The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Larry V. Mcintire - One of the best experts on this subject based on the ideXlab platform.
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GPIbα-vWF Rolling under Shear Stress Shows Differences between Type 2B and 2M von Willebrand Disease
Biophysical journal, 2011Co-Authors: L.a. Coburn, V.s. Damaraju, S. Dozic, Suzanne G. Eskin, Miguel A. Cruz, Larry V. McintireAbstract:Both type 2B and type 2M von Willebrand disease result in bleeding disorders; however, whereas type 2B has increased binding affinity between platelet glycoprotein Ibα and von Willebrand factor (vWF), type 2M has decreased binding affinity between these two molecules. We used R687E type 2B and G561S type 2M vWF-A1 mutations to study binding between flowing platelets and insolubilized vWF mutants. We measured rolling velocities, mean stop times, and mean go times at 37°C using high-speed video microscopy. The rolling velocities for wt-wt interactions first decrease, reach a minimum, and then increase with Increasing Shear Stress, indicating a catch-slip transition. By changing the viscosity, we were able to quantify the effects of force versus Shear rate for rolling velocities and mean stop times. Platelet interactions with loss-of-function vWF-A1 retain the catch-slip bond transition seen in wt-wt interactions, but at a higher Shear Stress compared with the wt-wt transition. The mean stop time for all vWF-A1 molecules reveals catch-slip transitions at different Shear Stresses (gain-of-function vWF-A1 < wt vWF-A1< loss-of-function vWF-A1). The shift in the catch-slip transition may indicate changes in how the different mutants become conformationally active, indicating different mechanisms leading to similar bleeding characteristics.
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Effect of Shear Stress on^86Rb^+ efflux from calf pulmonary artery endothelial cells
Annals of Biomedical Engineering, 1993Co-Authors: Barbara R. Alevriadou, Larry V. Mcintire, Suzanne G. Eskin, William P. SchillingAbstract:The effect of flow-induced Shear Stress on membrane K^+ permeability was investigated by measuring^86Rb^+ efflux in cultured calf pulmonary artery endothelial cells. Cells were subjected to step changes in Shear Stress from 1 dyn/cm^2 to 2.4, 4.8, or 10 dyn/cm^2 in a parallel-plate flow chamber. Increasing Shear Stress produced a graded, transient increase in^86Rb^+ efflux which peaked within 1 min and subsequently declined rapidly toward pre-stimulus levels. Upon returning Shear Stress to 1 dyn/cm^2,^86Rb^+ efflux initially decreased, but returned slowly to basal values. In contrast, application of bradykinin at a constant Shear Stress of 1 dyn/cm^2 produced a transient increase in^86Rb^+ efflux that was followed by a sustained elevated phase during which time efflux gradually returned to pre-stimulus levels. In order to exclude the possibility that the transient increase in^86Rb^+ efflux with Shear Stress simply reflects a flow-dependent change in the washout of radiotracer, the transient convection-diffusion equation was solved using finite element simulation. When the flux of^86Rb^+ from the cell monolayer was assumed to be constant with time, the mathematical model predicted an increase in efflux rate coefficients upon step increases in flow that were only 7–19% of that observed experimentally. The numerical predictions correlated well with the experimentally obtained peaks when the flux of^86Rb^+ from the cell monolayer was simultaneously increased with flow to a new steady value. These simulations however, could not predict the transient nature of the response to increased Shear Stress. The results from the computer modeling suggest that the transient increase in^86Rb^+ efflux does not reflect a washout phenomenon and supports the hypothesis that Shear Stress produces a graded, transient increase in the K^+ permeability of vascular endothelial cells.
Martin T Pusch - One of the best experts on this subject based on the ideXlab platform.
