Publikationen

Molluscs have a well-deserved reputation for being expert mineralizers of various shell types such as nacre. Nacre is defined as regularly arranged layers and stacks of similar to 0.5 mu m thick aragonite platelets that are extracellularly formed within a complex mixture of organic matrix. The control of species-specific layer thickness by the animal is still enigmatic. Despite the recent findings on the periodic layer-by-layer structures of chitin layers and silk-like protein layers in nacre-type biominerals, little is known about how the interface is defined between two different layers. In this paper, we demonstrate the presence of covalently attached, hydrophobic amino acid side chains in the chitin matrix in the bivalve mollusc Mytilus galloprovincialis by the combination of infrared spectroscopy and mass spectroscopy. The accumulation of the modified chitin matrix at the interface is quantified by the critical aggregate concentration of the purified chitin matrix, which is approximately an order of magnitude smaller than that of pure chitin. Our finding suggests an active role of such chemically modified chito-oligosaccharides in the creation of a defined interface and guidance of the periodic matrix textures, which would result in unique material properties of natural mollusc shells.

Nicotianamine chelates and transports micronutrient metal ions in plants. It has been speculated that nicotianamine is involved in seed loading with micronutrients. A tomato (Solanum lycopersicum) mutant (chloronerva) and a tobacco (Nicotiana tabacum) transgenic line have been utilized to analyze the effects of nicotianamine loss. These mutants showed early leaf chlorosis and had sterile flowers. Arabidopsis (Arabidopsis thaliana) has four NICOTIANAMINE SYNTHASE (NAS) genes. We constructed two quadruple nas mutants: one had full loss of NAS function, was sterile, and showed a chloronerva-like phenotype (nas4x-2); another mutant, with intermediate phenotype (nas4x-1), developed chlorotic leaves, which became severe upon transition from the vegetative to the reproductive phase and upon iron (Fe) deficiency. Residual nicotianamine levels were sufficient to sustain the life cycle. Therefore, the nas4x-1 mutant enabled us to study late nicotianamine functions. This mutant had no detectable nicotianamine in rosette leaves of the reproductive stage but low nicotianamine levels in vegetative rosette leaves and seeds. Fe accumulated in the rosette leaves, while less Fe was present in flowers and seeds. Leaves, roots, and flowers showed symptoms of Fe deficiency, whereas leaves also showed signs of sufficient Fe supply, as revealed by molecular-physiological analysis. The mutant was not able to fully mobilize Fe to sustain Fe supply of flowers and seeds in the normal way. Thus, nicotianamine is needed for correct supply of seeds with Fe. These results are fundamental for plant manipulation approaches to modify Fe homeostasis regulation through alterations of NAS genes.

The recent interest in fibrillar biological attachment systems, as found in the gecko, has led to the development of micropatterned elastomer adhesion surfaces. All reported studies have been performed at ambient humidity neglecting its possible influence on adhesion. The present paper investigates, for the first time, the effect of systematic changes in ambient humidity from 2 to 90%. Adhesion measurements were performed on PDMS (Sylgard 184) surfaces possessing micropillars with flat-ended and hemispherical contact shape. The pillar radius was varied between 2.5 and 25 µm; the pillar aspect ratio was kept at 1. While the adhesion of a flat sample was not affected by humidity, we found that pillar size and shape influenced the sensitivity to humidity changes: Thinner pillars, with higher pull-off forces in the dry state, exhibited decreasing adhesion values, by up to 35 %, with increasing humidity. The effect was stronger for the hemispherical tip shape, where the positive effect of finer pillars was even reversed. Possible explanations for these effects, which may lower the reliability of biomimetic adhesion devices in the presence of humidity, are given.

We explore the morphology space of nanocomposites prepared from poly(isoprene-block-ethylene oxide) (PI-b-PEO) diblock copolymers as structure directing agents for aluminosilicate nanoparticles prepared from (3-glycidyloxypropyl)trimethoxysilane (GLYMO) and aluminum(III) sec-butoxide. The results of structural investigations of over 60 polymer−inorganic nanocomposites are reported. They are obtained from 12 different block copolymers of varying molecular weight (~10−100 kg/mol) and PEO weight fraction (fw 0.1−0.8) through addition of different amounts of inorganic components. Eight different morphologies as well as composites with biphasic character are observed. Individual block copolymers show up to five different well-defined morphologies upon addition of the inorganic sols. Differential scanning calorimetry (DSC) studies on the composites show that the addition of the inorganic components suppresses PEO crystallization when the inorganic to PEO weight fraction ratio of the composites is greater than 1.3−1.5. The eight phases are mapped out using two- and three-component morphology diagrams.

The recently emerging interest in fibrillar biological attachment systems, as those found in the gecko, has led to the fabrication of micropatterned elastomer adhesion surfaces. Reported studies have demonstrated that measurements on micropatterned surfaces are affected by experimental parameters not relevant for flat samples. The present paper investigates the influence on adhesion values of the sample stiffness, the backing layer thickness, the ambient humidity, and of repetitive measurements at the same location. Measurements were performed on PDMS (Sylgard® 184) micropatterned surfaces possessing flat-ended pillars with 10 µm diameter and 10 µm height. We find that adhesion increased with decreasing sample stiffness and decreasing backing layer thickness, whereas it dropped when several tests were carried out at exactly the same location. For ambient humidities between 2 and 90%, no influence on adhesion performance was found.

The biomimetic reproduction of adhesion organs, as found in flies, beetles and geckoes, has become a topic of intense research over the past years. Successes, however, have so far been limited. This is due to the vast range of parameters involved, including fibril size, elastic modulus, contact shape, surface roughness and ambient humidity. In previous studies, design and materials selection charts to determine the optimum materials and design combination for dry adhesive systems have been established. The effect of shape on the adhesive properties of single fibers and fiber arrays has also been a research focus. In this paper both approaches are combined to provide more advanced guidelines for the design of optimal adhesive structures.

Current semiconductor technology demands the use of compliant substrates for flexible integrated circuits. However, the maximum total strain of such devices is often limited by the extensibility of the metallic components. Although cracking in thin films is extensively studied theoretically, little experimental work has been carried out thus far. Here, we present a systematic study of the cracking behavior of 34 to 506 nm thick Cu films on polyimide with 3.5 to 19 nm-thick Ta interlayers. The film systems have been investigated by a synchrotron-based tensile testing technique and in situ tensile tests in a scanning electron microscope. By relating the energy release during cracking obtained from the stress-strain curves to the crack area, the fracture toughness of the Cu films can be obtained. It increases with Cu film thickness and decreases with increasing Ta film thickness. Films thinner than 70 nm exhibit brittle fracture, indicating an increasing inherent brittleness of the Cu films.

Geckos können sich auf nahezu allen Oberflächen bewegen, egal ob glatt oder rau. Dabei entwickeln sie Haftkräfte, die ein Vielfaches ihres Körpergewichts tragen können. Ihr Haftsystem ist selbstreinigend, rückstandsfrei und nachwachsend. Grund genug, sich dieses einmal genauer anzusehen.

Geckos can adhere to nearly every kind of surface, independent of its chemical properties or roughness. The adhesive force generated is high enough to support their own weight multiple times and allows the gecko to walk upside down. Their adhesion system is self-cleaning, renewable (self healing), and can be removed from a surface without residues. It is these unique properties that have kindled steeply rising research interest over the last decade.