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End date: 2019 × DDC: 620 × WGL Institute: INM ×

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Now showing 1 - 10 of 64
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    Toward light‐regulated living biomaterials
    (Hoboken, NJ : Wiley, 2018) Sankaran, Shrikrishnan; Zhao, Shifang; Muth, Christina; Paez, Julieta; Del Campo, Aránzazu
    Living materials are an emergent material class, infused with the productive,adaptive, and regenerative properties of living organisms. Property regulation in living materials requires encoding responsive units in the living components to allow external manipulation of their function. Here, an optoregulated Escherichia coli (E. coli)-based living biomaterial that can be externally addressed using light to interact with mammalian cells is demonstrated. This is achieved by using a photoactivatable inducer of gene expression and bacterial surface display technology to present an integrin-specific miniprotein on the outer membrane of an endotoxin-free E. coli strain. Hydrogel surfaces functionalized with the bacteria can expose cell adhesive molecules upon in situ light-activation, and trigger cell adhesion. Surface immobilized bacteria are able to deliver a fluorescent protein to the mammalian cells with which they are interacting, indicating the potential of such a bacterial material to deliver molecules to cells in a targeted manner.
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    Mechanochemistry-assisted synthesis of hierarchical porous carbons applied as supercapacitors
    (Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2017) Leistenschneider, Desirée; Jäckel, Nicolas; Hippauf, Felix; Presser, Volker; Borchardt, Lars
    A solvent-free synthesis of hierarchical porous carbons is conducted by a facile and fast mechanochemical reaction in a ball mill. By means of a mechanochemical ball-milling approach, we obtained titanium(IV) citrate-based polymers, which have been processed via high temperature chlorine treatment to hierarchical porous carbons with a high specific surface area of up to 1814 m2 g−1 and well-defined pore structures. The carbons are applied as electrode materials in electric double-layer capacitors showing high specific capacitances with 98 F g−1 in organic and 138 F g−1 in an ionic liquid electrolyte as well as good rate capabilities, maintaining 87% of the initial capacitance with 1 M TEA-BF4 in acetonitrile (ACN) and 81% at 10 A g−1 in EMIM-BF4.
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    Mechanically reinforced catechol-containing hydrogels with improved tissue gluing performance
    (Basel : MDPI, 2017) Feng, Jun; Ton, Xuan-Anh; Zhao, Shifang; Paez, Julieta I.; del Campo, Aránzazu
    In situ forming hydrogels with catechol groups as tissue reactive functionalities are interesting bioinspired materials for tissue adhesion. Poly(ethylene glycol) (PEG)–catechol tissue glues have been intensively investigated for this purpose. Different cross-linking mechanisms (oxidative or metal complexation) and cross-linking conditions (pH, oxidant concentration, etc.) have been studied in order to optimize the curing kinetics and final cross-linking degree of the system. However, reported systems still show limited mechanical stability, as expected from a PEG network, and this fact limits their potential application to load bearing tissues. Here, we describe mechanically reinforced PEG–catechol adhesives showing excellent and tunable cohesive properties and adhesive performance to tissue in the presence of blood. We used collagen/PEG mixtures, eventually filled with hydroxyapatite nanoparticles. The composite hydrogels show far better mechanical performance than the individual components. It is noteworthy that the adhesion strength measured on skin covered with blood was >40 kPa, largely surpassing (>6 fold) the performance of cyanoacrylate, fibrin, and PEG–catechol systems. Moreover, the mechanical and interfacial properties could be easily tuned by slight changes in the composition of the glue to adapt them to the particular properties of the tissue. The reported adhesive compositions can tune and improve cohesive and adhesive properties of PEG–catechol-based tissue glues for load-bearing surgery applications.