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resistance to ship induced waves of benthic invertebrates in various littoral habitats
Freshwater Biology, 2008Co-Authors: Friederike Gabel, Xavierfrancois Garcia, Mario Brauns, Alexander Sukhodolov, M Leszinski, Martin T PuschAbstract:Summary 1. Ship-induced waves disturb benthic invertebrate assemblages colonizing littoral zones of lakes and rivers. However, the impact of ship-induced waves on invertebrates has rarely been quantified, and the influencing factors have not been addressed. 2. In an experimental wave tank, five benthic invertebrate species, Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeseli and Laccophilus hyalinus, were exposed to waves of Increasing Shear Stress (0.43–2.19 N m−2). Mean number of detached individuals was recorded for five littoral habitats [coarse woody debris (CWD), reeds, sand, stones and tree roots], representing different levels of structural complexity as quantified by their fractal dimensions (FD). 3. Results showed that detachment of invertebrates was significantly related to Shear Stress in all habitats except tree roots. Detachments averaged for the five species were significantly lower in habitats with a high degree of structural complexity, decreasing in the habitat sequence: sand, CWD, stones, reeds and tree roots. 4. Consistent with their different morphologies and methods of attachment to substrates, the five species displayed differences in their response to hydraulic Stress that were dependent on habitat. 5. The Increasing sheltering effect of structural habitat complexity was mirrored by Increasing dissipation of the kinetic energy of waves; i.e. the FD of the habitat was positively correlated with Shear Stress reduction due to the flow resistance of the habitat. 6. Network habitats such as tree roots provided the best sheltering conditions against hydraulic disturbance, because they combined good refuge availability for all studied invertebrate species and maximal dissipation of kinetic wave energy. Consequently, persistent anthropogenic impacts, such as lakeshore modification or long-term exposure to ship-induced waves, which cause disappearance of complex littoral habitats such as tree roots or dense reed belts, will drastically increase the adverse effects of boating and ship traffic on littoral invertebrate assemblages.
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Resistance to ship‐induced waves of benthic invertebrates in various littoral habitats
Freshwater Biology, 2008Co-Authors: Friederike Gabel, Xavierfrancois Garcia, Mario Brauns, Alexander Sukhodolov, M Leszinski, Martin T PuschAbstract:Summary 1. Ship-induced waves disturb benthic invertebrate assemblages colonizing littoral zones of lakes and rivers. However, the impact of ship-induced waves on invertebrates has rarely been quantified, and the influencing factors have not been addressed. 2. In an experimental wave tank, five benthic invertebrate species, Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeseli and Laccophilus hyalinus, were exposed to waves of Increasing Shear Stress (0.43–2.19 N m−2). Mean number of detached individuals was recorded for five littoral habitats [coarse woody debris (CWD), reeds, sand, stones and tree roots], representing different levels of structural complexity as quantified by their fractal dimensions (FD). 3. Results showed that detachment of invertebrates was significantly related to Shear Stress in all habitats except tree roots. Detachments averaged for the five species were significantly lower in habitats with a high degree of structural complexity, decreasing in the habitat sequence: sand, CWD, stones, reeds and tree roots. 4. Consistent with their different morphologies and methods of attachment to substrates, the five species displayed differences in their response to hydraulic Stress that were dependent on habitat. 5. The Increasing sheltering effect of structural habitat complexity was mirrored by Increasing dissipation of the kinetic energy of waves; i.e. the FD of the habitat was positively correlated with Shear Stress reduction due to the flow resistance of the habitat. 6. Network habitats such as tree roots provided the best sheltering conditions against hydraulic disturbance, because they combined good refuge availability for all studied invertebrate species and maximal dissipation of kinetic wave energy. Consequently, persistent anthropogenic impacts, such as lakeshore modification or long-term exposure to ship-induced waves, which cause disappearance of complex littoral habitats such as tree roots or dense reed belts, will drastically increase the adverse effects of boating and ship traffic on littoral invertebrate assemblages.
James M. Anderson - One of the best experts on this subject based on the ideXlab platform.
