Elastic Extension Research Articles

Mechanism of formation of functional components of diving suit cover with increased protective properties

This article presents the results of a questionnaire survey of specialists regarding the formation of components of diving suit packages to ensure the reliability of equipment and life safety when carrying out deep-sea diving for maintenance in hydraulic structures. The purpose of these studies was to identify the main indicators that require priority research items when creating a new diving suit with increased protective properties. 50 diving service specialists took part in the survey. The survey results were processed using standard methods. According to experts, the most significant are X4 - material structure, porosity and thickness considerations, X8 - strength and waterproofness of connecting seams, X3 - elasticity (extensibility) and X5 - wear resistance with a concordance coefficient ω=0.79>0.6 showing sufficient agreement between expert opinions. The results obtained revealed the priority areas of research for the development of a special diving suit that ensures maximum safety for a diver in deep-sea professional conditions.

Peridynamic correspondence model with strain gradient elasticity for microstructure dependent size effects

This study presents a peridynamic (PD) correspondence model with strain gradient elasticity (SGE) to capture size effect on strength of nano- and micro-scale structures. The classical elasticity theory lacking a length scale parameter does not account for the microstructure-dependent size effects. Strain Gradient (SG) elasticity is an extension of the classical elasticity with a length scale parameter(s) which can be linked to the microstructure of the material. Peridynamic theory introduces damage into the constitutive relations in a natural way by allowing for interactions of a material point within its horizon which is referred to as the internal length parameter. The correspondence model of the PD theory permits the incorporation of the constitutive relationship of SG theory. Therefore, the present approach combines the effects of PD and SGE length scale parameters on the stiffness and strength of the material. The resulting equations present two length parameters: the horizon of a material point in PD theory and the characteristic length in SGE theory. The PD equation of motion with SGE (PDSG) is free of spatial derivatives and allows for the imposition of classical and nonclassical boundary conditions. The PDSG is first applied to investigate the deformation response of a one-dimensional nanoscale film subjected to a quasi-static tensile load and a dynamic load through an initial constant strain. The static response is compared with the analytical solution for varying ratio of SG length parameter to PD horizon. The dynamic response is compared with a computational solution while satisfying the nonclassical boundary conditions. Subsequently, the PDSG is applied to study the deformation response of a two-dimensional nanoscale film subjected to a quasi-static axial load and a specified tangential end displacement. These two cases are considered under special displacement constraints to compare with the available analytical solutions. Subsequently, a two-dimensional nanoscale film with or without an internal crack is subjected to uniform tensile loading. Finally, crack propagation is simulated under incremental displacement loading. The results capture the analytical predictions and the expected increase in stiffness with increasing ratio of SG length parameter to PD horizon.

The fluid dynamics of a viscoelastic fluid dripping onto a substrate.

Extensional flows of complex fluids play an important role in many industrial applications, such as spraying and atomisation, as well as microfluidic-based drop deposition. The dripping-on-substrate (DoS) technique is a conceptually-simple, but dynamically-complex, probe of the extensional rheology of low-viscosity, non-Newtonian fluids. It incorporates the capillary-driven thinning of a liquid bridge, produced by a single drop as it is slowly dispensed from a syringe pump onto a solid partially-wetting substrate. By following the filament thinning and pinch-off process the extensional viscosity and relaxation time of the sample can be determined. Importantly, DoS allows experimentalists to measure the extensional properties of lower viscosity solutions than is possible with commercially available capillary break-up extensional rheometers. Understanding the fluid mechanics behind the operation of DoS will enable users to optimise and extend the performance of this protocol. To achieve this understanding, we employ a computational rheology approach, using adaptively-refined time-dependent axisymmetric numerical simulations with the open-source Eulerian code, Basilisk. The volume-of-fluid technique is used to capture the moving interface, and the log-conformation transformation enables a stable and accurate solution of the viscoelastic constitutive equation. Here, we focus on understanding the roles of surface tension, elasticity and finite chain extensibility in controlling the elasto-capillary (EC) regime, as well as the perturbative effects that gravity and substrate wettability play in setting the evolution of the self-similar thinning and pinch-off dynamics. To illustrate the interplay of these different forces, we construct a simple one-dimensional model that captures the initial rate of thinning when the dynamics are dominated by a balance between inertia and capillarity. This model also captures the structure of the transition region to the nonlinear EC regime in which the rapidly growing elastic stresses in the thread balance the capillary pressure as the filament thins towards breakup. Finally, we propose a fitting methodology based on the analytical solution for FENE-P fluids to improve the accuracy in determining the effective relaxation time of an unknown fluid.

