Publikationen

Cell responses to surface and contact cell guidance are of great interest in bio-applications especially on nano- and micro scale features. Recently we showed selective cell responses on Al/Al2O3 bi-phasic nanowires (NWs). In this context, Al/Al2O3 NWs were synthesized by the chemical vapor deposition of (tBuOAlH2)2. Afterwards, linear periodic nano- and micro structured NWs were formed using laser interference lithography (LIL) technique to study the contact guidance of neurons from rat dorsal root ganglion (DRG), human umbilical vein smooth muscle cells (HUVSMC), human umbilical vein endothelial cells (HUVEC) and human osteoblast (HOB). LIL treatment did not alter surface chemistry of NWs. From our preliminary research LIL patterned NWs lead to alignment of axons contrary to non-patterned NWs. Morphology of HUVSMC changed from poly- to linear shapes and strong alignment was observed while HUVEC and HOB were not affected.

A novel approach to tracking intercalation-induced phase transitions in Li-ion battery materials demonstrated herein consists of simultaneous analysis of intercalation charge and the accompanying mechanical (geometric) changes in a microarray electrode composed of LixFePO4 intercalation particles probed by the electrochemical quartz-crystal admittance (EQCA) method. A recently elaborated approach to population dynamics of active (phase-transforming) nanoparticles has been used here for modeling current transients applying small potential steps to LixFePO4 electrodes. The number fraction of (phase) transformed particles thus calculated was directly compared with the changes in the effective thickness and permeability length of the electrode coating derived by EQCA. Geometric changes of thin active mass originating from different molar volumes of the parent and transformed phase result in nonuniform deformations of intercalation particles. This study confirms the collective behavior of LixFePO4 intercalation particles during electrochemically induced phase transition. The use of EQCA as a highly precise and sensitive probe of mass and geometric changes in the electrode layer of intercalation particles paves the way for dynamic in situ studies of nonuniform intercalation particles deformations which can hardly be assessed by other available techniques.

By decomposing a molecular precursor we fabricated a novel surface based on an aluminium/ aluminiumoxide composite incorporating nanotopography gradient to address high-throughput and fast analysis method for studying stem cell differentiation by nanostructures. Depending on the topography of the nanostructures, mesenchymal stem cells exhibit a diverse proliferation and differentiation behavior.

For a detailed analysis of the biological effects of silver nanoparticles, discrimination between effects related to the nano-scale size of the particles and effects of released silver ions is required. Silver ions are either present in the initial particle dispersion or released by the nanoparticles over time. The aim of this study is to monitor the free silver ion activity {Ag+} in the presence of silver nanoparticles using a silver ion selective electrode. Therefore, silver in the form of silver nanoparticles, 4.2 ± 1.4 nm and 2-30 nm in size, or silver nitrate was added to cell culture media in the absence or presence of A549 cells as a model for human type II alveolar epithelial cells. The free silver ion activity measured after the addition of silver nanoparticles was determined by the initial ionic silver content. The p {Ag+} values indicated that the cell culture media decrease the free silver ion activity due to binding of silver ions by constituents of the media. In the presence of A549 cells, the free silver ion activity was further reduced. The morphology of A549 cells, cultivated in DME medium containing 9.1% (v/v) FBS, was affected by adding AgNO3 at concentrations of ≥30 μM after 24 h. In comparison, silver nanoparticles up to a concentration of 200 μM Ag did not affect cellular morphology. Our experiments indicate that the effect of silver nanoparticles is mainly mediated by silver ions. An effect of silver on cellular morphology was observed at p {Ag+} ≤ 9.2.

Hochauflösungs-TEM/STEM spektroskopiert und bildet Strukturen atomar aufgelöst ab. Mit einer Mikrofluid-Probenkammer eignet sich das Elektronenmikroskop auch für In-situ-Untersuchungen zu lebens- und materialwissenschaftlichen Fragen.

BACKGROUND: Mollusc shells are commonly investigated using high-resolution imaging techniques based on cryo-fixation. Less detailed information is available regarding the light-optical properties. Sea shells of Haliotis pulcherina were embedded for polishing in defined orientations in order to investigate the interface between prismatic calcite and nacreous aragonite by standard materialographic methods. A polished thin section of the interface was prepared with a defined thickness of 60 µm for quantitative birefringence analysis using polarized light and LC-PolScope microscopy. Scanning electron microscopy images were obtained for comparison. In order to study structural-mechanical relationships, nanoindentation experiments were performed.RESULTS:Incident light microscopy revealed a super-structure in semi-transparent regions of the polished cross-section under a defined angle. This super-structure is not visible in transmitted birefringence analysis due to the blurred polarization of small nacre platelets and numerous organic interfaces. The relative orientation and homogeneity of calcite prisms was directly identified, some of them with their optical axes exactly normal to the imaging plane. Co-oriented "prism colonies" were identified by polarized light analyses. The nacreous super-structure was also visualized by secondary electron imaging under defined angles. The domains of the super-structure were interpreted to consist of crystallographically aligned platelet stacks. Nanoindentation experiments showed that mechanical properties changed with the same periodicity as the domain size.CONCLUSIONS:In this study, we have demonstrated that insights into the growth mechanisms of nacre can be obtained by conventional light-optical methods. For example, we observed super-structures formed by co-oriented nacre platelets as previously identified using X-ray Photo-electron Emission Microscopy (X-PEEM) [Gilbert et al., Journal of the American Chemical Society 2008, 130:17519–17527]. Polarized optical microscopy revealed unprecedented super-structures in the calcitic shell part. This bears, in principle, the potential for in vivo studies, which might be useful for investigating the growth modes of nacre and other shell types.

