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Sample records for adhesive shear stress

  1. Inhibition of bacterial and leukocyte adhesion under shear stress conditions by material surface chemistry.

    PubMed

    Patel, Jasmine D; Ebert, Michael; Stokes, Ken; Ward, Robert; Anderson, James M

    2003-01-01

    Biomaterial-centered infections, initiated by bacterial adhesion, persist due to a compromised host immune response. Altering implant materials with surface modifying endgroups (SMEs) may enhance their biocompatibility by reducing bacterial and inflammatory cell adhesion. A rotating disc model, which generates shear stress within physiological ranges, was used to characterize adhesion of leukocytes and Staphylococcus epidermidis on polycarbonate-urethanes and polyetherurethanes modified with SMEs (polyethylene oxide, fluorocarbon and dimethylsiloxane) under dynamic flow conditions. Bacterial adhesion in the absence of serum was found to be mediated by shear stress and surface chemistry, with reduced adhesion exhibited on materials modified with polydimethylsiloxane and polyethylene oxide SMEs. In contrast, bacterial adhesion was enhanced on materials modified with fluorocarbon SMEs. In the presence of serum, bacterial adhesion was primarily neither material nor shear dependent. However, bacterial adhesion in serum was significantly reduced to < or = 10% compared to adhesion in serum-free media. Leukocyte adhesion in serum exhibited a shear dependency with increased adhesion occurring in regions exposed to lower shear-stress levels of < or = 7 dyne/cm2. Additionally, polydimethylsiloxane and polyethylene oxide SMEs reduced leukocyte adhesion on polyether-urethanes. In conclusion, these results suggest that surface chemistry and shear stress can mediate bacterial and cellular adhesion. Furthermore, materials modified with polyethylene oxide SMEs are capable of inhibiting bacterial adhesion, consequently minimizing the probability of biomaterial-centered infections.

  2. The Effect of Fluid Shear Stress on Endothelial Cell Adhesiveness to Polymer Surfaces with Wettability Gradient.

    PubMed

    Lee; Lee; Khang; Lee

    2000-10-01

    In this study, the adhesive strength of endothelial cells (ECs) attached on polymer surfaces with different hydrophilicity was investigated using wettability gradient polyethylene (PE) surfaces prepared by corona discharge treatment from a knife-type electrode whose power increases gradually along the sample length. The EC-attached wettability gradient surfaces were mounted on parallel-plate flow chambers in a flow system prepared for cell adhesiveness test. Three different shear stresses (150, 200, and 250 dyne/cm(2)) were applied to the flow chambers and each shear stress was maintained for 120 min to investigate the effect of shear stress and surface hydrophilicity on the EC adhesion strength. It was observed that the ECs were adhered more onto the positions with moderate hydrophilicity of the wettability gradient surface than onto the more hydrophobic or hydrophilic positions. The maximum adhesion of the cells appeared at around water contact angles of 55 degrees. The EC adhesion strength was higher on the hydrophilic positions than on the hydrophobic ones. However, the maximum adhesion strength of the cells also appeared at around water contact angles of 55 degrees. More than 90% of the adhered cells remained on that position after applying the shear stress, 250 dyne/cm(2) for 2 h, whereas the cells were completely detached on the hydrophobic position (water contact angle, about 86 degrees ) within 10 min after applying the same shear stress. It seems that surface hydrophilicity plays a very important role for cell adhesion strength. Copyright 2000 Academic Press.

  3. LDL decreases the membrane compliance and cell adhesion of endothelial cells under fluid shear stress.

    PubMed

    Wei, Dangheng; Chen, Yongpeng; Tang, Chaojun; Huang, Hua; Liu, Lushan; Wang, Zuo; Li, Ruming; Wang, Guixue

    2013-03-01

    Atherosclerosis is an inflammatory disease of large and medium sized arteriole walls that is precipitated by elevated levels of low-density lipoprotein (LDL) cholesterol in the blood. However, the mechanisms that lead to the initiation of atherosclerosis are not fully understood. In this study, endothelial cells (ECs) were incubated with LDL for 24 h, and then the lipid was detected with Oil Red O staining and cholesterol ester was assayed with high-performance liquid chromatography (HPLC). F-actin was examined by fluorescence microscopy and the viscoelasticity of ECs was investigated using the micropipette aspiration technique. Then, a parallel-plate flow chamber device was used to observe the adhesion and retention of ECs under shear stress. The results demonstrated that elevated LDL significantly increased the cellular lipid content and induced the rearrangement of cytoskeletal F-actin. The initial rapid deformability (l/K 1 + l/K 2) was reduced by elevated cellular LDL levels, while membrane viscosity (μ) was increased by LDL accumulation. After treatment with 150 mg L(-1) LDL for 24 h, the adhesion of ECs under fluid shear stress was significantly decreased (p < 0.05). These results suggested that LDL induced cellular lipid accumulation and cytoskeleton reorganization which increased the cellular stiffness and decreased the adhesion of ECs.

  4. Surface morphology of platelet adhesion influenced by activators, inhibitors and shear stress

    NASA Astrophysics Data System (ADS)

    Watson, Melanie Groan

    Platelet activation involves multiple events, one of which is the generation and release of nitric oxide (NO), a platelet aggregation inhibitor. Platelets simultaneously send and receive various agents that promote a positive and negative feedback control system during hemostasis. Although the purpose of platelet-derived NO is not fully understood, NO is known to inhibit platelet recruitment. NO's relatively large diffusion coefficient allows it to diffuse more rapidly than platelet agonists. It may thus be able to inhibit recruitment of platelets near the periphery of a growing thrombus before agonists have substantially accumulated in those regions. Results from two studies in our laboratory differed in the extent to which platelet-derived NO decreased platelet adhesion. Frilot studied the effect of L-arginine (L-A) and NG-Methyl-L-arginine acetate salt (L-NMMA) on platelet adhesion to collagen under static conditions in a Petri dish. Eshaq examined the percent coverage on collagen-coated and fibrinogen-coated microchannels under shear conditions with different levels of L-A and Adenosine Diphosphate (ADP). Frilot's results showed no effect of either L-A or L-NMMA on surface coverage, thrombus size or serotonin release, while Eshaq's results showed a decrease in surface coverage with increased levels of L-A. A possible explanation for these contrasting results is that platelet-derived NO may be more important under flow conditions than under static conditions. For this project, the effects of L-A. ADP and L-NMMA on platelet adhesion were studied at varying shear stresses on protein-coated glass slides. The surface exposed to platelet-rich-plasma in combination with each chemical solution was observed under AFM, FE-SEM and fluorescence microscopy. Quantitative and qualitative comparisons of images obtained with these techniques confirmed the presence of platelets on the protein coatings. AFM images of fibrinogen and collagen-coated slides presented characteristic

  5. Wall Shear Stress-Based Model for Adhesive Dynamics of Red Blood Cells in Malaria

    PubMed Central

    Fedosov, Dmitry A.; Caswell, Bruce; Karniadakis, George Em

    2011-01-01

    Red blood cells (RBCs) infected by the Plasmodium falciparum (Pf-RBCs) parasite lose their membrane deformability and they also exhibit enhanced cytoadherence to vascular endothelium and other healthy and infected RBCs. The combined effect may lead to severe disruptions of normal blood circulation due to capillary occlusions. Here we extend the adhesion model to investigate the adhesive dynamics of Pf-RBCs as a function of wall shear stress (WSS) and other parameters using a three-dimensional, multiscale RBC model. Several types of adhesive behavior are identified, including firm adhesion, flipping dynamics, and slow slipping along the wall. In particular, the flipping dynamics of Pf-RBCs observed in experiments appears to be due to the increased stiffness of infected cells and the presence of the solid parasite inside the RBC, which may cause an irregular adhesion behavior. Specifically, a transition from crawling dynamics to flipping behavior occurs at a Young's modulus approximately three times larger than that of healthy RBCs. The simulated dynamics of Pf-RBCs is in excellent quantitative agreement with available microfluidic experiments if the force exerted on the receptors and ligands by an existing bond is modeled as a nonlinear function of WSS. PMID:21539775

  6. Probing the adhesion of particles to responsive polymer coatings with hydrodynamic shear stresses

    NASA Astrophysics Data System (ADS)

    Toomey, Ryan; Efe, Gulnur

    2015-03-01

    Lower critical solution temperature (LCST) polymers in confined geometries have found success in applications that benefit from reversible modulation of surface properties, including drug delivery, separations, tissue cultures, and chromatography. In this talk, we present the adhesion of polystyrene microspheres to cross-linked poly(N-isopropylacrylamide), or poly(NIPAAm) coatings, as studied with a spinning disk method. This method applies a linear range of hydrodynamic shear forces to physically adsorbed microspheres along the radius of a coated disk. Quantification of detachment is accomplished by optical microscopy to evaluate the minimum shear stress to remove adherent particles. Experiments were performed to assess the relationship between the surface chemistry of the microsphere, the thickness and cross-link density of the poly(NIPAAm) coating, the adsorption (or incubation) time, and the temperature on the detachment profiles of the microspheres. Results show that both the shear modulus and slow dynamic processes in the poly(NIPAAm) films strongly influence the detachment shear stresses. Moreover, whether an adsorbed microsphere can be released (through a modulation in the swelling of the poly(NIPAAm) coating by temperature) depends on both the surface chemistry of the microsphere and the extent of the adsorption time. Finally, the results show that the structure of the poly(NIPAAm) coating can significantly affect performance, which may explain several of the conflicting findings that have been reported in the literature.

  7. Mechanism of platelet adhesion to von Willebrand factor and microparticle formation under high shear stress

    PubMed Central

    Reininger, Armin J.; Heijnen, Harry F. G.; Schumann, Hannah; Specht, Hanno M.; Schramm, Wolfgang; Ruggeri, Zaverio M.

    2006-01-01

    We describe here the mechanism of platelet adhesion to immobilized von Willebrand factor (VWF) and subsequent formation of platelet-derived microparticles mediated by glycoprotein Ibα (GPIbα) under high shear stress. As visualized in whole blood perfused in a flow chamber, platelet attachment to VWF involved one or few membrane areas of 0.05 to 0.1 μm2 that formed discrete adhesion points (DAPs) capable of resisting force in excess of 160 pN. Under the influence of hydrodynamic drag, membrane tethers developed between the moving platelet body and DAPs firmly adherent to immobilized VWF. Continued stretching eventually caused the separation of many such tethers, leaving on the surface tube-shaped or spherical microparticles with a diameter as low as 50 to 100 nm. Adhesion receptors (GPIbα, αIIbβ3) and phosphatidylserine were expressed on the surface of these microparticles, which were procoagulant. Shearing platelet-rich plasma at the rate of 10 000 s–1 in a cone-and-plate viscosimeter increased microparticle counts up to 55-fold above baseline. Blocking the GPIb-VWF interaction abolished microparticle generation in both experimental conditions. Thus, a biomechanical process mediated by GPIbα-VWF bonds in rapidly flowing blood may not only initiate platelet arrest onto reactive vascular surfaces but also generate procoagulant microparticles that further enhance thrombus formation. PMID:16449527

  8. [Comparison of adhesion of different endothelial cells under shear stress load in the flow field in vitro].

    PubMed

    Xiao, Zhenghua; Zhang, Bengui; Zhang, Eryong; Xu, Weilin; Shi, Yingkang; Guo, Yingqiang

    2011-02-01

    This study was aimed to compare the differences of adhesion properties of endothelial cells (EC) from arteries (AEC), veins (VEC) and capillaries (MVEC) under shear stress condition, and to explore whether they can get the same adhesive ability as graft in similar shear stress conditions. With mended parallel plate flow apparatus and peristalsis pump providing fluid shear stress used, endothelial culture models were established in vitro with the same environmental factors as steady culture. To compare the adhesion among three kinds of endothelial cells under dynamic condition and static condition, the dynamic change of cytoskeletal actin filaments and the effects of different adhesive proteins coated on the adhesion of EC to the glass were studied. The cultured endothelial cells under flow conditions were extended and arranged along the direction of flow. The adhesive ability from high to low under static condition were AEC, MVEC and VEC (VEC compared with AEC or MVEC, P < 0.05), sequentially. The adhesion of endothelial cells from variety sources under dynamic culture condition was significantly increased than that of the static groups. The ratio of cell retention was not significantly different between AEC and MVEC. But VEC was significantly different (P < 0.05) compared with AEC or MVEC. The actin filaments (F-actin) were bundled together and arranged along the direction of flow after fluid culture. Dense peripheral band (DPB) gradually disappeared and distinct stress fibers were formed, which even interconnected to form a whole in the MVEC. The adhesion of AEC, VEC and MVEC under shear stress conditions are more significantly increased than those under the static culture conditions, and the MVEC can achieve the same adhesion as AEC.

  9. A Flow Adhesion Assay to Study Leucocyte Recruitment to Human Hepatic Sinusoidal Endothelium Under Conditions of Shear Stress

    PubMed Central

    Shetty, Shishir; Weston, Christopher J.; Adams, David H.; Lalor, Patricia F.

    2014-01-01

    Leucocyte infiltration into human liver tissue is a common process in all adult inflammatory liver diseases. Chronic infiltration can drive the development of fibrosis and progression to cirrhosis. Understanding the molecular mechanisms that mediate leucocyte recruitment to the liver could identify important therapeutic targets for liver disease. The key interaction during leucocyte recruitment is that of inflammatory cells with endothelium under conditions of shear stress. Recruitment to the liver occurs within the low shear channels of the hepatic sinusoids which are lined by hepatic sinusoidal endothelial cells (HSEC). The conditions within the hepatic sinusoids can be recapitulated by perfusing leucocytes through channels lined by human HSEC monolayers at specific flow rates. In these conditions leucocytes undergo a brief tethering step followed by activation and firm adhesion, followed by a crawling step and subsequent transmigration across the endothelial layer. Using phase contrast microscopy, each step of this 'adhesion cascade' can be visualized and recorded followed by offline analysis. Endothelial cells or leucocytes can be pretreated with inhibitors to determine the role of specific molecules during this process. PMID:24686418

  10. Material characterization of structural adhesives in the lap shear mode

    NASA Technical Reports Server (NTRS)

    Sancaktar, E.; Schenck, S. C.

    1983-01-01

    A general method for characterizing structual adhesives in the bonded lap shear mode is proposed. Two approaches in the form of semiempirical and theoretical approaches are used. The semiempirical approach includes Ludwik's and Zhurkov's equations to describe respectively, the failure stresses in the constant strain rate and constant stress loading modes with the inclusion of the temperature effects. The theoretical approach is used to describe adhesive shear stress-strain behavior with the use of viscoelastic or nonlinear elastic constitutive equations. Two different model adhesives are used in the single lap shear mode with titanium adherends. These adhesives (one of which was developed at NASA Langley Research Center) are currently considered by NASA for possible aerospace applications. Use of different model adhesives helps in assessment of the generality of the method.

  11. Tensile and shear strength of adhesives

    NASA Technical Reports Server (NTRS)

    Stibolt, Kenneth A.

    1990-01-01

    This experiment is conducted in a freshman-level course: Introduction to Engineering Materials. There are no prerequisites for the course although students should have some knowledge of basic algebra. The objectives are to tension and shear test adhesives and to determine the tensile and shear properties of adhesives. Details of equipment of procedure are given.

  12. Bone morphogenic protein 4 produced in endothelial cells by oscillatory shear stress induces monocyte adhesion by stimulating reactive oxygen species production from a nox1-based NADPH oxidase.

    PubMed

    Sorescu, George P; Song, Hannah; Tressel, Sarah L; Hwang, Jinah; Dikalov, Sergey; Smith, Debra A; Boyd, Nolan L; Platt, Manu O; Lassègue, Bernard; Griendling, Kathy K; Jo, Hanjoong

    2004-10-15

    Atherosclerosis is an inflammatory disease occurring preferentially in arterial regions exposed to disturbed flow conditions including oscillatory shear stress (OS). OS exposure induces endothelial expression of bone morphogenic protein 4 (BMP4), which in turn may activate intercellular adhesion molecule-1 (ICAM-1) expression and monocyte adhesion. OS is also known to induce monocyte adhesion by producing reactive oxygen species (ROS) from reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, raising the possibility that BMP4 may stimulate the inflammatory response by ROS-dependent mechanisms. Here we show that ROS scavengers blocked ICAM-1 expression and monocyte adhesion induced by BMP4 or OS in endothelial cells (ECs). Similar to OS, BMP4 stimulated H2O2 and O2- production in ECs. Next, we used ECs obtained from p47phox-/- mice (MAE-p47-/-), which do not produce ROS in response to OS, to determine the role of NADPH oxidases. Similar to OS, BMP4 failed to induce monocyte adhesion in MAE-p47-/-, but it was restored when the cells were transfected with p47phox plasmid. Moreover, OS-induced O2- production was blocked by noggin (a BMP antagonist), suggesting a role for BMP. Furthermore, OS increased gp91phox (nox2) and nox1 mRNA levels while decreasing nox4. In contrast, BMP4 induced nox1 mRNA expression, whereas nox2 and nox4 were decreased or not affected, respectively. Also, OS-induced monocyte adhesion was blocked by knocking down nox1 with the small interfering RNA (siRNA). Finally, BMP4 siRNA inhibited OS-induced ROS production and monocyte adhesion. Together, these results suggest that BMP4 produced in ECs by OS stimulates ROS release from the nox1-dependent NADPH oxidase leading to inflammation, a critical early atherogenic step. PMID:15388638

  13. Shear adhesion strength of aligned electrospun nanofibers.

    PubMed

    Najem, Johnny F; Wong, Shing-Chung; Ji, Guang

    2014-09-01

    Inspiration from nature such as insects' foot hairs motivates scientists to fabricate nanoscale cylindrical solids that allow tens of millions of contact points per unit area with material substrates. In this paper, we present a simple yet robust method for fabricating directionally sensitive shear adhesive laminates. By using aligned electrospun nylon-6, we create dry adhesives, as a succession of our previous work on measuring adhesion energies between two single free-standing electrospun polymer fibers in cross-cylinder geometry, randomly oriented membranes and substrate, and peel forces between aligned fibers and substrate. The synthetic aligned cylindrical solids in this study are electrically insulating and show a maximal Mode II shear adhesion strength of 27 N/cm(2) on a glass slide. This measured value, for the purpose of comparison, is 270% of that reported from gecko feet. The Mode II shear adhesion strength, based on a commonly known "dead-weight" test, is 97-fold greater than the Mode I (normal) adhesion strength of the same. The data indicate a strong shear binding on and easy normal lifting off. Anisotropic adhesion (Mode II/Mode I) is pronounced. The size and surface boundary effects, crystallinity, and bending stiffness of fibers are used to understand these electrospun nanofibers, which vastly differ from otherwise known adhesive technologies. The anisotropic strength distribution is attributed to a decreasing fiber diameter and an optimized laminate thickness, which, in turn, influences the bending stiffness and solid-state "wettability" of points of contact between nanofibers and surface asperities.

  14. Improvement in endothelial cell adhesion and retention under physiological shear stress using a laminin–apatite composite layer on titanium

    PubMed Central

    He, Fupo; Wang, Xiupeng; Maruyama, Osamu; Kosaka, Ryo; Sogo, Yu; Ito, Atsuo; Ye, Jiandong

    2013-01-01

    Apatite (Ap), laminin–apatite composite (L5Ap, L10Ap, L20Ap and L40Ap) and albumin–apatite (AlbAp) composite layers were prepared on titanium (Ti) using a supersaturated calcium phosphate solution supplemented with laminin (0, 5, 10, 20 and 40 μg ml−1) or albumin (800 μg ml−1). With an increase in the concentrations of laminin in the supersaturated calcium phosphate solutions, the amounts of laminin immobilized on the Ti increased. The number of human umbilical vein endothelial cells (HUVECs) adhered to the laminin–apatite composite layers were remarkably higher than those to the untreated Ti, Ap layer and AlbAp composite layer. The number of cells adhered to the L40Ap was 4.3 times the untreated Ti. Moreover, cells adhered to the laminin–apatite composite layers showed significantly higher cell retention under the physiological shear stress for 1 h and 2 h than those to the untreated Ti, Ap layer and AlbAp composite layer. The number of cells remaining on the L40Ap under the physiological shear stress for 2 h was 9.5 times that of the untreated Ti. The laminin–apatite composite layer is a promising interfacial layer for endothelialization of blood-contacting materials. PMID:23407573

  15. The effect of bending on the stresses in adhesive joints

    NASA Technical Reports Server (NTRS)

    Yuceoglu, U.; Updike, D. P.

    1975-01-01

    The problem of stress distribution in adhesive joints where two orthotropic plates are bonded through a flexible adhesive layer is analyzed. It is shown that the effect of bending of the adherends on the stresses in the adhesive layer is very significant. The transverse shear deformations of the adherends appear to have little influence on the adhesive layer stresses. The maximum transverse normal stress in the adhesive is shown to be larger than the maximum longitudinal shear stress. The method of solution is applied to several examples of specific joint geometries and material combinations, and is proven to be applicable to other related problems.

  16. Friction and shear fracture of an adhesive contact under torsion

    NASA Astrophysics Data System (ADS)

    Chateauminois, Antoine; Fretigny, Christian; Olanier, Ludovic

    2010-02-01

    The shear failure or stiction of an adhesive contact between a poly(dimethylsiloxane) (PDMS) rubber and a glass lens has been investigated using a torsional contact configuration. As compared to linear sliding, torsion presents the advantage of inducing a shear failure under a pure mode III condition, while preserving the cylindrical symmetry of the contact. The surface of the transparent PDMS substrate was marked using a network of dots in order to monitor continuously the in-plane surface displacements during the stiction process. Using a previously developed inversion procedure (A. Chateauminois and C. Fretigny, Eur. Phys. J. E 27, 221 (2008)), the corresponding surface shear stress distributions were obtained from the displacement fields. Stiction was found to involve the progressive shrinkage of a central adhesive zone surrounded by an annular microslip region. Adhesion effects were especially evidenced from a stress overshoot at the boundary of the adhesive zone. The experimental data were analysis using an extension to torsional contact of the Maugis-Dugdale approach’s to adhesive contacts which takes into account frictional effects. This model allowed to extract an effective adhesion energy in the presence of friction, which dependence on kinetics effect is briefly discussed.

  17. Lap Shear Testing of Candidate Radiator Panel Adhesives

    NASA Technical Reports Server (NTRS)

    Ellis, David; Briggs, Maxwell; McGowan, Randy

    2013-01-01

    During testing of a subscale radiator section used to develop manufacturing techniques for a full-scale radiator panel, the adhesive bonds between the titanium heat pipes and the aluminum face sheets failed during installation and operation. Analysis revealed that the thermal expansion mismatch between the two metals resulted in relatively large shear stresses being developed even when operating the radiator at moderate temperatures. Lap shear testing of the adhesive used in the original joints demonstrated that the two-part epoxy adhesive fell far short of the strength required. A literature review resulted in several candidate adhesives being selected for lap shear joint testing at room temperature and 398 K, the nominal radiator operating temperature. The results showed that two-part epoxies cured at room and elevated temperatures generally did not perform well. Epoxy film adhesives cured at elevated temperatures, on the other hand, did very well with most being sufficiently strong to cause yielding in the titanium sheet used for the joints. The use of an epoxy primer generally improved the strength of the joint. Based upon these results, a new adhesive was selected for the second subscale radiator section.

  18. A Study of the Effect of Adhesive and Matrix Stiffnesses on the Axial, Normal, and Shear Stress Distributions of a Boron-epoxy Reinforced Composite Joint. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Howell, W. E.

    1974-01-01

    The mechanical properties of a symmetrical, eight-step, titanium-boron-epoxy joint are discussed. A study of the effect of adhesive and matrix stiffnesses on the axial, normal, and shear stress distributions was made using the finite element method. The NASA Structural Analysis Program (NASTRAN) was used for the analysis. The elastic modulus of the adhesive was varied from 345 MPa to 3100 MPa with the nominal value of 1030 MPa as a standard. The nominal values were used to analyze the stability of the joint. The elastic moduli were varied to determine their effect on the stresses in the joint.

  19. Adhesion study of silicone coatings: the interaction of thickness, modulus and shear rate on adhesion force.

    PubMed

    Kim, Jongsoo; Chisholm, Bret J; Bahr, James

    2007-01-01

    Interactions between coating thickness, modulus and shear rate on pseudobarnacle adhesion to a platinum-cured silicone coating were studied using a statistical experimental design. A combined design method was used for two mixture components and two process variables. The two mixture components, vinyl end-terminated polydimethylsiloxanes (V21: MW=6 kg mole(-1) and V35: MW=4 9.5 kg mole(-1), Gelest Inc.) were mixed at five different levels to vary the modulus. The dry coating thickness was varied from 160 - 740 microm and shear tests were performed at four different shear rates (2, 7, 12, and 22 microm s(-1)). The results of the statistical analysis showed that the mixture components were significant factors on shear stress, showing an interaction with the process variable. For the soft silicone coating based on the high molecular weight polydimethylsiloxane (E=0.08 MPa), shear stress significantly increased as coating thickness decreased, while shear rate slightly impacted shear force especially at 160 microm coating thickness. As the modulus was increased (E=1.3 MPa), more force was required to detach the pseudobarnacle from the coatings, but thickness and rate dependence on shear stress became less important. PMID:17453735

  20. A Piezoelectric Shear Stress Sensor

    NASA Technical Reports Server (NTRS)

    Kim, Taeyang; Saini, Aditya; Kim, Jinwook; Gopalarathnam, Ashok; Zhu, Yong; Palmieri, Frank L.; Wohl, Christopher J.; Jiang, Xiaoning

    2016-01-01

    In this paper, a piezoelectric sensor with a floating element was developed for shear stress measurement. The piezoelectric sensor was designed to detect the pure shear stress suppressing effects of normal stress generated from the vortex lift-up by applying opposite poling vectors to the: piezoelectric elements. The sensor was first calibrated in the lab by applying shear forces and it showed high sensitivity to shear stress (=91.3 +/- 2.1 pC/Pa) due to the high piezoelectric coefficients of PMN-33%PT (d31=-1330 pC/N). The sensor also showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is 0-800 Hz. Keywords: Piezoelectric sensor, shear stress, floating element, electromechanical symmetry

  1. Oscillatory shear stress stimulates endothelial production of O2- from p47phox-dependent NAD(P)H oxidases, leading to monocyte adhesion

    NASA Technical Reports Server (NTRS)

    Hwang, Jinah; Saha, Aniket; Boo, Yong Chool; Sorescu, George P.; McNally, J. Scott; Holland, Steven M.; Dikalov, Sergei; Giddens, Don P.; Griendling, Kathy K.; Harrison, David G.; Jo, Hanjoong

    2003-01-01

    Arterial regions exposed to oscillatory shear (OS) in branched arteries are lesion-prone sites of atherosclerosis, whereas those of laminar shear (LS) are relatively well protected. Here, we examined the hypothesis that OS and LS differentially regulate production of O2- from the endothelial NAD(P)H oxidase, which, in turn, is responsible for their opposite effects on a critical atherogenic event, monocyte adhesion. We used aortic endothelial cells obtained from C57BL/6 (MAE-C57) and p47phox-/- (MAE-p47-/-) mice, which lack a component of NAD(P)H oxidase. O2- production was determined by dihydroethidium staining and an electron spin resonance using an electron spin trap methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine. Chronic exposure (18 h) to an arterial level of OS (+/- 5 dynes/cm2) increased O2- (2-fold) and monocyte adhesion (3-fold) in MAE-C57 cells, whereas chronic LS (15 dynes/cm2, 18 h) significantly decreased both monocyte adhesion and O2- compared with static conditions. In contrast, neither LS nor OS were able to induce O2- production and monocyte adhesion to MAE-p47-/-. Treating MAE-C57 with a cell-permeable superoxide dismutase compound, polyethylene glycol-superoxide dismutase, also inhibited OS-induced monocyte adhesion. In addition, over-expressing p47phox in MAE-p47-/- restored OS-induced O2- production and monocyte adhesion. These results suggest that chronic exposure of endothelial cells to OS stimulates O2- and/or its derivatives produced from p47phox-dependent NAD(P)H oxidase, which, in turn, leads to monocyte adhesion, an early and critical atherogenic event.

  2. Material characterization of structural adhesives in the lap shear mode. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Schenck, S. C.; Sancaktar, E.

    1983-01-01

    A general method for characterizing structural adhesives in the bonded lap shear mode is proposed. Two approaches in the form of semi-empirical and theoretical approaches are used. The semi-empirical approach includes Ludwik's and Zhurkov's equations to describe respectively, the failure stresses in the constant strain rate and constant stress loading modes with the inclusion of the temperature effects. The theoretical approach is used to describe adhesive shear stress-strain behavior with the use of viscoelastic or nonlinear elastic constitutive equations. Three different model adhesives are used in the simple lap shear mode with titanium adherends. These adhesives (one of which was developed at NASA Langley Research Center) are currently considered by NASA for possible aerospace applications. Use of different model adhesives helps in assessment of the generality of the method.

  3. A piezoelectric shear stress sensor

    NASA Astrophysics Data System (ADS)

    Kim, Taeyang; Saini, Aditya; Kim, Jinwook; Gopalarathnam, Ashok; Zhu, Yong; Palmieri, Frank L.; Wohl, Christopher J.; Jiang, Xiaoning

    2016-04-01

    In this paper, a piezoelectric sensor with a floating element was developed for shear stress measurement. The piezoelectric sensor was designed to detect the pure shear stress, suppressing effects of normal stress components, by applying opposite poling vectors to the piezoelectric elements. The sensor was first calibrated in the lab by applying shear forces where it demonstrated high sensitivity to shear stress (91.3 +/- 2.1 pC/Pa) due to the high piezoelectric coefficients of 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-33%PT, d31=-1330 pC/N). The sensor also exhibited negligible sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is up to 800 Hz.

  4. Shear adhesion strength of thermoplastic gecko-inspired synthetic adhesive exceeds material limits.

    PubMed

    Gillies, Andrew G; Fearing, Ronald S

    2011-09-20

    Natural gecko array wearless dynamic friction has recently been reported for 30,000 cycles on a smooth substrate. Following these findings, stiff polymer gecko-inspired synthetic adhesives have been proposed for high-cycle applications such as robot feet. Here we examine the behavior of high-density polyethylene (HDPE) and polypropylene (PP) microfiber arrays during repeated cycles of engagement on a glass surface, with a normal preload of less than 40 kPa. We find that fiber arrays maintained 54% of the original shear stress of 300 kPa after 10,000 cycles, despite showing a marked plastic deformation of fiber tips. This deformation could be due to shear-induced plastic creep of the fiber tips from high adhesion forces, adhesive wear, or thermal effects. We hypothesize that a fundamental material limit has been reached for these fiber arrays and that future gecko synthetic adhesive designs must take into account the high adhesive forces generated to avoid damage. Although the synthetic material and natural gecko arrays have a similar elastic modulus, the synthetic material does not show the same wear-free dynamic friction as the gecko.

  5. Shear Adhesive Connections for Glass Structures

    NASA Astrophysics Data System (ADS)

    Machalická, K.; Horčičková, I.; Eliášová, M.

    2015-11-01

    Unique aesthetical properties of glass - not only transparency but also smooth, glossy and primarily reflective surface - give this material special importance in the contemporary architecture. In every structural application of glass it is necessary to solve the problem associated with connections between glass pane and other part from a different material or between two glass elements. Moreover, there are many types of hybrid structures that combine glass and different materials to achieve safe failure behaviour and high degree of transparency at the same time. Connection of brittle glass and reinforcing material is an essential part of these structures, where composite action between two parts is beneficially ensured by a glued joint. The current paper deals with the experimental analysis focused on the determination of mechanical characteristics of adhesives applied in planar connections under shear loading.

  6. Shear stress cleaning for surface departiculation

    NASA Technical Reports Server (NTRS)

    Musselman, R. P.; Yarbrough, T. W.

    1986-01-01

    A cleaning technique widely used by the nuclear utility industry for removal of radioactive surface contamination has proven effective at removing non-hazardous contaminant particles as small as 0.1 micrometer. The process employs a controlled high velocity liquid spray inside a vapor containment enclosure to remove particles from a surface. The viscous drag force generated by the cleaning fluid applies a shear stress greater than the adhesion force that holds small particles to a substrate. Fluid mechanics and field tests indicate general cleaning parameters.

  7. Fluid-shear method to evaluate bacterial adhesion to glass surfaces

    NASA Astrophysics Data System (ADS)

    Zhou, Yan; Torres, Ashley; Chen, Liangxian; Kong, Ying; Cirillo, Jeffrey D.; Liang, H.

    2012-07-01

    Adhered bacteria onto different surfaces cause infection that affects our health and environments. The understanding of the bacterial adhesive strength is crucial for better control and safe manufacturing in order to design adhesion resistant materials. The current evaluation methods lack precision and are often time consuming. In the present research, we developed a fluid-shear method to quantitatively evaluate bacterial adhesive strength on glass substrates. The glass was chosen based on its abundance in household, industrial, and medical environments. The fluid shear stress applied by a rheometer ranged from 0 to 3 Pa and the average surface roughness (Ra) of glass ranged from 1 to 23 nm. Bacterial adhesive stress was calculated based on the measurement of the critical radius. It was also found that the adhesive strength decreased with the increase of surface roughness, while the number of adhered bacteria increased when the surface become rougher. The fluid-shear method was proven to be effective in measure bacterial adhesion on a surface.

  8. Shear Strength of Conductive Adhesive Joints on Rigid and Flexible Substrates Depending on Adhesive Quantity

    NASA Astrophysics Data System (ADS)

    Hirman, Martin; Steiner, Frantisek

    2016-05-01

    This article deals with the impact of electrically conductive adhesive quantity on the shear strength of joints glued by adhesives "EPO-TEKⓇ H20S" and "MG8331S" on three types of substrates (FR-4, MELINEXⓇST504, DuPont™ PyraluxⓇAC). These joints were made by gluing chip resistors 1206, 0805 and 0603, with two curing profiles for each adhesive. Different thicknesses of stencil and reductions in the size of the hole in stencils were used for this experiment. These differences have an effect on the quantity of conductive adhesives which must be used on the samples. Samples were measured after the curing process by using a shear strength test applied by the device LabTest 3.030. This article presents the effects of different curing profiles, various types of substrates, and different quantities of adhesives on the mechanical strength of the joint.

  9. Theory of the mechanical response of focal adhesions to shear flow

    NASA Astrophysics Data System (ADS)

    Biton, Y. Y.; Safran, S. A.

    2010-05-01

    The response of cells to shear flow is primarily determined by the asymmetry of the external forces and moments that are sensed by each member of a focal adhesion pair connected by a contractile stress fiber. In the theory presented here, we suggest a physical model in which each member of such a pair of focal adhesions is treated as an elastic body subject to both a myosin-activated contractile force and the shear stress induced by the external flow. The elastic response of a focal adhesion complex is much faster than the active cellular processes that determine the size of the associated focal adhesions and the direction of the complex relative to the imposed flow. Therefore, the complex attains its mechanical equilibrium configuration which may change because of the cellular activity. Our theory is based on the experimental observation that focal adhesions modulate their cross-sectional area in order to attain an optimal shear. Using this assumption, our elastic model shows that such a complex can passively change its orientation to align parallel to the direction of the flow.

  10. MAPKs (ERK1/2, p38) and AKT can be phosphorylated by shear stress independently of platelet endothelial cell adhesion molecule-1 (CD31) in vascular endothelial cells.

    PubMed

    Sumpio, Bauer E; Yun, Sangseob; Cordova, Alfredo C; Haga, Masae; Zhang, Jin; Koh, Yongbok; Madri, Joseph A

    2005-03-25

    PECAM-1 (CD31) is a member of the Ig superfamily of cell adhesion molecules and is expressed on endothelial cells (EC) as several circulating blood elements including platelets, polymorphonuclear leukocytes, monocytes, and lymphocytes. PECAM-1 tyrosine phosphorylation has been observed following mechanical stimulation of EC but its role in mechanosensing is still incompletely understood. The aim of this study was to investigate the involvement of PECAM-1 in signaling cascades in response to fluid shear stress (SS) in vascular ECs. PECAM-1-deficient (KO) and PECAM-reconstituted murine microvascular ECs, 50 and 100% confluent bovine aortic EC (BAEC), and human umbilical vein EC (HUVEC) transfected with antisense PECAM-1 oligonucleotides were exposed to oscillatory SS (14 dynes/cm2) for 0, 5, 10, 30 or 60 min. The tyrosine phosphorylation level of PECAM-1 immunoprecipitated from SS-stimulated PECAM-reconstituted, but not PECAM-1-KO, murine ECs increased. Although PECAM-1 was phosphorylated in 100% confluent BAEC and HUVEC, its phosphorylation level in 50% confluent BAECs or HUVEC was not detected by SS. Likewise PECAM-1 phosphorylation was robust in the wild type and scrambled-transfected HUVEC but not in the PECAM-1 antisense-HUVEC. ERK(1/2), p38 MAPK, and AKT were activated by SS in all cell types tested, including the PECAM-1-KO murine ECs, 50% confluent BAECs, and HUVEC transfected with antisense PECAM-1. This suggests that PECAM-1 may not function as a major mechanoreceptor for activation of MAPK and AKT in ECs and that there are likely to be other mechanoreceptors in ECs functioning to detect shear stress and trigger intercellular signals. PMID:15668248

  11. Surface deformation and shear flow in ligand mediated cell adhesion.

    PubMed

    Sircar, Sarthok; Roberts, Anthony J

    2016-10-01

    We present a unified, multiscale model to study the attachment/detachment dynamics of two deforming, charged, near spherical cells, coated with binding ligands and subject to a slow, homogeneous shear flow in a viscous, ionic fluid medium. The binding ligands on the surface of the cells experience both attractive and repulsive forces in an ionic medium and exhibit finite resistance to rotation via bond tilting. The microscale drag forces and couples describing the fluid flow inside the small separation gap between the cells, are calculated using a combination of methods in lubrication theory and previously published numerical results. For a selected range of material and fluid parameters, a hysteretic transition of the sticking probability curves (i.e., the function [Formula: see text]) between the adhesion phase (when [Formula: see text]) and the fragmentation phase (when [Formula: see text]) is attributed to a nonlinear relation between the total nanoscale binding forces and the separation gap between the cells. We show that adhesion is favoured in highly ionic fluids, increased deformability of the cells, elastic binders and a higher fluid shear rate (until a critical threshold value of shear rate is reached). Within a selected range of critical shear rates, the continuation of the limit points (i.e., the turning points where the slope of [Formula: see text] changes sign) predict a bistable region, indicating an abrupt switching between the adhesion and the fragmentation regimes. Although, bistability in the adhesion-fragmentation phase diagram of two deformable, charged cells immersed in an ionic aqueous environment has been identified by some in vitro experiments, but until now, has not been quantified theoretically.

  12. A multi-shear perfusion bioreactor for investigating shear stress effects in endothelial cell constructs.

    PubMed

    Rotenberg, Menahem Y; Ruvinov, Emil; Armoza, Anna; Cohen, Smadar

    2012-08-01

    Tissue engineering research is increasingly relying on the use of advanced cultivation technologies that provide rigorously-controlled cell microenvironments. Herein, we describe the features of a micro-fabricated Multi-Shear Perfusion Bioreactor (MSPB) designed to deliver up to six different levels of physiologically-relevant shear stresses (1-13 dyne cm(-2)) to six cell constructs simultaneously, during a single run. To attain a homogeneous fluid flow within each construct, flow-distributing nets photo-etched with a set of openings for fluid flow were placed up- and down-stream from each construct. Human umbilical vein endothelial cells (HUVECs) seeded in alginate scaffolds within the MSPB and subjected to three different levels of shear stress for 24 h, responded accordingly by expressing three different levels of the membranal marker Intercellular Adhesion Molecule 1 (ICAM-1) and the phosphorylated endothelial nitric oxide synthetase (eNOS). A longer period of cultivation, 17 d, under two different levels of shear stress resulted in different lengths of cell sprouts within the constructs. Collectively, the HUVEC behaviour within the different constructs confirms the feasibility of using the MSPB system for simultaneously imposing different shear stress levels, and for validating the flow regime in the bioreactor vessel as assessed by the computational fluid dynamic (CFD) model. PMID:22622237

  13. Shear stress facilitates tissue-engineered odontogenesis.

    PubMed

    Honda, M J; Shinohara, Y; Sumita, Y; Tonomura, A; Kagami, H; Ueda, M

    2006-07-01

    Numerous studies have demonstrated the effect of shear stress on osteoblasts, but its effect on odontogenic cells has never been reported. In this study, we focused on the effect of shear stress on facilitating tissue-engineered odontogenesis by dissociated single cells. Cells were harvested from the porcine third molar tooth at the early stage of crown formation, and the isolated heterogeneous cells were seeded on a biodegradable polyglycolic acid fiber mesh. Then, cell-polymer constructs with and without exposure to shear stress were evaluated by in vitro and in vivo studies. In in vitro studies, the expression of both epithelial and mesenchymal odontogenic-related mRNAs was significantly enhanced by shear stress for 2 h. At 12 h after exposure to shear stress, the expression of amelogenin, bone sialoprotein and vimentin protein was significantly enhanced compared with that of control. Moreover, after 7 days, alkaline phosphatase activity exhibited a significant increase without any significant effect on cell proliferation in vitro. In vivo, enamel and dentin tissues formed after 15 weeks of in vivo implantation in constructs exposure to in vitro shear stress for 12 h. Such was not the case in controls. We concluded that shear stress facilitates odontogenic cell differentiation in vitro as well as the process of tooth tissue engineering in vivo.

  14. Determining Shear Stress Distribution in a Laminate

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.

    2010-01-01

    A "simplified shear solution" method approximates the through-thickness shear stress distribution within a composite laminate based on an extension of laminated beam theory. The method does not consider the solution of a particular boundary value problem; rather, it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply-level stresses can be efficiently determined from global load resultants at a given location in a structure and used to evaluate the margin of safety on a ply-by-ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. The method has been incorporated within the HyperSizer commercial structural sizing software to improve its predictive capability for designing composite structures. The HyperSizer structural sizing software is used extensively by NASA to design composite structures. In the case of through-thickness shear loading on panels, HyperSizer previously included a basic, industry-standard, method for approximating the resulting shear stress distribution in sandwich panels. However, no such method was employed for solid laminate panels. The purpose of the innovation is to provide an approximation of the through-thickness shear stresses in a solid laminate given the through-thickness shear loads (Qx and Qy) on the panel. The method was needed for implementation within the HyperSizer structural sizing software so that the approximated ply-level shear stresses could be utilized in a failure theory to assess the adequacy of a panel design. The simplified shear solution method was developed based on extending and generalizing bi-material beam theory to plate-like structures. It is assumed that the through-thickness shear stresses arise due to local bending of the laminate induced by the through-thickness shear load, and by imposing

  15. A fracture mechanics analysis of adhesive failure in a single lap shear joint.

    NASA Technical Reports Server (NTRS)

    Devries, K. L.; Williams, M. L.; Chang, M. D.

    1972-01-01

    Discussion of adhesive fracture of single lap shear joints in terms of a maximum stress criterion and an energy balance. The Goland and Reissner (1944) analysis is used to determine the stress distribution in the adhesive assembly, and the results obtained are introduced into an energy balance to determine the initiation of adhesive fracture. In the stress analysis the loads at the edges of the joint are first determined. This is a problem in which the deformation of the joint sheets must be taken into account and is solved by using the finite-deflection theory of cylindrically bent plates. Then the stress in the joint due to applied loads is determined. This problem is formulated as one in plane strain consisting of two rectangular sheets of equal thickness and unit width. With the aid of this stress analysis and the stresses obtained from the conditions of equilibrium the contributions to the energy change with crack length are calculated. The analysis performed is then compared with a maximum stress criterion for a lap joint.

  16. Adhesion through L-selectin requires a threshold hydrodynamic shear

    NASA Astrophysics Data System (ADS)

    Finger, Erik B.; Purl, Kamal D.; Alon, Ronen; Lawrence, Michael B.; von Andrian, Ulrich H.; Springer, Timothy A.

    1996-01-01

    SELECTINS are cell adhesion molecules that bind carbohydrate ligands and promote interaction between leukocytes and the vessel wall in vascular shear flow1,2. Selectin-ligand bonds have high mechanical strength, allowing initial tethering to the vessel wall through one or few bonds, and have fast on and off rates, permitting rolling in response to hydrodynamic drag3. The L-selectin molecule on leukocytes binds to peripheral node addressin on high endothelial venules of lymph nodes to mediate leukocyte rolling4,5 and binds to a ligand on neutrophils to mediate rolling of leukocytes over one another6. Here we describe a surprising mechanism for regulation of these interactions, both in vitro and in vivo. Shear above a critical threshold is required to promote and maintain rolling interactions through L-selectin, but not through E-selectin, P-selectin or VCAM-1. The shear threshold requirement for L-selectin may be physiologically important in low shear to prevent inappropriate aggregation of leukocytes and interaction with the vessel wall.

  17. Evaluation of the micro-shear bond strength of four adhesive systems to dentin with and without adhesive area limitation.

    PubMed

    Chai, Yuan; Lin, Hong; Zheng, Gang; Zhang, Xuehui; Niu, Guangliang; Du, Qiao

    2015-01-01

    The purpose of this study was to evaluate the bonding ability of four representative dentin-adhesive systems by applying the micro-shear bond strength (μ-SBS) test method and to evaluate the influence of adhesive area limitation on the bond strength. Two different adhesive application methods were used in the μ-SBS test (with and without adhesives area limitation), and four representative adhesive systems were used in this study. Each dentin surface was treated with one of the four representative adhesive systems, and with twenty samples per group (n=20), each of the four groups underwent a μ-SBS test. The results showed that the bond strength was significantly influenced by the adhesive application method (p<0.05), the adhesive type (p<0.05) and the interaction between the two factors (p<0.05). With regard to the four representative dentin-adhesive systems, 3-E&R has a much better bond quality compared to the other adhesive systems. Furthermore, the micro-shear bond strength test method of restricting the area of both the adhesive and the resin is more reliable for evaluating the bonding property of adhesives to dentin, and it is also adequate for comparing the different adhesives systems. PMID:26406058

  18. Nonlocal Shear Stress for Homogeneous Fluids

    NASA Astrophysics Data System (ADS)

    Todd, B. D.; Hansen, J. S.; Daivis, Peter J.

    2008-05-01

    It has been suggested that for fluids in which the rate of strain varies appreciably over length scales of the order of the intermolecular interaction range, the viscosity must be treated as a nonlocal property of the fluid. The shear stress can then be postulated to be a convolution of this nonlocal viscosity kernel with the strain rate over all space. In this Letter, we confirm that this postulate is correct by a combination of analytical and numerical methods for an atomic fluid out of equilibrium. Furthermore, we show that a gradient expansion of the nonlocal constitutive equation gives a reasonable approximation to the shear stress in the small wave vector limit.

  19. Surface Plasmon Resonance (SPR) for the Evaluation of Shear-Force-Dependent Bacterial Adhesion

    PubMed Central

    Zagorodko, Oleksandr; Bouckaert, Julie; Dumych, Tetiana; Bilyy, Rostyslav; Larroulet, Iban; Yanguas Serrano, Aritz; Alvarez Dorta, Dimitri; Gouin, Sebastien G.; Dima, Stefan-Ovidiu; Oancea, Florin; Boukherroub, Rabah; Szunerits, Sabine

    2015-01-01

    The colonization of Escherichia coli (E. coli) to host cell surfaces is known to be a glycan-specific process that can be modulated by shear stress. In this work we investigate whether flow rate changes in microchannels integrated on surface plasmon resonance (SPR) surfaces would allow for investigating such processes in an easy and high-throughput manner. We demonstrate that adhesion of uropathogenic E. coli UTI89 on heptyl α-d-mannopyranoside-modified gold SPR substrates is minimal under almost static conditions (flow rates of 10 µL·min−1), and reaches a maximum at flow rates of 30 µL·min−1 (≈30 mPa). This concept is applicable to the investigation of any ligand-pathogen interactions, offering a robust, easy, and fast method for screening adhesion characteristics of pathogens to ligand-modified interfaces. PMID:26018780

  20. Ice adhesions in relation to freeze stress.

    PubMed

    Olien, C R; Smith, M N

    1977-10-01

    In freezing, competitive interaction between ice and hydrophilic plant substances causes an energy of adhesion to develop through the interstitial liquid. The thermodynamic basis for the adhesion energy is discussed, with estimates of the energies involved. In this research, effects of adhesion energy were observed microscopically in conjunction with energies of crystallization and frost desiccation. The complex character of ice in intact crown tissue of winter barley (Hordeum vulgare L.) and the problems of sectioning frozen tissue without producing artifacts led to an alternative study of single barley cells in a mesh of ice and cell wall polymers. Adhesions between ice, cell wall polymers, and the plasmalemma form a complexly interacting system in which the pattern of crystallization is a major factor in determination of stress and injury. PMID:16660124

  1. Shear Pressed Aligned Carbon Nanotubes and their use as Composite and Adhesive Interlayers

    NASA Astrophysics Data System (ADS)

    Stahl, James Joseph, III

    The following studies utilize shearing force to consolidate and re-orient multi-walled carbon nanotubes (MWCNT) into a shear pressed sheet (SPS) preform. Carbon nanotube (CNT) array growth and shear pressing angle are studied to improve the quality of SPSs. Heat assisted vacuum infusion is used to form a nano-composite from the SPS preform, and mechanical properties are characterized and compared between non-functionalized and functionalized nano-composite tensile specimens. A novel functionalization technique is applied which rinses SPSs with an acidic wet chemical oxidation treatment of H2SO4 and KMnO4 in order to add sidewall carboxyl groups to the CNTs. This is shown to impart hydrophilicity to the SPS and improves composite modulus by 62%, strain-to-failure 42% and failure stress 113%. Composite laminates and joints are vulnerable to shearing forces which cause delamination in the former and failure in the latter. Damage is initiated and propagated at defects and free edges often due to high peel stress, which is much higher than the shear stress and functions as a tensile opening of the joint just as in Mode I delamination failure of laminate composites. In order to resist failure it is necessary to improve the strain-to-failure of the interphase where a crack propagates without sacrificing strength or modulus of the material, thus toughening the material without impacting the rigidity of the composite. Due to the similarity between peel stress/strain and Mode I delamination, the initiation fracture toughness of a double cantilever beam (DCB) test should provide a good indication of peel toughness at a joint free edge. Many studies have explored the possibility of improving Mode I fracture toughness (G IC) of a composite through locally incorporating a tough material into the interlaminar interphase; this material is termed an interleaf. Common interleaf categories are toughened adhesive, disperse particle, disperse fiber, short fiber nonwoven, and continuous

  2. Low shear stress gravel-bed river

    USGS Publications Warehouse

    Milhous, Robert T.

    1997-01-01

    A low stress gravel bed river is a river where the cross-sectional average dimensionless shear stress (??*) rarely exceeds 0.047. That is the case for the Gunnison River below Delta in Western Colorado. The cross-sectional average ??* in the Gunnison River has not exceeded 0.047, except at one cross section during one year, in the 87 years of record. A ??* of 0.047 is the critical ??* in the bed-load equation considered to be most applicable to gravel/cobble bed rivers (the Meyer-Peter, Mueller equation). According to this equation, there has been no bed-material movement in the Gunnison River since 1920; in fact there has been bed-material movement and this movement is biologically important. Bed-material is moved when the ??* is 0.016 or larger. Streamflows that cause a ??* of at least 0.016 maintain the aquatic habitat in a low shear stress river.

  3. The effects of molecular weight on the single lap shear creep and constant strain rate behavior of thermoplastic polyimidesulfone adhesive

    NASA Technical Reports Server (NTRS)

    Dembosky, Stanley K.; Sancaktar, Erol

    1985-01-01

    The bonded shear creep and constant strain rate behaviors of zero, one, and three percent endcapped thermoplastic polyimidesulfone adhesive were examined at room and elevated temperatures. Endcapping was accomplished by the addition of phthalic anhydrides. The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Ludwik's and Crochet's relations were used to describe the experimental failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed. The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Crochet's relations based on Maxwell and Chase-Goldsmith models were fit to delayed failure data. Ludwik's equations revealed negligible rate dependence. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced.

  4. Rectangle-capped and tilted micropillar array for enhanced anisotropic anti-shearing in biomimetic adhesion

    PubMed Central

    Wang, Yue; Li, Xiangming; Tian, Hongmiao; Hu, Hong; Tian, Yu; Shao, Jinyou; Ding, Yucheng

    2015-01-01

    Dry adhesion observed in the feet of various small creatures has attracted considerable attention owing to the unique advantages such as self-cleaning, adaptability to rough surfaces along with repeatable and reversible adhesiveness. Among these advantages, for practical applications, proper detachability is critical for dry adhesives with artificial microstructures. In this study, we present a microstructured array consisting of both asymmetric rectangle-capped tip and tilted shafts, which produce an orthogonal anisotropy of the shearing strength along the long and short dimensions of the tip, with a maximum anti-shearing in the two directions along the longer dimension. Meanwhile, the tilt feature can enhance anisotropic shearing adhesion by increasing shearing strength in the forward shearing direction and decreasing strength in the reverse shearing direction along the short dimension of the tip, leading to a minimum anti-shearing in only one of the two directions along the shorter dimension of the rectangular tip. Such a microstructured adhesive with only one weak shearing direction, leading to well-controlled attachment and detachment of the adhesive, is created in our experiment by conventional double-sided exposure of a photoresist followed by a moulding process. PMID:25808338

  5. Observation of deformation and damage at the tip of a crack in adhesive bonds loaded in shear and assessment of a criterion for fracture

    NASA Astrophysics Data System (ADS)

    Chai, Herzl

    1994-02-01

    The evolution of damage at the tip of a crack in adhesive bonds deforming in shear was monitored in real time using a high-magnification video camera. Brittle and ductile epoxy resins were evaluated, with the bond thickness, t, being an experimental variable. An extensive zone of plastic deformation was developed ahead of the crack tip, prior to fracture. In the case of the brittle adhesive, for relatively thick bonds, tensile microcracks formed within that zone. Increased loading caused the microcracks to grow from the interlayer to the metal/matrix interface, which led to a complete bond separation following the interlinking of interface cracks emanating from adjacent microcracks. In contrast, for the ductile adhesive, the crack always grew from the tip. Strain gradients tended to develop there when the bond thickness was large. The adhesive shear strain was determined from fine lines scratched on the specimen edge. For both adhesives, the critical average crack tip shear strain rapidly decreased with increasing t. This effect was attributed to the changing sensitivity of the bond to the presence of flaws; thicker bonds can accommodate larger microcracks or microvoids, which cause greater stress concentration. For a given bond thickness, the critical crack tip shear strain agreed well with the ultimate shear strain of the unflawed adhesive, gamma(sub f), previously determined by means of the napkin ring shear test. This suggests that the ultimate shear strain is a key material property, controlling crack growth.

  6. Fluid Shear Stress Increases Neutrophil Activation via Platelet-Activating Factor

    PubMed Central

    Mitchell, Michael J.; Lin, Kimberly S.; King, Michael R.

    2014-01-01

    Leukocyte exposure to hemodynamic shear forces is critical for physiological functions including initial adhesion to the endothelium, the formation of pseudopods, and migration into tissues. G-protein coupled receptors on neutrophils, which bind to chemoattractants and play a role in neutrophil chemotaxis, have been implicated as fluid shear stress sensors that control neutrophil activation. Recently, exposure to physiological fluid shear stresses observed in the microvasculature was shown to reduce neutrophil activation in the presence of the chemoattractant formyl-methionyl-leucyl-phenylalanine. Here, however, human neutrophil preexposure to uniform shear stress (0.1–2.75 dyn/cm2) in a cone-and-plate viscometer for 1–120 min was shown to increase, rather than decrease, neutrophil activation in the presence of platelet activating factor (PAF). Fluid shear stress exposure increased PAF-induced neutrophil activation in terms of L-selectin shedding, αMβ2 integrin activation, and morphological changes. Neutrophil activation via PAF was found to correlate with fluid shear stress exposure, as neutrophil activation increased in a shear stress magnitude- and time-dependent manner. These results indicate that fluid shear stress exposure increases neutrophil activation by PAF, and, taken together with previous observations, differentially controls how neutrophils respond to chemoattractants. PMID:24853753

  7. Effect of Molecular Flexibility upon Ice Adhesion Shear Strength

    NASA Technical Reports Server (NTRS)

    Smith, Joseph G.; Wohl, Christopher J.; Kreeger, Richard E.; Palacios, Jose; Knuth, Taylor; Hadley, Kevin

    2016-01-01

    Ice formation on aircraft surfaces effects aircraft performance by increasing weight and drag leading to loss of lift. Current active alleviation strategies involve pneumatic boots, heated surfaces, and usage of glycol based de-icing fluids. Mitigation or reduction of in-flight icing by means of a passive approach may enable retention of aircraft capabilities, i.e., no reduction in lift, while reducing the aircraft weight and mechanical complexity. Under a NASA Aeronautics Research Institute Seedling activity, the effect of end group functionality and chain length upon ice adhesion shear strength (IASS) was evaluated with the results indicating that chemical functionality and chain length (i.e. molecular flexibility) affected IASS. Based on experimental and modeling results, diamine monomers incorporating molecular flexibility as either a side chain or in between diamine functionalities were prepared, incorporated into epoxy resins that were subsequently used to fabricate coatings on aluminum substrates, and tested in a simulated icing environment. The IASS was found to be lower when molecular flexibility was incorporated in the polymer chain as opposed to a side chain.

  8. Flexible Micropost Arrays for Shear Stress Measurement

    NASA Technical Reports Server (NTRS)

    Wohl, Christopher J.; Palmieri, Frank L.; Hopkins, John W.; Jackson, Allen M.; Connell, John W.; Lin, Yi; Cisotto, Alexxandra A.

    2015-01-01

    Increased fuel costs, heightened environmental protection requirements, and noise abatement continue to place drag reduction at the forefront of aerospace research priorities. Unfortunately, shortfalls still exist in the fundamental understanding of boundary-layer airflow over aerodynamic surfaces, especially regarding drag arising from skin friction. For example, there is insufficient availability of instrumentation to adequately characterize complex flows with strong pressure gradients, heat transfer, wall mass flux, three-dimensionality, separation, shock waves, and transient phenomena. One example is the acoustic liner efficacy on aircraft engine nacelle walls. Active measurement of shear stress in boundary layer airflow would enable a better understanding of how aircraft structure and flight dynamics affect skin friction. Current shear stress measurement techniques suffer from reliability, complexity, and airflow disruption, thereby compromising resultant shear stress data. The state-of-the-art for shear stress sensing uses indirect or direct measurement techniques. Indirect measurements (e.g., hot-wire, heat flux gages, oil interferometry, laser Doppler anemometry, small scale pressure drag surfaces, i.e., fences) require intricate knowledge of the studied flow, restrictive instrument arrangements, large surface areas, flow disruption, or seeding material; with smaller, higher bandwidth probes under development. Direct measurements involve strain displacement of a sensor element and require no prior knowledge of the flow. Unfortunately, conventional "floating" recessed components for direct measurements are mm to cm in size. Whispering gallery mode devices and Fiber Bragg Gratings are examples of recent additions to this type of sensor with much smaller (?m) sensor components. Direct detection techniques are often single point measurements and difficult to calibrate and implement in wind tunnel experiments. In addition, the wiring, packaging, and installation

  9. Stent implantation influence wall shear stress evolution

    NASA Astrophysics Data System (ADS)

    Bernad, S. I.; Totorean, A. F.; Bosioc, A. I.; Petre, I.; Bernad, E. S.

    2016-06-01

    Local hemodynamic factors are known affect the natural history of the restenosis critically after coronary stenting of atherosclerosis. Stent-induced flows disturbance magnitude dependent directly on the strut design. The impact of flow alterations around struts vary as the strut geometrical parameters change. Our results provide data regarding the hemodynamic parameters for the blood flow in both stenosed and stented coronary artery under physiological conditions, namely wall shear stress and pressure drop.

  10. [Promotion of Function of Endothelial Progenitor Cells with Shexiang Baoxin Pill Treatment under Shear Stress].

    PubMed

    Li, Gang; Chen, Yang; Wu, Jiang

    2015-08-01

    The aim of this study was to investigate whether shear stress could promote function of endothelial progenitor cells (EPCs) with Shexiang Baoxin Pill (SBP) treatment in vitro, and to study whether shear stress contributed to vascular injury repair by EPCs. EPCs were isolated and characterized; EPCs' proliferation, migration, adhesion, tube formation and eNOS protein level in vitro were investigated by culturing confluent EPCs in 4 mg/mL SBP under physiological shear stress (15 dyne/cm2) for up to 24 hours. Afterwards, EPCs were transfused into rats after wire-induced carotid artery injury augmented re-endothelialization. The results showed that, compared to the SBP group, the shear stress+SBP group obviously enhanced EPCs proliferation, migration, adhesion, tube formation and eNOS protein expression in vitro (P<0.01). After one week, immunofluorescence staining showed that endothelial regeneration rate obviously enhanced in shear stress+SBP group (P<0.01). The present study demonstrates that shear stress can promote function of endothelial progenitor cells treated with SBP, which improves the vascular injury repair potentials of EPCs. PMID:26710458

  11. Shear Stress Sensing using Elastomer Micropillar Arrays

    NASA Technical Reports Server (NTRS)

    Wohl, Christopher J.; Palmieri, Frank L.; Lin, Yi; Jackson, Allen M.; Cissoto, Alexxandra; Sheplak, Mark; Connell, John W.

    2013-01-01

    The measurement of shear stress developed as a fluid moves around a solid body is difficult to measure. Stresses at the fluid-solid interface are very small and the nature of the fluid flow is easily disturbed by introducing sensor components to the interface. To address these challenges, an array of direct and indirect techniques have been investigated with various advantages and challenges. Hot wire sensors and other indirect sensors all protrude significantly into the fluid flow. Microelectromechanical systems (MEMS) devices, although facilitating very accurate measurements, are not durable, are prone to contamination, and are difficult to implement into existing model geometries. One promising approach is the use of engineered surfaces that interact with fluid flow in a detectable manner. To this end, standard lithographic techniques have been utilized to generate elastomeric micropillar arrays of various lengths and diameters. Micropillars of controlled length and width were generated in polydimethylsiloxane (PDMS) elastomer using a soft-lithography technique. The 3D mold for micropillar replication was fabricated using laser ablative micromachining and contact lithography. Micropillar dimensions and mechanical properties were characterized and compared to shear sensing requirements. The results of this characterization as well as shear stress detection techniques will be discussed.

  12. Biomechanics of shear-sensitive adhesion in climbing animals: peeling, pre-tension and sliding-induced changes in interface strength.

    PubMed

    Labonte, David; Federle, Walter

    2016-09-01

    Many arthropods and small vertebrates use adhesive pads for climbing. These biological adhesives have to meet conflicting demands: attachment must be strong and reliable, yet detachment should be fast and effortless. Climbing animals can rapidly and reversibly control their pads' adhesive strength by shear forces, but the mechanisms underlying this coupling have remained unclear. Here, we show that adhesive forces of stick insect pads closely followed the predictions from tape peeling models when shear forces were small, but strongly exceeded them when shear forces were large, resulting in an approximately linear increase of adhesion with friction. Adhesion sharply increased at peel angles less than ca 30°, allowing a rapid switch between attachment and detachment. The departure from classic peeling theory coincided with the appearance of pad sliding, which dramatically increased the peel force via a combination of two mechanisms. First, partial sliding pre-stretched the pads, so that they were effectively stiffer upon detachment and peeled increasingly like inextensible tape. Second, pad sliding reduces the thickness of the fluid layer in the contact zone, thereby increasing the stress levels required for peeling. In combination, these effects can explain the coupling between adhesion and friction that is fundamental to adhesion control across all climbing animals. Our results highlight that control of adhesion is not solely achieved by direction-dependence and morphological anisotropy, suggesting promising new routes for the development of controllable bio-inspired adhesives. PMID:27605165

  13. Biomechanics of shear-sensitive adhesion in climbing animals: peeling, pre-tension and sliding-induced changes in interface strength

    PubMed Central

    2016-01-01

    Many arthropods and small vertebrates use adhesive pads for climbing. These biological adhesives have to meet conflicting demands: attachment must be strong and reliable, yet detachment should be fast and effortless. Climbing animals can rapidly and reversibly control their pads' adhesive strength by shear forces, but the mechanisms underlying this coupling have remained unclear. Here, we show that adhesive forces of stick insect pads closely followed the predictions from tape peeling models when shear forces were small, but strongly exceeded them when shear forces were large, resulting in an approximately linear increase of adhesion with friction. Adhesion sharply increased at peel angles less than ca 30°, allowing a rapid switch between attachment and detachment. The departure from classic peeling theory coincided with the appearance of pad sliding, which dramatically increased the peel force via a combination of two mechanisms. First, partial sliding pre-stretched the pads, so that they were effectively stiffer upon detachment and peeled increasingly like inextensible tape. Second, pad sliding reduces the thickness of the fluid layer in the contact zone, thereby increasing the stress levels required for peeling. In combination, these effects can explain the coupling between adhesion and friction that is fundamental to adhesion control across all climbing animals. Our results highlight that control of adhesion is not solely achieved by direction-dependence and morphological anisotropy, suggesting promising new routes for the development of controllable bio-inspired adhesives. PMID:27605165

  14. Analysis of bonded joints. [shear stress and stress-strain diagrams

    NASA Technical Reports Server (NTRS)

    Srinivas, S.

