We have re-examined the lysosomal hypothesis of oxidative-stress-induced apoptosis using a new technique for exposing cells in culture to a low steady-state concentration of H2O2. This steady-state technique mimics the situation in vivo better than the bolus-administration method. A key aspect of H2O2-induced apoptosis is that the apoptosis is evident only after several hours, although cells may become committed within a few minutes of exposure to this particular reactive oxygen species. In the present work, we were able to show, for the first time, several correlative links between the triggering effect of H2O2 and the later onset of apoptosis: (i) a short (15min) exposure to H2O2 caused almost immediate, albeit limited, lysosomal rupture; (ii) early lysosomal damage, and later apoptosis, showed a similar dose-related response to H2O2; (iii) both events were inhibited by pre-treatment with iron chelators, including desferrioxamine. This compound is known to be taken up by endocytosis only and thus to become localized in the lysosomal compartment. After exposure to oxidative stress, when cells were again in standard culture conditions, a time-dependent continuous increase in lysosomal rupture was observed, resulting in a considerably lowered number of intact lysosomes in apoptotic cells, whereas non-apoptotic cells from the same batch of oxidative-stress-exposed cells showed mainly intact lysosomes. Taken together, our results reinforce earlier findings and strongly suggest that lysosomal rupture is an early upstream initiating event, and a consequence of intralysosomal iron-catalysed oxidative processes, when apoptosis is induced by oxidative stress.

The present paper studies the flexural behaviour of hand manufactured hybrid laminated composites with a hemp natural fibre/polypropylene core and two glass fibres/polypropylene surface layers at each side of the specimen. When compared with full glass fibres reinforced polypropylene laminates, the hybrid composites have economical, ecological and recycling advantages and also specific fatigue strength benefits. Static and fatigue tests were performed in three point bending for both laminates to evaluate flexural strength properties and fatigue behaviour. Fatigue damage was measured in terms of the stiffness loss. Failure sites and mechanisms were evaluated through microscopy studies and a 3D numerical analysis using finite element method.

Although the germicide role of H2O2 released during inflammation is well established, a hypothetical regulatory function, either promoting or inhibiting inflammation, is still controversial. In particular, after 15 years of highly contradictory results it remains uncertain whether H2O2 by itself activates NF-κB or if it stimulates or inhibits the activation of NF-κB by proinflammatory mediators. We investigated the role of H2O2 in NF-κB activation using, for the first time, a calibrated and controlled method of H2O2 delivery—the steady-state titration—in which cells are exposed to constant, low, and known concentrations of H2O2. This technique contrasts with previously applied techniques, which disrupt cellular redox homeostasis and/or introduce uncertainties in the actual H2O2 concentration to which cells are exposed. In both MCF-7 and HeLa cells, H2O2 at extracellular concentrations up to 25 μM did not induce significantly per se NF-κB translocation to the nucleus, but it stimulated the translocation induced by TNF-α. For higher H2O2 doses this stimulatory role shifts to an inhibition, which may explain published contradictory results. The stimulatory role was confirmed by the observation that 12.5 μM H2O2, a concentration found during inflammation, increased the expression of several proinflammatory NF-κB-dependent genes induced by TNF-α (e.g., IL-8, MCP-1, TLR2, and TNF-α). The same low H2O2 concentration also induced the anti-inflammatory gene coding for heme oxygenase-1 (HO-1) and IL-6. We propose that H2O2 has a fine-tuning regulatory role, comprising both a proinflammatory control loop that increases pathogen removal and an anti-inflammatory control loop, which avoids an exacerbated harmful inflammatory response.

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Selective laser melting has received a great deal of attention in recent years. Nevertheless, research has been mainly focused on the technical issues and their relationship with the final microstructure and monotonic properties. Fatigue behaviour has rarely been addressed, and the emphasis has been placed on high-cycle regimes. The aim of this paper is, therefore, to study, in a systematic manner, the cyclic plastic behaviour of AISI 18Ni300 maraging steel manufactured by selective laser melting. For this purpose, low-cycle fatigue tests, under fully-reversed strain-controlled conditions, with strain amplitudes ranging from 0.3% to 1.0%, were performed. After testing, fracture surfaces were examined by scanning electron microscopy to identify the main fatigue damage mechanisms. The analysis of results showed a non-Masing material, with a slight strain-softening behaviour, and non-linear response in both the elastic and plastic regimes. In addition, this steel exhibited a very low transition life of about 35 reversals, far below the values of conventional materials with equivalent monotonic mechanical properties, which can be attributed to the combination of high strength and low ductility. The total strain energy density, irrespective of strain amplitude, revealed itself to be a quite stable parameter throughout the lifetime. Finally, the SEM analysis showed for almost all the tested samples cracks initiated from the surface and inner defects which propagated through the rest of the cross section. A ductile/brittle fracture, with a predominance of brittle fracture, was observed in the samples, owing to the presence of defects which make it easier to spread the microcracks.

Numerical studies play a major role in the understanding and prediction of plasticity induced crack closure (PICC). However, the available numerical models can be considered simplifications of reality as they consider discrete crack propagations, relatively high fatigue crack growth rates (FCGR), sharp cracks, and propagation occurring at well-defined loads. Besides, there are a great number of numerical and physical parameters affecting the predictions of PICC. The aim of this paper is to discuss the numerical study of PICC. The numerical parameters affecting the accuracy of the numerical simulations, and the dependent parameters used to characterise the plastic wake and the closure level, are identified. The influence of the radial size of crack front elements and crack propagation is analysed. An extrapolation model is proposed, with excellent results. An intrinsic uncertainty is associated with the number of load cycles between crack increments and the definition of crack closure level. Finally, the effect of the stress ratio (R) on crack closure level is analysed.

No abstract

This article presents the results of a current study on the influence of interlayer delaminations on the static and fatigue behavior of composite laminates. The composite was manufactured by a vacuum molding method using 12 balanced bi-directional carbon fiber layers and epoxy resin. Delaminations with different length were artificially introduced. The specimens with dog bone shape were cut from the original plates having 3 mm thickness and fiber weight fraction of 0.66. Static tests were performed in order to study the influence of delamination size on the laminate stiffness and strength. Complementary finite element analysis was carried out showing the influence of angular misalignments of fiber/matrix delaminations on the laminate stiffness. Fatigue tests were performed in load control for R = 0.05 and R = —1, with a loading frequency of 10 Hz, at room temperature. The artificial interlayer delaminations have a negligible influence on the fatigue strength for tensile cycle loadings, but produce significant decreases in strength for R = —1 fatigue loadings.