Publikationen

Topography plays a major role on surface-cell interaction beside the surface chemistry. We investigated the effect of the nanotopography on vascular cell adhesion and proliferation in order to improve endothelialisation for restenosis treatment. In this context, Al2O3 nanowires (NWs) composed of a stable Al2O3 shell and an Al core were synthesized by chemical vapour deposition (CVD) of the molecular precursor (tBuOAlH2)2. After the detailed material characterization, human umbilical vein endothelial cells (HUVEC) and human umbilical vein smooth muscle cells (HUVSMC) were seeded and cultivated on these surfaces. Our preliminary results showed that there is a preference of HUVEC adhesion on NWs in comparison to that of HUVSMC. The control of the cell-surface interaction by the topography may represent a key issue for the future stent material design.

Thermal activation analysis of plastic deformation of peacock tail feathers, by temperature changes and stress relaxation, gave for the keratin cortex an activation enthalpy of 1.78±0.89eV and an activation volume of 0.83±0.13nm3, for both the blue and the white subspecies. These values suggest that breaking of electrostatic bonds is responsible for plasticity in feather keratin. These might be bonds between keratin and nonkeratinous matrix or keratin-keratin cross-links. The mechanical properties of the rachis cortex are surprisingly uniform along the length of the feathers.

Biological cells stick together via transmembrane proteins, which are linked to receptor molecules of the extracellular matrix (ECM). This specific biochemical adhesion plays a leading role in many cellular processes, among them cell differentiation, morphogenesis, and wound healing. Various medical applications require endogen cells to bind to an exogene substrate as in the case of an implant. Coatings with proteins that naturally belong to the ECM are known to enhance the cell adhesion. However, the choice of inorganic materials, which promote cell adhesion, is limited. Here, we report on a new engineered surface composed of Al/Al2O3 bi-phasic nanowires (NWs), which promotes the adhesion of fibroblast cells. Fibroblasts grow well on this inorganic layer and keep proliferating. Using the cell monolayer rheology (CMR) technique, we show that the adhesion of fibroblasts on Al/Al2O3 NWs is comparable to fibronectin coated surfaces. To our knowledge, this is one of the strongest cell adhesions on an inorganic surface, which has been reported on so far, since it compares to bio-organic layers such as fibronectin.

Luminescent Eu3+ and Er3+ doped SnO2 powders have been prepared by Sn4+ hydrolysis followed by a controlled growth reaction using a particle's surface modifier in order to avoid particles aggregation. The powders so obtained doped with up to 2 mol% rare earth ions are fully redispersable in water at pH>8 and present the cassiterite structure. Particles size range from 3 to 10 nm as determined by Photon Correlation Spectroscopy. Rare earth ions were found to be essentially incorporated into the cassiterite structure, substituting for Sn4+, for doping concentration smaller than 0.05 mol%. For higher concentration they are also located at the particles surface. The presence of Eu3+ ions at the surface of the particles hinder their growth and has therefore allowed the preparation of new materials consisting of water redispersable powders coated with Eu3+-β diketonate complexes. Enhanced UV excited photoluminescence was observed in water. SnO2 single layers with thickness up to 200 nm and multilayer coatings were spin coated on borosilicate glass substrates from the colloidal suspensions. Waveguiding properties were evaluated by the prism coupling technique. For a 0.3 μm planar waveguide single propagating mode was observed with attenuation coefficient of 3.5 dB/cm at 632.8 nm.