Impact of environmental factors on spider silk properties

Spider orb webs have evolved to stop flying prey, fast and slow alike. One of the main web elements dissipating impact energy is the radial fibers, or major ampullate silks, which possess a toughness surpassing most man-made materials. Orb webs are extended phenotypes, and as such their architectural elements, including major ampullate silks, have been selected to optimize prey capture under the respective environmental conditions. In this study, we investigated the correlation of three landscape scales and three microhabitat characteristics with intrinsic silk properties (elastic modulus, yield stress, tensile strength, extensibility, and toughness) to understand underlying ecological patterns. For this purpose, we collected and mechanically tested major ampullate silks from 50 spider species inhabiting large altitudinal and climatic gradients in Colombia. Using regression analysis and model selection, we investigated the environmental drivers of inter- and intra-specific patterns of major ampullate silk properties, taking into account phylogenetic relatedness based on newly sequenced mitochondrial genomes. We found that the total amount of energy absorbed, i.e., toughness and tensile strength, is higher for fibers from species inhabiting regions where heavy rainfall is common. Interestingly, we observe the same general trend between individuals of the same species, stressing the importance of this environmental driver. We also observe a phylogenetic conservation in the relation of environmental variables with silk tensile strength and yield stress. In conclusion, the increase in major ampullate silk tensile strength and toughness may reflect an adaptation to prevent frequent rain damage to orb webs and the associated energetic loss.

Experimental investigation on effect of loading rate on fracture behavior of coal-seam roof rock

The fracture behavior of coal-seam roof rock in coal mining is a key and controlling factor for the mode optimization of the artificial roof caving. However, the fracture mechanism of roof rock under loading is not clear. In the work, the split Hopkinson pressure bar (SHPB) experiment was carried out using semicircular bending samples from the sandstone of coal-seam roof rock in the Junger mining area of Inner Mongolia at the loading rate of 0.35–3.78 GPa·m0.5·s−1, and the dynamic fracture behavior and energy dissipation mechanism of samples under different loading rates were investigated. The result shows that the dynamic stress–strain process of the hard roof rock includes four stages: linear instantaneous compaction, linear elastic compression, failure, and fracture extension, in which the failure forms changes from brittle fracture to ductile fracture with the increase of loading rate. The mode I fracture toughness increases linearly under confining pressure. In addition, the propagation orientation of induced fractures is parallel to the loading direction, and the gravel in the samples can inhibit fracture extension, resulting in changing the fracture extension path. Further, the energy absorption efficiency of the samples during the fracture process decreases with the increase in the loading rate.