    1975-01-01

    A refined elastic analysis of bonded joints which accounts for transverse shear deformation and transverse normal stress was developed to obtain the stresses and displacements in the adherends and in the bond. The displacements were expanded in terms of polynomials in the thicknesswise coordinate; the coefficients of these polynomials were functions of the axial coordinate. The stress distribution was obtained in terms of these coefficients by using strain-displacement and stress-strain relations. The governing differential equations were obtained by integrating the equations of equilibrium, and were solved. The boundary conditions (interface or support) were satisfied to complete the analysis. Single-lap, flush, and double-lap joints were analyzed, along with the effects of adhesive properties, plate thicknesses, material properties, and plate taper on maximum peel and shear stresses in the bond. The results obtained by using the thin-beam analysis available in the literature were compared with the results obtained by using the refined analysis. In general, thin-beam analysis yielded reasonably accurate results, but in certain cases the errors were high. Numerical investigations showed that the maximum peel and shear stresses in the bond can be reduced by (1) using a combination of flexible and stiff bonds, (2) using stiffer lap plates, and (3) tapering the plates.

  15. Cooperative effects of matrix stiffness and fluid shear stress on endothelial cell behavior.

    PubMed

    Kohn, Julie C; Zhou, Dennis W; Bordeleau, François; Zhou, Allen L; Mason, Brooke N; Mitchell, Michael J; King, Michael R; Reinhart-King, Cynthia A

    2015-02-01

    Arterial hemodynamic shear stress and blood vessel stiffening both significantly influence the arterial endothelial cell (EC) phenotype and atherosclerosis progression, and both have been shown to signal through cell-matrix adhesions. However, the cooperative effects of fluid shear stress and matrix stiffness on ECs remain unknown. To investigate these cooperative effects, we cultured bovine aortic ECs on hydrogels matching the elasticity of the intima of compliant, young, or stiff, aging arteries. The cells were then exposed to laminar fluid shear stress of 12 dyn/cm(2). Cells grown on more compliant matrices displayed increased elongation and tighter EC-cell junctions. Notably, cells cultured on more compliant substrates also showed decreased RhoA activation under laminar shear stress. Additionally, endothelial nitric oxide synthase and extracellular signal-regulated kinase phosphorylation in response to fluid shear stress occurred more rapidly in ECs cultured on more compliant substrates, and nitric oxide production was enhanced. Together, our results demonstrate that a signaling cross talk between stiffness and fluid shear stress exists within the vascular microenvironment, and, importantly, matrices mimicking young and healthy blood vessels can promote and augment the atheroprotective signals induced by fluid shear stress. These data suggest that targeting intimal stiffening and/or the EC response to intima stiffening clinically may improve vascular health.

  16. Cooperative Effects of Matrix Stiffness and Fluid Shear Stress on Endothelial Cell Behavior

    PubMed Central

    Kohn, Julie C.; Zhou, Dennis W.; Bordeleau, François; Zhou, Allen L.; Mason, Brooke N.; Mitchell, Michael J.; King, Michael R.; Reinhart-King, Cynthia A.

    2015-01-01

    Arterial hemodynamic shear stress and blood vessel stiffening both significantly influence the arterial endothelial cell (EC) phenotype and atherosclerosis progression, and both have been shown to signal through cell-matrix adhesions. However, the cooperative effects of fluid shear stress and matrix stiffness on ECs remain unknown. To investigate these cooperative effects, we cultured bovine aortic ECs on hydrogels matching the elasticity of the intima of compliant, young, or stiff, aging arteries. The cells were then exposed to laminar fluid shear stress of 12 dyn/cm2. Cells grown on more compliant matrices displayed increased elongation and tighter EC-cell junctions. Notably, cells cultured on more compliant substrates also showed decreased RhoA activation under laminar shear stress. Additionally, endothelial nitric oxide synthase and extracellular signal-regulated kinase phosphorylation in response to fluid shear stress occurred more rapidly in ECs cultured on more compliant substrates, and nitric oxide production was enhanced. Together, our results demonstrate that a signaling cross talk between stiffness and fluid shear stress exists within the vascular microenvironment, and, importantly, matrices mimicking young and healthy blood vessels can promote and augment the atheroprotective signals induced by fluid shear stress. These data suggest that targeting intimal stiffening and/or the EC response to intima stiffening clinically may improve vascular health. PMID:25650915

  17. Shear bond strengths and microleakage of four types of dentin adhesive materials.

    PubMed

    Ateyah, Nasrien Z; Elhejazi, Ahmed A

    2004-02-15

    The aim of this investigation was to compare the microleakage of composite resin (Z-100) and shear bond strength to bovine dentin using different types of adhesive systems (Scotch Bond Multi-Purpose, All-Bond 2, One-Step, and Perma Quick) to compare and correlate microleakage to shear bond strength. For the microleakage aspect of the study, 20 class V were prepared (bovine incisors) with 90-degree cavosurface margins and were located at the cemento-enamel junction using a template. Each dentin bonding system was applied to five cavities following the manufacturer's instructions and restored with Z-100 composite resin. After 24 hours of storage in distilled water at 37 degrees C, the teeth were immersed in 2% basic fuchsin dye. All teeth were sectioned in a mesiodistal direction using a diamond saw, and each section was then inspected under a stereomacroscope. For the shear bond strength aspect of the study, 20 bovine incisors were centrally horizontally mounted in Teflon mold with cold cure acrylic resin. Flat labial dentin surfaces were prepared using different grit silicon carbide abrasive wheels. Five specimens were used for each of the bonding agent systems. Each specimen was bonded with restorative composite resin (Z-100) and applied to the treated dentinal surface through a split Teflon mold. All specimens were stored in distilled water at 37 degrees C for 24 hours. The bonds were stressed using shear forces at a crosshead speed of 0.5mm/min using an Instron Universal testing machine. Findings indicate none of the systems tested in this study were free from microleakage. Scotch bond multi-purpose achieved the best seal, with One-Step being second best, while All-Bond 2 and Perma Quick had the poorest seal. However, there were significant differences among the shear bond strengths of the four bonding systems tested. Scotch Bond Multi-Purpose has a higher bond strength to composite resin when compared to the other dentin adhesives. The study also concluded

  18. Lap shear strength and healing capability of self-healing adhesive containing epoxy/mercaptan microcapsules

    NASA Astrophysics Data System (ADS)

    Ghazali, Habibah; Ye, Lin; Zhang, Ming-Qiu

    2016-03-01

    The aim of this work is to develop a self-healing polymeric adhesive formulation with epoxy/mercaptan microcapsules. Epoxy/mercaptan microcapsules were dispersed into a commercialize two-part epoxy adhesive for developing self-healing epoxy adhesive. The influence of different content of microcapsules on the shear strength and healing capability of epoxy adhesive were investigated using single-lap-joints with average thickness of adhesive layer of about 180 µm. This self-healing adhesive was used in bonding of 5000 series aluminum alloys adherents after mechanical and alkaline cleaning surface treatment. The adhesion strength was measured and presented as function of microcapsules loading. The results indicated that the virgin lap shear strength was increased by about 26% with addition of 3 wt% of self-healing microcapsules. 12% to 28% recovery of the shear strength is achieved after self-healing depending on the microcapsules content. Scanning electron microscopy was used to study fracture surface of the joints. The self-healing adhesives exhibit recovery of both cohesion and adhesion properties with room temperature healing.

  19. Shear bond strength of one-step self-etch adhesives: pH influence

    PubMed Central

    Poggio, Claudio; Beltrami, Riccardo; Scribante, Andrea; Colombo, Marco; Chiesa, Marco

    2015-01-01

    Background: The aim of this study was to compare the shear bond strength of four one-step self-etch adhesives with different pH values to enamel and dentin. Materials and Methods: In this in vitro study, 200 bovine permanent mandibular incisors were used. Four one-step self-etch adhesives with different pH values were tested both on enamel and on dentin: Adper™ Easy Bond Self-Etch Adhesive (pH = 0.8-1), Futurabond NR (pH=2), G-aenial Bond (pH = 1.5), Clearfil S3 Bond (pH = 2.7). After adhesive systems application, a nanohybrid composite resin was inserted into the bonded surface. The specimens were placed in a universal testing machine. The shear bond strength was performed at a cross-head speed of 1 mm/min until the sample rupture. The shear bond strength values (MPa) of the different groups were compared with analysis of variance after that Kolmogorov and Smirnov tests were applied to assess normality of distributions. P < 0.05 was considered as significant. Results: In enamel shear bond strength, the highest shear bond strength values were reported with Futurabond NR (P < 0.01); however, no significant differences were found with Clearfil S3 Bond. The others adhesive systems showed lower shear bond strength values with significant differences between them (P < 0.05). When comparing the dentin shear bond strength, the lowest shear bond strength values were reported with Clearfil S3 Bond (P < 0.05), while there were no significant differences among the other three products (P > 0.05). Conclusion: The pH values of adhesive systems did not influence significantly their shear bond strength to enamel or dentin. PMID:26005459

  20. Stresses in adhesively bonded joints: A closed form solution. [plate theory

    NASA Technical Reports Server (NTRS)

    Delale, F.; Erdogan, F.; Aydinoglu, M. N.

    1980-01-01

    The plane strain of adhesively bonded structures which consist of two different orthotropic adherents is considered. Assuming that the thicknesses of the adherends are constant and are small in relation to the lateral dimensions of the bonded region, the adherends are treated as plates. The transverse shear effects in the adherends and the in-plane normal strain in the adhesive are taken into account. The problem is reduced to a system of differential equations for the adhesive stresses which is solved in closed form. A single lap joint and a stiffened plate under various loading conditions are considered as examples. To verify the basic trend of the solutions obtained from the plate theory a sample problem is solved by using the finite element method and by treating the adherends and the adhesive as elastic continua. The plate theory not only predicts the correct trend for the adhesive stresses but also gives rather surprisingly accurate results.

  1. Shear-stress relaxation and ensemble transformation of shear-stress autocorrelation functions.

    PubMed

    Wittmer, J P; Xu, H; Baschnagel, J

    2015-02-01

    We revisit the relation between the shear-stress relaxation modulus G(t), computed at finite shear strain 0<γ≪1, and the shear-stress autocorrelation functions C(t)|(γ) and C(t)|(τ) computed, respectively, at imposed strain γ and mean stress τ. Focusing on permanent isotropic spring networks it is shown theoretically and computationally that in general G(t)=C(t)|(τ)=C(t)|(γ)+G(eq) for t>0 with G(eq) being the static equilibrium shear modulus. G(t) and C(t)|(γ) thus must become different for solids and it is impossible to obtain G(eq) alone from C(t)|(γ) as often assumed. We comment briefly on self-assembled transient networks where G(eq)(f) must vanish for a finite scission-recombination frequency f. We argue that G(t)=C(t)|(τ)=C(t)|(γ) should reveal an intermediate plateau set by the shear modulus G(eq)(f=0) of the quenched network.

  2. Generation of Shear Adhesion Map Using SynVivo Synthetic Microvascular Networks

    PubMed Central

    Smith, Ashley M.; Prabhakarpandian, Balabhaskar; Pant, Kapil

    2014-01-01

    Cell/particle adhesion assays are critical to understanding the biochemical interactions involved in disease pathophysiology and have important applications in the quest for the development of novel therapeutics. Assays using static conditions fail to capture the dependence of adhesion on shear, limiting their correlation with in vivo environment. Parallel plate flow chambers that quantify adhesion under physiological fluid flow need multiple experiments for the generation of a shear adhesion map. In addition, they do not represent the in vivo scale and morphology and require large volumes (~ml) of reagents for experiments. In this study, we demonstrate the generation of shear adhesion map from a single experiment using a microvascular network based microfluidic device, SynVivo-SMN. This device recreates the complex in vivo vasculature including geometric scale, morphological elements, flow features and cellular interactions in an in vitro format, thereby providing a biologically realistic environment for basic and applied research in cellular behavior, drug delivery, and drug discovery. The assay was demonstrated by studying the interaction of the 2 µm biotin-coated particles with avidin-coated surfaces of the microchip. The entire range of shear observed in the microvasculature is obtained in a single assay enabling adhesion vs. shear map for the particles under physiological conditions. PMID:24893648

  3. Endothelial cell and model membranes respond to shear stress by rapidly decreasing the order of their lipid phases.

    PubMed

    Yamamoto, Kimiko; Ando, Joji

    2013-03-01

    Endothelial cells (ECs) sense shear stress and transduce blood flow information into functional responses that play important roles in vascular homeostasis and pathophysiology. A unique feature of shear-stress-sensing is the involvement of many different types of membrane-bound molecules, including receptors, ion channels and adhesion proteins, but the mechanisms remain unknown. Because cell membrane properties affect the activities of membrane-bound proteins, shear stress might activate various membrane-bound molecules by altering the physical properties of EC membranes. To determine how shear stress influences the cell membrane, cultured human pulmonary artery ECs were exposed to shear stress and examined for changes in membrane lipid order and fluidity by Laurdan two-photon imaging and FRAP measurements. Upon shear stress stimulation, the lipid order of EC membranes rapidly decreased in an intensity-dependent manner, and caveolar membrane domains changed from the liquid-ordered state to the liquid-disordered state. Notably, a similar decrease in lipid order occurred when the artificial membranes of giant unilamellar vesicles were exposed to shear stress, suggesting that this is a physical phenomenon. Membrane fluidity increased over the entire EC membranes in response to shear stress. Addition of cholesterol to ECs abolished the effects of shear stress on membrane lipid order and fluidity and markedly suppressed ATP release, which is a well-known EC response to shear stress and is involved in shear-stress Ca(2+) signaling. These findings indicate that EC membranes directly respond to shear stress by rapidly decreasing their lipid phase order and increasing their fluidity; these changes could be linked to shear-stress-sensing and response mechanisms. PMID:23378020

  4. Endothelial cell and model membranes respond to shear stress by rapidly decreasing the order of their lipid phases.

    PubMed

    Yamamoto, Kimiko; Ando, Joji

    2013-03-01

    Endothelial cells (ECs) sense shear stress and transduce blood flow information into functional responses that play important roles in vascular homeostasis and pathophysiology. A unique feature of shear-stress-sensing is the involvement of many different types of membrane-bound molecules, including receptors, ion channels and adhesion proteins, but the mechanisms remain unknown. Because cell membrane properties affect the activities of membrane-bound proteins, shear stress might activate various membrane-bound molecules by altering the physical properties of EC membranes. To determine how shear stress influences the cell membrane, cultured human pulmonary artery ECs were exposed to shear stress and examined for changes in membrane lipid order and fluidity by Laurdan two-photon imaging and FRAP measurements. Upon shear stress stimulation, the lipid order of EC membranes rapidly decreased in an intensity-dependent manner, and caveolar membrane domains changed from the liquid-ordered state to the liquid-disordered state. Notably, a similar decrease in lipid order occurred when the artificial membranes of giant unilamellar vesicles were exposed to shear stress, suggesting that this is a physical phenomenon. Membrane fluidity increased over the entire EC membranes in response to shear stress. Addition of cholesterol to ECs abolished the effects of shear stress on membrane lipid order and fluidity and markedly suppressed ATP release, which is a well-known EC response to shear stress and is involved in shear-stress Ca(2+) signaling. These findings indicate that EC membranes directly respond to shear stress by rapidly decreasing their lipid phase order and increasing their fluidity; these changes could be linked to shear-stress-sensing and response mechanisms.

  5. Biomechanics of P-selectin PSGL-1 bonds: Shear threshold and integrin-independent cell adhesion

    SciTech Connect

    Xiao, Zhihua; Goldsmith, Harry L.; MacIntosh, Fiona A.; Shankaran, Harish; Neelamegham, Sriram

    2006-03-01

    Platelet-leukocyte adhesion may contribute to thrombosis and inflammation. We examined the heterotypic interaction between unactivated neutrophils and either thrombin receptor activating peptide (TRAP) stimulated platelets or P-selectin bearing beads (Ps-beads) in suspension. Cone-plate viscometers were used to apply controlled shear rates from 14-3000/s. Platelet-neutrophil and bead-neutrophil adhesion analysis was performed using both flow cytometry and high-speed videomicroscopy. We observed that while blocking antibodies against either P-selectin or P-selectin glycoprotein ligand-1 (PSGL-1) alone inhibited platelet-neutrophil adhesion by ~60% at 140/s, these reagents completely blocked adhesion at 3000/s. Anti-Mac-1 alone did not alter platelet-neutrophil adhesion rates at any shear rate, though in synergy with selectin antagonists it abrogated cell binding. Unstimulated neutrophils avidly bound Ps-beads and activated platelets in an integrin-independent manner, suggesting that purely selectin-dependent cell adhesion is possible. In support of this, antagonists against P-selectin or PSGL-1 dissociated previously formed platelet-neutrophil and Ps-bead neutrophil aggregates under shear in a variety of experimental systems, including in assays performed with whole blood. In studies where medium viscosity and shear rate were varied, a subtle shear threshold for P-selectin PSGL-1 binding was also noted at shear rates<100/s and at force loading rates of ~300pN/sec. Results are discussed in light of biophysical computations that characterize the collision between unequal size particles in linear shear flow. Overall, our studies reveal an integrin-independent regime for cell adhesion that may be physiologically relevant.

  6. Lap Shear and Impact Testing of Ochre and Beeswax in Experimental Middle Stone Age Compound Adhesives.

    PubMed

    Kozowyk, P R B; Langejans, G H J; Poulis, J A

    2016-01-01

    The production of compound adhesives using disparate ingredients is seen as some of the best evidence of advanced cognition outside of the use of symbolism. Previous field and laboratory testing of adhesives has shown the complexities involved in creating an effective Middle Stone Age glue using Acacia gum. However, it is currently unclear how efficient different adhesive recipes are, how much specific ingredients influence their performance, and how difficult it may have been for those ingredients to be combined to maximum effect. We conducted a series of laboratory-based lap shear and impact tests, following modern adhesion testing standards, to determine the efficacy of compound adhesives, with particular regard to the ingredient ratios. We tested rosin (colophony) and gum adhesives, containing additives of beeswax and ochre in varying ratios. During both lap shear and impact tests compound rosin adhesives performed better than single component rosin adhesives, and pure acacia gum was the strongest. The large difference in performance between each base adhesive and the significant changes in performance that occur due to relatively small changes in ingredient ratios lend further support to the notion that high levels of skill and knowledge were required to consistently produce the most effective adhesives.

  7. Lap Shear and Impact Testing of Ochre and Beeswax in Experimental Middle Stone Age Compound Adhesives

    PubMed Central

    2016-01-01

    The production of compound adhesives using disparate ingredients is seen as some of the best evidence of advanced cognition outside of the use of symbolism. Previous field and laboratory testing of adhesives has shown the complexities involved in creating an effective Middle Stone Age glue using Acacia gum. However, it is currently unclear how efficient different adhesive recipes are, how much specific ingredients influence their performance, and how difficult it may have been for those ingredients to be combined to maximum effect. We conducted a series of laboratory-based lap shear and impact tests, following modern adhesion testing standards, to determine the efficacy of compound adhesives, with particular regard to the ingredient ratios. We tested rosin (colophony) and gum adhesives, containing additives of beeswax and ochre in varying ratios. During both lap shear and impact tests compound rosin adhesives performed better than single component rosin adhesives, and pure acacia gum was the strongest. The large difference in performance between each base adhesive and the significant changes in performance that occur due to relatively small changes in ingredient ratios lend further support to the notion that high levels of skill and knowledge were required to consistently produce the most effective adhesives. PMID:26983080

  8. Lap Shear and Impact Testing of Ochre and Beeswax in Experimental Middle Stone Age Compound Adhesives.

    PubMed

    Kozowyk, P R B; Langejans, G H J; Poulis, J A

    2016-01-01

    The production of compound adhesives using disparate ingredients is seen as some of the best evidence of advanced cognition outside of the use of symbolism. Previous field and laboratory testing of adhesives has shown the complexities involved in creating an effective Middle Stone Age glue using Acacia gum. However, it is currently unclear how efficient different adhesive recipes are, how much specific ingredients influence their performance, and how difficult it may have been for those ingredients to be combined to maximum effect. We conducted a series of laboratory-based lap shear and impact tests, following modern adhesion testing standards, to determine the efficacy of compound adhesives, with particular regard to the ingredient ratios. We tested rosin (colophony) and gum adhesives, containing additives of beeswax and ochre in varying ratios. During both lap shear and impact tests compound rosin adhesives performed better than single component rosin adhesives, and pure acacia gum was the strongest. The large difference in performance between each base adhesive and the significant changes in performance that occur due to relatively small changes in ingredient ratios lend further support to the notion that high levels of skill and knowledge were required to consistently produce the most effective adhesives. PMID:26983080

  9. Shear bond strength of new self-adhesive flowable composite resins.

    PubMed

    Wajdowicz, Michael N; Vandewalle, Kraig S; Means, Mark T

    2012-01-01

    Recently, new self-adhesive flowable composite resin systems have been introduced to the market. These new composite resin systems reportedly bond to dentin and enamel without the application of an adhesive bonding agent. The purpose of this study was to evaluate the shear bond strength to enamel of two new self-adhesive flowable composites with and without the use of an etch-and-rinse bonding agent. The new self-adhesive flowable composites had significantly lower bond strengths to enamel compared to a traditional adhesively bonded flowable composite. Both self-adhesive flowable composites had a significant increase in bond strength to enamel with the use of a phosphoric acid-etch and adhesive bonding agent. PMID:22414513

  10. Gecko toe and lamellar shear adhesion on macroscopic, engineered rough surfaces.

    PubMed

    Gillies, Andrew G; Henry, Amy; Lin, Hauwen; Ren, Angela; Shiuan, Kevin; Fearing, Ronald S; Full, Robert J

    2014-01-15

    The role in adhesion of the toes and lamellae - intermediate-sized structures - found on the gecko foot remains unclear. Insight into the function of these structures can lead to a more general understanding of the hierarchical nature of the gecko adhesive system, but in particular how environmental topology may relate to gecko foot morphology. We sought to discern the mechanics of the toes and lamellae by examining gecko adhesion on controlled, macroscopically rough surfaces. We used live Tokay geckos, Gekko gecko, to observe the maximum shear force a gecko foot can attain on an engineered substrate constructed with sinusoidal patterns of varying amplitudes and wavelengths in sizes similar to the dimensions of the toes and lamellae structures (0.5 to 6 mm). We found shear adhesion was significantly decreased on surfaces that had amplitudes and wavelengths approaching the lamella length and inter-lamella spacing, losing 95% of shear adhesion over the range tested. We discovered that the toes are capable of adhering to surfaces with amplitudes much larger than their dimensions even without engaging claws, maintaining 60% of shear adhesion on surfaces with amplitudes of 3 mm. Gecko adhesion can be predicted by the ratio of the lamella dimensions to surface feature dimensions. In addition to setae, remarkable macroscopic-scale features of gecko toes and lamellae that include compliance and passive conformation are necessary to maintain contact, and consequently, generate shear adhesion on macroscopically rough surfaces. Findings on the larger scale structures in the hierarchy of gecko foot function could provide the biological inspiration to drive the design of more effective and versatile synthetic fibrillar adhesives.

  11. Shear stress induced stimulation of mammalian cell metabolism

    NASA Technical Reports Server (NTRS)

    Mcintire, L. V.; Frangos, J. A.; Eskin, S. G.

    1988-01-01

    A flow apparatus was developed for the study of the metabolic response of anchorage dependent cells to a wide range of steady and pulsatile shear stresses under well controlled conditions. Human umbilical vein endothelial cell monolayers were subjected to steady shear stresses of up to 24 dynes/sq cm, and the production of prostacyclin was determined. The onset of flow led to a burst in prostacyclin production which decayed to a long term steady state rate (SSR). The SSR of cells exposed to flow was greater than the basal release level, and increased linearly with increasing shear stress. It is demonstrated that shear stresses in certain ranges may not be detrimental to mammalian cell metabolism. In fact, throughout the range of shear stresses studied, metabolite production is maximized by maximizing shear stress.

  12. Wall shear stress estimates in coronary artery constrictions

    NASA Technical Reports Server (NTRS)

    Back, L. H.; Crawford, D. W.

    1992-01-01

    Wall shear stress estimates from laminar boundary layer theory were found to agree fairly well with the magnitude of shear stress levels along coronary artery constrictions obtained from solutions of the Navier Stokes equations for both steady and pulsatile flow. The relatively simple method can be used for in vivo estimates of wall shear stress in constrictions by using a vessel shape function determined from a coronary angiogram, along with a knowledge of the flow rate.

  13. Colors Of Liquid Crystals Used To Measure Surface Shear Stresses

    NASA Technical Reports Server (NTRS)

    Reda, D. C.; Muratore, J. J., Jr.

    1996-01-01

    Developmental method of mapping shear stresses on aerodynamic surfaces involves observation, at multiple viewing angles, of colors of liquid-crystal surface coats illuminated by white light. Report describing method referenced in "Liquid Crystals Indicate Directions Of Surface Shear Stresses" (ARC-13379). Resulting maps of surface shear stresses contain valuable data on magnitudes and directions of skin friction forces associated with surface flows; data used to refine mathematical models of aerodynamics for research and design purposes.

  14. Arterial Shear Stress Reduces Eph-B4 Expression in Adult Human Veins

    PubMed Central

    Model, Lynn S.; Hall, Michael R.; Wong, Daniel J.; Muto, Akihito; Kondo, Yuka; Ziegler, Kenneth R.; Feigel, Amanda; Quint, Clay; Niklason, Laura; Dardik, Alan

    2014-01-01

    Vein graft adaptation to the arterial environment is characterized by loss of venous identity, with reduced Ephrin type-B receptor 4 (Eph-B4) expression but without increased Ephrin-B2 expression. We examined changes of vessel identity of human saphenous veins in a flow circuit in which shear stress could be precisely controlled. Medium circulated at arterial or venous magnitudes of laminar shear stress for 24 hours; histologic, protein, and RNA analyses of vein segments were performed. Vein endothelium remained viable and functional, with platelet endothelial cell adhesion molecule (PECAM)-expressing cells on the luminal surface. Venous Eph-B4 expression diminished (p = .002), Ephrin-B2 expression was not induced (p = .268), and expression of osteopontin (p = .002) was increased with exposure to arterial magnitudes of shear stress. Similar changes were not found in veins placed under venous flow or static conditions. These data show that human saphenous veins remain viable during ex vivo application of shear stress in a bioreactor, without loss of the venous endothelium. Arterial magnitudes of shear stress cause loss of venous identity without gain of arterial identity in human veins perfused ex vivo. Shear stress alone, without immunologic or hormonal influence, is capable of inducing changes in vessel identity and, specifically, loss of venous identity. PMID:25191151

  15. Impaired endothelial shear stress induces podosome assembly via VEGF up-regulation.

    PubMed

    Fey, Theres; Schubert, Kai Michael; Schneider, Holger; Fein, Evelyn; Kleinert, Eike; Pohl, Ulrich; Dendorfer, Andreas

    2016-08-01

    Podosomes are dynamic cytoskeletal membrane structures with local adhesive and proteolytic activity. They are critically involved in angiogenesis and vascular adaptive growth. Here, we studied in HUVECs and murine small vessels whether shear stress controls podosome assembly and local proteolytic activity. Podosomes were characterized by immunohistochemistry, and their proteolytic activity was assessed as degradation imprints in fluorescent gelatin that was used as growth substrate. Compared with controls (10 dyn/cm(2)), the number of podosomes formed per time was doubled when cells were exposed to low shear stress (0.3 dyn/cm(2)) or even increased 5-fold under static conditions. This was a result of an enhanced expression of VEGF after reduction of shear stress. Consequently, enhanced podosome formation could be prevented by a VEGF receptor antagonist as well by interruption of VEGF signaling via inhibition of PI3K, Src, or p38. Increase of podosome assembly went along with significantly augmented cell motility. In vivo experiments in mouse arteries confirmed increased endothelial podosome numbers when shear stress was abolished by vessel occlusion. We conclude that shear stress, by reducing VEGF release, inhibits podosome assembly. Hence, endothelial cell-mediated matrix proteolysis and migratory activity are inhibited, thereby stabilizing the structure of the vessel wall.-Fey, T., Schubert, K. M., Schneider, H., Fein, E., Kleinert, E., Pohl, U., Dendorfer, A. Impaired endothelial shear stress induces podosome assembly via VEGF up-regulation.

  16. Temporal oscillations of the shear stress and scattered light in a shear-banding--shear-thickening micellar solution.

    PubMed

    Azzouzi, H; Decruppe, J P; Lerouge, S; Greffier, O

    2005-08-01

    The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous.

  17. Temporal oscillations of the shear stress and scattered light in a shear-banding-shear-thickening micellar solution

    NASA Astrophysics Data System (ADS)

    Azzouzi, H.; Decruppe, J. P.; Lerouge, S.; Greffier, O.

    2005-08-01

    The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous.

  18. Adjustable shear stress erosion and transport flume

    DOEpatents

    Roberts, Jesse D.; Jepsen, Richard A.

    2002-01-01

    A method and apparatus for measuring the total erosion rate and downstream transport of suspended and bedload sediments using an adjustable shear stress erosion and transport (ASSET) flume with a variable-depth sediment core sample. Water is forced past a variable-depth sediment core sample in a closed channel, eroding sediments, and introducing suspended and bedload sediments into the flow stream. The core sample is continuously pushed into the flow stream, while keeping the surface level with the bottom of the channel. Eroded bedload sediments are transported downstream and then gravitationally separated from the flow stream into one or more quiescent traps. The captured bedload sediments (particles and aggregates) are weighed and compared to the total mass of sediment eroded, and also to the concentration of sediments suspended in the flow stream.

  19. Shear lag sutures: Improved suture repair through the use of adhesives.

    PubMed

    Linderman, Stephen W; Kormpakis, Ioannis; Gelberman, Richard H; Birman, Victor; Wegst, Ulrike G K; Genin, Guy M; Thomopoulos, Stavros

    2015-09-01

    Suture materials and surgical knot tying techniques have improved dramatically since their first use over five millennia ago. However, the approach remains limited by the ability of the suture to transfer load to tissue at suture anchor points. Here, we predict that adhesive-coated sutures can improve mechanical load transfer beyond the range of performance of existing suture methods, thereby strengthening repairs and decreasing the risk of failure. The mechanical properties of suitable adhesives were identified using a shear lag model. Examination of the design space for an optimal adhesive demonstrated requirements for strong adhesion and low stiffness to maximize the strength of the adhesive-coated suture repair construct. To experimentally assess the model, we evaluated single strands of sutures coated with highly flexible cyanoacrylates (Loctite 4903 and 4902), cyanoacrylate (Loctite QuickTite Instant Adhesive Gel), rubber cement, rubber/gasket adhesive (1300 Scotch-Weld Neoprene High Performance Rubber & Gasket Adhesive), an albumin-glutaraldehyde adhesive (BioGlue), or poly(dopamine). As a clinically relevant proof-of-concept, cyanoacrylate-coated sutures were then used to perform a clinically relevant flexor digitorum tendon repair in cadaver tissue. The repair performed with adhesive-coated suture had significantly higher strength compared to the standard repair without adhesive. Notably, cyanoacrylate provides strong adhesion with high stiffness and brittle behavior, and is therefore not an ideal adhesive for enhancing suture repair. Nevertheless, the improvement in repair properties in a clinically relevant setting, even using a non-ideal adhesive, demonstrates the potential for the proposed approach to improve outcomes for treatments requiring suture fixation. Further study is necessary to develop a strongly adherent, compliant adhesive within the optimal design space described by the model. PMID:26022966

  20. Shear lag sutures: Improved suture repair through the use of adhesives

    PubMed Central

    Linderman, Stephen W.; Kormpakis, Ioannis; Gelberman, Richard H.; Birman, Victor; Wegst, Ulrike G. K.; Genin, Guy M.; Thomopoulos, Stavros

    2015-01-01

    Suture materials and surgical knot tying techniques have improved dramatically since their first use over five millennia ago. However, the approach remains limited by the ability of the suture to transfer load to tissue at suture anchor points. Here, we predict that adhesive-coated sutures can improve mechanical load transfer beyond the range of performance of existing suture methods, thereby strengthening repairs and decreasing the risk of failure. The mechanical properties of suitable adhesives were identified using a shear lag model. Examination of the design space for an optimal adhesive demonstrated requirements for strong adhesion and low stiffness to maximize the strength of the adhesive-coated suture repair construct. To experimentally assess the model, we evaluated single strands of sutures coated with highly flexible cyanoacrylates (Loctite 4903 and 4902), cyanoacrylate (Loctite QuickTite Instant Adhesive Gel), rubber cement, rubber/gasket adhesive (1300 Scotch-Weld Neoprene High Performance Rubber & Gasket Adhesive), an albumin-glutaraldehyde adhesive (BioGlue), or poly(dopamine). As a clinically relevant proof-of-concept, cyanoacrylate-coated sutures were then used to perform a clinically relevant flexor digitorum tendon repair in cadaver tissue. The repair performed with adhesive-coated suture had significantly higher strength compared to the standard repair without adhesive. Notably, cyanoacrylate provides strong adhesion with high stiffness and brittle behavior, and is therefore not an ideal adhesive for enhancing suture repair. Nevertheless, the improvement in repair properties in a clinically relevant setting, even using a non-ideal adhesive, demonstrates the potential for the proposed approach to improve outcomes for treatments requiring suture fixation. Further study is necessary to develop a strongly adherent, compliant adhesive within the optimal design space described by the model. PMID:26022966

  1. Peeling off an adhesive layer with spatially varying topography and shear modulus

    NASA Astrophysics Data System (ADS)

    Ghatak, Animangsu

    2014-03-01

    Inspired by recent experiments on hierarchically structured adhesives, we analyze here the effect of spatial variation in surface topography and shear modulus of an elastomeric adhesive on its ability to adhere strongly to a flexible contactor. The undulation of surface and modulus both were assumed to be periodic with periodicity, which is either identical or different for the two parameters; for identical periodicity, the phase lag between the respective undulations is also systematically varied. Calculations show that during continuous lifting of the flexible contactor from complete initial contact, the interfacial crack between the two adherents does not propagate continuously but intermittently, with crack arrest and initiation at the vicinity of minimum thickness and modulus of the layer; the torque required to initiate an arrested crack increases significantly over that required to propagate it on a smooth adhesive surface. The adhesion strength estimated from the corresponding force vs displacement plot is calculated to be higher than that achieved on a smooth and featureless adhesive surface. For in-phase variation in topography and shear modulus of the layer, the adhesive strength is found to be higher than for nonzero phase lag between the two parameters. The adhesion strength is found to diminish also for nonidentical periodicity between modulus and surface undulation. We have derived a scaling law for relating adhesion strength to several of these parameters.

  2. Peeling off an adhesive layer with spatially varying topography and shear modulus.

    PubMed

    Ghatak, Animangsu

    2014-03-01

    Inspired by recent experiments on hierarchically structured adhesives, we analyze here the effect of spatial variation in surface topography and shear modulus of an elastomeric adhesive on its ability to adhere strongly to a flexible contactor. The undulation of surface and modulus both were assumed to be periodic with periodicity, which is either identical or different for the two parameters; for identical periodicity, the phase lag between the respective undulations is also systematically varied. Calculations show that during continuous lifting of the flexible contactor from complete initial contact, the interfacial crack between the two adherents does not propagate continuously but intermittently, with crack arrest and initiation at the vicinity of minimum thickness and modulus of the layer; the torque required to initiate an arrested crack increases significantly over that required to propagate it on a smooth adhesive surface. The adhesion strength estimated from the corresponding force vs displacement plot is calculated to be higher than that achieved on a smooth and featureless adhesive surface. For in-phase variation in topography and shear modulus of the layer, the adhesive strength is found to be higher than for nonzero phase lag between the two parameters. The adhesion strength is found to diminish also for nonidentical periodicity between modulus and surface undulation. We have derived a scaling law for relating adhesion strength to several of these parameters. PMID:24730852

  3. Two-axis direct fluid shear stress sensor

    NASA Technical Reports Server (NTRS)

    Bajikar, Sateesh (Inventor); Scott, Michael A. (Inventor); Adcock, Edward E. (Inventor)

    2011-01-01

    A micro sized multi-axis semiconductor skin friction/wall shear stress induced by fluid flow. The sensor design includes a shear/strain transduction gimble connected to a force collecting plate located at the flow boundary surface. The shear force collecting plate is interconnected by an arm to offset the tortional hinges from the fluid flow. The arm is connected to the shear force collecting plate through dual axis torsional hinges with piezoresistive torsional strain gauges. These gauges are disposed on the tortional hinges and provide a voltage output indicative of applied shear stress acting on the force collection plate proximate the flow boundary surface. Offsetting the torsional hinges creates a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from small shear stress, or small displacement of the collecting plate. The design also isolates the torsional sensors from exposure to the fluid flow.

  4. Environmental and viscoelastic effects on stresses in adhesive joints

    SciTech Connect

    Palazotto, A.N.; Birman, V.

    1995-04-01

    This paper considers the state of the art in several important areas of research on adhesively bonded joints. The paper reviews the studies dealing with environmental and viscoelastic effects on stresses in adhesive joints. Environmental factors that affect stresses include temperature and moisture. These factors are analyzed and practical examples that illustrate their impact on adhesives are given for the solid-rocket motor, which is a structural component paramount to the U.S. space program. The paper deals with viscoelastic effects on adhesive joints, and a number of viscoelastic models used in the analysis of viscoelastic materials, including adhesives, are reviewed. The use of the solid-rocket motor as an example characterizes the circumstances where viscoelastic properties of adhesive layers are essential. Close attention is paid to the fractional derivative model of Bagley and Torvik, which may be a good candidate for an analytical study of adhesive joints. Finally, existing studies on viscoelastic adhesive joints are considered. 54 refs.

  5. Effect of shear forces and ageing on the compliance of adhesive pads in adult cockroaches.

    PubMed

    Zhou, Yanmin; Robinson, Adam; Viney, Christine; Federle, Walter

    2015-09-01

    The flexibility of insect adhesive pads is crucial for their ability to attach on rough surfaces. Here, we used transparent substrates with micropillars to test in adult cockroaches (Nauphoeta cinerea) whether and how the stiffness of smooth adhesive pads changes when shear forces are applied, and whether the insect's age has any influence. We found that during pulls towards the body, the pad's ability to conform to the surface microstructures was improved in comparison to a contact without shear, suggesting that shear forces make the pad more compliant. The mechanism underlying this shear-dependent increase in compliance is still unclear. The effect was not explained by viscoelastic creep, changes in normal pressure, or shear-induced pad rolling, which brings new areas of cuticle into surface contact. Adhesive pads were significantly stiffer in older cockroaches. Stiffness increased most rapidly in cockroaches aged between 2.5 and 4 months. This increase is probably based on wear and repair of the delicate adhesive cuticle. Recent wear (visualised by Methylene Blue staining) was not age dependent, whereas permanent damage (visible as brown scars) accumulated with age, reducing the pads' flexibility.

  6. Casein Phosphopeptide-Amorphous Calcium Phosphate and Shear Bond Strength of Adhesives to Primary Teeth Enamel

    PubMed Central

    Farokh Gisovar, Elham; Hedayati, Nassim; Shadman, Niloofar; Shafiee, Leila

    2015-01-01

    Background: CPP-ACP (Phosphopeptide-Amorphous Calcium Phosphate) has an important role in caries prevention in pediatric patients. This study was done, because of the great use of CPP-ACP and the need for restoration for teeth treated with CPP-ACP as well as the importance of shear bond strength of adhesives in the success of restorations. Objectives: This study aimed to evaluate the effect of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on shear bond strength of dental adhesives to enamel of primary teeth molars. Materials and Methods: This in vitro study was conducted on 180 extracted primary molars. They were randomly divided into 6 groups and each group was divided into 2 subgroups (treated with CPP-ACP and untreated). In subgroups with CPP-ACP, enamel was treated with CPP-ACP paste 1 h/d for 5 days. Types of adhesives that were evaluated in this study were Tetric N-Bond, AdheSE, AdheSE One F, single Bond 2, SE Bond, and Adper Prompt L-Pop. Shear bond strength was tested with a universal testing machine and mode of failure was evaluated under stereomicroscope. Data were analyzed by T test, 2-way analysis of variance (ANOVA), Tukey and Fisher exact test using SPSS18. P < 0.05 was considered as significance level. Results: Shear bond strengths of different adhesive systems to enamel of primary teeth treated and untreated with CPP-ACP showed no significant difference (P > 0.05). Mode of failure in all groups regardless of CPP-ACP administration was mainly adhesive type. Our results indicated that CPP-ACP did not affect shear bond strength of studied adhesives to primary teeth enamel. Conclusions: To have a successful and durable composite restoration, having a high strength bonding is essential. Considering the wide use of CPP-ACP in preventing tooth decay and the role of adhesive shear bond strength (SBS) in success of composite restoration, we conducted the present study to evaluate the effect of CPP-ACP on the SBS of adhesives to primary teeth

  7. State diagram for adhesion dynamics of deformable capsules under shear flow.

    PubMed

    Luo, Zheng Yuan; Bai, Bo Feng

    2016-08-17

    Due to the significance of understanding the underlying mechanisms of cell adhesion in biological processes and cell capture in biomedical applications, we numerically investigate the adhesion dynamics of deformable capsules under shear flow by using a three-dimensional computational fluid dynamic model. This model is based on the coupling of the front tracking-finite element method for elastic mechanics of the capsule membrane and the adhesion kinetics simulation for adhesive interactions between capsules and functionalized surfaces. Using this model, three distinct adhesion dynamic states are predicted, such as detachment, rolling and firm-adhesion. Specifically, the effects of capsule deformability quantified by the capillary number on the transitions of these three dynamic states are investigated by developing an adhesion dynamic state diagram for the first time. At low capillary numbers (e.g. Ca < 0.0075), whole-capsule deformation confers the capsule a flattened bottom in contact with the functionalized surface, which hence promotes the rolling-to-firm-adhesion transition. It is consistent with the observations from previous studies that cell deformation promotes the adhesion of cells lying in the rolling regime. However, it is surprising to find that, at relatively high capillary numbers (e.g. 0.0075 < Ca < 0.0175), the effect of capsule deformability on its adhesion dynamics is far more complex than just promoting adhesion. High deformability of capsules makes their bottom take a concave shape with no adhesion bond formation in the middle. The appearance of this specific capsule shape inhibits the transitions of both rolling-to-firm-adhesion and detachment-to-rolling, and it means that capsule deformation no longer promotes the capsule adhesion. Besides, it is interesting to note that, when the capillary number exceeds a critical value (e.g. Ca = 0.0175), the rolling state no longer appears, since capsules exhibit large deviation from the spherical shape

  8. Statistical Investigation of the Effect of Process Parameters on the Shear Strength of Metal Adhesive Joints

    NASA Astrophysics Data System (ADS)

    Rajkumar, Goribidanur Rangappa; Krishna, Munishamaih; Narasimhamurthy, Hebbale Narayanrao; Keshavamurthy, Yalanabhalli Channegowda

    2016-03-01

    The objective of the work was to optimize sheet metal joining parameters such as adhesive material, adhesive thickness, adhesive overlap length and surface roughness for single lap joint of aluminium sheet shear strength using robust design. An orthogonal array, main effect plot, signal-to-noise ratio and analysis of variance were employed to investigate the shear strength of the joints. The statistical result shows vinyl ester is best candidate among other two polymers viz. epoxy and polyester due to its low viscosity value compared to other two polymers. The experiment results shows that the adhesive thickness 0.6 mm, overlap length 50 mm and surface roughness 2.12 µm for obtained maximum shear strength of Al sheet joints. The ANOVA result shows one of the most significant factors is overlap length which affect joint strength in addition to adhesive thickness, adhesive material, and surface roughness. A confirmation test was carried out as the optimal combination of parameters will not match with the any of the experiments in the orthogonal array.

  9. Influence of polymer charge on the shear yield stress of silica aggregated with adsorbed cationic polymers.

    PubMed

    Zhou, Ying; Yu, Hai; Wanless, Erica J; Jameson, Graeme J; Franks, George V

    2009-08-15

    Flocs were produced by adding three cationic polymers (10% charge density, 3.0x10(5) g/mol molecular weight; 40% charge density, 1.1x10(5) g/mol molecular weight; and 100% charge density, 1.2x10(5) g/mol molecular weight) to 90 nm diameter silica particles. The shear yield stresses of the consolidated sediment beds from settled and centrifuged flocs were determined via the vane technique. The polymer charge density plays an important role in influencing the shear yield stresses of sediment beds. The shear yield stresses of sediment beds from flocs induced by the 10% charged polymer were observed to increase with an increase in polymer dose, initial solid concentration and background electrolyte concentration at all volume fractions. In comparison, polymer dose has a marginal effect on the shear yield stresses of sediment beds from flocs induced by the 40% and 100% charged polymers. The shear yield stresses of sediments from flocs induced by the 40% charged polymer are independent of salt concentration whereas the addition of salt decreases the shear yield stresses of sediments from flocs induced by the 100% charged polymer. When flocculated at the optimum dose for each polymer (12 mg/g silica for the 10% charged polymer at 0.03 M NaCl, 12 mg/g for 40% and 2 mg/g for 100%), shear yield stress increases as polymer charge increases. The effects observed are related to the flocculation mechanism (bridging, patch attraction or charge neutralisation) and the magnitude of the adhesive force. Comparison of shear and compressive yield stresses show that the network is only slightly weaker in shear than in compression. This is different than many other systems (mainly salt and pH coagulation) which have shear yield stress much less than compressive yield stress. The existing models relating the power law exponent of the volume fraction dependence of the shear yield stress to the network fractal structure are not satisfactory to predict all the experimental behaviour.

  10. Passive wireless wall shear stress sensors

    NASA Astrophysics Data System (ADS)

    Sells, Jeremy

    The design and realization of the first ever passive wireless wall shear stress sensors are presented. The sensors are capable of directly measuring shear forces, 4 mPa to 4 Pa, created at the solid-fluid boundary of a flow. To capture the spatially small structures of a turbulent flow, a micromachined, variable-capacitor floating element sensor is designed. Passive wireless capability is achieved with the addition of an inductive coil and interrogating antenna. These sensors will enable characterization of complex flow phenomena. The primary benefit of the system is that the sensors operate without the need of a direct electrical connection. This simplifies installation of the sensors and enables their placement in locations where the rest of the system either will not fit or cannot survive. By using a passive wireless technique, a power source is not required, extending the life of the sensor and simplifying fabrication. The system makes use of frequency separation, allowing one interrogating antenna to query multiple sensors configured as an array simultaneously. Two generations of the wireless sensor are presented. The design, fabrication, packaging, and characterization of two first-generation sensors have dynamic ranges of 37 and 52 dB. Following this work, specific design improvements were identified and integrated into a second-generation sensor design, resulting in an improvement to 62 dB dynamic range and an order of magnitude reduction in parasitic capacitance and humidity sensitivity. Ideas for a third generation are presented, but realization of this design is left for future work.

  11. Effect of adhesive thickness and surface treatment on shear strength on single lap joint Al/CFRP using adhesive of epoxy/Al fine powder

    NASA Astrophysics Data System (ADS)

    Diharjo, Kuncoro; Anwar, Miftahul; Tarigan, Roy Aries P.; Rivai, Ahmad

    2016-02-01

    The objective of this study is to investigate the effect of adhesive thickness and surface treatment on the shear strength and failure type characteristic of single lap joint (SLJ) CFRP/Al using adhesive epoxy/Al-fine-powder. The CFRP was produced by using hand layup method for 30% of woven roving carbon fiber (w/w) and the resin used was bisphenolic. The adhesive was prepared using 12.5% of aluminum fine powder (w/w) in the epoxy adhesive. The powder was mixed by using a mixing machine at 60 rpm for 6 minutes, and then it was used to join the Al plate-2024 and CFRP. The start time to pressure for the joint process was 20 minutes after the application of adhesive on the both of adherends. The variables in this research are adhesive thickness (i.e. 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm and 1 mm) and surface treatment of adherends (i.e. acetone, chromate sulphuric acid, caustic etch and tucker's reagent). Before shear testing, all specimens were post-cured at 100 °C for 15 minutes. The result shows that the SLJ has the highest shear strength for 0.4 mm of adhesive thickness. When the adhesive thickness is more than 0.4 mm (0.6-1 mm), the shear strength decreases significantly. It might be caused by the property change of adhesive from ductile to brittle. The acetone surface treatment produces the best bonding between the adhesive and adherends (CFRP and Al-plate 2024), and the highest shear strength is 9.31 MPa. The surface treatment give the humidification effect of adherend surfaces by adhesive. The failure characteristic shows that the mixed failure of light-fiber-tear-failure and cohesive-failure are occurred on the high shear strength of SLJ, and the low shear strength commonly has the adhesive-failure type.

  12. Haemostatic agents on the shear bond strength of self-adhesive resin

    PubMed Central

    Anil, Akansha; Sekhar, Anand; Ginjupalli, Kishor

    2015-01-01

    Background Dentin surface contaminated with haemostatic agents can interfere with the bonding of self-adhesive resin cement. Therefore the purpose of this study was to evaluate the effect of various haemostatic agents such as Aluminium chloride, Ferric sulphate and Tannic acid on the shear bond strength of self-adhesive resin luting agent. Material and Methods The buccal surfaces of extracted premolars were flattened to expose the dentine. The teeth were then randomly divided into four groups. In Group I Aluminium Chloride was applied on the flattened dentinal surface, in Group II Ferric Sulphate was applied to exposed dentin surface, in Group III tannic acid was applied on to the dentinal surface, and the control group, i.e. Group IV was rinsed with saline. After the surface treatment, all the teeth were air dried. Then a predetermined dimension of RelyX™ U200 self-adhesive resin cement was bonded to the pretreated dentin surfaces. The samples were then stored under 370C in distilled water for 24 hours under 100 % humidity. Following this each sample was tested for shear bond strength with an Instron testing machine at a crosshead speed of 1mm/min. Results There was significant difference in the shear bond strength of control and tannic acid contaminated group (p<0.05), whereas there was no significant differences between the shear bond strength between control and aluminium chloride and ferric sulphate groups (p>0.05). Conclusions The usage of haemostatic agent can negatively affect the bond strength of self-adhesive resin cement (Rely X) on to the dentin surface. As per the study Tannic acid significantly weakened the bond between the self-adhesive resin and dentin. Key words:Aluminium chloride, Ferric sulphate, haemostatic agent, self-adhesive resin cement, shear bond strength, Tannic acid. PMID:26330930

  13. An in-plane cantilever for wall shear stress measurement

    NASA Astrophysics Data System (ADS)

    Allen, N. J.; Sims-Williams, D. B.; Wood, D.

    2012-07-01

    A sensor capable of measuring small shear stresses in wind tunnel applications is presented. The sensor utilizes an in-plane cantilever concept for shear stress measurement, designed to minimize intrusiveness into the airflow and allow easy incorporation into wind tunnel test models. The sensor operates independently of input voltage, and can measure <1 Pa shear stresses with a sensitivity of 8.6 (mV V-1) Pa. Altering the geometry of the sensor has a direct effect on the sensitivity and so can be used to adapt the sensor for different applications.

  14. Shear bond strength of orthodontic color-change adhesives with different light-curing times

    PubMed Central

    Bayani, Shahin; Ghassemi, Amirreza; Manafi, Safa; Delavarian, Mohadeseh

    2015-01-01

    Background: The purpose of this study was to evaluate the effect of light-curing time on the shear bond strength (SBS) of two orthodontic color-change adhesives (CCAs). Materials and Methods: A total of 72 extracted premolars were randomly assigned into 6 groups of 12 teeth each. Subsequent to primer application, a metal bracket was bonded to the buccal surface using an orthodontic adhesive. Two CCAs (Greengloo and Transbond Plus) were tested and one conventional light-cured adhesive (Resilience) served as control. For each adhesive, the specimens were light-cured for two different times of 20 and 40 s. All the specimens underwent mechanical testing using a universal testing machine to measure the SBS. Adhesive remnant index (ARI) was used to assess the remnant adhesive material on the tooth surface. All statistical analyses were performed using SPSS software. The significance level for all statistical tests was set at P ≤ 0.05. Results: The SBSs of the tested groups were in the range of 14.05-31.25 MPa. Greengloo adhesive showed the highest SBS values when light-cured for 40 s, and Transbond Plus adhesive showed the lowest values when light-cured for 20 s. ARI scores of Transbond Plus adhesive were significantly higher than those of controls, while other differences in ARI values were not significant. Conclusion: Within the limitations of his study, decreasing the light-curing time from 40 to 20 s decreased the SBS of the tested adhesives; however, this decline in SBS was statistically significant only in Transbond Plus adhesive PMID:26005468

  15. Aortic wall shear stress in Marfan syndrome.

    PubMed

    Geiger, Julia; Arnold, Raoul; Herzer, Lena; Hirtler, Daniel; Stankovic, Zoran; Russe, Max; Langer, Mathias; Markl, Michael

    2013-10-01

    The aim of this study was to quantify changes in thoracic aortic wall shear stress (WSS) in asymptomatic patients with Marfan syndrome (MFS) compared with healthy controls. WSS in the thoracic aorta was quantified based on time-resolved 3D phase contrast MRI with three-directional velocity encoding (4D flow MRI, temporal resolution ∼44 ms, spatial resolution ∼2.5 mm) in 24 patients with confirmed MFS (age = 18 ± 12 years) and in 12 older healthy volunteers (age = 25 ± 3 years). Diameters of the thoracic aorta normalized to body surface area were similar for both groups. Peak systolic velocity, absolute WSS, time-averaged WSS, circumferential WSS, peak systolic WSS, and WSS eccentricity were calculated in eight analysis planes distributed along the thoracic aorta. Plane-wise comparison revealed significant differences between MFS patients and volunteers in the proximal ascending aorta for peak systolic velocities (1.11 ± 0.23 m/s vs. 1.34 ± 0.18 m/s, P = 0.004) and circumferential WSS (0.14 ± 0.03 N/m(2) vs. 0.11 ± 0.02 N/m(2), P = 0.007). WSS eccentricity was altered in most of the ascending aorta and proximal arch (P = 0.009-0.020). MFS patients demonstrated segmental differences in peak systolic WSS with a significantly higher WSS at the inner curvature in the proximal ascending aorta and at the anterior part in the more distal ascending aorta (P < 0.01). These findings indicate differences in WSS associated with MFS despite similar aortic dimensions compared to controls.

  16. Dilute rigid dumbbell suspensions in large-amplitude oscillatory shear flow: Shear stress response

    NASA Astrophysics Data System (ADS)

    Bird, R. B.; Giacomin, A. J.; Schmalzer, A. M.; Aumnate, C.

    2014-02-01

    We examine the simplest relevant molecular model for large-amplitude shear (LAOS) flow of a polymeric liquid: the suspension of rigid dumbbells in a Newtonian solvent. We find explicit analytical expressions for the shear rate amplitude and frequency dependences of the first and third harmonics of the alternating shear stress response. We include a detailed comparison of these predictions with the corresponding results for the simplest relevant continuum model: the corotational Maxwell model. We find that the responses of both models are qualitatively similar. The rigid dumbbell model relies entirely on the dumbbell orientation to explain the viscoelastic response of the polymeric liquid, including the higher harmonics in large-amplitude oscillatory shear flow. Our analysis employs the general method of Bird and Armstrong ["Time-dependent flows of dilute solutions of rodlike macromolecules," J. Chem. Phys. 56, 3680 (1972)] for analyzing the behavior of the rigid dumbbell model in any unsteady shear flow. We derive the first three terms of the deviation of the orientational distribution function from the equilibrium state. Then, after getting the "paren functions," we use these for evaluating the shear stress for LAOS flow. We find the shapes of the shear stress versus shear rate loops predicted to be reasonable.

  17. Determination of the Shear Stress Distribution in a Laminate from the Applied Shear Resultant--A Simplified Shear Solution

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.

    2007-01-01

    The simplified shear solution method is presented for approximating the through-thickness shear stress distribution within a composite laminate based on laminated beam theory. The method does not consider the solution of a particular boundary value problem, rather it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply level stresses can be efficiently determined from global load resultants (as determined, for instance, by finite element analysis) at a given location in a structure and used to evaluate the margin of safety on a ply by ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. Comparisons to existing theories are made for a variety of laminates, and design examples are provided illustrating the use of the method for determining through-thickness shear stress margins in several types of composite panels and in the context of a finite element structural analysis.

  18. Simplified Shear Solution for Determination of the Shear Stress Distribution in a Composite Panel from the Applied Shear Resultant

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Yarrington, Phillip W.; Collier, Craig S.

    2008-01-01

    The simplified shear solution method is presented for approximating the through-thickness shear stress distribution within a composite laminate or panel based on laminated beam theory. The method does not consider the solution of a particular boundary value problem; rather it requires only knowledge of the global shear loading, geometry, and material properties of the laminate or panel. It is thus analogous to lamination theory in that ply level stresses can be efficiently determined from global load resultants (as determined, for instance, by finite element analysis) at a given location in a structure and used to evaluate the margin of safety on a ply by ply basis. The simplified shear solution stress distribution is zero at free surfaces, continuous at ply boundaries, and integrates to the applied shear load. Comparisons to existing theories are made for a variety of laminates, and design examples are provided illustrating the use of the method for determining through-thickness shear stress margins in several types of composite panels and in the context of a finite element structural analysis.

  19. Adhesion behavior of endothelial progenitor cells to endothelial cells in simple shear flow

    NASA Astrophysics Data System (ADS)

    Gong, Xiao-Bo; Li, Yu-Qing; Gao, Quan-Chao; Cheng, Bin-Bin; Shen, Bao-Rong; Yan, Zhi-Qiang; Jiang, Zong-Lai

    2011-12-01

    The adhesion of endothelial progenitor cells (EPCs) on endothelial cells (ECs) is one of the critical physiological processes for the regenesis of vascular vessels and the prevention of serious cardiovascular diseases. Here, the rolling and adhesion behavior of EPCs on ECs was studied numerically. A two-dimensional numerical model was developed based on the immersed boundary method for simulating the rolling and adhesion of cells in a channel flow. The binding force arising from the catch bond of a receptor and ligand pair was modeled with stochastic Monte Carlo method and Hookean spring model. The effect of tumor necrosis factor alpha (TNF- α) on the expression of the number of adhesion molecules in ECs was analyzed experimentally. A flow chamber system with CCD camera was set up to observe the top view of the rolling of EPCs on the substrate cultivated with ECs. Numerical results prove that the adhesion of EPC on ECs is closely related to membrane stiffness of the cell and shear rate of the flow. It also suggests that the adhesion force between EPC and EC by P-selectin glycoprotein ligand-1 only is not strong enough to bond the cell onto vessel walls unless contributions of other catch bond are considered. Experimental results demonstrate that TNF- α enhanced the expressions of VCAM, ICAM, P-selectin and E-selectin in ECs, which supports the numerical results that the rolling velocity of EPC on TNF- α treated EC substrate decreases obviously compared with its velocity on the untreated one. It is found that because the adhesion is affected by both the rolling velocity and the deformability of the cell, an optimal stiffness of EPC may exist at a given shear rate of flow for achieving maximum adhesion rates.

  20. Shear bond strength of self-etching adhesive systems to Er:YAG-laser-prepared dentin.

    PubMed

    Brulat, Nathalie; Rocca, Jean-Paul; Leforestier, Eric; Fiorucci, Gilbert; Nammour, Samir; Bertrand, Marie-France

    2009-01-01

    This study was conducted to compare the shear bond strengths of composite resin bonded to Er:YAG laser or bur-prepared dentin surfaces using three self-etching adhesive systems. The occlusal surfaces of 120 human third molars were ground flat to expose dentin. The dentin was prepared using either a carbide bur or an Er:YAG laser at 350 mJ/pulse and 10 Hz (fluence, 44.5 J/cm(2)). Three different self-etching adhesive systems were applied: iBond, Xeno III and Clearfil SE Bond. Rods of composite resin were bonded to dentin surfaces and shear bond tests were carried out. Both dentin surfaces after debonding and resin rods were observed using a scanning electron microscope. When the Xeno III was used, no difference was observed on shear bond strength values when bur and Er:YAG laser were compared. When using iBond and Clearfil SE Bond, bond strength values measured on Er:YAG-laser-prepared surfaces were lower than those observed on bur-prepared surfaces. The absence of smear layer formation during the preparation of the dentin by the Er:YAG laser did not improve the adhesion values of self-etching adhesive systems.

  1. Production of functional proteins: balance of shear stress and gravity

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas John (Inventor); Hammond, Timothy Grant (Inventor); Kaysen, James Howard (Inventor)

    2011-01-01

    A method for the production of functional proteins including hormones by renal cells in a three dimensional culturing process responsive to shear stress uses a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-.alpha.-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D.sub.3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating an in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.

  2. Production of functional proteins: balance of shear stress and gravity

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas John (Inventor); Hammond, Timothy Grant (Inventor); Kaysen, James Howard (Inventor)

    2007-01-01

    The present invention provides a method for production of functional proteins including hormones by renal cells in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-a-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.

  3. Production of functional proteins: balance of shear stress and gravity

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas John (Inventor); Hammond, Timothy Grant (Inventor); Kaysen, James Howard (Inventor)

    2004-01-01

    The present invention provides a method for production of functional proteins including hormones by renal cells in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-a-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.

  4. Stress evolution in a conductive adhesive during curing and cooling

    NASA Astrophysics Data System (ADS)

    Mei, Yuhai

    2000-10-01

    There is increasing interest in using conductive adhesives, which are composites of polymers and conductive fillers, as replacements for solder in different types of microelectronic assemblies. However, conductive adhesives still suffer from several deficiencies, such as unstable electrical conductivity and inadequate adhesion. The reliability of the conductive adhesive joints is always one of the major considerations during their design and operation, and the curing and thermal stresses generated in polymers and composites during curing, cooling and thermal cycling play a very important role in determining reliability. Because of the mismatch in the mechanical properties between the conductive adhesive and the substrate, appreciable curing and thermal stress is generated during manufacturing, which may be detrimental to the reliability of conductive adhesive joints. In this dissertation, an interactive linear viscoelastic model which considers interaction between the initial gel network and the other networks that form during curing is proposed to simulate stress and volume shrinkage during the thermoset curing process, and an effective method for measuring volume shrinkage during the thermoset cure is developed. A systematic experimental study of the material properties of the conductive adhesive and its epoxy matrix during the curing and cooling processes has been conducted. Based on these experimental data, stresses generated during several spatially homogeneous curing and cooling processes of the conductive adhesive and its epoxy matrix are also calculated. It is found that the conductive adhesive possesses mechanical properties which are substantially different from those of the constituents, and that the conductive adhesive has a relaxation process which is similar to its matrix and generates appreciable curing and thermal stresses during curing and cooling. Finally, a processing procedure designed to provide desired residual stresses is discussed.

  5. Differential adhesion, activity, and carbohydrate: Protein ratios ofPseudomonas atlantica monocultures attaching to stainless steel in a linear shear gradient.

    PubMed

    Mittelman, M W; Nivens, D E; Low, C; White, D C

    1990-05-01

    Biofilm formation on metallic surfaces in marine and freshwater environments often precedes corrosion and other biofouling conditions. Attachment is mediated by such environmental factors as the presence of surface conditioning films, fluid dynamics, bulk-phase nutrient levels, and surface chemistry. In this study, we utilized a Fowler Cell Adhesion Measurement Module to demonstrate that the changes in cellular concentration and composition of a monoculture ofPseudomonas atlantica biofilms on stainless steel were a function of the applied shear force. At shear forces in the range of 3-10 dynes cm(-2) (1.0 liter min(-1)), attachment as measured by acridine orange direct microscopic counts was greatest at the higher shear forces.(14)C-Acetate uptake activity on the stainless steel surfaces increased with shear stress. Acetate incorporation ranged from 1×10(-5) to 19×10(-5) μmol cm(-2) between 0.15 and 30 dynes cm(-2) for 30 min uptake periods. On a per cell basis, however, activity decreased with shear, indicating a shift in metabolism. Fourier transform infrared spectroscopy revealed that protein and carbohydrate concentrations also increased with the applied shear. Increased biofilm C∶N ratios and total fatty acids were associated with the higher shear stresses. Neither radius of interaction nor biofilm age appeared to significantly influence the relationship between fluid shear and attachment and cellular composition ofP. atlantica biofilms in the range of 1-10 dynes cm(-2). PMID:24196364

  6. Effects of Fluid Shear Stress on Cancer Stem Cell Viability

    NASA Astrophysics Data System (ADS)

    Sunday, Brittney; Triantafillu, Ursula; Domier, Ria; Kim, Yonghyun

    2014-11-01

    Cancer stem cells (CSCs), which are believed to be the source of tumor formation, are exposed to fluid shear stress as a result of blood flow within the blood vessels. It was theorized that CSCs would be less susceptible to cell death than non-CSCs after both types of cell were exposed to a fluid shear stress, and that higher levels of fluid shear stress would result in lower levels of cell viability for both cell types. To test this hypothesis, U87 glioblastoma cells were cultured adherently (containing smaller populations of CSCs) and spherically (containing larger populations of CSCs). They were exposed to fluid shear stress in a simulated blood flow through a 125-micrometer diameter polyetheretherketone (PEEK) tubing using a syringe pump. After exposure, cell viability data was collected using a BioRad TC20 Automated Cell Counter. Each cell type was tested at three physiological shear stress values: 5, 20, and 60 dynes per centimeter squared. In general, it was found that the CSC-enriched U87 sphere cells had higher cell viability than the CSC-depleted U87 adherent cancer cells. Interestingly, it was also observed that the cell viability was not negatively affected by the higher fluid shear stress values in the tested range. In future follow-up studies, higher shear stresses will be tested. Furthermore, CSCs from different tumor origins (e.g. breast tumor, prostate tumor) will be tested to determine cell-specific shear sensitivity. National Science Foundation Grant #1358991 supported the first author as an REU student.

