INMdok (Leibniz Institute for New Materials)
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Kinetic and spectroscopic responses of pH-sensitive nanoparticles: influence of the silica matrix
Get PDFIntracellular pH sensing with fluorescent nanoparticles is an emerging topic as pH plays several roles in physiology and pathologic processes. Here, nanoparticle-sized pH sensors (diameter far below 50 nm) for fluorescence imaging have been described. Consequently, a fluorescent derivative of pH-sensitive hydroxypyrene with pKa = 6.1 was synthesized and subsequently embedded in core and core–shell silica nanoparticles via a modified Stöber process. The detailed fluorescence spectroscopic characterization of the produced nanoparticles was carried out for retrieving information about the environment within the nanoparticle core. Several steady-state and time-resolved fluorescence spectroscopic methods hint to the screening of the probe molecule from the solvent, but it sustained interactions with hydrogen bonds similar to that of water. The incorporation of the indicator dye in the water-rich silica matrix neither changes the acidity constant nor dramatically slows down the protonation kinetics. However, cladding by another SiO2 shell leads to the partial substitution of water and decelerating the response of the probe molecule toward pH. The sensor is capable of monitoring pH changes in a physiological range by using ratiometric fluorescence excitation with λex = 405 nm and λex = 488 nm, as confirmed by the confocal fluorescence imaging of intracellular nanoparticle uptake
Membrane Tension Orchestrates Rear Retraction in Matrix-Directed Cell Migration
Get PDFSummary In development, wound healing, and cancer metastasis, vertebrate cells move through 3D interstitial matrix, responding to chemical and physical guidance cues. Protrusion at the cell front has been extensively studied, but the retraction phase of the migration cycle is not well understood. Here, we show that fast-moving cells guided by matrix cues establish positive feedback control of rear retraction by sensing membrane tension. We reveal a mechanism of rear retraction in 3D matrix and durotaxis controlled by caveolae, which form in response to low membrane tension at the cell rear. Caveolae activate RhoA-ROCK1/PKN2 signaling via the RhoA guanidine nucleotide exchange factor (GEF) Ect2 to control local F-actin organization and contractility in this subcellular region and promote translocation of the cell rear. A positive feedback loop between cytoskeletal signaling and membrane tension leads to rapid retraction to complete the migration cycle in fast-moving cells, providing directional memory to drive persistent cell migration in complex matrices
In Vitro Entero-Capillary Barrier Exhibits Altered Inflammatory and Exosomal Communication Pattern after Exposure to Silica Nanoparticles
Get PDFThe intestinal microvasculature (iMV) plays multiple pathogenic roles during chronic inflammatory bowel disease (IBD). The iMV acts as a second line of defense and is, among other factors, crucial for the innate immunity in the gut. It is also the therapeutic location in IBD targeting aggravated leukocyte adhesion processes involving ICAM-1 and E-selectin. Specific targeting is stressed via nanoparticulate drug vehicles. Evaluating the iMV in enterocyte barrier models in vitro could shed light on inflammation and barrier-integrity processes during IBD. Therefore, we generated a barrier model by combining the enterocyte cell line Caco-2 with the microvascular endothelial cell line ISO-HAS-1 on opposite sides of a transwell filter-membrane under culture conditions which mimicked the physiological and inflamed conditions of IBD. The IBD model achieved a significant barrier-disruption, demonstrated via transepithelial-electrical resistance (TER), permeability-coefficient (Papp) and increase of sICAM sE-selectin and IL-8. In addition, the impact of a prospective model drug-vehicle (silica nanoparticles, aSNP) on ongoing inflammation was examined. A decrease of sICAM/sE-selectin was observed after aSNP-exposure to the inflamed endothelium. These findings correlated with a decreased secretion of ICAM/E-selectin bearing exosomes/microvesicles, as evaluated via ELISA. Our findings indicate that aSNP treatment of the inflamed endothelium during IBD may hamper exosomal/microvesicular systemic communication
Strong Wet and Dry Adhesion by Cupped Microstructures
Get PDFRecent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are considerably weakened underwater, fibrillar adhesives are however far less effective in wet environments. Although various strategies have been proposed to achieve strong reversible underwater adhesion, strong adhesives that work both in air and underwater without additional surface treatments have yet to be developed. In this study, we report a novel design—cupped microstructures (CM)—that generates strong controllable adhesion in air and underwater. We measured the adhesive performance of cupped polyurethane microstructures with three different cup angles (15, 30, and 45°) and the same cup diameter of 100 μm in dry and wet conditions in comparison to standard mushroom-shaped microstructures (MSMs) of the same dimensions. In air, 15°CM performed comparably to the flat MSM of the same size with an adhesion strength (force per real contact area) of up to 1.3 MPa, but underwater, 15°CM achieved 20 times stronger adhesion than MSM ( ∼ 1 MPa versus ∼ 0.05 MPa). Furthermore, the cupped microstructures exhibit self-sealing properties, whereby stronger pulls lead to longer stable attachment and much higher adhesion through the formation of a better seal
