Scientific publications

This work reports an in vivo approach for identifying the function of biomineralization-related proteins. Synthetic sequences of n16N, OC-17 and perlucin with signal peptides are produced in a novel Gateway expression system for Dictyostelium under the control of the [ecmB] promoter. A fast and easy scanning electron microscopic screening method was used to differentiate on the colony level between interplay effects of the proteins expressed in the extracellular matrix (ECM). Transformed Dictyostelium, which migrated as multicellular colonies on calcite crystals and left their ECM remnants on the surface were investigated by scanning electron microscopy. Calcium minerals with and without phosphorous accumulated very frequently within the matrix of the Dictyostelium colonies when grown on calcite. Magnesium containing phosphorous granules were observed when colonies were exposed on silica. The absence of calcium EDX signals in these cases suggests that the external calcite crystals but not living cells represent the major source of calcium in the ECM. Several features of the system provide first evidence that each protein influences the properties of the matrix in a characteristic mode. Colonies transformed with perlucin produced a matrix with cracks on the length scale of a few microns throughout the matrix patch. For colonies with OC-17, almost no cracks were observed, regardless of the length scale. The non-transformed Dictyostelium (Ax3-Orf+) produced larger cracks. The strategy presented here develops the first step towards an efficient eukaryotic screening system for the combinatorial functionalization of materials by bioengineering in close analogy to natural biomineralization concepts.

This paper reports a rapid HILIC-ESI–MS assay to quantify dipalmitoylphosphatidylcholine (DPPC) as component of lung surfactant for nanosafety studies. The technique was used to investigate the concentration-dependent sorption of DPPC to two-sizes of amorphous SiO2 nanoparticles (SiO2-NPs) in a MeOH:H2O (50/50 v/v) mixture and in cell culture medium. In MeOH:H2O (50/50 v/v), the sorption of DPPC was positively correlated with the nanoparticles concentration. A substantial affinity of small amorphous SiO2-NPs (25 nm) to DPPC standard solution compared to bigger SiO2-NPs (75 nm) was not confirmed for biological specimens. After dispersion of SiO2-NPs in DPPC containing cell culture medium, the capacity of the SiO2-NPs to bind DPPC was reduced in comparison to a mixture of MeOH:H2O (50/50 v/v) regardless from the nanoparticles size. Furthermore, HILIC-ESI–MS revealed that A549 cells internalized DPPC during growth in serum containing medium complemented with DPPC. This finding was in a good agreement with the potential of alveolar type II cells to recycle surfactant components. Binding of lipids present in the cell culture medium to amorphous SiO2-NPs was supported by means of HILIC-ESI–MS, TEM and ICP-MS independently.

In this study, we report p-coumaric acid as novel and effective response marker for indirectly measuring the levels of hypoxia in normal primary bronchial epithelial cells. We developed a simple and rapid technique based on hydrophilic interaction chromatography-electrospray ionization-mass spectrometry (HILIC-ESI–MS). During 168 h of hypoxia without induction of reactive oxygen species (ROS), an almost linear increase of p-coumaric acid levels was observed. We interpret the increasing p-coumaric acid concentrations during hypoxia as a result of cell damage, triggered by reduced co-enzyme Q10 levels, because the oxidative cascade was not able to supply sufficient energy. The HILIC-ESI–MS assay within p-coumaric acid exhibited a linear dynamic range from 60 to 610 ng/μL with correlation coefficient of 0.9998. The precision of the assay was ≤15% RSD and method accuracies between 97 and 108%.

In this study, a simple, rapid and inexpensive approach for the screening of heavy metals with photometric reagents was developed based on porous, anodic aluminium oxide (AAO) films, with detection limits of 0.45 mg L-1 (Co2+), 0.25 mg L-1 (Pb2+) and 0.59 mg L-1 (Ni2+). Noble metal ions Ag+ and Pd2+, as well as Cu2+, formed nanoparticles within the AAO channels during micro-solid phase extraction driven by galvanic electroless displacement followed by UV detection.

We report a simple fast, practical and effective method for the replication of the complex venation patterns of natural leaves into PDMS with accuracy down to a lateral size of 500 nm. Optimising the amount of crosslinker enabled the replication and sealing of the microvascular structures to yield enclosed microfluidic networks. The use of plant leaves as templates for soft lithography was demonstrated across over ten species and included reticulate, arcuate, pinnate, parallel and palmate venation patterns. SEM imaging revealed replication of the plants microscopic and sub-microscopic topography into the PDMS structures, making this method especially attractive for mimicking biological structures for in vitro assays. Flow analysis revealed that the autonomous liquid transport velocity in 1st-order microchannel was 1.5-2.2 times faster than that in the 2nd-order microchannels across three leaf types, with the sorptivity rule surprisingly preserved during self-powered flow through leaf-inspired vascularity from Carpinus betulus.