Influence of Storage Conditions on Decellularized Porcine Conjunctiva

Porcine decellularized conjunctiva (PDC) represents a promising alternative source for conjunctival reconstruction. Methods of its re-epithelialization in vitro with primary human conjunctival epithelial cells (HCEC) have already been established. However, a long-term storage method is required for a simplified clinical use of PDC. This study investigates the influence of several storage variants on PDC. PDC were stored in (1) phosphate-buffered saline solution (PBS) at 4 °C, (2) in glycerol-containing epithelial cell medium (EM/gly) at -80 °C and (3) in dimethyl sulfoxide-containing epithelial cell medium (EM/DMSO) at -196 °C in liquid nitrogen for two and six months, respectively. Fresh PDC served as control. Histological structure, biomechanical parameters, the content of collagen and elastin and the potential of re-epithelialization with primary HCEC under cultivation for 14 days were compared (n = 4-10). In all groups, PDC showed a well-preserved extracellular matrix without structural disruptions and with comparable fiber density (p ≥ 0.74). Collagen and elastin content were not significantly different between the groups (p ≥ 0.18; p ≥ 0.13, respectively). With the exception of the significantly reduced tensile strength of PDC after storage at -196 °C in EM/DMSO for six months (0.46 ± 0.21 MPa, p = 0.02), no differences were seen regarding the elastic modulus, tensile strength and extensibility compared to control (0.87 ± 0.25 MPa; p ≥ 0.06). The mean values of the epithelialized PDC surface ranged from 51.9 ± 8.8% (-196 °C) to 78.3 ± 4.4% (-80 °C) and did not differ significantly (p ≥ 0.35). In conclusion, all examined storage methods were suitable for storing PDC for at least six months. All PDC were able to re-epithelialize, which rules out cytotoxic influences of the storage conditions and suggests preserved biocompatibility for in vivo application.

Экспериментальное исследование подъема уровня жидкости в плоском капилляре, образуемом эластичными периодически растягиваемыми стенками

A water rise in a plane capillary with elastic periodically stretched walls is experimentally demonstrated. Dependence of the water meniscus rise height on the value of time-periodic elastic extension of capillary walls was measured. A deviation of the measured dependence from the linear dependence was recorded. The latter one could be realized in the mode of an ideal pinning of a meniscus edge.

Structural hierarchy of mechanical extensibility in human von Willebrand factor multimers.

The von Willebrand factor (VWF) is a multimeric glycoprotein composed of 80- to 120-nm-long protomeric units and plays a fundamental role in mediating platelet function at high shear. The exact nature of the shear-induced structural transitions have remained elusive; uncovering them requires the high-resolution quantitative analysis of gradually extended VWF. Here, we stretched human blood-plasma-derived VWF with molecular combing and analyzed the axial structure of the elongated multimers with atomic force microscopy. Protomers extended through structural intermediates that could be grouped into seven distinct topographical classes. Protomer extension thus progresses through the uncoiling of the C1-6 domain segment, rearrangements among the N-terminal VWF domains, and unfolding and elastic extension of the A2 domain. The least and most extended protomer conformations were localized at the ends and the middle of the multimer, respectively, revealing an apparent necking phenomenon characteristic of plastic-material behavior. The structural hierarchy uncovered here is likely to provide a spatial control mechanism to the complex functions of VWF.

Experimental investigation on the correlation between critical storage of elastic strain energy and crack extension in elastic–plastic materials

AbstractTo better solve the issues of steady crack extension with broad plasticity and the crack‐related problems in general yielding situations when the assumption of small‐scale plastic yielding fails, it is of great significance to further study the macroscopic mechanism of crack extension. In this paper, a new insight into the elastic–plastic crack extension is proposed on the foundation of critical storage of elastic strain energy (SESE). The feasibility of the new methodology is validated by designing and implementing two different experimental schemes in three typical elastic–plastic materials. The experimental results indicate that the critical SESE decreases linearly with the increase of crack length and U‐notch initial length. Besides, the SESE release rate is obtained through experimental and theoretical methods, and they are in the same order of magnitude and their value sequences are also accordant with all tested materials. Therefore, this investigation provides a new approach to characterizing crack extension in elastic–plastic materials.

Study of Energy Evolution Law and Damage Characteristics during Uniaxial Cyclic Loading and Unloading of Sandstone

