortex. In this thesis, through the spatiotemporal control of the availability of adhesive ligands at the surface of a biomaterial, these biomaterials allow directing the migration of neuron. This Thesis is structured in four parts. The first part presents microcontact printed patterns with adhesive compositions and geometries to allow directional migration and, uniquely, in vitro reconstruction of the somal translocation events occurring during cortical layering. In part 2 in situ directed neurites extension in defined directions is demonstrated using biomaterials functionalized with photo-activatable peptidomimetics of the laminin. In part 3 spatiotemporal and reversible regulations of actin dynamics in living cells is demonstrated using light-dosed delivery of Cytochalasin D. In the last part, the first demonstration of a light-regulated adhesive interaction between mammalian cells and a bacterial biointerface is provided.Strategien zur Regeneration nach Verletzungen oder während des Alterns benötigen die Entwicklung von Biomaterialien, die essentielle Komponenten und Eigenschaften der nativen extrazellulären Mikroumgebung rekonstruieren können. Eine besondere Eigenschaft in der Regeneration von Nervengewebe ist die elongierte Morphologie und gerichtete Disposition von Neuronen in Nerven und Kortex. Die räumlich-zeitliche Kontrolle der Verfügbarkeit von Zell-adhesiven Liganden auf der Oberfläche des Biomaterials, wie in dieser These beschrieben,erlaubt es hierbei die Migration von Neuronen steuern. Diese These ist in vier Abschnitte gegliedert. Der erste Teil präsentiert Mikrokontakt gedruckte Muster mit optimisierten, adhesiven Komponenten und Geometrien, um eine gerichtete Migration und in vitro erstmalig die Rekonstruktion der somalen Translokation zu gewährleisten, welche während der embryonalen Entwicklung des zerebralen Kortex stattfindet. In Teil 2 wird in situ der gerichtete Neuritenauswuchs in definierter Richtung gezeigt. Hierbei werden Biomaterialien verwendet, die mit Photo-aktivierbaren Peptidomimetika des Matrixproteins Laminin funktionalisiert sind. Im Teil 3 wird die räumlich-zeitliche und reversible Regulation der Dynamik des Actinzytoskellettes unter Zugabe von Licht-dosiertem Cytochalasin D gezeigt. Im letzten Teil, wird erstmalig die Licht-regulierte Interaktion zwischen Säugetierzellen und einer bakteriellen Biogrenzfläche demonstriert
Ordered Mesoporous TiO2 Gyroids: Effects of Pore Architecture and Nb-Doping on Photocatalytic Hydrogen Evolution under UV and Visible Irradiation
Get PDFAbstract Pure and Nb-doped TiO2 photocatalysts with highly ordered alternating gyroid architecture and well-controllable mesopore size of 15 nm via co-assembly of a poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide) block copolymer are synthesized. A combined effort by electron microscopy, X-ray scattering, photoluminescence, X-ray photoelectron spectroscopy, Raman spectroscopy, and density functional theory simulations reveals that the addition of small amounts of Nb results in the substitution of Ti4+ with isolated Nb5+ species that introduces inter-bandgap states, while at high concentrations, Nb prefers to cluster forming shallow trap states within the conduction band minimum of TiO2. The gyroidal photocatalysts are remarkably active toward hydrogen evolution under UV and visible light due to the open 3D network, where large mesopores ensure efficient pore diffusion and high photon harvesting. The gyroids yield unprecedented high evolution rates beyond 1000 µmol h−1 (per 10 mg catalyst), outperforming even the benchmark P25-TiO2 more than fivefold. Under UV light, the Nb-doping reduces the activity due to the introduction of charge recombination centers, while the activity in the visible triple upon incorporation is owed to a more efficient absorption due to inter-bandgap states. This unique pore architecture may further offer hitherto undiscovered optical benefits to photocatalysis, related to chiral and metamaterial-like behavior, which will stimulate further studies focusing on novel light–matter interactions
Reducing the Effect of Spurious Phase Variations in Neural Oscillatory Signals
Get PDFThe phase-reset model of oscillatory EEG activity has received a lot of attention in the last decades for decoding different cognitive processes. Based on this model, the ERPs are assumed to be generated as a result of phase reorganization in ongoing EEG. In addition, the study of oscillatory EEG signals can be used to overcome limitations regarding the study of segmented EEG data, i.e., ERPs. Measuring the level of instantaneous phase (IP) synchronization has been used in numerous studies of ERPs as well as oscillatory activity for a better understanding of the underlying neural activities. However, the reliability of results can be challenged as a result of noise artefact in IP. Phase distortion due to environmental noise artifacts as well as different pre-processing steps on signals can lead to generation of artificial phase jumps. One of such effects presented recently is the effect of low envelope on the IP of signal. It has been shown that as the instantaneous envelope of the analytic signal approaches zero, the variations in the phase increase, effectively leading to abrupt transitions in the phase. These abrupt transitions can distort the phase synchronization results as they are not related to any neurophysiological effect. These transitions are called spurious phase variation. In this study, we present a model to remove generated artificial phase variations due to the effect of low envelope. The proposed method is based on a simplified form of a Kalman smoother, that is able to model the IP behavior in narrow-bandpassed oscillatory signals. The method is not only evaluated on synthetic data but also in experimental EEG measurements recorded using a listening dichotic paradigm designed to assess auditory selective attention between an attended and unattended conditions
Vimentin Diversity in Health and Disease
Get PDFVimentin is a protein that has been linked to a large variety of pathophysiological conditions, including cataracts, Crohn’s disease, rheumatoid arthritis, HIV and cancer. Vimentin has also been shown to regulate a wide spectrum of basic cellular functions. In cells, vimentin assembles into a network of filaments that spans the cytoplasm. It can also be found in smaller, non-filamentous forms that can localise both within cells and within the extracellular microenvironment. The vimentin structure can be altered by subunit exchange, cleavage into different sizes, re-annealing, post-translational modifications and interacting proteins. Together with the observation that different domains of vimentin might have evolved under different selection pressures that defined distinct biological functions for different parts of the protein, the many diverse variants of vimentin might be the cause of its functional diversity. A number of review articles have focussed on the biology and medical aspects of intermediate filament proteins without particular commitment to vimentin, and other reviews have focussed on intermediate filaments in an in vitro context. In contrast, the present review focusses almost exclusively on vimentin, and covers both ex vivo and in vivo data from tissue culture and from living organisms, including a summary of the many phenotypes of vimentin knockout animals. Our aim is to provide a comprehensive overview of the current understanding of the many diverse aspects of vimentin, from biochemical, mechanical, cellular, systems biology and medical perspective
Ultrafast dissolution and creation of bonds in IrTe<sub>2</sub> induced by photodoping
Get PDFThe observation and control of interweaving spin, charge, orbital, and structural degrees of freedom in materials on ultrafast time scales reveal exotic quantum phenomena and enable new active forms of nanotechnology. Bonding is the prime example of the relation between electronic and nuclear degrees of freedom. We report direct evidence illustrating that photoexcitation can be used for ultrafast control of the breaking and recovery of bonds in solids on unprecedented time scales, near the limit for nuclear motions. We describe experimental and theoretical studies of IrTe2 using femtosecond electron diffraction and density functional theory to investigate bonding instability. Ir-Ir dimerization shows an unexpected fast dissociation and recovery due to the filling of the antibonding dxy orbital. Bond length changes of 20% in IrTe2 are achieved by effectively addressing the bonds directly through this relaxation process. These results could pave the way to ultrafast switching between metastable structures by photoinduced manipulation of the relative degree of bonding in this manner