  7. Adhesive fracture mechanics. [stress analysis for bond line interface

    NASA Technical Reports Server (NTRS)

    Bennett, S. J.; Devries, K. L.; Williams, M. L.

    1974-01-01

    In studies of fracture mechanics the adhesive fracture energy is regarded as a fundamental property of the adhesive system. It is pointed out that the value of the adhesive fracture energy depends on surface preparation, curing conditions, and absorbed monolayers. A test method reported makes use of a disk whose peripheral part is bonded to a substrate material. Pressure is injected into the unbonded central part of the disk. At a certain critical pressure value adhesive failure can be observed. A numerical stress analysis involving arbitrary geometries is conducted.

  8. Cell-Activation by Shear Stresses in Abdominal Aortic Aneurysms (AAA)

    NASA Astrophysics Data System (ADS)

    Salsac, Anne-Virginie; Sparks, Steven; Chomaz, Jean-Marc; Lasheras, Juan C.

    2003-11-01

    Increasing experimental evidence indicates that low and oscillatory shear stresses promote proliferative, thrombotic, adhesive and inflammatory-mediated degenerative conditions throughout the wall of the aorta. These degenerative conditions have been shown to be involved in the pathogenesis of AAAs, a permanent, localized dilatation of the abdominal aorta. The purpose of this study is to measure both the magnitude and the duration of the shear stresses acting on both the arterial walls and on the blood cells inside AAAs, and to characterize their changes as the AAA enlarges. We conducted a parametric in-vitro study of the pulsatile blood flow in elastic models of AAAs while systematically varying the blood flow parameters, and the geometry of the aneurysm's bulging. The instantaneous flow characteristic inside the AAA was measured using DPIV at a sampling rate of 15 Hertz. A "cell-activation parameter" defined as the integral of the product of the magnitude of the shear stress and the time during which the stress acts was computed along each of the blood cell pathlines. The Lagrangian tracking of the blood cells shows that a large majority of them are subjected first to very high level of shear-induced "cell-activation" while later on they are entrained in regions of stasis where their residence time can increase up to several cardiac cycles. This cell-activation followed by the entrainment in low shear regions creates the optimal cell-adhesive and inflammatory-mediated degenerative conditions that are postulated to play an important role in the etiology and progressive enlargement of AAAs.

  9. Interfacial shear stress measurement using high spatial resolution multiphase PIV

    NASA Astrophysics Data System (ADS)

    André, Matthieu A.; Bardet, Philippe M.

    2015-06-01

    In multiphase flows, form drag and viscous shear stress transfer momentum between phases. For numerous environmental and man-made flows, it is of primary importance to predict this transfer at a liquid-gas interface. In its general expression, interfacial shear stress involves local velocity gradients as well as surface velocity, curvature, and surface tension gradients. It is therefore a challenging quantity to measure experimentally or compute numerically. In fact, no experimental work to date has been able to directly resolve all the terms contributing to the shear stress in the case of curved and moving surfaces. In an attempt to fully resolve the interface shear stress when surface tension gradients are negligible, high-resolution particle image velocimetry (PIV) data are acquired simultaneously on both sides of a water-air interface. The flow consists of a well-conditioned uniform and homogeneous water jet discharging in quiescent air, which exhibits two-dimensional surface waves as a result of a shear layer instability below the surface. PIV provides velocity fields in both phases, while planar laser-induced fluorescence is used to track the interface and obtain its curvature. To compute the interfacial shear stress from the data, several processing schemes are proposed and compared, using liquid and/or gas phase data. Vorticity at the surface, which relates to the shear stress through the dynamic boundary condition at the surface, is also computed and provides additional strategies for estimating the shear. The various schemes are in agreement within the experimental uncertainties, validating the methodology for experimentally resolving this demanding quantity.

  10. Flexible tactile sensor for shear stress measurement using transferred sub-µm-thick Si piezoresistive cantilevers

    NASA Astrophysics Data System (ADS)

    Noda, Kentaro; Onoe, Hiroaki; Iwase, Eiji; Matsumoto, Kiyoshi; Shimoyama, Isao

    2012-11-01

    We propose a flexible tactile sensor using sub-µm-thick Si piezoresistive cantilevers for shear stress detection. The thin Si piezoresistive cantilevers were fabricated on the device layer of a silicon on insulator (SOI) wafer. By using an adhesion-based transfer method, only these thin and fragile cantilevers were transferred from the rigid handling layer of the SOI wafer to the polydimethylsiloxane layer without damage. Because the thin Si cantilevers have high durability of bending, the proposed sensor can be attached to a thin rod-type structure serving as the finger of a robotic hand. The cantilevers were arrayed in orthogonal directions to measure the X and Y directional components of applied shear stresses independently. We evaluated the bending durability of our flexible tactile sensor and confirmed that the sensor can be attached to a rod with a radius of 10 mm. The sensitivity of the flexible tactile sensor attached to a curved surface was 1.7 × 10-6 Pa-1 on average for a range of shear stresses from -1.8 × 103 to 1.8 × 103 Pa applied along its surface. It independently detected the X and Y directional components of the applied shear stresses.

  11. Prediction of plantar shear stress distribution by artificial intelligence methods.

    PubMed

    Yavuz, Metin; Ocak, Hasan; Hetherington, Vincent J; Davis, Brian L

    2009-09-01

    Shear forces under the human foot are thought to be responsible for various foot pathologies such as diabetic plantar ulcers and athletic blisters. Frictional shear forces might also play a role in the metatarsalgia observed among hallux valgus (HaV) and rheumatoid arthritis (RA) patients. Due to the absence of commercial devices capable of measuring shear stress distribution, a number of linear models were developed. All of these have met with limited success. This study used nonlinear methods, specifically neural network and fuzzy logic schemes, to predict the distribution of plantar shear forces based on vertical loading parameters. In total, 73 subjects were recruited; 17 had diabetic neuropathy, 14 had HaV, 9 had RA, 11 had frequent foot blisters, and 22 were healthy. A feed-forward neural network (NN) and adaptive neurofuzzy inference system (NFIS) were built. These systems were then applied to a custom-built platform, which collected plantar pressure and shear stress data as subjects walked over the device. The inputs to both models were peak pressure, peak pressure-time integral, and time to peak pressure, and the output was peak resultant shear. Root-mean-square error (RMSE) values were calculated to test the models' accuracy. RMSE/actual shear ratio varied between 0.27 and 0.40 for NN predictions. Similarly, NFIS estimations resulted in a 0.28-0.37 ratio for local peak values in all subject groups. On the other hand, error percentages for global peak shear values were found to be in the range 11.4-44.1. These results indicate that there is no direct relationship between pressure and shear magnitudes. Future research should aim to decrease error levels by introducing shear stress dependent variables into the models. PMID:19725696

  12. Elevated Shear Stress in Arteriovenous Fistulae: Is There Mechanical Homeostasis?

    NASA Astrophysics Data System (ADS)

    McGah, Patrick; Leotta, Daniel; Beach, Kirk; Aliseda, Alberto

    2011-11-01

    Arteriovenous fistulae are created surgically to provide access for dialysis in patients with renal failure. The current hypothesis is that the rapid remodeling occurring after the fistula creation is in part a process to restore the mechanical stresses to some preferred level (i.e. mechanical homeostasis). Given that nearly 50% of fistulae require an intervention after one year, understanding the altered hemodynamic stress is important in improving clinical outcomes. We perform numerical simulations of four patient-specific models of functioning fistulae reconstructed from 3D Doppler ultrasound scans. Our results show that the vessels are subjected to `normal' shear stresses away from the anastomosis; about 1 Pa in the veins and about 2.5 Pa in the arteries. However, simulations show that part of the anastomoses are consistently subjected to very high shear stress (>10Pa) over the cardiac cycle. These elevated values shear stresses are caused by the transitional flows at the anastomoses including flow separation and quasiperiodic vortex shedding. This suggests that the remodeling process lowers shear stress in the fistula but that it is limited as evidenced by the elevated shear at the anastomoses. This constant insult on the arterialized venous wall may explain the process of late fistula failure in which the dialysis access become occluded after years of use. Supported by an R21 Grant from NIDDK (DK081823).

  13. Shear stress induces osteogenic differentiation of human mesenchymal stem cells

    PubMed Central

    Yourek, Gregory; McCormick, Susan M; Mao, Jeremy J; Reilly, Gwendolen C

    2014-01-01

    Aim To determine whether fluid flow-induced shear stress affects the differentiation of bone marrow-derived human mesenchymal stem cells (hMSCs) into osteogenic cells. Materials & methods hMSCs cultured with or without osteogenic differentiation medium were exposed to fluid flow-induced shear stress and analyzed for alkaline phosphatase activity and expression of osteogenic genes. Results Immediately following shear stress, alkaline phosphatase activity in osteogenic medium was significantly increased. At days 4 and 8 of culture the mRNA expression of bone morphogenetic protein-2 and osteopontin was significantly higher in hMSCs subjected to shear stress than those cultured in static conditions. However, hMSCs cultured in osteogenic differentiation medium were less responsive in gene expression of alkaline phosphatase and bone morphogenetic protein-2. Conclusion These data demonstrate that shear stress stimulates hMSCs towards an osteoblastic phenotype in the absence of chemical induction, suggesting that certain mechanical stresses may serve as an alternative to chemical stimulation of stem cell differentiation. PMID:20868327

  14. Stresses in adhesively bonded joints - A closed-form solution

    NASA Technical Reports Server (NTRS)

    Delale, F.; Erdogan, F.; Aydinoglu, M. N.

    1981-01-01

    The general plane strain problem of adhesively bonded structures consisting of two different, orthotropic adherends is considered, under the assumption that adherend thicknesses are constant and small in relation to the lateral dimensions of the bonded region, so that they may be treated as plates. The problem is reduced to a system of differential equations for the adhesive stresses which is solved in closed form, with a single lap joint and a stiffened plate under various loading conditions being considered as examples. It is found that the plate theory used in the analysis not only predicts the correct trend for adhesive stresses but gives surprisingly accurate results, the solution being obtained by assuming linear stress-strain relations for the adhesive.

  15. Shear Stress Sensing with Elastic Microfence Structures

    NASA Technical Reports Server (NTRS)

    Cisotto, Alexxandra; Palmieri, Frank L.; Saini, Aditya; Lin, Yi; Thurman, Christopher S; Kim, Jinwook; Kim, Taeyang; Connell, John W.; Zhu, Yong; Gopalarathnam, Ashok; Jiang, Xiaoning; Wohl, Christopher J.

    2015-01-01

    In this work, elastic microfences were generated for the purpose of measuring shear forces acting on a wind tunnel model. The microfences were fabricated in a two part process involving laser ablation patterning to generate a template in a polymer film followed by soft lithography with a two-part silicone. Incorporation of a fluorescent dye was demonstrated as a method to enhance contrast between the sensing elements and the substrate. Sensing elements consisted of multiple microfences prepared at different orientations to enable determination of both shear force and directionality. Microfence arrays were integrated into an optical microscope with sub-micrometer resolution. Initial experiments were conducted on a flat plate wind tunnel model. Both image stabilization algorithms and digital image correlation were utilized to determine the amount of fence deflection as a result of airflow. Initial free jet experiments indicated that the microfences could be readily displaced and this displacement was recorded through the microscope.

  16. Effects of shear stress on endothelial progenitor cells.

    PubMed

    Obi, Syotaro; Yamamoto, Kimiko; Ando, Joji

    2014-10-01

    Endothelial progenitor cells (EPCs) are adult stem cells that play a central role in neovascularization. EPCs are mobilized from bone marrow into peripheral blood, attach to existing endothelial cells, and then transmigrate across the endothelium into tissues, where they proliferate, differentiate, and form new blood vessels. In the process, EPCs are exposed to shear stress, a biomechanical force generated by flowing blood and tissue fluid flow. When cultured EPCs are exposed to controlled levels of shear stress in a flow-loading device, their bioactivities in terms of proliferation, anti-apoptosis, migration, production of bioactive substances, anti-thrombosis, and tube formation increase markedly. Expression of endothelial marker genes and proteins by EPCs also increases in response to shear stress, and they differentiate into mature endothelial cells. Great advances have been made in elucidating the mechanisms by which mature endothelial cells sense and respond to shear stress, but not in EPCs. Further study of EPC responses to shear stress will be necessary to better understand the physiological and pathophysiological roles of EPCs and to apply EPCs to new therapies in the field of regenerative medicine. PMID:25992410

  17. Determination of surface shear stress with the naphthalene sublimation technique

    NASA Technical Reports Server (NTRS)

    Lee, J. A.; Greeley, Ronald

    1987-01-01

    Aeolian entrainment and transport are functions of surface shear stress and particle characteristics. Measuring surface shear stress is difficult, however, where logarithmic wind profiles are not found, such as regions around large roughness elements. An outline of a method whereby shear stress can be mapped on the surface around an object is presented. The technique involves the sublimation of naphthalene (C10H8) which is a function of surface shear stress and surface temperature. This technique is based on the assumption that the transfer of momentum, heat and mass are analogous (Reynolds analogy). If the Reynolds analogy can be shown to be correct for a given situation, then knowledge of the diffusion of one property allows the determination of the others. The analytical framework and data acquisition for the method are described. The technique was tested in the Planetary Geology Wind Tunnel. Results show that the naphthalene sublimation technique is a reasonably accurate method for determining shear stress, particularly around objects where numerous point values are needed.

  18. Gyrokinetic Simulation of Residual Stress from Diamagnetic Velocity Shears

    NASA Astrophysics Data System (ADS)

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2010-11-01

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the parallel velocity (and parallel velocity itself) vanishes. Previously [1] we demonstrated with gyrokinetic (GYRO) simulations that TAM pinching from the diamagnetic level shear in the ExB velocity could provide the residual stress needed for spontaneous toroidal rotation. Here we show that the shear in the diamagnetic velocities themselves provide comparable residual stress (and level of stabilization). The sign of the residual stress, quantified by the ratio of TAM flow to ion power flow (M/P), depends on the signs of the various velocity shears as well as ion (ITG) versus electron (TEM) mode directed turbulence. The residual stress from these temperature and density gradient diamagnetic velocity shears is demonstrated in global gyrokinetic simulation of ``null'' rotation DIIID discharges by matching M/P profiles within experimental error. 8pt [1] R.E. Waltz, G.M. Staebler, J. Candy, and F.L. Hinton, Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009).

  19. Molecular origins of higher harmonics in large-amplitude oscillatory shear flow: Shear stress response

    NASA Astrophysics Data System (ADS)

    Gilbert, P. H.; Giacomin, A. J.

    2016-10-01

    Recent work has focused on deepening our understanding of the molecular origins of the higher harmonics that arise in the shear stress response of polymeric liquids in large-amplitude oscillatory shear flow. For instance, these higher harmonics have been explained by just considering the orientation distribution of rigid dumbbells suspended in a Newtonian solvent. These dumbbells, when in dilute suspension, form the simplest relevant molecular model of polymer viscoelasticity, and this model specifically neglects interactions between the polymer molecules [R. B. Bird et al., "Dilute rigid dumbbell suspensions in large-amplitude oscillatory shear flow: Shear stress response," J. Chem. Phys. 140, 074904 (2014)]. In this paper, we explore these interactions by examining the Curtiss-Bird model, a kinetic molecular theory designed specifically to account for the restricted motions that arise when polymer chains are concentrated, thus interacting and specifically, entangled. We begin our comparison using a heretofore ignored explicit analytical solution [X.-J. Fan and R. B. Bird, "A kinetic theory for polymer melts. VI. Calculation of additional material functions," J. Non-Newtonian Fluid Mech. 15, 341 (1984)]. For concentrated systems, the chain motion transverse to the chain axis is more restricted than along the axis. This anisotropy is described by the link tension coefficient, ɛ, for which several special cases arise: ɛ = 0 corresponds to reptation, ɛ > 1/8 to rod-climbing, 1/5 ≤ ɛ ≤ 3/4 to reasonable predictions for shear-thinning in steady simple shear flow, and ɛ = 1 to the dilute solution without hydrodynamic interaction. In this paper, we examine the shapes of the shear stress versus shear rate loops for the special cases ɛ = (" separators=" 0 , 1 / 8 , 3 / 8 , 1 ) , and we compare these with those of rigid dumbbell and reptation model predictions.

  20. Contraction stress in dentin adhesives bonded to dentin.

    PubMed

    Hashimoto, M; de Gee, A J; Kaga, M; Feilzer, A J

    2006-08-01

    Adhesives cured under constrained conditions develop contraction stresses. We hypothesized that, with dentin as a bonding substrate, the stress would reach a maximum, followed by a continuous decline. Stress development was determined with a tensilometer for two total-etch systems and two systems with self-etching primers. The adhesives were placed in a thin layer between a glass plate and a flat dentin surface pretreated with phosphoric acid or self-etching primer. After an initial maximum shortly after light-curing, the stress decreased dramatically for the total-etch systems (70%) and, to a lesser extent, for the adhesives with self-etching primers (30%). The greater stress decrease for the total-etch systems was ascribed to water and/or solvents released into the adhesives from the fully opened dentinal tubules by the pulling/sucking action of the contraction stress. This happened less with the adhesives with self-etching primers, where the tubules remained mainly closed.

  1. Effects of dynamic shear and transmural pressure on wall shear stress sensitivity in collecting lymphatic vessels.

    PubMed

    Kornuta, Jeffrey A; Nepiyushchikh, Zhanna; Gasheva, Olga Y; Mukherjee, Anish; Zawieja, David C; Dixon, J Brandon

    2015-11-01

    Given the known mechanosensitivity of the lymphatic vasculature, we sought to investigate the effects of dynamic wall shear stress (WSS) on collecting lymphatic vessels while controlling for transmural pressure. Using a previously developed ex vivo lymphatic perfusion system (ELPS) capable of independently controlling both transaxial pressure gradient and average transmural pressure on an isolated lymphatic vessel, we imposed a multitude of flow conditions on rat thoracic ducts, while controlling for transmural pressure and measuring diameter changes. By gradually increasing the imposed flow through a vessel, we determined the WSS at which the vessel first shows sign of contraction inhibition, defining this point as the shear stress sensitivity of the vessel. The shear stress threshold that triggered a contractile response was significantly greater at a transmural pressure of 5 cmH2O (0.97 dyne/cm(2)) than at 3 cmH2O (0.64 dyne/cm(2)). While contraction frequency was reduced when a steady WSS was applied, this inhibition was reversed when the applied WSS oscillated, even though the mean wall shear stresses between the conditions were not significantly different. When the applied oscillatory WSS was large enough, flow itself synchronized the lymphatic contractions to the exact frequency of the applied waveform. Both transmural pressure and the rate of change of WSS have significant impacts on the contractile response of lymphatic vessels to flow. Specifically, time-varying shear stress can alter the inhibition of phasic contraction frequency and even coordinate contractions, providing evidence that dynamic shear could play an important role in the contractile function of collecting lymphatic vessels.

  2. Antibacterial effect and shear bond strength of an orthodontic adhesive cement containing Galla chinensis extract

    PubMed Central

    WANG, LU-FEI; LUO, FENG; XUE, CHAO-RAN; DENG, MENG; CHEN, CHEN; WU, HAO

    2016-01-01

    Galla chinensis extract (GCE), a naturally-derived agent, has a significant inhibitory effect on cariogenic bacteria. The present study aims to evaluate the antibacterial effect and shear bond strength of an orthodontic adhesive cement containing GCE. A resin-modified glass ionomer cement incorporated GCE at five mass fractions (0, 0.1, 0.2, 0.4, and 0.8%) to prepare GCE-containing cement for analysis. For the agar diffusion test, cement specimens were placed on agar disk inoculated with Streptococcus mutans (strain ATCC 25175). Following 48 h incubation, the inhibition halo diameter was measured. To assess bacteria colonization susceptibility, S. mutans adhesion to cement specimens was detected by scanning electron microscopy (SEM) following 48 h incubation. To evaluate bond strength, a total of 50 metal brackets were bonded on premolar surfaces by using cement (10 teeth/group). Following immersion in an artificial saliva for 3 days, shear bond strength (SBS) was measured. The results demonstrated that GCE-containing samples exhibited a larger bacterial inhibition halo than control, and the inhibition zone increased as the GCE mass fraction increased. SEM analysis demonstrated that S. mutans presented a weaker adherent capacity to all GCE-containing cements compared with control, but the difference between each GCE-containing group was not significant. SBS values of each GCE-containing group exhibited no difference compared with the control. In conclusion, GCE-containing adhesive cement exhibits a promising inhibitory effect on S. mutans growth and adhesion. Without compromising bond strength, adding GCE in adhesive cement may be an attractive option for preventing white spot lesions during orthodontic treatment. PMID:27073642

  3. High shear stress induces atherosclerotic vulnerable plaque formation through angiogenesis

    PubMed Central

    Wang, Yi; Qiu, Juhui; Luo, Shisui; Xie, Xiang; Zheng, Yiming; Zhang, Kang; Ye, Zhiyi; Liu, Wanqian; Gregersen, Hans; Wang, Guixue

    2016-01-01

    Rupture of atherosclerotic plaques causing thrombosis is the main cause of acute coronary syndrome and ischemic strokes. Inhibition of thrombosis is one of the important tasks developing biomedical materials such as intravascular stents and vascular grafts. Shear stress (SS) influences the formation and development of atherosclerosis. The current review focuses on the vulnerable plaques observed in the high shear stress (HSS) regions, which localizes at the proximal region of the plaque intruding into the lumen. The vascular outward remodelling occurs in the HSS region for vascular compensation and that angiogenesis is a critical factor for HSS which induces atherosclerotic vulnerable plaque formation. These results greatly challenge the established belief that low shear stress is important for expansive remodelling, which provides a new perspective for preventing the transition of stable plaques to high-risk atherosclerotic lesions. PMID:27482467

  4. Bed Shear Stress in Channels with Emergent Vegetation

    NASA Astrophysics Data System (ADS)

    Yang, Q.; Kerger, F.; Nepf, H. M.

    2014-12-01

    The shear stress at the bed of a channel influences important benthic processes such as sediment transport. Several methods exist to estimate the bed shear stress in open channel flow, but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production. This study proposes a new model to estimate the bed shear stress in both vegetated and bare channels. The model is based on the observation that, for both bare and vegetated channels, within a viscous sub-layer at the bed, the viscous stress decreases linearly with increasing distance from the bed, resulting in a parabolic velocity profile at the bed. For emergent canopies of sufficient density, the thickness of this linear-stress layer is set by the stem diameter, leading to a simple estimate for bed shear stress. For bare channels, the model describes the velocity profile in the overlap region of the Law of the Wall. The model is supported by high-resolution experiments. Furthermore, the changes in turbulence isotropy and integral length across a range of vegetation density, from bare bed to dense canopy, have been explored.

  5. A Rotary Flow Channel for Shear Stress Sensor Calibration

    NASA Technical Reports Server (NTRS)

    Zuckerwar, Allan J.; Scott, Michael A.

    2004-01-01

    A proposed shear sensor calibrator consists of a rotating wheel with the sensor mounted tangential to the rim and positioned in close proximity to the rim. The shear stress generated by the flow at the sensor position is simply tau(sub omega) = (mu)r(omega)/h, where mu is the viscosity of the ambient gas, r the wheel radius, omega the angular velocity of the wheel, and h the width of the gap between the wheel rim and the sensor. With numerical values of mu = 31 (mu)Pa s (neon at room temperature), r = 0.5 m, omega = 754 /s (7200 rpm), and h = 50.8 m, a shear stress of tau(sub omega) = 231 Pa can be generated. An analysis based on one-dimensional flow, with the flow velocity having only an angular component as a function of the axial and radial coordinates, yields corrections to the above simple formula for the curvature of the wheel, flatness of the sensor, and finite width of the wheel. It is assumed that the sensor mount contains a trough (sidewalls) to render a velocity release boundary condition at the edges of the rim. The Taylor number under maximum flow conditions is found to be 62.3, sufficiently low to obviate flow instability. The fact that the parameters entering into the evaluation of the shear stress can be measured to high accuracy with well-defined uncertainties makes the proposed calibrator suitable for a physical standard for shear stress calibration.

  6. Pressure and wall shear stress in blood hammer - Analytical theory.

    PubMed

    Mei, Chiang C; Jing, Haixiao

    2016-10-01

    We describe an analytical theory of blood hammer in a long and stiffened artery due to sudden blockage. Based on the model of a viscous fluid in laminar flow, we derive explicit expressions of oscillatory pressure and wall shear stress. To examine the effects on local plaque formation we also allow the blood vessel radius to be slightly nonuniform. Without resorting to discrete computation, the asymptotic method of multiple scales is utilized to deal with the sharp contrast of time scales. The effects of plaque and blocking time on blood pressure and wall shear stress are studied. The theory is validated by comparison with existing water hammer experiments. PMID:27474207

  7. Pressure and wall shear stress in blood hammer - Analytical theory.

    PubMed

    Mei, Chiang C; Jing, Haixiao

    2016-10-01

    We describe an analytical theory of blood hammer in a long and stiffened artery due to sudden blockage. Based on the model of a viscous fluid in laminar flow, we derive explicit expressions of oscillatory pressure and wall shear stress. To examine the effects on local plaque formation we also allow the blood vessel radius to be slightly nonuniform. Without resorting to discrete computation, the asymptotic method of multiple scales is utilized to deal with the sharp contrast of time scales. The effects of plaque and blocking time on blood pressure and wall shear stress are studied. The theory is validated by comparison with existing water hammer experiments.

  8. Influence of Adhesives and Methods of Enamel Pretreatment on the Shear Bond Strength of Orthodontic Brackets

    PubMed Central

    Jurišić, Sanja; Jurišić, Gordan

    2015-01-01

    Aim The objective of present study was to examine influence of adhesives and methods of enamel pretreatment on the shear bond strength (SBS) of orthodontic brackets. The adhesives used were resin-reinforced glass ionomer cements-GIC (Fuji Ortho LC) and composite resin (Transbond XT). Material and Methods The experimental sample consisted of 80 extracted human first premolars. The sample was divided into four equal groups, and the metal brackets were bonded with different enamel pretreatments by using two adhesives: group A-10% polyacrylic acid; Fuji Ortho LC, group B–37% phosphoric acid; Fuji Ortho LC, group C–self etching primer; Transbond XT, group D–37% phosphoric acid, primer; Transbond XT. SBS of brackets was measured. After debonding of brackets, the adhesive remnant index (ARI) was evaluated. Results After the statistical analysis of the collected data was performed (ANOVA; Sheffe post-hoc test), the results showed that significantly lower SBS of the group B was found in relation to the groups C (p=0.031) and D (p=0.026). The results of ARI were similar in all testing groups and it was not possible to determine any statistically significant difference of the ARI (Chi- square test) between all four experimental groups. Conclusion The conclusion is that the use of composite resins material with appropriate enamel pretreatment according to manufacturer’s recommendation is the “gold standard” for brackets bonding for fixed orthodontic appliances. PMID:27688410

  9. Influence of Adhesives and Methods of Enamel Pretreatment on the Shear Bond Strength of Orthodontic Brackets

    PubMed Central

    Jurišić, Sanja; Jurišić, Gordan

    2015-01-01

    Aim The objective of present study was to examine influence of adhesives and methods of enamel pretreatment on the shear bond strength (SBS) of orthodontic brackets. The adhesives used were resin-reinforced glass ionomer cements-GIC (Fuji Ortho LC) and composite resin (Transbond XT). Material and Methods The experimental sample consisted of 80 extracted human first premolars. The sample was divided into four equal groups, and the metal brackets were bonded with different enamel pretreatments by using two adhesives: group A-10% polyacrylic acid; Fuji Ortho LC, group B–37% phosphoric acid; Fuji Ortho LC, group C–self etching primer; Transbond XT, group D–37% phosphoric acid, primer; Transbond XT. SBS of brackets was measured. After debonding of brackets, the adhesive remnant index (ARI) was evaluated. Results After the statistical analysis of the collected data was performed (ANOVA; Sheffe post-hoc test), the results showed that significantly lower SBS of the group B was found in relation to the groups C (p=0.031) and D (p=0.026). The results of ARI were similar in all testing groups and it was not possible to determine any statistically significant difference of the ARI (Chi- square test) between all four experimental groups. Conclusion The conclusion is that the use of composite resins material with appropriate enamel pretreatment according to manufacturer’s recommendation is the “gold standard” for brackets bonding for fixed orthodontic appliances.

  10. Estimation of bed shear stresses in the pearl river estuary

    NASA Astrophysics Data System (ADS)

    Liu, Huan; Wu, Jia-xue

    2015-03-01

    Mean and fluctuating velocities were measured by use of a pulse coherent acoustic Doppler profiler (PC-ADP) and an acoustic Doppler velocimeter in the tidal bottom boundary layer of the Pearl River Estuary. The bed shear stresses were estimated by four different methods: log profile (LP), eddy correlation (EC), turbulent kinetic energy (TKE), and inertial dissipation (ID). The results show that (a) all four methods for estimating bed stresses have advantages and disadvantages, and they should be applied simultaneously to obtain reliable frictional velocity and to identify potential sources of errors; (b) the LP method was found to be the most suitable to estimate the bed stresses in non-stratified, quasi-steady, and homogeneous flows; and (c) in the estuary where the semi-diurnal tidal current is dominant, bed shear stresses exhibit a strong quarter-diurnal variation.

  11. Transient shear banding in a simple yield stress fluid.

    PubMed

    Divoux, Thibaut; Tamarii, David; Barentin, Catherine; Manneville, Sébastien

    2010-05-21

    We report a large set of experimental data which demonstrates that a simple yield stress fluid, i.e., which does not present aging or thixotropy, exhibits transient shear banding before reaching a steady state characterized by a homogeneous, linear velocity profile. The duration of the transient regime decreases as a power law with the applied shear rate γ. This power-law behavior, observed here in carbopol dispersions, does not depend on the gap width and on the boundary conditions for a given sample preparation. For γ≲0.1  s(-1), heterogeneous flows could be observed for as long as 10(5)  s. These local dynamics account for the ultraslow stress relaxation observed at low shear rates. PMID:20867072

  12. A Two-Axis Direct Fluid Shear Stress Sensor

    NASA Technical Reports Server (NTRS)

    Adcock, Edward E.; Scott, Michael A.; Bajikar, Sateesh S.

    2010-01-01

    This innovation is a miniature or micro sized semiconductor sensor design that provides two axis direct non-intrusive measurement of skin friction or wall shear stress in fluid flow. The sensor is fabricated by micro-electro-mechanical system (MEMS) technology, enabling small size and low cost reproductions. The sensors have been fabricated by utilizing MEMS fabrication processes to bond a sensing element wafer to a fluid coupling wafer. This layering technique provides for an out of plane dimension that is on the same order of length as the inplane dimensions. The sensor design has the following characteristics: a shear force collecting plate with dimensions that can be tailored to various application specific requirements such as spatial resolution, temporal resolution and shear force range and resolution. This plate is located coplanar to both the sensor body and flow boundary, and is connected to a dual axis gimbal structure by a connecting column or lever arm. The dual axis gimbal structure has torsional hinges with embedded piezoresistive torsional strain gauges which provide a voltage output that is correlated to the applied shear stress (and excitation current) on force collection plate that is located on the flow boundary surface (hence the transduction method). This combination of design elements create a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from the small shear stress on the flow boundary wall. This design as well as the use of back side electrical contacts establishes a non-intrusive method to quantitatively measure the shear force vector on aerodynamic bodies.

  13. Production of Functional Proteins: Balance of Shear Stress and Gravity

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas John (Inventor); Hammond, Timothy Grant (Inventor); Haysen, James Howard (Inventor)

    2005-01-01

    The present invention provides for a method of culturing cells and inducing the expression of at least one gene in the cell culture. The method provides for contacting the cell with a transcription factor decoy oligonucleotide sequence directed against a nucleotide sequence encoding a shear stress response element.

  14. Incomplete restoration of homeostatic shear stress within arteriovenous fistulae.

    PubMed

    McGah, Patrick M; Leotta, Daniel F; Beach, Kirk W; Eugene Zierler, R; Aliseda, Alberto

    2013-01-01

    Arteriovenous fistulae are surgically created to provide adequate access for dialysis patients suffering from end-stage renal disease. It has long been hypothesized that the rapid blood vessel remodeling occurring after fistula creation is, in part, a process to restore the mechanical stresses to some preferred level, i.e., mechanical homeostasis. We present computational hemodynamic simulations in four patient-specific models of mature arteriovenous fistulae reconstructed from 3D ultrasound scans. Our results suggest that these mature fistulae have remodeled to return to ''normal'' shear stresses away from the anastomoses: about 1.0 Pa in the outflow veins and about 2.5 Pa in the inflow arteries. Large parts of the anastomoses were found to be under very high shear stresses >15 Pa, over most of the cardiac cycle. These results suggest that the remodeling process works toward restoring mechanical homeostasis in the fistulae, but that the process is limited or incomplete, even in mature fistulae, as evidenced by the elevated shear at or near the anastomoses. Based on the long term clinical viability of these dialysis accesses, we hypothesize that the elevated nonhomeostatic shear stresses in some portions of the vessels were not detrimental to fistula patency. PMID:23363216

  15. Liquid Crystals Indicate Directions Of Surface Shear Stresses

    NASA Technical Reports Server (NTRS)

    Reda, Daniel C.

    1996-01-01

    Report consisting of main text of U.S. Patent 5,394,752 presents detailed information on one aspect of method of using changes in colors of liquid-crystal coatings to indicate instantaneous directions of flow-induced shear stresses (skin friction) on aerodynamic surfaces.

  16. The Need for a Shear Stress Calibration Standard

    NASA Technical Reports Server (NTRS)

    Scott, Michael A.

    2004-01-01

    By surveying current research of various micro-electro mechanical systems (MEMS) shear stress sensor development efforts we illustrate the wide variety of methods used to test and characterize these sensors. The different methods of testing these sensors make comparison of results difficult in some cases, and also this comparison is further complicated by the different formats used in reporting the results of these tests. The fact that making these comparisons can be so difficult at times clearly illustrates a need for standardized testing and reporting methodologies. This need indicates that the development of a national or international standard for the calibration of MEMS shear stress sensors should be undertaken. As a first step towards the development of this standard, two types of devices are compared and contrasted. The first type device is a laminar flow channel with two different versions considered: the first built with standard manufacturing techniques and the second with advanced precision manufacturing techniques. The second type of device is a new concept for creating a known shear stress consisting of a rotating wheel with the sensor mounted tangentially to the rim and positioned in close proximity to the rim. The shear stress generated by the flow at the sensor position is simply tau = (mu)r(omega)/h, where mu is the viscosity of the ambient gas, r the wheel radius, omega the angular velocity of the wheel, and h the width of the gap between the wheel rim and the sensor. Additionally, issues related to the development of a standard for shear stress calibration are identified and discussed.

  17. Shear stress related blood damage in laminar couette flow.

    PubMed

    Paul, Reinhard; Apel, Jörn; Klaus, Sebastian; Schügner, Frank; Schwindke, Peter; Reul, Helmut

    2003-06-01

    Artificial organs within the blood stream are generally associated with flow-induced blood damage, particularly hemolysis of red blood cells. These damaging effects are known to be dependent on shear forces and exposure times. The determination of a correlation between these flow-dependent properties and actual hemolysis is the subject of this study. For this purpose, a Couette device has been developed. A fluid seal based on fluorocarbon is used to separate blood from secondary external damage effects. The shear rate within the gap is controlled by the rotational speed of the inner cylinder, and the exposure time by the amount of blood that is axially pumped through the device per given time. Blood damage is quantified by the index of hemolysis (IH), which is calculated from photometric plasma hemoglobin measurements. Experiments are conducted at exposure times from texp=25 - 1250 ms and shear rates ranging from tau=30 up to 450 Pa ensuring Taylor-vortex free flow characteristics. Blood damage is remarkably low over a broad range of shear rates and exposure times. However, a significant increase in blood damage can be observed for shear stresses of tau>or= 425 Pa and exposure times of texp>or= 620 ms. Maximum hemolysis within the investigated range is IH=3.5%. The results indicate generally lower blood damage than reported in earlier studies with comparable devices, and the measurements clearly indicate a rather abrupt (i.e., critical levels of shear stresses and exposure times) than gradual increase in hemolysis, at least for the investigated range of shear rates and exposure times. PMID:12780506

  18. Arrest stress of uniformly sheared wet granular matter

    NASA Astrophysics Data System (ADS)

    Ebrahimnazhad Rahbari, S. H.; Brinkmann, M.; Vollmer, J.

    2015-06-01

    We conduct extensive independent numerical experiments considering frictionless disks without internal degrees of freedom (rotation, etc.) in two dimensions. We report here that for a large range of the packing fractions below random-close packing, all components of the stress tensor of wet granular materials remain finite in the limit of zero shear rate. This is direct evidence for a fluid-to-solid arrest transition. The offset value of the shear stress characterizes plastic deformation of the arrested state which corresponds to dynamic yield stress of the system. Based on an analytical line of argument, we propose that the mean number of capillary bridges per particle, ν , follows a nontrivial dependence on the packing fraction, ϕ , and the capillary energy, ɛ . Most noticeably, we show that ν is a generic and universal quantity which does not depend on the driving protocol. Using this universal quantity, we calculate the arrest stress, σa, analytically based on a balance of the energy injection rate due to the external force driving the flow and the dissipation rate accounting for the rupture of capillary bridges. The resulting prediction of σa is a nonlinear function of the packing fraction, ϕ , and the capillary energy, ɛ . This formula provides an excellent, parameter-free prediction of the numerical data. Corrections to the theory for small and large packing fractions are connected to the emergence of shear bands and of contributions to the stress from repulsive particle interactions, respectively.

  19. The Role of Shear Failure on Stress Characterization

    NASA Astrophysics Data System (ADS)

    Chan, A. W.; Hauser, M.; Couzens-Schultz, B. A.; Gray, G.

    2014-09-01

    Leak-off pressure and lost circulation data are generally thought to be reflective of minimum stress. We propose an alternative interpretation should be considered where the data may reflect a shear failure along zones of pre-existing weakness rather than opening of tensile fractures against the minimum stress. This mechanism has been discussed in a small number of borehole stability and hydraulic fracture papers, but has not been widely applied to leak-off test or lost circulation interpretation. In this paper, we will revisit and expand the concept introduced recently by Couzens-Schultz and Chan (J Struct Geol, doi: 10.1016/j.jsg.2010.06.013, 2010) based on abnormally low leak-off tests in an active thrust belt to the analysis of lost circulation observations in modern-day deltaic environments. In the Gulf of Mexico, lost circulations historically are interpreted as a representation of the minimum horizontal stress due to initiating or reopening of a fracture in tensile mode. However, shear failure or fault reactivation can occur at pressures well below the minimum far-field stress that is typically considered a safe upper bound for mud pressure if pre-existing planes of weakness such as faults or fracture networks exist. We demonstrated a mud loss event is shown to be inconsistent with the tensile failure mode in a normal stress environment, but in good agreement with expectations for shear failure along pre-existing faults.

  20. Arrest stress of uniformly sheared wet granular matter.

    PubMed

    Rahbari, S H Ebrahimnazhad; Brinkmann, M; Vollmer, J

    2015-06-01

    We conduct extensive independent numerical experiments considering frictionless disks without internal degrees of freedom (rotation, etc.) in two dimensions. We report here that for a large range of the packing fractions below random-close packing, all components of the stress tensor of wet granular materials remain finite in the limit of zero shear rate. This is direct evidence for a fluid-to-solid arrest transition. The offset value of the shear stress characterizes plastic deformation of the arrested state which corresponds to dynamic yield stress of the system. Based on an analytical line of argument, we propose that the mean number of capillary bridges per particle, ν, follows a nontrivial dependence on the packing fraction, ϕ, and the capillary energy, ɛ. Most noticeably, we show that ν is a generic and universal quantity which does not depend on the driving protocol. Using this universal quantity, we calculate the arrest stress, σ(a), analytically based on a balance of the energy injection rate due to the external force driving the flow and the dissipation rate accounting for the rupture of capillary bridges. The resulting prediction of σ(a) is a nonlinear function of the packing fraction, ϕ, and the capillary energy, ɛ. This formula provides an excellent, parameter-free prediction of the numerical data. Corrections to the theory for small and large packing fractions are connected to the emergence of shear bands and of contributions to the stress from repulsive particle interactions, respectively.

  1. Characterization of fractures subjected to normal and shear stress

    NASA Astrophysics Data System (ADS)

    Choi, Min-Kwang

    Results from a series of laboratory experiments to determine fracture specific stiffness, for a fracture subjected to shear and normal stress, are presented and analyzed. The experimental work focuses on the determination of relations between normal and shear fracture specific stiffness and between spatial distribution of fracture specific stiffness and fluid flow through the fracture The ratio of shear to normal fracture specific stiffness is experimentally investigated on a fracture subjected to shear as well as normal stress. Synthetic fractures made of gypsum and lucite were prepared with different fracture surface conditions: either well-mated or non-mated. For well-mated fracture surfaces, asperities were created by casting gypsum against sandpaper. A block of gypsum was cast against the sandpaper and then a second block was cast against the first block such that the two contact surfaces were well-mated. The surface roughness was controlled by using the sandpapers with different average grit size. Non-mated fracture surfaces were fabricated with two lucite blocks that were polished (lucite PL) or sand-blasted (lucite SB) along their contact surface. In the experiments, each specimen was subjected to normal and shear loading while the fracture was probed with transmitted and reflected compressional and shear waves. Shear and normal fracture specific stiffnesses were calculated using the displacement discontinuity theory. For non-mated fractures, the stiffness ratio was not sensitive to the application of shear stress and, as normal stress increased, approached a theoretical ratio which was determined assuming that the transmission of compressional and shear waves was equal. The stiffness ratio obtained from well-mated fractures ranged from 0.5 to 1.4, which deviated from the conventional assumption that shear and normal fracture specific stiffness are equal. The stiffness ratio increased with increasing surface roughness and with increasing shear stress. For

  2. Endothelial cell activation by hemodynamic shear stress derived from arteriovenous fistula for hemodialysis access.

    PubMed

    Franzoni, Marco; Cattaneo, Irene; Longaretti, Lorena; Figliuzzi, Marina; Ene-Iordache, Bogdan; Remuzzi, Andrea

    2016-01-01

    Intimal hyperplasia (IH) is the first cause of failure of an arteriovenous fistula (AVF). The aim of the present study was to investigate the effects on endothelial cells (ECs) of shear stress waveforms derived from AVF areas prone to develop IH. We used a cone-and-plate device to obtain real-time control of shear stress acting on EC cultures. We exposed human umbilical vein ECs for 48 h to different shear stimulations calculated in a side-to-end AVF model. Pulsatile unidirectional flow, representative of low-risk stenosis areas, induced alignment of ECs and actin fiber orientation with flow. Shear stress patterns of reciprocating flow, derived from high-risk stenosis areas, did not affect EC shape or cytoskeleton organization, which remained similar to static cultures. We also evaluated flow-induced EC expression of genes known to be involved in cytoskeletal remodeling and expression of cell adhesion molecules. Unidirectional flow induced a significant increase in Kruppel-like factor 2 mRNA expression, whereas it significantly reduced phospholipase D1, α4-integrin, and Ras p21 protein activator 1 mRNA expression. Reciprocating flow did not increase Kruppel-like factor 2 mRNA expression compared with static controls but significantly increased mRNA expression of phospholipase D1, α4-integrin, and Ras p21 protein activator 1. Reciprocating flow selectively increased monocyte chemoattractant protein-1 and IL-8 production. Furthermore, culture medium conditioned by ECs exposed to reciprocating flows selectively increased smooth muscle cell proliferation compared with unidirectional flow. Our results indicate that protective vascular effects induced in ECs by unidirectional pulsatile flow are not induced by reciprocating shear forces, suggesting a mechanism by which oscillating flow conditions may induce the development of IH in AVF and vascular access dysfunction. PMID:26497959

  3. Sensor for Boundary Shear Stress in Fluid Flow

    NASA Technical Reports Server (NTRS)

    Bao, Xiaoqi; Badescu, Mircea; Sherrit, Stewart; Bar-Cohen, Yoseph; Lih, Shyh-Shiuh; Chang, Zensheu; Trease, Brian P.; Kerenyi, Kornel; Widholm, Scott E.; Ostlund, Patrick N.

    2012-01-01

    The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex and lead to low-fidelity results. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear stress, normal stress, and their fluctuations are attractive alternatives. However, most direct-measurement shear sensors are bulky in size or not compatible to fluid flow. A sensor has been developed that consists of a floating plate with folded beam support and an optical grid on the back, combined with a high-resolution optical position probe. The folded beam support makes the floating plate more flexible in the sensing direction within a small footprint, while maintaining high stiffness in the other directions. The floating plate converts the shear force to displacement, and the optical probe detects the plate s position with nanometer resolution by sensing the pattern of the diffraction field of the grid through a glass window. This configuration makes the sensor compatible with liquid flow applications.

  4. An EMAT-based shear horizontal (SH) wave technique for adhesive bond inspection

    NASA Astrophysics Data System (ADS)

    Arun, K.; Dhayalan, R.; Balasubramaniam, Krishnan; Maxfield, Bruce; Peres, Patrick; Barnoncel, David

    2012-05-01

    The evaluation of adhesively bonded structures has been a challenge over the several decades that these structures have been used. Applications within the aerospace industry often call for particularly high performance adhesive bonds. Several techniques have been proposed for the detection of disbonds and cohesive weakness but a reliable NDE method for detecting interfacial weakness (also sometimes called a kissing bond) has been elusive. Different techniques, including ultrasonic, thermal imaging and shearographic methods, have been proposed; all have had some degree of success. In particular, ultrasonic methods, including those based upon shear and guided waves, have been explored for the assessment of interfacial bond quality. Since 3-D guided shear horizontal (SH) waves in plates have predominantly shear displacement at the plate surfaces, we conjectured that SH guided waves should be influenced by interfacial conditions when they propagate between adhesively bonded plates of comparable thickness. This paper describes a new technique based on SH guided waves that propagate within and through a lap joint. Through mechanisms we have yet to fully understand, the propagation of an SH wave through a lap joint gives rise to a reverberation signal that is due to one or more reflections of an SH guided wave mode within that lap joint. Based upon a combination of numerical simulations and measurements, this method shows promise for detecting and classifying interfacial bonds. It is also apparent from our measurements that the SH wave modes can discriminate between adhesive and cohesive bond weakness in both Aluminum-Epoxy-Aluminum and Composite-Epoxy-Composite lap joints. All measurements reported here used periodic permanent magnet (PPM) Electro-Magnetic Acoustic Transducers (EMATs) to generate either or both of the two lowest order SH modes in the plates that comprise the lap joint. This exact configuration has been simulated using finite element (FE) models to

  5. A Shearing-Stretching Device That Can Apply Physiological Fluid Shear Stress and Cyclic Stretch Concurrently to Endothelial Cells.

    PubMed

    Meza, Daphne; Abejar, Louie; Rubenstein, David A; Yin, Wei

    2016-03-01

    Endothelial cell (EC) morphology and functions can be highly impacted by the mechanical stresses that the cells experience in vivo. In most areas in the vasculature, ECs are continuously exposed to unsteady blood flow-induced shear stress and vasodilation-contraction-induced tensile stress/strain simultaneously. Investigations on how ECs respond to combined shear stress and tensile strain will help us to better understand how an altered mechanical environment affects EC mechanotransduction, dysfunction, and associated cardiovascular disease development. In the present study, a programmable shearing and stretching device that can apply dynamic fluid shear stress and cyclic tensile strain simultaneously to cultured ECs was developed. Flow and stress/strain conditions in the device were simulated using a fluid structure interaction (FSI) model. To characterize the performance of this device and the effect of combined shear stress-tensile strain on EC morphology, human coronary artery ECs (HCAECs) were exposed to concurrent shear stress and cyclic tensile strain in the device. Changes in EC morphology were evaluated through cell elongation, cell alignment, and cell junctional actin accumulation. Results obtained from the numerical simulation indicated that in the "in-plane" area of the device, both fluid shear stress and biaxial tensile strain were uniform. Results obtained from the in vitro experiments demonstrated that shear stress, alone or combined with cyclic tensile strain, induced significant cell elongation. While biaxial tensile strain alone did not induce any appreciable change in EC elongation. Fluid shear stress and cyclic tensile strain had different effects on EC actin filament alignment and accumulation. By combining various fluid shear stress and cyclic tensile strain conditions, this device can provide a physiologically relevant mechanical environment to study EC responses to physiological and pathological mechanical stimulation. PMID:26810848

  6. Effects of stress on the adhesive behavior of photoresist

    NASA Astrophysics Data System (ADS)

    Yu, Geng; Wei, Zhang; Hou, Changlun; Bai, Jian

    2009-05-01

    In this paper, the effects of stress on the adhesive behavior of photoresist are described. The sources of internal stress of photoresist could be the shrinkage of photoresist during curing process and the shrinkage difference between the photoresist and the substrate. Due to high exothermicity of resin curing process, the temperature of photoresist is not uniform, which causes shrinkage difference in photoresist. Further more, when the substrate cools down, the difference of thermal expansion coefficients between the substrate and the photoresist would cause more stress. A digital phase-shifting interferometer is used to measure the curvature of substrate and then Stoney´s Formula is adopted to calculate stress. Then, a 2-D model is used to simulate temperature distribution, photoresist deformation and stress. Our results show that there is huge stress at the interface between photoresist and substrate and the stress can be reduced by anneal.

  7. Shear bond strength of fibre-reinforced composite nets using two different adhesive systems.

    PubMed

    Sfondrini, Maria Francesca; Cacciafesta, Vittorio; Scribante, Andrea

    2011-02-01

    The purpose of this study was to evaluate the effect of two different adhesive systems (Tetric Flow and Transbond XT) in combination with fibre-reinforced composites (FRC) net (Ever Stick) on the shear bond strength (SBS) of orthodontic brackets. Eighty bovine permanent mandibular incisors were randomly divided into four equal groups. Stainless steel maxillary central incisor brackets with a 0.018 inch slot (DB Leone) were bonded to the teeth using the two different adhesive systems. Fifty per cent of the brackets were bonded without and 50 per cent with a FRC net under the bracket base. After bonding, all samples were stored in distilled water at room temperature for 24 hours and subsequently tested for SBS. Analysis of variance indicated significant differences among the various groups. Brackets bonded with FRC nets under the base showed a significantly lower SBS than those bonded without nets (P < 0.05). Moreover, teeth bonded with Transbond XT showed a significantly higher SBS than the other groups. Additionally, significant differences in debond locations [adhesive remnant index (ARI) score] were found among the various groups. Transbond XT can successfully be used for direct bonding of FRC nets, thus improving their SBS values. PMID:20573712

  8. Cerebral microcirculation shear stress levels determine Neisseria meningitidis attachment sites along the blood–brain barrier

    PubMed Central

    Mairey, Emilie; Genovesio, Auguste; Donnadieu, Emmanuel; Bernard, Christine; Jaubert, Francis; Pinard, Elisabeth; Seylaz, Jacques; Olivo-Marin, Jean-Christophe; Nassif, Xavier; Duménil, Guillaume

    2006-01-01

    Neisseria meningitidis is a commensal bacterium of the human nasopharynx. Occasionally, this bacterium reaches the bloodstream and causes meningitis after crossing the blood–brain barrier by an unknown mechanism. An immunohistological study of a meningococcal sepsis case revealed that neisserial adhesion was restricted to capillaries located in low blood flow regions in the infected organs. This study led to the hypothesis that drag forces encountered by the meningococcus in the bloodstream determine its attachment site in vessels. We therefore investigated the ability of N. meningitidis to bind to endothelial cells in the presence of liquid flow mimicking the bloodstream with a laminar flow chamber. Strikingly, average blood flows reported for various organs strongly inhibited initial adhesion. As cerebral microcirculation is known to be highly heterogeneous, cerebral blood velocity was investigated at the level of individual vessels using intravital imaging of rat brain. In agreement with the histological study, shear stress levels compatible with meningococcal adhesion were only observed in capillaries, which exhibited transient reductions in flow. The flow chamber assay revealed that, after initial attachment, bacteria resisted high blood velocities and even multiplied, forming microcolonies resembling those observed in the septicemia case. These results argue that the combined mechanical properties of neisserial adhesion and blood microcirculation target meningococci to transiently underperfused cerebral capillaries and thus determine disease development. PMID:16864659

  9. Shear Bond Strength of Orthodontic Brackets Fixed with Remineralizing Adhesive Systems after Simulating One Year of Orthodontic Treatment.

    PubMed

    Bezerra, Gisele Lima; Torres, Carlos Rocha Gomes; Tonetto, Mateus Rodrigues; Borges, Alvaro Henrique; Kuga, Milton Carlos; Bandeca, Matheus Coelho; Firoozmand, Leily Macedo

    2015-01-01

    The objective of this study is to assess, in vitro, the shear bond strength of orthodontic brackets fixed with remineralizing adhesive systems submitted to thermomechanical cycling, simulating one year of orthodontic treatment. Sixty-four bovine incisor teeth were randomly divided into 4 experimental groups (n = 16): XT: Transbond XT, QC: Quick Cure, OL: Ortholite Color, and SEP: Transbond Plus Self-Etching Primer. The samples were submitted to thermomechanical cycling simulating one year of orthodontic treatment. Shear bond strength tests were carried out using a universal testing machine with a load cell of 50 KgF at 0.5 mm/minute. The samples were examined with a stereomicroscope and a scanning electron microscope (SEM) in order to analyze enamel surface and Adhesive Remnant Index (ARI). Kruskal-Wallis and Mann-Whitney (with Bonferroni correction) tests showed a significant difference between the studied groups (p < 0.05). Groups XT, QC, and SEP presented the highest values of adhesive resistance and no statistical differences were found between them. The highest frequency of failures between enamel and adhesive was observed in groups XT, QC, and OL. Quick Cure (QC) remineralizing adhesive system presented average adhesive resistance values similar to conventional (XT) and self-etching (SEP) adhesives, while remineralizing system (OL) provided the lowest values of adhesive resistance. PMID:26380371

  10. Shear Bond Strength of Orthodontic Brackets Fixed with Remineralizing Adhesive Systems after Simulating One Year of Orthodontic Treatment

    PubMed Central

    Bezerra, Gisele Lima; Torres, Carlos Rocha Gomes; Tonetto, Mateus Rodrigues; Borges, Alvaro Henrique; Kuga, Milton Carlos; Bandeca, Matheus Coelho; Firoozmand, Leily Macedo

    2015-01-01

    The objective of this study is to assess, in vitro, the shear bond strength of orthodontic brackets fixed with remineralizing adhesive systems submitted to thermomechanical cycling, simulating one year of orthodontic treatment. Sixty-four bovine incisor teeth were randomly divided into 4 experimental groups (n = 16): XT: Transbond XT, QC: Quick Cure, OL: Ortholite Color, and SEP: Transbond Plus Self-Etching Primer. The samples were submitted to thermomechanical cycling simulating one year of orthodontic treatment. Shear bond strength tests were carried out using a universal testing machine with a load cell of 50 KgF at 0.5 mm/minute. The samples were examined with a stereomicroscope and a scanning electron microscope (SEM) in order to analyze enamel surface and Adhesive Remnant Index (ARI). Kruskal-Wallis and Mann-Whitney (with Bonferroni correction) tests showed a significant difference between the studied groups (p < 0.05). Groups XT, QC, and SEP presented the highest values of adhesive resistance and no statistical differences were found between them. The highest frequency of failures between enamel and adhesive was observed in groups XT, QC, and OL. Quick Cure (QC) remineralizing adhesive system presented average adhesive resistance values similar to conventional (XT) and self-etching (SEP) adhesives, while remineralizing system (OL) provided the lowest values of adhesive resistance. PMID:26380371

  11. The effect of cavity disinfectants on the micro-shear bond strength of dentin adhesives

    PubMed Central

    Elkassas, Dina Wafik; Fawzi, Elham Mostafa; El Zohairy, Ahmed

    2014-01-01

    Objectives: This study was carried out to examine the effect of application of four different disinfecting agents on the micro-shear bond strength (μ-SBS) of an etch-and-rinse and self-etch adhesive systems. Materials and Methods: One hundred flat dentin surfaces of human molars were produced by wet grinding the buccal surfaces. Specimens were randomly assigned to five groups according to the disinfectant used: Group I: Control (no disinfectant); Group II: 5.25% sodium hypochlorite based; Group III: 2% chlorhexidine based (Consepsis), Group IV: 0.1% benzalkoniumchloride based (Tubulicid red) and Group V: 3% doxycycline based (Biopure, MTAD). Specimens were bonded using either Adper Single Bond 2 or Clearfil S3 Bond, which were employed according to the manufacturer's instructions. Resin composite microcylinders were bonded using Tygon® tubes for μ-SBS testing. The modes of failure were noted after visual examination using a binocular stereomicroscope at ×25 magnification. Failures were classified as adhesive, or mixed. μ-SBS results were analyzed using two-way ANOVA followed by Tukey's post-hoc test. Results: Dentin disinfectants tested significantly negated the bonding of Adper Single bond 2 and the groups were ranked; Group I > Group V = Group IV > Group II = Group III, meanwhile they enhanced significantly the μ-SBS values upon using Clearfil S3 Bond and were ranked; Group II > Group III = Group IV = Group V > Group I. Most failures were adhesive with the Adper single bond adhesive system. Mixed modes of failure were evident with Clearfil S3 bond. Conclusions: The disinfectants tested should not be used with Adper Single Bond 2 when applied before the etching step, However they could be used safely prior to bonding with Clearfil S3 Bond. PMID:24966768

  12. Shear stress, reactive oxygen species, and arterial structure and function.

    PubMed

    Matlung, Hanke L; Bakker, Erik N T P; VanBavel, Ed

    2009-07-01

    Shear stress is well known to be a key factor in the regulation of small-artery tone and structure. Although nitric oxide is a major endothelium-derived factor involved in short- and long-term regulation of vascular caliber, it is clear that other mechanisms also can be involved. This review discusses the evidence for endothelium-derived reactive oxygen species (ROS) as mediators for shear-dependent arterial tone and remodeling. The work focuses on resistance vessels, because their caliber determines local perfusion. However, work on large vessels is included where needed. Attention is given to the shear-stress levels and profiles that exist in the arterial system and the differential effects of steady and oscillating shear on NO and ROS production. We furthermore address the relation between microvascular tone and remodeling and the effect of ROS and inflammation on the activity of remodeling enzymes such as matrix metalloproteinases and transglutaminases. We conclude that future work should address the role of H(2)O(2) as an endothelium-derived factor mediating tone and influencing structure of small arteries over the long term.

  13. Fluid shear, intercellular stress, and endothelial cell alignment

    PubMed Central

    Steward, Robert; Tambe, Dhananjay; Hardin, C. Corey; Krishnan, Ramaswamy

    2015-01-01

    Endothelial cell alignment along the direction of laminar fluid flow is widely understood to be a defining morphological feature of vascular homeostasis. While the role of associated signaling and structural events have been well studied, associated intercellular stresses under laminar fluid shear have remained ill-defined and the role of these stresses in the alignment process has remained obscure. To fill this gap, we report here the tractions as well as the complete in-plane intercellular stress fields measured within the human umbilical vein endothelial cell (HUVEC) monolayer subjected to a steady laminar fluid shear of 1 Pa. Tractions, intercellular stresses, as well as their time course, heterogeneity, and anisotropy, were measured using monolayer traction microscopy and monolayer stress microscopy. Prior to application of laminar fluid flow, intercellular stresses were largely tensile but fluctuated dramatically in space and in time (317 ± 122 Pa). Within 12 h of the onset of laminar fluid flow, the intercellular stresses decreased substantially but continued to fluctuate dramatically (142 ± 84 Pa). Moreover, tractions and intercellular stresses aligned strongly and promptly (within 1 h) along the direction of fluid flow, whereas the endothelial cell body aligned less strongly and substantially more slowly (12 h). Taken together, these results reveal that steady laminar fluid flow induces prompt reduction in magnitude and alignment of tractions and intercellular stress tensor components followed by the retarded elongation and alignment of the endothelial cell body. Appreciably smaller intercellular stresses supported by cell-cell junctions logically favor smaller incidence of gap formation and thus improved barrier integrity. PMID:25652451

  14. Evaluation of the time dependent surface shear stress in turbulent flows

    NASA Technical Reports Server (NTRS)

    Sandborn, V. A.

    1979-01-01

    The time dependent surface shear stress has been evaluated using surface heat transfer measurements. For fully developed turbulent pipe and open channel water flows, and incompressible and compressible turbulent boundary layer air flows the measurements indicate the absolute magnitude of the surface shear stress fluctuations will be greater than two times the mean values. The root-mean-square shear stress fluctuations were of the order of 0.2 to 0.4 times the mean surface shear values. Due to these large surface shear stress fluctuations and the nonlinear relation between heat transfer and shear stress, a special technique has been developed to evaluate the measurements. It was found that the non-linear averaging errors for a hot film-surface shear stress gauge in a fully developed pipe flow was of the order of 10 percent at low velocities. A hot wire-surface shear stress gauge was employed for measurements of turbulent boundary layers in air.

  15. Non-motile primary cilia as fluid shear stress mechanosensors.

    PubMed

    Nauli, Surya M; Jin, Xingjian; AbouAlaiwi, Wissam A; El-Jouni, Wassim; Su, Xuefeng; Zhou, Jing

    2013-01-01

    Primary cilia are sensory organelles that transmit extracellular signals into intracellular biochemical responses. Structural and functional defects in primary cilia are associated with a group of human diseases, known as ciliopathies, with phenotypes ranging from cystic kidney and obesity to blindness and mental retardation. Primary cilia mediate mechano- and chemosensation in many cell types. The mechanosensory function of the primary cilia requires the atypical G-protein-coupled receptor polycystin-1 and the calcium-permeable nonselective cation channel polycystin-2. Mechanical stimulations such as fluid-shear stress of the primary cilia initiate intracellular calcium rise, nitric oxide release, and protein modifications. In this review, we describe a set of protocols for cell culture to promote ciliation, mechanical stimulations of the primary cilia, and measurements of calcium rise and nitric oxide release induced by fluid shear stress. PMID:23522462

  16. Mathematical Modeling of Intravascular Blood Coagulation under Wall Shear Stress.

    PubMed

    Rukhlenko, Oleksii S; Dudchenko, Olga A; Zlobina, Ksenia E; Guria, Georgy Th

    2015-01-01

    Increased shear stress such as observed at local stenosis may cause drastic changes in the permeability of the vessel wall to procoagulants and thus initiate intravascular blood coagulation. In this paper we suggest a mathematical model to investigate how shear stress-induced permeability influences the thrombogenic potential of atherosclerotic plaques. Numerical analysis of the model reveals the existence of two hydrodynamic thresholds for activation of blood coagulation in the system and unveils typical scenarios of thrombus formation. The dependence of blood coagulation development on the intensity of blood flow, as well as on geometrical parameters of atherosclerotic plaque is described. Relevant parametric diagrams are drawn. The results suggest a previously unrecognized role of relatively small plaques (resulting in less than 50% of the lumen area reduction) in atherothrombosis and have important implications for the existing stenting guidelines.

  17. Structure-Enhanced Yield Shear Stress in Electrorheological Fluids

    NASA Astrophysics Data System (ADS)

    Tao, R.; Lan, Y. C.; Xu, X.

    A new technology, compression-assisted aggregation, is developed to enhance the strength of electrorheological (ER) fluids. The yield shear stress of ER fluids depends on the fluid microstructure. The unassisted electric-field induced ER structure mainly consists of single chains, whose weak points are at their ends. This new technology produces a structure consisting of robust thick columns with strong ends. As the weak points of the original ER structure are greatly enforced, the new structure makes ER fluids super-strong: At a moderate electric field and moderate pressure the yield shear stress of ER fluids at 35% volume fraction exceeds 100 kPa, well above any requirement for major industrial applications.