Using the rock mechanics test (RMT) and acoustic emission acquisition system (DS9), based on the energy principle, uniaxial compression, uniaxial cyclic loading, and unloading tests are used to study the energy transformation characteristics of the process of sandstone absorbing axial strain energy, accumulating and releasing elastic strain energy, plastic deformation, and crack extension dissipation energy. The study results show the increase of loading rate, rock fracture surface increases, number of fragments increases, and size of fragments decreases; the sandstone damage process causes: shear damage to tensile shear damage and then splitting damage for change; the input energy and elastic energy increase nonlinearly with an increase of stress, and the dissipative energy is larger at the beginning of loading. After a small decrease, it enters the nonlinear growth stage, and the input energy density grows the fastest. The elastic energy density is the second fastest, and the dissipative energy density grows the slowest; with an increase of loading rate, in any deformation stage, the elastic energy density and dissipation energy density are increased, proportion of elastic energy density is decreased, and proportion of dissipation energy density is increased. Near the peak stress stage, the proportion of elastic energy decreases, and the proportion of dissipative energy increases; the damage variable stress curve of sandstone is “weakly concave”, which is consistent with the logistic function, and the damage evolution process has chaotic dynamics properties; the acoustic emission energy of sandstone in cyclic loading and unloading test has a similar variation with the theoretical calculation of dissipated energy. The cumulative energy curve shows a step-up law, and the stress corresponding to the step point is near the historical maximum stress.

A Generalized Linear Joint Trained Framework for Semi-Supervised Learning of Sparse Features

The elastic net is among the most widely used types of regularization algorithms, commonly associated with the problem of supervised generalized linear model estimation via penalized maximum likelihood. Its attractive properties, originated from a combination of ℓ1 and ℓ2 norms, endow this method with the ability to select variables, taking into account the correlations between them. In the last few years, semi-supervised approaches that use both labeled and unlabeled data have become an important component in statistical research. Despite this interest, few researchers have investigated semi-supervised elastic net extensions. This paper introduces a novel solution for semi-supervised learning of sparse features in the context of generalized linear model estimation: the generalized semi-supervised elastic net (s2net), which extends the supervised elastic net method, with a general mathematical formulation that covers, but is not limited to, both regression and classification problems. In addition, a flexible and fast implementation for s2net is provided. Its advantages are illustrated in different experiments using real and synthetic data sets. They show how s2net improves the performance of other techniques that have been proposed for both supervised and semi-supervised learning.

Nonlocal elasticity of Klein–Gordon type: Fundamentals and wave propagation

A nonlocal elasticity theory with nonlocality in space and time is developed by considering nonlocal constitutive equations with a dynamical scalar nonlocal kernel function. The proposed theory is specified to isotropic nonlocal elasticity of Klein–Gordon type, which is an extension of nonlocal elasticity of Helmholtz type, and it possesses one characteristic internal length scale parameter as well as one characteristic internal time scale parameter in addition to the elastic material parameters. Dynamical nonlocal kernels are analytically derived as retarded Green functions of the Klein–Gordon operator. The dispersion relations of the considered isotropic nonlocal elasticity model of Klein–Gordon type are analytically determined. The obtained results reveal the advantage of the proposed nonlocal elasticity model, that is, its ability to predict for the first time in the framework of nonlocal elasticity in addition to the acoustic modes (low-frequency modes), optic modes (high-frequency modes) as well as frequency band-gaps between the acoustic and optic modes. A qualitative examination of the phase and group velocities for all four modes (acoustic and optic branches of longitudinal and transverse waves) shows that the proposed model allows for physically realistic dispersive wave propagation.

Hydrodynamic Interactions Between Macroalgae and Their Epibionts

Macroalgae provide surfaces where other organisms live. Unlike organisms on rigid substrata, epibionts on host macroalgae sit on flexible surfaces that bend, stretch, and move in turbulent water currents and waves. We used blade-like red algae,Mazzaella splendens, and encrusting bryozoans,Membranipora membranacea, to investigate the biomechanical and hydrodynamic effects of encrusting epibionts on macroalgae, and of flexible hosts on epibiotic bryozoans. Passive flapping by algae in wave-driven ambient flow enhanced renewal of water near hosts and epibionts. Wave exposure and the presence of a surrounding canopy of flexible algae altered the locations along algal blades where bryozoans encountered the highest time-averaged boundary shear velocities. Hydrodynamic forces on flexible algae moving back-and-forth with the water were lower in waves than in unidirectional flow. Bryozoan epibionts increased hydrodynamic forces on host algae by affecting their reconfiguration in moving water. Encrusting bryozoans increased the flexural stiffness of algal blades, but the elastic modulus, extensibility, and strength of blade tissue was unaffected by bryozoan epibionts. Algal blades were more extensible and stronger than bryozoans, so bryozoans fractured or popped off stretched algae. Algae in rapid-flow habitats had few epibionts, and encrusted algae transplanted from a protected to a wave-exposed habitat lost their epibionts.