Block copolymer derived three-dimensional ordered hybrid materials for energy storage and conversion
Get PDFIn this thesis, block copolymers are used to rationally structure inorganic and hybrid materials into ordered, percolating nanostructures. The tunability of the microstructure, chemical composition, and porosity is explored and correlated with the materials’ performance in energy storage and conversion applications. Dense and thick mesoporous TiO2/C hybrid monoliths were prepared by co-assembly with a triblock copolymer and characterized as potential lithium ion battery anodes. The structure-directing polymer was carbonized to retain a thin conductive carbon layer at the electrolyte|electrode interface that increases the intrinsic conductivity of the active material. Polymer electrolytes were prepared by tailoring the individual blocks of the block copolymer. A minor conductive block decoupled ionic mobility from slow polymer relaxation, while sufficient mechanical stability was provided by covalently linked, mechanically stronger, insulating blocks. This combination overcomes a common trade-off between high conductivity and strength. Photocatalysis requires direct access of reactants and incident photons to a catalysts’ surface. The final part of the thesis shows that complete thermal removal of the template can create a mesoporous inorganic percolating network. Structuring the catalyst in this way improved the efficiency of photocatalysis as it combines high pore diffusibility with improved charge carrier transport properties.Diese Doktorarbeit untersucht die Herstellung hochgeordneter, perkolierender Nanostrukturen mittels Blockcopolymeren und diskutiert deren Einfluss auf die Leistungsfähigkeit darauf basierender Materialien in Anwendungen der modernen Energiespeicherung und –umwandlung. In einer ersten Studie wurden mesoporöse, monolithische TiO2/C-Hybride mittels eines Triblockcopolymers hergestellt und als Lithium-Ionen-Batterieanode getestet. Die Karbonisierung des strukturgebenden Polymers ergab eine leitfähige Kohlenstoffschicht an der Grenzfläche zum Elektrolyten und erhöhte so die intrinsische Leitfähigkeit. Einzelne Polymerblöcke wurden optimiert, um makroskopische Eigenschaften von Polymerelektrolyten unabhängig voneinander einzustellen. Eine besonders kleine, leitfähige Komponente erlaubte die Entkopplung der ionischen Leitfähigkeit von der Kettenmobilität, während kovalent gebundene, isolierenden Blöcke gleichzeitig hohe mechanische Stabilität gewährleisteten. Der verbreitete Widerspruch zwischen hoher Leitfähigkeit und Stabilität dieser Materialklasse konnte so vermieden werden. Photokatalyse erfordert direkten Zugang der Reaktanden und der Ladungsträger zur katalytisch aktiven Oberfläche. Im letzten Teil der Arbeit wird gezeigt, dass die Entfernung des strukturgebenden Polymers zu mesoporösen, perkolierenden, anorganischen Netzwerken führte. Diese erhöhten die Effizienz der Photokatalyse, da verbesserte Porendiffusivität und hohe Ladungsträgermobilitäten kombiniert wurden
Use of ionic crosslinking for pressure-sensitive adhesives
Get PDFPressure Sensitive Adhesives (PSA) need to integrate viscous and elastic properties to ensure tackiness and resistance to strain in the application. The use of physical interactions as crosslinks has been proposed as a design strategy to solve these apparently contradictory requirements. In this context, this PhD Thesis proposes synthesis routes to obtain PSA formulations with physical crosslinks based on oppositely charged moieties. The derived materials present improved adhesion performance based on stress dissipation by the remodeling of the ionic bonds during deformation. In a first approach, the emulsion polymerization of n-butylacrylate (n-BA) and styrene with ionic comonomers methacrylic acid and 2-(Methacryloyloxy)ethyl trimethylammonium chloride (MAETAC) was studied. The hydrophilicity of the cationic monomer led to homopolymerization in the water phase and hindered the formulation of adhesive mixtures. In a second alternative, the synthesis of acrylate-based polyampholytes was attempted by polymerization of n-BA, Methyl methacrylate, MAETAC and 2-hydroxyethyl methacrylate ester phosphoric acid in isopropanol. The adhesive performance could be tuned by the content, the stoichiometry and the nature of ionic monomers. Finally, secondary water-borne dispersions were developed from these copolymers to avoid the presence of organic solvent in the final product. The polymer networks showed high adhesion-cohesion balance and competed with commercialized products.Haftklebstoffe müssen Viskosität und Elastizität in die gleiche Formulierung integrieren, um Klebrigkeit und Beständigkeit gegen Dehnung in den Anwendungen zu gewährleisten. Um diesen Konflikt zu lösen, könnten die physikalischer Wechselwirkungen als Vernetzungspunkte