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Shear Stress induced apoptosis of adherent neutrophils a mechanism for persistence of cardiovascular device infections
Proceedings of the National Academy of Sciences of the United States of America, 2000Co-Authors: Matthew S. Shive, Mariah L Salloum, James M. AndersonAbstract:The mechanisms underlying problematic cardiovascular device-associated infections are not understood. Because the outcome of the acute response to infection is largely dependent on the function of neutrophils, the persistence of these infections suggests that neutrophil function may be compromised because of cellular responses to Shear Stress. A rotating disk system was used to generate physiologically relevant Shear Stress levels (0–18 dynes/cm2; 1 dyne = 10 μN) at the surface of a polyetherurethane urea film. We demonstrate that Shear Stress diminishes phagocytic ability in neutrophils adherent to a cardiovascular device material, and causes morphological and biochemical alterations that are consistent with those described for apoptosis. Complete neutrophil apoptosis occurred at Shear Stress levels above 6 dynes/cm2 after only 1 h. Morphologically, these cells displayed irreversible cytoplasmic and nuclear condensation while maintaining intact membranes. Analysis of neutrophil area and filamentous actin content demonstrated concomitant decreases in both cell area and actin content with Increasing levels of Shear Stress. Neutrophil phagocytosis of adherent bacteria decreased with Increasing Shear Stress. Biochemical alterations included membrane phosphatidylserine exposure and DNA fragmentation, as evaluated by in situ annexin V and terminal deoxynucleotidyltransferase-mediated dUTP end labeling (TUNEL) assays, respectively. The potency of the Shear-Stress effect was emphasized by comparative inductive studies with adherent neutrophils under static conditions. The combination of tumor necrosis factor-α and cycloheximide was ineffective in inducing >21% apoptosis after 3 h. These findings suggest a mechanism through which Shear Stress plays an important role in the development of bacterial infections at the sites of cardiovascular device implantation.
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Shear Stress effects on bacterial adhesion, leukocyte adhesion, and leukocyte oxidative capacity on a polyetherurethane
Journal of biomedical materials research, 1999Co-Authors: Matthew S. Shive, Sakeena M. Hasan, James M. AndersonAbstract:Infection of implanted cardiovascular biomaterials still occurs despite inherent host defense mechanisms. Using a rotating disk system, we investigated Staphylococcus epidermidis and polymorphonuclear leukocyte (PMN) adhesion to a polyetherurethane urea (PEUU-A′) under Shear Stress (0–17.5 dynes/cm2) for time periods up to 6 h. In addition, the superoxide (SO) release capacity of PMNs after transient exposure to PEUU-A′ under Shear Stress was determined. Bacterial adhesion in phosphate-buffered saline (PBS) showed a linear Shear dependence, decreasing with Increasing Shear Stress. Overall adhesion in PBS decreased with time. However, bacterial adhesion in 25% human serum was similar for all time points up to 360 min. Adhesion was observed at all Shear levels, displaying no Shear dependence. In contrast, PMN adhesion demonstrated a strong Shear dependence similarly for times up to 240 min, decreasing sharply with Increasing Shear Stress. Although PMNs preexposed to Shear Stress showed a slightly diminished SO release response compared to fresh cells for all stimuli, it was not statistically significant regardless of the stimulus. We conclude that circulating leukocytes are unable to adhere in regions of high Shear which may contain adherent bacteria. In addition, exposure to PEUU-A′ and Shear Stress (in the range 0–18 dynes/cm2) is insufficient to cause a depression in the oxidative response of PMNs. © 1999 John Wiley & Sons, Inc. J Biomed Mater Res, 46, 511–519, 1999.
