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- ItemA Printable Paste Based on a Stable n-Type Poly[Ni-tto] Semiconducting Polymer(Basel : MDPI, 2019) Tkachov, Roman; Stepien, Lukas; Greifzu, Moritz; Kiriy, Anton; Kiriy, Nataliya; Schüler, Tilman; Schmiel, Tino; López, Elena; Brückner, Frank; Leyens, ChristophPolynickeltetrathiooxalate (poly[Ni-tto]) is an n-type semiconducting polymer having outstanding thermoelectric characteristics and exhibiting high stability under ambient conditions. However, its insolubility limits its use in organic electronics. This work is devoted to the production of a printable paste based on a poly[Ni-tto]/PVDF composite by thoroughly grinding the powder in a ball mill. The resulting paste has high homogeneity and is characterized by rheological properties that are well suited to the printing process. High-precision dispenser printing allows one to apply both narrow lines and films of poly[Ni-tto]-composite with a high degree of smoothness. The resulting films have slightly better thermoelectric properties compared to the original polymer powder. A flexible, fully organic double-leg thermoelectric generator with six thermocouples was printed by dispense printing using the poly[Ni-tto]-composite paste as n-type material and a commercial PEDOT-PSS paste as p-type material. A temperature gradient of 100 K produces a power output of about 20 nW. © 2019 by the authors.
- ItemThe Orientation of Strain-Induced Crystallites in Uniaxially-Strained, Thin and Wide Bands Made from Natural Rubber(Basel : MDPI, 2019) Schneider, Konrad; Schwartzkopf, MatthiasVulcanized natural rubber (unfilled and filled with 20 phr carbon black) is strained. We suppress the macroscopic formation of fiber symmetry by choosing strip-shaped samples ("pure-shear geometry") and investigate the orientation of the resulting crystallites by two-dimensional wide-angle X-ray diffraction (WAXD), additionally rotating the sample tape about the straining direction. Indications of a directed reinforcing effect of the strain-induced crystallization (SIC) in the thin strip are found. In the filled material fewer crystallites are oriented and the orientation distribution of the oriented crystallites is less perfect. The results confirm, that it is important for the evaluation of crystallinity under deformation to check, whether fiber symmetry can be assumed. This has consequences in particular on the quantitative interpretation of space-resolved scanning experiments in the vicinity of crack tips. Furthermore it raises the question, whether there is an asymmetric reinforcing effect of the SIC in the vicinity of crack tips inside natural rubber. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemNaturally drug-loaded chitin: Isolation and applications(Basel : MDPI, 2019) Kovalchuk, Valentine; Voronkina, Alona; Binnewerg, Björn; Schubert, Mario; Muzychka, Liubov; Wysokowski, Marcin; Tsurkan, Mikhail V.; Bechmann, Nicole; Petrenko, Iaroslav; Fursov, Andriy; Martinovic, Rajko; Ivanenko, Viatcheslav N.; Fromont, Jane; Smolii, Oleg B.; Joseph, Yvonne; Giovine, Marco; Erpenbeck, Dirk; Gelinsky, Michael; Springer, Armin; Guan, Kaomei; Bornstein, Stefan R.; Ehrlich, HermannNaturally occurring three-dimensional (3D) biopolymer-based matrices that can be used in different biomedical applications are sustainable alternatives to various artificial 3D materials. For this purpose, chitin-based structures from marine sponges are very promising substitutes. Marine sponges from the order Verongiida (class Demospongiae) are typical examples of demosponges with well-developed chitinous skeletons. In particular, species belonging to the family Ianthellidae possess chitinous, flat, fan-like fibrous skeletons with a unique, microporous 3D architecture that makes them particularly interesting for applications. In this work, we focus our attention on the demosponge Ianthella flabelliformis (Linnaeus, 1759) for simultaneous extraction of both naturally occurring (“ready-to-use”) chitin scaffolds, and biologically active bromotyrosines which are recognized as potential antibiotic, antitumor, and marine antifouling substances. We show that selected bromotyrosines are located within pigmental cells which, however, are localized within chitinous skeletal fibers of I. flabelliformis. A two-step reaction provides two products: treatment with methanol extracts the bromotyrosine compounds bastadin 25 and araplysillin-I N20 sulfamate, and a subsequent treatment with acetic acid and sodium hydroxide exposes the 3D chitinous scaffold. This scaffold is a mesh-like structure, which retains its capillary network, and its use as a potential drug delivery biomaterial was examined for the first time. The results demonstrate that sponge-derived chitin scaffolds, impregnated with decamethoxine, effectively inhibit growth of the human pathogen Staphylococcus aureus in an agar diffusion assay
- ItemA new way of toughening of thermoset by dual-cured thermoplastic/thermosetting blend(Basel : MDPI, 2019) Khatiwada, Shankar P.; Gohs, Uwe; Lach, Ralf; Heinrich, Gert; Adhikari, RameshwarThe work aims at establishing the optimum conditions for dual thermal and electron beam curing of thermosetting systems modified by styrene/butadiene (SB)-based triblock copolymers in order to develop transparent and toughened materials. The work also investigates the effects of curing procedures on the ultimate phase morphology and mechanical properties of these thermoset-SB copolymer blends. It was found that at least 46 mol% of the epoxidation degree of the SB copolymer was needed to enable the miscibility of the modified block copolymer into the epoxy resin. Hence, an electron beam curing dose of ~50 kGy was needed to ensure the formation of micro- and nanostructured transparent blends. The micro- and nanophase-separated thermosets obtained were analyzed by optical as well as scanning and transmission electron microscopy. The mechanical properties of the blends were enhanced as shown by their impact strengths, indentation, hardness, and fracture toughness analyses, whereby the toughness values were found to mainly depend on the dose. Thus, we have developed a new route for designing dual-cured toughened micro- and nanostructured transparent epoxy thermosets with enhanced fracture toughness. © 2019 by the authors.
