INMdok (Leibniz Institute for New Materials)
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When Ultimate Adhesive Mechanism Meets Ultimate Anti-Fouling Surfaces—Polydopamine Versus SLIPS: Which One Prevails?
Get PDFAbstract What happens when the extremely adhesive and versatile chemistry of polydopamine (PDA) is in contact with the extremely slippery surfaces known as slippery liquid-infused porous substrates (SLIPS)? Inspired by the pitcher plant, SLIPS possess excellent repellence against a variety of complex liquids and have been proposed as promising antifouling surfaces because of their successful performance even in marine environments. In the counterpart, inspired by the adhesive proteins enabling the strong adhesion of mussels to multiple substrates, PDA has been extensively studied for its ability to adhere on nearly every type of substrate. The interaction between various SLIPS systems and the highly fouling medium from the oxidative polymerization of dopamine is explored here. A PDA coating is observed on all the SLIPS evaluated, modifying their hydrophobicity in most cases. In-depth study of silicone-based SLIPS shows that hydrophobicity of PDA coated SLIPS partially recovers with time due to percolation of the lubricant through the coating. “Strongly” bound PDA species are attributed to the formation of dopamine-polydimethylsiloxane species on the crosslinked matrix, rendering a coating that withstands repeated washing steps in various solvents including water, hexane, and toluene. The results not only satisfy scientific curiosity but also imply a strategy to modify/bond SLIPS
Acid-Base Interactions of Pyrazine, Ethyl Acetate, Di-alcohols, and Lysine with the cyclic Alumosiloxane (Ph2SiO)8[Al(O)OH]4 in View of Mimicking Al2O3(H2O) Surface Reactions
Get PDFThe etherate of (Ph2SiO)8[Al(O)OH]4 can be transformed into the pyrazine adduct (Ph2SiO)8[Al(O)OH]4·3N(C2H2)2N (1), the ethyl acetate adduct (Ph2SiO)8[Al(O)OH]4·3H3C-C(O)OC2H5 (2), the 1,6-hexane diol adduct (Ph2SiO)8[Al(O)OH]4·2HO–CH2(CH2)4CH2–OH (3) and the 1,4-cyclohexane diol adduct (Ph2SiO)8[Al(O)OH]4·4HO–CH(CH2CH2)2CH–OH (4). In all compounds the OH groups of the starting material bind to the bases through O–H···N (1) or O–H···O hydrogen bonds (2, 3, 4) as found from single-crystal X-ray diffraction analyses. Whereas in 1 only three of the central OH groups bind to the pyrazines, in 2 two of them bind to the same carbonyl oxygen atom of the ethyl acetate resulting in an unprecedented O–H···O···H–O double hydrogen bridge. The hexane diol adduct 3 in the crystal forms a one-dimensional coordination polymer with an intramolecularly to two OH groups grafted hexane diol loop, while the second hexane diol is connecting intermolecularly. In the cyclohexane diol adduct 4 all OH groups of the central Al4(OH)4 ring bind to different diols, leaving one alcohol group per diol uncoordinated. These “free” OH groups form an (O-H···)4 assembly creating a three-dimensional overall structure. When reacting with (Ph2SiO)8[Al(O)OH]4 lysine loses water, turns into the cyclic 3-amino-2-azepanone, and transforms through chelation of one of the aluminum atoms the starting material into a new polycycle. The isolated compound has the composition (Ph2SiO)12[Al(O)OH]4[Al2O3]2·4 C6H12N2O·6(CH2)4O (5)
High glucose distinctively regulates Ca2+ influx in cytotoxic T lymphocytes upon target recognition and thapsigargin stimulation
Get PDFIn CTLs: High glucose-culture enhances thapsigargin-induced SOCE but decreases target recognition-induced Ca2+ influx. High glucose-culture regulates expression of ORAIs and STIMs without affecting glucose uptake. More high glucose-cultured CTLs are prone to necrosis after execution of killing
Open Access at a Glance! More Visibility of Open Access Publications in the Library – The visOA Project