  18. [Exercise-induced shear stress: Physiological basis and clinical impact].

    PubMed

    Rodríguez-Núñez, Iván; Romero, Fernando; Saavedra, María Javiera

    2016-01-01

    The physiological regulation of vascular function is essential for cardiovascular health and depends on adequate control of molecular mechanisms triggered by endothelial cells in response to mechanical and chemical stimuli induced by blood flow. Endothelial dysfunction is one of the major risk factors for cardiovascular disease, where an imbalance between synthesis of vasodilator and vasoconstrictor molecules is one of its main mechanisms. In this context, the shear stress is one of the most important mechanical stimuli to improve vascular function, due to endothelial mechanotransduction, triggered by stimulation of various endothelial mechanosensors, induce signaling pathways culminating in increased bioavailability of vasodilators molecules such as nitric oxide, that finally trigger the angiogenic mechanisms. These mechanisms allow providing the physiological basis for the effects of exercise on vascular health. In this review it is discussed the molecular mechanisms involved in the vascular response induced by shear stress and its impact in reversing vascular injury associated with the most prevalent cardiovascular disease in our population. PMID:27118039

  19. Inverse method for estimating shear stress in machining

    NASA Astrophysics Data System (ADS)

    Burns, T. J.; Mates, S. P.; Rhorer, R. L.; Whitenton, E. P.; Basak, D.

    2016-01-01

    An inverse method is presented for estimating shear stress in the work material in the region of chip-tool contact along the rake face of the tool during orthogonal machining. The method is motivated by a model of heat generation in the chip, which is based on a two-zone contact model for friction along the rake face, and an estimate of the steady-state flow of heat into the cutting tool. Given an experimentally determined discrete set of steady-state temperature measurements along the rake face of the tool, it is shown how to estimate the corresponding shear stress distribution on the rake face, even when no friction model is specified.

  20. Wall shear stress measurements using a new transducer

    NASA Technical Reports Server (NTRS)

    Vakili, A. D.; Wu, J. M.; Lawing, P. L.

    1986-01-01

    A new instrument has been developed for direct measurement of wall shear stress. This instrument is simple and symmetric in design with small moving mass and no internal friction. Features employed in the design of this instrument eliminate most of the difficulties associated with the traditional floating element balances. Vibration problems associated with the floating element skin friction balances have been found to be minimized by the design features and optional damping provided. The unique design of this instrument eliminates or reduces the errors associated with conventional floating-element devices: such as errors due to gaps, pressure gradient, acceleration, heat transfer and temperature change. The instrument is equipped with various sensing systems and the output signal is a linear function of the wall shear stress. Measurement made in three different tunnels show good agreement with theory and data obtained by the floating element devices.

  1. Mathematical Modeling of Intravascular Blood Coagulation under Wall Shear Stress

    PubMed Central

    Rukhlenko, Oleksii S.; Dudchenko, Olga A.; Zlobina, Ksenia E.; Guria, Georgy Th.

    2015-01-01

    Increased shear stress such as observed at local stenosis may cause drastic changes in the permeability of the vessel wall to procoagulants and thus initiate intravascular blood coagulation. In this paper we suggest a mathematical model to investigate how shear stress-induced permeability influences the thrombogenic potential of atherosclerotic plaques. Numerical analysis of the model reveals the existence of two hydrodynamic thresholds for activation of blood coagulation in the system and unveils typical scenarios of thrombus formation. The dependence of blood coagulation development on the intensity of blood flow, as well as on geometrical parameters of atherosclerotic plaque is described. Relevant parametric diagrams are drawn. The results suggest a previously unrecognized role of relatively small plaques (resulting in less than 50% of the lumen area reduction) in atherothrombosis and have important implications for the existing stenting guidelines. PMID:26222505

  2. [Exercise-induced shear stress: Physiological basis and clinical impact].

    PubMed

    Rodríguez-Núñez, Iván; Romero, Fernando; Saavedra, María Javiera

    2016-01-01

    The physiological regulation of vascular function is essential for cardiovascular health and depends on adequate control of molecular mechanisms triggered by endothelial cells in response to mechanical and chemical stimuli induced by blood flow. Endothelial dysfunction is one of the major risk factors for cardiovascular disease, where an imbalance between synthesis of vasodilator and vasoconstrictor molecules is one of its main mechanisms. In this context, the shear stress is one of the most important mechanical stimuli to improve vascular function, due to endothelial mechanotransduction, triggered by stimulation of various endothelial mechanosensors, induce signaling pathways culminating in increased bioavailability of vasodilators molecules such as nitric oxide, that finally trigger the angiogenic mechanisms. These mechanisms allow providing the physiological basis for the effects of exercise on vascular health. In this review it is discussed the molecular mechanisms involved in the vascular response induced by shear stress and its impact in reversing vascular injury associated with the most prevalent cardiovascular disease in our population.

  3. Calculation of turbulent shear stress in supersonic boundary layer flows

    NASA Technical Reports Server (NTRS)

    Sun, C. C.; Childs, M. E.

    1974-01-01

    An analysis of turbulent boundary layer flow characteristics and the computational procedure used are discussed. The integrated mass and momentum flux profiles and differentials of the integral quantities are used in the computations so that local evaluation of the streamwise velocity gradient is not necessary. The computed results are compared with measured shear stress data obtained by using hot wire anemometer and laser velocimeter techniques. The flow measurements were made upstream and downstream of an adiabatic unseparated interaction of an oblique shock wave with the turbulent boundary layer on the flat wall of a two dimensional wind tunnel. A comparison of the numerical analysis and actual measurements is made and the effects of small differences in mean flow profiles on the computed shear stress distributions are discussed.

  4. Non-volcanic tremor driven by large transient shear stresses.

    PubMed

    Rubinstein, Justin L; Vidale, John E; Gomberg, Joan; Bodin, Paul; Creager, Kenneth C; Malone, Stephen D

    2007-08-01

    Non-impulsive seismic radiation or 'tremor' has long been observed at volcanoes and more recently around subduction zones. Although the number of observations of non-volcanic tremor is steadily increasing, the causative mechanism remains unclear. Some have attributed non-volcanic tremor to the movement of fluids, while its coincidence with geodetically observed slow-slip events at regular intervals has led others to consider slip on the plate interface as its cause. Low-frequency earthquakes in Japan, which are believed to make up at least part of non-volcanic tremor, have focal mechanisms and locations that are consistent with tremor being generated by shear slip on the subduction interface. In Cascadia, however, tremor locations appear to be more distributed in depth than in Japan, making them harder to reconcile with a plate interface shear-slip model. Here we identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude M(w) = 7.8, 2002 Denali, Alaska, earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate), implying that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the effective stress on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases on the subduction interface-effectively a frictional failure response to the driving stress.

  5. Non-volcanic tremor driven by large transient shear stresses

    USGS Publications Warehouse

    Rubinstein, J.L.; Vidale, J.E.; Gomberg, J.; Bodin, P.; Creager, K.C.; Malone, S.D.

    2007-01-01

    Non-impulsive seismic radiation or 'tremor' has long been observed at volcanoes and more recently around subduction zones. Although the number of observations of non-volcanic tremor is steadily increasing, the causative mechanism remains unclear. Some have attributed non-volcanic tremor to the movement of fluids, while its coincidence with geodetically observed slow-slip events at regular intervals has led others to consider slip on the plate interface as its cause. Low-frequency earthquakes in Japan, which are believed to make up at least part of non-volcanic tremor, have focal mechanisms and locations that are consistent with tremor being generated by shear slip on the subduction interface. In Cascadia, however, tremor locations appear to be more distributed in depth than in Japan, making them harder to reconcile with a plate interface shear-slip model. Here we identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude Mw = 7.8, 2002 Denali, Alaska, earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate), implying that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the effective stress on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases on the subduction interface - effectively a frictional failure response to the driving stress. ??2007 Nature Publishing Group.

  6. FOXC2 and fluid shear stress stabilize postnatal lymphatic vasculature.

    PubMed

    Sabine, Amélie; Bovay, Esther; Demir, Cansaran Saygili; Kimura, Wataru; Jaquet, Muriel; Agalarov, Yan; Zangger, Nadine; Scallan, Joshua P; Graber, Werner; Gulpinar, Elgin; Kwak, Brenda R; Mäkinen, Taija; Martinez-Corral, Inés; Ortega, Sagrario; Delorenzi, Mauro; Kiefer, Friedemann; Davis, Michael J; Djonov, Valentin; Miura, Naoyuki; Petrova, Tatiana V

    2015-10-01

    Biomechanical forces, such as fluid shear stress, govern multiple aspects of endothelial cell biology. In blood vessels, disturbed flow is associated with vascular diseases, such as atherosclerosis, and promotes endothelial cell proliferation and apoptosis. Here, we identified an important role for disturbed flow in lymphatic vessels, in which it cooperates with the transcription factor FOXC2 to ensure lifelong stability of the lymphatic vasculature. In cultured lymphatic endothelial cells, FOXC2 inactivation conferred abnormal shear stress sensing, promoting junction disassembly and entry into the cell cycle. Loss of FOXC2-dependent quiescence was mediated by the Hippo pathway transcriptional coactivator TAZ and, ultimately, led to cell death. In murine models, inducible deletion of Foxc2 within the lymphatic vasculature led to cell-cell junction defects, regression of valves, and focal vascular lumen collapse, which triggered generalized lymphatic vascular dysfunction and lethality. Together, our work describes a fundamental mechanism by which FOXC2 and oscillatory shear stress maintain lymphatic endothelial cell quiescence through intercellular junction and cytoskeleton stabilization and provides an essential link between biomechanical forces and endothelial cell identity that is necessary for postnatal vessel homeostasis. As FOXC2 is mutated in lymphedema-distichiasis syndrome, our data also underscore the role of impaired mechanotransduction in the pathology of this hereditary human disease.

  7. Pulse shear stress for anaerobic membrane bioreactor fouling control.

    PubMed

    Yang, Jixiang; Spanjers, Henri; van Lier, Jules B

    2011-01-01

    Increase of shear stress at membrane surfaces is a generally applied strategy to minimize membrane fouling. It has been reported that a two-phase flow, better known as slug flow, is an effective way to increase shear stress. Hence, slug flow was introduced into an anaerobic membrane bioreactor for membrane fouling control. Anaerobic suspended sludge was cultured in an anaerobic membrane bioreactor (AMBR) operated with a side stream inside-out tubular membrane unit applying sustainable flux flow regimes. The averaged particle diameter decreased from 20 to 5 microm during operation of the AMBR. However, the COD removal efficiency did not show any significant deterioration, whereas the specific methanogenic activity (SMA) increased from 0.16 to 0.41 gCOD/g VSS/day. Nevertheless, the imposed gas slug appeared to be insufficient for adequate fouling control, resulting in rapidly increasing trans membrane pressures (TMP) operating at a flux exceeding 16 L/m2/h. Addition of powdered activated carbon (PAC) enhanced the effect of slug flow on membrane fouling. However, the combined effect was still considered as not being significant. The tubular membrane was subsequently equipped with inert inserts for creating a locally increased shear stress for enhanced fouling control. Results show an increase in the membrane flux from 16 L/m2/h to 34 L/m2/h after the inserts were mounted in the membrane tube. PMID:22097007

  8. FOXC2 and fluid shear stress stabilize postnatal lymphatic vasculature

    PubMed Central

    Sabine, Amélie; Bovay, Esther; Demir, Cansaran Saygili; Kimura, Wataru; Jaquet, Muriel; Agalarov, Yan; Zangger, Nadine; Scallan, Joshua P.; Graber, Werner; Gulpinar, Elgin; Kwak, Brenda R.; Mäkinen, Taija; Martinez-Corral, Inés; Ortega, Sagrario; Delorenzi, Mauro; Kiefer, Friedemann; Davis, Michael J.; Djonov, Valentin; Miura, Naoyuki; Petrova, Tatiana V.

    2015-01-01

    Biomechanical forces, such as fluid shear stress, govern multiple aspects of endothelial cell biology. In blood vessels, disturbed flow is associated with vascular diseases, such as atherosclerosis, and promotes endothelial cell proliferation and apoptosis. Here, we identified an important role for disturbed flow in lymphatic vessels, in which it cooperates with the transcription factor FOXC2 to ensure lifelong stability of the lymphatic vasculature. In cultured lymphatic endothelial cells, FOXC2 inactivation conferred abnormal shear stress sensing, promoting junction disassembly and entry into the cell cycle. Loss of FOXC2-dependent quiescence was mediated by the Hippo pathway transcriptional coactivator TAZ and, ultimately, led to cell death. In murine models, inducible deletion of Foxc2 within the lymphatic vasculature led to cell-cell junction defects, regression of valves, and focal vascular lumen collapse, which triggered generalized lymphatic vascular dysfunction and lethality. Together, our work describes a fundamental mechanism by which FOXC2 and oscillatory shear stress maintain lymphatic endothelial cell quiescence through intercellular junction and cytoskeleton stabilization and provides an essential link between biomechanical forces and endothelial cell identity that is necessary for postnatal vessel homeostasis. As FOXC2 is mutated in lymphedema-distichiasis syndrome, our data also underscore the role of impaired mechanotransduction in the pathology of this hereditary human disease. PMID:26389677

  9. Rheological investigations of ferrofluids with a shear stress controlled rheometer.

    PubMed

    Shahnazian, Hamid; Odenbach, Stefan

    2008-05-21

    The appearance of field- and shear-dependent changes of viscosity-the magnetoviscous effect-is correlated to the formation of chains and structures of magnetic nanoparticles. Moreover, the formation of these structures leads to the appearance of viscoelastic effects or other non-Newtonian features in ferrofluids in the presence of a magnetic field. In order to describe these phenomena, different theoretical approaches have been developed which explain the mechanism of these effects with different assumptions. One point in which these models differ, and which has to be clarified, is the appearance of yield stress and its dependence on magnetic field strength. With this aim, a stress controlled rheometer has been designed to prove the existence of this very small field-dependent yield stress for ferrofluids. The results presented here show a dependence of the yield stress on the magnetic field strength as well as on the interparticle interaction and particle size distribution. Finally, yield stress experiments have been performed for different geometries of the shear cell in order to get more information about the microstructure formed by the magnetic particles. PMID:21694266

  10. Role of PECAM-1 in the shear-stress-induced activation of Akt and the endothelial nitric oxide synthase (eNOS) in endothelial cells.

    PubMed

    Fleming, Ingrid; Fisslthaler, Beate; Dixit, Madhulika; Busse, Rudi

    2005-09-15

    The application of fluid shear stress to endothelial cells elicits the formation of nitric oxide (NO) and phosphorylation of the endothelial NO synthase (eNOS). Shear stress also elicits the enhanced tyrosine phosphorylation of endothelial proteins, especially of those situated in the vicinity of cell-cell contacts. Since a major constituent of these endothelial cell-cell contacts is the platelet endothelial cell adhesion molecule-1 (PECAM-1) we assessed the role of PECAM-1 in the activation of eNOS. In human endothelial cells, shear stress induced the tyrosine phosphorylation of PECAM-1 and enhanced the association of PECAM-1 with eNOS. Endothelial cell stimulation with shear stress elicited the phosphorylation of Akt and eNOS as well as of the AMP-activated protein kinase (AMPK). While the shear-stress-induced tyrosine phosphorylation of PECAM-1 as well as the serine phosphorylation of Akt and eNOS were abolished by the pre-treatment of cells with the tyrosine kinase inhibitor PP1 the phosphorylation of AMPK was unaffected. Down-regulation of PECAM-1 using a siRNA approach attenuated the shear-stress-induced phosphorylation of Akt and eNOS, as well as the shear-stress-induced accumulation of cyclic GMP levels while the shear-stress-induced phosphorylation of AMPK remained intact. A comparable attenuation of Akt and eNOS (but not AMPK) phosphorylation and NO production was also observed in endothelial cells generated from PECAM-1-deficient mice. These data indicate that the shear-stress-induced activation of Akt and eNOS in endothelial cells is modulated by the tyrosine phosphorylation of PECAM-1 whereas the shear-stress-induced phosphorylation of AMPK is controlled by an alternative signaling pathway. PMID:16118242

  11. Mechanical properties of jammed packings of frictionless spheres under an applied shear stress

    NASA Astrophysics Data System (ADS)

    Liu, Hao; Tong, Hua; Xu, Ning

    2014-11-01

    By minimizing a thermodynamic-like potential, we unbiasedly sample the potential energy landscape of soft and frictionless spheres under a constant shear stress. We obtain zero-temperature jammed states under desired shear stresses and investigate their mechanical properties as a function of the shear stress. As a comparison, we also obtain the jammed states from the quasistatic-shear sampling in which the shear stress is not well-controlled. Although the yield stresses determined by both samplings show the same power-law scaling with the compression from the jamming transition point J at zero temperature and shear stress, for finite size systems the quasistatic-shear sampling leads to a lower yield stress and a higher critical volume fraction at point J. The shear modulus of the jammed solids decreases with increasing shear stress. However, the shear modulus does not decay to zero at yielding. This discontinuous change of the shear modulus implies the discontinuous nature of the unjamming transition under nonzero shear stress, which is further verified by the observation of a discontinuous jump in the pressure from the jammed solids to the shear flows. The pressure jump decreases upon decompression and approaches zero at the critical-like point J, in analogy with the well-known phase transitions under an external field. The analysis of the force networks in the jammed solids reveals that the force distribution is more sensitive to the increase of the shear stress near point J. The force network anisotropy increases with increasing shear stress. The weak particle contacts near the average force and under large shear stresses it exhibit an asymmetric angle distribution.

  12. Molecular Origins of Higher Harmonics in Large-Amplitude Oscillatory Shear Flow: Shear Stress Response

    NASA Astrophysics Data System (ADS)

    Gilbert, Peter; Giacomin, A. Jeffrey; Schmalzer, Andrew; Bird, R. B.

    Recent work has focused on understanding the molecular origins of higher harmonics that arise in the shear stress response of polymeric liquids in large-amplitude oscillatory shear flow. These higher harmonics have been explained using only the orientation distribution of a dilute suspension of rigid dumbbells in a Newtonian fluid, which neglects molecular interactions and is the simplest relevant molecular model of polymer viscoelasticity [R.B. Bird et al., J Chem Phys, 140, 074904 (2014)]. We explore these molecular interactions by examining the Curtiss-Bird model, a kinetic molecular theory that accounts for restricted polymer motions arising when chains are concentrated [Fan and Bird, JNNFM, 15, 341 (1984)]. For concentrated systems, the chain motion transverse to the chain axis is more restricted than along the axis. This anisotropy is described by the link tension coefficient, ɛ, for which several special cases arise: ɛ =0 corresponds to reptation, ɛ > 1 1 8 8 to rod-climbing, 1 1 2 2 >= ɛ >= 3 3 4 4 to reasonable shear-thinning predictions in steady simple shear flow, and ɛ =1 to a dilute solution of chains. We examine the shapes of the shear stress versus shear rate loops for the special cases, ɛ = 0 , 1 0 , 1 8 , 3 3 8 8 8 , 3 3 8 8 , 1 , of the Curtiss-Bird model, and we compare these with those

  13. Bone morphogenic protein 4 produced in endothelial cells by oscillatory shear stress stimulates an inflammatory response

    NASA Technical Reports Server (NTRS)

    Sorescu, George P.; Sykes, Michelle; Weiss, Daiana; Platt, Manu O.; Saha, Aniket; Hwang, Jinah; Boyd, Nolan; Boo, Yong C.; Vega, J. David; Taylor, W. Robert; Jo, Hanjoong

    2003-01-01

    Atherosclerosis is now viewed as an inflammatory disease occurring preferentially in arterial regions exposed to disturbed flow conditions, including oscillatory shear stress (OS), in branched arteries. In contrast, the arterial regions exposed to laminar shear (LS) are relatively lesion-free. The mechanisms underlying the opposite effects of OS and LS on the inflammatory and atherogenic processes are not clearly understood. Here, through DNA microarrays, protein expression, and functional studies, we identify bone morphogenic protein 4 (BMP4) as a mechanosensitive and pro-inflammatory gene product. Exposing endothelial cells to OS increased BMP4 protein expression, whereas LS decreased it. In addition, we found BMP4 expression only in the selective patches of endothelial cells overlying foam cell lesions in human coronary arteries. The same endothelial patches also expressed higher levels of intercellular cell adhesion molecule-1 (ICAM-1) protein compared with those of non-diseased areas. Functionally, we show that OS and BMP4 induced ICAM-1 expression and monocyte adhesion by a NFkappaB-dependent mechanism. We suggest that BMP4 is a mechanosensitive, inflammatory factor playing a critical role in early steps of atherogenesis in the lesion-prone areas.

  14. Imaging shear stress distribution and evaluating the stress concentration factor of the human eye

    NASA Astrophysics Data System (ADS)

    Joseph Antony, S.

    2015-03-01

    Healthy eyes are vital for a better quality of human life. Historically, for man-made materials, scientists and engineers use stress concentration factors to characterise the effects of structural non-homogeneities on their mechanical strength. However, such information is scarce for the human eye. Here we present the shear stress distribution profiles of a healthy human cornea surface in vivo using photo-stress analysis tomography, which is a non-intrusive and non-X-ray based method. The corneal birefringent retardation measured here is comparable to that of previous studies. Using this, we derive eye stress concentration factors and the directional alignment of major principal stress on the surface of the cornea. Similar to thermometers being used for monitoring the general health in humans, this report provides a foundation to characterise the shear stress carrying capacity of the cornea, and a potential bench mark for validating theoretical modelling of stresses in the human eye in future.

  15. ESTIMATION OF EFFECTIVE SHEAR STRESS WORKING ON FLAT SHEET MEMBRANE USING FLUIDIZED MEDIA IN MBRs

    NASA Astrophysics Data System (ADS)

    Zaw, Hlwan Moe; Li, Tairi; Nagaoka, Hiroshi; Mishima, Iori

    This study was aimed at estimating effective shear stress working on flat sheet membrane by the addition of fluidized media in MBRs. In both of laboratory-scale aeration tanks with and without fluidized media, shear stress variations on membrane surface and water phase velocity variations were measured and MBR operation was conducted. For the evaluation of the effective shear stress working on membrane surface to mitigate membrane surface, simulation of trans-membrane pressure increase was conducted. It was shown that the time-averaged absolute value of shear stress was smaller in the reactor with fluidized media than without fluidized media. However, due to strong turbulence in the reactor with fluidized media caused by interaction between water-phase and media and also due to the direct interaction between membrane surface and fluidized media, standard deviation of shear stress on membrane surface was larger in the reactor with fluidized media than without media. Histograms of shear stress variation data were fitted well to normal distribution curves and mean plus three times of standard deviation was defined to be a maximum shear stress value. By applying the defined maximum shear stress to a membrane fouling model, trans-membrane pressure curve in the MBR experiment was simulated well by the fouling model indicting that the maximum shear stress, not time-averaged shear stress, can be regarded as an effective shear stress to prevent membrane fouling in submerged flat-sheet MBRs.

  16. Investigation of shear force of a single adhesion cell using a self-sensitive cantilever and fluorescence microscopy

    NASA Astrophysics Data System (ADS)

    Hashimoto, Shigetaka; Adachi, Makoto; Iwata, Futoshi

    2015-08-01

    In this paper, we describe a measurement system based on an atomic force microscope (AFM) for the measurement of the shear force and detachment energy of a single adhesion cell on a substrate. The shear force was quantitatively measured from the deflection of a self-sensitive cantilever that was employed for the simple configuration of the AFM manipulator. The shear force behavior of a single cell detaching from the substrate was observed. By staining cells with a fluorescence dye, the deformation shape of the cell being pushed with the cantilever could be clearly observed. The shear force and detachment energy of the cell increased with the size of the cell. The difference in the shear force of single cells on different substrates with different surface energies was quantitatively evaluated. The loading force applied to a single cell increased with the feed speed of the cantilever. The viability of cells after measurement under different feed speeds of the cantilever was also evaluated.

  17. Wall shear stress indicators in abnormal aortic geometries

    NASA Astrophysics Data System (ADS)

    Prahl Wittberg, Lisa; van Wyk, Stevin; Fuchs, Laszlo; Gutmark, Ephraim; Gutmark-Little, Iris

    2015-11-01

    Cardiovascular disease, such as atherosclerosis, occurs at specific locations in the arterial tree. Characterizing flow and forces at these locations is crucial to understanding the genesis of disease. Measures such as time average wall shear stress, oscillatory shear index, relative residence time and temporal wall shear stress gradients have been shown to identify plaque prone regions. The present paper examines these indices in three aortic geometries obtained from patients whose aortas are deformed due to a genetic pathology and compared to one normal geometry. This patient group is known to be prone to aortic dissection and our study aims to identify early indicators that will enable timely intervention. Data obtained from cardiac magnetic resonance imaging is used to reconstruct the aortic arch. The local unsteady flow characteristics are calculated, fully resolving the flow field throughout the entire cardiac cycle. The Quemada model is applied to account for the non-Newtonian properties of blood, an empirical model valid for different red blood cell loading. The impact of the deformed aortic geometries is analyzed to identify flow patterns that could lead to arterial disease at certain locations.

  18. Serial analysis of the vascular endothelial transcriptome under static and shear stress conditions.

    PubMed

    Chu, Tian Jiao; Peters, David G

    2008-07-15

    We have utilized serial analysis of gene expression (SAGE) to analyze the response of human coronary artery endothelial cells (HCAECs) to laminar shear stress (LSS). Primary cultures of HCAECs were exposed to 15 dyn/cm(2) LSS for 24 h in a parallel plate flow chamber and compared with identical same passage cells cultured under static conditions. The expression levels of a number of functional categories of genes were reduced by shear stress including those encoding proteins involved in cell proliferation (CDC10, CDC20, CDC23, CCND1, CCNB1), angiogenesis (ANGPTL4, CTGF, CYR61, ENG, EPAS1, EGFR, LGALS3, PGK1, and SPARC), extracellular matrix and cell-matrix adhesion (EFEMP1, LOXL2, P4HB, FBN1, FN1, ITGA5, ITGAE, ITGAV, ILK, LAMR1) and ATP synthesis (ATP5G3, ATP5J2, ATP5L, ATP5D). We also observed an increase in the LSS-responsive expression of genes encoding stress response proteins, including HMOX1, which is significant since HMOX1 may have anti-inflammatory and vasodilatory vascular effects. The autosomal dominant polycystic kidney disease (ADPKD) genes PKD1 and PKD2 were also elevated by LSS. ADPKD is associated with vascular malfunction, including the impairment of vasoreactive processes. To our knowledge, this is the first SAGE-based analysis of the shear stress-responsive endothelial cell transcriptome. These immortal data provide a resource for further analyses of the molecular mechanisms underlying the biological response to LSS and contribute to the expanding collection of publicly available SAGE data. PMID:18505769

  19. Spatiotemporal evolution of a fault shear stress patch due to viscoelastic interseismic fault zone rheology

    NASA Astrophysics Data System (ADS)

    Sone, Hiroki; Uchide, Takahiko

    2016-08-01

    We conducted numerical studies to explore how shear stress anomalies on fault planes (shear stress patches) evolve spatiotemporally during the interseismic period under the influence of viscoelastic rheology assigned to fault zones of finite thickness. 2-D viscoelastic models consisting of a fault zone and host rock were sheared to simulate shear stress accumulation along fault zones due to tectonic loading. No fault slip along a distinct fault planes is implied in the model, thus all fault shear motion is accommodated by distributed deformation in the viscoelastic fault zone. Results show that magnitudes of shear stress patches evolve not only temporally, but also spatially, especially when the stress anomaly is created by a geometrical irregularity (asperity) along the interface of an elastic host rock and viscoelastic fault zone. Such shear stress anomalies diffuse spatially so that the spatial dimension of the shear stress patch appears to grow over time. Models with varying fault zone viscoelastic properties and varying fault zone viscosity both show that such spatial diffusion of shear stress is enhanced by increasing the contribution of the viscous behavior. The absolute rate at which shear stress patches grow spatially is generally not influenced by the size of the shear stress patch. Therefore shear stress patches with smaller dimensions will appear to grow quicker, in the relative sense, compared to larger stress patches. These results suggest that the minimum dimensions of shear stress patches that can exist along a fault could be governed by the effective viscosity of the fault zone. Therefore patterns of accumulated shear stress could vary along faults when viscous properties are heterogeneous, for instance due to depth or material heterogeneity, which has implications on how earthquake rupture behavior could vary along faults.

  20. Adhesion mechanism of a gecko-inspired oblique structure with an adhesive tip for asymmetric detachment

    NASA Astrophysics Data System (ADS)

    Sekiguchi, Yu; Takahashi, Kunio; Sato, Chiaki

    2015-12-01

    An adhesion model of an oblique structure with an adhesive tip is proposed by considering a limiting stress for adhesion to describe the detachment mechanism of gecko foot hairs. When a force is applied to the root of the oblique structure, normal and shear stresses are generated at contact and the adhesive tip is detached from the surface when reaching the limiting stress. An adhesion criterion that considers both the normal and shear stresses is introduced, and the asymmetric detachment of the oblique structure is theoretically investigated. In addition, oblique beam array structures are manufactured, and an inclination effect of the structure on the asymmetric detachment is experimentally verified.

  1. Application and improvement of Raupach's shear stress partitioning model

    NASA Astrophysics Data System (ADS)

    Walter, B. A.; Lehning, M.; Gromke, C.

    2012-12-01

    Aeolian processes such as the entrainment, transport and redeposition of sand, soil or snow are able to significantly reshape the earth's surface. In times of increasing desertification and land degradation, often driven by wind erosion, investigations of aeolian processes become more and more important in environmental sciences. The reliable prediction of the sheltering effect of vegetation canopies against sediment erosion, for instance, is a clear practical application of such investigations to identify suitable and sustainable counteractive measures against wind erosion. This study presents an application and improvement of a theoretical model presented by Raupach (Boundary-Layer Meteorology, 1992, Vol.60, 375-395 and Journal of Geophysical Research, 1993, Vol.98, 3023-3029) which allows for quantifying the sheltering effect of vegetation against sediment erosion. The model predicts the shear stress ratios τS'/τ and τS''/τ. Here, τS is the part of the total shear stress τ that acts on the ground beneath the plants. The spatial peak τS'' of the surface shear stress is responsible for the onset of particle entrainment whereas the spatial mean τS' can be used to quantify particle mass fluxes. The precise and accurate prediction of these quantities is essential when modeling wind erosion. Measurements of the surface shear stress distributions τS(x,y) on the ground beneath live vegetation canopies (plant species: lolium perenne) were performed in a controlled wind tunnel environment to determine the model parameters and to evaluate the model performance. Rigid, non-porous wooden blocks instead of the plants were additionally tested for the purpose of comparison, since previous wind tunnel studies used exclusively artificial plant imitations for their experiments on shear stress partitioning. The model constant c, which is needed to determine the total stress τ for a canopy of interest and which remained rather unspecified to date, was found to be c ≈ 0

  2. Liposome clusters with shear stress-induced membrane permeability.

    PubMed

    Yoshimoto, Makoto; Tamura, Ryota; Natsume, Tomotaka

    2013-09-01

    Clusters of negatively charged liposomes were prepared by the addition of Ca(2+) and characterized in their structure and membrane permeability under shear stress. The liposomes mainly used were composed of zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 20 mol% negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) and 30 mol% cholesterol. The liposomes with mean diameter of 193 nm were aggregated into the clusters with a distribution peak at about 1.5 μm in the 50mM Tris buffer solution of pH 8.5 at the lipid and Ca(2+) concentrations of 1.0mM and 40 mM, respectively. More than 90% of liposomes were redispersed at the Ca(2+) concentration of 80 mM. POPG-rich liposomes (POPC/POPG/cholesterol=5:65:30 [lipid]=1.0mM) were irreversibly aggregated at [Ca(2+)]≥ 10 mM, indicating the significant contribution of POPC to the reversible clustering of liposomes. The membranes of liposome clusters were impermeable to 5(6)-carboxyfluorescein (CF) in the static liquid system at 25°C due to the decrease in specific surface area of the liposomal system. In the shear flow, in clear contrast, continuous membrane permeation of CF was observed at the shear rate of 1.5 × 10(3)s(-1), exhibiting comparable membrane permeability to the non-clustered liposomes. The theoretical analysis of modified DLVO potential indicated that liposome membranes were not in contact with each other within the clusters. Therefore, the liposome clusters are structurally flexible under the applied shear stress, providing sufficient lipid membrane-water interfacial area for the permeation of CF. The results obtained would be important to control the formation of liposome clusters and their permeabilization for biochemical and biomedical applications.

  3. Effects of long-term repeated topical fluoride applications and adhesion promoter on shear bond strengths of orthodontic brackets

    PubMed Central

    Endo, Toshiya; Ishida, Rieko; Komatsuzaki, Akira; Sanpei, Shinya; Tanaka, Satoshi; Sekimoto, Tsuneo

    2014-01-01

    Objective: The purpose of this study was to assess the effects of long-term repeated topical application of fluoride before bonding and an adhesion promoter on the bond strength of orthodontic brackets. Materials and Methods: A total of 76 bovine incisors were collected and divided equally into four groups. In group 1, the brackets were bonded without topical fluoride application or adhesion promoter. In group 2, before bonding, the adhesion promoter was applied to nonfluoridated enamel. In group 3, the brackets were bonded without the application of the adhesion promoter to enamel, which had undergone long-term repeated topical fluoride treatments. Teeth in group 4 received the long-term repeated topical applications of fluoride, and the brackets were bonded using the adhesion promoter. All the brackets were bonded using BeautyOrtho Bond self-etching adhesive. The shear bond strength was measured and the bond failure modes were evaluated with the use of the adhesive remnant index (ARI) after debonding. Results: The mean shear bond strength was significantly lower in group 3 than in groups 1, 2, and 4, and there were no significant differences between the groups except for group 3. There were significant differences in the distribution of ARI scores between groups 2 and 3, and between groups 3 and 4. Conclusions: The adhesion promoter can recover the bond strength reduced by the long-term repeated topical applications of fluoride to the prefluoridation level and had a significantly great amount of adhesives left on either fluoridated or nonfluoridated enamel. PMID:25512720

  4. Effects of mechanical properties of adhesive resin cements on stress distribution in fiber-reinforced composite adhesive fixed partial dentures.

    PubMed

    Yokoyama, Daiichiro; Shinya, Akikazu; Gomi, Harunori; Vallittu, Pekka K; Shinya, Akiyoshi

    2012-01-01

    Using finite element analysis (FEA), this study investigated the effects of the mechanical properties of adhesive resin cements on stress distributions in fiber-reinforced resin composite (FRC) adhesive fixed partial dentures (AFPDs). Two adhesive resin cements were compared: Super-Bond C&B and Panavia Fluoro Cement. The AFPD consisted of a pontic to replace a maxillary right lateral incisor and retainers on a maxillary central incisor and canine. FRC framework was made of isotropic, continuous, unidirectional E-glass fibers. Maximum principal stresses were calculated using finite element method (FEM). Test results revealed that differences in the mechanical properties of adhesive resin cements led to different stress distributions at the cement interfaces between AFPD and abutment teeth. Clinical implication of these findings suggested that the safety and longevity of an AFPD depended on choosing an adhesive resin cement with the appropriate mechanical properties. PMID:22447051

  5. Rubbing salt into wounded endothelium: sodium potentiates proatherogenic effects of TNF-α under non-uniform shear stress.

    PubMed

    Wild, J; Soehnlein, O; Dietel, B; Urschel, K; Garlichs, C D; Cicha, I

    2014-07-01

    Increased consumption of sodium is a risk factor for hypertension and cardiovascular diseases. In vivo studies indicated that high dietary sodium may have a direct negative influence on endothelium. We investigated the effects of high sodium on the endothelial activation during early steps of atherogenesis. Endothelial cells (HUVECs) grown in a model of arterial bifurcations were exposed to shear stress in the presence of normal or high (+ 30 mmol/l) sodium. Adherent THP-1 cells, and the adhesion molecule expression were quantified. Sodium channel blockers, pathways' inhibitors, and siRNA against tonicity-responsive enhancer binding protein (TonEBP) were used to identify the mechanisms of sodium effects on endothelium. ApoE-deficient mice on low-fat diet received water containing normal or high salt (8% w/v) for four weeks, and the influence of dietary salt on inflammatory cell adhesion in the common carotid artery and carotid bifurcation was measured by intravital microscopy. In vitro, high sodium dramatically increased the endothelial responsiveness to tumour necrosis factor-α under non-uniform shear stress. Sodium-induced increase in monocytic cell adhesion was mediated by reactive oxygen species and the endothelial nitric oxygen synthase, and was sensitive to the knockdown of TonEBP. The results were subsequently confirmed in the ApoE-deficient mice. As compared with normal-salt group, high-salt intake significantly enhanced the adhesion of circulating CD11b+ cells to carotid bifurcations, but not to the straight segment of common carotid artery. In conclusion, elevated sodium has a direct effect on endothelial activation under atherogenic shear stress in vitro and in vivo, and promotes the endothelial-leukocyte interactions even in the absence of increased lipid concentrations. PMID:24573382

  6. Essential role for focal adhesion kinase in regulating stress hematopoiesis

    PubMed Central

    Ramdas, Baskar; Hanneman, Philip; Martin, Joseph; Beggs, Hilary E.

    2010-01-01

    Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that has been extensively studied in fibroblasts; however its function in hematopoiesis remains an enigma. FAK is thought to be expressed in myeloid and erythroid progenitors, and its expression is enhanced in response to cytokines such as granu-locyte macrophage colony-stimulating factor. Furthermore, bone marrow cells cultured in granulocyte macrophage colony-stimulating factor show active migration and chemoattractant-induced polarization, which correlates with FAK induction. While loss of FAK in mice results in embryonic lethality, we have deleted FAK in the adult bone marrow. We show an essential role for FAK in regulating hemolytic, myelotoxic, as well as acute inflammatory stress responses in vivo. In vitro, loss of FAK in erythroid and myeloid progenitor's results in impaired cytokine induced growth and survival, as well as defects in the activation and expression of antiapoptotic proteins caspase 3 and Bcl-xL. Additionally, reduced migration and adhesion of myeloid cells on extracellular matrix proteins, as well as impaired activation of Rac GTPase is also observed in the absence of FAK. Our studies reveal an essential role for FAK in integrating growth/survival and adhesion based functions in myeloid and erythroid cells predominantly under conditions of stress. PMID:20664055

  7. MicroRNA-30 mediates anti-inflammatory effects of shear stress and KLF2 via repression of angiopoietin 2.

    PubMed

    Demolli, Shemsi; Doebele, Carmen; Doddaballapur, Anuradha; Lang, Victoria; Fisslthaler, Beate; Chavakis, Emmanouil; Vinciguerra, Manlio; Sciacca, Sergio; Henschler, Reinhard; Hecker, Markus; Savant, Soniya; Augustin, Hellmut G; Kaluza, David; Dimmeler, Stefanie; Boon, Reinier A

    2015-11-01

    MicroRNAs are endogenously expressed small noncoding RNAs that regulate gene expression. Laminar blood flow induces atheroprotective gene expression in endothelial cells (ECs) in part by upregulating the transcription factor KLF2. Here, we identified KLF2- and flow-responsive miRs that affect gene expression in ECs. Bioinformatic assessment of mRNA expression patterns identified the miR-30-5p seed sequence to be highly enriched in mRNAs that are downregulated by KLF2. Indeed, KLF2 overexpression and shear stress stimulation in vitro and in vivo increased the expression of miR-30-5p family members. Furthermore, we identified angiopoietin 2 (Ang2) as a target of miR-30. MiR-30 overexpression reduces Ang2 levels, whereas miR-30 inhibition by LNA-antimiRs induces Ang2 expression. Consistently, miR-30 reduced basal and TNF-α-induced expression of the inflammatory cell–cell adhesion molecules E-selectin, ICAM1 and VCAM1, which was rescued by stimulation with exogenous Ang2. In summary, KLF2 and shear stress increase the expression of the miR-30-5p family which acts in an anti-inflammatory manner in ECs by impairing the expression of Ang2 and inflammatory cell–cell adhesion molecules. The upregulation of miR-30-5p family members may contribute to the atheroprotective effects of shear stress.

  8. Neuron adhesion and strengthening

    NASA Astrophysics Data System (ADS)

    Rocha, Aracely; Jian, Kuihuan; Ko, Gladys; Liang, Hong

    2010-07-01

    Understanding the neuron/material adhesion is important for neuron stimulation and growth. The current challenges remain in the lack of precision of measuring techniques and understanding the behavior of neuron. Here, we report a fluid shear method to investigate adhesion at the neuron/poly-D-lysine interface. In this study, the adhesion of 12-day-old chick embryo-retina neurons cultured on poly-D-lysine coated glass coverslips was measured via parallel disk rotational flow. The shear stress experienced by the cells increases with the disk radius. There is a critical point along the radius (Rc) where the stress experienced by the neurons equals their adhesion. The measured Rc can be used to calculate the neuron adhesion. Our results demonstrate that neurons adhered to the poly-D-lysine had a strain hardening effect. The adhesive shear stress of the neuron-material increased with applied shear (τa). When the τa reached or exceeded the value of 40 dyn/cm2, the adhesion remained constant at approximately 30 dyn/cm2. The present work allowed us not only to quantify the adhesive strength and force but also to evaluate the value of strain hardening at the neuron/poly-D-lysine interface.

  9. Increased shear stress inhibits angiogenesis in veins and not arteries during vascular development.

    PubMed

    Chouinard-Pelletier, Guillaume; Jahnsen, Espen D; Jones, Elizabeth A V

    2013-01-01

    Vascular development is believed to occur first by vasculogenesis followed by angiogenesis. Though angiogenesis is the formation of new vessels, we found that vascular density actually decreases during this second stage. The onset of the decrease coincided with the entry of erythroblasts into circulation. We therefore measured the level of shear stress at various developmental stages and found that it was inversely proportional to vascular density. To investigate whether shear stress was inhibitory to angiogenesis, we altered shear stress levels either by preventing erythroblasts from entering circulation ("low" shear stress) or by injection of a starch solution to increase the blood plasma viscosity ("high" shear stress). By time-lapse microscopy, we show that reverse intussusception (merging of two vessels) is inversely proportional to the level of shear stress. We also found that angiogenesis (both sprouting and splitting) was inversely proportional to shear stress levels. These effects were specific to the arterial or venous plexus however, such that the effect on reverse intussusception was present only in the arterial plexus and the effect on sprouting only in the venous plexus. We cultured embryos under altered shear stress in the presence of either DAPT, a Notch inhibitor, or DMH1, an inhibitor of the bone morphogenetic protein (BMP) pathway. DAPT treatment phenocopied the inhibition of erythroblast circulation ("low" shear stress) and the effect of DAPT treatment could be partially rescued by injection of starch. Inhibition of the BMP signaling prevented the reduction in vascular density that was observed when starch was injected to increase shear stress levels.

  10. Permeability of fault gouge under confining pressure and shear stress.

    USGS Publications Warehouse

    Morrow, C.A.; Shi, L.Q.; Byerlee, J.D.

    1984-01-01

    The permeability of both clay-rich and non-clay gouges, as well as several pure clays, was studied as a function of confining pressures from 5 to 200 MPa and shear strain to 10. Permeability ranged over 4 orders of magnitude, from around 10-22 to 10-18 m2 (1 darcy = 0.987 X 10-12 m2). Grain size was an important factor in determining permeability, particularly for the clay-rich samples. The permeabilities of the non-clay samples were not significantly different than those of the clays. Strength of the saturated samples under drained (low pore pressure) conditions did not correlate with high or low permeability. However, the low permeabilities of these gouges could be a factor in the measured low shear stresses along fault regions if excess pore pressures were created as a result of shearing or compaction, and this pressure was unable to dissipate through a thick section of the material.-from Authors

  11. Stress analysis of the cracked lap shear specimens: An ASTM round robin

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1986-01-01

    This ASTM Round Robin was conducted to evaluate the state of the art in stress analysis of adhesively bonded joint specimens. Specifically, the participants were asked to calculate the strain-energy-release rate for two different geometry cracked lap shear (CLS) specimens at four different debond lengths. The various analytical techniques consisted of 2- and 3-dimensional finite element analysis, beam theory, plate theory, and a combination of beam theory and finite element analysis. The results were examined in terms of the total strain-energy-release rate and the mode I to mode II ratio as a function of debond length for each specimen geometry. These results basically clustered into two groups: geometric linear or geometric nonlinear analysis. The geometric nonlinear analysis is required to properly analyze the CLS specimens. The 3-D finite element analysis gave indications of edge closure plus some mode III loading. Each participant described his analytical technique and results. Nine laboratories participated.

  12. Stress analysis of the cracked-lap-shear specimen - An ASTM round-robin

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.

    1987-01-01

    This ASTM Round Robin was conducted to evaluate the state of the art in stress analysis of adhesively bonded joint specimens. Specifically, the participants were asked to calculate the strain-energy-release rate for two different geometry cracked lap shear (CLS) specimens at four different debond lengths. The various analytical techniques consisted of 2- and 3-dimensional finite element analysis, beam theory, plate theory, and a combination of beam theory and finite element analysis. The results were examined in terms of the total strain-energy-release rate and the mode I to mode II ratio as a function of debond length for each specimen geometry. These results basically clustered into two groups: geometric linear or geometric nonlinear analysis. The geometric nonlinear analysis is required to properly analyze the CLS specimens. The 3-D finite element analysis gave indications of edge closure plus some mode III loading. Each participant described his analytical technique and results. Nine laboratories participated.

  13. Differentiation of Crohn’s Disease-Associated Isolates from Other Pathogenic Escherichia coli by Fimbrial Adhesion under Shear Force

    PubMed Central

    Szunerits, Sabine; Zagorodko, Oleksandr; Cogez, Virginie; Dumych, Tetiana; Chalopin, Thibaut; Alvarez Dorta, Dimitri; Sivignon, Adeline; Barnich, Nicolas; Harduin-Lepers, Anne; Larroulet, Iban; Yanguas Serrano, Aritz; Siriwardena, Aloysius; Pesquera, Amaia; Zurutuza, Amaia; Gouin, Sébastien G.; Boukherroub, Rabah; Bouckaert, Julie

    2016-01-01

    Shear force exerted on uropathogenic Escherichia coli adhering to surfaces makes type-1 fimbriae stretch out like springs to catch on to mannosidic receptors. This mechanism is initiated by a disruption of the quaternary interactions between the lectin and the pilin of the two-domain FimH adhesin and transduces allosterically to the mannose-binding pocket of FimH to increase its affinity. Mannose-specific adhesion of 14 E. coli pathovars was measured under flow, using surface plasmon resonance detection on functionalized graphene-coated gold interfaces. Increasing the shear had important differential consequences on bacterial adhesion. Adherent-invasive E. coli, isolated from the feces and biopsies of Crohn’s disease patients, consistently changed their adhesion behavior less under shear and displayed lower SPR signals, compared to E. coli opportunistically infecting the urinary tract, intestines or loci of knee and hip prostheses. We exemplified this further with the extreme behaviors of the reference strains UTI89 and LF82. Whereas their FimA major pilins have identical sequences, FimH of LF82 E. coli is marked by the Thr158Pro mutation. Positioned in the inter-domain region known to carry hot spots of mutations in E. coli pathotypes, residue 158 is indicated to play a structural role in the allosteric regulation of type-1 fimbriae-mediated bacterial adhesion. PMID:27043645

  14. Interfacial shear stress in stratified flow in a horizontal rectangular duct

    SciTech Connect

    Lorencez, C.; Kawaji, M.; Murao, Y.

    1995-09-01

    Interfacial shear stress has been experimentally examined for both cocurrent and countercurrent stratified wavy flows in a horizontal interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress values at high gas flow rates which could be attributed to the assumptions and procedures involved in each method. The interfacial waves and secondary motions were also found to have significant effects on the accuracy of Reynolds stress and turbulence kinetic energy extrapolation methods.

  15. A review of Reynolds stress models for turbulent shear flows

    NASA Technical Reports Server (NTRS)

    Speziale, Charles G.

    1995-01-01

    A detailed review of recent developments in Reynolds stress modeling for incompressible turbulent shear flows is provided. The mathematical foundations of both two-equation models and full second-order closures are explored in depth. It is shown how these models can be systematically derived for two-dimensional mean turbulent flows that are close to equilibrium. A variety of examples are provided to demonstrate how well properly calibrated versions of these models perform for such flows. However, substantial problems remain for the description of more complex turbulent flows where there are large departures from equilibrium. Recent efforts to extend Reynolds stress models to nonequilibrium turbulent flows are discussed briefly along with the major modeling issues relevant to practical naval hydrodynamics applications.

  16. Endovascular Treatment of Thoracic Aortic Dissection: Hemodynamic Shear Stress Study

    NASA Astrophysics Data System (ADS)

    Tang, Yik Sau; Lai, Siu Kai; Cheng, Stephen Wing Keung; Chow, Kwok Wing

    2012-11-01

    Thoracic Aortic Dissection (TAD), a life threatening cardiovascular disease, occurs when blood intrudes into the layers of the aortic wall, creating a new artificial channel (the false lumen) beside the original true lumen. The weakened false lumen wall may expand, enhancing the risk of rupture and resulting in high mortality. Endovascular treatment involves the deployment of a stent graft into the aorta, thus blocking blood from entering the false lumen. Due to the irregular geometry of the aorta, the stent graft, however, may fail to conform to the vessel curvature, and would create a ``bird-beak'' configuration, a wedge-shaped domain between the graft and the vessel wall. Computational fluid dynamics analysis is employed to study the hemodynamics of this pathological condition. With the `beaking' configuration, the local hemodynamic shear stress will drop below the threshold of safety reported earlier in the literature. The oscillating behavior of the shear stress might lead to local inflammation, atherosclerosis and other undesirable consequences. Supported by the Innovation and Technology Fund of the Hong Kong Government.

  17. Dynamic response of wall shear stress on the stenosed artery.

    PubMed

    Sen, S; Chakravarty, S

    2009-10-01

    The present study deals with an appropriate mathematical model of an artery in the presence of constriction in which the generated wall shear stress due to blood flow is analysed. The geometry of the stenosed arterial segment in the diseased state, causing malfunction of the cardiovascular system, is formed mathematically. The flowing blood contained in the stenosed artery is treated as non-Newtonian and the flow is considered to be two-dimensional. The motion of the arterial wall and its effect on local fluid mechanics is not ruled out from the present pursuit. The flow analysis applies the time-dependent, two-dimensional incompressible nonlinear Navier-Stokes equations for non-Newtonian fluids. The flow-field can be obtained primarily following the radial coordinate transformation, using the appropriate boundary conditions and finally adopting a suitable finite difference scheme numerically. The influences of flow unsteadiness, the arterial wall distensibility and the presence of stenosis on the flow-field and the wall shear stresses are quantified in order to indicate the susceptibility to atherosclerotic lesions and thereby to validate the applicability of the present theoretical model. PMID:19294542

  18. The Effect of Temperature on Shear Bond Strength of Clearfil SE Bond and Adper Single Bond Adhesive Systems to Dentin

    PubMed Central

    Sharafeddin, Farahnaz; Nouri, Hossein; Koohpeima, Fatemeh

    2015-01-01

    Statement of the Problem Monomer viscosity and solvent evaporation can be affected by the adhesive system temperature. Higher temperature can elevate the vapor pressure in solution and penetration of adhesive in smear layer. Bonding mechanism may be influenced by the adhesive temperature. Purpose This study aimed to evaluate the effect of pre-heating on shear bond strength of etch-and-rinse and self-etching adhesives to ground bovine dentin surfaces, at temperatures of 4˚C, 25˚C and 40˚C. Materials and Method In this experimental study, 60 maxillary bovine incisors were randomly divided into 6 groups (n=10). The central part of labial dentin surfaces was exposed with a diamond bur and standardized smear layer was created by using silicon carbide paper (600 grit) under water-coolant while the specimens were mounted in acrylic resin. Two adhesive systems, an etch-and-rinse (Adper single bond) and a self-etch (Clearfil SE Bond) were stored at temperatures of 4˚C, 25˚C and 40˚C for 30 minutes and were then applied on the prepared labial surface according to the manufacturer’s instructions. The composite resin (Z350) was packed in Teflon mold (5 mm in diameter) on this surface and was cured. The shear bond strength (MPa) was evaluated by universal testing machine (Zwick/Roell Z020, Germany) at cross head speed of 1mm/min. The results were statistically analyzed by using ANOVA and Tukey tests (p< 0.05). Results No significant difference was found between the shear bond strength of Clearfil SE Bond adhesive in different temperature and single Bond adhesive system at 25 ˚C and 40 ˚C. However, there were significant differences between 4 ˚C of Adper single bond in comparison with 25˚C and 40˚C (p= 0.0001). Conclusion Pre-heating did not affect the shear bond strength of SE Bond, but could promote the shear bond strength of Adper Single Bond. PMID:25759852

  19. Relationship between types of surface shear stress profiles and membrane fouling.

    PubMed

    Chan, C C V; Bérubé, P R; Hall, E R

    2011-12-01

    Shear stress has been recognized as an important parameter in controlling particle back-transport from membrane surfaces. However, little is known of the relationship between transient shear conditions induced by air sparging and fouling control near membrane surfaces. In this paper, the different types of surface shear stress profiles that had beneficial effects on minimizing reversible surface fouling were examined. The relationship between different statistical shear parameters (e.g. time-averaged shear, standard deviation of shear and amplitude of shear) and fouling control that have been used by others were examined as well. It was found that the fouling rate for membranes subjected to transient shear conditions was lower than for membranes subjected to constant shear conditions. The magnitude, duration and frequency of the shear conditions were found to have an impact on the fouling rate of membranes. It was also found that although some statistical shear parameters could generally be used to relate shear and fouling, they were inadequate to relate surface shear stress to fouling, for all transient shear conditions examined.

  20. A failure criterion for laminates governed by free edge interlaminar shear stress

    NASA Astrophysics Data System (ADS)

    Joo, J. W.; Sun, C. T.

    1992-01-01

    Interlaminar shear stresses in balanced and symmetric laminates with free edges and failure due to these stresses were studied. It was shown that the average interlaminar shear stress near the free edge is linearly related to the mismatch of the extension-shear coupling of the top and bottom sublaminates separated by the interface of interest. A simple failure criterion based on the mismatch of the extension shear coupling was introduced to predict laminate failure stress and strain. The validity of this criterion was verified by experiments using AS4/3501-6 graphite/epoxy composite laminates.

  1. Distinct kinetic and mechanical properties govern mucin 16- and podocalyxin-mediated tumor cell adhesion to E- and L-selectin in shear flow

    PubMed Central

    Shea, Daniel J.; Wirtz, Denis; Stebe, Kathleen J.; Konstantopoulos, Konstantinos

    2015-01-01

    Selectin-mediated tumor cell tethering to host cells, such as vascular endothelial cells, is a critical step in the process of cancer metastasis. We recently identified sialofucosylated mucin16 (MUC16) and podocalyxin (PODXL) as the major functional E- and L-selectin ligands expressed on the surface of metastatic pancreatic cancer cells. While the biophysics of leukocyte binding to selectins has been well studied, little is known about the mechanics of selectin-mediated adhesion pertinent to cancer metastasis. We thus sought to evaluate the critical parameters of selectin-mediated pancreatic tumor cell tethering and rolling. Using force spectroscopy, we characterized the binding interactions of MUC16 and PODXL to E- and L-selectin at the single-molecule level. To further analyze the response of these molecular interactions under physiologically relevant regimes, we used a microfluidic assay in conjunction with a mathematical model to study the biophysics of selectin-ligand binding as a function of fluid shear stress. We demonstrate that both MUC16 and PODXL-E-selectin-mediated interactions are mechanically stronger than like L-selectin interactions at the single-molecule level, and display a higher binding frequency at all contact times. The single-molecule kinetic and micromechanical properties of selectin-ligand bonds, along with the number of receptor-ligand bonds needed to initiate tethering, regulate the average velocity of ligand-coated microspheres rolling on selectin-coated surfaces in shear flow. Understanding the biophysics of selectin-ligand bonds and their responses to physiologically relevant shear stresses is vital for developing diagnostic assays and/or preventing the metastatic spread of tumor cells by interfering with selectin-mediated adhesion. PMID:26329844

  2. Analysis of micro-shear bond strength of self-etch adhesive systems with dentine: An in vitro study

    PubMed Central

    Shakya, Vijay Kumar; Singh, Rajeev Kumar; Pathak, Anjani Kumar; Singh, Balendra Pratap; Chandra, Anil; Bharti, Ramesh; Yadav, Rakesh Kumar

    2015-01-01

    Background Success or failure of a composite restoration largely depends on its bonding to enamel/dentine. Several better adhesive systems have been developed during the last few years due to rapid advancement in the technology. Recent self-etched adhesives have fewer clinical steps and are less technique sensitive. Methods Ninety extracted human permanent molars were collected, grounded and finished to prepare flat dentine-bonding surfaces on their occlusal surface. All specimens were divided into three groups (n = 30) on the basis of three adhesive systems Adper Easy Bond (AE), Beautibond (BB) and Xeno IV (XE). These adhesive systems were applied on prepared mid-dentine-bonding surface. A restorative resin was added with the help of a transparent tube of 2 mm height and 1.7 mm internal diameter and cured. Fifteen specimens in each group were loaded to failure in an Instron Universal Testing Machine after storage for 24 h at 37 °C to check micro-shear bond strength. Another fifteen specimens from each group were thermocycled 500 times at 5 °C and 55 °C with dwell time of 1 min in each bath followed by loading to failure. The data obtained was analyzed with SPSS version 21 at significance level of <05. Results After 24 h, micro-shear bond strength of BB was higher (26.04 MPa) than XE (23.69 MPa) and AE (21.50 MPa). After thermocycling, micro-shear bond strength decreased significantly in BB (P = .001) and XE (P = .03). Conclusion The micro-shear bond strength of BB was highest among three groups, which decreased after thermocycling. PMID:26605144

  3. Impact of bifurcation dual stenting on endothelial shear stress

    PubMed Central

    Chen, Henry Y.; Koo, Bon-Kwon

    2015-01-01

    Despite advances in percutaneous coronary interventions and the introduction of drug eluding stents, in-stent restenosis and stent thrombosis remain a clinically significant problem for bifurcations. The aim of this study is to determine the effect of dual bifurcation stenting on hemodynamic parameters known to influence restenosis and thrombosis. We hypothesized that double stenting, especially with a longer side branch (SB) stent, likely has a negative effect on wall shear stress (WSS), WSS gradient (WSSG), and oscillatory shear index (OSI). To test this hypothesis, we developed computational models of dual stents at bifurcations and non-Newtonian blood simulations. The models were then interfaced, meshed, and solved in a validated finite-element package. Longer and shorter stents at the SB and provisional stenting were compared. It was found that stents placed in the SB at a bifurcation lowered WSS, but elevated WSSG and OSI. Dual stenting with longer SB stent had the most adverse impact on SB endothelial WSS, WSSG, and OSI, with low WSS region up to 50% more than the case with shorter SB stent. The simulations also demonstrated flow disturbances resulting from SB stent struts protruding into the main flow field near the carina, which may have implications on stent thrombosis. The simulations predict a negative hemodynamic role for SB stenting, which is exaggerated with a longer stent, consistent with clinical trial findings that dual-stenting is comparable or inferior to provisional stenting. PMID:26183473

  4. Shear stress reduces protease activated receptor-1 expression in human endothelial cells

    NASA Technical Reports Server (NTRS)

    Nguyen, K. T.; Eskin, S. G.; Patterson, C.; Runge, M. S.; McIntire, L. V.

    2001-01-01

    Shear stress has been shown to regulate several genes involved in the thrombotic and proliferative functions of endothelial cells. Thrombin receptor (protease-activated receptor-1: PAR-1) increases at sites of vascular injury, which suggests an important role for PAR-1 in vascular diseases. However, the effect of shear stress on PAR-1 expression has not been previously studied. This work investigates effects of shear stress on PAR-1 gene expression in both human umbilical vein endothelial cells (HUVECs) and microvascular endothelial cells (HMECs). Cells were exposed to different shear stresses using a parallel plate flow system. Northern blot and flow cytometry analysis showed that shear stress down-regulated PAR-1 messenger RNA (mRNA) and protein levels in both HUVECs and HMECs but with different thresholds. Furthermore, shear-reduced PAR-1 mRNA was due to a decrease of transcription rate, not increased mRNA degradation. Postshear stress release of endothelin-1 in response to thrombin was reduced in HUVECs and HMECs. Moreover, inhibitors of potential signaling pathways applied during shear stress indicated mediation of the shear-decreased PAR-1 expression by protein kinases. In conclusion, shear stress exposure reduces PAR-1 gene expression in HMECs and HUVECs through a mechanism dependent in part on protein kinases, leading to altered endothelial cell functional responses to thrombin.

  5. Evaluation of Self-Etching Adhesive and Er:YAG Laser Conditioning on the Shear Bond Strength of Orthodontic Brackets

    PubMed Central

    Contreras-Bulnes, Rosalía; Scougall-Vilchis, Rogelio J.; Rodríguez-Vilchis, Laura E.; Centeno-Pedraza, Claudia; Olea-Mejía, Oscar F.; Alcántara-Galena, María del Carmen Z.

    2013-01-01

    The purpose of this study was to evaluate the shear bond strength, the adhesive remnant index scores, and etch surface of teeth prepared for orthodontic bracket bonding with self-etching primer and Er:YAG laser conditioning. One hundred and twenty bovine incisors were randomly divided into four groups. In Group I (Control), the teeth were conditioned with 35% phosphoric acid for 15 seconds. In Group II the teeth were conditioned with Transbond Plus SEP (5 sec); III and IV were irradiated with the Er:YAG 150 mJ (11.0 J/cm2), 150 mJ (19.1 J/cm2), respectively, at 7–12 Hz with water spray. After surface preparation, upper central incisor stainless steel brackets were bonded with Transbond Plus Color Change Adhesive. The teeth were stored in water at 37°C for 24 hours and shear bond strengths were measured, and adhesive remnant index (ARI) was determined. The conditioned surface was observed under a scanning electron microscope. One-way ANOVA and chi-square test were used. Group I showed the significantly highest values of bond strength with a mean value of 8.2 megapascals (MPa). The lesser amount of adhesive remnant was found in Group III. The results of this study suggest that Er:YAG laser irradiation could not be an option for enamel conditioning. PMID:24228014

  6. The Influence of No-Primer Adhesives and Anchor Pylons Bracket Bases on Shear Bond Strength of Orthodontic Brackets

    PubMed Central

    Sfondrini, Maria Francesca; Fraticelli, Danilo; Daina, Paola; Tamagnone, Alessandra; Gandini, Paola

    2013-01-01

    Objective. The aim of this study was to compare the shear bond strength (SBS) and adhesive remnant index (ARI) scores of no-primer adhesives tested with two different bracket bases. Materials and Methods. 120 bovine permanent mandibular incisors were divided into 6 groups of 20 specimens. Two brackets (ODP) with different bracket bases (anchor pylons and 80-gauge mesh) were bonded to the teeth using a conventional adhesive (Transbond XT) and two different no-primer adhesive (Ortho Cem; Heliosit) systems. Groups were tested using an instron universal testing machine. SBS values were recorded. ARI scores were measured. SEM microphotographs were taken to evaluate the pattern of bracket bases. Statistical analysis was performed. ANOVA and Tukey tests were carried out for SBS values, whereas a chi-squared test was applied for ARI scores. Results. Highest bond strength values were reported with Transbond XT (with both pad designs), Ortho Cem bonded on anchor pylons and Heliosit on 80-gauge mesh. A higher frequency of ARI score of “3” was reported for Transbond XT groups. Other groups showed a higher frequency of ARI score “2” and “1.” Conclusion. Transbond XT showed the highest shear bond strength values with both pad designs. PMID:23984339

  7. The shear bond strength of MTA with three different types of adhesive systems: An in vitro study

    PubMed Central

    Tyagi, Nimish; Chaman, Chandrakar; Tyagi, Shashi Prabha; Singh, Udai Pratap; Sharma, Apoorv

    2016-01-01

    Aim: To evaluate the shear bond strength of MTA with three different types of adhesive systems- self-adhering flowable composite, etch and rinse adhesive system and self etch adhesive system. Methodology: MTA specimens (n = 60) were prepared using cylindrical acrylic blocks, having a central cavity with 4 mm diameter and 2 mm depth. MTA was mixed and placed in the prepared cavity, and was covered with a moist cotton pellet and temporary filling material. The specimens were divided into 3 groups which were further divided into 2 sub-groups (45 Minutes and 24 hours). After the application of bonding agents composite resin was placed over the MTA surface. The specimens were tested for shear bond strength and readings were statically analyzed. Result: After 24 hrs the mean value of etch and rinse group was significantly higher than self etch and the self adhering composite groups. Among the 45 minutes groups there were no significant difference. Conclusion: In single visit after 45 minutes self adhering flowable can be used successfully as a final restorative material in place of conventional flowable composite without using any alternative adhesive system over MTA. PMID:27099417

  8. Wrinkling Phenomena of Thin Flat Plates Subjected to Shear Stresses

    NASA Technical Reports Server (NTRS)

    Bollenrath, F

    1931-01-01

    This report covers a series of tests on thin flat elastic strips restrained at two parallel edges and subjected to shear by conversely directed stresses. Theoretical treatments, particularly those of Lilly, Southwell and Skan, and Timoshenko are briefly outlined. The problem to be solved by these tests was to find out whether, and to what extent the conditions and assumptions upon which the calculations are based are complied with in the tests. Three materials were used: celluloid, duralumin, brass. Owing to the high elastic deformability of celluloid, it was not only possible to observe the beginning but also to ascertain the type of deflection. The test data on celluloid was affirmed by the experiments with duralumin and brass.