- ItemVolumetrical characterization of sheet molding compounds(Basel : MDPI, 2010) Calvimontes, A.; Grund, K.; Müller, A.For a comprehensive study of Sheet Molding Compound (SMC) surfaces, topographical data obtained by chromatic confocal imaging were submitted systematically for the development of a profile model to understand the formation of cavities on the surface. In order to qualify SMC surfaces and to predict their coatability, a characterization of cavities is applied. To quantify the effect of surface modification treatments, a new parameter (Surface Relative Smooth) is presented, applied and probed. The parameter proposed can be used for any surface modification of any solid material. © 2010 by the authors.
- ItemSynergistic effects of anionic/cationic dendrimers and levofloxacin on antibacterial activities(Basel : MDPI, 2019) Wrońska, Natalia; Majoral, Jean Pierre; Appelhans, Dietmar; Bryszewska, Maria; Lisowska, KatarzynaDespite the numerous studies on dendrimers for biomedical applications, the antibacterial activity of anionic phosphorus dendrimers has not been explored. In our research, we evaluated the antibacterial activity of modified polycationic and polyanionic dendrimers in combination with levofloxacin (LVFX) against Gram-negative (Escherichia coli ATCC 25922, Proteus hauseri ATCC 15442) and Gram-positive (Staphylococcus aureus ATCC 6538) bacteria. In the case of Gram-negative bacteria, we concluded that a combination of dendrimers and antibiotic gave satisfactory results due to a synergistic effect. The use of fluoroquinolone antibiotics, such as LVFX, not only caused resistance in disease-causing microorganisms but also increased environmental pollution. Therefore, reduction of drug dosage is of general interest. © 2019 by the authors.
- ItemSpider chitin: An Ultrafast Microwave-Assisted Method for Chitin Isolation from Caribena versicolor Spider Molt Cuticle(Basel : MDPI, 2019) Machałowski, Tomasz; Wysokowski, Marcin; Tsurkan, Mikhail V.; Galli, Roberta; Schimpf, Christian; Rafaja, David; Brendler, Erica; Viehweger, Christine; Zółtowska-Aksamitowska, Sonia; Petrenko, Iaroslav; Czaczyk, Katarzyna; Kraft, Michael; Bertau, Martin; Bechmann, Nicole; Guan, Kaomei; Bornstein, Stefan R.; Voronkina, Alona; Fursov, Andriy; Bejger, Magdalena; Biniek-Antosiak, Katarzyna; Rypniewski, Wojciech; Figlerowicz, Marek; Pokrovsky, Oleg; Jesionowski, Teofil; Ehrlich, HermannChitin, as a fundamental polysaccharide in invertebrate skeletons, continues to be actively investigated, especially with respect to new sources and the development of effective methods for its extraction. Recent attention has been focused on marine crustaceans and sponges; however, the potential of spiders (order Araneae) as an alternative source of tubular chitin has been overlooked. In this work, we focused our attention on chitin from up to 12 cm-large Theraphosidae spiders, popularly known as tarantulas or bird-eating spiders. These organisms “lose” large quantities of cuticles during their molting cycle. Here, we present for the first time a highly effective method for the isolation of chitin from Caribena versicolor spider molt cuticle, as well as its identification and characterization using modern analytical methods. We suggest that the tube-like molt cuticle of this spider can serve as a naturally prefabricated and renewable source of tubular chitin with high potential for application in technology and biomedicine. © 2019 by the authors.