Get PDFUm Open-Access-Publikationen stärker in den Wahrnehmungsbereich der Bibliotheksbenutzer zu bringen, ist es notwendig, sie besser sichtbar zu machen. Im visOA-Projekt, das von der NTNM-Bibliothek des INM durchgeführt wurde, wurden Open-Access-Publikationen sowohl im OPAC als auch im Discovery-System und in den Publikationslisten des INM deutlich hervorgehoben. Eine selbstprogrammierte virtuelle Zeitschriftenanzeige (VIDIJO)1 bietet eine fachspezifische Auswahl von Open-Access-Zeitschriften. Die Wirksamkeit der im Projekt ergriffenen Maßnahmen wurde durch Begleitforschung überprüft.In order to bring Open Access publications more into the perception of library users, it is necessary to make them more visible. In the visOA project, carried out by the NTNM library of the INM, Open Access publications were clearly highlighted in the OPAC as well as in the Discovery System and in the publication lists of the INM. A self-programmed virtual journal display (VIDIJO) also offers a subject-specific selection of Open Access journals. The effectiveness of the measures taken in the project was verified by accompanying research
Role of Hair Coverage and Sweating for Textile Friction on the Forearm
Get PDFFriction of textiles on the human forearm is an important factor in comfort sensations of garments. We built an experiment to measure friction for textiles sliding on the forearm under loading conditions which are characteristic for wearing shirts or jackets. The hair coverage of the participants’ forearm was quantified by image analysis of photographs of the arm in the region of contact. Friction results for five standard textiles suggest to treat hair coverage in two classes. Sweating after physical activity leads to an increase of friction by factors of 2 to 5 for participants with less hairy forearms, while an increase by a factor of 1 to 1.7 only was found for participants with more hairy forearms. We introduce a method of wetting the forearm of study participants in a controlled way with water, which results in similar friction as for the sweating forearm after physical activity. The method allows for efficient studies of the role of skin moisture for friction including varying hair coverage of the skin
High-Resolution Inkjet Printing of Quantum Dot Light-Emitting Microdiode Arrays
Get PDFAbstract The direct printing of microscale quantum dot light-emitting diodes (QLEDs) is a cost-effective alternative to the placement of pre-formed LEDs. The quality of printed QLEDs currently is limited by nonuniformities in droplet formation, wetting, and drying during inkjet printing. Here, optimal ink formulation which can suppress nonuniformities at the pixel and array levels is demonstrated. A solvent mixture is used to tune the ejected droplet size, ensure wetting, and provoke Marangoni flows that prevent coffee stain rings. Arrays of green QLED devices are printed at a resolution of 500 pixels in.−1 with a maximum luminance of ≈3000 cd m−2 and a peak current efficiency of 2.8 cd A−1. The resulting array quality is sufficient to print displays at state-of-the-art resolutions
Contact Aging Enhances Adhesion of Micropatterned Silicone Adhesives to Glass Substrates
Get PDFThe transfer of biological concepts into synthetic micropatterned adhesives has recently enabled a new generation of switchable, reversible handling devices. Over the last two decades, many design principles have been explored that helped to understand the underlying mechanics and to optimize such adhesives for certain applications. An aspect that has been overlooked so far is the influence of longer hold times on the adhesive contacts. Exemplarily, the pull-off stress and work of separation of a micropatterned adhesive specimen are enhanced by factors 3 and 6, respectively, after 1000 min in contact with a glass substrate. In addition to such global measures, the increase of adhesion of all individual micropillars is analyzed. It is found that contact aging varied across the microarray, as it drastically depends on local conditions. Despite great differences on the micropillar scale, the adhesion of entire specimens increased with very similar power laws, as this is determined by the mean contact ageing of the individual structures. Overall, contact aging must be critically evaluated before using micropatterned adhesives, especially for long-term fixations and material combinations that are chemically attractive to each other