  9. Shear Bond Strengths of Methacrylate- and Silorane-based Composite Resins to Feldspathic Porcelain using Different Adhesive Systems.

    PubMed

    Mohammadi, Narmin; Shakur Shahabi, Maryam; Kimyai, Soodabeh; Pournagi Azar, Fatemeh; Ebrahimi Chaharom, Mohammad Esmaeel

    2015-01-01

    Background and aims. Use of porcelain as inlays, laminates and metal-ceramic and all-ceramic crowns is common in modern dentistry. The high cost of ceramic restorations, time limitations and difficulty of removing these restorations result in delays in replacing fractured restorations; therefore, their repair is indicated. The aim of the present study was to compare the shear bond strengths of two types of composite resins (methacrylate-based and silorane-based) to porcelain, using three adhesive types. Materials and methods. A total of 156 samples of feldspathic porcelain surfaces were prepared with air-abrasion and randomly divided into 6 groups (n=26). In groups 1-3, Z250 composite resin was used to repair porcelain samples with Ad-per Single Bond 2 (ASB), Clearfil SE Bond (CSB) and Silorane Adhesive (SA) as the bonding systems, afterapplication of silane, respectively. In groups 4-6, the same adhesives were used in the same manner with Filtek Silorane composite resin. Finally, the shear bond strengths of the samples were measured. Two-way ANOVA and post hoc Tukey tests were used to compare bond strengths between the groups with different adhesives at P<0.05. Results. There were significant differences in the mean bond strength values in terms of the adhesive type (P<0.001). In addition, the interactive effect of the adhesive type and composite resin type had no significant effect on bond strength (P=0.602). Conclusion. The results of the present study showed the highest repair bond strength values to porcelain with both composite resin types with the application of SA and ASB. PMID:26697151

  10. Shear Bond Strengths of Methacrylate- and Silorane-based Composite Resins to Feldspathic Porcelain using Different Adhesive Systems

    PubMed Central

    Mohammadi, Narmin; Shakur Shahabi, Maryam; Kimyai, Soodabeh; Pournagi Azar, Fatemeh; Ebrahimi Chaharom, Mohammad Esmaeel

    2015-01-01

    Background and aims. Use of porcelain as inlays, laminates and metal-ceramic and all-ceramic crowns is common in modern dentistry. The high cost of ceramic restorations, time limitations and difficulty of removing these restorations result in delays in replacing fractured restorations; therefore, their repair is indicated. The aim of the present study was to compare the shear bond strengths of two types of composite resins (methacrylate-based and silorane-based) to porcelain, using three adhesive types. Materials and methods. A total of 156 samples of feldspathic porcelain surfaces were prepared with air-abrasion and randomly divided into 6 groups (n=26). In groups 1-3, Z250 composite resin was used to repair porcelain samples with Ad-per Single Bond 2 (ASB), Clearfil SE Bond (CSB) and Silorane Adhesive (SA) as the bonding systems, afterapplication of silane, respectively. In groups 4-6, the same adhesives were used in the same manner with Filtek Silorane composite resin. Finally, the shear bond strengths of the samples were measured. Two-way ANOVA and post hoc Tukey tests were used to compare bond strengths between the groups with different adhesives at P<0.05. Results. There were significant differences in the mean bond strength values in terms of the adhesive type (P<0.001). In addition, the interactive effect of the adhesive type and composite resin type had no significant effect on bond strength (P=0.602). Conclusion. The results of the present study showed the highest repair bond strength values to porcelain with both composite resin types with the application of SA and ASB. PMID:26697151

  11. Shear stress-induced transcriptional regulation via hybrid promoters as a potential tool for promoting angiogenesis.

    PubMed

    Silberman, Michal; Barac, Yaron D; Yahav, Hava; Wolfovitz, Efrat; Einav, Shmuel; Resnick, Nitzan; Binah, Ofer

    2009-01-01

    Among the key effects of fluid shear stress on vascular endothelial cells is modulation of gene expression. Promoter sequences termed shear stress response elements (SSREs) mediate the responsiveness of endothelial genes to shear stress. While previous studies showed that shear stress responsiveness is mediated by a single SSRE, these endogenous promoters often encode for multiple SSREs. Moreover, hybrid promoters encoding a single SSRE rarely respond to shear stress at the same magnitude as the endogenous promoter. Thus, to better understand the interplay between the various SSREs, and between SSREs and endothelial-specific sequences (ESS), we generated a series of constructs regulated by SSREs cassettes alone, or in combination with ESS, and tested their response to shear stress and endothelial specific expression. Among these constructs, the most responsive promoter (NR1/2) encoded a combination of two GAGACC/SSREs, the Sp1/Egr1 sequence, as well as a TPA response element (TRE). This construct was four- to five-fold more responsive to shear stress than a promoter encoding a single SSRE. The expression of constructs containing other SSRE combinations was unaffected or suppressed by shear stress. Addition of ESS derived from the Tie2 promoter, either 5' or 3' to NR1/2 resulted in shear stress transcriptional suppression, yet retained endothelial specific expression. Thus, the combination and localization order of the various SSREs in a single promoter is crucial in determining the pattern and degree of shear stress responsiveness. These shear stress responsive cassettes may prove beneficial in our attempt to time the expression of an endothelial transgene in the vasculature.

  12. Experimental measurement of dynamic fluid shear stress on the aortic surface of the aortic valve leaflet

    PubMed Central

    Yap, Choon Hwai; Saikrishnan, Neelakantan; Tamilselvan, Gowthami

    2011-01-01

    Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. Although exact causes and mechanisms of AV calcification are unclear, previous studies suggest that mechanical forces play a role. Since calcium deposits occur almost exclusively on the aortic surfaces of AV leaflets, it has been hypothesized that adverse patterns of fluid shear stress on the aortic surface of AV leaflets promote calcification. The current study characterizes AV leaflet aortic surface fluid shear stresses using Laser Doppler velocimetry and an in vitro pulsatile flow loop. The valve model used was a native porcine valve mounted on a suturing ring and preserved using 0.15% glutaraldehyde solution. This valve model was inserted in a mounting chamber with sinus geometries, which is made of clear acrylic to provide optical access for measurements. To understand the effects of hemodynamics on fluid shear stress, shear stress was measured across a range of conditions: varying stroke volumes at the same heart rate and varying heart rates at the same stroke volume. Systolic shear stress magnitude was found to be much higher than diastolic shear stress magnitude due to the stronger flow in the sinuses during systole, reaching up to 20 dyn/cm2 at mid-systole. Upon increasing stroke volume, fluid shear stresses increased due to stronger sinus fluid motion. Upon increasing heart rate, fluid shear stresses decreased due to reduced systolic duration that restricted the formation of strong sinus flow. Significant changes in the shear stress waveform were observed at 90 beats/ min, most likely due to altered leaflet dynamics at this higher heart rate. Overall, this study represents the most well-resolved shear stress measurements to date across a range of conditions on the aortic side of the AV. The data presented can be used for further investigation to understand AV biological response to shear stresses. PMID:21416247

  13. Predicting boundary shear stress and sediment transport over bed forms

    USGS Publications Warehouse

    McLean, S.R.; Wolfe, S.R.; Nelson, J.M.

    1999-01-01

    To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of the internal boundary layer with semiempirical structure functions to predict the velocity at the crest of a bedform, where the flow is most similar to a uniform boundary layer. Significantly, the methodology is directed toward making specific predictions only at the bed-form crest, and as a result it avoids the difficulty and questionable validity of spatial averaging. The model provides an accurate estimate of the skin friction at the crest where transport rates are highest. Simple geometric constraints can be used to derive the mean transport rates as long as bed load is dominant.To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of

  14. Effect of placement agitation and placement time on the shear bond strength of 3 self-etching adhesives.

    PubMed

    Velasquez, Lina Maria; Sergent, Robert S; Burgess, John O; Mercante, D E

    2006-01-01

    This study measured the shear bond strength (SBS) of 3 self-etching bonding agents to enamel and dentin with and without agitation at 3 different application times. The null hypotheses tested were that agitation and application time have no effect on bond strength. Occlusal surfaces of 180 recently extracted caries-free human molars were wet ground with 600 grit wet-dry silica carbide abrasive paper to obtain a flat enamel surface. The teeth were divided into 18 groups of 10 teeth. Three self-etching bonding agents, Clearfil SE BOND (Kuraray America), Xeno III (Dentsply) and AdheSE (Ivoclar-Vivadent) were applied using application times of 10, 20 or 30 seconds with or without agitation, thinned with a gentle stream of air and cured for 10 seconds, according to manufacturers' directions. Z100 (3M ESPE) composite, A2 shade, was placed over the cured adhesive and cured for 40 seconds. The samples were stored in distilled water at room temperature until testing. The samples were tested in shear to failure with a 1-mm/minute crosshead speed. After enamel shear bond strength testing, the teeth were again ground with 400 and 600-grit wet-dry SiC paper to obtain a flat dentin surface. The protocol used for preparing the enamel bond test samples was repeated, and the teeth were stored until testing in distilled water at room temperature. The samples were again tested in shear at a 1-mm/minute crosshead speed. Values were converted to MPa and data analyzed for intergroup differences using ANOVA and Tukey post-hoc tests. Agitation did not improve enamel SBS for any of the materials tested, but there was a significant difference in enamel SBS among materials: Clearfil SE Bond shear bond strength was greater than Xeno III, which was greater than AdheSE. At 10 seconds application time on dentin, agitation improved the Clearfil SE Bond SBS and, at 20 seconds application time on dentin, agitation significantly improved SBS to dentin for all systems tested. Agitation had no affect

  15. Measurement of wall shear stress in a pulsatile pipe flow system using micro-pillar shear sensor (MPS3)

    NASA Astrophysics Data System (ADS)

    Raghav, Vrishank; Garcia, Christine; Gnanamanickam, Ebenezer; Yoganathan, Ajit; GT-Embry-Riddle Collaboration

    2014-11-01

    The measurement of unsteady wall shear stress (WSS) in a pulsatile flow system is quite a challenge in experimental fluid mechanics. Recent developments in micro fabrication techniques have resulted in a novel measurement technique called the micro-pillar shear stress sensor (MPS3). It is a micro-pillar mounted on the surface of interest, which deflects an amount proportional to the shear stress it experiences. This technique has been widely used, validated and applied to measure turbulent WSS in several flow configurations. In this work, the MPS3 technique is used to measure WSS for a pulsatile fully developed pipe flow. The main objective here is to validate this technique for pulsatile pipe flow applications. For this purpose the WSS measurements obtained are compared with those obtained from analytical womersley solutions of the pulsatile flow system in the laminar flow regime. Statistical metrics will be used to better understand the measured WSS through the time period of the pulsatile flow.

  16. Surface temperatures and glassy state investigations in tribology, part 3. [limiting shear stress rheological model

    NASA Technical Reports Server (NTRS)

    Bair, S.; Winer, W. O.

    1980-01-01

    Research related to the development of the limiting shear stress rheological model is reported. Techniques were developed for subjecting lubricants to isothermal compression in order to obtain relevant determinations of the limiting shear stress and elastic shear modulus. The isothermal compression limiting shear stress was found to predict very well the maximum traction for a given lubricant. Small amounts of side slip and twist incorporated in the model were shown to have great influence on the rising portion of the traction curve at low slide-roll ratio. The shear rheological model was also applied to a Grubin-like elastohydrodynamic inlet analysis for predicting film thicknesses when employing the limiting shear stress model material behavior.

  17. Effect of three adhesive primers for a noble metal on the shear bond strengths of three resin cements.

    PubMed

    Yoshida, K; Kamada, K; Sawase, T; Atsuta, M

    2001-01-01

    The purpose of this study was to evaluate the durability and shear bond strengths of the different combinations of three adhesive primers and three resin cements to a silver-palladium-copper-gold (Ag-Pd-Cu-Au) alloy. The adhesive primers Alloy Primer (AP), Metal PrimerII (MPII) and Metaltite (MT), and the resin cements BistiteII (BRII), Panavia Fluoro Cement (PFC) and Super-Bond C&B (SB) were used. Two sizes of casting alloy disks were either non-primed or primed and cemented with each of the three resin cements. The specimens were stored in a 37 degrees C water bath for 24 h and then immersed alternately in 4 and 60 degrees C water baths for 1 min each for up to 100,000 thermal cycles. Shear mode testing at a crosshead speed of 0.5 mm/min was then performed. The application of MPII or MT was effective for improving the shear bond strength between each of the three resin cements and the Ag-Pd-Cu-Au alloy compared with non-primed specimens. However, when primed with MPII or MT and cemented with SB, the bond strength at 100,000 thermal cycles was significantly lower than that at thermal cycle 0. When primed with AP, the specimens cemented with BRII or PFC showed lower bond strength than non-primed specimens and failed at the metal-resin cement interface at 100,000 thermal cycles. On the other hand, AP was effective in enhancing the shear bond strength of SB to the Ag-Pd-Cu-Au alloy. The five combined uses of an adhesive metal primer and resin cement (combinations of MPII or MT and BRII or PFC and AP and SB) are applicable to the cementation of prosthodontic restorations without complicated surface modification of the noble alloy.

  18. Mixed mode stress field effect in adhesive fracture

    NASA Technical Reports Server (NTRS)

    Anderson, G. P.; Devries, K. L.; Williams, M. L.

    1974-01-01

    Numerical or analytical analyses were performed on seven different test specimens including blister test, 90-degree peel test, torsion test, and various cone tests. These specimens are in general subjected to complex stress fields having various amounts of Mode I, Mode II, and Mode III loads. The specimens were then constructed using polymethyl methacrylate for the adherends and a transparent polyurethane elastomer (Solithane 113) for the adhesive. This combination permitted direct observation of the bondline as load was applied. Although initial debonds as well as bond end termination singularities were present in all specimens, in some cases the debond did not initiate at the singularity points as would normally have been expected. An explanation for this behavior is presented, as well as a comparison of loading mode effect on those specimens for which the debond did propagate from a bond terminus singular point.

  19. Adhesion

    MedlinePlus

    ... as the shoulder Eyes Inside the abdomen or pelvis Adhesions can become larger or tighter over time. ... Other causes of adhesions in the abdomen or pelvis include: Appendicitis , most often when the appendix breaks ...

  20. The effect of shear stress on human endothelial cells seeded on cylindrical viscoelastic conduits: an investigation of gene expression.

    PubMed

    Vara, Dina S; Punshon, Geoffrey; Sales, Kevin M; Hamilton, George; Seifalian, Alexander M

    2006-11-01

    The present study assesses the effect of physiological shear stress on gene expression from human ECs (endothelial cells) seeded on a small-diameter cylindrical bypass graft constructed from nanocomposite based on poly(carbonate-silsesquioxane-bridge-urea)urethane. ECs were seeded on to 5-mm-diameter conduits, placed in a physiological flow circuit and exposed to 1 or 4 h of shear stress at 1.4+/-0.3 Pa. Subsets of conduits were incubated at 37 degrees C and 5% CO2/95% O2 for a further 4 h to determine if gene expression returned to basal levels. PCR was conducted for glyceraldehyde-3-phosphate dehydrogenase, TGFbeta-1 (transforming growth factor beta-1), COL-1 (collagen-1) and PECAM-1 (platelet/EC adhesion molecule-1). Increases in gene expression were seen following flow in nanocomposite conduits. These were significant at 4 h for TGFbeta-1, COL-1 and PECAM-1. After a 4 h recovery period, there were no significant differences in gene intensity, suggesting that this change is transient. These data prove that mRNA can be obtained from ECs seeded on tubular conduits and exposed to shear stress and that gene-expression studies can be successfully carried out. We believe this is a substantial improvement on studies based on flat sheets.

  1. Harnessing tunable scanning probe techniques to measure shear enhanced adhesion of gecko-inspired fibrillar arrays.

    PubMed

    Li, Yasong; Zhou, James H-W; Zhang, Cheng; Menon, Carlo; Gates, Byron D

    2015-02-01

    The hierarchical arrays of mesoscale to nanoscale fibrillar structures on a gecko's foot enable the animal to climb surfaces of varying roughness. Adhesion force between the fibrillar structures and various surfaces is maximized after the gecko drags its foot in one direction, which has also been demonstrated to improve the adhesion forces of artificial fibrillar arrays. Essential conditions that influence the magnitude of these interactions include the lateral distance traveled and velocity between the contacting surfaces, as well as the velocity at which the two surfaces are subsequently separated. These parameters have, however, not been systematically investigated to assess the adhesion properties of artificial adhesives. We introduce a systematic study that investigates these conditions using a scanning probe microscope to measure the adhesion forces of artificial adhesives through a process that mimics the mechanism by which a gecko climbs. The measured adhesion response was different for arrays of shorter and longer fibrils. These results from 9000 independent measurements also provide further insight into the dynamics of the interactions between fibrillar arrays and contacting surfaces. These studies establish scanning probe microscopy techniques as a versatile approach for measuring a variety of adhesion properties of artificial fibrillar adhesives.

  2. Shear Strength at 75 F to 500 F of Fourteen Adhesives Used to Bond a Glass-fabric-reinforced Phenolic Resin Laminate to Steel

    NASA Technical Reports Server (NTRS)

    Davidson, John R

    1956-01-01

    Fourteen adhesives used to bond a glass-fabric-reinforced phenolic resin laminate to steel were tested in order to determine their shear strengths at temperatures from 75 F to 500 F. Fabrication methods were varied to evaluate the effect of placing cloth between the facing surfaces to maintain a uniform bond-line thickness. One glass-fabric supported phenolic adhesive was found to have a shear strength of 3,400 psi at 300 F and over 1,000 psi at 500 F. Strength and fabrication data are tabulated for all adhesives tested.

  3. Studies on stress distribution in pavements subjected to surface shear forces

    PubMed Central

    KIMURA, Tsutomu

    2014-01-01

    It has been pointed out by some researchers1,2) that road pavements are subjected to vertical stress due to vehicles on them as well as shear stress at the time of braking or acceleration of vehicles. In this paper, the results of elastic analysis to obtain the rigorous solution for an elastic two-layer system subjected to surface shear stress are described and it is shown that the effect of shear stresses applied at the surface gives rise to fairly large stresses in the system. On the basis of these findings, the author attempts to explain why pavement failure takes place frequently at places such as crossings and curved parts where pavements are subjected to high magnitude of surface shear stresses. PMID:24522154

  4. Defective fluid shear stress mechanotransduction mediates hereditary hemorrhagic telangiectasia.

    PubMed

    Baeyens, Nicolas; Larrivée, Bruno; Ola, Roxana; Hayward-Piatkowskyi, Brielle; Dubrac, Alexandre; Huang, Billy; Ross, Tyler D; Coon, Brian G; Min, Elizabeth; Tsarfati, Maya; Tong, Haibin; Eichmann, Anne; Schwartz, Martin A

    2016-09-26

    Morphogenesis of the vascular system is strongly modulated by mechanical forces from blood flow. Hereditary hemorrhagic telangiectasia (HHT) is an inherited autosomal-dominant disease in which arteriovenous malformations and telangiectasias accumulate with age. Most cases are linked to heterozygous mutations in Alk1 or Endoglin, receptors for bone morphogenetic proteins (BMPs) 9 and 10. Evidence suggests that a second hit results in clonal expansion of endothelial cells to form lesions with poor mural cell coverage that spontaneously rupture and bleed. We now report that fluid shear stress potentiates BMPs to activate Alk1 signaling, which correlates with enhanced association of Alk1 and endoglin. Alk1 is required for BMP9 and flow responses, whereas endoglin is only required for enhancement by flow. This pathway mediates both inhibition of endothelial proliferation and recruitment of mural cells; thus, its loss blocks flow-induced vascular stabilization. Identification of Alk1 signaling as a convergence point for flow and soluble ligands provides a molecular mechanism for development of HHT lesions. PMID:27646277

  5. Contact Pressure and Shear Stress Analysis on Conforming Contact Problem

    NASA Astrophysics Data System (ADS)

    Nagatani, Haruo; Imou, Akitoshi

    Two methods to solve a conforming contact problem are proposed. First method is general and can be applicable to the contact case between elastic arbitrary shape bodies. For verification FEA is performed on the convex-concave sphere contact, and the result of this method is well corresponding to the FEA result. However, the accuracy deteriorates when the mesh aspect ratio is extremely large. This phenomenon is caused by the usage of numerical integration for the calculation of influence coefficient. The second method is devised to avoid this problem, while this improved method is applicable only to the case when the contact area can be considered to be on a cylinder surface. By using this method, the contact pressure can be obtained without the deterioration even in the case of edge load occurring between ball bearing race shoulder and ball. The results of the contact pressure and the shear stress that is necessary for bearing life estimation are compared with the FEA result, which showed well correspondence.

  6. Characterizations and Correlations of Wall Shear Stress in Aneurysmal Flow.

    PubMed

    Arzani, Amirhossein; Shadden, Shawn C

    2016-01-01

    Wall shear stress (WSS) is one of the most studied hemodynamic parameters, used in correlating blood flow to various diseases. The pulsatile nature of blood flow, along with the complex geometries of diseased arteries, produces complicated temporal and spatial WSS patterns. Moreover, WSS is a vector, which further complicates its quantification and interpretation. The goal of this study is to investigate WSS magnitude, angle, and vector changes in space and time in complex blood flow. Abdominal aortic aneurysm (AAA) was chosen as a setting to explore WSS quantification. Patient-specific computational fluid dynamics (CFD) simulations were performed in six AAAs. New WSS parameters are introduced, and the pointwise correlation among these, and more traditional WSS parameters, was explored. WSS magnitude had positive correlation with spatial/temporal gradients of WSS magnitude. This motivated the definition of relative WSS gradients. WSS vectorial gradients were highly correlated with magnitude gradients. A mix WSS spatial gradient and a mix WSS temporal gradient are proposed to equally account for variations in the WSS angle and magnitude in single measures. The important role that WSS plays in regulating near wall transport, and the high correlation among some of the WSS parameters motivates further attention in revisiting the traditional approaches used in WSS characterizations. PMID:26592536

  7. Tubular shear stress and phenotype of renal proximal tubular cells.

    PubMed

    Essig, Marie; Friedlander, Gérard

    2003-06-01

    Phenotypic alterations resulting from flow-induced mechanical strains is a growing field of research in many cell types such as vascular endothelial and smooth muscle cells, chondrocytes, and osteocytes. Because renal mass reduction is followed by a dramatic increase in GFR in the remaining nephron, modulation of tubular cell phenotype by flow-induced mechanical strains could be one of the events initiating the deleterious pathways that lead to the destruction of renal parenchyma after renal mass reduction. This study demonstrates that increased flow induced, in vitro and in vivo, a reinforcement of the apical domain of actin cytoskeleton and an inhibition of plasminogen activator expression. These effects of flow on plasminogen activator expression were prevented by blocking the reorganization of actin cytoskeleton and were associated with an increase in a shear-stress responsive element binding activity. These results confirm that tubular flow affects the phenotype of renal epithelial cells and suggest that flow-induced mechanical strains could be one determinant of tubulointerstitial lesions during the progression of renal diseases. PMID:12761236

  8. Sediment transport and shear stress partitioning in a vegetated flow

    NASA Astrophysics Data System (ADS)

    Le Bouteiller, Caroline; Venditti, J. G.

    2015-04-01

    Vegetation is a common feature in natural coastal and riverine water ways, interacting with both the water flow and sediment transport. However, the physical processes governing these interactions are still poorly understood, which makes it difficult to predict sediment transport and morphodynamics in a vegetated environment. We performed a simple experiment to study how sediment transport responds to the presence of flexible, single-blade vegetation, and how this response is influenced by the vegetation density. We found that the skin friction and sediment transport are reduced in a plant patch, and that this effect is larger for denser vegetation. We then evaluated several methods to calculate the skin friction in a vegetated flow, which is the key to sediment transport prediction. Among these, the inversion of bed load transport formulas and the Einstein and Banks (1950) methods appeared to produce the most reasonable values of the skin friction. Finally, we suggest using the parameter α, which is the ratio of the skin friction computed by these methods to the total bed shear stress, to make more realistic sediment transport predictions in morphodynamic models.

  9. New methods to directly measure adhesive stress and movement on glass

    NASA Astrophysics Data System (ADS)

    Watts, David C.; Marouf, A. S.; Heindl, Detlef

    2002-09-01

    Practical scientific methods have been devised to measure cure-shrinkage phenomena for a small-volume disk geometry of adhesive agents, in liquid or paste form. These can be conducted simply, reproducibly and quickly, typically 5-120 min, once the apparati are set up. Originally utilised to measure shrinkage behavior in photocuring dental adhesives and biomaterials, the measurements may be applied as well to adhesives for fiber optic and optical applications. They are especially suitable for UV and visible-light curing adhesives. The 'bonded-disk' method is used for the measurement of shrinkage-strain kinetics and the Bioman method for shrinkage-stress of adhesives.

  10. The Effect of Peel Stress on the Strength of Adhesively Bonded Joints

    SciTech Connect

    Guess, T.R.; Metzinger, K.E.

    1998-10-14

    Composite wind turbine blades are often attached to a metallic structure with an adhesive bond. The objective of this investigation is to determine which parameters affect the durability of these adhesively bonded joints. The composite-to-steel joint considered in this study typically fails when the adhesive debonds from the steel adherend. Previously, this joint was monotonically loaded in either compression or tension. Compressive and tensile axial loads of the same magnitude produce adhesive stresses with very similar magnitudes but opposite signs. (For the joint considered, tensile loads produce compressive peeh stresses in the adhesive at the location where debonding initiates.) The tensile specimens failed at much higher loads, establishing that the sign of the adhesive peel stresses strongly influences the single-cycle strength of these joints. Building on this earlier work, this study demonstrates that the adhesive peel stresses are also critical for fatigue loading. The results of low-cycle (axial) and high- cycle (bending) fatigue tests are presented. To complement the test results, finite element analyses demonstrate the localized nature of the peel stresses that develop in the adhesive. In addition, these analyses are used to investigate some of the causes of these peel stresses.

  11. Effect of Bioactive Glass air Abrasion on Shear Bond Strength of Two Adhesive Resins to Decalcified Enamel

    PubMed Central

    Eshghi, Alireza; Khoroushi, Maryam; Rezvani, Alireza

    2014-01-01

    Objective: Bioactive glass air abrasion is a conservative technique to remove initial decalcified tissue and caries. This study examined the shear bond strength of composite resin to sound and decalcified enamel air-abraded by bioactive glass (BAG) or alumina using etch-and-rinse and self-etch adhesives. Materials and Methods: Forty-eight permanent molars were root-amputated and sectioned mesiodistally. The obtained 96 specimens were mounted in acrylic resin; the buccal and lingual surfaces remained exposed. A demineralizing solution was used to decalcify half the specimens. Both sound and decalcified specimens were divided into two groups of alumina and bioactive glass air abrasion. In each group, the specimens were subdivided into two subgroups of Clearfil SE Bond or OptiBond FL adhesives (n=12). Composite resin cylinders were bonded on enamel surfaces cured and underwent thermocycling. The specimens were tested for shear bond strength. Data were analyzed using SPSS 16.0 and three-way ANOVA (α=0.05). Similar to the experimental groups, the enamel surface of one specimen underwent SEM evaluation. Results: No significant differences were observed in composite resin bond strength subsequent to alumina or bioactive glass air abrasion preparation techniques (P=0.987). There were no statistically significant differences between the bond strength of etch-and-rinse and self-etch adhesive groups (P=1). Also, decalcified or intact enamel groups had no significant difference (P=0.918). However, SEM analysis showed much less enamel irregularities with BAG air abrasion compared to alumina air abrasion. Conclusion: Under the limitations of this study, preparation of both intact and decalcified enamel surfaces with bioactive glass air abrasion results in similar bond strength of composite resin in comparison with alumina air abrasion using etch-&-rinse or self-etch adhesives. PMID:25628694

  12. Shear Bond Strength of Calcium Enriched Mixture Cement and Mineral Trioxide Aggregate to Composite Resin with Two Different Adhesive Systems

    PubMed Central

    Savadi Oskoee, Siavash; Bahari, Mahmoud; Kimyai, Soodabeh; Motahhari, Paria; Eghbal, Mohammad Jafar; Asgary, Saeed

    2014-01-01

    Objective: Immediate restoration after vital pulp therapy is essential in order to create and maintain effective coronal seal. Purpose of Study: The aim of this study was to evaluate the shear bond strength of recently used pulp capping materials: white mineral trioxide aggregate (MTA), and calcium enriched mixture cement (CEM) to composite resin with the use of etch-and-rinse and self-etch adhesive systems and compare them with the bond strength of commonly used resin modified glass ionomer (RMGI) cement. Materials and Methods: Forty specimens from each test material were fabricated, measuring 4 mm in diameter and 2 mm in depth. The specimens of each material were divided into 2 groups of 20 specimens according to the adhesive system (Single Bond vs. Clearfil SE Bond) used for bonding of resin composite. The shear bond strength values were measured at a crosshead speed of 1.0 mm/min and fractured surfaces were examined. Data were analyzed using two-way ANOVA and a post hoc Tukey’s test (P<0.05). Results: Analysis of data showed a significantly higher bond strength for RMGI compared to MTA and CEM (P<0.001); however, no significant differences were observed in the bond strength values of MTA and CEM (P=0.9). Furthermore, there were no significant differences in relation to the type of the adhesive system irrespective of the type of the material used (P=0.95) All the failures were of cohesive type in RMGI, MTA and CEM. Conclusion: Bond strength of RMGI cement to composite resin was higher than that of MTA or CEM cement irrespective of the type of the adhesive system. PMID:25628696

  13. In vitro evaluation of casein phosphopeptide-amorphous calcium phosphate effect on the shear bond strength of dental adhesives to enamel

    PubMed Central

    Shadman, Niloofar; Ebrahimi, Shahram Farzin; Shoul, Maryam Azizi; Sattari, Hasti

    2015-01-01

    Background: Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) is applied for remineralization of early caries lesions or tooth sensitivity conditions and may affect subsequent resin bonding. This in vitro study investigated the effect of CPP-ACP on the shear bond strength of dental adhesives to enamel. Materials and Methods: Sixty extracted human molar teeth were selected and randomly divided into three groups and six subgroups. Buccal or lingual surfaces of teeth were prepared to create a flat enamel surface. Adhesives used were Tetric N-Bond, AdheSE and AdheSE One F. In three subgroups, before applying adhesives, enamel surfaces were treated with Tooth Mousse CPP-ACP for one hour, rinsed and stored in 37°C temperature with 100% humidity. This procedure was repeated for 5 days and then adhesives were applied and Tetric N-Ceram composite was adhered to the enamel. This procedure was also fulfilled for the other three subgroups without CPP-ACP treatment. After 24 hour water storage, samples were tested for shear bond strength test in a universal testing machine. Failure modes were determined by stereomicroscope. Data were analyzed by t-test and one-way analysis of variance with P < 0.05 as the level of significance. Results: In comparison between applied and non-applied CPP-ACP subgroups, there was no significant decrease in the shear bond strength to enamel only in Tetric N-Bond (P > 0.05). In non-applied CPP-ACP subgroups, there were statistically significant differences among all subgroups. Tetric N-Bond had the highest and AdheSE One F had the lowest shear bond strength. Conclusion: CPP-ACP application reduces the shear bond strength of AdheSE and AdheSE One F to enamel but not Tetric N-Bond. PMID:25878683

  14. Estimation of the shear stress on the surface of an aortic valve leaflet.

    PubMed

    Weston, M W; LaBorde, D V; Yoganathan, A P

    1999-01-01

    The limited durability of xenograft heart valves and the limited supply of allografts have sparked interest in tissue engineered replacement valves. A bioreactor for tissue engineered valves must operate at conditions that optimize the biosynthetic abilities of seeded cells while promoting their adherence to the leaflet matrix. An important parameter is shear stress, which is known to influence cellular behavior and may thus be crucial in bioreactor optimization. Therefore, an accurate estimate of the shear stress on the leaflet surface would not only improve our understanding of the mechanical environment of aortic valve leaflets, but it would also aid in bioreactor design. To estimate the shear stress on the leaflet surface, two-component laser-Doppler velocimetry measurements have been conducted inside a transparent polyurethane valve with a trileaflet structure similar to the native aortic valve. Steady flow rates of 7.5, 15.0, and 22.5 L/min were examined to cover the complete range possible during the cardiac cycle. The laminar shear stresses were calculated by linear regression of four axial velocity measurements near the surface of the leaflet. The maximum shear stress recorded was 79 dyne/cm2, in agreement with boundary layer theory and previous experimental and computational studies. This study has provided a range of shear stresses to be explored in bioreactor design and has defined a maximum shear stress at which cells must remain adherent upon a tissue engineered construct.

  15. Research on measurement of bed shear stress under wave-current interaction

    NASA Astrophysics Data System (ADS)

    Xu, Hua; Xia, Yun-feng; Ma, Bing-he; Hao, Si-yu; Zhang, Shi-zhao; Du, De-jun

    2015-06-01

    The movement of sediment in estuary and on coast is directly restricted by the bed shear stress. Therefore, the research on the basic problem of sediment movement by the bed shear stress is an important way to research the theory of sediment movement. However, there is not a measuring and computing method to measure the bed shear stress under a complicated dynamic effect like wave and current. This paper describes the measurement and test research on the bed shear stress in a long launder of direct current by the new instrument named thermal shearometer based on micro-nanotechnology. As shown by the research results, the thermal shearometer has a high response frequency and strong stability. The measured results can reflect the basic change of the bed shear stress under wave and wave-current effect, and confirm that the method of measuring bed shear stress under wave-current effect with thermal shearometer is feasible. Meanwhile, a preliminary method to compute the shear stress compounded by wave-current is put forward according to the tested and measured results, and then a reference for further study on the basic theory of sediment movement under a complicated dynamic effect is provided.

  16. Effects of Two Soft Drinks on Shear Bond Strength and Adhesive Remnant Index of Orthodontic Metal Brackets

    PubMed Central

    Sajadi, Soodabeh Sadat; Eslami Amirabadi, Gholamreza; Sajadi, Sepideh

    2014-01-01

    Objective: Bond failure of brackets during orthodontic treatment is a common problem; which results in treatment interference, increased treatment time and prolonged clinical time for rebonding of failed brackets. The purpose of this study was to evaluate the effects of Coca-Cola and a non-alcoholic beer on the shear bond strength and adhesive remnant index (ARI) of orthodontic metal brackets in vitro. Materials and Methods: Eighty intact human premolars were divided into two experimental groups of Coca-Cola and non-alcoholic beer (Istak), and a control group of artificial saliva. Over a period of thirty days, the test groups were immersed in the respective soft drinks for 5 minutes, twice a day. For the remainder of the time, they were kept in artificial saliva at 37°C. The control group was stored in artificial saliva during the experiment. All samples were subjected to shearing forces using Universal Testing Machine. ARI was determined with a stereomicroscope at ×12 magnification. The data of shear bond strength were statistically analyzed by one-way ANOVA and Tukey’s Post-Hoc test and the data of ARI scores were analyzed by Kruskal-Wallis test. Results: No significant difference was observed in ARIs of the three groups (P≤ 0.552). The shear bond strength of Coke group was significantly lower than that of the two other groups (P≤ 0.035); but there was no significant difference between the shear bond strength of Istak and the control group (P≤ 0.999). Conclusion: Coca-Cola decreased the shear bond strength of orthodontic brackets. PMID:25584049

  17. Red blood cell damage by shear stress for different blood types

    NASA Astrophysics Data System (ADS)

    Arwatz, Gilad; Bedkowski, Katherine; Smits, Alexander

    2011-11-01

    In surgical practice, blood damage caused by medical devices is often a limiting factor in the duration of an acute procedure or in chronic exposures such as hemodialysis. In order to establish guidelines for designing medical devices, a study was conducted to determine the relationship between shear stress and damage to red blood cells using a concentric Couette device. By measuring the hemolysis level for various shear stresses and exposure times, a non-dimensional relationship between shear stress and blood damage for different blood types was established. Funding provided by Princeton University's Project X.

  18. On the axial and interfacial shear stresses due to thermal mismatch in hybrid composites

    SciTech Connect

    Rossettos, J.N.; Shen, X.

    1994-12-31

    An analytical model is formulated which attempts to account for the axial and the interfacial shear stresses which can develop in hybrid fiber composites due to the mismatch in coefficients of thermal expansion and Youngs modulus. A finite width hybrid composite monolayer with alternating high modulus and low modulus fibers is considered. To properly account for the interfacial shear between fiber and matrix, a modified shear lag model is used, which permits extensional deformation in the matrix in the fiber direction. Typical stresses due solely to temperature changes are calculated, and show steep boundary layer edge stresses at free corners.

  19. Adhesion of platelets to purified solid-phase von Willebrand factor: effects of wall shear rate, ADP, thrombin, and ristocetin.

    PubMed

    Olson, J D; Zaleski, A; Herrmann, D; Flood, P A

    1989-07-01

    When platelets are stimulated with adenosine diphosphate (ADP), thrombin, or ristocetin, they bind soluble von Willebrand factor (vWF). In contrast, platelets adhere to solid-phase vWF without apparent stimulus. This work characterizes the adhesion of washed human platelets to highly purified solid-phase human vWF. VWF (iodine 125-labeled vWF) was demonstrated to bind in a quantifiable fashion to the internal surfaces of glass capillary tubes, saturating at a surface density of 3.0 mg/ml. The multimeric structure of bound vWF was the same as that of normal vWF. Platelets were washed, labeled with indium 111, and resuspended with washed red blood cells (RBCs) in balanced salt solution containing Ca++, Mg++, and apyrase. The washed platelet RBC suspension was aspirated through capillary tubes to which vWF was adsorbed. Adhesion of platelets to adsorbed vWF was directly dependent on the surface density of vWF. Increasing wall shear rate (100 to 5000 sec-1) produced increasing platelet adhesion to maximum reached at 2500 sec-1. Platelets bound to the solid-phase vWF in an irreversible fashion, and, as demonstrated with scanning electron microscopy, they spread on the surface. When used to stimulate the platelets, ADP, thrombin, and ristocetin all increased the platelet adhesion to solid-phase vWF. ADP- and thrombin-stimulated reactions were inhibited by prior treatment of the platelets with 5'-p-fluorosulfonylbenzoyl adenosine. This inhibitor of ADP binding had no effect on the baseline platelet adhesion reaction (without ADP or thrombin). Adenosine in concentration up to 1 mmol/L failed to inhibit adhesion. The data demonstrate that washed platelets adhere to solid-phase vWF without added agonists, that the reaction is dependent on surface density vWF and wall shear rate, that they bind irreversibly, and that they demonstrate surface spreading. In addition, these platelets can be stimulated to increase their adherence to vWF by using ADP, thrombin, and ristocetin.

  20. Method for measuring surface shear stress magnitude and direction using liquid crystal coatings

    NASA Technical Reports Server (NTRS)

    Reda, Daniel C. (Inventor)

    1995-01-01

    A method is provided for determining surface shear magnitude and direction at every point on a surface. The surface is covered with a shear stress sensitive liquid crystal coating and illuminated by white light from a normal direction. A video camera is positioned at an oblique angle above the surface to observe the color of the liquid crystal at that angle. The shear magnitude and direction are derived from the color information. A method of calibrating the device is also provided.

  1. Plantar shear stress distributions in diabetic patients with and without neuropathy

    PubMed Central

    Yavuz, Metin

    2014-01-01

    Background The exact pathology of diabetic foot ulcers remains to be resolved. Evidence suggests that plantar shear forces play a major role in diabetic ulceration. Unfortunately, only a few manuscripts exist on the clinical implications of plantar shear. The purpose of this study was to compare global and regional peak plantar stress values in three groups; diabetic patients with neuropathy, diabetic patients without neuropathy and healthy control subjects. Methods Fourteen diabetic neuropathic patients, 14 non-neuropathic diabetic control and 11 non-diabetic control subjects were recruited. Subjects walked on a custom-built stress plate that quantified plantar pressures and shear. Four stress variables were analyzed; peak pressure, peak shear, peak pressure-time and shear-time integral. Findings Global peak values of peak shear (p=0.039), shear-time integral (p=0.002) and pressure-time integral (p=0.003) were significantly higher in the diabetic neuropathic group. Local peak shear stress and shear-time integral were also significantly higher in diabetic neuropathic patients compared to both control groups, in particular, at the hallux and central forefoot. Local peak pressure and pressure-time integral were significantly different between the three groups at the medial and lateral forefoot. Interpretation Plantar shear and shear-time integral magnitudes were elevated in diabetic patients with peripheral neuropathy, which indicates the potential clinical significance of these factors in ulceration. It is thought that further investigation of plantar shear would lead to a better understanding of ulceration pathomechanics, which in turn will assist researchers in developing more effective preventive devices and strategies. PMID:24332719

  2. Effect of Wall Shear Stress on Corrosion Inhibitor Film Performance

    NASA Astrophysics Data System (ADS)

    Canto Maya, Christian M.

    In oil and gas production, internal corrosion of pipelines causes the highest incidence of recurring failures. Ensuring the integrity of ageing pipeline infrastructure is an increasingly important requirement. One of the most widely applied methods to reduce internal corrosion rates is the continuous injection of chemicals in very small quantities, called corrosion inhibitors. These chemical substances form thin films at the pipeline internal surface that reduce the magnitude of the cathodic and/or anodic reactions. However, the efficacy of such corrosion inhibitor films can be reduced by different factors such as multiphase flow, due to enhanced shear stress and mass transfer effects, loss of inhibitor due to adsorption on other interfaces such as solid particles, bubbles and droplets entrained by the bulk phase, and due to chemical interaction with other incompatible substances present in the stream. The first part of the present project investigated the electrochemical behavior of two organic corrosion inhibitors (a TOFA/DETA imidazolinium, and an alkylbenzyl dimethyl ammonium chloride), with and without an inorganic salt (sodium thiosulfate), and the resulting enhancement. The second part of the work explored the performance of corrosion inhibitor under multiphase (gas/liquid, solid/liquid) flow. The effect of gas/liquid multiphase flow was investigated using small and large scale apparatus. The small scale tests were conducted using a glass cell and a submersed jet impingement attachment with three different hydrodynamic patterns (water jet, CO 2 bubbles impact, and water vapor cavitation). The large scale experiments were conducted applying different flow loops (hilly terrain and standing slug systems). Measurements of weight loss, linear polarization resistance (LPR), and adsorption mass (using an electrochemical quartz crystal microbalance, EQCM) were used to quantify the effect of wall shear stress on the performance and integrity of corrosion inhibitor

  3. Visualization and Measurement of Surface Shear Stress Vector Distributions Using Liquid Crystal Coatings

    NASA Technical Reports Server (NTRS)

    Reda, Daniel C.; Wilder, Michael C.

    1998-01-01

    When a shear-sensitive liquid crystal coating is illuminated from the normal direction by white light and observed from an oblique above-plane view angle, its color-change response to shear depends on both shear stress vector magnitude and the direction of the applied shear vector relative to the observer's in-plane line of sight. At any point, the maximum color change is always seen or measured when the local shear vector is aligned with, and directed away from, the observer; the magnitude of the color change at this vector/observer aligned orientation scales directly with shear stress magnitude. Conversely, any point exposed to a shear vector with a component directed toward the observer exhibits a noncolor-change response, always characterized by a rusty red or brown color, independent of both shear magnitude and direction. Based on this knowledge, full-surface shear stress vector visualization and measurement methodologies were formulated and successfully demonstrated. The present paper reviews the observations and measurements that led to the development of these methodologies and applications of both are discussed.

  4. Effect of salivary contamination during different bonding stages on shear dentin bond strength of one-step self-etch and total etch adhesive

    PubMed Central

    Kermanshah, H.; Ghabraei, Sh.; Bitaraf, T.

    2010-01-01

    Objective: This study evaluated the effect of saliva contamination during bonding procedures without removing saliva on shear dentin bond strength of three adhesive generations when rubber dam isolation is not feasible. Materials and Methods: Flat superficial dentin surfaces of seventy-two extracted human molars were randomly divided into three groups (A: Scotch Bond MP Plus (SBMP), B: Single Bond (SB), C: Prompt L-Pop) according to the applied adhesives and twelve subgroups (n=6) according to the following saliva contamination applied in different bonding steps. The specimens were contaminated with saliva after etching (A1 and B1), after primer application (A2), after adhesive application before polymerization (A3, B2 and C1), and after adhesive polymerization (A4, B3 and C2). Three subgroups were not contaminated as controls (A5, B4 and C3). Resin composite was placed on dentin subsequently followed by thermocycling. Shear test was performed by Universal testing machine at 0.5 mm/min crosshead speed. The collected data were statically analyzed using one and two-way ANOVA and Tukey HSD. Results: In contrast to SBMP and SB, the mean shear bond strength of Promote L-Pop was not significantly different between contaminated and uncontaminated subgroups. Mean shear bond strengths of SBMP subgroups contaminated after adhesive polymerization or uncontaminated were significantly higher compared to the other two groups (p<0.05). Conclusion: Unlike Promote L-Pop, saliva contamination could reduce shear bond strength of the total-etch adhesives. Furthermore, the step of bonding procedures and the type of adhesive seems to be effective on the bond strength of adhesive contaminated with saliva. PMID:21998787

  5. Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears

    SciTech Connect

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2011-04-15

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium ExB velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or ''profile shear'' in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) ExB and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a ''null'' toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the ExB shear and parallel velocity (Coriolis force) pinching components from the larger ''diffusive'' parallel velocity shear driven component and

  6. Concurrent shear stress and chemical stimulation of mechano-sensitive cells by discontinuous dielectrophoresis.

    PubMed

    Soffe, Rebecca; Baratchi, Sara; Tang, Shi-Yang; Mitchell, Arnan; McIntyre, Peter; Khoshmanesh, Khashayar

    2016-03-01

    Microfluidic platforms enable a variety of physical or chemical stimulation of single or multiple cells to be examined and monitored in real-time. To date, intracellular calcium signalling research is, however, predominantly focused on observing the response of cells to a single mode of stimulation; consequently, the sensitising/desensitising of cell responses under concurrent stimuli is not well studied. In this paper, we provide an extended Discontinuous Dielectrophoresis procedure to investigate the sensitising of chemical stimulation, over an extensive range of shear stress, up to 63 dyn/cm(2), which encompasses shear stresses experienced in the arterial and venus systems (10 to 60 dyn/cm(2)). Furthermore, the TRPV4-selective agonist GSK1016790A, a form of chemical stimulation, did not influence the ability of the cells' to remain immobilised under high levels of shear stress; thus, enabling us to investigate shear stress stimulation on agonism. Our experiments revealed that shear stress sensitises GSK1016790A-evoked intracellular calcium signalling of cells in a shear-stimulus dependent manner, as observed through a reduction in the cellular response time and an increase in the pharmacological efficacy. Consequently, suggesting that the role of TRPV4 may be underestimated in endothelial cells-which experience high levels of shear stress. This study highlights the importance of conducting studies at high levels of shear stress. Additionally, our approach will be valuable for examining the effect of high levels of shear on different cell types under different conditions, as presented here for agonist activation. PMID:27099646

  7. Matrix mechanics and fluid shear stress control stem cells fate in three dimensional microenvironment.

    PubMed

    Chen, Guobao; Lv, Yonggang; Guo, Pan; Lin, Chongwen; Zhang, Xiaomei; Yang, Li; Xu, Zhiling

    2013-07-01

    Stem cells have the ability to self-renew and to differentiate into multiple mature cell types during early life and growth. Stem cells adhesion, proliferation, migration and differentiation are affected by biochemical, mechanical and physical surface properties of the surrounding matrix in which stem cells reside and stem cells can sensitively feel and respond to the microenvironment of this matrix. More and more researches have proven that three dimensional (3D) culture can reduce the gap between cell culture and physiological environment where cells always live in vivo. This review summarized recent findings on the studies of matrix mechanics that control stem cells (primarily mesenchymal stem cells (MSCs)) fate in 3D environment, including matrix stiffness and extracellular matrix (ECM) stiffness. Considering the exchange of oxygen and nutrients in 3D culture, the effect of fluid shear stress (FSS) on fate decision of stem cells was also discussed in detail. Further, the difference of MSCs response to matrix stiffness between two dimensional (2D) and 3D conditions was compared. Finally, the mechanism of mechanotransduction of stem cells activated by matrix mechanics and FSS in 3D culture was briefly pointed out.

  8. Theory to Predict Shear Stress on Cells in Turbulent Blood Flow

    PubMed Central

    Morshed, Khandakar Niaz; Bark Jr., David; Forleo, Marcio; Dasi, Lakshmi Prasad

    2014-01-01

    Shear stress on blood cells and platelets transported in a turbulent flow dictates the fate and biological activity of these cells. We present a theoretical link between energy dissipation in turbulent flows to the shear stress that cells experience and show that for the case of physiological turbulent blood flow: (a) the Newtonian assumption is valid, (b) turbulent eddies are universal for the most complex of blood flow problems, and (c) shear stress distribution on turbulent blood flows is possibly universal. Further we resolve a long standing inconsistency in hemolysis between laminar and turbulent flow using the theoretical framework. This work demonstrates that energy dissipation as opposed to bulk shear stress in laminar or turbulent blood flow dictates local mechanical environment of blood cells and platelets universally. PMID:25171175

  9. Animal models of surgically manipulated flow velocities to study shear stress-induced atherosclerosis.

    PubMed

    Winkel, Leah C; Hoogendoorn, Ayla; Xing, Ruoyu; Wentzel, Jolanda J; Van der Heiden, Kim

    2015-07-01

    Atherosclerosis is a chronic inflammatory disease of the arterial tree that develops at predisposed sites, coinciding with locations that are exposed to low or oscillating shear stress. Manipulating flow velocity, and concomitantly shear stress, has proven adequate to promote endothelial activation and subsequent plaque formation in animals. In this article, we will give an overview of the animal models that have been designed to study the causal relationship between shear stress and atherosclerosis by surgically manipulating blood flow velocity profiles. These surgically manipulated models include arteriovenous fistulas, vascular grafts, arterial ligation, and perivascular devices. We review these models of manipulated blood flow velocity from an engineering and biological perspective, focusing on the shear stress profiles they induce and the vascular pathology that is observed.

  10. Experimental and computational validation of Hele-Shaw stagnation flow with varying shear stress

    NASA Astrophysics Data System (ADS)

    Tefft, Brandon J.; Kopacz, Adrian M.; Liu, Wing Kam; Liu, Shu Q.

    2013-12-01

    An in vitro flow model system with continuous variation of fluid shear stress can be used to test cell responses to a range of shear stresses. In this investigation, we validated such a flow system computationally for steady and unsteady flow conditions and experimentally for steady flow conditions. The unsteady flow validation is important for studying cells such as endothelial cells that experience unsteady flow conditions in their native environment. The system is capable of exposing cells in different regions of the chamber to steady or unsteady shear stress conditions with average values ranging linearly from 0 to 30 dyn/cm. These tests and analyses demonstrate that the variable-width parallel plate flow system can be used to test the influence of a range of steady and unsteady fluid shear stress levels on cell activities.

  11. Relationship between Microtubule Network Structure and Intracellular Transport in Cultured Endothelial Cells Affected by Shear Stress

    NASA Astrophysics Data System (ADS)

    Kudo, Susumu; Ikezawa, Kenji; Ikeda, Mariko; Tanishita, Kazuo

    Endothelial cells (ECs) that line the inner surface of blood vessels are barriers to the transport of various substances into or from vessel walls, and are continuously exposed to shear stress induced by blood flow in vivo. Shear stress affects the cytoskeleton (e.g., microtubules, microfilaments, intermediate filaments), and affects the transport of macromolecules. Here, the relationship between the microtubule network structure and this transport process for albumin uptake within cultured aortic endothelial cells affected by shear stress was studied. Based on fluorescent images of albumin uptake obtained by using confocal laser scanning microscopy (CLSM), both the microtubule network and albumin uptake in ECs were disrupted by colchicine and were affected by shear stress loading.

  12. Theory to predict shear stress on cells in turbulent blood flow.

    PubMed

    Morshed, Khandakar Niaz; Bark, David; Forleo, Marcio; Dasi, Lakshmi Prasad

    2014-01-01

    Shear stress on blood cells and platelets transported in a turbulent flow dictates the fate and biological activity of these cells. We present a theoretical link between energy dissipation in turbulent flows to the shear stress that cells experience and show that for the case of physiological turbulent blood flow: (a) the Newtonian assumption is valid, (b) turbulent eddies are universal for the most complex of blood flow problems, and (c) shear stress distribution on turbulent blood flows is possibly universal. Further we resolve a long standing inconsistency in hemolysis between laminar and turbulent flow using the theoretical framework. This work demonstrates that energy dissipation as opposed to bulk shear stress in laminar or turbulent blood flow dictates local mechanical environment of blood cells and platelets universally.

  13. An equilibrium method for prediction of transverse shear stresses in a thick laminated plate

    NASA Technical Reports Server (NTRS)

    Chaudhuri, R. Z.

    1986-01-01

    First two equations of equilibrium are utilized to compute the transverse shear stress variation through thickness of a thick laminated plate after in-plane stresses have been computed using an assumed quadratic displacement triangular element based on transverse inextensibility and layerwise constant shear angle theory (LCST). Centroid of the triangle is the point of exceptional accuracy for transverse shear stresses. Numerical results indicate close agreement with elasticity theory. An interesting comparison between the present theory and that based on assumed stress hybrid finite element approach suggests that the latter does not satisfy the condition of free normal traction at the edge. Comparison with numerical results obtained by using constant shear angle theory suggests that LCST is close to the elasticity solution while the CST is closer to classical (CLT) solution. It is also demonstrated that the reduced integration gives faster convergence when the present theory is applied to a thin plate.

  14. Quantification of Interfibrillar Shear Stress in Aligned Soft Collagenous Tissues via Notch Tension Testing

    NASA Astrophysics Data System (ADS)

    Szczesny, Spencer E.; Caplan, Jeffrey L.; Pedersen, Pal; Elliott, Dawn M.

    2015-10-01

    The mechanical function of soft collagenous tissues is largely determined by their hierarchical organization of collagen molecules. While collagen fibrils are believed to be discontinuous and transfer load through shearing of the interfibrillar matrix, interfibrillar shear stresses have never been quantified. Scaling traditional shear testing procedures down to the fibrillar length scale is impractical and would introduce substantial artifacts. Here, through the use of a novel microscopic variation of notch tension testing, we explicitly demonstrate the existence of interfibrillar shear stresses within tendon fascicles and provide the first measurement of their magnitude. Axial stress gradients along the sample length generated by notch tension testing were measured and used to calculate a value of 32 kPa for the interfibrillar shear stress. This estimate is comparable to the interfibrillar shear stress predicted by previous multiscale modeling of tendon fascicles, which supports the hypothesis that fibrils are discontinuous and transmit load through interfibrillar shear. This information regarding the structure-function relationships of tendon and other soft collagenous tissues is necessary to identify potential causes for tissue impairment with degeneration and provide the foundation for developing regenerative repair strategies or engineering biomaterials for tissue replacement.

  15. A High shear stress segment along the San Andreas Fault: Inferences based on near-field stress direction and stress magnitude observations in the Carrizo Plain Area

    SciTech Connect

    Castillo, D. A.,; Younker, L.W.

    1997-01-30

    Nearly 200 new in-situ determinations of stress directions and stress magnitudes near the Carrizo plain segment of the San Andreas fault indicate a marked change in stress state occurring within 20 km of this principal transform plate boundary. A natural consequence of this stress transition is that if the observed near-field ``fault-oblique`` stress directions are representative of the fault stress state, the Mohr-Coulomb shear stresses resolved on San Andreas sub-parallel planes are substantially greater than previously inferred based on fault-normal compression. Although the directional stress data and near-hydrostatic pore pressures, which exist within 15 km of the fault, support a high shear stress environment near the fault, appealing to elevated pore pressures in the fault zone (Byerlee-Rice Model) merely enhances the likelihood of shear failure. These near-field stress observations raise important questions regarding what previous stress observations have actually been measuring. The ``fault-normal`` stress direction measured out to 70 km from the fault can be interpreted as representing a comparable depth average shear strength of the principal plate boundary. Stress measurements closer to the fault reflect a shallower depth-average representation of the fault zone shear strength. If this is true, only stress observations at fault distances comparable to the seismogenic depth will be representative of the fault zone shear strength. This is consistent with results from dislocation monitoring where there is pronounced shear stress accumulation out to 20 km of the fault as a result of aseismic slip within the lower crust loading the upper locked section. Beyond about 20 km, the shear stress resolved on San Andreas fault-parallel planes becomes negligible. 65 refs., 15 figs.

  16. Shear Stress in Nickel and Ni-60Co under One-Dimensional Shock Loading

    SciTech Connect

    Workman, A.; Wallwork, A.; Meziere, Y. J. E.; Millett, J. C. F.; Bourne, N. K.

    2006-07-28

    The dynamic response of pure nickel (Ni), and its alloy, Ni-60Co (by weight %), has been investigated during one-dimensional shock loading. Few materials' properties are different and the only significantly altered feature is the reduced stacking fault energy (SFE) for the Ni-60Co. This paper considers the effect of this reduced SFE on the shear strength. Data (in terms of shock stress, particle velocity and shock velocity) are also presented. The influence on the shear stress, {tau} of cobalt additions in nickel are then investigated and presented. Results indicate that the lateral stress is increasing in both materials with the increasing impact stress. The shear stress was found to be higher in the nickel than in the Ni-60Co. The progressive decrease of the lateral stress noted during loading indicates a complex mechanism of deformation behind the shock front.

  17. Effect of hydrofluoric acid etching on shear bond strength of an indirect resin composite to an adhesive cement.

    PubMed

    Hori, Sayaka; Minami, Hiroyuki; Minesaki, Yoshito; Matsumura, Hideo; Tanaka, Takuo

    2008-07-01

    This study evaluated the effect of 1% hydrofluoric acid (HF) treatment on the bonding of an adhesive cement (Panavia F 2.0) to an indirect resin composite (Estenia C&B). Pairs of composite disks (10 and 8 mm in diameter by 3 mm thickness) were prepared. Adhesive surfaces were pretreated with either airborne particle abrasion or HF etching before being soaked for 30 seconds, five minutes or 10 minutes, with or without application of silane coupling agent. Adhesive specimens were fabricated by cementing a pair of treated disks. Shear bond strength was determined before and after 50,000 times of thermocycling (4 and 60 degrees C). All data were statistically analyzed using two-way ANOVA and Bonferroni's test (a=0.05). Bond strength achieved with five minutes of HF etching (18.3+/-1.1 MPa) was significantly higher (P=0.0025) than that obtained with airborne particle abrasion followed by application of silane coupling agent (14.3+/-1.8 MPa) after thermocycling.

  18. Bed Shear Stress under Complex Flow Conditions - The Case of Megech River, Ethiopia

    NASA Astrophysics Data System (ADS)

    Mehari, Michael; Dessie, Mekete; Abate, Mengiste

    2014-05-01

    Bed shear stress is a fundamental variable in river studies to link flow conditions to sediment transport. It is, however, difficult to estimate this variable accurately, particularly in complex flow conditions. This study compares shear stress estimated from the log profile, the depth-slope product and outputs from a two-dimensional hydraulic model. Vertical velocity profile observations from Megech River (one of the main rivers flowing into Lake Tana, upper Blue Nile Basin, Ethiopia) using SEBA Mini current meter M1attached with signal counter Z6-SEBA HAD under typical field conditions are used to evaluate the precision of different methods for estimating local boundary shear stress from velocity measurements. Results show that the velocity profile approach gives consistently lesser shear stress estimates. A comparison of the shear stress distributions derived using the two-dimensional hydraulic model and those estimated using the 1D reach-averaged equation (i.e. the depth-slope product) shows a close correspondence. Mean shear stresses determined using local depth and mean channel slope are only 14% greater than those values determined for the same data using local predictions of both depth and energy slope. As the overall mean shear stress provides a useful index of flow strength, this comparison suggests a good level of confidence in using the reach averaged one-dimensional equation, for which data can easily be collected from cross sectional surveys. However, the variance of the modelled shear stress distribution shows some differences by a factor of 3 to that calculated using the mean channel slope because of the larger uncertainity associated with point depth measurements. Although such models using 1D reach averaged equations are limited to different channel characteristics adhering to diverse model assumptions, they can still provide a useful tool for river-rehabilitation design and assessment, including sediment transport studies.

  19. Association of SIRT1 expression with shear stress induced endothelial progenitor cell differentiation.

    PubMed

    Cheng, Bin-Bin; Yan, Zhi-Qiang; Yao, Qing-Ping; Shen, Bao-Rong; Wang, Ji-Yao; Gao, Li-Zhi; Li, Yu-Qing; Yuan, Hai-Tao; Qi, Ying-Xin; Jiang, Zong-Lai

    2012-12-01

    Shear stress imposed by blood flow is crucial for differentiation of endothelial progenitor cells (EPCs). Histone deacetylase SIRT1 has been shown to play a pivotal role in many physiological processes. However, association of SIRT1 expression with shear stress-induced EPC differentiation remains to be elucidated. The present study was designed to determine the effect of SIRT1 on EPC differentiation induced by shear stress, and to seek the underlying mechanisms. Human umbilical cord blood-derived EPCs were exposed to laminar shear stress of 15 dyn/cm(2) by parallel plate flow chamber system. Shear stress enhanced EPC differentiation toward endothelial cells (ECs) while inhibited to smooth muscle cells (SMCs). The expressions of phospho-Akt, SIRT1 and histone H3 acetylation (Ac-H3) in EPCs were detected after exposure to shear stress for 2, 6, 12, and 24 h, respectively. Shear stress significantly activated Akt phosphorylation, augmented SIRT1 expression and downregulated Ac-H3. SIRT1 siRNA in EPCs diminished the expression of EC markers, but increased the expression of SMC markers, and resulted in upregulation of Ac-H3. Whereas, resveratrol, an activator of SIRT1, had the opposite effects on both EPC differentiation and histone H3 acetylation. Wortmannin, an inhibitor of PI3-kinase, suppressed endothelial differentiation of EPCs, decreased SIRT1, and upregulated Ac-H3 expression. In addition, SIRT1 promoted tube formation of EPCs in matrix gels. These results provided a mechanobiological basis of shear stress-induced EPC differentiation into ECs and suggest that PI3k/Akt-SIRT1-Ac-H3 pathway is crucial in such a process.

  20. Control of shear stress in the epicardial coronary arteries of humans: impairment by atherosclerosis.

    PubMed

    Vita, J A; Treasure, C B; Ganz, P; Cox, D A; Fish, R D; Selwyn, A P

    1989-11-01

    Altered arterial wall shear stress may adversely affect vascular endothelium and contribute to atherogenesis. This study examined the hypothesis that, in humans, dilation of normal coronary arteries with increased flow limits increases in shear stress and that loss of flow-mediated dilation in atherosclerosis results in failure to control shear stress. Coronary blood flow was increased by infusing adenosine (0.022 to 2.2 mg/min) through a 2.5F Doppler flow catheter positioned in the middle segment of the left anterior descending coronary artery in 8 patients with mild atherosclerosis but no flow-limiting stenosis and in 10 patients with entirely smooth coronary arteries. Quantitative angiography and coronary flow velocity were used to estimate shear stress in a proximal segment of the left anterior descending artery exposed to increased flow, but not to adenosine. The peak increase in blood flow was the same in smooth (371 +/- 65%) and irregular (377 +/- 50%) arteries. However, at peak flow, dilation was greater in smooth segments (16.3 +/- 2.7%) than in irregular segments (2.0 +/- 1.5%) (p less than 0.001). In each patient, smooth segments dilated with increasing shear stress (slope 7.4 +/- 0.9%), whereas irregular segments dilated less (slope 0.9 +/- 0.6%) and showed greater increases in shear stress (p less than 0.01). The peak increase in shear stress was less in smooth (189 +/- 23%) than in irregular (365 +/- 52%) segments (p less than 0.01). These results suggest a control mechanism in normal coronary arteries whereby increases in shear stress stimulate vasodilation and thus limit further increases in this force at the endothelial surface.(ABSTRACT TRUNCATED AT 250 WORDS)

  1. Fluid Shear Stress Sensitizes Cancer Cells to Receptor-Mediated Apoptosis via Trimeric Death Receptors

    PubMed Central

    Mitchell, Michael J.