Evolution Prediction of Hysteresis Behavior of Sand under Cyclic Loading

Soil cyclic degradation is a serious issue that should be considered in engineering design and maintenance. The hysteretic response causes strength degradation and excessive settlement of soil structure in engineered and natural geosystems. Hysteresis is essentially the coupling deformation of elastic and plastic components during reloading and unloading processes. Conventional hysteretic models for sand in the elastoplastic framework rely highly on yield surface or potential surface evolution and fall short on complexity and inaccuracy. This study proposes a decoupling method to describe the hysteretic response of sand. In contrast to the conventional elastoplastic approach, this decoupling method can directly decouple the elastic and plastic components by determining the boundary between the elastic strain extension domain and the plastic strain extension domain for each stress cycle. In this way, the elastic and plastic stress–strain branches during cyclic loading can be separately obtained, and the corresponding elastic and plastic parameters are employed to characterize mechanical behavior. With the respective evolution of elastic and plastic strains, the hysteretic behavior of sand is reproduced by combining all the branches. Finally, this decoupling method is validated by three conventional cyclic loading tests. The predictions are consistent with the experiments, indicating that the decoupling method is generally effective in describing the hysteretic behavior under cyclic loading. This decoupling method provides new insight to obtain elastic and plastic deformation behaviors separately, without recourse to complicated plastic surface and hardening law.

Regulation of Substrate Dissipation via Tunable Linear Elasticity Controls Cell Activity

AbstractNatural tissues and extracellular matrices (ECMs) are not purely elastic materials but exhibit dissipative properties. Although it has recently emerged as a novel regulator of cellular responses, the contribution of material dissipation to guiding cell‐fate decisions is still in its infancy. Here, a strategy for tuning the dissipation rate of viscoplastic substrates while precisely regulating linear elasticity is reported. Semi‐interpenetrating substrates consisting of a rigid hydrogel network intertwined with a branched biopolymer are described. The release of these weak physical entanglements under loading dissipates the applied stress and leads to the extension of the linear elasticity. These results reveal a crucial link between this material property and cell response in 2D cultures, impacting cell migration mode and speed, vinculin‐dependent focal adhesion geometry and size, F‐actin organization, the transmission of forces, and Yes‐associated protein nuclear translocation. It is shown that cells require joint actomyosin contractility and microtubule tension to probe the substrate and decide whether or not to adhere, revealing a clear correlation between force transmission, substrate dissipation rate, and amount of anchoring points. Overall, these findings introduce linear elasticity as a novel design parameter for assembling tunable dissipative materials to study cell mechanosensing in 2D and possibly also in 3D cultures.