Adhesion modulation In bio-inspired micropatterned adhesives by electrical fields
Get PDFWith steps towards Industry 4.0, it becomes imperative to the development of next-generation industrial assembly lines, to be able to modulate adhesion dynamically for handling complex and diverse substrates. The inspiration for the design and functionality of such adhesive pads comes from gecko’s remarkable ability to traverse rough and smooth topographies with great ease and agility. The emphasis in this thesis was to equip artificial micropatterned adhesives with such functionalities of tunability and devise an on-demand release mechanism. The project evaluates the potential of electric fields in this direction. The first part of this work focusses on integrating electric fields with polymeric micropatterns and studying the synergistic effect of Van der Waals and electrostatic forces. An in-house electroadhesion set up was built to measure the pull-off forces with and without electric fields. As a function of the applied voltage, adhesion forces can be tuned. The second part of the work demonstrates a novel route that exploits the in-plane actuation of the dielectric elastomeric actuators integrated with microstructure to induce peeling in them. Voltage-dependent actuation has been harnessed to generate the requisite peel force to detach the micropatterns. Overall, the findings of this thesis combine disciplines of electroadhesion, electroactuation, and reversible dry adhesives to gain dynamic control over adhesion.Im Einklang mit dem Fortschreiten in Richtung Industrie 4.0, wird es auch für die Entwicklung von industriellen Montagelinien der nächsten Generation unerlässlich sein, die Handhabung komplexer und unterschiedlicher Objekte zu flexibilisieren. Bioinspirierte Haftpads nach dem Vorbild des Gecko könnten zukünftig hierzu wesentlich beitragen. Der Schwerpunkt dieser Arbeit bestand darin, künstliche mikrostrukturierte Haftpads mit einem elektrisch schaltbaren Adhäsions- und Ablösemechanismus zu funktionalisieren, um die Grundlage für einen schnell schaltbaren, intelligenten Greifer zu schaffen. Der erste Teil dieser Arbeit konzentriert sich auf die Kombination elektrischer Felder mit elastomeren Mikrostrukturen und die Untersuchung der synergistischen Wirkung von Van der Waals- und elektrostatischen Kräften. Zur Messung der Adhäsion wurde ein individueller Aufbau realisiert und mit diesem die Feldstärkeabhängigkeit der Haftkräfte nachgewiesen. Der zweite Teil der Arbeit demonstriert einen neuartigen Ablösemechanismus unter Ausnutzung der lateralen Bewegung dielektrischer elastomerer Aktuatoren, um so ein Abschälen der Haftpads vom Substrat zu induzieren. Durch Variation der elektrischen Spannung wurde untersucht, wie sich diese auf die Ablösegeschwindigkeit der Haftpads auswirkt. Insgesamt kombinieren die Ergebnisse dieser Arbeit die Disziplinen Elektroadhäsion, Elektroaktuation und reversible trockene Klebstoffe, um so eine dynamische Kontrolle über die Adhäsion zu erhalten
Engineered antigen-presenting hydrogels: model platforms for studies of T cell mechanotransduction
Get PDFT cells apply forces and eventually sense and then respond to the mechanical properties of their surroundings, including those of antigen presenting cells (APC) when they form the immunological synapse (IS). The identification of the mechanosensitive receptors and time scales at which they sense and actuate is experimentally difficult at the natural cell-cell interface. Inspired by the tools used in cell-matrix mechanobiology, this thesis presents synthetic, hydrogel-based models of APCs to study T cell mechanotransduction, focusing on the early T cell activation. Polyacrylamide (PAAm) hydrogels (1-50 kPa) were micropatterned with streptavidin and APC ligands (antibody against CD3 co-receptor (anti-CD3) and intercellular cell adhesion molecule-1 (ICAM-1)) at controlled ligand density and in geometries with defined dimensions. The anti-CD3 patterned hydrogels were used to study the interplay between hydrogel stiffness and CD3-mediated early T cell activation markers. In the last