Mesenchymal stem cell adhesion but not plasticity is affected by high substrate stiffness

The acknowledged ability of synthetic materials to induce cell-specific responses regardless of biological supplies provides tissue engineers with the opportunity to find the appropriate materials and conditions to prepare tissue-targeted scaffolds. Stem and mature cells have been shown to acquire distinct morphologies in vitro and to modify their phenotype when grown on synthetic materials with tunable mechanical properties. The stiffness of the substrate used for cell culture is likely to provide cells with mechanical cues mimicking given physiological or pathological conditions, thus affecting the biological properties of cells. The sensitivity of cells to substrate composition and mechanical properties resides in multiprotein complexes called focal adhesions, whose dynamic modification leads to cytoskeleton remodeling and changes in gene expression. In this study, the remodeling of focal adhesions in human mesenchymal stem cells in response to substrate stiffness was followed in the first phases of cell–matrix interaction, using poly-ε-caprolactone planar films with similar chemical composition and different elasticity. As compared to mature dermal fibroblasts, mesenchymal stem cells showed a specific response to substrate stiffness, in terms of adhesion, as a result of differential focal adhesion assembly, while their multipotency as a bulk was not significantly affected by matrix compliance. Given the sensitivity of stem cells to matrix mechanics, the mechanobiology of such cells requires further investigations before preparing tissue-specific scaffolds.     

Dynamics of two coupled generators with a delay

The interaction of two coupled generators with a delay is investigated. Each of the generators contains an inertial element. The operation of the system is considered in the case when the subsystems have asymmetric characteristics. It is shown that, in this case, the coupled system can operate in chaotic modes with a small delay when only regular oscillations are excited autonomously. Results of the numerical analysis of an original scenario of motion chaotization developing in the presence of a small delay are presented. Chaotic mutual synchronization in the coupled system is considered in the case when the delay in the feedback loops of the partial generators is large.     

Simulation-Based Performance Prediction for Large Parallel Machines

We present a performance prediction environment for large scale computers such as the Blue Gene machine. It consists of a parallel simulator, BigSim, for predicting performance of machines with a very large number of processors, and BigNetSim, which incorporates a pluggable module of a detailed contention-based network model. The simulators provide the ability to make performance predictions for very large machines such as Blue Gene/L. We illustrate the utility of our simulators using validation and prediction studies of several applications using smaller numbers of processors for simulations.     

A new type of nanostructure in Si/C composite electrodes for lithium-ion batteries

The composition and structure of thin-film Si/C composite anodes produced by alternately depositing controlled amounts of silicon and carbon using magnetron plasma sputtering have been determined by atomic force microscopy, x-ray diffraction, and optical spectroscopy (Raman and UV through IR specular reflectance spectra). The silicon-to-carbon volume ratio in the films was varied from 39.5: 60.5 to 87: 13, and their thickness ranged from 100 to 480 nm. The surface of the films was found to have a nanogranular structure, which had not been reported previously for Si/C composites. This morphology is atypical of structureless silicon layers deposited under the same conditions but is similar to the nanostructure of a thin carbon film consisting of grains uniform in shape and size (D _av = 20–25 nm). Reducing the carbon content of the composites from 60 to 36% increases the grain size from 25 to 45–50 nm. At high silicon contents (near 80%), the nanostructure of the composites is less homogeneous: in addition to nanograins, there are structureless silicon zones. The homogeneity of the nanostructure depends on the Si: C ratio and the sequence and thicknesses of the deposited Si and C layers. Thin (104–173 nm) films containing more than 30% carbon (they have isolated silicon clusters) reveal the highest activity for the lithium intercalation-deintercalation process. Their Raman spectra show strong luminescence characteristic of silicon nanoparticles less than 5–6 nm in size. This effect is missing in the thicker films, in which the silicon forms an infinite cluster and which have a stronger tendency to degrade.     

Health Council Report 'Radiofrequency electromagnetic fields (300 Hz-300 GHz). The Health Council of the Netherlands

The Health Council of the Netherlands in 1997 issued a report updating the guidelines for maximum acceptable exposure to radiofrequency electromagnetic fields formulated in 1975. The new recommendations are based on thermal effects for frequencies over 10 MHz. The committee considers the results of studies indicating non-thermal effects such as direct damage to DNA, not reliable enough to be used in setting exposure limits. Electromagnetic interference by electromagnetic fields generated by hand-held telephones may indirectly result in threats to health if vital medical equipment is affected. The committee advises people wearing an implanted pacemaker not to carry a portable telephone that is in stand-by mode in close proximity to the pacemaker; a minimum distance of 15 cm should be observed.     