Anisotrope Partikel sind eine Materialklasse, die es erlaubt, multifunktionelle Eigenschaften in einen partikulär aufgebauten Festkörper zu induzieren. Dadurch können unterschiedliche Funktionen in ein und dasselbe Partikel eingebaut werden, beispielsweise unterschiedliche Polaritäten oder magnetische und optische Eigenschaften. Durch ihre außergewöhnliche Struktur, mit zwei unterschiedlichen Kompartimenten an der Oberfläche, erhielt diese Partikelart den Namen Janus-Partikel. Für die Chemie besteht die Herausforderung in der Synthese solcher Partikel. Es muss dafür gesorgt werden, dass die Reaktionsräume auf der Längenskala der Partikel so differenziert werden, dass es zu einer Anisotropie von Wachstums- oder Funktionalisierungsprozessen kommt. Hierbei spielen insbesondere Reaktionen an Phasengrenzen eine wichtige Rolle. Mittlerweile ist eine Vielzahl an unterschiedlichen Janus-Materialkombinationen bekannt und die ersten Systeme werden in technologischen Anwendungen verwendet.
Anisotropic particles are a materials class, which allows to induce multifunctional properties in a particular solid. This approach presents the possibility that different functions are packed in one particle, for example different surface polarities or optical and magnetic properties. The extraordinary structure of this particle consisting of two different compartments is expressed by the name Janus-Particles. The chemical challenge is the synthetic approach to such particle structures. The reaction rooms on the length scale of the particle have to be differentiated in such a way that an anisotropy of growth and functionalization processes is generated. In this regard reactions at interphases play a major role. Meanwhile many different Janus-material combinations are established and the first systems are transferred to technological processes.

Classical hydrodynamic models predict that infinite work is required to move a three-phase contact line, defined here as the line where a liquid/vapor interface intersects a solid surface. Assuming a slip boundary condition, in which the liquid slides against the solid, such an unphysical prediction is avoided. In this article, we present the results of experiments in which a contact line moves and where slip is a dominating and controllable factor. Spherical cap-shaped polystyrene microdroplets, with nonequilibrium contact angle, are placed on solid self-assembled monolayer coatings from which they dewet. The relaxation is monitored using in situ atomic force microscopy. We find that slip has a strong influence on the droplet evolutions, both on the transient nonspherical shapes and contact line dynamics. The observations are in agreement with scaling analysis and boundary element numerical integration of the governing Stokes equations, including a Navier slip boundary condition.

We study the effect of long-term habituation signatures of auditory selective attention reflected in the instantaneous phase information of the auditory event-related potentials (ERPs) at four distinct stimuli levels of 60, 70, 80, and 90 dB SPL. The analysis is based on the single-trial level. The effect of habituation can be observed in terms of the changes (jitter) in the instantaneous phase information of ERPs. In particular, the absence of habituation is correlated with a consistently high phase synchronization over ERP trials. We estimate the changes in phase concentration over trials using a Bayesian approach, in which the phase is modeled as being drawn from a von Mises distribution with a concentration parameter which varies smoothly over trials. The smoothness assumption reflects the fact that habituation is a gradual process. We differentiate between different stimuli based on the relative changes and absolute values of the estimated concentration parameter using the proposed Bayesian model.

The extraordinary adherence and climbing agility of geckos on rough surfaces has been attributed to the multiscale hierarchical structures on their feet. Hundreds of thousands of elastic hairs called setae , each of which split into several spatulae , create a large number of contact points that generate substantial adhesion through van der Waals interactions. The hierarchical architecture provides increased structural compliance on surfaces with roughness features ranging from micrometers to millimeters. We review synthetic adhesion surfaces that mimic the naturally occurring hierarchy with an emphasis on microfabrication strategies, material choice and the adhesive performance achieved.

Bio-inspired adhesion of micropatterned surfaces due to intermolecular interactions has attracted much research interest over the last decade. Experiments show that the best adhesion is achieved with compliant "mushroom"-shaped fibrils. This paper analyses numerically the effects of different mushroom shapes on adhesion to a rigid substrate. When a remote stress is applied on the free end of a fibril perfectly bonded to a rigid substrate, the resultant stress distribution along the fibril is found to change dramatically between the straight punch and mushroom fibrils. A singular stress field is present at the edge of the fibril where it contacts the substrate and, in this work, the amplitude of the singularity is evaluated for fibrils perfectly bonded to a flat substrate so that sliding cannot occur there. This exercise is carried out for fibril geometries involving combinations of different diameters and thicknesses of the mushroom cap. By assuming a pre-existing detachment length at the corner where the stress singularity lies, we predict the adhesive strength for various mushroom cap shapes. Our study shows that a smaller stalk diameter and a thinner mushroom cap lead to higher adhesive strengths. A limited number of results are also given for other shapes, including those having a fillet radius connecting the stalk to the cap. The results support the rational optimisation of synthetic micropatterned adhesives.