    2013-01-01

    Cancer metastasis, the process of cancer cell migration from a primary to distal location, typically leads to a poor patient prognosis. Hematogenous metastasis is initiated by intravasation of circulating tumor cells (CTCs) into the bloodstream, which are then believed to adhere to the luminal surface of the endothelium and extravasate into distal locations. Apoptotic agents such as tumor necrosis factor (TNF) apoptosis-inducing ligand (TRAIL), whether in soluble ligand form or expressed on the surface of natural killer (NK) cells, have shown promise in treating CTCs to reduce the probability of metastasis. The role of hemodynamic shear forces in altering the cancer cell response to receptor-mediated apoptosis has not been previously investigated. Here, we report that human colon cancer COLO 205 and prostate cancer PC-3 cells exposed to a uniform fluid shear stress in a cone-and-plate viscometer become sensitized to TRAIL-induced apoptosis. Shear-induced sensitization directly correlated with the application of fluid shear stress, and TRAIL-induced apoptosis increased in a fluid shear stress force- and time-dependent manner. In contrast, TRAIL-induced necrosis was not affected by the application fluid shear stress. Interestingly, fluid shear stress did not sensitize cancer cells to apoptosis when treated with doxorubicin, which also induces apoptosis in cancer cells. Caspase inhibition experiments revealed that shear stress-induced sensitization to TRAIL occurs via caspase-dependent apoptosis. These results suggest that physiological fluid shear force can modulate receptor-mediated apoptosis of cancer cells in the presence of apoptotic agents. PMID:25110459

  2. Activation and shedding of platelet glycoprotein IIb/IIIa under non-physiological shear stress.

    PubMed

    Chen, Zengsheng; Mondal, Nandan K; Ding, Jun; Koenig, Steven C; Slaughter, Mark S; Griffith, Bartley P; Wu, Zhongjun J

    2015-11-01

    The purpose of this study was to investigate the influence of non-physiological high shear stress on activation and shedding of platelet GP IIb/IIIa receptors. The healthy donor blood was exposed to three levels of high shear stresses (25, 75, 125 Pa) from the physiological to non-physiological status with three short exposure time (0.05, 0.5, 1.5 s), created by a specific blood shearing system. The activation and shedding of the platelet GPIIb/IIIa were analyzed using flow cytometry and enzyme-linked immunosorbent assay. In addition, platelet P-selectin expression of sheared blood, which is a marker for activated platelets, was also analyzed. The results from the present study showed that the number of activated platelets, as indicated by the surface GPIIb/IIIa activation and P-selectin expression, increased with increasing the shear stress level and exposure time. However, the mean fluorescence of GPIIb/IIIa on the platelet surface, decreased with increasing the shear stress level and exposure time. The reduction of GPIIb/IIIa on the platelet surface was further proved by the reduction of further activated platelet GPIIb/IIIa surface expression induced by ADP and the increase in GPIIb/IIIa concentration in microparticle-free plasma with increasing the applied shear stress and exposure time. It is clear that non-physiological shear stress induce a paradoxical phenomenon, in which both activation and shedding of the GPIIb/IIIa on the platelet surface occur simultaneously. This study may offer a new perspective to explain the reason of both increased thrombosis and bleeding events in patients implanted with high shear blood-contacting medical devices. PMID:26160282

  3. Shear Stress-Triggered Nitric Oxide Release From Schlemm's Canal Cells

    PubMed Central

    Ashpole, Nicole E.; Overby, Darryl R.; Ethier, C. Ross; Stamer, W. Daniel

    2014-01-01

    Purpose. Endothelial nitric oxide (NO) synthase is regulated by shear stress. At elevated intraocular pressures when the Schlemm's canal (SC) begins to collapse, shear stress is comparable with that in large arteries. We investigated the relationship between NO production and shear stress in cultured human SC cells. Methods. Schlemm's canal endothelial cells isolated from three normal and two glaucomatous human donors were seeded into Ibidi flow chambers at confluence, cultured for 7 days, and subjected to steady shear stress (0.1 or 10 dynes/cm2) for 6, 24, or 168 hours. Cell alignment with flow direction was monitored, and NO production was measured using 4-amino-5-methylamino-2′,7′-difluorofluorescein (DAF-FM) and Griess reagents. Human trabecular meshwork (TM) and umbilical vein endothelial cells (HUVECs) were used as controls. Results. Normal SC strains aligned with the direction of flow by 7 days. Comparing 0.1 vs. 10 dynes/cm2, NO levels increased by 82% at 24 hours and 8-fold after 7 days by DAF-FM, and similar results were obtained with Griess reagent. Shear responses by SC cells at 24 hours were comparable with HUVECs, and greater than TM cells, which appeared shear-insensitive. Nitric oxide production by SC cells was detectable as early as 6 hours and was inhibited by 100 μM nitro-L-arginine methyl ester. Two glaucomatous SC cell strains were either unresponsive or lifted from the plate in the face of shear. Conclusions. Shear stress triggers NO production in human SC cells, similar to other vascular endothelia. Increased shear stress and NO production during SC collapse at elevated intraocular pressures may in part mediate IOP homeostasis. PMID:25395486

  4. Effect of Varying Fluid Shear Stress on Cancer Stem Cell Viability & Protein Expression

    NASA Astrophysics Data System (ADS)

    Domier, Ria; Kim, Yonghyun; Dozier, David; Triantafillu, Ursula

    2013-11-01

    Cancer stem cells cultured in vitro in stirred bioreactors are exposed to shear stress. By observing the effect of shear stress on cancer stem cell viability, laboratory cell growth could be optimized. In addition, metastasized cancer stem cells in vivo are naturally exposed to shear stress, a factor influencing stem cell differentiation, while circulating in the bloodstream. Changes in protein expression after exposure to shear stress could allow for identification and targeting of circulating cancer cells. In this study, blood flow through capillaries was simulated by using a syringe pump to inject suspensions of Kasumi-1 leukemia stem cells into model blood vessels composed of PEEK tubing 125 microns in diameter. The Hagen-Poisseuille equation was used to solve for operating flow rates based on specified amounts of shear stress. After exposure, cell counts and viabilities were observed using an optical microscope and proteins were analyzed using Western blotting. It was observed that at a one minute exposure to stress, cell viability increased as the amount of shear was increased from 10 to 60 dynes per square centimeter. Results from this research are applicable to optimization of large-scale stem cell growth in bioreactors as well as to the design of targeted cancer therapies. Funding from NSF REU grant #1062611 is gratefully acknowledged.

  5. Transverse shear stresses and their sensitivity coefficients in multilayered composite panels

    NASA Technical Reports Server (NTRS)

    Noor, Ahmed K.; Kim, Yong H.; Peters, Jeanne M.

    1994-01-01

    A computational procedure is presented for the accurate determination of transverse shear stresses and their sensitivity coefficients in flat multilayered composite panels subjected to mechanical and thermal loads. The sensitivity coefficients measure the sensitivity of the transverse shear stresses to variations in the different lamination and material parameters of the panel. The panel is discretized by using either a three-field mixed finite element model based on a two-dimensional first- order shear deformation plate theory or a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the laminate. The evaluation of transverse shear stresses can be conveniently divided into two phases. The first phase consists of using a superconvergent recovery technique for evaluating the in-plane stresses in the different layers. In the second phase, the transverse shear stresses are evaluated by using piecewise integration, in the thickness direction, of the three-dimensional equilibrium equations. The same procedure is used for evaluating the sensitivity coefficients of the transverse shear stresses. The effectiveness of the computational procedure is demonstrated by means of numerical examples of multilayered cross-ply panels subjected to transverse loading, uniform temperature change, and uniform temperature gradient through the thickness of the panel. In each case the standard of the comparison is taken to be the exact solution of the three dimensional thermoelasticity equations of the panel.

  6. Human brain microvascular endothelial cells resist elongation due to shear stress.

    PubMed

    Reinitz, Adam; DeStefano, Jackson; Ye, Mao; Wong, Andrew D; Searson, Peter C

    2015-05-01

    Endothelial cells in straight sections of vessels are known to elongate and align in the direction of flow. This phenotype has been replicated in confluent monolayers of bovine aortic endothelial cells and human umbilical vein endothelial cells (HUVECs) in cell culture under physiological shear stress. Here we report on the morphological response of human brain microvascular endothelial cells (HBMECs) in confluent monolayers in response to shear stress. Using a microfluidic platform we image confluent monolayers of HBMECs and HUVECs under shear stresses up to 16 dyne cm(-2). From live-cell imaging we quantitatively analyze the cell morphology and cell speed as a function of time. We show that HBMECs do not undergo a classical transition from cobblestone to spindle-like morphology in response to shear stress. We further show that under shear stress, actin fibers are randomly oriented in the cells indicating that there is no cytoskeletal remodeling. These results suggest that HBMECs are programmed to resist elongation and alignment under shear stress, a phenotype that may be associated with the unique properties of the blood-brain barrier.

  7. Vascular endothelial cell membranes differentiate between stretch and shear stress through transitions in their lipid phases.

    PubMed

    Yamamoto, Kimiko; Ando, Joji

    2015-10-01

    Vascular endothelial cells (ECs) respond to the hemodynamic forces stretch and shear stress by altering their morphology, functions, and gene expression. However, how they sense and differentiate between these two forces has remained unknown. Here we report that the plasma membrane itself differentiates between stretch and shear stress by undergoing transitions in its lipid phases. Uniaxial stretching and hypotonic swelling increased the lipid order of human pulmonary artery EC plasma membranes, thereby causing a transition from the liquid-disordered phase to the liquid-ordered phase in some areas, along with a decrease in membrane fluidity. In contrast, shear stress decreased the membrane lipid order and increased membrane fluidity. A similar increase in lipid order occurred when the artificial lipid bilayer membranes of giant unilamellar vesicles were stretched by hypotonic swelling, indicating that this is a physical phenomenon. The cholesterol content of EC plasma membranes significantly increased in response to stretch but clearly decreased in response to shear stress. Blocking these changes in the membrane lipid order by depleting membrane cholesterol with methyl-β-cyclodextrin or by adding cholesterol resulted in a marked inhibition of the EC response specific to stretch and shear stress, i.e., phosphorylation of PDGF receptors and phosphorylation of VEGF receptors, respectively. These findings indicate that EC plasma membranes differently respond to stretch and shear stress by changing their lipid order, fluidity, and cholesterol content in opposite directions and that these changes in membrane physical properties are involved in the mechanotransduction that activates membrane receptors specific to each force.

  8. Doppler optical coherence tomography imaging of local fluid flow and shear stress within microporous scaffolds

    NASA Astrophysics Data System (ADS)

    Jia, Yali; Bagnaninchi, Pierre O.; Yang, Ying; Haj, Alicia El; Hinds, Monica T.; Kirkpatrick, Sean J.; Wang, Ruikang K.

    2009-05-01

    Establishing a relationship between perfusion rate and fluid shear stress in a 3D cell culture environment is an ongoing and challenging task faced by tissue engineers. We explore Doppler optical coherence tomography (DOCT) as a potential imaging tool for in situ monitoring of local fluid flow profiles inside porous chitosan scaffolds. From the measured fluid flow profiles, the fluid shear stresses are evaluated. We examine the localized fluid flow and shear stress within low- and high-porosity chitosan scaffolds, which are subjected to a constant input flow rate of 0.5 ml.min-1. The DOCT results show that the behavior of the fluid flow and shear stress in micropores is strongly dependent on the micropore interconnectivity, porosity, and size of pores within the scaffold. For low-porosity and high-porosity chitosan scaffolds examined, the measured local fluid flow and shear stress varied from micropore to micropore, with a mean shear stress of 0.49+/-0.3 dyn.cm-2 and 0.38+/-0.2 dyn.cm-2, respectively. In addition, we show that the scaffold's porosity and interconnectivity can be quantified by combining analyses of the 3D structural and flow images obtained from DOCT.

  9. Application of Entropy Concept for Shear Stress Distribution in Laminar Pipe Flow

    NASA Astrophysics Data System (ADS)

    Choo, Yeon Moon; Choo, Tai Ho; Jung, Donghwi; Seon, Yun Gwan; Kim, Joong Hoon

    2016-04-01

    In the river fluid mechanics, shear stress is calculated from frictional force caused by viscosity and fluctuating velocity. Traditional shear stress distribution equations have been widely used because of their simplicity. However, they have a critical limitation of requiring energy gradient which is generally difficult to estimate in practice. Especially, measuring velocity/velocity gradient on the boundary layer is difficult in practice. It requires point velocity throughout the entire cross section to calculate velocity gradient. This study proposes shear stress distribution equations for laminar flow based on entropy theory using mean velocity and entropy coefficient. The proposed equations are demonstrated and compared with measured shear stress distribution using Nikuradse's data. Results showed that the coefficient of determination is around 0.99 indicating that the proposed method well describes the true shear stress distribution. Therefore, it was proved that shear stress distribution can be easily and accurately estimated by using the proposed equations. (This research was supported by a gran(13AWMP-B066744-01) from Advanced Water Management Research Program funded by Ministry of Land, Infrastructure and Transport of Korean Government)

  10. ESTIMATION OF SHEAR STRESS WORKING ON SUBMERGED HOLLOW FIBRE MEMBRANE BY CFD METHOD IN MBRs

    NASA Astrophysics Data System (ADS)

    Zaw, Hlwan Moe; Li, Tairi; Nagaoka, Hiroshi

    This study was conducted to evaluate shear stress working on submerged hollow fibre membrane by CFD (Computation Fluid Dynamics) method in MBRs. Shear stress on hollow fibre membrane caused by aeration was measured directly using a two-direction load sensor. The measurement of water-phase flow velocity was done also by using laser doppler velocimeter. It was confirmed that the shear stress was possible to be evaluated from the water-phase flow velocityby the result of comparison of time average shear stress actually measured with one hollow fibre membrane and the one calculated by the water-phase flow velocity. In the estimation of the water-phase flow velocity using the CFD method, time average water-phase flow velocity estimated by consideration of the fluid resistance of the membrane module nearly coincided with the measured values, and it was shown that it was possible to be estimated also within the membrane module. Moreover, the measured shear stress and drag force well coincided with the values calculated from the estimated water-phase flow velocity outside of membrane module and in the center of membrane module, and it was suggested that the shear stress on the hollow fibre membrane could be estimated by the CFD method in MBRs.

  11. Stress ratio effect on cyclic debonding in adhesively bonded composite joints

    NASA Technical Reports Server (NTRS)

    Mall, S.; Ramamurthy, G.; Rezaizdeh, M. A.

    1987-01-01

    A study was conducted to investigate the stress ratio effect on cyclic debond growth behavior in adhesively bonded composite joints. The system studied consisted of graphite/epoxy adherends bonded with a toughened epoxy adhesive. This study showed that the strain energy release rate range was the driving factor for cyclic debonding of the tested bonded system when subjected to cyclic loads with different stress ratios for both mode I and mixed mode I-II loadings.

  12. Effect of aqueous tobacco smoke extract and shear stress on PECAM-1 expression and cell motility in human uterine endothelial cells.

    PubMed

    Soghomonians, Arlen; Thirkill, Twanda L; Mariano, Natalie F; Barakat, Abdul I; Douglas, Gordon C

    2004-10-01

    Tobacco smoke constituents have several adverse effects on endothelial cells. Exposure to tobacco smoke during pregnancy is associated with adverse effects on pregnancy outcome possibly related to endothelial dysfunction. Platelet endothelial cell adhesion molecule-1 (PECAM-1) is an important regulator of endothelial function. This study tests the idea that an aqueous extract of cigarette smoke alters the expression of PECAM-1 in uterine endothelial cells. Human uterine microvascular endothelial cells were cultured in cigarette smoke-conditioned medium (CSM) under arterial physiological flow conditions (shear or frictional stress in the range 7.5-15 dyne/cm(2)) and the expression of PECAM-1 was assessed by immunofluorescence microscopy and Western blotting. Thick reticular PECAM-1-associated bands found at cell-cell junctions in static cultures became significantly thinner or disappeared when the cells were exposed to shear stress or to CSM for 24 h. This diminution at cell junctions was accompanied by increased punctate cytoplasmic/cell surface staining. Under shear stress conditions, PECAM-1 was equally distributed between cell surface and intracellular sites. In contrast, when cells were exposed to both shear stress and CSM, PECAM-1 was predominantly localized to the cell surface. It was shown that shear stress increased endothelial cell migration and that CSM abrogated this effect. These results suggest that, under shear stress conditions, PECAM-1 is not predominantly concentrated at intercellular junctions in uterine endothelial cells. Exposure of cells to unidentified soluble components of cigarette smoke leads to alterations in PECAM-1 distribution that may cause endothelial dysfunction. If this occurs in vivo it could contribute to the adverse effects on pregnancy outcome associated with exposure to cigarette smoke.

  13. Venous levels of shear support neutrophil-platelet adhesion and neutrophil aggregation in blood via P-selectin and beta2-integrin

    NASA Technical Reports Server (NTRS)

    Konstantopoulos, K.; Neelamegham, S.; Burns, A. R.; Hentzen, E.; Kansas, G. S.; Snapp, K. R.; Berg, E. L.; Hellums, J. D.; Smith, C. W.; McIntire, L. V.; Simon, S. I.

    1998-01-01

    BACKGROUND: After activation, platelets adhere to neutrophils via P-selectin and beta2-integrin. The molecular mechanisms and adhesion events in whole blood exposed to venous levels of hydrodynamic shear in the absence of exogenous activation remain unknown. METHODS AND RESULTS: Whole blood was sheared at approximately 100 s(-1). The kinetics of neutrophil-platelet adhesion and neutrophil aggregation were measured in real time by flow cytometry. P-selectin was upregulated to the platelet surface in response to shear and was the primary factor mediating neutrophil-platelet adhesion. The extent of neutrophil aggregation increased linearly with platelet adhesion to neutrophils. Blocking either P-selectin, its glycoprotein ligand PSGL-1, or both simultaneously by preincubation with a monoclonal antibody resulted in equivalent inhibition of neutrophil-platelet adhesion (approximately 30%) and neutrophil aggregation (approximately 70%). The residual amount of neutrophil adhesion was blocked with anti-CD11b/CD18. Treatment of blood with prostacyclin analogue ZK36374, which raises cAMP levels in platelets, blocked P-selectin upregulation and neutrophil aggregation to baseline. Complete abrogation of platelet-neutrophil adhesion required both ZK36374 and anti-CD18. Electron microscopic observations of fixed blood specimens revealed that platelets augmented neutrophil aggregation both by forming bridges between neutrophils and through contact-mediated activation. CONCLUSIONS: The results are consistent with a model in which venous levels of shear support platelet adherence to neutrophils via P-selectin binding PSGL-1. This interaction alone is sufficient to mediate neutrophil aggregation. Abrogation of platelet adhesion and aggregation requires blocking Mac-1 in addition to PSGL-1 or P-selectin. The described mechanisms are likely of key importance in the pathogenesis and progression of thrombotic disorders that are exacerbated by leukocyte-platelet aggregation.

  14. Acid stress suggests different determinants for polystyrene and HeLa cell adhesion in Lactobacillus casei.

    PubMed

    Haddaji, N; Khouadja, S; Fdhila, K; Krifi, B; Ben Ismail, M; Lagha, R; Bakir, K; Bakhrouf, A

    2015-07-01

    Adhesion has been regarded as one of the basic features of probiotics. The aim of this study was to investigate the influence of acid stress on the functional properties, such as hydrophobicity, adhesion to HeLa cells, and composition of membrane fatty acids, of Lactobacillus probiotics strains. Two strains of Lactobacillus casei were used. Adhesion on polystyrene, hydrophobicity, epithelial cells adhesion, and fatty acids analysis were evaluated. Our results showed that the membrane properties such as hydrophobicity and fatty acid composition of stressed strains were significantly changed with different pH values. However, we found that acid stress caused a change in the proportions of unsaturated and saturated fatty acid. The ratio of saturated fatty acid to unsaturated fatty acids observed in acid-stressed Lactobacillus casei cells was significantly higher than the ration in control cells. In addition, we observed a significant decrease in the adhesion ability of these strains to HeLa cells and to a polystyrene surface at low pH. The present finding could first add new insight about the acid stress adaptation and, thus, enable new strategies to be developed aimed at improving the industrial performance of this species under acid stress. Second, no relationship was observed between changes in membrane composition and fluidity induced by acid treatment and adhesion to biotic and abiotic surfaces. In fact, the decrease of cell surface hydrophobicity and the adhesion ability to abiotic surface and the increase of the capacity of adhesion to biotic surface demonstrate that adhesive characteristics will have little relevance in probiotic strain-screening procedures.

  15. Dynamic Deformation and Recovery Response of Red Blood Cells to a Cyclically Reversing Shear Flow: Effects of Frequency of Cyclically Reversing Shear Flow and Shear Stress Level

    PubMed Central

    Watanabe, Nobuo; Kataoka, Hiroyuki; Yasuda, Toshitaka; Takatani, Setsuo

    2006-01-01

    Dynamic deformation and recovery responses of red blood cells (RBCs) to a cyclically reversing shear flow generated in a 30-μm clearance, with the peak shear stress of 53, 108, 161, and 274 Pa at the frequency of 1, 2, 3, and 5 Hz, respectively, were studied. The RBCs' time-varying velocity varied after the glass plate velocity without any time lag, whereas the L/W change, where L and W were the major and minor axes of RBCs' ellipsoidal shape, exhibited a rapid increase and gradual decay during the deformation and recovery phase. The time of minimum L/W occurrence lagged behind the zero-velocity time of the glass plate (zero stress), and the delay time normalized to the one-cycle duration remained constant at 8.0%. The elongation of RBCs at zero stress time became larger with the reversing frequency. A simple mechanical model consisting of an elastic linear element during a rapid elongation period and a parallel combination of elements such as a spring and dashpot during the nonlinear recovery phase was suggested. The dynamic response behavior of RBCs under a cyclically reversing shear flow was different from the conventional shape change where a steplike force was applied to and completely released from the RBCs. PMID:16766612

  16. A new technique for the measurement of surface shear stress vectors using liquid crystal coatings

    NASA Technical Reports Server (NTRS)

    Reda, Daniel C.; Muratore, J. J., Jr.

    1994-01-01

    Research has recently shown that liquid crystal coating (LCC) color-change response to shear depends on both shear stress magnitude and direction. Additional research was thus conducted to extend the LCC method from a flow-visualization tool to a surface shear stress vector measurement technique. A shear-sensitive LCC was applied to a planar test surface and illuminated by white light from the normal direction. A fiber optic probe was used to capture light scattered by the LCC from a point on the centerline of a turbulent, tangential-jet flow. Both the relative shear stress magnitude and the relative in-plane view angle between the sensor and the centerline shear vector were systematically varied. A spectrophotometer was used to obtain scattered-light spectra which were used to quantify the LCC color (dominant wavelength) as a function of shear stress magnitude and direction. At any fixed shear stress magnitude, the minimum dominant wavelength was measured when the shear vector was aligned with and directed away from the observer; changes in the relative in-plane view angle to either side of this vector/observer aligned position resulted in symmetric Gaussian increases in measured dominant wavelength. Based on these results, a vector measurement methodology, involving multiple oblique-view observations of the test surface, was formulated. Under present test conditions, the measurement resolution of this technique was found to be +/- 1 deg for vector orientations and +/- 5% for vector magnitudes. An approach t o extend the present methodology to full-surface applications is proposed.

  17. Effect of oxygen and shear stress on molecular weight of hyaluronic acid.

    PubMed

    Duan, Xu-Jie; Yang, Li; Zhang, Xu; Tan, Wen-Song

    2008-04-01

    Dissolved oxygen (DO) and shear stress have pronounced effects on hyaluronic acid (HA) production, yet various views persist about their effect on the molecular weight of HA. Accordingly, this study investigated the effects of DO and shear stress during HA fermentation. The results showed that both cell growth and HA synthesis were suppressed under anaerobic conditions, and the HA molecular mass was only (1.22+/-0.02) x 106 Da. Under aerobic conditions, although the DO level produced no change in the biomass or HA yield, a high DO level favored the HA molecular mass, which reached a maximum value of (2.19+/- 0.05) x 106 Da at 50% DO. Furthermore, a high shear stress delayed the rate of HA synthesis and decreased the HA molecular weight, yet had no clear effect on the HA yield. Therefore, a high DO concentration and mild shear environment would appear to be essential to enhance the HA molecular weight.

  18. Two dimensional mechanical correlation analysis on nonlinear oscillatory shear flow of yield stress fluids

    NASA Astrophysics Data System (ADS)

    Yang, Kai; Wang, Jun; Yu, Wei

    2016-08-01

    Large amplitude oscillation shear (LAOS) is used to investigate the yielding and flow behavior of yield stress materials. Considering the problems in determination of the yield stress from the apparent dynamic moduli and relative harmonic intensity using Fourier Transform Rheology, we proposed a new approach based on 2D mechanical correlation spectra (2D-MCS) to quantify the yield stress. We have proved that the nonlinear synchronous self-correlation intensity as functions of stress/strain amplitude can be used to determine the yield stress unambiguously from the change of scaling exponent. The yield stresses from 2D-MCS analysis are well consistent with those from the stress ramp experiments.

  19. Effect of cell size and shear stress on bacterium growth rate

    NASA Astrophysics Data System (ADS)

    Fadlallah, Hadi; Jarrahi, Mojtaba; Herbert, Éric; Peerhossaini, Hassan; PEF Team

    2015-11-01

    Effect of shear stress on the growth rate of Synechocystis and Chlamydomonas cells is studied. An experimental setup was prepared to monitor the growth rate of the microorganisms versus the shear rate inside a clean room, under atmospheric pressure and 20 °C temperature. Digital magnetic agitators are placed inside a closed chamber provided with airflow, under a continuous uniform light intensity over 4 weeks. In order to study the effect of shear stress on the growth rate, different frequencies of agitation are tested, 2 vessels filled with 150 ml of each specie were placed on different agitating system at the desired frequency. The growth rate is monitored daily by measuring the optical density and then correlate it to the cellular concentration. The PH was adjusted to 7 in order to maintain the photosynthetic activity. Furthermore, to measure the shear stress distribution, the flow velocity field was measured using PIV. Zones of high and low shear stress were identified. Results show that the growth rate is independent of the shear stress magnitude, mostly for Synechocystis, and with lower independency for Chlamydomonas depending on the cell size for each species.

  20. Orbital fluid shear stress promotes osteoblast metabolism, proliferation and alkaline phosphates activity in vitro

    SciTech Connect

    Aisha, M.D.; Nor-Ashikin, M.N.K.; Sharaniza, A.B.R.; Nawawi, H.; Froemming, G.R.A.

    2015-09-10

    Prolonged disuse of the musculoskeletal system is associated with reduced mechanical loading and lack of anabolic stimulus. As a form of mechanical signal, the multidirectional orbital fluid shear stress transmits anabolic signal to bone forming cells in promoting cell differentiation, metabolism and proliferation. Signals are channeled through the cytoskeleton framework, directly modifying gene and protein expression. For that reason, we aimed to study the organization of Normal Human Osteoblast (NHOst) cytoskeleton with regards to orbital fluid shear (OFS) stress. Of special interest were the consequences of cytoskeletal reorganization on NHOst metabolism, proliferation, and osteogenic functional markers. Cells stimulated at 250 RPM in a shaking incubator resulted in the rearrangement of actin and tubulin fibers after 72 h. Orbital shear stress increased NHOst mitochondrial metabolism and proliferation, simultaneously preventing apoptosis. The ratio of RANKL/OPG was reduced, suggesting that orbital shear stress has the potential to inhibit osteoclastogenesis and osteoclast activity. Increase in ALP activity and OCN protein production suggests that stimulation retained osteoblast function. Shear stress possibly generated through actin seemed to hold an anabolic response as osteoblast metabolism and functional markers were enhanced. We hypothesize that by applying orbital shear stress with suitable magnitude and duration as a non-drug anabolic treatment can help improve bone regeneration in prolonged disuse cases. - Highlights: • OFS stress transmits anabolic signals to osteoblasts. • Actin and tubulin fibers are rearranged under OFS stress. • OFS stress increases mitochondrial metabolism and proliferation. • Reduced RANKL/OPG ratio in response to OFS inhibits osteoclastogenesis. • OFS stress prevents apoptosis and stimulates ALP and OCN.

  1. Evaluating the shear bond strength of enamel and dentin with or without etching: A comparative study between dimethacrylate-based and silorane-based adhesives

    PubMed Central

    Hajizadeh, Hila; Nasseh, Atefeh; Rahmanpour, Naim

    2015-01-01

    Background Silorane-based composites and their specific self-etch adhesive were introduced to conquest the polymerization shrinkage of methacrylate-based composites. It has been shown that additional etching of enamel and dentin can improve the bond strength of self-etch methacrylate-based adhesives but this claim is not apparent about silorane-based adhesives. Our objective was to compare the shear bond strength (SBS) of enamel and dentin between silorane-based adhesive resin and a methacrylate-based resin with or without additional etching. Material and Methods 40 sound human premolars were prepared and divided into two groups: 1- Filtek P60 composite and Clearfil SE Bond adhesive; 2- Filtek P90 composite and Silorane adhesive. Each group divided into two subgroups: with or without additional etching. For additional etching, 37% acid phosphoric was applied before bonding procedure. A cylinder of the composite was bonded to the surface. After 24 hours storage and 500 thermo cycling between 5-55°C, shear bond strength was assessed with the cross head speed of 0.5 mm/min. Then, bonded surfaces were observed under stereomicroscope to determine the failure mode. Data were analyzed with two-way ANOVA and Fischer exact test. Results Shear bond strength of Filtek P60 composite was significantly higher than Filtek P90 composite both in enamel and dentin surfaces (P<0.05). However, additional etching had no significant effect on shear bond strength in enamel or dentin for each of the composites (P>0.05). There was no interaction between composite type and additional etching (P>0.05). Failure pattern was mainly adhesive and no significant correlation was found between failure and composite type or additional etching (P>0.05). Conclusions Shear bond strength of methacrylate-based composite was significantly higher than silorane-based composite both in enamel and dentin surfaces and additional etching had no significant effect on shear bond strength in enamel or dentin for

  2. Measurement of particle trajectories, dynamics, surface adhesion and detachment in near-wall shear flows using 3D velocimetry

    NASA Astrophysics Data System (ADS)

    Guasto, Jeffrey; Schmidt, Brian; Lawrence, Michael; Breuer, Kenneth

    2007-11-01

    Three-dimensional total internal reflection velocimetry (3D-TIRV) is used to measure the trajectories of fluorescent tracer particles within 200 nm of a wall. Diffusion and shear-induced motion can result in mean velocity measurement errors, and by taking measurements using different particle sizes and sampling times, we quantify these effects and compare with theory. We also use 3D-TIRV to observe and characterize the adhesion, surface rolling and release dynamics of particles that can adhere to the surface through the action of biological binding proteins. Particles coated with P-Selectin are allowed to adhere to and detach from a PSGL-1-coated microchannel surface, modeling the interaction between leukocytes (white blood cells) and blood vessels, respectively. Binding affinities, bond strengths and hydrodynamic interactions are inferred from the trajectory data.

  3. Parallel-plate flow chamber and continuous flow circuit to evaluate endothelial progenitor cells under laminar flow shear stress.

    PubMed

    Lane, Whitney O; Jantzen, Alexandra E; Carlon, Tim A; Jamiolkowski, Ryan M; Grenet, Justin E; Ley, Melissa M; Haseltine, Justin M; Galinat, Lauren J; Lin, Fu-Hsiung; Allen, Jason D; Truskey, George A; Achneck, Hardean E

    2012-01-01

    The overall goal of this method is to describe a technique to subject adherent cells to laminar flow conditions and evaluate their response to well quantifiable fluid shear stresses. Our flow chamber design and flow circuit (Fig. 1) contains a transparent viewing region that enables testing of cell adhesion and imaging of cell morphology immediately before flow (Fig. 11A, B), at various time points during flow (Fig. 11C), and after flow (Fig. 11D). These experiments are illustrated with human umbilical cord blood-derived endothelial progenitor cells (EPCs) and porcine EPCs. This method is also applicable to other adherent cell types, e.g. smooth muscle cells (SMCs) or fibroblasts. The chamber and all parts of the circuit are easily sterilized with steam autoclaving. In contrast to other chambers, e.g. microfluidic chambers, large numbers of cells (> 1 million depending on cell size) can be recovered after the flow experiment under sterile conditions for cell culture or other experiments, e.g. DNA or RNA extraction, or immunohistochemistry (Fig. 11E), or scanning electron microscopy. The shear stress can be adjusted by varying the flow rate of the perfusate, the fluid viscosity, or the channel height and width. The latter can reduce fluid volume or cell needs while ensuring that one-dimensional flow is maintained. It is not necessary to measure chamber height between experiments, since the chamber height does not depend on the use of gaskets, which greatly increases the ease of multiple experiments. Furthermore, the circuit design easily enables the collection of perfusate samples for analysis and/or quantification of metabolites secreted by cells under fluid shear stress exposure, e.g. nitric oxide (Fig. 12).

  4. The Role of Shear Stress in Arteriovenous Fistula Maturation and Failure: A Systematic Review

    PubMed Central

    Browne, Leonard D.; Bashar, Khalid; Griffin, Philip; Kavanagh, Eamon G.; Walsh, Stewart R.; Walsh, Michael T.

    2015-01-01

    Introduction Non-maturation and post-maturation venous stenosis are the primary causes of failure within arteriovenous fistulae (AVFs). Although the exact mechanisms triggering failure remain unclear, abnormal hemodynamic profiles are thought to mediate vascular remodelling and can adversely impact on fistula patency. Aim The review aims to clarify the role of shear stress on outward remodelling during maturation and evaluate the evidence supporting theories related to the localisation and development of intimal hyperplasia within AVFs. Methods A systematic review of studies comparing remodelling data with hemodynamic data obtained from computational fluid dynamics of AVFs during and after maturation was conducted. Results Outward remodelling occurred to reduce or normalise the level of shear stress over time in fistulae with a large radius of curvature (curved) whereas shear stress was found to augment over time in fistulae with a small radius of curvature (straight) coinciding with minimal to no increases in lumen area. Although this review highlighted that there is a growing body of evidence suggesting low and oscillating shear stress may stimulate the initiation and development of intimal medial thickening within AVFs. Further lines of evidence are needed to support the disturbed flow theory and outward remodelling findings before surgical configurations and treatment strategies are optimised to conform to them. This review highlighted that variation between the time of analysis, classification of IH, resolution of simulations, data processing techniques and omission of various shear stress metrics prevented forming pooling of data amongst studies. Conclusion Standardised measurements and data processing techniques are needed to comprehensively evaluate the relationship between shear stress and intimal medial thickening. Advances in image acquisition and flow quantifications coupled with the increasing prevalence of longitudinal studies commencing from fistula

  5. Shear stress-induced mitochondrial biogenesis decreases the release of microparticles from endothelial cells

    PubMed Central

    Kim, Ji-Seok; Kim, Boa; Lee, Hojun; Thakkar, Sunny; Babbitt, Dianne M.; Eguchi, Satoru; Brown, Michael D.

    2015-01-01

    The concept of enhancing structural integrity of mitochondria has emerged as a novel therapeutic option for cardiovascular disease. Flow-induced increase in laminar shear stress is a potent physiological stimulant associated with exercise, which exerts atheroprotective effects in the vasculature. However, the effect of laminar shear stress on mitochondrial remodeling within the vascular endothelium and its related functional consequences remain largely unknown. Using in vitro and in vivo complementary studies, here, we report that aerobic exercise alleviates the release of endothelial microparticles in prehypertensive individuals and that these salutary effects are, in part, mediated by shear stress-induced mitochondrial biogenesis. Circulating levels of total (CD31+/CD42a−) and activated (CD62E+) microparticles released by endothelial cells were significantly decreased (∼40% for both) after a 6-mo supervised aerobic exercise training program in individuals with prehypertension. In cultured human endothelial cells, laminar shear stress reduced the release of endothelial microparticles, which was accompanied by an increase in mitochondrial biogenesis through a sirtuin 1 (SIRT1)-dependent mechanism. Resveratrol, a SIRT1 activator, treatment showed similar effects. SIRT1 knockdown using small-interfering RNA completely abolished the protective effect of shear stress. Disruption of mitochondrial integrity by either antimycin A or peroxisome proliferator-activated receptor-γ coactivator-1α small-interfering RNA significantly increased the number of total, and activated, released endothelial microparticles, and shear stress restored these back to basal levels. Collectively, these data demonstrate a critical role of endothelial mitochondrial integrity in preserving endothelial homeostasis. Moreover, prolonged laminar shear stress, which is systemically elevated during aerobic exercise in the vessel wall, mitigates endothelial dysfunction by promoting mitochondrial

  6. Modelling of porphyroclasts in simple shear and the role of stress variations at grain boundaries

    NASA Astrophysics Data System (ADS)

    Wilson, Christopher J. L.; Evans, Lynn; Delle Piane, Claudio

    2009-11-01

    Grain-scale numerical experiments involving simple shear of a two-phase non-linear viscous material are described and compared with mineral fish or lozenge-shaped porphyroclasts, such as muscovite. Two types of 2D models are considered; either a single elongate grain or two parallel elongate grains, in both cases supported by a weaker polygonal grain matrix. The relative viscosities of the contrasting grain structures were systematically varied, allowing us to observe the effects of non-linear viscous rheology on the resulting microstructure and flow patterns. The results show that the finite rotation of the hard elongate grain was similar within any one experiment, but was largely influenced by viscosity contrast, the geometry of the model and the imposed shear strain. Models involving single elongate hard grains show increasing instability at their ends and less strain compatibility with the deforming matrix grains, as the viscosity contrast is increased. In the paired grain models the greatest variation in the matrix grain microstructure is seen in the region where the two hard grains are oriented at a high-angle to the direction of shear. Finally, we consider the changes in intragranular stress by comparing microstructural observations using different viscosities with the distribution of stress in space and during progressive shear. In the plane approximately parallel to the maximum principal stress direction ( σ1), a localised change of stress occurs across and along the interface between the hard and soft grains. Variations in the mean stress at these boundaries are directly attributable to changes in the minimum principal stress. We propose that with shear strains greater than γ = 2 it is the minimum principal stress that can control diffusion processes at the grain boundary rather than mean stress. In conclusion we suggest that our models have the potential for providing useful insights into why metamorphic reactions can occur at the interface between a

  7. Exploring the Role of Shear Stress and Severe Turbulence in Downstream Fish Passage

    SciTech Connect

    Cada, G.; Carlson, T.; Ferguson, J.; Richmond, M.; Sale, M.

    1999-07-06

    Fish may be exposed to damaging levels of fluid shear stress and turbulence while passing through hydroelectric power plants. The generally assumed locations for such potential damage are the turbine and draft tube passages, although it is possible that fish are also injured during passage over the spillway or through sluiceways and fish bypass outfalls. Unless mitigated, fluid-induced injuries and mortality could frustrate efforts to develop advanced, fish-friendly turbines or to provide safe alternate downstream passages. The effects of shear stress and turbulence on fish are poorly understood, in part because of the difficulties in conceptualizing these phenomena, determining their magnitudes and distribution within hydroelectric systems, and then recreating them in a controlled laboratory environment. We define the fluid phenomena that are relevant to the assessment of effects on fish. The magnitudes of fluid stresses associated with man-altered aquatic environments are often considerably higher than those found in natural environments (e.g., normal river flows). However, levels of shear stresses that occur during flash floods appear to be comparable to those expected within a turbine. Past studies of the effects of shear stress on fish are of limited value, mainly because of their narrow scope and lack of instrumentation to measure velocities on appropriately small scales. A laboratory experiment to study the effects of shear stress and turbulence on fish is described.

  8. Investigation of strength of a hybrid adhesive anchor system used in precast concrete welded repair applications subjected to tensile and eccentric shear loading

    NASA Astrophysics Data System (ADS)

    Eilers, Michael Glenn

    A common precast industry repair for missing or misplaced connection plates is the use of an adhesive anchor system to fasten repair plates to precast members. Typically, the repair plate will experience elevated temperatures during the welding of the loose erection plate to the repair plate. Limited testing and theoretical data are currently available to provide design guidelines on how the elevated temperatures induced by welding affect the behavior and capacity of the adhesive anchoring systems. This dissertation outlines bond tests, eccentric shear tests, and a temperature investigation performed using a hybrid adhesive system in precast concrete repair applications. In addition, limited bond strength testing data using a high strength two-part epoxy adhesive is also included. The overall aim of this work is to provide test data and guidance to the industry and design professionals when designing adhesive anchoring systems for repair applications exposed to welding.

  9. Shear wave transducer for stress measurements in boreholes

    DOEpatents

    Mao, Nai-Hsien

    1987-01-01

    A technique and apparatus for estimating in situ stresses by measuring stress-induced velocity anisotropy around a borehole. Two sets each of radially and tangentially polarized transducers are placed inside the hole with displacement directions either parallel or perpendicular to the principal stress directions. With this configuration, relative travel times are measured by both a pulsed phase-locked loop technique and a cross correlation of digitized waveforms. The biaxial velocity data is used to back-calculate the applied stress.

  10. Propagation of shear waves in viscoelastic heterogeneous layer overlying an initially stressed half space

    NASA Astrophysics Data System (ADS)

    Chatterjee, Mita; Dhua, Sudarshan; Chattopadhyay, Amares

    2015-12-01

    The present paper is concerned with the propagation of shear waves in an isotropic, viscoelastic, heterogeneous layer lying over a homogeneous half space under initial stress. For the layer the inhomogeneity associated to rigidity, internal friction and density is assumed to be linear function of depth. The dispersion equation of shear waves has been obtained in closed form. The dimensionless phase velocity and damping velocity have been plotted against dimensionless wave number for different values of inhomogeneity parameter and initial stress. The effects of inhomogeneity and initial stress have been shown in the dispersion curves.

  11. Suppression of endothelial t-PA expression by prolonged high laminar shear stress

    SciTech Connect

    Ulfhammer, Erik; Carlstroem, Maria; Bergh, Niklas; Larsson, Pia; Karlsson, Lena; Jern, Sverker

    2009-02-06

    Primary hypertension is associated with an impaired capacity for acute release of endothelial tissue-type plasminogen activator (t-PA), which is an important local protective response to prevent thrombus extension. As hypertensive vascular remodeling potentially results in increased vascular wall shear stress, we investigated the impact of shear on regulation of t-PA. Cultured human endothelial cells were exposed to low ({<=}1.5 dyn/cm{sup 2}) or high (25 dyn/cm{sup 2}) laminar shear stress for up to 48 h in two different experimental models. Using real-time RT-PCR and ELISA, shear stress was observed to time and magnitude-dependently suppress t-PA transcript and protein secretion to approximately 30% of basal levels. Mechanistic experiments revealed reduced nuclear protein binding to the t-PA specific CRE element (EMSA) and an almost completely abrogated shear response with pharmacologic JNK inhibition. We conclude that prolonged high laminar shear stress suppresses endothelial t-PA expression and may therefore contribute to the enhanced risk of arterial thrombosis in hypertensive disease.

  12. Shear bond strength and ultrastructural interface analysis of different adhesive systems to Er:YAG laser-prepared dentin.

    PubMed

    Guven, Yeliz; Aktoren, Oya

    2015-02-01

    The aim of this study was to evaluate the shear bond strength (SBS) of a microhybrid composite resin bonded with three different adhesive systems to Er:YAG laser- (EL) or bur-prepared dentin surfaces and to analyze the quality and ultrastructure of the adhesive-dentin interfaces by scanning electron microscopy (SEM). The specimens prepared for SBS test and SEM analysis were randomly assigned to eight groups (G1-G8): G1, EL (Fidelis PlusIII, Fotona) + Clearfil S3 Bond (C3S); G2, EL + AdperSE Plus (SE); G3, EL + laser etch + Adper Single Bond2 (SB2); G4, EL + acid etch + SB2; G5, EL + SB2 (no etching); G6, bur + acid etch + SB2; G7, bur + S3; G8, bur + SE. Laser was used in very short pulse mode at a setting of 200 mJ/20 Hz for dentin preparation and at 80 mJ/10 Hz for dentin etching. Bond strength test: 3.5 × 2.0 mm cylindrical molds were placed onto adhesives and filled with the composites. After 24 h in distilled water, SBS was tested at a crosshead speed of 0.5 mm/min. SEM analysis: The dentin-adhesive interfaces were evaluated for the ultrastructure of hybrid layer. Data of SBS (MPa) were statistically analyzed by ANOVA and Tukey HSD. ER:YAG laser-prepared dentin has demonstrated significantly more SBS (p < 0.01) for SE when compared to bur-prepared dentin. No significancies (p > 0.05) in SBS have been determined between the total-etch adhesive applied groups with regard to etching types. SEM analysis revealed that hybrid layers obtained in Er:YAG laser-irradiated dentin exhibited more irregular and non-homogeneous pattern than the conventionally prepared dentin. In conclusion, SE Bond demonstrated superior results in Er:YAG laser-ablated dentin compared to bur-prepared dentin. PMID:23982720

  13. Yield shear stress model of magnetorheological fluids based on exponential distribution

    NASA Astrophysics Data System (ADS)

    Guo, Chu-wen; Chen, Fei; Meng, Qing-rui; Dong, Zi-xin

    2014-06-01

    The magnetic chain model that considers the interaction between particles and the external magnetic field in a magnetorheological fluid has been widely accepted. Based on the chain model, a yield shear stress model of magnetorheological fluids was proposed by introducing the exponential distribution to describe the distribution of angles between the direction of magnetic field and the chain formed by magnetic particles. The main influencing factors were considered in the model, such as magnetic flux density, intensity of magnetic field, particle size, volume fraction of particles, the angle of magnetic chain, and so on. The effect of magnetic flux density on the yield shear stress was discussed. The yield stress of aqueous Fe3O4 magnetreological fluids with volume fraction of 7.6% and 16.2% were measured by a device designed by ourselves. The results indicate that the proposed model can be used for calculation of yield shear stress with acceptable errors.

  14. Adhesions

    MedlinePlus

    ... surfaces so they can shift easily as the body moves. Adhesions cause tissues and organs to stick together. They might connect the loops of the intestines to each other, to nearby ... can occur anywhere in the body. But they often form after surgery on the ...

  15. Effect of different adhesives combined with two resin composite cements on shear bond strength to polymeric CAD/CAM materials.

    PubMed

    Bähr, Nora; Keul, Christine; Edelhoff, Daniel; Eichberger, Marlis; Roos, Malgorzata; Gernet, Wolfgang; Stawarczyk, Bogna

    2013-01-01

    This study tested the impact of different adhesives and resin composite cements on shear bond strength (SBS) to polymethyl methacrylate (PMMA)- and composite-based CAD/CAM materials. SBS specimens were fabricated and divided into five main groups (n=30/group) subject to conditioning: 1. Monobond Plus/Heliobond (MH), 2. Visio.link (VL), 3. Ambarino P60 (AM), 4. exp. VP connect (VP), and 5. no conditioning-control group (CG). All cemented specimens using a. Clearfil SA Cement and b. Variolink II were stored in distilled water for 24 h at 37 °C. Additionally, one half of the specimens were thermocycled for 5,000 cycles (5 °C/55 °C, dwell time 20 s). SBS was measured; data were analyzed using descriptive statistics, four- and one-way ANOVA, unpaired two-sample t-test and Chi(2)-test. CAD/CAM materials without additional adhesives showed no bond to resin composite cements. Highest SBS showed VL with Variolink II on composite-based material, before and after thermocycling.

  16. Rheometry of granular materials in cylindrical Couette cells: Anomalous stress caused by gravity and shear

    NASA Astrophysics Data System (ADS)

    Gutam, Kamala Jyotsna; Mehandia, Vishwajeet; Nott, Prabhu R.

    2013-07-01

    The cylindrical Couette device is commonly employed to study the rheology of fluids, but seldom used for dense granular materials. Plasticity theories used for granular flows predict a stress field that is independent of the shear rate, but otherwise similar to that in fluids. In this paper we report detailed measurements of the stress as a function of depth, and show that the stress profile differs fundamentally from that of fluids, from the predictions of plasticity theories, and from intuitive expectation. In the static state, a part of the weight of the material is transferred to the walls by a downward vertical shear stress, bringing about the well-known Janssen saturation of the stress in vertical columns. When the material is sheared, the vertical shear stress changes sign, and the magnitudes of all components of the stress rise rapidly with depth. These qualitative features are preserved over a range of the Couette gap and shear rate, for smooth and rough walls and two model granular materials. To explain the anomalous rheological response, we consider some hypotheses that seem plausible a priori, but show that none survive after careful analysis of the experimental observations. We argue that the anomalous stress is due to an anisotropic fabric caused by the combined actions of gravity, shear, and frictional walls, for which we present indirect evidence from our experiments. A general theoretical framework for anisotropic plasticity is then presented. The detailed mechanics of how an anisotropic fabric is brought about by the above-mentioned factors is not clear, and promises to be a challenging problem for future investigations.

  17. Experimental investigation of the wall shear stress in a circular impinging jet

    NASA Astrophysics Data System (ADS)

    El Hassan, M.; Assoum, H. H.; Martinuzzi, R.; Sobolik, V.; Abed-Meraim, K.; Sakout, A.

    2013-07-01

    The influence of the large-scale vortical structures on the wall shear stress in a circular impinging jet is investigated experimentally for a Reynolds number of 1260. Time-resolved particle image velocimetry and polarographic measurements are performed simultaneously. It is found that the instantaneous wall shear stress is strongly dependent on the vortex dynamics, particularly for different parts of the transverse vortex. The influence of the vortex ring, the secondary and tertiary vortices on the ejection/sweep process near the wall is the main mechanism involved in the wall shear stress variation. In the region of the boundary layer separation, the wall shear stress amplitude increases just upstream of the separation and dramatically decreases in the recirculation zone downstream from the separation. The interaction between primary and secondary structures and their pairing process with the tertiary structure affects the sweep/ejection process near the wall and subsequently the wall shear stress variation. A comparison between the Finite Time Lyapunov Exponent (FTLE) method and the phase average technique is performed. It is shown that both methods describe the flow dynamics in the impinging region of the vortex ring. However, the FTLE method is more suitable for describing the unsteady separation of the boundary layer.

  18. Nature's rheologists: Lymphatic endothelial cells control migration in response to shear stress

    NASA Astrophysics Data System (ADS)

    Fuller, Gerald; Dunn, Alex; Surya, Vinay

    2015-03-01

    Endothelial cells (ECs) line the inner surface of blood and lymphatic vessels and are sensitive to fluid flow as part of their physiological function. EC organization, migration and vessel development are profoundly influenced by shear stresses, with important implications in cardiovascular disease and tumor metastasis. How ECs sense fluid flow is a central and unanswered question in cardiovascular biology. We developed a high-throughput live-cell flow chamber that models the gradients in wall shear stress experienced by ECs in vivo. Live-cell imaging allows us to probe cellular responses to flow, most notably EC migration, which has a key role in vessel remodeling. We find that most EC subtypes, including ECs from the venous, arterial, and microvascular systems, migrate in the flow direction. In contrast, human lymphatic microvascular ECs (hLMVECs) migrate against flow and up spatial gradients in wall shear stress. Further experiments reveal that hLMVECs are sensitive to the magnitude, direction, and the local spatial gradients in wall shear stress. Lastly, recent efforts have aimed to link this directional migration to spatial gradients in cell-mediated small molecule emission that may be linked to the gradient in wall shear stress.

  19. Large scale structures in a turbulent boundary layer and their imprint on wall shear stress

    NASA Astrophysics Data System (ADS)

    Pabon, Rommel; Barnard, Casey; Ukeiley, Lawrence; Sheplak, Mark

    2015-11-01

    Experiments were performed on a turbulent boundary layer developing on a flat plate model under zero pressure gradient flow. A MEMS differential capacitive shear stress sensor with a 1 mm × 1 mm floating element was used to capture the fluctuating wall shear stress simultaneously with streamwise velocity measurements from a hot-wire anemometer traversed in the wall normal direction. Near the wall, the peak in the cross correlation corresponds to an organized motion inclined 45° from the wall. In the outer region, the peak diminishes in value, but is still significant at a distance greater than half the boundary layer thickness, and corresponds to a structure inclined 14° from the wall. High coherence between the two signals was found for the low-frequency content, reinforcing the belief that large scale structures have a vital impact on wall shear stress. Thus, estimation of the wall shear stress from the low-frequency velocity signal will be performed, and is expected to be statistically significant in the outer boundary layer. Additionally, conditionally averaged mean velocity profiles will be presented to assess the effects of high and low shear stress. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

  20. Shear stress-induced redistribution of the glycocalyx on endothelial cells in vitro.

    PubMed

    Bai, Ke; Wang, Wen

    2014-04-01

    The glycocalyx is the inner most layer of the endothelium that is in direct contact with the circulating blood. Shear stress affects its synthesis and reorganization. This study focuses on changes in the spatial distribution of the glycocalyx caused by shear stimulation and its recovery following the removal of the shear stress. Sialic acid components of the glycocalyx on human umbilical vain endothelial cells are observed using confocal microscopy. The percentage area of the cell membrane covered by the glycocalyx, as well as the average fluorescence intensity ratio between the apical and edge areas of the cell is used to assess the spatial distribution of the glycocalyx on the cell membrane. Our results show that following 24 h shear stimulation, the glycocalyx relocates near the edge of endothelial cells (i.e., cell-cell junction regions). Following the removal of the shear stress, the glycocalyx redistributes and gradually appears in the apical region of the cell membrane. This redistribution is faster in the early hours (<4 h) after shear stimulation than that in the later stage (e.g., between 8 and 24 h). We further investigate the recovery of the glycocalyx after its enzyme degradation under either static or shear flow conditions. Our results show that following 24 h recovery under shear flow, the glycocalyx reappears predominantly near the edge of endothelial cells. Static and shear flow conditions result in notable changes in the spatial recovery of the glycocalyx, but the difference is not statistically significant. We hypothesize that newly synthesized glycocalyx is not structurally well developed. Its weak interaction with flow results in less than significant redistribution, contrary to what has been observed for a well-developed glycocalyx layer.

  1. Migration arising from gradients in shear stress: Particle distributions in Poiseuille flow

    NASA Technical Reports Server (NTRS)

    Leighton, D. T., Jr.

    1988-01-01

    Experimental evidence for the existence of shear induced migration processes is reviewed and the mechanism by Leighton and Acrivos (1987b) is described in detail. The proposed mechanism is shown to lead to the existence of an additional shear induced migration in the presence of gradients in shear stress such as would be found in Poiseuille flow, and which may be used to predict the amplitude of the observed short-term viscosity increase. The concentration and velocity profiles which result from such a migration are discussed in detail and are compared to the experimental observations of Karnis, Goldsmith and Mason (1966).

  2. Rheological regional properties of brain tissue studied under cyclic creep/ recovery shear stresses

    NASA Astrophysics Data System (ADS)

    Boudjema, F.; Lounis, M.; Khelidj, B.; Bessai, N.

    2015-04-01

    The rheological properties of brain tissue were studied by repeated creep-recovery shear tests under static conditions for different regions. Corpus callosum CC, Thalamus Th and Corona radiata CR. Non-linear viscoelastic model was also proposed to characterize the transient/steady states of shear creep results. From the creep-recovery data it was obvious that the brain tissues show high regional anisotropy. However. the both samples exhibit fluid viscoelastic properties in the first shear stress cycle of 100 Pa, while this behaviour evolutes to solid viscoelastic with cyclic effect.

  3. Analysis of adhesively bonded composite lap joints

    SciTech Connect

    Tong, L.; Kuruppu, M.; Kelly, D.

    1994-12-31

    A new nonlinear formulation is developed for the governing equations for the shear and peel stresses in adhesively bonded composite double lap joints. The new formulation allows arbitrary nonlinear stress-strain characteristics in both shear and peel behavior. The equations are numerically integrated using a shooting technique and Newton-Raphson method behind a user friendly interface. The failure loads are predicted by utilizing the maximum stress criterion, interlaminar delamination and the energy density failure criteria. Numerical examples are presented to demonstrate the effect of the nonlinear adhesive behavior on the stress distribution and predict the failure load and the associated mode.

  4. Influence of thickness and permeability of endothelial surface layer on transmission of shear stress in capillaries

    NASA Astrophysics Data System (ADS)

    Zhang, SongPeng; Zhang, XiangJun; Tian, Yu; Meng, YongGang; Lipowsky, Herbert

    2015-07-01

    The molecular coating on the surface of microvascular endothelium has been identified as a barrier to transvascular exchange of solutes. With a thickness of hundreds of nanometers, this endothelial surface layer (ESL) has been treated as a porous domain within which fluid shear stresses are dissipated and transmitted to the solid matrix to initiate mechanotransduction events. The present study aims to examine the effects of the ESL thickness and permeability on the transmission of shear stress throughout the ESL. Our results indicate that fluid shear stresses rapidly decrease to insignificant levels within a thin transition layer near the outer boundary of the ESL with a thickness on the order of ten nanometers. The thickness of the transition zone between free fluid and the porous layer was found to be proportional to the square root of the Darcy permeability. As the permeability is reduced ten-fold, the interfacial fluid and solid matrix shear stress gradients increase exponentially two-fold. While the interfacial fluid shear stress is positively related to the ESL thickness, the transmitted matrix stress is reduced by about 50% as the ESL thickness is decreased from 500 to 100 nm, which may occur under pathological conditions. Thus, thickness and permeability of the ESL are two main factors that determine flow features and the apportionment of shear stresses between the fluid and solid phases of the ESL. These results may shed light on the mechanisms of force transmission through the ESL and the pathological events caused by alterations in thickness and permeability of the ESL.

  5. Adhesives deliver low-shrink low-stress bonds and fast UV cure

    NASA Astrophysics Data System (ADS)

    Rhodes, Kyle T.

    2001-03-01

    Lower stress, higher quality assemblies as well as quantum increases in productivity are now possible with `new generation', light curing adhesives. This new technology makes obsolete the industry-accepted assumption that low strain requires slow curing UV adhesives, epoxies and cements. Curing in only seconds and without the need for secondary thermal cure, these new light curing adhesives produce laminates which are essentially strain-free, and edge bonds with shrinkage as low as 0.2%. This paper will compare and contrast these new adhesives with existing bonding technologies in typical applications. Included are comparison between epoxies, UV curing mercaptoesters, and the new light curing Aerobic Acrylates, as well as the incorporation of adhesives into optical component design.

  6. Adhesives deliver low-shrink low-stress bonds and fast UV cure

    NASA Astrophysics Data System (ADS)

    Rhodes, Kyle T.

    2001-06-01

    Lower stress, higher quality assemblies as well as quantum increases in productivity are now possible with `new generation', light curing adhesives. This new technology makes obsolete the industry-accepted assumption that low strain requires slow curing UV adhesives, epoxies and cements. Curing in only seconds and without the need for secondary thermal cure, these new light curing adhesives produce laminates which are essentially strain-free, and edge bonds with shrinkage as low as 0.2%. This paper will compare and contrast these new adhesives with existing bonding technologies in typical applications. Included are comparisons between epoxies, UV curing mercaptoesters, and the new light curing Aerobic Acrylates, as well as the incorporation of adhesives into optical component design.

  7. Effects of fluid shear stress on polyelectrolyte multilayers by neutron scattering studies

    SciTech Connect

    Singh, Saurabh; Junghans, Ann; Watkins, Erik; Kapoor, Yash; Toomey, Ryan; Majewski, Jaroslaw

    2015-02-17

    The structure of layer-by-layer (LbL) deposited nanofilm coatings consists of alternating polyethylenimine (PEI) and polystyrenesulfonate (PSS) films deposited on a single crystal quartz substrate. LbL-deposited nanofilms were investigated by neutron reflectomery (NR) in contact with water in the static and fluid shear stress conditions. The fluid shear stress was applied through a laminar flow of the liquid parallel to the quartz/polymer interface in a custom-built solid–liquid interface cell. The scattering length density profiles obtained from NR results of these polyelectrolyte multilayers (PEM), measured under different shear conditions, showed proportional decrease of volume fraction of water hydrating the polymers. For the highest shear rate applied (ca. 6800 s–1) the water volume fraction decreased by approximately 7%. The decrease of the volume fraction of water was homogeneous through the thickness of the film. Since there were not any significant changes in the total polymer thickness, it resulted in negative osmotic pressures in the film. The PEM films were compared with the behavior of thin films of thermoresponsive poly(N-isopropylacrylamide) (pNIPAM) deposited via spin-coating. The PEM and pNIPAM differ in their interactions with water molecules, and they showed opposite behaviors under the fluid shear stress. In both cases the polymer hydration was reversible upon the restoration of static conditions. Furthermore, a theoretical explanation is given to explain this difference in the effect of shear on hydration of polymeric thin films.

  8. The adaptive remodeling of endothelial glycocalyx in response to fluid shear stress.

    PubMed

    Zeng, Ye; Tarbell, John M

    2014-01-01

    The endothelial glycocalyx is vital for mechanotransduction and endothelial barrier integrity. We previously demonstrated the early changes in glycocalyx organization during the initial 30 min of shear exposure. In the present study, we tested the hypothesis that long-term shear stress induces further remodeling of the glycocalyx resulting in a robust layer, and explored the responses of membrane rafts and the actin cytoskeleton. After exposure to shear stress for 24 h, the glycocalyx components heparan sulfate, chondroitin sulfate, glypican-1 and syndecan-1, were enhanced on the apical surface, with nearly uniform spatial distributions close to baseline levels that differed greatly from the 30 min distributions. Heparan sulfate and glypican-1 still clustered near the cell boundaries after 24 h of shear, but caveolin-1/caveolae and actin were enhanced and concentrated across the apical aspects of the cell. Our findings also suggest the GM1-labelled membrane rafts were associated with caveolae and glypican-1/heparan sulfate and varied in concert with these components. We conclude that remodeling of the glycocalyx to long-term shear stress is associated with the changes in membrane rafts and the actin cytoskeleton. This study reveals a space- and time- dependent reorganization of the glycocalyx that may underlie alterations in mechanotransduction mechanisms over the time course of shear exposure.

  9. Measurement of shear stress-mediated intracellular calcium dynamics in human dermal lymphatic endothelial cells

    PubMed Central

    Jafarnejad, M.; Cromer, W. E.; Kaunas, R. R.; Zhang, S. L.; Zawieja, D. C.

    2015-01-01

    The shear stress applied to lymphatic endothelial cells (LEC) by lymph flow changes dramatically under normal conditions as well as in response to disease conditions and immune reactions. In general, LEC are known to regulate the contraction frequency and strength of lymphatic pumping in response to shear stress. Intracellular calcium concentration ([Ca2+]i) is an important factor that regulates lymphatic contraction characteristics. In this study, we measured changes in the [Ca2+]i under different shear stress levels and determined the source of this calcium signal. Briefly, human dermal LEC were cultured in custom-made microchannels for 3 days before loading with 2 µM fura-2 AM, a ratiometric calcium dye to measure [Ca2+]i. Step changes in shear stress resulted in a rapid increase in [Ca2+]i followed by a gradual return to the basal level and sometimes below the initial baseline (45.2 ± 2.2 nM). The [Ca2+]i reached a peak at 126.2 ± 5.6 nM for 10 dyn/cm2 stimulus, whereas the peak was only 71.8 ± 5.4 nM for 1 dyn/cm2 stimulus, indicating that the calcium signal depends on the magnitude of shear stress. Removal of the extracellular calcium from the buffer or pharmocological blockade of calcium release-activated calcium (CRAC) channels significantly reduced the peak [Ca2+]i, demonstrating a role of extracellular calcium entry. Inhibition of endoplasmic reticulum (ER) calcium pumps showed the importance of intracellular calcium stores in the initiation of this signal. In conclusion, we demonstrated that the shear-mediated calcium signal is dependent on the magnitude of the shear and involves ER store calcium release and extracellular calcium entry. PMID:25617358

  10. Exercise-Mediated Wall Shear Stress Increases Mitochondrial Biogenesis in Vascular Endothelium

    PubMed Central

    Kim, Boa; Lee, Hojun; Kawata, Keisuke; Park, Joon-Young

    2014-01-01

    Objective Enhancing structural and functional integrity of mitochondria is an emerging therapeutic option against endothelial dysfunction. In this study, we sought to investigate the effect of fluid shear stress on mitochondrial biogenesis and mitochondrial respiratory function in endothelial cells (ECs) using in vitro and in vivo complementary studies. Methods and Results Human aortic- or umbilical vein-derived ECs were exposed to laminar shear stress (20 dyne/cm2) for various durations using a cone-and-plate shear apparatus. We observed significant increases in the expression of key genes related to mitochondrial biogenesis and mitochondrial quality control as well as mtDNA content and mitochondrial mass under the shear stress conditions. Mitochondrial respiratory function was enhanced when cells were intermittently exposed to laminar shear stress for 72 hrs. Also, shear-exposed cells showed diminished glycolysis and decreased mitochondrial membrane potential (ΔΨm). Likewise, in in vivo experiments, mice that were subjected to a voluntary wheel running exercise for 5 weeks showed significantly higher mitochondrial content determined by en face staining in the conduit (greater and lesser curvature of the aortic arch and thoracic aorta) and muscle feed (femoral artery) arteries compared to the sedentary control mice. Interestingly, however, the mitochondrial biogenesis was not observed in the mesenteric artery. This region-specific adaptation is likely due to the differential blood flow redistribution during exercise in the different vessel beds. Conclusion Taken together, our findings suggest that exercise enhances mitochondrial biogenesis in vascular endothelium through a shear stress-dependent mechanism. Our findings may suggest a novel mitochondrial pathway by which a chronic exercise may be beneficial for vascular function. PMID:25375175

  11. Tumor cell cycle arrest induced by shear stress: Roles of integrins and Smad

    PubMed Central

    Chang, Shun-Fu; Chang, Cheng Allen; Lee, Ding-Yu; Lee, Pei-Ling; Yeh, Yu-Ming; Yeh, Chiuan-Ren; Cheng, Cheng-Kung; Chien, Shu; Chiu, Jeng-Jiann

    2008-01-01

    Interstitial flow in and around tumor tissue affects the mechanical microenvironment to modulate tumor cell growth and metastasis. We investigated the roles of flow-induced shear stress in modulating cell cycle distribution in four tumor cell lines and the underlying mechanisms. In all four cell lines, incubation under static conditions for 24 or 48 h led to G0/G1 arrest; in contrast, shear stress (12 dynes/cm2) induced G2/M arrest. The molecular basis of the shear effect was analyzed, and the presentation on molecular mechanism is focused on human MG63 osteosarcoma cells. Shear stress induced increased expressions of cyclin B1 and p21CIP1 and decreased expressions of cyclins A, D1, and E, cyclin-dependent protein kinases (Cdk)-1, -2, -4, and -6, and p27KIP1 as well as a decrease in Cdk1 activity. Using specific antibodies and small interfering RNA, we found that the shear-induced G2/M arrest and corresponding changes in G2/M regulatory protein expression and activity were mediated by αvβ3 and β1 integrins through bone morphogenetic protein receptor type IA-specific Smad1 and Smad5. Shear stress also down-regulated runt-related transcription factor 2 (Runx2) binding activity and osteocalcin and alkaline phosphatase expressions in MG63 cells; these responses were mediated by αvβ3 and β1 integrins through Smad5. Our findings provide insights into the mechanism by which shear stress induces G2/M arrest in tumor cells and inhibits cell differentiation and demonstrate the importance of mechanical microenvironment in modulating molecular signaling, gene expression, cell cycle, and functions in tumor cells. PMID:18310319

  12. Fracture transmissivity as a function of normal and shear stress: First results in Opalinus Clay

    NASA Astrophysics Data System (ADS)

    Cuss, Robert J.; Milodowski, Antoni; Harrington, Jon F.