chapter, the regulatory role of ICAM-1 coupled to anti-CD3 and hydrogel stiffness in early T cell activation was studied on hydrogels with patterned anti-CD3 microdots surrounded by a background of ICAM-1. The results contribute to the understanding of the factors involved in T cell mechanotransduction, providing useful information for the future design of immunomodulatory materials.T-Zellen üben auf ihre Umgebung Kräfte aus und erfassen und reagieren auf die mechanischen Eigenschaften ihrer Umgebung, insbesondere auf Antigen-präsentierende Zellen (APC), wenn sie die immunologische Synapse (IS) bilden. Die Identifizierung der mechanosensitiven Rezeptoren und der Zeitskalen, in denen sie aktiviert werden, ist an der natürlichen Zell-Zell-Grenzfläche experimentell schwierig. Inspiriert von Werkzeugen aus der Zellmatrix-Mechanobiologie werden in dieser Arbeit synthetische hydrogelbasierte Modelle der IS entwickelt, um die T-Zell-Mechanotransduktion zu untersuchen, wobei der Schwerpunkt auf der frühen T-Zell-Aktivierung liegt. Dazu wurden Polyacrylamid (PAAm)-Hydrogele (1-50 kPa) hergestellt und mit Streptavidin- und APC-Liganden (Antikörper gegen CD3-Co-Rezeptor (Anti-CD3) und interzelluläres Zelladhäsionsmolekül-1 (ICAM-1)) mikrostrukturiert. Anhand von Hydrogelen mit Anti-CD3-Mustern wurde die Korrelation zwischen der CD3-vermittelten frühen T-Zell-Aktivierung und der Steifigkeit des Hydrogels untersucht. Anschließend wurde die zusätzliche regulatorische Rolle von ICAM-1 an Hydrogelen mit strukturierten Anti-CD3-Mikropunkten auf einem ICAM-1 Hintergrund untersucht. Die Ergebnisse tragen zum Verständnis der Faktoren bei, die an der T-Zell-Mechanotransduktion beteiligt sind, und liefern nützliche Informationen für das zukünftige Design immunmodulatorischer Materialien
Dynamic polydimethylsiloxane based polymer composites for functional materials
Get PDFPolymer networks with dynamic covalent bonds show properties and functions not achievable with covalently crosslinked systems. Among of the different polymers connected by dynamic covalent bonds, this Thesis is based on polydimethylsiloxane (PDMS) elastomers prepared via acid-catalyzed ring-opening polymerization of cyclic monomer and cross-link. This reaction presents different dynamic equilibrium reactions, such as polymer-oligomer equilibrium and bond exchange reaction. In this Thesis, I have developed three different functional materials based on acid-catalyzed PDMS. In Chapter 1, the basic concepts of dynamic bond chemistry and the state-of-the-art of dynamic covalent polymer networks are described. In Chapter 2, a new PDMS-based elastomer that can self-grow and self-degrow is presented. Chapter 3 describes how the acid-catalyzed PDMS was used to fabricate a strain sensor that could flexibly post-tailor the sensor properties. In the last part (Chapter 4), a gas-flow enhanced relaxation behavior observed in CB/dPDMS composite is described.Polymernetzwerke mit dynamischen kovalenten Bindungen zeigen besondere Eigenschaften und Funktionen, die mit kovalent vernetzten Systemen nicht erreichbar sind. Diese Arbeit befasst sich mit Polydimethylsiloxan (PDMS) -Elastomeren, die durch säurekatalysierte Ringöffnungspolymerisation von cyclischem Monomer und Quervernetzung hergestellt werden. In dieser Reaktion sind verschiedene dynamische Gleichgewichte beteiligt, z.B. das Polymer-Oligomer-Gleichgewicht und die Bindungsaustauschreaktion. In dieser Arbeit wurden drei verschiedene funktionelle Materialien auf der Basis von säurekatalysiertem PDMS entwickelt. In Kapitel 1 werden die Grundkonzepte der dynamischen Bindungschemie und der Stand der Technik dynamischer kovalenter Polymernetzwerke beschrieben. In Kapitel 2 wird ein neues PDMS-basiertes Elastomer vorgestellt, das Selbstwachstum und Selbstabbau zeigt. Kapitel 3 beschreibt, wie ein säurekatalysiertes PDMS verwendet wurde, um einen Dehnungssensor herzustellen, dessen Sensoreigenschaften nachträglich flexibel anpassbar sind. Im letzten Teil (Kapitel 4) wird eine Verbesserung des Relaxationsverhaltens durch einen Gasfluss beschrieben, das in DB/dPDMS-Verbundwerkstoffen beobachtet wird