COMPARISON OF TECHNOLOGICAL PROPERTIES OF DIFFERENT WHEAT SPECIES

For the widespread introduction of different species of wheat into processing, it is necessary to understand the features of the physicochemical properties of these wheats, which determine the behavior of the grain during its milling and the obtaining flour during the dough making process. Technological properties of grain of four different wheat species and the laboratory milling flour obtained from them were investigated.
 It was found that according to grain quality indicators, milling properties and quality flour indicators, 4 species of wheat grain grown in the same agro-climatic conditions showed significant differences. Hard wheat with GPC-B1 gene (breeding line) has a superior baking strength due to the GPC-B1 gene, which significantly increases the protein content in grain (13.51%), gluten content (26.1%), test Zeleny (58 ml) and ash content (1.69%) compare to common hard wheat (Kuyalnyk variety). As a result, flour shown high values of: strength (W=396×10-4 J), high SRC in lactic acid (160%), high dough stability (>30 minutes), low degree of softening of the dough (43 UF). According to the obtained data, waxy wheat (Sofiika variety) consimilar with common baking wheat, excluding low value of Falling Number (FN=70 seconds). When determining on the alveograph, the dough is very tight (L<40 mm) due to high water absorption capacity (WAC=67.3%). The results of SRC test in sodium carbonate confirmed the high value of starch damage with the highest result (108%). Soft wheat (Bilyava variety) differs significantly from common hard wheat. In terms of wheat quality indicators, it can be attributed to medium bread-baking strength. Such flour characterized by less ash content (0.47%), but higher whiteness (70.7 units), less protein content (10.79%), less elasticity (Ie=44.3), but greater extensibility, resulting in a lower P/L ratio (0.83) and less water absorption capacity (WAC=52.7%).
 According to milling properties was investigated that hard wheat with the GPC-B1 locus and common hard wheat Kuyalnik shown similar results. The total yield of flours from these wheats during milling is above 70%, which indicates the economic feasibility of their processing into flour. During milling waxy wheat has a decrease in the reduction flour yield and an increase in the reduction bran yield. Absolutely different results in milling properties show soft wheat. The total yield of soft flour is less – 67.17% with significant increasing of break flour yield and decreasing reduction flour yield.
 Different properties of grain and flour determine the different end use of grain of each wheat species. Wheat with the GPC-B1 gene can be used in production of flour which is used in low-temperature technologies for the manufacture of frozen convenience foods and also as improver for increase the rheological properties of the dough or for pasta-making properties. For end use of waxy wheat (Sofiika variety) can be recommended in the production of pasta products. Although waxy flour can be used as regulator in flour blending for correcting the indicators of common baking wheat. Blends of flour from waxy wheat grain and flour from hard wheat grain with GPC-B1 gene are ideal for making frozen products. Soft wheat (Belyava variety) flour preferred for low moisture crackers, cookies and can be added in a small amount to special types of bread to give a lighter color to the crumb.

Role of elastic upper limit in shakedown study for granular soils

The shakedown study for determining plastic shakedown limit is desirable for preventing geotechnical infrastructure failure under cyclic loads. The plastic shakedown limit is conceptually clear but difficult to determine experimentally since the permanent strain accumulation response is a gradual process, and the criterion for determining the plastic shakedown limit is sensitive and variable limited by lack of further understanding of mechanisms during shake down process. Motivated by the need to clarify the mechanism of shakedown limit, a new concept of elastic upper limit of quasi-elasticity extension is hypothesized in this paper. Three-stage slow cyclic triaxial tests are carried out on three types of sand to clarify this new concept. The results show that the quasi-elastic curve extends as the cyclic stress level increases until it reaches the elastic upper limit and then the deviation occurs. The objective of this study is to explore the role of elastic upper limit (the elastic extension domain limit) in the shakedown theory. It is found that the derived elastic upper limit is close to the plastic shakedown limit, especially at high levels of confining pressure. A new criterion is proposed to determine the plastic shakedown limit based on the linear dependence of the degree of elasticity on the cyclic stress level. The introduction of the concept of elastic upper limit provides new insights into shakedown study for granular soils.

Positive disclination in a thin elastic sheet with boundary.

An isolated positive wedge disclination deforms an initially flat elastic sheet into a perfect cone when the sheet is of infinite extent and is elastically inextensible. The latter requires the elastic stretching strains to be vanishingly small. In this paper, rigorous analytical and numerical results are obtained for the disclination-induced deformed shape and stress field of a bounded Föppl-von Kármán elastic sheet with finite extensibility, while emphasizing the deviations from the perfect cone solution. In particular, the Gaussian curvature field is no longer localized as a Dirac singularity at the defect location whenever elastic extensibility is allowed and is necessarily negative in large regions away from the defect. The stress field, similarly, has no Dirac singularity in the presence of elastic extensibility. However, with increasing Young's modulus of the sheet, while keeping the bending modulus and the domain size fixed, both of these fields tend to develop a Dirac singularity. Noticeably, in this limiting behavior, inextensibility eludes the bounded elastic sheet due to persisting regions of nontrivial Gaussian curvature away from the defect. Other results in the paper include studying the effect of specific boundary conditions (free, simply supported, or partially clamped) on the Gaussian curvature field away from the defect and on the buckling transition from the flat to a conical solution.