    Fracture transmissivity has been investigated along an idealised fracture for the influence of normal stress and for the transient behaviour during a slow shear experiment. A linear trend for the relationship between effective stress and transmissivity has been proposed for normal loads between 1 and 5 MPa; as effective stress increases transmissivity decreases. Transmissivity was very low throughout the complete spectrum of effective stresses examined and was close to the permeability for intact Opalinus Clay, suggesting that the fracture had effectively closed. During active shearing at a constant normal load, fracture transmissivity was seen to initially reduce, probably due to clear smearing. A series of flux events were seen, with transmissivity increasing by a factor of four. Some of the flux events corresponded with dilation, whilst others did not. This suggests that the opening flow paths were localised and did not result in bulk dilatancy. During the course of the shear test the sample formed its own series of fractures and a complex pattern of deformation occurred along the fracture surface to a depth of less than 1 mm. The impression of the end of the injection hole clearly shows that the block underwent at least 5 mm of the total 6 mm of shear displacement. The injection of fluorescein showed that flow along the fracture was not uniformly radial, as one might expect for such an experimental geometry. At the time of injection there were a number of dominant flow features, mainly in the direction of shear and only perpendicular on one side of the fracture surface. Flow occurred along the original fracture surface as well as the newly formed shear surface, indicating multiple pathways in a complex manner. The evolution of fracture transmissivity is very complex, even along initially planar surfaces. Fracture transmissivity has been seen to be a function of normal stress and porewater pressure, and has also been seen to be a dynamic feature during shear.

  13. Interaction of Vascular Smooth Muscle Cells Under Low Shear Stress

    NASA Technical Reports Server (NTRS)

    Seidel, Charles L.

    1998-01-01

    The blood vessel wall consists of three cellular layers, an outer adventitial, a middle medial and an inner intimal layer. When the blood vessel forms in the embryo it begins as a tube composed of a single cell type called endothelial cells. Over time, other cells are recruited from the surrounding tissue to form additional layers on the outer surface of the endothelial tube. The cells that are recruited are called mesenchymal cells. Mesenchymal cells are responsible for the production of connective tissue that holds the blood vessel together and for developing into vascular smooth muscle cells that are responsible for regulating the diameter of the vessel (1) and therefore, blood flow. In a fully developed blood vessel, the endothelial cells make- up the majority of cells in the intimal layer while the mesenchymal cells make-up the majority of cells in the medial and adventitial layers. Within the medial layer of a mature vessel, cells are organized into multiple circular layers of alternating bands of connective tissue and cells. The cell layer is composed of a mixture of mesenchymal cells that have not developed into smooth muscle cells and fully developed smooth muscle cells (2). The assembly and organization of complex tissues is directed in part by a signaling system composed of proteins on the cell surface called adhesion molecules. Adhesion molecules enable cells to recognize each other as well as the composition of the connective tissue in which they reside (3). It was hypothesized that the different cell types that compose the vascular wall possess different adhesion molecules that enable them to recognize each other and through this recognition system, form the complex layered organization of the vascular wall. In other words, the layered organization is an intrinsic property of the cells. If this hypothesis is correct then the different cells that make up the vessel wall, when mixed together, should organize themselves into a layered structure

  14. Monitoring the Contact Stress Distribution of Gecko-Inspired Adhesives Using Mechano-Sensitive Surface Coatings.

    PubMed

    Neubauer, Jens W; Xue, Longjian; Erath, Johann; Drotlef, Dirk-M; Campo, Aránzazu Del; Fery, Andreas

    2016-07-20

    The contact geometry of microstructured adhesive surfaces is of high relevance for adhesion enhancement. Theoretical considerations indicate that the stress distribution in the contact zone is crucial for the detachment mechanism, but direct experimental evidence is missing so far. In this work, we propose a method that allows, for the first time, the detection of local stresses at the contact area of biomimetic adhesive microstructures during contact formation, compression and detachment. We use a mechano-sensitive polymeric layer, which turns mechanical stresses into changes of fluorescence intensity. The biomimetic surface is brought into contact with this layer in a well-defined fashion using a microcontact printer, while the contact area is monitored with fluorescence microscopy in situ. Thus, changes in stress distribution across the contact area during compression and pull-off can be visualized with a lateral resolution of 1 μm. We apply this method to study the enhanced adhesive performance of T-shaped micropillars, compared to flat punch microstructures. We find significant differences in the stress distribution of the both differing contact geometries during pull-off. In particular, we find direct evidence for the suppression of crack nucleation at the edge of T-shaped pillars, which confirms theoretical models for the superior adhesive properties of these structures. PMID:27327111

  15. Monitoring the Contact Stress Distribution of Gecko-Inspired Adhesives Using Mechano-Sensitive Surface Coatings.

    PubMed

    Neubauer, Jens W; Xue, Longjian; Erath, Johann; Drotlef, Dirk-M; Campo, Aránzazu Del; Fery, Andreas

    2016-07-20

    The contact geometry of microstructured adhesive surfaces is of high relevance for adhesion enhancement. Theoretical considerations indicate that the stress distribution in the contact zone is crucial for the detachment mechanism, but direct experimental evidence is missing so far. In this work, we propose a method that allows, for the first time, the detection of local stresses at the contact area of biomimetic adhesive microstructures during contact formation, compression and detachment. We use a mechano-sensitive polymeric layer, which turns mechanical stresses into changes of fluorescence intensity. The biomimetic surface is brought into contact with this layer in a well-defined fashion using a microcontact printer, while the contact area is monitored with fluorescence microscopy in situ. Thus, changes in stress distribution across the contact area during compression and pull-off can be visualized with a lateral resolution of 1 μm. We apply this method to study the enhanced adhesive performance of T-shaped micropillars, compared to flat punch microstructures. We find significant differences in the stress distribution of the both differing contact geometries during pull-off. In particular, we find direct evidence for the suppression of crack nucleation at the edge of T-shaped pillars, which confirms theoretical models for the superior adhesive properties of these structures.

  16. The Effects of Hemodynamic Shear Stress on Stemness of Acute Myelogenous Leukemia (AML)

    NASA Astrophysics Data System (ADS)

    Raddatz, Andrew; Triantafillu, Ursula; Kim, Yonghyun (John)

    2015-11-01

    Cancer stem cells (CSCs) have recently been identified as the root cause of tumors generated from cancer cell populations. This is because these CSCs are drug-resistant and have the ability to self-renew and differentiate. Current methods of culturing CSCs require much time and money, so cancer cell culture protocols, which maximize yield of CSCs are needed. It was hypothesized that the quantity of Acute myelogenous leukemia stem cells (LSCs) would increase after applying shear stress to the leukemia cells based on previous studies with breast cancer in bioreactors. The shear stress was applied by pumping the cells through narrow tubing to mimic the in vivo bloodstream environment. In support of the hypothesis, shear stress was found to increase the amount of LSCs in a given leukemia population. This work was supported by NSF REU Site Award 1358991.

  17. An integrated temperature-compensated flexible shear-stress sensor microarray with concentrated leading-wire

    NASA Astrophysics Data System (ADS)

    Tang, Jian; Liu, Wu; Zhang, Weiping; Sun, Yongming; Chen, Honghai

    2016-02-01

    Flexible shear stress sensor is quite important for characterizing curved surface flows. In this work, a novel integrated shear stress sensor microarray is designed with twenty parallel channels, which share the concentrated leading-wire to transmit the ground signal. Electrical pads in rows are easily connected to the circuits with two separate Wheatstone bridges and constant-temperature-difference mode operation is provided for the hot-wires. Temperature crosstalk between adjacent hot-wires is prevented well and the effectiveness of the temperature compensated circuits is verified. Relatively large output response is obtained as the shear stress varies and the sensitivity of the sensors is measured about 0.086 V2/Pa1/3 with nonlinearity lower than 1%, revealing high performance characteristic of the sensors.

  18. On determining wall shear stress in spatially developing two-dimensional wall-bounded flows

    NASA Astrophysics Data System (ADS)

    Mehdi, Faraz; Johansson, T. Gunnar; White, Christopher M.; Naughton, Jonathan W.

    2014-01-01

    A full momentum integral-based method for determining wall shear stress is presented. The method is mathematically exact and has the advantage of having no explicit streamwise gradient terms. It is applicable for flows that change rapidly in the streamwise direction and, in particular, to flows with ill-defined outer boundary conditions or when the measurement grid does not extend over the whole boundary layer thickness. The method is applied to two different experimental plane turbulent wall jet data sets for which independent estimates of wall shear stress were known, and the different results compare favorably. Complications owing to experimental limitations and measurement error in determining wall shear stress from the proposed method are presented, and mitigating strategies are described.

  19. Accuracy and grid convergence of wall shear stress measured by lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Kang, Xiuying; Dun, Zhiya

    2014-04-01

    Based on a two-dimensional Poiseuille and Wormersley flow, accuracy and grid convergence of velocity, shear stress and wall shear stress (WSS) measurements were investigated using the single-relaxation-time (SRT) and multiple-relaxation-time (MRT) lattice Boltzmann models under various open and wall boundary conditions. The results showed that grid convergence of shear stress and WSS are not consistent with that of velocity when flow channels are not aligned to the grids, and strongly rely on the used wall boundary conditions. And the MRT model is slightly superior to the SRT when simulating the complicated border flow. Moreover the WSS should be approximately calculated on the fluid nodes closest to walls under the curved boundary (CB) condition but not for the bounce-back (BB) boundary scheme. As applications, distributions of WSS in a wavy-walled channel and distensible carotid artery were simulated which would much more depend on local roughness of vessel intima than channel diameters.

  20. Online quantitative phase imaging of vascular endothelial cells under fluid shear stress utilizing digital holographic microscopy

    NASA Astrophysics Data System (ADS)

    Odenthal-Schnittler, Maria; Schnittler, Hans Joachim; Kemper, Björn

    2016-03-01

    We have explored the utilization of quantitative phase imaging with digital holographic microscopy (DHM) as a novel tool for quantifying the dynamics of morphologic parameters (morphodynamics) of confluent endothelial cell layers under fluid shear stress conditions. Human umbilical vein endothelial cells (HUVECs) were exposed to fluid shear stress in a transparent cone/plate flow device (BioTech-Flow-System) and imaged with a modular setup for quantitative DHM phase imaging for up to 48 h. The resulting series of quantitative phase image sequences were analyzed for the average surface roughness of the cell layers and cell alignment. Our results demonstrate that quantitative phase imaging is a powerful and reliable tool to quantify the dynamics of morphological adaptation of endothelial cells to fluid shear stress.

  1. An integrated temperature-compensated flexible shear-stress sensor microarray with concentrated leading-wire.

    PubMed

    Tang, Jian; Liu, Wu; Zhang, Weiping; Sun, Yongming; Chen, Honghai

    2016-02-01

    Flexible shear stress sensor is quite important for characterizing curved surface flows. In this work, a novel integrated shear stress sensor microarray is designed with twenty parallel channels, which share the concentrated leading-wire to transmit the ground signal. Electrical pads in rows are easily connected to the circuits with two separate Wheatstone bridges and constant-temperature-difference mode operation is provided for the hot-wires. Temperature crosstalk between adjacent hot-wires is prevented well and the effectiveness of the temperature compensated circuits is verified. Relatively large output response is obtained as the shear stress varies and the sensitivity of the sensors is measured about 0.086 V(2)/Pa(1/3) with nonlinearity lower than 1%, revealing high performance characteristic of the sensors. PMID:26931882

  2. Crack initiation observation and local stress analysis in shear fracture tests of ultra-high strength steels

    NASA Astrophysics Data System (ADS)

    Ma, Ninshu; Takada, Kenji; Sugimoto, Nao

    2016-08-01

    To investigate the local strain and stress at the crack initiation position in shear fracture test pieces of ultra-high strength steels, a butterfly shear fracture specimen was employed. The crack initiation position and propagation direction were observed during shear fracture tests by high speed cameras and investigated through analysing the fracture surface by scanning electron microscope. Further, the finite element method was employed and the stress-triaxiality at the crack initiation position was investigated. It can be obtained that the crack initiated at the position where the stress state is close to uniaxial tensile state or plane strain state more than pure shear stress state.

  3. Assessment of the Shear Bond Strength between Nanofilled Composite Bonded to Glass-ionomer Cement Using Self-etch Adhesive with Different pHs and Total-Etch Adhesive

    PubMed Central

    Sharafeddin, Farahnaz; Choobineh, Mohammad Mehdi

    2016-01-01

    Statement of the Problem In the sandwich technique, the undesirable bond between the composite resin and glass-ionomer cement (GIc) is one of the most important factors which lead to the failure of restoration. Total-etch and self-etch adhesives may improve the bond strength based on their pH. Purpose The purpose of this study was to evaluate the shear bond strength between the nanofilled composite resin and GIc using different adhesives. Materials and Method In this experimental study, 40 specimens (6×6mm) in 4 groups (n=10) were prepared in acrylic mold. Each specimen contained conventional GI ChemFil Superior with a height of 3mm, bonded to Z350 composite resin with a height measured 3mm. In order to bond the composite to the GI, the following adhesives were used, respectively: A: mild Clearfil SE Bond self-etch (pH=2), B: intermediate OptiBond self-etch (pH=1.4), C: strong Adper Prompt L-Pop (pH=1), and D: Adper Single Bond 2 total-etch (pH=7.2). The shear bond strength was measured by using universal testing machine with a crosshead speed of 1mm/min. One-way ANOVA and Tukey’s test were used to analyze the data (p< 0.05). Results The shear bond strength in group A was significantly higher than group B (p= 0.002), C (p< 0.001), and D (p< 0.001). Moreover, the shear bond strength of groups A and B (self-etch) was significantly different from group D (total-etch) (p< 0.001); and C (self-etch) with D (p= 0.024). Conclusion The results of this study showed that applying the mild self-etch adhesive between the composite and the GIc results in stronger shear bond strength compared to intermediate and strong self-etch adhesives. Moreover, the self-etch adhesive increased the shear bond strength between composite resin and GIc more significantly than total-etch adhesive. PMID:26966701

  4. Estimation of the bed shear stress in vegetated and bare channels with smooth beds

    NASA Astrophysics Data System (ADS)

    Yang, Judy Q.; Kerger, Francois; Nepf, Heidi M.

    2015-05-01

    The shear stress at the bed of a channel influences important benthic processes such as sediment transport. Several methods exist to estimate the bed shear stress in bare channels without vegetation, but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production. This study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds. The model, which is supported by measurements, indicates that for both bare and vegetated channels with smooth beds, within a viscous sublayer at the bed, the viscous stress decreases linearly with increasing distance from the bed, resulting in a parabolic velocity profile at the bed. For bare channels, the model describes the velocity profile in the overlap region of the Law of the Wall. For emergent canopies of sufficient density (frontal area per unit canopy volume a≥4.3 m-1), the thickness of the linear-stress layer is set by the stem diameter, leading to a simple estimate for bed shear stress.

  5. Shear Stress Transmission Model for the Flagellar Rotary Motor

    PubMed Central

    Mitsui, Toshio; Ohshima, Hiroyuki

    2008-01-01

    Most bacteria that swim are propelled by flagellar filaments, which are driven by a rotary motor powered by proton flux. The mechanism of the flagellar motor is discussed by reforming the model proposed by the present authors in 2005. It is shown that the mean strength of Coulomb field produced by a proton passing the channel is very strong in the Mot assembly so that the Mot assembly can be a shear force generator and induce the flagellar rotation. The model gives clear calculation results in agreement with experimental observations, e g., for the charasteristic torque-velocity relationship of the flagellar rotation. PMID:19325821

  6. Theory and Practice of Shear/Stress Strain Gage Hygrometry

    NASA Technical Reports Server (NTRS)

    Shams, Qamar A.; Fenner, Ralph L.

    2006-01-01

    Mechanical hygrometry has progressed during the last several decades from crude hygroscopes to state-of-the art strain-gage sensors. The strain-gage devices vary from different metallic beams to strain-gage sensors using cellulose crystallite elements, held in full shear restraint. This old technique is still in use but several companies are now actively pursuing development of MEMS miniaturized humidity sensors. These new sensors use polyimide thin film for water vapor adsorption and desorption. This paper will provide overview about modern humidity sensors.

  7. Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears

    NASA Astrophysics Data System (ADS)

    Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

    2011-04-01

    Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium E ×B velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or "profile shear" in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) E ×B and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a "null" toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the E ×B shear and parallel velocity (Coriolis force) pinching components from the larger "diffusive" parallel velocity shear driven component and

  8. Shear-stress fluctuations in self-assembled transient elastic networks.

    PubMed

    Wittmer, J P; Kriuchevskyi, I; Cavallo, A; Xu, H; Baschnagel, J

    2016-06-01

    Focusing on shear-stress fluctuations, we investigate numerically a simple generic model for self-assembled transient networks formed by repulsive beads reversibly bridged by ideal springs. With Δt being the sampling time and t_{☆}(f)∼1/f the Maxwell relaxation time (set by the spring recombination frequency f), the dimensionless parameter Δx=Δt/t_{☆}(f) is systematically scanned from the liquid limit (Δx≫1) to the solid limit (Δx≪1) where the network topology is quenched and an ensemble average over m-independent configurations is required. Generalizing previous work on permanent networks, it is shown that the shear-stress relaxation modulus G(t) may be efficiently determined for all Δx using the simple-average expression G(t)=μ_{A}-h(t) with μ_{A}=G(0) characterizing the canonical-affine shear transformation of the system at t=0 and h(t) the (rescaled) mean-square displacement of the instantaneous shear stress as a function of time t. This relation is compared to the standard expression G(t)=c[over ̃](t) using the (rescaled) shear-stress autocorrelation function c[over ̃](t). Lower bounds for the m configurations required by both relations are given.

  9. A Multi-Phase Based Fluid-Structure-Microfluidic interaction sensor for Aerodynamic Shear Stress

    NASA Astrophysics Data System (ADS)

    Hughes, Christopher; Dutta, Diganta; Bashirzadeh, Yashar; Ahmed, Kareem; Qian, Shizhi

    2014-11-01

    A novel innovative microfluidic shear stress sensor is developed for measuring shear stress through multi-phase fluid-structure-microfluidic interaction. The device is composed of a microfluidic cavity filled with an electrolyte liquid. Inside the cavity, two electrodes make electrochemical velocimetry measurements of the induced convection. The cavity is sealed with a flexible superhydrophobic membrane. The membrane will dynamically stretch and flex as a result of direct shear cross-flow interaction with the seal structure, forming instability wave modes and inducing fluid motion within the microfluidic cavity. The shear stress on the membrane is measured by sensing the induced convection generated by membrane deflections. The advantages of the sensor over current MEMS based shear stress sensor technology are: a simplified design with no moving parts, optimum relationship between size and sensitivity, no gaps such as those created by micromachining sensors in MEMS processes. We present the findings of a feasibility study of the proposed sensor including wind-tunnel tests, microPIV measurements, electrochemical velocimetry, and simulation data results. The study investigates the sensor in the supersonic and subsonic flow regimes. Supported by a NASA SBIR phase 1 contract.

  10. Shear-stress fluctuations in self-assembled transient elastic networks

    NASA Astrophysics Data System (ADS)

    Wittmer, J. P.; Kriuchevskyi, I.; Cavallo, A.; Xu, H.; Baschnagel, J.

    2016-06-01

    Focusing on shear-stress fluctuations, we investigate numerically a simple generic model for self-assembled transient networks formed by repulsive beads reversibly bridged by ideal springs. With Δ t being the sampling time and t(f ) ˜1 /f the Maxwell relaxation time (set by the spring recombination frequency f ), the dimensionless parameter Δ x =Δ t /t(f ) is systematically scanned from the liquid limit (Δ x ≫1 ) to the solid limit (Δ x ≪1 ) where the network topology is quenched and an ensemble average over m -independent configurations is required. Generalizing previous work on permanent networks, it is shown that the shear-stress relaxation modulus G (t ) may be efficiently determined for all Δ x using the simple-average expression G (t ) =μA-h (t ) with μA=G (0 ) characterizing the canonical-affine shear transformation of the system at t =0 and h (t ) the (rescaled) mean-square displacement of the instantaneous shear stress as a function of time t . This relation is compared to the standard expression G (t ) =c ˜(t ) using the (rescaled) shear-stress autocorrelation function c ˜(t ) . Lower bounds for the m configurations required by both relations are given.

  11. Shear-stress fluctuations in self-assembled transient elastic networks.

    PubMed

    Wittmer, J P; Kriuchevskyi, I; Cavallo, A; Xu, H; Baschnagel, J

    2016-06-01

    Focusing on shear-stress fluctuations, we investigate numerically a simple generic model for self-assembled transient networks formed by repulsive beads reversibly bridged by ideal springs. With Δt being the sampling time and t_{☆}(f)∼1/f the Maxwell relaxation time (set by the spring recombination frequency f), the dimensionless parameter Δx=Δt/t_{☆}(f) is systematically scanned from the liquid limit (Δx≫1) to the solid limit (Δx≪1) where the network topology is quenched and an ensemble average over m-independent configurations is required. Generalizing previous work on permanent networks, it is shown that the shear-stress relaxation modulus G(t) may be efficiently determined for all Δx using the simple-average expression G(t)=μ_{A}-h(t) with μ_{A}=G(0) characterizing the canonical-affine shear transformation of the system at t=0 and h(t) the (rescaled) mean-square displacement of the instantaneous shear stress as a function of time t. This relation is compared to the standard expression G(t)=c[over ̃](t) using the (rescaled) shear-stress autocorrelation function c[over ̃](t). Lower bounds for the m configurations required by both relations are given. PMID:27415324

  12. Low shear stress induces M1 macrophage polarization in murine thin-cap atherosclerotic plaques.

    PubMed

    Seneviratne, Anusha N; Cole, Jennifer E; Goddard, Michael E; Park, Inhye; Mohri, Zahra; Sansom, Stephen; Udalova, Irina; Krams, Rob; Monaco, Claudia

    2015-12-01

    Macrophages, a significant component of atherosclerotic plaques vulnerable to acute complications, can be pro-inflammatory (designated M1), regulatory (M2), lipid- (Mox) or Heme-induced (Mhem). We showed previously that low (LSS) and oscillatory (OSS) shear stress cause thin-cap fibroatheroma and stable smooth muscle cell-rich plaque formation respectively in ApoE-knockout (ApoE(-/-)) mice. Here we investigated whether different shear stress conditions relate to specific changes in macrophage polarization and plaque morphology by applying a shear stress-altering cast to the carotid arteries of high fat-fed ApoE(-/-) mice. The M1 markers iNOS and IRF5 were highly expressed in macrophage-rich areas of LSS lesions compared to OSS lesions 6weeks after cast placement, while the M2 marker Arginase-1, and Mox/Mhem markers HO-1 and CD163 were elevated in OSS lesions. Our data indicates shear stress could be an important determinant of macrophage polarization in atherosclerosis, with low shear promoting M1 programming.

  13. Interface shear stresses during ambulation with a below-knee prosthetic limb.

    PubMed

    Sanders, J E; Daly, C H; Burgess, E M

    1992-01-01

    Shear stresses on a residual limb in a prosthetic socket are considered clinically to contribute to tissue breakdown in below-knee amputees. When applied simultaneously with normal stresses, they can cause injury within the skin or can generate an abrasion on the surface. To gain insight into shear stresses and parameters that affect them, interface stresses were recorded on below-knee amputee subjects during walking trials. On the tibial flares, resultant shear ranged from 5.6 kPa to 39.0 kPa, while on the posterior surface it ranged from 5.0 kPa to 40.7 kPa. During stance phase, anterior resultant shears on a socket were directed toward the apex while posterior resultant shears were directed downward approximately perpendicular to the ground. Waveform shapes were usually double-peaked, with the first peak at 25% to 40% into stance phase and the second peak at 65% to 85% into stance. Application of these results to residual limb tissue mechanics and prosthetic design is discussed.

  14. Critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires

    USGS Publications Warehouse

    Moody, J.A.; Dungan, Smith J.; Ragan, B.W.

    2005-01-01

    [1] Increased erosion is a well-known response after wildfire. To predict and to model erosion on a landscape scale requires knowledge of the critical shear stress for the initiation of motion of soil particles. As this soil property is temperature-dependent, a quantitative relation between critical shear stress and the temperatures to which the soils have been subjected during a wildfire is required. In this study the critical shear stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures (40??-550??C) for 1 hour. Results were obtained for four replicates of soils derived from three different types of parent material (granitic bedrock, sandstone, and volcanic tuffs). In general, the relation between critical shear stress and temperature can be separated into three different temperature ranges (275??C), which are similar to those for water repellency and temperature. The critical shear stress was most variable (1.0-2.0 N m-2) for temperatures 2.0 N m-2) between 175?? and 275??C, and was essentially constant (0.5-0.8 N m-2) for temperatures >275??C. The changes in critical shear stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds. Wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils. Our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire. Copyright 2005 by the American Geophysical Union.

  15. Vascular endothelial cell membranes differentiate between stretch and shear stress through transitions in their lipid phases.

    PubMed

    Yamamoto, Kimiko; Ando, Joji

    2015-10-01

    Vascular endothelial cells (ECs) respond to the hemodynamic forces stretch and shear stress by altering their morphology, functions, and gene expression. However, how they sense and differentiate between these two forces has remained unknown. Here we report that the plasma membrane itself differentiates between stretch and shear stress by undergoing transitions in its lipid phases. Uniaxial stretching and hypotonic swelling increased the lipid order of human pulmonary artery EC plasma membranes, thereby causing a transition from the liquid-disordered phase to the liquid-ordered phase in some areas, along with a decrease in membrane fluidity. In contrast, shear stress decreased the membrane lipid order and increased membrane fluidity. A similar increase in lipid order occurred when the artificial lipid bilayer membranes of giant unilamellar vesicles were stretched by hypotonic swelling, indicating that this is a physical phenomenon. The cholesterol content of EC plasma membranes significantly increased in response to stretch but clearly decreased in response to shear stress. Blocking these changes in the membrane lipid order by depleting membrane cholesterol with methyl-β-cyclodextrin or by adding cholesterol resulted in a marked inhibition of the EC response specific to stretch and shear stress, i.e., phosphorylation of PDGF receptors and phosphorylation of VEGF receptors, respectively. These findings indicate that EC plasma membranes differently respond to stretch and shear stress by changing their lipid order, fluidity, and cholesterol content in opposite directions and that these changes in membrane physical properties are involved in the mechanotransduction that activates membrane receptors specific to each force. PMID:26297225

  16. Dynamic deformation capability of a red blood cell under a cyclically reciprocating shear stress.

    PubMed

    Watanabe, N; Yasuda, T; Kataoka, H; Takatani, S

    2004-01-01

    Red blood cells (RBCs) in the cardiovascular devices are exposed to varying degree of the shear stress from all the directions. However the RBCs' deformability or the deformation capability under such a shear stress is not well understood. In this study, we designed and built a system that can induce a cyclically reciprocating shear stress to a RBC suspension. The arm of the cyclically reciprocating shear stress device was attached to the upper piece of the parallel glass plates between which a suspension of human RBCs (1% hematocrit whole blood diluted in a 32 weight% dextran phosphate buffer solution) was contained. The cyclic reciprocating motion of the upper glass plate of 3.0 mm stroke length was produced using a slider-crank shaft mechanism that was linked to an eccentric cam-motor system. Each rotation of the motor produced a 3.0 mm stroke each in the forward and backward direction of the slider block. The clearance between the two glass plates was adjusted to 30 micrometer. The cyclic reciprocating glass plate apparatus was attached to a light microscope stage (IX71 Olympus with x40 objective lens) for illumination with a 350 watt metal halide light source. A high speed camera (MEMREMCAM fx-K3 Nac, 5000 frames per second with shutter kept open) was attached to the microscope to capture the deformation process of the RBCs under cyclic shear stress. The preliminary result indicated that the correlation between the amplitude of the maximum shear stress and the RBCs' deformability. This indicates a potential application of the cyclic reciprocating device to evaluate the temporal response of the RBCs deformability prior to its destruction. The future study will focus on the study of the relative velocity of the erythrocytes with respect to the velocity of the reciprocating plate. PMID:17271457

  17. Mode selective generation of guided waves by systematic optimization of the interfacial shear stress profile

    NASA Astrophysics Data System (ADS)

    Yazdanpanah Moghadam, Peyman; Quaegebeur, Nicolas; Masson, Patrice

    2015-01-01

    Piezoelectric transducers are commonly used in structural health monitoring systems to generate and measure ultrasonic guided waves (GWs) by applying interfacial shear and normal stresses to the host structure. In most cases, in order to perform damage detection, advanced signal processing techniques are required, since a minimum of two dispersive modes are propagating in the host structure. In this paper, a systematic approach for mode selection is proposed by optimizing the interfacial shear stress profile applied to the host structure, representing the first step of a global optimization of selective mode actuator design. This approach has the potential of reducing the complexity of signal processing tools as the number of propagating modes could be reduced. Using the superposition principle, an analytical method is first developed for GWs excitation by a finite number of uniform segments, each contributing with a given elementary shear stress profile. Based on this, cost functions are defined in order to minimize the undesired modes and amplify the selected mode and the optimization problem is solved with a parallel genetic algorithm optimization framework. Advantages of this method over more conventional transducers tuning approaches are that (1) the shear stress can be explicitly optimized to both excite one mode and suppress other undesired modes, (2) the size of the excitation area is not constrained and mode-selective excitation is still possible even if excitation width is smaller than all excited wavelengths, and (3) the selectivity is increased and the bandwidth extended. The complexity of the optimal shear stress profile obtained is shown considering two cost functions with various optimal excitation widths and number of segments. Results illustrate that the desired mode (A0 or S0) can be excited dominantly over other modes up to a wave power ratio of 1010 using an optimal shear stress profile.

  18. Effect of bubble flow velocity on drag-force and shear stress working on submerged hollow fibre membrane.

    PubMed

    Nagaoka, H; Kurosaka, M; Shibata, N; Kobayashi, M

    2006-01-01

    This study is aimed at elucidating the mechanism by which rising air bubbles induce shear stress on hollow fibre membrane surfaces. Shear stress on hollow fibre membrane surfaces (laterally-set and vertically-set) caused by aeration was measured directly using a two-direction load sensor. In the laterally-set hollow fibre module, time-averaged upward-direction shear stress on the membrane surface was compared to theoretical shear stress values considering the effect of water flow on membrane surface. Measured time-average shear stress values were almost 200 times larger than theoretical values implying strong interactions between bubbles and solid surface. In the vertically-set membrane module, velocity measurement of bubble flow using laser Doppler velocimeter revealed that drag force working on membrane surface was closely related to upward-direction water velocity. Also fluctuation of drag force and shear force on membrane surface was found to be related to velocity fluctuation (turbulence).

  19. Wall shear stress in the development of in-stent restenosis revisited. A critical review of clinical data on shear stress after intracoronary stent implantation.

    PubMed

    Jenei, Csaba; Balogh, Emília; Szabó, Gábor Tamás; Dézsi, Csaba András; Kőszegi, Zsolt

    2016-01-01

    The average wall shear stress (WSS) is in 1 Pa range in coronary arteries, while the stretching effect of an implanted coronary stent can generate up to 3 × 105 times higher circumferential stress in the vessel wall. It is widely accepted that WSS plays a critical role in the development of restenosis after coronary stent implantation, but relevant clinical endpoint studies are lack-ing. Fluid dynamics modeling suggests an association between WSS and intimal hyperplasia, however, such an association is not established when the compensating healing process becomes an overshoot phenomenon. This review summarizes available clinical results and concepts of potential clinical importance. PMID:27439365

  20. Evaluation of the effect of stent strut profile on shear stress distribution using statistical moments

    PubMed Central

    Mejia, Juan; Ruzzeh, Bilal; Mongrain, Rosaire; Leask, Richard; Bertrand, Olivier F

    2009-01-01

    Background In-stent restenosis rates have been closely linked to the wall shear stress distribution within a stented arterial segment, which in turn is a function of stent design. Unfortunately, evaluation of hemodynamic performance can only be evaluated with long term clinical trials. In this work we introduce a set of metrics, based on statistical moments, that can be used to evaluate the hemodynamic performance of a stent in a standardized way. They are presented in the context of a 2D flow study, which analyzes the impact of different strut profiles on the wall shear stress distribution for stented coronary arteries. Results It was shown that the proposed metrics have the ability to evaluate hemodynamic performance quantitatively and compare it to a common standard. In the context of the simulations presented here, they show that stent's strut profile significantly affect the shear stress distribution along the arterial wall. They also demonstrates that more streamlined profiles exhibit better hemodynamic performance than the standard square and circular profiles. The proposed metrics can be used to compare results from different research groups, and provide an improved method of quantifying hemodynamic performance in comparison to traditional techniques. Conclusion The strut shape found in the latest generations of stents are commonly dictated by manufacturing limitations. This research shows, however, that strut design can play a fundamental role in the improvement of the hemodynamic performance of stents. Present results show that up to 96% of the area between struts is exposed to wall shear stress levels above the critical value for the onset of restenosis when a tear-drop strut profile is used, while the analogous value for a square profile is 19.4%. The conclusions drawn from the non-dimensional metrics introduced in this work show good agreement with an ordinary analysis of the wall shear stress distribution based on the overall area exposed to

  1. Optimization of multiplane μPIV for wall shear stress and wall topography characterization

    NASA Astrophysics Data System (ADS)

    Rossi, Massimiliano; Lindken, Ralph; Westerweel, Jerry

    2010-02-01

    Multiplane μPIV can be utilized to determine the wall shear stress and wall topology from the measured flow over a structured surface. A theoretical model was developed to predict the measurement error for the surface topography and shear stress, based on a theoretical analysis of the precision in PIV measurements. The main parameters that affect the accuracy of the measurement are identified. The effect of different parameter settings is studied by means of Monte Carlo simulations, and the results are compared with an experimental test case. The results are used to determine the recommended parameter settings for this measurement approach.

  2. Representation of turbulent shear stress by a product of mean velocity differences

    NASA Technical Reports Server (NTRS)

    Braun, W. H.

    1977-01-01

    A quadratic form in the mean velocity for the turbulent shear stress is presented. It is expressed as the product of two velocity differences whose roots are the maximum velocity in the flow and a cutoff velocity below which the turbulent shear stress vanishes. Application to pipe and channel flows yields the centerline velocity as a function of pressure gradient, as well as the velocity profile. The flat plate, boundary-layer problem is solved by a system of integral equations to obtain friction coefficient, displacement thickness, and momentum-loss thickness. Comparisons are made with experiment.

  3. Surface Shear Stress Around a Single Flexible Live Plant and a Rigid Cylinder

    NASA Astrophysics Data System (ADS)

    Walter, B. A.; Gromke, C.; Leonard, K. C.; Clifton, A.; Lehning, M.

    2010-12-01

    The sheltering effect of vegetation against soil erosion and snow transport has direct implications on land degradation and local water storage as snow in many arid and semi arid regions. Plants influence the erosion, transport and redeposition of soil and snow by the wind through momentum absorption, local stress concentration, trapping particles in motion and reducing the area of sediment exposed to the wind. The shear stress distributions on the ground beneath plant canopies determine the onset and magnitude of differential soil and snow erosion on rough or vegetated surfaces, but this has been studied exclusively with artificial and rigid vegetation elements thus far. Real plants have highly irregular structures that can be extremely flexible and porous. They align with the flow at higher wind speeds, resulting in considerable changes to the drag and flow regimes relative to rigid imitations of comparable size. We present measurements in the SLF atmospheric boundary layer wind tunnel of the surface shear stress distribution around a live grass plant (Lolium Perenne) and a solid cylinder of comparable size. Irwin sensors are used to measure pressure differences close to the surface which can be calibrated with surface shear stress velocities. The basal to frontal area index of the plant and the cylinder as well as the Reynolds number of the two experimental setups have been checked for similarity and show good agreement. Distinctive differences between the shear stress pattern around the plant and the cylinder can be attributed to the influence of the plant’s porosity and flexibility. The sheltered zone behind the plant is narrower in cross-stream and longer in streamwise direction than that of the cylinder. For the plant, the lowest shear stresses in the sheltered zone are 50% lower than the mean surface shear stress (τ = 0.15 N/m2) in the undisturbed flow. The sheltering was higher behind the cylinder with values reduced by 70% relative to background.

  4. A two-dimensional stress analysis of a butt adhesive joint containing circular holes and rigid fillers in an adhesive subjected to a tensile load

    SciTech Connect

    Sawa, Toshiyuki; Nakano, Katsuyuki; Nakano, Yuichi

    1995-11-01

    This study deals with a stress analysis of a butt adhesive joint which contains circular holes and rigid fillers in the adhesive and is subjected to a tensile load. In the analysis, the adherends are assumed to be rigid and the adhesive is replaced with a finite strip having holes and rigid fillers in it and the stress distribution in the joint is analyzed using a two-dimensional theory of elasticity. The effects of size and locations of rigid fillers and circular holes on the stress distributions at the interface and around the fillers and holes are clarified by numerical calculations. For verification, photoelastic experiments are performed using an epoxide resin plate modeled as an adhesive in the joint. The analytical results are in fairly good agreement with the experimental ones. In addition, the stress singularity at the edge of the interface is discussed.

  5. Adhesion and stress relaxation forces between melanoma and cerebral endothelial cells.

    PubMed

    Végh, Attila G; Fazakas, Csilla; Nagy, Krisztina; Wilhelm, Imola; Molnár, Judit; Krizbai, István A; Szegletes, Zsolt; Váró, György

    2012-02-01

    Mechanical parameters play a crucial role in proper cellular functions. This article examines the process of the appearance and breaking of adhesion forces during contact between the confluent cerebral endothelial cell layer and a melanoma cell attached to a tipless cantilever. This adhesion is the initial phase of melanoma transmigration through the endothelial cell layer. Taking the force measurement, if the contact was prolonged for several seconds, a decrease in the load force was observed, which corresponds to stress relaxation of the cells. The dependence of adhesion force and stress relaxation on dwell time showed a saturation-like behavior. These stress relaxation curves could be fitted with the sum of two exponentials, suggesting that two independent processes take place simultaneously. The breakup of the adhesion during the retraction of the cantilever with the attached melanoma cell is not continuous but shows jumps. Between living endothelial and melanoma cells, a minimum jump size of about 20 pN could be determined. The minimum jump is independent of the dwell time and load force. It seems to be the elementary binding force between these two cell types. In case of fixed endothelial cells, the adhesion force was strongly decreased and the jumps disappeared, whereas the stress relaxation did not show considerable change upon fixation. PMID:22038122

  6. Mechanism and kinetics of biofilm growth process influenced by shear stress in sewers.

    PubMed

    Ai, Hainan; Xu, Jingwei; Huang, Wei; He, Qiang; Ni, Bingjie; Wang, Yinliang

    2016-01-01

    Sewer biofilms play an important role in the biotransformation of substances for methane and sulfide emission in sewer networks. The dynamic flows and the particular shear stress in sewers are the key factors determining the growth of the sewer biofilm. In this work, the development of sewer biofilm with varying shear stress is specifically investigated to gain a comprehensive understanding of the sewer biofilm dynamics. Sewer biofilms were cultivated in laboratory-scale gravity sewers under different hydraulic conditions with the corresponding shell stresses are 1.12 Pa, 1.29 Pa and 1.45 Pa, respectively. The evolution of the biofilm thickness were monitored using microelectrodes, and the variation in total solids (TS) and extracellular polymer substance (EPS) levels in the biofilm were also measured. The results showed that the steady-state biofilm thickness were highly related to the corresponding shear stresses with the biofilm thickness of 2.4 ± 0.1 mm, 2.7 ± 0.1 mm and 2.2 ± 0.1 mm at shear stresses of 1.12 Pa, 1.29 Pa and 1.45 Pa, respectively, which the chemical oxygen demand concentration is 400 mg/L approximately. Based on these observations, a kinetic model for describing the development of sewer biofilms was developed and demonstrated to be capable of reproducing all the experimental data. PMID:27054728

  7. Shear-Stress Partitioning in Live Plant Canopies and Modifications to Raupach's Model

    NASA Astrophysics Data System (ADS)

    Walter, Benjamin; Gromke, Christof; Lehning, Michael

    2012-08-01

    The spatial peak surface shear stress {tau _S^'' on the ground beneath vegetation canopies is responsible for the onset of particle entrainment and its precise and accurate prediction is essential when modelling soil, snow or sand erosion. This study investigates shear-stress partitioning, i.e. the fraction of the total fluid stress on the entire canopy that acts directly on the surface, for live vegetation canopies (plant species: Lolium perenne) using measurements in a controlled wind-tunnel environment. Rigid, non-porous wooden blocks instead of the plants were additionally tested for the purpose of comparison since previous wind-tunnel studies used exclusively artificial plant imitations for their experiments on shear-stress partitioning. The drag partitioning model presented by Raupach (Boundary-Layer Meteorol 60:375-395, 1992) and Raupach et al. (J Geophys Res 98:3023-3029, 1993), which allows the prediction of the total shear stress τ on the entire canopy as well as the peak {(tau _S ^''/tau )^{1/2}} and the average {(tau _S^'/tau )^{1/2}} shear-stress ratios, is tested against measurements to determine the model parameters and the model's ability to account for shape differences of various roughness elements. It was found that the constant c, needed to determine the total stress τ and which was unspecified to date, can be assumed a value of about c = 0.27. Values for the model parameter m, which accounts for the difference between the spatial surface average {tau _S^' and the peak {tau _S ^'' shear stress, are difficult to determine because m is a function of the roughness density, the wind velocity and the roughness element shape. A new definition for a parameter a is suggested as a substitute for m. This a parameter is found to be more closely universal and solely a function of the roughness element shape. It is able to predict the peak surface shear stress accurately. Finally, a method is presented to determine the new a parameter for different kinds

  8. An investigation of stress wave propagation in a shear deformable nanobeam based on modified couple stress theory

    NASA Astrophysics Data System (ADS)

    Akbarzadeh Khorshidi, Majid; Shariati, Mahmoud

    2016-04-01

    This paper presents a new investigation for propagation of stress wave in a nanobeam based on modified couple stress theory. Using Euler-Bernoulli beam theory, Timoshenko beam theory, and Reddy beam theory, the effect of shear deformation is investigated. This nonclassical model contains a material length scale parameter to capture the size effect and the Poisson effect is incorporated in the current model. Governing equations of motion are obtained by Hamilton's principle and solved explicitly. This solution leads to obtain two phase velocities for shear deformable beams in different directions. Effects of shear deformation, material length scale parameter, and Poisson's ratio on the behavior of these phase velocities are investigated and discussed. The results also show a dual behavior for phase velocities against Poisson's ratio.

  9. Estimates of Shear Stress and Measurements of Water Levels in the Lower Fox River near Green Bay, Wisconsin

    USGS Publications Warehouse

    Westenbroek, Stephen M.

    2006-01-01

    Turbulent shear stress in the boundary layer of a natural river system largely controls the deposition and resuspension of sediment, as well as the longevity and effectiveness of granular-material caps used to cover and isolate contaminated sediments. This report documents measurements and calculations made in order to estimate shear stress and shear velocity on the Lower Fox River, Wisconsin. Velocity profiles were generated using an acoustic Doppler current profiler (ADCP) mounted on a moored vessel. This method of data collection yielded 158 velocity profiles on the Lower Fox River between June 2003 and November 2004. Of these profiles, 109 were classified as valid and were used to estimate the bottom shear stress and velocity using log-profile and turbulent kinetic energy methods. Estimated shear stress ranged from 0.09 to 10.8 dynes per centimeter squared. Estimated coefficients of friction ranged from 0.001 to 0.025. This report describes both the field and data-analysis methods used to estimate shear-stress parameters for the Lower Fox River. Summaries of the estimated values for bottom shear stress, shear velocity, and coefficient of friction are presented. Confidence intervals about the shear-stress estimates are provided.

  10. Shear stress behavior in mesoscale simulations of granular materials

    NASA Astrophysics Data System (ADS)

    Fujino, Don; Lomov, Ilya; Antoun, Tarabay; Vitali, Efrem

    2012-03-01

    3D mesoscale simulations of shock propagation in porous solids and powders have been performed with the Eulerian hydrocode GEODYN. The results indicate that voids can have a profound effect on the stress state in the material behind the shock front. The simulations can explain experimentally observed wave profiles that are difficult to interpret in the context of the classical elastic-plastic theory. In particular, a quasielastic precursor is observed in reshock simulations. This effect persists even at extremely low porosity values, down to 0.1% by volume. Stress relaxation is pronounced in simulations involving wave propagation, but is not observed in uniform ramp loading. In this sense, the relaxation phenomenon is non-local in nature and classic continuum models are inadequate for its description. Simulations show that the response of highly porous powders is dominated by deviatoric stress relaxation in the shock regime. We propose an enhancement which can be easily integrated into most existing porous material continuum models for modeling the shockinduced relaxation phenomena observed in the mesoscale simulation. The model calculates the microkinetic energy generated by dynamic loading and stores it as an internal state variable. The rate of production and dissipation of microkinetic energy and other model parameters are calibrated based on the mesoscale results. The augmented continuum model represents the deviatoric stress behavior observed under different regimes of dynamic loading.

  11. Shear Stress Behavior in Mesoscale Simulations of Granular Materials

    NASA Astrophysics Data System (ADS)

    Fujino, Don; Lomov, Ilya; Vitali, Efrem; Antoun, Tarabay

    2011-06-01

    3D mesoscale simulations of shock propagation in porous solids and powder have been performed with the hydrocode GEODYN. The results indicate that voids can have a profound effect on the stress state in the material behind the shock front. The simulations can explain experimentally observed quasielastic precursors in reshock profiles that are difficult to interpret in the context of the classical elastic-plastic theory. This effect persists even at extremely low porosity values, down to 0.01% by volume. Stress relaxation is pronounced in simulations involving wave propagation, but is not observed in uniform ramp loading. Thus this relaxation mechanism is non-local in nature and continuum models may not be inadequate for its description. Simulations show that response of highly porous powders are dominated by deviatoric stress relaxation in the shock regime. We propose an enhancement which can be easily integrated into most existing porous material continuum models for modeling the shock-induced relaxation phenomena observed in the mesoscale simulation. The model calculates microkinetic energy generated by dynamic loading and store it as an internal state variable. The rate of production and dissipation of microkinetic energy is calibrated based on the mesoscale results. The augmented continuum model represent deviatoric stress behavior observed under different loading regimes.

  12. Measurement of turbulent wall shear-stress using micro-pillars

    NASA Astrophysics Data System (ADS)

    Gnanamanickam, E. P.; Nottebrock, B.; Große, S.; Sullivan, J. P.; Schröder, W.

    2013-12-01

    In experimental fluid mechanics, measuring spatially and temporally resolved wall shear-stress (WSS) has proved a challenging problem. The micro-pillar shear-stress sensor (MPS3) has been developed with the goal of filling this gap in measurement techniques. The MPS3 comprises an array of flexible micro-pillars flush mounted on the wall of a wall-bounded flow field. The deflection of these micro-pillars in the presence of a shear field is a direct measure of the WSS. This paper presents the MPS3 development work carried out by RWTH Aachen University and Purdue University. The sensor concept, static and dynamic characterization and data reduction issues are discussed. Also presented are demonstrative experiments where the MPS3 was used to measure the WSS in both water and air. The salient features of the measurement technique, sensor development issues, current capabilities and areas for improvement are highlighted.

  13. Evaluation of Transverse Thermal Stresses in Composite Plates Based on First-Order Shear Deformation Theory

    NASA Technical Reports Server (NTRS)

    Rolfes, R.; Noor, A. K.; Sparr, H.

    1998-01-01

    A postprocessing procedure is presented for the evaluation of the transverse thermal stresses in laminated plates. The analytical formulation is based on the first-order shear deformation theory and the plate is discretized by using a single-field displacement finite element model. The procedure is based on neglecting the derivatives of the in-plane forces and the twisting moments, as well as the mixed derivatives of the bending moments, with respect to the in-plane coordinates. The calculated transverse shear stiffnesses reflect the actual stacking sequence of the composite plate. The distributions of the transverse stresses through-the-thickness are evaluated by using only the transverse shear forces and the thermal effects resulting from the finite element analysis. The procedure is implemented into a postprocessing routine which can be easily incorporated into existing commercial finite element codes. Numerical results are presented for four- and ten-layer cross-ply laminates subjected to mechanical and thermal loads.

  14. Correlation between Generated Shear Stress and Generated Permittivity for the Electrorheological Response of Colloidal Silica Suspensions.

    PubMed

    Saimoto; Satoh; Konno

    1999-11-01

    Electrorheological response was experimentally studied by the use of silicone oil suspensions containing submicrometer-sized and supermicrometer-sized silica particles with different amounts of adsorbed water. The simultaneous measurements of dielectric permittivity and shear stress of the suspensions were carried out after the application of alternating current voltage under steady shear in ranges of shear rate (150-1400 s(-1)), electric field strength (0-4 kV/mm), its frequency (30-1000 Hz), and particle volume fraction (0.1-0.3). For the particles with small amounts of adsorbed water, steady shear stress was attained within several minutes after the application of electric field. The steady-state data for both the particles at each electric field strength showed that the shear stress generated by the application of electric field, Deltatau, varied correlatively with the generated permittivity, Deltaepsilon(r) (= epsilon(r) - epsilon(r,oil)), where epsilon(r) and epsilon(r,oil) are the permittivities of the suspension and the silicon oil, respectively. Under a wide variety of experimental conditions, the steady-state data for both the particle sizes could be correlated with a simple relationship, Deltatau ~ (Deltaepsilon(r)E)(2), where E is electric field strength. For the particles with large amounts of adsorbed water, steady state was not attained, and the evolutions of shear stress and permittivity of the suspensions were measured after the application of electric field. Remarkably, the transient values of Deltatau varied with (Deltaepsilon(r)E)(2) and fell along the same correlation line as the steady-state data. Copyright 1999 Academic Press.

  15. Microvascular permeability to water is independent of shear stress, but dependent on flow direction

    PubMed Central

    Adamson, R. H.; Sarai, R. K.; Altangerel, A.; Clark, J. F.; Weinbaum, S.

    2013-01-01

    Endothelial cells in a cultured monolayer change from a “cobblestone” configuration when grown under static conditions to a more elongated shape, aligned with the direction of flow, after exposure to sustained uniform shear stress. Sustained blood flow acts to protect regions of large arteries from injury. We tested the hypothesis that the stable permeability state of individually perfused microvessels is also characteristic of flow conditioning. In individually perfused rat mesenteric venular microvessels, microvascular permeability, measured as hydraulic conductivity (Lp), was stable [mean 1.0 × 10−7 cm/(s × cmH2O)] and independent of shear stress (3–14 dyn/cm2) for up to 3 h. Vessels perfused opposite to the direction of normal blood flow exhibited a delayed Lp increase [ΔLp was 7.6 × 10−7 cm/(s × cmH2O)], but the increase was independent of wall shear stress. Addition of chondroitin sulfate and hyaluronic acid to perfusates increased the shear stress range, but did not modify the asymmetry in response to flow direction. Increased Lp in reverse-perfused vessels was associated with numerous discontinuities of VE-cadherin and occludin, while both proteins were continuous around the periphery of forward-perfused vessels. The results are not consistent with a general mechanism for graded shear-dependent permeability increase, but they are consistent with the idea that a stable Lp under normal flow contributes to prevention of edema formation and also enables physiological regulation of shear-dependent small solute permeabilities (e.g., glucose). The responses during reverse flow are consistent with reports that disturbed flows result in a less stable endothelial barrier in venular microvessels. PMID:23417864

  16. Microflow-induced shear stress on biomaterial wall by ultrasound-induced encapsulated microbubble oscillation

    NASA Astrophysics Data System (ADS)

    Hu, Ji-Wen; Qian, Sheng-You; Sun, Jia-Na; Lü, Yun-Bin; Hu, Ping

    2015-09-01

    A model of an ultrasound-driven encapsulated microbubble (EMB) oscillation near biomaterial wall is presented and used for describing the microflow-induced shear stress on the wall by means of a numerical method. The characteristic of the model lies in the explicit treatment of different types of wall for the EMB responses. The simulation results show that the radius-time change trends obtained by our model are consistent with the existing models and experimental results. In addition, the effect of the elastic wall on the acoustic EMB response is stronger than that of the rigid wall, and the shear stress on the elastic wall is larger than that of the rigid wall. The closer the EMB to the wall, the greater the shear stress on the wall. The substantial shear stress on the wall surface occurs inside a circular zone with a radius about two-thirds of the bubble radius. This paper may be of interest in the study of potential damage mechanisms to the microvessel for drug and gene delivery due to sonoporation. Projects supported by the National Natural Science Foundation of China (Grant Nos. 11174077 and 11474090), the Natural Science Foundation of Hunan Province, China (Grant No. 13JJ3076), the Science Research Program of Education Department of Hunan Province, China (Grant No. 14A127), and the Doctoral Fund of University of South China (Grant No. 2011XQD46).

  17. Quantitative morphodynamics of endothelial cells within confluent cultures in response to fluid shear stress.

    PubMed

    Dieterich, P; Odenthal-Schnittler, M; Mrowietz, C; Krämer, M; Sasse, L; Oberleithner, H; Schnittler, H J

    2000-09-01

    To evaluate shear stress-induced effects on cultured cells we have extended the mechanical setup of a multichannel in vitro rheological system and developed software allowing entire processing control and image data analysis. The values of cell motility, degree of orientation (alignment), and cell elongation were correlated as a function of time (morphodynamics). Collective and individual endothelial cells within confluent cultures displayed a shear stress-dependent characteristic phase behavior of the following time course: resting conditions (phase I), change of motility (phase II), onset of alignment (phase III), and finally cell elongation (phase IV). Especially cell motility was characterized by a randomized zigzag movement around mean trajectories (fluctuations) together with mean cell locomotion. Onset of shear stress caused a down-regulation of fluctuations of 30% within <10 min and simultaneously increased locomotion velocities preferring the flow direction (phase II). After a lag period of 10 to 20 min cells orientated in the direction of flow (phase III) without significant cell elongation, which finally occurs within hours (phase IV). These data provide first evidence that cells within confluent endothelial monolayers respond to shear stress with a characteristic phase behavior. PMID:10968992

  18. Direct Measurement Sensor of the Boundary Shear Stress in Fluid Flow

    NASA Technical Reports Server (NTRS)

    Badescu, Mircea; Bao, Xiaoqi; Bar-Cohen, Yoseph; Chang, Zensheu; Kerenyi, Kornel; Lih, Shyh-Shiuh; Sherrit, Stewart; Trease, Brian P.; Widholm, Scott

    2010-01-01

    The flow fields and boundary erosion that are associated with scour at bridge piers are very complex. Direct measurement of the boundary shear stress and boundary pressure fluctuations in experimental scour research has always been a challenge and high spatial resolution and fidelity have been almost impossible. Most researchers have applied an indirect process to determine shear stress using precise measured velocity profiles. Laser Doppler Anemometry and Particle Image Velocimetry are common techniques used to accurately measure velocity profiles. These methods are based on theoretical assumptions to estimate boundary shear stress. In addition, available turbulence models cannot very well account for the effect of bed roughness which is fundamentally important for any CFD simulation. The authors have taken on the challenge to advance the magnitude level to which direct measurements of the shear stress in water flow can be performed. This paper covered the challenges and the efforts to develop a higher accuracy and small spatial resolution sensor. Also, preliminary sensor designs and test results are presented.

  19. A numerical and experimental study of a dynamic resonant shear stress sensor

    NASA Astrophysics Data System (ADS)

    Zhang, Xu

    A new dynamic resonant wall shear stress sensor based on an oscillating sensor element operating near its resonant frequency has been investigated both numerically and experimentally. The experimental results of this study showed that, with a change in the mean shear stress acting on the sensor surface, measurable sensor sensitivity in the oscillation amplitude occurs for both open loop and closed loop control of the sensor. This is definitive experimental evidence that a resonant system can be made sensitive to wall shear stress and it is suggested that the concept of a dynamic resonant wall shear stress sensor would work. Furthermore, these results agree qualitatively with numerical results in boundary layer flow and provide a rigorous basis upon which further development of the dynamic resonant sensor can be pursued. At the same time, the sensor's working principle was numerically investigated and sensor parameters effects (oscillating amplitude, oscillating frequency; and sensor size), pressure gradient effects were also numerical estimated. In the end three dimensional effects that include aspect ratio effects, inflow angle effects and gap effects were also discussed by building three-dimensional dynamic models in Fluent.

  20. Cloning the Gravity and Shear Stress Related Genes from MG-63 Cells by Subtracting Hybridization

    NASA Astrophysics Data System (ADS)

    Zhang, Shu; Dai, Zhong-quan; Wang, Bing; Cao, Xin-sheng; Li, Ying-hui; Sun, Xi-qing

    2008-06-01

    Background The purpose of the present study was to clone the gravity and shear stress related genes from osteoblast-like human osteosarcoma MG-63 cells by subtractive hybridization. Method MG-63 cells were divided into two groups (1G group and simulated microgravity group). After cultured for 60 h in two different gravitational environments, two groups of MG-63 cells were treated with 1.5Pa fluid shear stress (FSS) for 60 min, respectively. The total RNA in cells was isolated. The gravity and shear stress related genes were cloned by subtractive hybridization. Result 200 clones were gained. 30 positive clones were selected using PCR method based on the primers of vector and sequenced. The obtained sequences were analyzed by blast. changes of 17 sequences were confirmed by RT-PCR and these genes are related to cell proliferation, cell differentiation, protein synthesis, signal transduction and apoptosis. 5 unknown genes related to gravity and shear stress were found. Conclusion In this part of our study, our result indicates that simulated microgravity may change the activities of MG-63 cells by inducing the functional alterations of specific genes.

  1. The effect of roughness elements on wind erosion: The importance of surface shear stress distribution

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Representation of surface roughness effects on aeolian sediment transport is a key source of uncertainty in wind erosion models. Drag partitioning schemes are used to account for roughness by scaling the soil entrainment threshold by the ratio of shear stress on roughness elements to that on the veg...

  2. Oscillatory motion based measurement method and sensor for measuring wall shear stress due to fluid flow

    DOEpatents

    Armstrong, William D.; Naughton, Jonathan; Lindberg, William R.

    2008-09-02

    A shear stress sensor for measuring fluid wall shear stress on a test surface is provided. The wall shear stress sensor is comprised of an active sensing surface and a sensor body. An elastic mechanism mounted between the active sensing surface and the sensor body allows movement between the active sensing surface and the sensor body. A driving mechanism forces the shear stress sensor to oscillate. A measuring mechanism measures displacement of the active sensing surface relative to the sensor body. The sensor may be operated under periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor measurably changes the amplitude or phase of the motion of the active sensing surface, or changes the force and power required from a control system in order to maintain constant motion. The device may be operated under non-periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor change the transient motion of the active sensor surface or change the force and power required from a control system to maintain a specified transient motion of the active sensor surface.

  3. Hemodynamic shear stress characteristic of atherosclerosis-resistant regions promotes glycocalyx formation in cultured endothelial cells.

    PubMed

    Koo, Andrew; Dewey, C Forbes; García-Cardeña, Guillermo

    2013-01-15

    The endothelial glycocalyx, a glycosaminoglycan layer located on the apical surface of vascular endothelial cells, has been shown to be important for several endothelial functions. Previous studies have documented that the glycocalyx is highly abundant in the mouse common carotid region, where the endothelium is exposed to laminar shear stress, and it is resistant to atherosclerosis. In contrast, the glycocalyx is scarce or absent in the mouse internal carotid sinus region, an area exposed to nonlaminar shear stress and highly susceptible to atherosclerosis. On the basis of these observations, we hypothesized that the expression of components of the endothelial glycocalyx is differentially regulated by distinct hemodynamic environments. To test this hypothesis, human endothelial cells were exposed to shear stress waveforms characteristic of atherosclerosis-resistant or atherosclerosis-susceptible regions of the human carotid, and the expression of several components of the glycocalyx was assessed. These experiments revealed that expression of several components of the endothelial glycocalyx is differentially regulated by distinct shear stress waveforms. Interestingly, we found that heparan sulfate expression is increased and evenly distributed on the apical surface of endothelial cells exposed to the atheroprotective waveform and is irregularly present in cells exposed to the atheroprone waveform. Furthermore, expression of a heparan sulfate proteoglycan, syndecan-1, is also differentially regulated by the two waveforms, and its suppression mutes the atheroprotective flow-induced cell surface expression of heparan sulfate. Collectively, these data link distinct hemodynamic environments to the differential expression of critical components of the endothelial glycocalyx.

  4. Field observations of bed shear stress and sediment resuspension on continental shelves, Alaska and California

    USGS Publications Warehouse

    Drake, D.E.; Cacchione, D.A.

    1986-01-01

    Bed shear stress was estimated using wave and current measurements obtained with the GEOPROBE bottom-tripod system during resuspension events in Norton Sound, Alaska, and on the northern California shelf. The boundary-layer model of Grant and Madsen (1979, Journal of Geophysical Research, 84, 1797-1808) was used to compute the bed shear stress under combined wave-generated and quasi-steady currents. Resuspension events were identified by sudden, large increases in light scattering at 1.9 m above the sea floor. The shear-stress values were used to compute the Shields parameter (??). The results for Norton Sound are in excellent agreement with the Shields threshold criterion; the data for the California shelf plot somewhat above the Shields threshold curve, though generally within the scatter envelope. Although the surface sediments in each area contain substantial fine-grained fractions (mean diameters were 0.007 cm in Norton Sound and 0.002 cm on the California shelf), the results do not indicate significant cohesion, because the sediment was entrained at bed shear-stress values close to those predicted by the modified Shields curve for cohesionless fine-grained particles. We suspect that frequent wave stirring and observed plowing of the surface sediment by benthonic animals maintain a high water content and contribute to the ease with which these materials are resuspended. ?? 1986.

  5. Development of a MEMS dual-axis differential capacitance floating element shear stress sensor

    SciTech Connect

    Barnard, Casey; Griffin, Benjamin

    2015-09-01

    A single-axis MEMS wall shear stress sensor with differential capacitive transduction method is produced. Using a synchronous modulation and demodulation interface circuit, the system is capable of making real time measurements of both mean and fluctuating wall shear stress. A sensitivity of 3.44 mV/Pa is achieved, with linearity in response demonstrated up to testing limit of 2 Pa. Minimum detectable signals of 340 μPa at 100 Hz and 120 μPa at 1 kHz are indicated, with a resonance of 3.5 kHz. Multiple full scale wind tunnel tests are performed, producing spectral measurements of turbulent boundary layers in wind speeds ranging up to 0.5 Ma (18 Pa of mean wall shear stress). The compact packaging allows for minimally invasive installation, and has proven relatively robust over multiple testing events. Temperature sensitivity, likely due to poor CTE matching of packaged materials, is an ongoing concern being addressed. These successes are being directly leveraged into a development plan for a dual-axis wall shear stress sensor, capable of producing true vector estimates at the wall.