Paracrine PDGF-B/PDGF-Rbeta signaling controls mesangial cell development in kidney glomeruli

Kidney glomerulus mesangial cells fail to develop in mice carrying targeted null mutations in the platelet-derived growth factor (PDGF)-B or PDGF-Rbeta genes. We have examined the pattern of expression of these genes and smooth muscle markers during kidney development, to address the possible mechanisms underlying the mutant phenotypes. In wild-type embryos, PDGF-B was expressed in vascular endothelial cells, particularly in capillary endothelial cells in the developing glomeruli, whereas PDGF-Rbeta was found in perivascular mesenchymal cells in the developing renal cortex. In the course of glomerular development, small groups of PDGF-Rbeta and desmin-expressing cells collected in the 'S'-shaped and early cup-shaped vesicles, and at later stages such cells were found in the glomerular mesangium. In PDGF-B or -Rbeta null embryos, some PDGF-Rbeta/desmin or desmin-positive cells, respectively, were seen in early cup-shaped vesicles, but fewer than in the wild type, and further development of the mesangium failed. In mouse chimeras composed of PDGF-Rbeta +/+ and -/- cells, the Rbeta-/- cells failed to populate the glomerular mesangium. Our results show that while the mesangial cell lineage is specified independently of PDGF-B/Rbeta, these molecules provide critical permissive signals in mesangial cell development. We propose a model in which mesangial cells originate from PDGF-Rbeta-positive progenitors surrounding the developing glomerular afferent and efferent arterioles, and are co-recruited in response to PDGF-B during angiogenic formation of the glomerular capillary tuft.     

Controlled chaos in an oscillator with additional oscillatory circuit

A system comprising the classical van der Pol oscillator coupled with an additional oscillator circuit is considered in the presence of an algorithm ensuring chaotization of the self-sustained oscillations. A mathematical model of the system is described and the results of numerical analysis illustrating the new method of chaotizing coupling are presented.     

Chaotization of mitron oscillations

The possibility of obtaining chaotic oscillations in a mitron (voltage-tuned magnetron) is considered and illustrated by experimental results. It is shown that a mitron is capable of operating in a chaotic regime characterized by a scenario of transition to chaos via period-doubling (flip) bifurcations.     

Real-time detection of allele-specific polymerase chain reaction products by automated ultra-thin-layer agarose gel electrophoresis

Ultra-thin-layer agarose gel electrophoresis, a novel combination of agarose slab gel electrophoresis and capillary gel electrophoresis was introduced in conjunction with laser-induced fluorescence (LIF) scanning detection for the analysis of polymerase chain reaction (PCR) products. Allele-specific fragments, amplified from genomic DNA of patients with congenital adrenal hyperplasia (most often caused by mutations of 21-hydroxylase gene, CYP-21), were used as a model system to investigate the applicability, sensitivity and resolving power of the method. The allele-specific products were generated by PCR and separated by ultra-thin-layer agarose gel electrophoresis. The double-stranded DNA fragments were easily visualized in real-time via complexation during the separation process by the intercalator dye TO-PRO-3 which was part of the separation gel-buffer system. In this way, the migrating dsDNA-dye complexes were detected in real-time by a scanning LIF detection system with sub-nanogram sensitivity. The system employs a 632-nm solid-state laser and an avalanche photodiode detector scanning to the separation platform by means of a fiber bundle system. Automated ultra-thin-layer agarose gel electrophoresis with 'on the fly' TO-PRO-3 staining of dsDNA fragments and LIF detection system proved to be a very fast, high-throughput separation method for individual or multiplexed PCR products, with excellent sensitivity.     

Chaotic attractors formed using bistable systems

A new method of nonautonomous excitation of chaotic oscillations is proposed which makes use of bistable systems. The formation of an original chaotic attractor in a bistable system, representing decaying motions between two basins of attraction, is demonstrated by numerical methods.