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adhesion of staphylococcus epidermidis to biomedical polymers contributions of surface thermodynamics and hemodynamic Shear conditions
Journal of Biomedical Materials Research, 1995Co-Authors: Iwen W Wang, James M. Anderson, Michael R. Jacobs, Roger E MarchantAbstract:Adhesion studies of Staphylococcus epidermidis RP62A were conducted using a rotating disk system to determine the roles of surface physicochemistry and topographies under physiologic Shear conditions. Six materials were investigated: biomedical reference polyethylene and polydimethylsiloxane; argon plasma-treated reference polyethylene (Ar-PE); Silastic®; expanded polytetrafluoroethylene; and woven Dacron. All of the polymers except Dacron demonstrated reduced bacterial adhesion with Increasing Shear Stress. Argon plasma treatment of polyethylene reduced the level of staphylococcal adhesion. Adsorption of human plasma proteins effected significantly lower numbers of adherent bacteria. The lowest adhesion was observed for Ar-PE in 1% human plasma protein solution, whereas Dacron had the highest number of adherent bacteria. The high adhesion on Dacron was attributed to increased bacterial flux caused by topography-induced turbulent flow and physical entrapment of the bacteria in the fiber interstices. The results indicate that the driving force for S. epidermidis adhesion is strongly influenced by substrate physicochemistry, but this may be dominated by physical forces such as Shear and turbulence. © 1995 John Wiley & Sons, Inc.
Filip Van Bockstaele - One of the best experts on this subject based on the ideXlab platform.
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non linear creep recovery measurements as a tool for evaluating the viscoelastic properties of wheat flour dough
Journal of Food Engineering, 2011Co-Authors: Filip Van Bockstaele, Ingrid De Leyn, Mia Eeckhout, Koen DewettinckAbstract:Abstract Creep-recovery measurements were used to analyze the non-linear viscoelastic properties of wheat flour. First the effect of creep time, recovery time and Shear Stress was investigated on the non-linear viscoelastic properties of Bussard dough. The Burgers model was fitted to the creep and recovery curves. A linear increase of maximum creep compliance was observed with Increasing creep time. On the other hand, maximum recovery compliance remained constant but an increase of the retardation time was observed which indicates a slower recovery. A recovery time of 10 min seemed to be sufficient to obtain most of the recovery. Maximum creep compliance increased proportionally with Increasing Shear Stress until a plateau was reached. Maximum recovery was constant between 100 and 500 Pa but the speed of the recovery increased as Shear Stress increased. Finally, the optimised creep-recovery methodology was used to analyze the non-linear viscoelastic properties of 17 pure wheat cultivars. By applying principal component analysis, it was possible to identify three groups of wheat cultivars with similar rheological properties and bread volumes.
Fawaz Deri - One of the best experts on this subject based on the ideXlab platform.
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Preparation and studying properties of thermoplastic starch/acrylonitrile–butadiene–styrene blend
International Journal of Plastics Technology, 2012Co-Authors: Mosab Kaseem, Kotiba Hamad, Fawaz DeriAbstract:In this work, blends of acrylonitrile–butadiene–styrene (ABS) and thermoplastic starch (TPS) were prepared by using a single screw extruder (SSE), the starch was plasticized in the single screw extruder by using glycerol as a plasticizer. The blends were characterized by studying rheological and mechanical properties. The rheological results indicated that ABS/TPS blend melts were pseudo plastic and exhibited Shear–thinning behavior, and the viscosity of the blend decreased with Increasing glycerol content. Also the values of flow activation energy at a constant Shear Stress (E τ ) of ABS1/TPS25G blend were determined, and it was found that E τ increased with Increasing Shear Stress. Die swell measurements of the blend showed that die swell ratio increases with Increasing Shear Stress and glycerol content in the blend, while it decreases with Increasing L/R. Mechanical results showed that, the values of Stress at break and strain at break decreased with Increasing TPS content in the blend, which was attributed to the immiscibility between TPS and ABS.
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Melt Rheology of Poly(Lactic Acid)/Low Density Polyethylene Polymer Blends
Advances in Chemical Engineering and Science, 2011Co-Authors: Kotiba Hamad, Mosab Kaseem, Fawaz DeriAbstract:In this work, rheological properties of poly (lactic acid) (PLA), low density polyethylene (LDPE) polymer blends were investigated in the molten state. The experiments were carried on a capillary rheometer. The effect of Shear Stress, temperature and blending ratio on the flow activation energy at a constant Shear Stress and melt viscosity of the blends are described. The results showed that the PLA/LDPE polymer blends are pseudo plastic in nature, where there viscosity decreases with Increasing Shear Stress. Also it was found the melt viscosity of the blends decreases with Increasing PLA content in the blend