- ItemThe Anomalous Influence of Polyelectrolyte Concentration on the Deposition and Nanostructure of Poly(ethyleneimine)/Poly(acrylic acid) Multilayers(Basel : MDPI, 2019) Müller, MartinThe deposition and nanostructure of polyelectrolyte (PEL) multilayers (PEMs) of branched poly(ethyleneimine)/poly(acrylic acid) (PEI/PAA) onto silicon substrates was studied in terms of the dependence of pH and the PEL concentration (cPEL) in the individual adsorption steps z. Both a commercial automatic dipping device and a homebuilt automatic stream coating device (flow cell) were used. Gravimetry, SFM, transmission (TRANS) and in situ attenuated total reflection (ATR) FTIR spectroscopy were used for the quantitative determination of the adsorbed amount, thickness, chemical composition and morphology of deposited PEMs, respectively. Firstly, the combination of pH = 10 for PEI and pH = 4 for PAA, where both PEL were predominantly in the neutral state, resulted in an extraordinarily high PEM deposition, while pH combinations, where one PEL component was charged, resulted in a significantly lower PEM deposition. This was attributed to both PEL conformation effects and acid/base interactions between basic PEI and acidic PAA. Secondly, for that pH combination an exponential relationship between PEM thickness and adsorption step z was found. Thirdly, based on the results of three independent methods, the course of the deposited amount of a PEM-10 (z = 10) versus cPEL in the range 0.001 to 0.015 M at pH = 10/4 was non-monotonous showing a pronounced maximum at cPEL = 0.005 M. Analogously, for cPEL = 0.005 M a maximum of roughness and structure size was found. Fourthly, related to that finding, in situ ATR-FTIR measurements gave evidence for the release of outermost located PEI upon PAA immersion (even step) and of outermost PAA upon PEI immersion (odd step) under formation of PEL complexes in solution. These studies help us to prepare PEL-based films with a defined thickness and morphology for interaction with biofluids in the biomedical and food fields. © 2019 by the author.
- ItemPoly(propylene imine) dendrimers and amoxicillin as dual-action antibacterial agents(Basel : MDPI, 2015) Wrońska, Natalia; Felczak, Aleksandra; Zawadzka, Katarzyna; Poszepczyńska, Martyna; Różalska, Sylwia; Bryszewska, Maria; Appelhans, Dietmar; Lisowska, KatarzynaBesides acting as antimicrobial compounds, dendrimers can be considered as agents that improve the therapeutic effectiveness of existing antibiotics. In this work we present a new approach to using amoxicillin (AMX) against reference strains of common Gram-negative pathogens, alone and in combination with poly(propylene imine) (PPI) dendrimers, or derivatives thereof, in which 100% of the available hydrogen atoms are substituted with maltose (PPI 100%malG3). The concentrations of dendrimers used remained in the range non-toxic to eukaryotic cells. The results indicate that PPI dendrimers significantly enhance the antibacterial effect of amoxicillin alone, allowing antibiotic doses to be reduced. It is important to reduce doses of amoxicillin because its widespread use in medicine could lead to the development of bacterial resistance and environmental pollution. This is the first report on the combined antibacterial activity of PPI surface-modified maltose dendrimers and amoxicillin.
- ItemStacks of Azobenzene Stars: Self-Assembly Scenario and Stabilising Forces Quantified in Computer Modelling(Basel : MDPI, 2019) Savchenko, Vladyslav; Koch, Markus; Pavlov, Aleksander S.; Saphiannikova, Marina; Guskova, OlgaIn this paper, the columnar supramolecular aggregates of photosensitive star-shaped azobenzenes with benzene-1,3,5-tricarboxamide core and azobenzene arms are analyzed theoretically by applying a combination of computer simulation techniques. Without a light stimulus, the azobenzene arms adopt the trans-state and build one-dimensional columns of stacked molecules during the first stage of the noncovalent association. These columnar aggregates represent the structural elements of more complex experimentally observed morphologies-fibers, spheres, gels, and others. Here, we determine the most favorable mutual orientations of the trans-stars in the stack in terms of (i) the p - p distance between the cores lengthwise the aggregate, (ii) the lateral displacements due to slippage and (iii) the rotation promoting the helical twist and chirality of the aggregate. To this end, we calculate the binding energy diagrams using density functional theory. The model predictions are further compared with available experimental data. The intermolecular forces responsible for the stability of the stacks in crystals are quantified using Hirshfeld surface analysis. Finally, to characterize the self-assembly mechanism of the stars in solution, we calculate the hydrogen bond lengths, the normalized dipole moments and the binding energies as functions of the columnar length. For this, molecular dynamics trajectories are analyzed. Finally, we conclude about the cooperative nature of the self-assembly of star-shaped azobenzenes with benzene-1,3,5-tricarboxamide core in aqueous solution.