We analyze theoretically the moment of inertia of the desert ant Cataglyphis (C. bicolor and C. fortis) around a vertical axis through its own center of mass when the animal raises its gaster to a vertical position. Compared to the value when the gaster is horizontal, the moment of inertia is reduced to one half; this implies that when increasing its angular acceleration the ant need apply only half the level of torque when the gaster is raised, compared to when the gaster is lowered. As an example, we analyze the cases of an ant running on circular and sinusoidal paths. In both cases, the ant must apply a sideways thrust, anti-roll and anti-pitch torques to avoid toppling, and, on the circular path when accelerating and throughout the sinusoidal trajectory, a torque to enable turning as the path curves. When the ant is accelerating in a very tight circle or running on a very narrow sinusoidal path, in which the amplitude of the sinusoid is less than the length of the ant's body, the forces required for the turning torque can equal and exceed those required for the sideways thrust, and can be reduced significantly by the ant raising the gaster, whereas the foot-thrust for the anti-roll and anti-pitch torques rises only modestly when the gaster is up. This suggests that there may be an evolutionary advantage for employing the gaster-raising mode of locomotion, since this habit will allow desert ants to use lower forces and less energy, and perhaps run faster on more tortuous paths.

Localization and intracellular migration of 32 and 83 nm SiO2 nanoparticles in relation to the nucleus was evaluated in vitro on undifferentiated human colon carcinoma (Caco-2) cells. The fluorescence dye Atto647N was incorporated into the particles, which enabled detection by high resolution, nondiffraction limited stimulated emission depletion (STED) microscopy. The distribution and agglomeration of nanoparticles was measured with STED microscopy after 5, 24, 48, and 72 h. Analyses revealed that only 32 nm silica particles penetrated into the nucleus of Caco-2 cells upon exposure for 24 h. Here, they formed agglomerates up to 300 nm after 72 h of incubation. Quantitative evaluation of the migration of 32 nm compared to 83 nm particles demonstrated that 32 nm particles obviously migrated faster into and through the cell in the beginning (5 h time point). The presence and agglomeration inside the cells and the penetration into the nucleus were considered to potentially activate cytotoxic responses. Therefore, the cytotoxic (WST-1 assay) and genotoxic (comet assay) effects of the silica nanoparticles were evaluated. Even though 32 nm silica particles are penetrating into the nucleus, neither cytotoxic nor genotoxic effects were detected for either particle size.

We describe here a chemically controlled pathway for the designed synthesis of iron oxide nanoparticles by thermal decomposition of iron(II) and iron(III) oxalates in high-boiling solvents in the presence of oleylamine and oleic acid acting as capping ligands. The phase composition of the nanocrystals (Fe, FeO, Fe3O4, or α-Fe2O3) could be precisely controlled by adjusting the synthesis conditions or by addition of appropriate oxidants, such as trimethylamine-N-oxide (TMAO), which produced highly monodisperse iron(III) oxide particles in the range of 6-25 nm in good yields. The decomposition behavior of different precursor/TMAO mixtures was elucidated by differential scanning calorimetry and thermogravimetry, and resulting particles were characterized by comprehensive HR-TEM and XRD analyses.

Colloidal particles are continuously assembled into crystalline particle coatings using convective fluid flows. Assembly takes place inside a meniscus on a wetting reservoir. The shape of the meniscus defines the profile of the convective flow and the motion of the particles. We use optical interference microscopy, particle image velocimetry and particle tracking to analyze the particles? trajectory from the liquid reservoir to the film growth front and inside the deposited film as a function of temperature. Our results indicate a transition from assembly at a static film growth front at high deposition temperatures to assembly in a precursor film with high particle mobility at low deposition temperatures. A simple model that compares the convective drag on the particles to the thermal agitation explains this behavior. Convective assembly mechanisms exhibit a pronounced temperature dependency and require a temperature that provides sufficient evaporation. Capillary mechanisms are nearly temperature independent and govern assembly at lower temperatures. The model fits the experimental data with temperature and particle size as variable parameters and allows prediction of the transition temperatures. While the two mechanisms are markedly different, dried particle films from both assembly regimes exhibit hexagonal particle packings. We show that films assembled by convective mechanisms exhibit greater regularity than those assembled by capillary mechanisms.