Nanopartikel auf subnanometer dünnen oxidischen Filmen: Skalierung von Modellsystemen

Durch die Abscheidung von ultradünnen Oxidschichten auf atomar‐flachen Metalloberflächen konnte die elektronische Struktur des Metalls und hierdurch dessen katalytische Aktivität beeinflusst werden. Die Skalierung dieser Architekturen für eine technische Nutzbarkeit war bisher aber kaum möglich. Durch die Verwendung einer flüssigkristallinen Phase aus Fluorhectorit‐Nanoschichten, können wir solche Architekturen in skalierbarem Maßstab imitieren. Synthetischer Natriumfluorhectorit (NaHec) quillt spontan und repulsiv in Wasser zu einer nematischen flüssigkristallinen Phase aus individuellen Nanoschichten. Diese tragen eine permanente negative Schichtladung, sodass selbst bei einer Separation von über 60 nm eine parallele Anordnung der Schichten behalten wird. Zwischen diesen Nanoschichten können Palladium‐Nanopartikel mit entgegengesetzter Ladung eingelagert werden, wodurch die nematische Phase kollabiert und separierte Nanopartikel zwischen den Schichten fixiert werden. Die Aktivität zur CO‐Oxidation des so entstandenen Katalysators war höher als z. B. die der gleichen Nanopartikel auf konventionellem Al2O3</sub oder der externen Oberfläche von NaHec. Durch Röntgenphotoelektronenspektroskopie konnte eine Verschiebung der Pd‐3d‐Elektronen zu höheren Bindungsenergien beobachtet werden, womit die erhöhte Aktivität erklärt werden kann. Berechnungen zeigten, dass mit erhöhter positiver Ladung des Pd die Adsorptionsstärke von CO erniedrigt und damit auch die Vergiftung durch CO vermindert wird

Stimuli-Responsive Multilayers Based on Thiolated Polysaccharides That Affect Fibroblast Cell Adhesion

Control of the biomaterial properties through stimuli-responsive polymeric platforms has become an essential technique in recent biomedical applications. A multilayer system of thiolated chitosan (t-Chi) and thiolated chondroitin sulfate (t-CS), consisting of five double layers ([t-Chi/t-CS]5), was fabricated here by applying a layer-by-layer coating strategy. To represent a novel class of chemically tunable nanostructures, the ability to cross-link pendant thiol groups was tested by a rise from pH 4 during layer formation to pH 9.3 and a more powerful chemical stimulus by using chloramine-T (ChT). Following both treatments, the resulting multilayers showed stimuli-dependent behavior, as demonstrated by their content of free thiols, wettability, surface charge, elastic modulus, roughness, topography, thickness, and binding of fibronectin. Studies with human dermal fibroblasts further demonstrated the favorable potential of the ChT-responsive multilayers as a cell-adhesive surface compared to pH-induced cross-linking. Because the [t-Chi/t-CS]5 multilayer system is responsive to stimuli such as the pH and redox environment, multilayer systems with disulfide bond formation may help to tailor their interaction with cells, film degradation, and controlled release of bioactive substances like growth factors in a stimuli-responsive manner useful in future wound healing and tissue engineering applications

Functionality of surface-coupled oxidised glycosaminoglycans towards fibroblast adhesion

Glycosaminoglycans are able to bind many growth factors and adhesive proteins, which affect cell activities such as adhesion, migration, growth and differentiation. Chondroitin sulphate, hyaluronan, sulphated hyaluronan and heparin were oxidised here (aldehyde glycosaminoglycans) to generate aldehydes on vicinal hydroxyl groups of the uronic monomers of glycosaminoglycans for subsequent direct covalent binding to amino-terminated model substrata. The properties of modified surfaces were monitored by water contact angle, zeta potential, ellipsometry measurements and atomic force microscopy showing successful immobilisation of aldehyde glycosaminoglycans. Wetting properties and zeta potentials were related to sulphate content of aldehyde glycosaminoglycans with aldehyde heparin as most wettable and negative surface and aldehyde hyaluronan as the least. The thickness of surface layers measured by ellipsometry indicated a predominant side-on immobilisation of all aldehyde glycosaminoglycans. Atomic force microscopy studies showed that immobilisation of aldehyde hyaluronan lead to a rather smooth surface coating while immobilisation of sulphated aldehyde glycosaminoglycans was characterised by a globular appearance of surfaces with higher roughness. The experiments with human fibroblast studying adhesion under serum-free conditions were carried out to learn about bioactivity of aldehyde glycosaminoglycans. It was observed that the increase in sulphation degree of aldehyde glycosaminoglycans was accompanied by increased adhesion and spreading of cells with stronger expression of focal adhesions and cytoskeletal structures. By contrast, cell adhesion and spreading were lower on aldehyde hyaluronan. Immunofluorescence staining of cells in contact with aldehyde hyaluronan revealed a stronger expression of CD44, which can represent an alternative route of cell adhesion. The results show that oxidised glycosaminoglycans can be successfully applied for the development of bioactive surface coatings. The created biomimetic microenvironment may be useful to engineer surfaces of implants and scaffolds for tissue regeneration.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was carried out under the scope of the EU 7th Framework Programme (FP7/2007-2013) under grant agreement no. NMP4-SL-2009-229292 (Find & Bind)