verwendet werden. Dadurch werden in dieser Arbeit Synthesewege vorgeschlagen, um Haftklebemassen Formulierungen mit physikalischen Vernetzungen auf der Basis von entgegengesetzt geladenen Einheiten zu erhalten. Die Produkte zeigen eine verbesserte Haftung bei gutem Spannungsabbau während der Verformung. Zunächst wurde die Emulsionspolymerisation von n-Butylacrylat (n-BA) und Styrol mit ionische Comonomere Methacrylsäure und 2-(Methacryloyloxy)ethyltrimethylammoniumchlorid (MAETAC) untersucht. Durch hohe Hydrophilie, neigte das kationische Monomer allerdings zu einer Homopolymerisation und behinderte die Formulierung von Klebstoffen. Daraufhin wurden Polyampholyte auf Acrylatbasis durch die Polymerisation von n-BA, Methylmethacrylat, MAETAC und Phosphorsäure 2-hydroxyethyl Methacrylester in Isopropanol hergestellt. Das Adhäsionsverhalten konnte durch Änderung des Gehalts, der Stöchiometrie und der Art der ionischen Monomere eingestellt werden. Schließlich wurden aus diesen Copolymeren sekundäre Dispersionen auf Wasserbasis entwickelt, um organische Lösungsmittel im Endprodukt zu vermeiden. Es wurde ein gutes Adhäsions-Kohäsions Verhältnis gefunden, sogar konkurrenzfähig zu bestehenden kommerziellen Produkten
PTFEP–Al2O3 hybrid nanowires reducing thrombosis and biofouling
Get PDFThrombosis and bacterial infection are major problems in cardiovascular implants. Here we demonstrated that a superhydrophobic surface composed of poly(bis(2,2,2-trifluoroethoxy)phosphazene) (PTFEP)–Al2O3 hybrid nanowires (NWs) is effective to reduce both platelet adhesion/activation and bacterial adherence/colonization. The proposed approach allows surface modification of cardiovascular implants which have 3D complex geometries
Reversibly compressible and freestanding monolithic carbon spherogels
Get PDFWe present a versatile strategy to tailor the nanostructure of monolithic carbon aerogels. By use of an aqueous colloidal solution of polystyrene in the sol-gel processing of resorcinol-formaldehyde gels, we can prepare, after supercritical drying and successive carbonization, freestanding monolithic carbon aerogels, solely composed of interconnected and uniformly sized hollow spheres, which we name carbon spherogels. Each sphere is enclosed by a microporous carbon wall whose thickness can be adjusted by the polystyrene concentration, which affects the pore texture as well as the mechanical properties of the aerogel monolith. In this study, we used monodisperse polystyrene spheres of approximately 250 nm diameter, which result in an inner diameter of the final hollow carbon spheres of approximately 200 ± 5 nm due to shrinkage during the carbonization process. The excellent homogeneity of the samples, as well as uniform sphere geometries, are confirmed by small- and angle X-ray scattering. The presence of macropores between the hollow spheres creates a monolithic network with the benefit of being reversibly compressible up to 10% linear strain without destruction. Electrochemical tests demonstrate the applicability of ground and CO2 activated carbon spherogels as electrode materials
Low voltage operation of a silver/silver chloride battery with high desalination capacity in seawater
Get PDFTechnologies for the effective and energy efficient removal of salt from saline media for advanced water remediation are in high demand. Capacitive deionization using carbon electrodes is limited to highly diluted salt water. Our work demonstrates the high desalination performance of the silver/silver chloride conversion reaction by a chloride ion rocking-chair desalination mechanism. Silver nanoparticles are used as positive electrodes while their chlorination into AgCl particles produces the negative electrode in such a combination that enables a very low cell voltage of only Δ200 mV. We used a chloride-ion desalination cell with two flow channels separated by a polymeric cation exchange membrane. The optimized electrode paring between Ag and AgCl achieves a low energy consumption of 2.5 kT per ion when performing treatment with highly saline feed (600 mM NaCl). The cell affords a stable desalination capacity of 115 mg g−1 at a charge efficiency of 98%. This performance aligns with a charge capacity of 110 mA h g−1
Gallium and Indium Alkoxides with Hydride, Cyclopentadienediide and Copper(I) tert-Butoxide as further Components
Get PDFGallium hydride stabilized by the base quinonuclidine reacts with acetone under addition of the Ga-H function to the carbon–oxygen double bond yielding (HGa)5(OiPr)8O (1) as isolable compound. (HGa)5(OiPr)8O may be formally split in to four entities of HGa(OiPr)2 and one entity HGaO. The inner atomic skeleton of 1 is a novel Ga5O9 heterocluster with gallium atoms occupying the corners of a distorted trigonal bi-pyramid, an oxygen atom in the center and the remaining alcoholate oxygen atoms bridging eight of the nine edges of the bi-pyramid (X-ray diffraction analysis). Potassium indium alkoxide KIn(OtBu)4 has been used to synthesize several new compounds like In4(OtBu)8(C5H4)2 (2), (py)2CuIn(OtBu)4 (3), and [CuIn(OtBu)4]2 (4) by reaction with TiCl2cp2 (2) and CuCl (3, 4). All compounds were characterized by spectroscopic means and by X-ray structure analyses revealing novel polycyclic structures