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    Funnel-shaped microstructures for strong reversible adhesion
    (Hoboken, NJ : Wiley, 2017) Fischer, Sarah C.L.; Groß, Katja; Abad, Oscar Torrents; Becker, MIchael M.; Park, Euiyoung; Hensel, René; Arzt, Eduard
    The potential of a new design of adhesive microstructures in the micrometer range for enhanced dry adhesion is investigated. Using a two-photon lithography system, complex 3D master structures of funnel-shaped microstructures are fabricated for replication into poly(ethylene glycol) dimethacrylate polymer. The diameter, the flap thickness, and the opening angle of the structures are varied systematically. The adhesion of single structures is characterized using a triboindenter system equipped with a flat diamond punch. The pull-off stresses obtained reaches values up to 5.6 MPa, which is higher than any values reported in literature for artificial dry adhesives. Experimental and numerical results suggest a characteristic attachment mechanism that leads to intimate contact formation from the edges toward the center of the structures. van der Waals interactions most likely dominate the adhesion, while contributions by suction or capillarity play only a minor role. Funnel-shaped microstructures are a promising concept for strong and reversible adhesives, applicable in novel pick and place handling systems or wall-walking robots.
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    On the process of co-deformation and phase dissolution in a hard-soft immiscible CuCo alloy system during high-pressure torsion deformation
    (Amsterdam : Elsevier, 2016) Bachmaier, Andrea; Schmauch, Jörg; Aboulfadl, Hisham; Verch, Andreas; Motz, Christian
    In this study, dual phase Cusingle bondCo composites with a total immiscibility in the solid state and a very different initial phase strength are deformed by severe plastic deformation. Nanocrystalline supersaturated solid solutions are reached in all Cusingle bondCo composites independent of the initial composition. The deformation and mechanical mixing process is studied thoroughly by combining scanning electron microscopy, transmission electron microscopy, three-dimensional atom probe tomography and nanoindentation. The indentation hardness of the Cu and Co phase and its evolution as a function of the applied strain is linked to deformation and mechanical mixing process to gain a better understanding how the phase strength mismatch of the Cu and Co phase effects the amount of co-deformation and deformation-induced mixing. Our results show that co-deformation is not a necessary requirement to achieve mechanical mixing.
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    Composite pillars with a tunable interface for adhesion to rough substrates
    (Washington D.C. : American Chemical Society, 2017) Fischer, Sarah C.L.; Arzt, Eduard; Hensel, René
    The benefits of synthetic fibrillar dry adhesives for temporary and reversible attachment to hard objects with smooth surfaces have been successfully demonstrated in previous studies. However, surface roughness induces a dramatic reduction in pull-off stresses and necessarily requires revised design concepts. Toward this aim, we introduce cylindrical two-phase single pillars, which are composed of a mechanically stiff stalk and a soft tip layer. Adhesion to smooth and rough substrates is shown to exceed that of conventional pillar structures. The adhesion characteristics can be tuned by varying the thickness of the soft tip layer, the ratio of the Young’s moduli and the curvature of the interface between the two phases. For rough substrates, adhesion values similar to those obtained on smooth substrates were achieved. Our concept of composite pillars overcomes current practical limitations caused by surface roughness and opens up fields of application where roughness is omnipresent.
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    Monitoring the contact stress distribution of gecko-inspired adhesives using mechano-sensitive surface coatings
    (Washington D.C. : American Chemical Society, 2018) Neubauer, Jens W.; Xue, Longjian; Erath, Johann; Drotlef, Dirk-Michael; del Campo, Aránzazu; Fery, Andreas
    The contact geometry of microstructured adhesive surfaces is of high relevance for adhesion enhancement. Theoretical considerations indicate that the stress distribution in the contact zone is crucial for the detachment mechanism, but direct experimental evidence is missing so far. In this work, we propose a method that allows, for the first time, the detection of local stresses at the contact area of biomimetic adhesive microstructures during contact formation, compression and detachment. We use a mechano-sensitive polymeric layer, which turns mechanical stresses into changes of fluorescence intensity. The biomimetic surface is brought into contact with this layer in a well-defined fashion using a microcontact printer, while the contact area is monitored with fluorescence microscopy in situ. Thus, changes in stress distribution across the contact area during compression and pull-off can be visualized with a lateral resolution of 1 μm. We apply this method to study the enhanced adhesive performance of T-shaped micropillars, compared to flat punch microstructures. We find significant differences in the stress distribution of the both differing contact geometries during pull-off. In particular, we find direct evidence for the suppression of crack nucleation at the edge of T-shaped pillars, which confirms theoretical models for the superior adhesive properties of these structures.