Surface microstructuring and protein patterning using hyaluronan derivatives

Natural polymers, such as hyaluronan, are considered as good candidates to substitute synthetic materials in many biological applications due to their intrinsic biocompatibility for in vitro and living cell experiments. This work describes surface modifications performed over modified hyaluronan derivatives which could help to understand the physical and biochemical cues on the cell-behaviour. A photocrosslinkable methacrylated hyaluronan was microstructured using soft lithography techniques to obtain a microenvironment suitable for cell-behaviour experiments, which might mimic the extra-cellular matrix. In addition, sulphated and non-sulphated oxidized hyaluronan were immobilized on bare substrates and micrometric features of cell adhesive and non-adhesive proteins were patterned by microcontact printing on top of them. The obtained structures were characterized by optical microscopy, profilometry and atomic force microscopy. The stability of structures was tested by immersion in physiological salt solutions. The observed results prove the suitability of the materials and protocols described.This work was supported and carried out under the scope of the European Project Find and Bind (NMP4-SL-2009-229292)

Mechanistic insights into the catalytic methanol steam reforming performance of Cu/ZrO2 catalysts by in situ and operando studies

We assessed the catalytic properties of the Cu/ZrO2 interface in methanol and formaldehyde steam reforming (MSR and FSR) on powder catalysts by using a comparative approach with respect to the influence of the ZrO2 polymorph support structure (monoclinic (m-)ZrO2 vs. tetragonal (t-)ZrO2), its synthesis routine and the choice of the precursor material on the CO2 selectivity. Our studies reveal that ZrO2 exhibits a pronounced versatility as a support material and its catalytic properties depend most strongly on its surface properties governed by its synthesis, especially by the choice of the Zr precursor. The way of combining the support with copper introduces an additional layer of complexity, but its influence on the MSR performance is limited to a modification of the conditions provided by the ZrO2 support. Exploiting the comparative approach regarding the Cu-ZrO2 catalysts in FSR and MSR – including the pure support materials – in combination with in situ Fourier transform infrared (FT-IR) spectroscopy shows that the CO observed in MSR on Cu/m-ZrO2 can be attributed to a spillover of formaldehyde to the support. Side reactions of m-ZrO2 are suppressed at lower temperatures due to its lack of highly reactive sites, resulting in a CO2-selective MSR performance. In Cu/t-ZrO2, however, the amount of CO is higher and a combination of a formaldehyde spillover to the support and a Cu-ZrO2 phase boundary yielding CO leads to the lower CO2 selectivity of these samples. An elevated number of defects and reactive Lewis acidic and Brønsted basic centers of t-ZrO2 explains this increased activity towards side reactions in contrast to Cu/m-ZrO2 catalysts

Mechanistic insights into the catalytic methanol steam reforming performance of Cu/ZrO₂ catalysts by in situ and operando studies

We assessed the catalytic properties of the Cu/ZrO2 interface in methanol and formaldehyde steam reforming (MSR and FSR) on powder catalysts by using a comparative approach with respect to the influence of the ZrO2 polymorph support structure (monoclinic (m-)ZrO2vs. tetragonal (t-)ZrO2), its synthesis routine and the choice of the precursor material on the CO2 selectivity. Our studies reveal that ZrO2 exhibits a pronounced versatility as a support material and its catalytic properties depend most strongly on its surface properties governed by its synthesis, especially by the choice of the Zr precursor. The way of combining the support with copper introduces an additional layer of complexity, but its influence on the MSR performance is limited to a modification of the conditions provided by the ZrO2 support. Exploiting the comparative approach regarding the Cu-ZrO2 catalysts in FSR and MSR – including the pure support materials – in combination with in situ Fourier transform infrared (FT-IR) spectroscopy shows that the CO observed in MSR on Cu/m-ZrO2 can be attributed to a spillover of formaldehyde to the support. Side reactions of m-ZrO2 are suppressed at lower temperatures due to its lack of highly reactive sites, resulting in a CO2-selective MSR performance. In Cu/t-ZrO2, however, the amount of CO is higher and a combination of a formaldehyde spillover to the support and a Cu-ZrO2 phase boundary yielding CO leads to the lower CO2 selectivity of these samples. An elevated number of defects and reactive Lewis acidic and Brønsted basic centers of t-ZrO2 explains this increased activity towards side reactions in contrast to Cu/m-ZrO2 catalysts