Droplet-based microfluidic systems are an expansion of the lab on a chip concept toward flexible, reconfigurable setups based on the modification and analysis of individual droplets. Superhydrophobic surfaces are one suitable candidate for the realization of droplet-based microfluidic systems as the high mobility of aqueous liquids on such surfaces offers possibilities to use novel or more efficient approaches to droplet movement. Here, copper-based superhydrophobic surfaces were produced either by the etching of polycrystalline copper samples along the grain boundaries using etchants common in the microelectronics industry, by electrodeposition of copper films with subsequent nanowire decoration based on thermal oxidization, or by a combination of both. The surfaces could be easily hydrophobized with thiol-modified fluorocarbons, after which the produced surfaces showed a water contact angle as high as 171 degrees +/- 2 degrees . As copper was chosen as the base material, established patterning techniques adopted from printed circuit board fabrication could be used to fabricate macrostructures on the surfaces with the intention to confine the droplets and, thus, to reduce the system's sensitivity to tilting and vibrations. A simple droplet-based microfluidic chip with inlets, outlets, sample storage, and mixing areas was produced. Wire guidance, a relatively new actuation method applicable to aqueous liquids on superhydrophobic surfaces, was applied to move the droplets.
A method to fabricate inexpensive and transparent nanowire impalement devices is invented based on CuO nanowire arrays grown by thermal oxidation. By employing a novel process the nanowires are transferred to a transparent, cell-compatible epoxy membrane. Cargo delivery and detailed cell-nanowire interaction studies are performed, revealing that the cell plasma membrane tightly wraps the nanowires, while cell membrane penetration is not observed. The presented device offers an efficient investigation platform for further optimization, leading towards a simple and versatile impalement delivery system.
We report a simple and fast approach to fabricate large, non-flaking arrays of CuO nanowires by oxidizing thin copper substrates in air. Oxidative CuO nanowire growth is commonly accompanied by oxide layer flaking due to stress at the copper-copper oxide interface. Using thin substrates is shown to prevent this flaking by introducing favourable material thickness ratios in the samples after oxidation. Additionally, thin foils allow larger scale topographic patterns to be transferred from an underlying mould to realize non-flat, nanowire-decorated surfaces. Further patterning is possible by electrodeposition of a nickel layer, which restricts nanowire growth to specific areas of the sample.
Lipopolysaccharides (LPS; endotoxin) activate immunocompetent cells of the host via a transmembrane signaling process. In this study, we investigated the function of the LPS-binding protein (LBP) in this process. The cytoplasmic membrane of the cells was mimicked by lipid liposomes adsorbed on mica, and the lateral organization of LBP in these membranes and its interaction with LPS aggregates were characterized by atomic force microscopy. Using cantilever tips functionalized with anti-LBP antibodies, single LBP molecules were localized in the membrane at low concentrations. At higher concentrations, LBP formed clusters of several molecules and caused cross-linking of lipid bilayers. The addition of LPS to LBP-containing liposomes led to the formation of LPS domains in the membranes, which could be inhibited by anti-LBP antibodies. Thus, LBP mediates the fusion of lipid membranes and LPS aggregates.Membrane-embedded proteins or serum proteins interacting with membranes very often play a particular role in cell functioning (e.g. in signal transduction induced by various pathogenic factors). In these cases, signaling occurs across the cytoplasmic membrane via one or more transmembrane or membrane-bound proteins. The participating components are usually known; however, their lateral organization and the mechanism of their interaction are unknown.The cell wall of Gram-negative bacteria consists of the cytoplasmic and an additional outer membrane. This outer membrane is an extremely asymmetric bilayer with respect to the lipid composition. The inner leaflet is composed of a phospholipid mixture, and the outer leaflet is composed of glycolipids, in most cases lipopolysaccharide (LPS). 2When released from the bacterial surface into the blood circulation of the host, LPS plays an important role in the pathogenesis and manifestation of Gram-negative inflammation, in general, and of septic shock, in particular. It is therefore also named endotoxin. The important biological aim of this study was to get an understanding of an early step in the activation mechanism of immune cells (mononuclear cells, MNCs) by LPS. A comparison of the capacity of LPS monomers and aggregates to induce cytokines such as tumor necrosis factor-␣ showed that the aggregates play a biologically important role in the initial step of cell activation (1). One important step in the signal transduction process is the interaction between LPS and the acute phase serum protein LPSbinding protein (LBP). LBP is synthesized by hepatocytes (2) and different epithelial cells (3, 4) and has been described in the literature as a shuttle protein for monomers of LPS or lipid A, the endotoxic principle of LPS, toward the surface of MNCs (5-9). Our group provided evidence for binding of LBP to and intercalation into lipid membranes composed of negatively charged phosphatidylserine (PS) or zwitterionic phosphatidylcholine (PC) and also in LPS aggregates by using fluorescence resonance energy transfer and surface plasmon resonance experiments (10). Furthermore, we also p...
A biopolymer-based template assembly constructed around the spines of the bristle worm Aphrodita aculeata (sea mouse) was used to fabricate very high aspect ratio nanowires and nanotubes using established methods adopted from nanofabrication in porous membranes. The easily available bio-originated template contains more than 100 000 highly ordered, very high aspect ratio nanochannels, each about 150 to 200 nm in diameter but up to a centimetre in length. Their parallel, hexagonal arrangement in the spine constitutes a photonic crystal, which gives the animal its colourful, iridescent appearance. Around the nanochannels, the spines consist of a chitin/protein composite material, which has been shown to withstand the chemical and thermal conditions needed for established template-assisted nanofabrication strategies. A template preparation procedure was developed and the template was used to fabricate copper and nickel nanowires by electrodeposition and aluminium oxide nanotubes by atomic layer deposition. Due to their high thermal and chemical stability, decomposition of the filled templates proved to be difficult, and different approaches to obtain separated nanostructures are described and discussed. Alongside this, the presented system of parallel nanowires or nanotubes in a biopolymer matrix might be utilized in applications, where such separated structures are not needed. Comparing to porous membranes, the presented template allows us to increase the maximum length of nanotubes and nanowires produced using nanochannel-based templates by at least one order of magnitude.
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