Micro- and nanostructured Al2O3 surfaces for controlled vascular endothelial and smooth muscle cell adhesion and proliferation

The effect of the micro- and nanotopography on vascular cell-surface interaction is investigated using nano- and microstructured Al₂O₃ as model substrate. Two different nanostructured Al₂O₃ surfaces composed of low density (LD) and high density (HD) nanowires (NWs) were synthesized by chemical vapour deposition (CVD) and commercially available microstructured Al₂O₃ plates were used for comparison. A clear diverging response of human umbilical vein endothelial cells (HUVEC) and human umbilical vein smooth muscle cells (HUVSMC) was observed on these nano- and microstructured surfaces. LD Al₂O₃ NWs seem to enhance the proliferation of HUVECs selectively. This selective control of the cell-surface interaction by topography may represent a key issue for the future stent material design.     

Fracture Mechanics: A Tool for Evaluating Structural Adhesives

Some of the basic concepts of fracture mechanics are reviewed, emphasizing those aspects of the discipline that are applicable to the evaluation of structural adhesives.

Test methods for measuring both the plane strain fracture toughness of joints, i.e. G_ic, and the resistance of joints to crack extension in the presence of an aggressive environment, i.e. G_iscc, are also described.     

Wood‐Plastic‐Composites: Rheologische Charakterisierung und Füllverhalten im Spritzgießprozess

Wood‐plastic composites (WPC) show a complex and completely different material and flow behavior in comparison to pure polymers. Especially the flow behavior is very important for the processing of these composites. In the following article results of rheological characterization and investigations of the filling behavior during the injection molding process are presented. Furthermore, appearing challenges and possible methods of resolution are discussed.     

A mixed-mode crack analysis of rectilinear anisotropic solids using conservation laws of elasticity

A very simple and convenient method of analysis for studying two-dimensional mixed-mode crack problems in rectilinear anisotropic solids is presented. The analysis is formulated on the basis of conservation laws of anisotropic elasticity and of fundamental relationships in anisotropic fracture mechanics. The problem is reduced to a system of linear algebraic equations in mixed-mode stress intensity factors. One of the salient features of the present approach is that it can determine directly the mixed-mode stress intensity solutions from the conservation integrals evaluated along a path removed from the crack-tip region without the need of solving the corresponding complex near-field boundary value problem. Several examples with solutions available in the literature are solved to ensure the accuracy of the current analysis. This method is further demonstrated to be superior to other approaches in its numerical simplicity and computational efficiency. Solutions of more complicated and practical engineering problems dealing with the crack emanating from a circular hole in composites are presented also to illustrate the capacity of this method.

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Résumé On présente une méthode d'analyse simple et bien adaptée à l'étude de problèmes de fissuration bidimensionnelle de mode mixte dans des solides rectilinéaires anisotropes. L'analyse est formulée sur la base des lois de conservation de l'élasticité anisotrope et sur les relations fondamentales dans la mécanique de rupture anisotrope. Le problème est ramené à un système d'équations algébriques linéaires exprimant les facteurs d'intensité d'entaille pour un mode mixte. L'un des faits saillants de l'approche envisagée est qu'elle peut déterminer directement les solutions d'intensité de contrainte suivant un mode mixte à partir des intégrales de conservation évaluées le long d'un parcours éloigné par rapport à l'extrémité de la fissure, sans qu'il soit nécessaire de résoudre le problème correspondant de la valeur du champ proche complexe. Divers exemples, ainsi que des solutions disponibles dans la littérature, sont résolus et confrontés en vue de tester la fiabilité de l'analyse réalisée. La méthode s'avère supérieure aux autres approches de par sa simplicité numérique et son efficacité de calcul. Des solutions à des problèmes plus compliqués et pratiques rencontrés en ingénièrie où une fissure émane d'un trou circulaire dans des matières composites sont également présentées, en vue d'illustrer les capacités de cette méthode.

     

Functional Coupling of Slack Channels and P2X3 Receptors Contributes to Neuropathic Pain Processing

The sodium-activated potassium channel Slack (K_Na1.1, Slo2.2, or Kcnt1) is highly expressed in populations of sensory neurons, where it mediates the sodium-activated potassium current (I_KNa) and modulates neuronal activity. Previous studies suggest that Slack is involved in the processing of neuropathic pain. However, mechanisms underlying the regulation of Slack activity in this context are poorly understood. Using whole-cell patch-clamp recordings we found that Slack-mediated I_KNa in sensory neurons of mice is reduced after peripheral nerve injury, thereby contributing to neuropathic pain hypersensitivity. Interestingly, Slack is closely associated with ATP-sensitive P2X3 receptors in a population of sensory neurons. In vitro experiments revealed that Slack-mediated I_KNa may be bidirectionally modulated in response to P2X3 activation. Moreover, mice lacking Slack show altered nocifensive responses to P2X3 stimulation. Our study identifies P2X3/Slack signaling as a mechanism contributing to hypersensitivity after peripheral nerve injury and proposes a potential novel strategy for treatment of neuropathic pain.     

Testing methods for determination of fracture toughness of metals

The determination of the fracture toughness properties of pressure vessel materials is of increasing importance in reducing the risk of low stress fracture. This paper reviews the present status of testing methods and indicates their ranges of application.     

Thermoplastic Polyurethane Elastomers with Aliphatic Hard Segments Based on Plant‐Oil‐Derived Long‐Chain Diisocyanates

Novel plant‐oil‐derived long‐chain (C₁₉ and C₂₃) α,ω‐diisocyanates, optionally in combination with the corresponding long‐chain diols, provide entirely aliphatic hard segments in segmented thermoplastic polyurethane elastomers (TPUs), with carbohydrate‐based poly(trimethylene glycol) soft segments. Compared to materials based on a mid‐chain monomer analog, phase separation is higher due to an increased flexibility of the aliphatic segments. Although melting points are slightly lower than for HDPE, the long‐chain TPU's solid‐state structure is still dominated by hydrogen‐bonding.     

Overview: Fracture Control of Adhesively Bonded Components

In recent years increased use of adhesive joining has occurred because improved adhesives have become available and adhesive joining is ideally suited for many highly stressed lightweight structures. Notable among the ideally suited applications are panels and components employing honeycomb-skin construction and high performance fibrous composites.