The protective ability of hybrid nano-composite oxysilane coatings, deposited via sol-gel method on AA2024-T3 – aluminium alloy, were studied by linear voltammetry (LVA) and electrochemical impedance spectroscopy (EIS) methods in 0.05 M solution of NaCl. Cerium chloride (CeCl3) was incorporated as an inhibitor into a sol-gel hybrid matrix in two different routes: directly and via filled porous Al2O3 nano-particle aggregates with diameters up to 500 nm. The influences of the inhibitor concentration, as well as the influence of nano-particles on the barrier properties and the susceptibility against corrosion, were evaluated and EIS spectra were fitted by appropriated equivalent circuits. The values for Ccoat, Rcoat, Coxy and Roxy were achieved and their evolution over time was investigated. The investigated coatings possess highly expressed barrier properties (106 to 107 Ω cm2). Despite of the chloride ions inside of the matrix, some samples illustrated a significant durability of over 4000 h during exposure to the corrosion medium before first signs of corrosion appeared. The electrochemical results were compared with the neutral salt spray test. Thus, it was proved that the potential of these coatings is to be used as anticorrosive protective materials and are candidate to replace Cr(VI)-based anti-corrosion coatings.

Small ceramic particles with implied high ferroelectric properties are highly demanded for achieving fine-grained ceramics as well as in the preparation of ceramic/polymer composites. While a variety of synthetic methods offers ferroelectric particles with different sizes and crystallographic phases, a simple possibility to directly compare the ferroelectric properties of such particles is lacking. Besides the industrial importance, accessing the intrinsic ferroelectric properties of small particles will certainly help to enlighten the discussion about the existence of a size effect in ferroelectricity. We report on a setup to correctly determine ferroelectricity of BaTiO3 particles, well dispersed in an organic polymer matrix.

Transparent and scratch-resistant zirconium oxide thin films were deposited in radio-frequency plasma-enhanced chemical vapor deposition process on glass and polycarbonate substrates using zirconium-tetra-tert-butoxide, [Zr(OtBu)4], as the precursor. Investigations on film morphology (AFM), thickness (cross-sectional SEM), phase structure (X-ray diffraction), chemical composition (X-ray photoelectron spectroscopy), and optical properties (UV/Vis, ellipsometry) revealed the interplay of process parameters (plasma power, gas composition, deposition time, and precursor flux) on the composition and properties of the coatings. High-quality transparent coatings (>90%) with a tunable refractive index (n=1.7-2.1) and abrasion-resistant properties were deposited on both polymer and glass substrates. Despite low deposition temperatures (<100°C), the coatings showed good adherence to the substrate and extraordinary barrier properties that were further improved by depositing intermediary SiOx-layers. Phase analysis of the predominantly amorphous films showed the incipient crystallization of ZrO2.

Two-step chemical vapor deposition (CVD) in combination with metal-catalyzed vapor-liquid-solid (VLS) growth mechanism was used as a new approach to synthesize and modify the morphology of SnO2-TiO2 core-shell nanowires. SnO2 nanowires were grown by decomposition of Sn(OtBu)4 precursor on Au-coated Al2O3 substrates followed by the growth of a TiO2 overlayer by the CVD of Ti(OiPr)4. Structural characterization of SnO2-TiO2 heterostructures by X-ray diffraction and high-resolution TEM revealed the formation of mixed SnxTi1–xO2 compositions (x = 0.857-1.0) at the SnO2-TiO2 phase boundaries, where x depended on the annealing temperatures. The observed oriented attachment of TiO2 nanoclusters on single crystal SnO2 core was possibly due to low lattice mismatch. The photocatalytic studies suggested an enhanced activity in SnO2-TiO2 heterostructures due to higher surface area and change in the electronic structures caused by Sn4+ doping in TiO2.

Oriented SnO2 nanowire (NW) arrays were grown on TiO2(001) substrates by molecule-based chemical vapor deposition of Sn(OtBu)4. Preferred growth directions ([101], [-101], [011], and [0-11]) of SnO2 NWs were correlated to surface energy consideration and crystallographic relationship between the substrate and NW material by comprehensive electron microscopy and bulk tomographic studies. The proposed growth incubation model (tilting of catalyst/NW interface due to driving force of surface energy) explains the formation mechanism of oriented SnO2 NWs on TiO2 substrates. These results allowed us to also study the I-V characteristics and gas-sensing properties of individual SnO2 NWs grown with a perfectly defined crystal orientation ([101]).