Abstract 12566: Aortic Smooth Muscle Cell Focal Adhesion Kinase (FAK) Activation is Prominently Associated With Acute Aortic Dissections in Patients and Mouse Models and Loss of FAK Signaling Augments Dissections in Mice

Introduction: Genetic variants predisposing to thoracic aortic disease disrupt proteins either in the extracellular matrix (ECM) or the smooth muscle cell (SMC) contractile unit, and focal adhesions (FAs) are molecular bridges between these aortic wall components. We sought to identify molecular triggers for acute aortic dissection (AAD) in a mouse model with AAD induced by β-aminopropionitrile (BAPN) and patients with type A AAD. Methods: At postnatal day 21 (P21), C57BL/6J mice were exposed to BAPN in drinking water (0.5%) and proximal aortas were harvested for single-cell RNA sequencing (scRNA-seq), proteomics assays and transmission electron microscopic (TEM) analysis at P35. Ascending aortic scRNA-seq assays were performed on AAD patients (n=3) and age-matched, cardiac transplantation donors (n=3). Results: In the BAPN mice, ruptured AAD-deaths started at P36, and 54% of mice died by P49, despite a significant decrease of BP (111/79 to 95/66 mmHg, p<0.0001). ScRNA-seq and KEGG pathway analysis identified increased FA signaling as the top altered pathway in the BAPN-treated SMC clusters. Similarly, FA signaling was identified as a top upregulated pathway in SMCs from patients’ aortas. Western blots confirmed increased level of FAK phosphorylation in BAPN-treated aortas. Proteomics analysis revealed a FAK-interacting protein, cortactin, and apoptotic proteins, annexin A1, A3 and A5 (p<0.01), as the top proteins increased with BAPN treatment, which was consistent with increased TUNEL signal in BAPN-treated aortas (p<0.01). TEM analysis identified collagen deposition between SMCs and elastic fibers and loss of elastic extensions in BAPN-treated aortic media. Importantly, administration of a FAK inhibitor, PF-573228, starting at P30 in BAPN-treated mice significantly increased AAD-deaths (starting at P35 and all mice died by P48) when compared to BAPN-only treated mice (p<0.0001). Conclusions: FA signaling is the major pathway activated in SMCs in mouse pre-dissection aortas and human dissected aortas, thus implicating disruption of SMC-ECM interactions in AADs. Disruption of FAK signaling augments AADs, suggesting that maintenance of FA signaling delays AADs in the ECM-compromised, BAPN-treated aortas.

Differential responses of roots for varying tolerance to salinity stress in wheat with special reference to elasticity

Two salt-sensitive (Yongliang-15, GS-6058) and two salt-tolerant (JS-7, Xinchun-31) wheat cultivars were used to investigate the extension, extensibility (viscoelastic parameters), and chemical composition of the cell walls in their root elongation regions (apical 10 mm-long root segments), under salinity stress. The elasticity of the root cell wall, indicated by E0, significantly decreased in the salt-sensitive cultivars, whereas the E0 in the salt-tolerant cultivars was maintained at the same level as that in the non-saline condition. Root extension and the differences among cultivars were largely dependent on elastic extension, which accounts for one-half to two-thirds of the total extension. Viscosity, indicated by η0, and the plastic extension of the root cell walls did not change across the treatments and cultivars. The significant decrease in cell wall elasticity in the root elongation region was one of the factors that depressed root growth in salt-sensitive cultivars under the saline condition. The well-maintained elasticity of salt-tolerant cultivars alleviated the depression of root growth by NaCl. Cell wall elasticity was positively correlated with the relative pectin and hemicellulose I contents and negatively correlated with the relative cellulose content. Under saline conditions, the relative hemicellulose II content did not change in the salt-sensitive cultivars; however, it decreased in the salt-tolerant ones. Thus, changes in chemical composition of the cell wall were correspond with the cell wall extensibility and root growth in wheat cultivars with different degrees of salt tolerance.