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    In-situ nanodiamond to carbon onion transformation in metal matrix composites
    (Amsterdam : Elsevier, 2018) Suarez, Sebastian; Reinert, Leander; Zeiger, Marco; Miska, Patrice; Grandthyll, Samuel; Müller, Frank; Presser, Volker; Mücklich, Frank
    In the present study, nickel matrix composites reinforced with a fine distribution of nanodiamonds (6.5 vol%) as reinforcement phase are annealed in vacuum at different temperatures ranging from 750 °C to 1300 °C. This is carried out to evaluate the in-situ transformation of nanodiamonds to carbon onions within a previously densified composite. The resulting materials are thoroughly analyzed by complementary analytical methods, including Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The proposed in-situ transformation method presents two main benefits. On one hand, since the particle distribution of a nanodiamond-reinforced composite is significantly more homogenous than in case of the carbon onions, it is expected that the transformed particles will preserve the initial distribution features of nanodiamonds. On the other hand, the proposed process allows for the tuning of the sp3/sp2 carbon ratio by applying a single straightforward post-processing step.
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    Vacuum or flowing argon: What is the best synthesis atmosphere for nanodiamond-derived carbon onions for supercapacitor electrodes?
    (Amsterdam : Elsevier, 2015) Zeiger, Marco; Jäckel, Nicolas; Weingarth, Daniel; Presser, Volker
    We present a comprehensive study on the influence of the synthesis atmosphere on the structure and properties of nanodiamond-derived carbon onions. Carbon onions were synthesized at 1300 and 1700 °C in high vacuum or argon flow, using rapid dynamic heating and cooling. High vacuum annealing yielded carbon onions with nearly perfect spherical shape. An increase in surface area was caused by a decrease in particle density when transitioning from sp3 to sp2 hybridization and negligible amounts of disordered carbon were produced. In contrast, carbon onions from annealing nanodiamonds in flowing argon are highly interconnected by few-layer graphene nanoribbons. The presence of the latter improves the electrical conductivity, which is reflected by an enhanced power handling ability of supercapacitor electrodes operated in an organic electrolyte (1 M tetraethylammonium tetrafluoroborate in acetonitrile). Carbon onions synthesized in argon flow at 1700 °C show a specific capacitance of 20 F/g at 20 A/g current density and 2.7 V cell voltage which is an improvement of more than 40% compared to vacuum annealing. The same effect was measured for a synthesis temperature of 1300 °C, with a 140% higher capacitance at 20 A/g for argon flow compared to vacuum annealing.
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    Quinone-decorated onion-like carbon/carbon fiber hybrid electrodes for high-rate supercapacitor applications
    (Hoboken, NJ : Wiley, 2015) Zeiger, Marco; Weingarth, Daniel; Presser, Volker
    The energy performance of carbon onions can be significantly enhanced by introducing pseudocapacitive materials, but this is commonly at the cost of power handling. In this study, a novel synergistic electrode preparation method was developed by using carbon-fiber substrates loaded with quinone-decorated carbon onions. The electrodes are free standing, binder free, extremely conductive, and the interfiber space filling overcomes the severely low apparent density commonly found for electrospun fibers. Electrochemical measurements were performed in organic and aqueous electrolytes. For both systems, a high electrochemical stability after 10 000 cycles was measured, as well as a long-term voltage floating test for the organic electrolyte. The capacitance in 1 M H2SO4 was 288 F g^−1 for the highest loading of quinones, which is similar to literature values, but with a very high power handling, showing more than 100 F g^−1 at a scan rate of 2 Vs^−1.