Gunthard Benecke

Evidence for an elementary process in bone plasticity with an activation enthalpy of 1 eV

The molecular mechanisms for plastic deformation of bone tissue are not well understood. We analysed temperature and strain-rate dependence of the tensile deformation behaviour in fibrolamellar bone, using a technique originally developed for studying plastic deformation in metals. We show that, beyond the elastic regime, bone is highly strain-rate sensitive, with an activation volume of ca 0.6 nm3. We find an activation energy of 1.1 eV associated with the basic step involved in the plastic deformation of bone at the molecular level. This is much higher than the energy of hydrogen bonds, but it is lower than the energy required for breaking covalent bonds inside the collagen fibrils. Based on the magnitude of these quantities, we speculate that disruption of electrostatic bonds between polyelectrolyte molecules in the extrafibrillar matrix of bone, perhaps mediated by polyvalent ions such as calcium, may be the rate-limiting elementary step in bone plasticity.

A customizable software for fast reduction and analysis of large X‐ray scattering data sets: applications of the new DPDAK package to small‐angle X‐ray scattering and grazing‐incidence small‐angle X‐ray scattering

DPDAK is a software for simple and fast on- and offline reduction and analysis of X-ray scattering data. It is an open-source software with a plug-in structure allowing tailored extensions.

Digital image correlation shows localized deformation bands in inelastic loading of fibrolamellar bone

Irreversible or plastic deformation in bone is associated with both permanent plastic strain as well as localized microdamage. Whereas mechanisms at the molecular and mesoscopic level have been proposed to explain aspects of irreversible deformation, a quantitative correlation of mechanical yielding, microstructural deformation, and macroscopic plastic strain does not exist. To address this issue, we developed and applied a two-dimensional image correlation technique to the tensile deformation of bovine fibrolamellar bone, to determine the spatial distribution of strain fields at the length scale of 10 mm to 1 mm in bone during irreversible tensile deformation. We find that tensile deformation is relatively homogeneous in the elastic regime and starts at the yield point, showing regions of locally higher strain. Multiple regions of high deformation can exist at the same time over a length scale of 1 to 10 mm. Macroscopic fracture always occurs at one of the locally highly deformed regions, but the selection of which region cannot be predicted. Locally, strain rates can be enhanced by a factor of 3 to 10 over global strain rates in the highly deformed zones and are lower but always positive in all other regions. Light microscopic imaging shows the onset of structural “banding” in the regions of high deformation, which is most likely correlated to microstructural damage at the inter- and intrafibrillar level.

Influence of nanoparticle surface functionalization on the thermal stability of colloidal polystyrene films.

The installation of large scale colloidal nanoparticle thin films is of great interest in sensor technology or data storage. Often, such devices are operated at elevated temperatures. In the present study, we investigate the effect of heat treatment on the structure of colloidal thin films of polystyrene (PS) nanoparticles in situ by using the combination of grazing incidence small-angle X-ray scattering (GISAXS) and optical ellipsometry. In addition, the samples are investigated with optical microscopy, atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). To install large scale coatings on silicon wafers, spin-coating of colloidal pure PS nanoparticles and carboxylated PS nanoparticles is used. Our results indicate that thermal annealing in the vicinity of the glass transition temperature T(g) of pure PS leads to a rapid loss in the ordering of the nanoparticles in spin-coated films. For carboxylated particles, this loss of order is shifted to a higher temperature, which can be useful for applications at elevated temperatures. Our model assumes a softening of the boundaries between the individual colloidal spheres, leading to strong changes in the nanostructure morphology. While the nanostructure changes drastically, the macroscopic morphology remains unaffected by annealing near T(g).

In Situ Grazing Incidence Small-Angle X-ray Scattering Investigation of Polystyrene Nanoparticle Spray Deposition onto Silicon

We investigated the spray deposition and subsequent self-assembly during drying of a polystyrene nanoparticle dispersion with in situ grazing incidence small-angle X-ray scattering at high time resolution. During the fast deposition of the dispersion and the subsequent evaporation of the solvent, different transient stages of nanoparticle assembly can be identified. In the first stage, the solvent starts to evaporate without ordering of the nanoparticles. During the second stage, large-scale structures imposed by the breakup of the liquid film are observable. In this stage, the solvent evaporates further and nanoparticle ordering starts. In the late third drying stage, the nanoparticles self-assemble into the final layer structure.

Measuring the distribution of cellulose microfibril angles in primary cell walls by small angle X-ray scattering

BackgroundX-ray scattering is a well-established method for measuring cellulose microfibril angles in secondary cell walls. However, little data is available on the much thinner primary cell walls. Here, we show that microfibril orientation distributions can be determined by small angle X-ray scattering (SAXS) even in primary cell walls. The technique offers a number of advantages: samples can be analyzed in the native hydrated state without any preparation which minimizes the risk of artifacts and allows for fast data acquisition. The method provides data averaged over a specimen region, determined by the size of the used X-ray beam and, thus, yields the microfibril orientation distribution within this region.ResultsCellulose microfibril orientation distributions were obtained for single cells of the alga Chara corallina, as well as for the multicellular hypocotyl of Arabidopsis thaliana. In both, Chara and Arabidopsis, distributions with a broad scattering around mean microfibril angles of approximately 0° and 90° towards the longitudinal axis of the cells were found.ConclusionsWith SAXS, the structure of primary cell walls can be analysed in their native state and new insights into the cellulose microfibril orientation of primary cell walls can be gained. The data shows that SAXS can serve as a valuable tool for the analysis of cellulose microfibril orientation in primary cell walls and, in consequence, add to the understanding of its mechanical behaviour and the intriguing mechanisms behind cell growth.

From Atoms to Layers: Gold Cluster Growth Kinetics during Sputter Deposition

The adjustment of the size-dependent catalytic and optoelectronic properties of gold cluster assemblies is a very significant topic in modern applied nanotechnology [1]. For an efficient and controlled production of active nanostructured cluster surfaces, sputter deposition plays an important role [2]. In order to characterize the self-organization during nanocluster film formation, it is mandatory to understand how growth kinetics influences the cluster film morphology during sputter deposition. The first real-time investigations of gold nanocluster growth kinetics into a gold layer are enabled by combining sputter deposition and surface sensitive X-ray scattering (GISAXS). High frame-rate 2D X-ray detectors in combination with the high photon flux of micro beam spot size, available at the PETRA III beamline P03, enables a non-invasive in situ and real-time investigation of gold growth during sputter deposition. With an acquisition throughput of 67 frames per second, we were able to identify 4 different stages of growth including their thresholds with sub-monolayer resolution and concomitant phase transitions. Each stage can be characterized by a predominant surface process and its intrinsic kinetic: nucleation, diffusion, adsorption and grain growth. Moreover we introduced a flexible geometrical model to extract morphological real space parameters, such as cluster size, correlation distance, layer porosity and surface coverage, directly from the reciprocal space scattering data. The model allowed simulating, visualizing and interpreting gold cluster growth kinetics in terms of nanoscopic processes. Furthermore, we were able to deduce wetting angle on the nanoscale and onset of long-range connectivity during the deposition process [3]. This approach is a prerequisite for future investigations of the influence of different process parameters on thin metal film morphology, which is essential for optimization of manufacturing parameters, saving energy and resources.