  6. Diagnostics of boundary layer transition by shear stress sensitive liquid crystals

    NASA Astrophysics Data System (ADS)

    Shapoval, E. S.

    2016-10-01

    Previous research indicates that the problem of boundary layer transition visualization on metal models in wind tunnels (WT) which is a fundamental question in experimental aerodynamics is not solved yet. In TsAGI together with Khristianovich Institute of Theoretical and Applied Mechanics (ITAM) a method of shear stress sensitive liquid crystals (LC) which allows flow visualization was proposed. This method allows testing several flow conditions in one wind tunnel run and does not need covering the investigated model with any special heat-insulating coating which spoils the model geometry. This coating is easily applied on the model surface by spray or even by brush. Its' thickness is about 40 micrometers and it does not spoil the surface quality. At first the coating obtains some definite color. Under shear stress the LC coating changes color and this change is proportional to shear stress. The whole process can be visually observed and during the tests it is recorded by camera. The findings of the research showed that it is possible to visualize boundary layer transition, flow separation, shock waves and the flow image on the whole. It is possible to predict that the proposed method of shear stress sensitive liquid crystals is a promise for future research.

  7. Fluid shear of low magnitude increases growth and expression of TGFbeta1 and adhesion molecules in human bone cells in vitro.

    PubMed

    Liegibel, U M; Sommer, U; Bundschuh, B; Schweizer, B; Hilscher, U; Lieder, A; Nawroth, P; Kasperk, C

    2004-07-01

    Deformation of the bone matrix by mechanical strain causes fluid shifts within the osteocytic canaliculi which affect osteocytic cell metabolism. We applied low fluid shear (1 - 63 micro Pa for 10 - 48 h) to human osteoblastic cells (HOB) in vitro to study its impact on cell proliferation and differentiated functions. Proteins involved in translating the physical force into a cellular response were characterised. Low fluid shear stress stimulated proliferation of HOB 1.2-fold when stress was applied intermittently for 24 h. Shear stress also increased differentiated cellular properties such as alkaline phosphatase (ALP) activity (121 % of control), fibronectin (FN) and fibronectin receptor (FNR) expression (290 % and 200 %, respectively). Prostaglandin E (2) (PGE (2)) and TGFbeta1 release into the medium were significantly stimulated when shear stress was applied for 6 - 12 h and 24 - 48 h, respectively. TGFbeta1 + 2 neutralising antibodies or the presence of indomethacine inhibited the mitogenic effect of fluid shear and reduced ALP activity to its control level. Furthermore, TGFbeta treatment induced a dose-dependent increase in FN and FNR expression. Therefore, fluid shear stress of low magnitude (a) suffices to affect HOB metabolism and (b) regulates anchorage of HOB via FN and FNR by stimulating osteoblastic PGE (2) and TGFbeta secretion.

  8. Quantification of Shear Deformations and Corresponding Stresses in the Biaxially Tested Human Myocardium.

    PubMed

    Sommer, Gerhard; Haspinger, Daniel Ch; Andrä, Michaela; Sacherer, Michael; Viertler, Christian; Regitnig, Peter; Holzapfel, Gerhard A

    2015-10-01

    One goal of cardiac research is to perform numerical simulations to describe/reproduce the mechanoelectrical function of the human myocardium in health and disease. Such simulations are based on a complex combination of mathematical models describing the passive mechanical behavior of the myocardium and its electrophysiology, i.e., the activation of cardiac muscle cells. The problem in developing adequate constitutive models is the shortage of experimental data suitable for detailed parameter estimation in specific functional forms. A combination of shear and biaxial extension tests with different loading protocols on different specimen orientations is necessary to capture adequately the direction-dependent (orthotropic) response of the myocardium. In most experimental animal studies, where planar biaxial extension tests on the myocardium have been conducted, the generated shear stresses were neither considered nor discussed. Hence, in this study a method is presented which allows the quantification of shear deformations and related stresses. It demonstrates an approach for experimenters as to how the generation of these shear stresses can be minimized during mechanical testing. Experimental results on 14 passive human myocardial specimens, obtained from nine human hearts, show the efficiency of this newly developed method. Moreover, the influence of the clamping technique of the specimen, i.e., the load transmission between the testing device and the tissue, on the stress response is determined by testing an isotropic material (Latex). We identified that the force transmission between the testing device and the specimen by means of hooks and cords does not influence the performed experiments. We further showed that in-plane shear stresses definitely exist in biaxially tested human ventricular myocardium, but can be reduced to a minimum by preparing the specimens in an appropriate manner. Moreover, we showed whether shear stresses can be neglected when performing

  9. Some constraints on levels of shear stress in the crust from observations and theory.

    USGS Publications Warehouse

    McGarr, A.

    1980-01-01

    In situ stress determinations in North America, southern Africa, and Australia indicate that on the average the maximum shear stress increases linearly with depth to at least 5.1 km measured in soft rock, such as shale and sandstone, and to 3.7 km in hard rock, including granite and quartzite. Regression lines fitted to the data yield gradients of 3.8 MPa/km and 6.6 MPa/km for soft and hard rock, respectively. Generally, the maximum shear stress in compressional states of stress for which the least principal stress is oriented near vertically is substantially greater than in extensional stress regimes, with the greatest principal stress in a vertical direction. The equations of equilibrium and compatibility can be used to provide functional constrains on the state of stress. If the stress is assumed to vary only with depth z in a given region, then all nonzero components must have the form A + Bz, where A and B are constants which generally differ for the various components. - Author

  10. Mechanisms relating to reducing stress in curing thick sections of UV adhesives

    NASA Astrophysics Data System (ADS)

    Norland, Eric A.; Martin, Frank S.

    1993-09-01

    Ultraviolet curing adhesives are widely used in optical lamination of precision optical lenses, safety windows, holographic displays, and flat panel displays. In most of these applications they are being used in relatively thin films from 3 microns to 40 mils, because most formulations will only allow uv light to penetrate to a certain depth. If the formulation does cure in thicker sections, the stress due to shrinkage typically becomes a problem. U.V. adhesives have been developed which can be cured in relatively thick sections with minimum stress. In this paper, a number of formulations are compared for variations in stress when cured in thick sections and the conditions and mechanism to minimize stress are characterized.

  11. Using a co-culture microsystem for cell migration under fluid shear stress.

    PubMed

    Yeh, Chia-Hsien; Tsai, Shen-Hsing; Wu, Li-Wha; Lin, Yu-Cheng

    2011-08-01

    We have successfully developed a microsystem to co-cultivate two types of cells with a minimum defined gap of 50 μm, and to quantitatively study the impact of fluid shear stress on the mutual influence of cell migration velocity and distance. We used the hydrostatic pressure to seed two different cells, endothelial cells (ECs) and smooth muscle cells (SMCs), on opposite sides of various gap sizes (500 μm, 200 μm, 100 μm, and 50 μm). After cultivating the cells for 12 h and peeling the co-culture microchip from the culture dish, we studied the impacts of gap size on the migration of either cell type in the absence or presence of fluid shear stress (7 dyne cm(-2) and 12 dyne cm(-2)) influence. We found that both gap size and shear stress have profound influence on cell migration. Smaller gap sizes (100 μm and 50 μm) significantly enhanced cell migration, suggesting a requirement of an effective concentration of released factor(s) by either cell type in the gap region. Flow-induced shear stress delayed the migration onset of either cell type in a dose-dependent manner regardless of the gap size. Moreover, shear stress-induced decrease of cell migration becomes evident when the gap size was 500 μm. We have developed a co-culture microsystem for two kinds of cells and overcome the conventional difficulties in observation and mixed culture, and it would have more application for bio-manipulation and tissue repair engineering.

  12. Using a co-culture microsystem for cell migration under fluid shear stress.

    PubMed

    Yeh, Chia-Hsien; Tsai, Shen-Hsing; Wu, Li-Wha; Lin, Yu-Cheng

    2011-08-01

    We have successfully developed a microsystem to co-cultivate two types of cells with a minimum defined gap of 50 μm, and to quantitatively study the impact of fluid shear stress on the mutual influence of cell migration velocity and distance. We used the hydrostatic pressure to seed two different cells, endothelial cells (ECs) and smooth muscle cells (SMCs), on opposite sides of various gap sizes (500 μm, 200 μm, 100 μm, and 50 μm). After cultivating the cells for 12 h and peeling the co-culture microchip from the culture dish, we studied the impacts of gap size on the migration of either cell type in the absence or presence of fluid shear stress (7 dyne cm(-2) and 12 dyne cm(-2)) influence. We found that both gap size and shear stress have profound influence on cell migration. Smaller gap sizes (100 μm and 50 μm) significantly enhanced cell migration, suggesting a requirement of an effective concentration of released factor(s) by either cell type in the gap region. Flow-induced shear stress delayed the migration onset of either cell type in a dose-dependent manner regardless of the gap size. Moreover, shear stress-induced decrease of cell migration becomes evident when the gap size was 500 μm. We have developed a co-culture microsystem for two kinds of cells and overcome the conventional difficulties in observation and mixed culture, and it would have more application for bio-manipulation and tissue repair engineering. PMID:21695290

  13. Sox18 preserves the pulmonary endothelial barrier under conditions of increased shear stress.

    PubMed

    Gross, Christine M; Aggarwal, Saurabh; Kumar, Sanjiv; Tian, Jing; Kasa, Anita; Bogatcheva, Natalia; Datar, Sanjeev A; Verin, Alexander D; Fineman, Jeffrey R; Black, Stephen M

    2014-11-01

    Shear stress secondary to increased pulmonary blood flow (PBF) is elevated in some children born with congenital cardiac abnormalities. However, the majority of these patients do not develop pulmonary edema, despite high levels of permeability inducing factors. Previous studies have suggested that laminar fluid shear stress can enhance pulmonary vascular barrier integrity. However, little is known about the mechanisms by which this occurs. Using microarray analysis, we have previously shown that Sox18, a transcription factor involved in blood vessel development and endothelial barrier integrity, is up-regulated in an ovine model of congenital heart disease with increased PBF (shunt). By subjecting ovine pulmonary arterial endothelial cells (PAEC) to laminar flow (20 dyn/cm(2) ), we identified an increase in trans-endothelial resistance (TER) across the PAEC monolayer that correlated with an increase in Sox18 expression. Further, the TER was also enhanced when Sox18 was over-expressed and attenuated when Sox18 expression was reduced, suggesting that Sox18 maintains the endothelial barrier integrity in response to shear stress. Further, we found that shear stress up-regulates the cellular tight junction protein, Claudin-5, in a Sox18 dependent manner, and Claudin-5 depletion abolished the Sox18 mediated increase in TER in response to shear stress. Finally, utilizing peripheral lung tissue of 4 week old shunt lambs with increased PBF, we found that both Sox18 and Claudin-5 mRNA and protein levels were elevated. In conclusion, these novel findings suggest that increased laminar flow protects endothelial barrier function via Sox18 dependent up-regulation of Claudin-5 expression. PMID:24677020

  14. Sox18 preserves the pulmonary endothelial barrier under conditions of increased shear stress

    PubMed Central

    Gross, Christine M.; Aggarwal, Saurabh; Kumar, Sanjiv; Tian, Jing; Kasa, Anita; Bogatcheva, Natalia; Datar, Sanjeev A.; Verin, Alexander D.; Fineman, Jeffrey R.; Black, Stephen M.

    2014-01-01

    Shear stress secondary to increased pulmonary blood flow (PBF) is elevated in some children born with congenital cardiac abnormalities. However, the majority of these patients do not develop pulmonary edema, despite high levels of permeability inducing factors. Previous studies have suggested that laminar fluid shear stress can enhance pulmonary vascular barrier integrity. However, little is known about the mechanisms by which this occurs. Using microarray analysis, we have previously shown that Sox18, a transcription factor involved in blood vessel development and endothelial barrier integrity, is up-regulated in an ovine model of congenital heart disease with increased PBF (shunt). By subjecting ovine pulmonary arterial endothelial cells (PAEC) to laminar flow (20 dyn/cm2), we identified an increase in trans-endothelial resistance (TER) across the PAEC monolayer that correlated with an increase in Sox18 expression. Further, the TER was also enhanced when Sox18 was over-expressed and attenuated when Sox18 expression was reduced, suggesting that Sox18 maintains the endothelial barrier integrity in response to shear stress. Further, we found that shear stress up-regulates the cellular tight junction protein, Claudin-5, in a Sox18 dependent manner, and Claudin-5 depletion abolished the Sox18 mediated increase in TER in response to shear stress. Finally, utilizing peripheral lung tissue of 4 week old shunt lambs with increased PBF, we found that both Sox18 and Claudin-5 mRNA and protein levels were elevated. In conclusion, these novel findings suggest that increased laminar flow protects endothelial barrier function via Sox18 dependent up-regulation of Claudin-5 expression. PMID:24677020

  15. Application of a Reynolds stress turbulence model to the compressible shear layer

    NASA Technical Reports Server (NTRS)

    Sarkar, S.; Balakrishnan, L.

    1990-01-01

    Theoretically based turbulence models have had success in predicting many features of incompressible, free shear layers. However, attempts to extend these models to the high-speed, compressible shear layer have been less effective. In the present work, the compressible shear layer was studied with a second-order turbulence closure, which initially used only variable density extensions of incompressible models for the Reynolds stress transport equation and the dissipation rate transport equation. The quasi-incompressible closure was unsuccessful; the predicted effect of the convective Mach number on the shear layer growth rate was significantly smaller than that observed in experiments. Having thus confirmed that compressibility effects have to be explicitly considered, a new model for the compressible dissipation was introduced into the closure. This model is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and on direct numerical simulation of compressible, isotropic turbulence. The use of the new model for the compressible dissipation led to good agreement of the computed growth rates with the experimental data. Both the computations and the experiments indicate a dramatic reduction in the growth rate when the convective Mach number is increased. Experimental data on the normalized maximum turbulence intensities and shear stress also show a reduction with increasing Mach number.

  16. Transmission of steady and oscillatory fluid shear stress across epithelial and endothelial surface structures

    NASA Astrophysics Data System (ADS)

    Han, Yuefeng; Ganatos, Peter; Weinbaum, Sheldon

    2005-03-01

    The glycocalyx on the apical surface of vascular endothelial cells and the microvilli and cilia on kidney epithelial cells have been modeled as surface layers with a hexagonal arrangement of structural elements. These elements have been proposed to serve a mechanosensory function in the initiation of intracellular signaling by fluid shear stress. In this paper we examine the response of these surface layers when steady or oscillating shear is applied at their outer edge. In the case of steady shear, our results show that the deflection of the structural elements is proportional to the product of the applied shear stress and their length L and inversely proportional to the natural damped vibration frequency of the structural element ωc. A fluid velocity boundary layer develops at the outer edge of the surface layers when the dimensionless Brinkman parameter α =L/√KP , where KP is the Darcy permeability, is asymptotically large. In the case of oscillating shear, we find that the motions of both the fluid and structural elements are in a quasisteady state at physiological conditions. No attenuation or phase shift of the torque is induced by the hydrodynamic drag when the applied frequency ω <ωc or ωr(=ω/ωc)<1. However, the velocity at the tips of the structural element is π /2 out of phase with the applied shear in this frequency range, due to the elastic recoil of the element. Furthermore, the fluid velocity at the tips can also be out of phase with the applied shear at large α if the closely spaced structural elements of the glycocalyx on endothelial cells or microvilli on proximal tubule cells transport substantial fluid with them.

  17. Analysis of residual stress in the resin of metal-resin adhesion structures by scanning acoustic microscopy.

    PubMed

    Ohno, Hiroki; Endo, Kazuhiko; Nagano-Takebe, Futami; Ida, Yusuke; Kakino, Ken; Narita, Toshio

    2013-01-01

    The residual stress caused by polymerization shrinkage and thermal contraction of a heat-curing resin containing 4-META on a metal-resin structure was measured by a scanning acoustic microscope. The tensile residual stress in the resin occurred within 70 µm of the adhesion interface with a flat plate specimen. The maximum tensile stress was about 58 MPa at the interface. On a metal plate specimen with retention holes, ring-like cracks in the resin occurred around the retention holes with the adhesive specimen and many linear cracks occurred in the resin vertical to the longitudinal direction of the metal frame with the non-adhesive specimens. There was tensile residual stress on the resin surface at the center of the retention holes of the adhesion specimen, indicating that the stress in the specimen with surface treatment for adhesion was higher than in that without surface treatment. PMID:24240901

  18. Analysis of residual stress in the resin of metal-resin adhesion structures by scanning acoustic microscopy.

    PubMed

    Ohno, Hiroki; Endo, Kazuhiko; Nagano-Takebe, Futami; Ida, Yusuke; Kakino, Ken; Narita, Toshio

    2013-01-01

    The residual stress caused by polymerization shrinkage and thermal contraction of a heat-curing resin containing 4-META on a metal-resin structure was measured by a scanning acoustic microscope. The tensile residual stress in the resin occurred within 70 µm of the adhesion interface with a flat plate specimen. The maximum tensile stress was about 58 MPa at the interface. On a metal plate specimen with retention holes, ring-like cracks in the resin occurred around the retention holes with the adhesive specimen and many linear cracks occurred in the resin vertical to the longitudinal direction of the metal frame with the non-adhesive specimens. There was tensile residual stress on the resin surface at the center of the retention holes of the adhesion specimen, indicating that the stress in the specimen with surface treatment for adhesion was higher than in that without surface treatment.

  19. Effects of fluid shear stress on polyelectrolyte multilayers by neutron scattering studies

    DOE PAGES

    Singh, Saurabh; Junghans, Ann; Watkins, Erik; Kapoor, Yash; Toomey, Ryan; Majewski, Jaroslaw

    2015-02-17

    The structure of layer-by-layer (LbL) deposited nanofilm coatings consists of alternating polyethylenimine (PEI) and polystyrenesulfonate (PSS) films deposited on a single crystal quartz substrate. LbL-deposited nanofilms were investigated by neutron reflectomery (NR) in contact with water in the static and fluid shear stress conditions. The fluid shear stress was applied through a laminar flow of the liquid parallel to the quartz/polymer interface in a custom-built solid–liquid interface cell. The scattering length density profiles obtained from NR results of these polyelectrolyte multilayers (PEM), measured under different shear conditions, showed proportional decrease of volume fraction of water hydrating the polymers. For themore » highest shear rate applied (ca. 6800 s–1) the water volume fraction decreased by approximately 7%. The decrease of the volume fraction of water was homogeneous through the thickness of the film. Since there were not any significant changes in the total polymer thickness, it resulted in negative osmotic pressures in the film. The PEM films were compared with the behavior of thin films of thermoresponsive poly(N-isopropylacrylamide) (pNIPAM) deposited via spin-coating. The PEM and pNIPAM differ in their interactions with water molecules, and they showed opposite behaviors under the fluid shear stress. In both cases the polymer hydration was reversible upon the restoration of static conditions. Furthermore, a theoretical explanation is given to explain this difference in the effect of shear on hydration of polymeric thin films.« less

  20. Adaptive response of vascular endothelial cells to an acute increase in shear stress frequency

    PubMed Central

    Zhang, Ji

    2013-01-01

    Local shear stress sensed by arterial endothelial cells is occasionally altered by changes in global hemodynamic parameters, e.g., heart rate and blood flow rate, as a result of normal physiological events, such as exercise. In a recently study (41), we demonstrated that during the adaptive response to increased shear magnitude, porcine endothelial cells exhibited an unique phenotype featuring a transient increase in permeability and the upregulation of a set of anti-inflammatory and antioxidative genes. In the present study, we characterize the adaptive response of these cells to an increase in shear frequency, another important hemodynamic parameter with implications in atherogenesis. Endothelial cells were preconditioned by a basal-level sinusoidal shear stress of 15 ± 15 dyn/cm2 at 1 Hz, and the frequency was then elevated to 2 Hz. Endothelial permeability increased slowly after the frequency step-up, but the increase was relatively small. Using microarrays, we identified 37 genes that are sensitive to the frequency step-up. The acute increase in shear frequency upregulates a set of cell-cycle regulation and angiogenesis-related genes. The overall adaptive response to the increased frequency is distinctly different from that to a magnitude step-up. However, consistent with the previous study, our data support the notion that endothelial function during an adaptive response is different than that of fully adapted endothelial cells. Our studies may also provide insights into the beneficial effects of exercise on vascular health: transient increases in frequency may facilitate endothelial repair, whereas similar increases in shear magnitude may keep excessive inflammation and oxidative stress at bay. PMID:23851277

  1. Reynolds stress flow shear and turbulent energy transfer in reversed field pinch configuration

    NASA Astrophysics Data System (ADS)

    Vianello, Nicola; Spolaore, Monica; Serianni, Gianluigi; Regnoli, Giorgio; Spada, Emanuele; Antoni, Vanni; Bergsåker, Henric; Drake, James R.

    2003-10-01

    The role of Reynolds Stress tensor on flow generation in turbulent fluids and plasmas is still an open question and the comprehension of its behavior may assist the understanding of improved confinement scenario. It is generally believed that shear flow generation may occur by an interaction of the turbulent Reynolds stress with the shear flow. It is also generally believed that this mechanism may influence the generation of zonal flow shears. The evaluation of the complete Reynolds Stress tensor requires contemporary measurements of its electrostatic and magnetic part: this requirement is more restrictive for Reversed Field Pinch configuration where magnetic fluctuations are larger than in tokamak . A new diagnostic system which combines electrostatic and magnetic probes has been installed in the edge region of Extrap-T2R reversed field pinch. With this new probe the Reynolds stress tensor has been deduced and its radial profile has been reconstructed on a shot to shot basis exploring differen plasma conditions. These profiles have been compared with the naturally occurring velocity flow profile, in particular during Pulsed Poloidal Current Drive experiment, where a strong variation of ExB flow radial profile has been registered. The study of the temporal evolution of Reynolds stress reveals the appearance of strong localized bursts: these are considered in relation with global MHD relaxation phenomena, which naturally occur in the core of an RFP plasma sustaining its configuration.

  2. Effect of solid contents on the controlled shear stress rheological properties of different types of sludge.

    PubMed

    Li, Ting; Wang, Yili; Dong, Yujing

    2012-01-01

    Controlled shear stress (CSS) test was used to study the effect of solid contents on the corresponding rheological parameters for sludge. Three types of sludge with or without conditioning, including activated sludge (AS), anaerobic digested sludge (ADS), and water treatment residuals (WTRs), were collected for the CSS test. Results showed that the yield stress and the cohesion energy of the sludge networks were improved with increased total suspending solid (TSS) contents in most cases. For the conditioned AS/ADS and the raw WTRs, exponential law was observed in the relationships between cohesion energy of material networks or yield stress and the TSS contents, whereas for the conditioned WTRs, only exponential law dependence was found between the parameters of shear modulus or critical strain and the TSS contents.

  3. Effect of shear stress on electromagnetic behaviors in superconductor-ferromagnetic bilayer structure

    NASA Astrophysics Data System (ADS)

    Yong, Huadong; Zhao, Meng; Jing, Ze; Zhou, Youhe

    2014-09-01

    In this paper, the electromagnetic response and shielding behaviour of superconductor-ferromagnetic bilayer structure are studied. The magnetomechanical coupling in ferromagnetic materials is also considered. Based on the linear piezomagnetic coupling model and anti-plane shear deformation, the current density and magnetic field in superconducting strip are obtained firstly. The effect of shear stress on the magnetization of strip is discussed. Then, we consider the magnetic cloak for superconductor-ferromagnetic bilayer structure. The magnetic permeability of ferromagnetic material is obtained for perfect cloaking in uniform magnetic field with magnetomechanical coupling in ferromagnet. The simulation results show that the electromagnetic response in superconductors will change by applying the stress only to the ferromagnetic material. In addition, the performance of invisibility of structure for non-uniform field will be affected by mechanical stress. It may provide a method to achieve tunability of superconducting properties with mechanical loadings.

  4. Effect of simulated microgravity on osteocytes responding to fluid shear stress

    NASA Astrophysics Data System (ADS)

    Yang, Xiao; Sun, Lian-Wen; Wu, Xin-Tong; Wang, Xiao-Nan; Fan, Yu-Bo

    2013-03-01

    Osteocytes, as most abundant cells and major mechanical sensor in bone, play an important role in the mechanism of microgravity-induced bone loss. The response of osteocytes to fluid flow stress under simulated microgravity was investigated in this study. MLO-Y4, an osteocyte-like cell line, was cultured under simulated microgravity condition for 5 days. Then cells were sheared at 15 dyn/cm2 in flow chamber. After 15 min shear, nitric oxide (NO) was examined by Griess Reagent and prostaglandin E2 (PGE2) by ELISA. After 6 h shear, alkaline phosphatase (ALP) was examined by PNPP, osteocalcin (OC) and procollagen type I N propeptide (PINP) by ELISA. Cells were divided into four groups: CON (1 G with no shear), CON-S (1 G with shear), SM (simulated microgravity with no shear) and SM-S (simulated microgravity with shear). The results showed that (1) NO, ALP activity, OC and PINP increased significantly while PGE2 showed no change in SM compared with CON. (2) NO, PGE2, ALP activity and PINP increased significantly while OC decreased significantly in CON-S compared with CON. (3) NO in SM-S had no significant difference compared to SM, PGE2 and OC increased while ALP activity and PINP decreased significantly in SM-S compared with SM. (4) The increasing amplitude of PGE2 and OC, the decreasing amplitude of ALP activity in SM-S to SM was lower than that in CON-S to CON. In addition, some changes of F-actin cytoskeleton were observed by confocal microscopy. All results indicated that the response induced by fluid shear in osteocytes could be inhibited by simulated microgravity, namely the mechanosensibility of osteocytes decreased under simulated microgravity. This may partly contribute to the mechanism of microgravity-induced osteoporosis and will be helpful to find out effective description.

  5. Separating Fluid Shear Stress from Acceleration during Vibrations in Vitro: Identification of Mechanical Signals Modulating the Cellular Response

    PubMed Central

    Uzer, Gunes; Manske, Sarah L; Chan, M Ete; Chiang, Fu-Pen; Rubin, Clinton T; Frame, Mary D; Judex, Stefan

    2012-01-01

    The identification of the physical mechanism(s) by which cells can sense vibrations requires the determination of the cellular mechanical environment. Here, we quantified vibration-induced fluid shear stresses in vitro and tested whether this system allows for the separation of two mechanical parameters previously proposed to drive the cellular response to vibration – fluid shear and peak accelerations. When peak accelerations of the oscillatory horizontal motions were set at 1g and 60Hz, peak fluid shear stresses acting on the cell layer reached 0.5Pa. A 3.5-fold increase in fluid viscosity increased peak fluid shear stresses 2.6-fold while doubling fluid volume in the well caused a 2-fold decrease in fluid shear. Fluid shear was positively related to peak acceleration magnitude and inversely related to vibration frequency. These data demonstrated that peak shear stress can be effectively separated from peak acceleration by controlling specific levels of vibration frequency, acceleration, and/or fluid viscosity. As an example for exploiting these relations, we tested the relevance of shear stress in promoting COX-2 expression in osteoblast like cells. Across different vibration frequencies and fluid viscosities, neither the level of generated fluid shear nor the frequency of the signal were able to consistently account for differences in the relative increase in COX-2 expression between groups, emphasizing that the eventual identification of the physical mechanism(s) requires a detailed quantification of the cellular mechanical environment. PMID:23074384

  6. Measuring bed shear stress along vegetated river beds using FST-hemispheres.

    PubMed

    Bockelmann-Evans, B N; Davies, R; Falconer, R A

    2008-09-01

    The measurement of the bed shear stress along vegetated river beds is essential for accurately predicting the water level, velocity and solute and sediment transport fluxes in computational hydroenvironmental models. Details are given herein of an experimental and theoretical study to determine the bed boundary shear stress along vegetated river beds introducing a novel field measuring method, namely the FliessWasserStammtisch (FST)-hemispheres. Although investigations have been conducted previously for sedimentary channels using the FST-hemispheres, this preliminary study is thought to be the first time that such hemispheres have been used to investigate the bed shear stresses in vegetated channels. FST-hemispheres were first developed by Statzner and Müller [1989. Standard hemispheres as indicators of flow characteristics in lotic benthos research. Freshwater Biology 21, 445-459] to act as an integrated indicator of the gross hydrodynamic stresses present near the bed. Test and validation data were found to be at least of the same order of magnitude for the stresses predicted from literature for sedimentary channels, with this study establishing the commencement of a database of calibrated FST-hemisphere laboratory data for vegetated channel beds. In a series of experiments, depths ranging from 0.1 to 0.28 m were considered, equating directly to comparable conditions in small rivers or streams. The results of this study provide a basis for enabling the FST-hemispheres to be used to evaluate the boundary shear stress for a wider range of applications in the future, including vegetated river beds.

  7. Effect of Shear Stress on Pseudomonas aeruginosa Isolated from the Cystic Fibrosis Lung

    PubMed Central

    Dingemans, Jozef; Monsieurs, Pieter; Yu, Sung-Huan; Crabbé, Aurélie; Förstner, Konrad U.; Malfroot, Anne

    2016-01-01

    ABSTRACT Chronic colonization of the lungs by Pseudomonas aeruginosa is one of the major causes of morbidity and mortality in cystic fibrosis (CF) patients. To gain insights into the characteristic biofilm phenotype of P. aeruginosa in the CF lungs, mimicking the CF lung environment is critical. We previously showed that growth of the non-CF-adapted P. aeruginosa PAO1 strain in a rotating wall vessel, a device that simulates the low fluid shear (LS) conditions present in the CF lung, leads to the formation of in-suspension, self-aggregating biofilms. In the present study, we determined the phenotypic and transcriptomic changes associated with the growth of a highly adapted, transmissible P. aeruginosa CF strain in artificial sputum medium under LS conditions. Robust self-aggregating biofilms were observed only under LS conditions. Growth under LS conditions resulted in the upregulation of genes involved in stress response, alginate biosynthesis, denitrification, glycine betaine biosynthesis, glycerol metabolism, and cell shape maintenance, while genes involved in phenazine biosynthesis, type VI secretion, and multidrug efflux were downregulated. In addition, a number of small RNAs appeared to be involved in the response to shear stress. Finally, quorum sensing was found to be slightly but significantly affected by shear stress, resulting in higher production of autoinducer molecules during growth under high fluid shear (HS) conditions. In summary, our study revealed a way to modulate the behavior of a highly adapted P. aeruginosa CF strain by means of introducing shear stress, driving it from a biofilm lifestyle to a more planktonic lifestyle. PMID:27486191

  8. Inhibition of cell adhesion by a synthetic polymer adsorbed to glass shown under defined hydrodynamic stress.

    PubMed

    Owens, N F; Gingell, D; Rutter, P R

    1987-06-01

    A co-polymer with hydrophobic and hydrophilic segments was allowed to adsorb from aqueous solution onto glass previously made hydrophobic by derivatization with octadecyl dimethylchlorosilane. The polymer is thought to adsorb via its hydrophobic segments, leaving the hydrophilic segments free to extend into the water. After allowing cells to settle on the treated surface, the shear stress at the chamber wall required to remove red blood cells, Dictyostelium discoideum amoebae and Escherichia coli was determined in a calibrated laminar flow chamber. On octadecyl glass a shear stress of 2-3 Nm-2 evicts 50% of adherent red cells and E. coli. No D. discoideum amoebae could be removed at 5Nm-2. In striking contrast, the lowest experimentally obtainable shear stress of 0.03 Nm-2 removes 97.0-99.5% of cells of all three types from the polymer-treated surface, even after a cell residence time of 1 h without flow in the absence of free polymer. The minimum shear stress of 0.03Nm-2 corresponds to only approximately equal to 20 times the force of gravity on a red cell. The mechanism of action of the polymer and the implications of the results are discussed. PMID:3312253

  9. Basal shear stress under alpine glaciers: insights from experiments using the iSOSIA and Elmer/Ice models

    NASA Astrophysics Data System (ADS)

    Brædstrup, C. F.; Egholm, D. L.; Ugelvig, S. V.; Pedersen, V. K.

    2016-02-01

    Shear stress at the base of glaciers exerts a significant control on basal sliding and hence also glacial erosion in arctic and high-altitude areas. However, the inaccessible nature of glacial beds complicates empirical studies of basal shear stress, and little is therefore known of its spatial and temporal distribution. In this study we seek to improve our understanding of basal shear stress using a higher-order numerical ice model (iSOSIA). In order to test the validity of the higher-order model, we first compare the detailed distribution of basal shear stress in iSOSIA and in a three-dimensional full-Stokes model (Elmer/Ice). We find that iSOSIA and Elmer/Ice predict similar first-order stress and velocity patterns, and that differences are restricted to local variations at length scales of the order of the grid resolution. In addition, we find that subglacial shear stress is relatively uniform and insensitive to subtle changes in local topographic relief. Following the initial comparison studies, we use iSOSIA to investigate changes in basal shear stress as a result of landscape evolution by glacial erosion. The experiments with landscape evolution show that subglacial shear stress decreases as glacial erosion transforms preglacial V-shaped valleys into U-shaped troughs. These findings support the hypothesis that glacial erosion is most efficient in the early stages of glacial landscape development.

  10. Staphylococcus aureus biofilm formation and tolerance to antibiotics in response to oscillatory shear stresses of physiological levels.

    PubMed

    Kostenko, Victoria; Salek, Mohammad Mehdi; Sattari, Pooria; Martinuzzi, Robert John

    2010-08-01

    Bacterial infections in the blood system are usually associated with blood flow oscillation generated by some cardiovascular pathologies and insertion of indwelling devices. The influence of hydrodynamically induced shear stress fluctuations on the Staphylococcus aureus biofilm morphology and tolerance to antibiotics was investigated. Fluctuating shear stresses of physiologically relevant levels were generated in wells of a six-well microdish agitated by an orbital shaker. Numerical simulations were performed to determine the spatial distribution and local fluctuation levels of the shear stress field on the well bottom. It is found that the local biofilm deposition and morphology correlate strongly with shear stress fluctuations and maximum magnitude levels. Tolerance to killing by antibiotics correlates with morphotype and is generally higher in high shear regions. PMID:20528928

  11. The Effect of Shear and Deviatoric Stress on Permeability Evolution in Fractured Diorite and Novaculite

    NASA Astrophysics Data System (ADS)

    Faoro, I.; Elsworth, D.; Marone, C.; Niemeijer, A.

    2006-12-01

    The evolution of the permeability in fractured rocks, subject to changing stress conditions is a complex issue. In this contribution, we report on experiments in which rock surfaces were sheared under controlled pore pressure and true-triaxial stress conditions while permeability was monitored via flow parallel to the shear direction. Direct shear tests were performed in a pressure vessel under drained conditions on samples of novaculite and of diorite (Coso Geothermal field, CA). Smoothed-faced, prismatic blocks were roughened by grinding with 60# grit, assembled face-to-face, and jacketed within a sealed membrane. Normal stress was applied by a hydraulic ram, and confining- and pore-pressures were maintained via high precision servo- controlled pressure intensifiers. The sample pairs are sheared to 18 mm of final displacement at 5 μm/sec, at room temperature, and at effective normal stresses ranging from 5 to 20 MPa. Permeability evolution is measured throughout shearing via flow of distilled water from an upstream reservoir at 0.1 MPa and discharged at atmospheric pressure. The permeability of the smooth fracture in novaculite varied only slightly with applied effective normal stress (0.5×10^{-14} m2 at 5 MPa, 10^{-14} m2 at 10 MPa and 10^{-14} m2 at 20 MPa). The corresponding hydraulic apertures were respectively 20 μm, 15 μm and 13 μm. In all three tests, permeability dropped one order of magnitude upon shearing. Steady state values for permeability and shear strength were typically reached after ~ 10 mm of load point displacement. An associated reduction of ~10 μm was observed in the hydraulic apertures. Similar behavior was recorded in the diorite sample but only at the highest effective normal stresses. The initial permeability of ~10^{-13 m2 dropped four orders of magnitude before reaching a steady state value. This corresponds to a reduction in hydraulic aperture of ~23 μm, reaching a steady state magnitude of ~1.5 μm. At lower effective normal

  12. Nature of stress accommodation in sheared granular material: Insights from 3D numerical modeling

    NASA Astrophysics Data System (ADS)

    Mair, Karen; Hazzard, James F.

    2007-07-01

    Active faults often contain distinct accumulations of granular wear material. During shear, this granular material accommodates stress and strain in a heterogeneous manner that may influence fault stability. We present new work to visualize the nature of contact force distributions during 3D granular shear. Our 3D discrete numerical models consist of granular layers subjected to normal loading and direct shear, where gouge particles are simulated by individual spheres interacting at points of contact according to simple laws. During shear, we observe the transient microscopic processes and resulting macroscopic mechanical behavior that emerge from interactions of thousands of particles. We track particle translations and contact forces to determine the nature of internal stress accommodation with accumulated slip for different initial configurations. We view model outputs using novel 3D visualization techniques. Our results highlight the prevalence of transient directed contact force networks that preferentially transmit enhanced stresses across our granular layers. We demonstrate that particle size distribution (psd) controls the nature of the force networks. Models having a narrow (i.e. relatively uniform) psd exhibit discrete pipe-like force clusters with a dominant and focussed orientation oblique to but in the plane of shear. Wider psd models (e.g. power law size distributions D = 2.6) also show a directed contact force network oblique to shear but enjoy a wider range of orientations and show more out-of-plane linkages perpendicular to shear. Macroscopic friction level, is insensitive to these distinct force network morphologies, however, force network evolution appears to be linked to fluctuations in macroscopic friction. Our results are consistent with predictions, based on recent laboratory observations, that force network morphologies are sensitive to grain characteristics such as particle size distribution of a sheared granular layer. Our numerical

  13. Rod climbing and normal stresses in heavy crude oils at low shears

    SciTech Connect

    Nunez, G.A. ); Ribeiro, G.S.; Arney, M.S.; Feng, J.; Joseph, D.D. )

    1994-09-01

    This paper gives the results of a study of the nonlinear viscoelastic behavior of three heavy crude oils from California and Venezuela. A linear combination of normal stress coefficients at zero shear is expressed in terms of the quantity (the climbing constant) used to measure the height rise on a rotating rod. Measurements of the climbing constants are given for the crude oils. Values of both the first and second normal stress coefficients at zero shear are determined by the climbing constant when another combination of the two coefficients is known. In principle, the required information can be obtained by back extrapolation of the first normal stress difference, by back extrapolation of the dynamic modulus or by back extrapolation of the ratio of the second to first normal stress difference. Back extrapolation of data can be achieved when measurements are available at shear rates low enough to enter onto the second-order plateau of the functions generated by different instruments. Examination of previously published data for well-characterized solutions suggests that second-order rheology is most readily obtained in rod climbing.

  14. A Multichannel Dampened Flow System for Studies on Shear Stress-Mediated Mechanotransduction

    PubMed Central

    Voyvodic, Peter L.; Min, Daniel; Baker, Aaron B.

    2012-01-01

    Shear stresses are powerful regulators of cellular function and potent mediators of the development of vascular disease. We have designed and optimized a system allowing the application of flow to cultured cells in a multichannel format. By using a multichannel peristaltic pump, flow can be driven continuously in the system for long-term studies in multiple isolated flow loops. A key component of the system is a dual-chamber pulse dampener that removes the pulsatility of the flow without the need for having an open system or elevated reservoir. We optimized the design parameters of the pulse dampening chambers for the maximum reduction in flow pulsation while minimizing the fluid needed for each isolated flow channel. Human umbilical vein endothelial cells (HUVECs) were exposed to steady and pulsatile shear stress using the system. We found that cells under steady flow had a marked increased production of eNOS and formation of actin stress fibers in comparison to those under pulsatile flow conditions. Overall, the results confirm the utility of the device as a practical means to apply shear stress to cultured cells in the multichannel format and provide steady, long term flow to microfluidic devices. PMID:22836694

  15. A multichannel dampened flow system for studies on shear stress-mediated mechanotransduction.

    PubMed

    Voyvodic, Peter L; Min, Daniel; Baker, Aaron B

    2012-09-21

    Shear stresses are powerful regulators of cellular function and potent mediators of the development of vascular disease. We have designed and optimized a system allowing the application of flow to cultured cells in a multichannel format. By using a multichannel peristaltic pump, flow can be driven continuously in the system for long-term studies in multiple isolated flow loops. A key component of the system is a dual-chamber pulse dampener that removes the pulsatility of the flow without the need for having an open system or elevated reservoir. We optimized the design parameters of the pulse dampening chambers for the maximum reduction in flow pulsation while minimizing the fluid needed for each isolated flow channel. Human umbilical vein endothelial cells (HUVECs) were exposed to steady and pulsatile shear stress using the system. We found that cells under steady flow had a marked increased production of eNOS and formation of actin stress fibers in comparison to those under pulsatile flow conditions. Overall, the results confirm the utility of the device as a practical means to apply shear stress to cultured cells in the multichannel format and provide steady, long term flow to microfluidic devices.

  16. Scale-up of high shear granulation based on the internal stress measurement.

    PubMed

    Watano, Satoru; Okamoto, Takumi; Sato, Yoshinobu; Osako, Yoshifumi

    2005-04-01

    Scale-up of wet granulation in a vertical high shear mixer was conducted. Pharmaceutical excipient powders composed of lactose, cornstarch and micro-crystallinecellulose, and hydroxypropylcellulose as a binder were mixed together and then granulated with purified water under various operating conditions and vessel scales. A novel internal stress measurement system was developed and stress of normal and tangential directions that granules received from the agitator blade during the granulation was continuously measured. The results indicated that granules received stress mainly from the tangential direction, which also showed the largest value near at the vessel wall. The effects of the agitator tip speed and the centrifugal acceleration on the measured stress was investigated. It was found that the tip speed of the agitator blade could be the main factor for the granule growth. The physical properties such as strength, size distribution and compressibility of granules prepared by changing the operating conditions and the vessel scales were evaluated and the scale-up characteristics of high shear granulation were investigated experimentally. The results showed that these physical properties had linear correlations with the tip speed. It was finally concluded that the scale-up of high shear granulation could be well conducted by means of the tip speed of the agitator blade. PMID:15802830

  17. Modeling bed shear-stress fluctuations in a shallow tidal channel

    NASA Astrophysics Data System (ADS)

    Mathis, R.; Marusic, I.; Cabrit, O.; Jones, N. L.; Ivey, G. N.

    2014-05-01

    Recently, Mathis et al. (2013) developed a model for predicting the instantaneous fluctuations of the wall shear-stress in turbulent boundary layers. This model is based on an inner-outer scale interaction mechanism, incorporating superposition, and amplitude-modulation effects, and the only input required for the model is a time series measurement of the streamwise velocity signal taken in the logarithmic region of the flow. The present study applies this new approach for the first time to environmental flows, for which the near-bed information is typically inaccessible. The data used here are acoustic Doppler velocimeter time series measurements from a shallow tidal channel (Suisun Slough in North San Francisco Bay). We first extract segments of data sharing properties with canonical turbulent boundary layers. The wall (bed) shear-stress model is then applied to these selected data. Statistical and spectral analysis demonstrates that the field data predictions are consistent with laboratory and DNS results. The model is also applied to the whole available data set to demonstrate, even for situations far from the canonical boundary layer case, its ability to preserve the overall Reynolds number trend. The predicted instantaneous bed stress is highly skewed and amplitude modulated with the variations in the large-scale streamwise velocity. Finally, the model is compared to conventional methods employed to predict the bed shear-stress. A large disparity is observed, but the present model is the only one able to predict both the correct spectral content and the probability density function.

  18. Analysis of fluid flow and wall shear stress patterns inside partially filled agitated culture well plates.

    PubMed

    Salek, M Mehdi; Sattari, Pooria; Martinuzzi, Robert J

    2012-03-01

    The appearance of highly resistant bacterial biofilms in both community and hospitals environments is a major challenge in modern clinical medicine. The biofilm structural morphology, believed to be an important factor affecting the behavioral properties of these "super bugs", is strongly influenced by the local hydrodynamics over the microcolonies. Despite the common use of agitated well plates in the biology community, they have been used rather blindly without knowing the flow characteristics and influence of the rotational speed and fluid volume in these containers. The main purpose of this study is to characterize the flow in these high-throughput devices to link local hydrodynamics to observed behavior in cell cultures. In this work, the flow and wall shear stress distribution in six-well culture plates under planar orbital translation is simulated using Computational Fluid Dynamics (CFD). Free surface, flow pattern and wall shear stress for two shaker speeds (100 and 200 rpm) and two volumes of fluid (2 and 4 mL) were investigated. Measurements with a non-intrusive optical shear stress sensor and High Frame-rate Particle Imaging Velocimetry (HFPIV) are used to validate CFD predictions. An analytical model to predict the free surface shape is proposed. Results show a complex three-dimensional flow pattern, varying in both time and space. The distribution of wall shear stress in these culture plates has been related to the topology of flow. This understanding helps explain observed endothelial cell orientation and bacterial biofilm distributions observed in culture dishes. The results suggest that the mean surface stress field is insufficient to capture the underlying dynamics mitigating biological processes. PMID:22042624

  19. Spatio-Temporal Surface Shear-Stress Variability in Live Plant Canopies and Cube Arrays

    NASA Astrophysics Data System (ADS)

    Walter, Benjamin; Gromke, Christof; Leonard, Katherine C.; Manes, Costantino; Lehning, Michael

    2012-05-01

    This study presents spatiotemporally-resolved measurements of surface shear-stress τ s in live plant canopies and rigid wooden cube arrays to identify the sheltering capability against sediment erosion of these different roughness elements. Live plants have highly irregular structures that can be extremely flexible and porous resulting in considerable changes to the drag and flow regimes relative to rigid imitations mainly used in other wind-tunnel studies. Mean velocity and kinematic Reynolds stress profiles show that well-developed natural boundary layers were generated above the 8 m long wind-tunnel test section covered with the roughness elements at four different roughness densities ( λ = 0, 0.017, 0.08, 0.18). Speed-up around the cubes caused higher peak surface shear stress than in experiments with plants at all roughness densities, demonstrating the more effective sheltering ability of the plants. The sheltered areas in the lee of the plants are significantly narrower with higher surface shear stress than those found in the lee of the cubes, and are dependent on the wind speed due to the plants ability to streamline with the flow. This streamlining behaviour results in a decreasing sheltering effect at increasing wind speeds and in lower net turbulence production than in experiments with cubes. Turbulence intensity distributions suggest a suppression of horseshoe vortices in the plant case. Comparison of the surface shear-stress measurements with sediment erosion patterns shows that the fraction of time a threshold skin friction velocity is exceeded can be used to assess erosion of, and deposition on, that surface.

  20. Analysis of fluid flow and wall shear stress patterns inside partially filled agitated culture well plates.

    PubMed

    Salek, M Mehdi; Sattari, Pooria; Martinuzzi, Robert J

    2012-03-01

    The appearance of highly resistant bacterial biofilms in both community and hospitals environments is a major challenge in modern clinical medicine. The biofilm structural morphology, believed to be an important factor affecting the behavioral properties of these "super bugs", is strongly influenced by the local hydrodynamics over the microcolonies. Despite the common use of agitated well plates in the biology community, they have been used rather blindly without knowing the flow characteristics and influence of the rotational speed and fluid volume in these containers. The main purpose of this study is to characterize the flow in these high-throughput devices to link local hydrodynamics to observed behavior in cell cultures. In this work, the flow and wall shear stress distribution in six-well culture plates under planar orbital translation is simulated using Computational Fluid Dynamics (CFD). Free surface, flow pattern and wall shear stress for two shaker speeds (100 and 200 rpm) and two volumes of fluid (2 and 4 mL) were investigated. Measurements with a non-intrusive optical shear stress sensor and High Frame-rate Particle Imaging Velocimetry (HFPIV) are used to validate CFD predictions. An analytical model to predict the free surface shape is proposed. Results show a complex three-dimensional flow pattern, varying in both time and space. The distribution of wall shear stress in these culture plates has been related to the topology of flow. This understanding helps explain observed endothelial cell orientation and bacterial biofilm distributions observed in culture dishes. The results suggest that the mean surface stress field is insufficient to capture the underlying dynamics mitigating biological processes.

  1. Interfibrillar shear stress is the loading mechanism of collagen fibrils in tendon.

    PubMed

    Szczesny, Spencer E; Elliott, Dawn M

    2014-06-01

    Despite the critical role tendons play in transmitting loads throughout the musculoskeletal system, little is known about the microstructural mechanisms underlying their mechanical function. Of particular interest is whether collagen fibrils in tendon fascicles bear load independently or if load is transferred between fibrils through interfibrillar shear forces. We conducted multiscale experimental testing and developed a microstructural shear lag model to explicitly test whether interfibrillar shear load transfer is indeed the fibrillar loading mechanism in tendon. Experimental correlations between fascicle macroscale mechanics and microscale interfibrillar sliding suggest that fibrils are discontinuous and share load. Moreover, for the first time, we demonstrate that a shear lag model can replicate the fascicle macroscale mechanics as well as predict the microscale fibrillar deformations. Since interfibrillar shear stress is the fundamental loading mechanism assumed in the model, this result provides strong evidence that load is transferred between fibrils in tendon and possibly other aligned collagenous tissues. Conclusively establishing this fibrillar loading mechanism and identifying the involved structural components should help develop repair strategies for tissue degeneration and guide the design of tissue engineered replacements. PMID:24530560

  2. [Stress profile during curing contraction of composite resin adhesives].

    PubMed

    Kunzelmann, K H; Hickel, R

    1990-11-01

    The wall-to-wall curing contraction of thin composite resin layers was recorded with a tensometer. The composite resin was applied to cylindrically shaped ceramic sample holders with diameters of 3 mm, 4 mm and 8 mm. The distances of the sample holders was set at 50 microns, 100 microns, 150 microns, 200 microns and 300 microns. The shrinkage stress recordings clearly show that the shrinkage forces are governed by the distance of the sample holders and not by the volume or the configuration factor of the composite resin layers.

  3. Mechanical loading by fluid shear stress of myotube glycocalyx stimulates growth factor expression and nitric oxide production.

    PubMed

    Juffer, Petra; Bakker, Astrid D; Klein-Nulend, Jenneke; Jaspers, Richard T

    2014-07-01

    Skeletal muscle fibers have the ability to increase their size in response to a mechanical overload. Finite element modeling data suggest that mechanically loaded muscles in vivo may experience not only tensile strain but also shear stress. However, whether shear stress affects biological pathways involved in muscle fiber size adaptation in response to mechanical loading is unknown. Therefore, our aim was twofold: (1) to determine whether shear stress affects growth factor expression and nitric oxide (NO) production by myotubes, and (2) to explore the mechanism by which shear stress may affect myotubes in vitro. C2C12 myotubes were subjected to a laminar pulsating fluid flow (PFF; mean shear stress 0.4, 0.7 or 1.4 Pa, 1 Hz) or subjected to uni-axial cyclic strain (CS; 15 % strain, 1 Hz) for 1 h. NO production during 1-h PFF or CS treatment was quantified using Griess reagent. The glycocalyx was degraded using hyaluronidase, and stretch-activated ion channels (SACs) were blocked using GdCl3. Gene expression was analyzed immediately after 1-h PFF (1.4 Pa, 1 Hz) and at 6 h post-PFF treatment. PFF increased IGF-I Ea, MGF, VEGF, IL-6, and COX-2 mRNA, but decreased myostatin mRNA expression. Shear stress enhanced NO production in a dose-dependent manner, while CS induced no quantifiable increase in NO production. Glycocalyx degradation and blocking of SACs ablated the shear stress-stimulated NO production. In conclusion, shear stress activates signaling pathways involved in muscle fiber size adaptation in myotubes, likely via membrane-bound mechanoreceptors. These results suggest that shear stress exerted on myofiber extracellular matrix plays an important role in mechanotransduction in muscle.

  4. Characterizing Wave- and Current-Induced Bottom Shear Stress: U.S. Middle Atlantic Bight

    NASA Astrophysics Data System (ADS)

    Dalyander, S.; Butman, B.

    2011-12-01

    The combined action of waves and currents at the seabed creates bottom shear stress, impacting local geology, habitat, and anthropogenic use. In this study, a methodology is developed to characterize the magnitude of benthic disturbance based on spatially and seasonally-resolved statistics (mean, standard deviation, 95th percentile) of wave-current bottom shear stress. The frequency of stress forcing is used to distinguish regions dominated by storms (return interval longer than 33 hours) from those dominated by the tides (periods shorter than 33 hours). In addition, the relative magnitude of the contribution to stress from waves, tides, and storm-driven currents is investigated by comparing wave stress, tidal current stress, and stress from the residual current (currents with tides removed), as well as through cross-correlation of wave and current stress. The methodology is applied to numerical model time-series data for the Middle Atlantic Bight (MAB) off the U.S. East Coast for April 2010 to April 2011; currents are provided from the Integrated Ocean Observing System (IOOS) operational hydrodynamic forecast Experimental System for Predicting Shelf and Slope Optics (ESPreSSO) and waves are provided from a Simulating WAves Nearshore (SWAN) hindcast developed for this project. Spatial resolution of the model is about 5 km and time-series wave and current data are at 1 and 2-hours respectively. Regions of the MAB delineated by stress characteristics include a tidally-dominated shallow region with relative high stress southeast of Massachusetts over Nantucket Shoals; a coastal band extending offshore to about 30 m water depth dominated by waves; a region dominated by waves and wind-driven currents offshore of the Outer Banks of North Carolina; and a low stress region southeast of Long Island, approximately coincident with an area of fine-grained sediments called the "Mud Patch". Comparison of the stress distribution with surface sediment texture data shows that

  5. Characterizing wave- and current- induced bottom shear stress: U.S. middle Atlantic continental shelf

    USGS Publications Warehouse

    Dalyander, P. Soupy; Butman, Bradford; Sherwood, Christopher R.; Signell, Richard P.; Wilkin, John L.

    2013-01-01

    Waves and currents create bottom shear stress, a force at the seabed that influences sediment texture distribution, micro-topography, habitat, and anthropogenic use. This paper presents a methodology for assessing the magnitude, variability, and driving mechanisms of bottom stress and resultant sediment mobility on regional scales using numerical model output. The analysis was applied to the Middle Atlantic Bight (MAB), off the U.S. East Coast, and identified a tidally-dominated shallow region with relatively high stress southeast of Massachusetts over Nantucket Shoals, where sediment mobility thresholds are exceeded over 50% of the time; a coastal band extending offshore to about 30 m water depth dominated by waves, where mobility occurs more than 20% of the time; and a quiescent low stress region southeast of Long Island, approximately coincident with an area of fine-grained sediments called the “Mud Patch”. The regional high in stress and mobility over Nantucket Shoals supports the hypothesis that fine grain sediment winnowed away in this region maintains the Mud Patch to the southwest. The analysis identified waves as the driving mechanism for stress throughout most of the MAB, excluding Nantucket Shoals and sheltered coastal bays where tides dominate; however, the relative dominance of low-frequency events varied regionally, and increased southward toward Cape Hatteras. The correlation between wave stress and local wind stress was lowest in the central MAB, indicating a relatively high contribution of swell to bottom stress in this area, rather than locally generated waves. Accurate prediction of the wave energy spectrum was critical to produce good estimates of bottom shear stress, which was sensitive to energy in the long period waves.

  6. Endothelial dysfunction following prolonged sitting is mediated by a reduction in shear stress.

    PubMed

    Restaino, Robert M; Walsh, Lauren K; Morishima, Takuma; Vranish, Jennifer R; Martinez-Lemus, Luis A; Fadel, Paul J; Padilla, Jaume

    2016-03-01

    We and others have recently reported that prolonged sitting impairs endothelial function in the leg vasculature; however, the mechanism(s) remain unknown. Herein, we tested the hypothesis that a sustained reduction in flow-induced shear stress is the underlying mechanism by which sitting induces leg endothelial dysfunction. Specifically, we examined whether preventing the reduction in shear stress during sitting would abolish the detrimental effects of sitting on popliteal artery endothelial function. In 10 young healthy men, bilateral measurements of popliteal artery flow-mediated dilation were performed before and after a 3-h sitting period during which one foot was submerged in 42°C water (i.e., heated) to increase blood flow and thus shear stress, whereas the contralateral leg remained dry and served as internal control (i.e., nonheated). During sitting, popliteal artery mean shear rate was reduced in the nonheated leg (pre-sit, 42.9 ± 4.5 s(-1); and 3-h sit, 23.6 ± 3.3 s(-1); P < 0.05) but not in the heated leg (pre-sit, 38.9 ± 3.4 s(-1); and 3-h sit, 63.9 ± 16.9 s(-1); P > 0.05). Popliteal artery flow-mediated dilation was impaired after 3 h of sitting in the nonheated leg (pre-sit, 7.1 ± 1.4% vs. post-sit, 2.8 ± 0.9%; P < 0.05) but not in the heated leg (pre-sit: 7.3 ± 1.5% vs. post-sit, 10.9 ± 1.8%; P > 0.05). Collectively, these data suggest that preventing the reduction of flow-induced shear stress during prolonged sitting with local heating abolishes the impairment in popliteal artery endothelial function. Thus these findings are consistent with the hypothesis that sitting-induced leg endothelial dysfunction is mediated by a reduction in shear stress. PMID:26747508

  7. Dependence of fungal characteristics on seed morphology and shear stress in bioreactors.

    PubMed

    Lu, Hongzhong; Li, Chao; Tang, Wenjun; Wang, Zejian; Xia, Jianye; Zhang, Siliang; Zhuang, Yingping; Chu, Ju; Noorman, Henk

    2015-05-01

    The fungal morphology during submerged cultivations has a profound influence on the overall performance of bioreactors. In this research, glucoamylase production by Aspergillus niger has been taken as a model to improve more insights. The morphology engineering could be conducted effectively by changing the seed morphology, as well as specific power input. During the fed-batch cultivations, pellet formation under milder shear stress field helped to reduce the broth viscosity, thus relieving oxygen limitation and promoting the enzyme production. Furthermore, we found that the relation between the shear stress field, which was characterized by energy dissipation rate/circulation function (EDCF), and enzyme activity was consistent with quadratic parabola, which threw light on the process optimization and scale-up for industrial enzyme production.

  8. Controlling Shear Stress in 3D Bioprinting is a Key Factor to Balance Printing Resolution and Stem Cell Integrity.

    PubMed

    Blaeser, Andreas; Duarte Campos, Daniela Filipa; Puster, Uta; Richtering, Walter; Stevens, Molly M; Fischer, Horst

    2016-02-01

    A microvalve-based bioprinting system for the manufacturing of high-resolution, multimaterial 3D-structures is reported. Applying a straightforward fluid-dynamics model, the shear stress at the nozzle site can precisely be controlled. Using this system, a broad study on how cell viability and proliferation potential are affected by different levels of shear stress is conducted. Complex, multimaterial 3D structures are printed with high resolution. This work pioneers the investigation of shear stress-induced cell damage in 3D bioprinting and might help to comprehend and improve the outcome of cell-printing studies in the future.

  9. Controlling Shear Stress in 3D Bioprinting is a Key Factor to Balance Printing Resolution and Stem Cell Integrity.

    PubMed

    Blaeser, Andreas; Duarte Campos, Daniela Filipa; Puster, Uta; Richtering, Walter; Stevens, Molly M; Fischer, Horst

    2016-02-01

    A microvalve-based bioprinting system for the manufacturing of high-resolution, multimaterial 3D-structures is reported. Applying a straightforward fluid-dynamics model, the shear stress at the nozzle site can precisely be controlled. Using this system, a broad study on how cell viability and proliferation potential are affected by different levels of shear stress is conducted. Complex, multimaterial 3D structures are printed with high resolution. This work pioneers the investigation of shear stress-induced cell damage in 3D bioprinting and might help to comprehend and improve the outcome of cell-printing studies in the future. PMID:26626828

  10. Shear stress influences the pluripotency of murine embryonic stem cells in stirred suspension bioreactors.

    PubMed

    Gareau, Tia; Lara, Giovanna G; Shepherd, Robert D; Krawetz, Roman; Rancourt, Derrick E; Rinker, Kristina D; Kallos, Michael S

    2014-04-01

    Pluripotent embryonic stem cells (ESCs) have been used increasingly in research as primary material for various tissue-engineering applications. Pluripotency, or the ability to give rise to all cells of the body, is an important characteristic of ESCs. Traditional methods use leukaemia inhibitory factor (LIF) to maintain murine embryonic stem cell (mESC) pluripotency in static and bioreactor cultures. When LIF is removed from mESCs in static cultures, pluripotency genes are downregulated and the cultures will spontaneously differentiate. Recently we have shown the maintenance of pluripotency gene expression of mESCs in stirred suspension bioreactors during differentiation experiments in the absence of LIF. This is undesired in a differentiation experiment, where the goal is downregulation of pluripotency gene expression and upregulation of gene expression characteristic to the differentiation. Thus, the objective of this study was to examine how effectively different levels of shear stress [100 rpm (6 dyne/cm(2) ), 60 rpm (3 dyne/cm(2) )] maintained and influenced pluripotency in suspension bioreactors. The pluripotency markers Oct-4, Nanog, Sox-2 and Rex-1 were assessed using gene expression profiles and flow-cytometry analysis and showed that shear stress does maintain and influence the gene expression of certain pluripotency markers. Some significant differences between the two levels of shear stress were seen and the combination of shear stress and LIF was observed to synergistically increase the expression of certain pluripotency markers. Overall, this study provides a better understanding of the environmental conditions within suspension bioreactors and how these conditions affect the pluripotency of mESCs.

  11. A Fiber Optic Sensor Sensitive To Normal Pressure And Shear Stress

    NASA Astrophysics Data System (ADS)

    Cuomo, Frank W.; Kidwell, Robert S.; Hu, Andong

    1986-11-01

    A fiber optic lever sensing technique that can be used to measure normal pressure as well as shear stresses is discussed. This method uses three unequal fibers combining small size and good sensitivity. Static measurements appear to confirm the theoretical models predicted by geometrical optics and dynamic tests performed at frequencies up to 10 kHz indicate a flat response within this frequency range. These sensors are intended for use in a low speed wind tunnel environment.

  12. Two-Axis Direct Fluid Shear Stress Sensor for Aerodynamic Applications

    NASA Technical Reports Server (NTRS)

    Bajikar, Sateesh S.; Scott, Michael A.; Adcock, Edward E.

    2011-01-01

    This miniature or micro-sized semiconductor sensor design provides direct, nonintrusive measurement of skin friction or wall shear stress in fluid flow situations in a two-axis configuration. The sensor is fabricated by microelectromechanical system (MEMS) technology, enabling small size and multiple, low-cost reproductions. The sensors may be fabricated by bonding a sensing element wafer to a fluid-coupling element wafer. Using this layered machine structure provides a truly three-dimensional device.

  13. Imaging the cellular response to transient shear stress using time-resolved digital holography

    NASA Astrophysics Data System (ADS)

    Arita, Yoshihiko; Antkowiak, Maciej; Gunn-Moore, Frank; Dholakia, Kishan

    2014-02-01

    Shear stress has been recognized as one of the biophysical methods by which to permeabilize plasma membranes of cells. In particular, high pressure transient hydrodynamic flows created by laser-induced cavitation have been shown to lead to the uptake of fluorophores and plasmid DNA. While the mechanism and dynamics of cavitation have been extensively studied using a variety of time-resolved imaging techniques, the cellular response to the cavitation bubble and cavitation induced transient hydrodynamic flows has never been shown in detail. We use time-resolved quantitative phase microscopy to study cellular response to laser-induced cavitation bubbles. Laser-induced breakdown of an optically trapped polystyrene nanoparticle (500nm in diameter) irradiated with a single nanosecond laser pulse at 532nm creates transient shear stress to surrounding cells without causing cell lysis. A bi-directional transient displacement of cytoplasm is observed during expansion and collapse of the cavitation bubble. In some cases, cell deformation is only observable at the microsecond time scale without any permanent change in cell shape or optical thickness. On a time scale of seconds, the cellular response to shear stress and cytoplasm deformation typically leads to retraction of the cellular edge most exposed to the flow, rounding of the cell body and, in some cases, loss of cellular dry mass. These results give a new insight into the cellular response to laser-induced shear stress and related plasma membrane permeabilization. This study also demonstrates that laser-induced breakdown of an optically trapped nanoparticle offers localized cavitation (70 μm in diameter), which interacts with a single cell.

  14. Low-Shear modeled microgravity alters the Salmonella enterica serovar typhimurium stress response in an RpoS-independent manner

    NASA Technical Reports Server (NTRS)

    Wilson, James W.; Ott, C. Mark; Ramamurthy, Rajee; Porwollik, Steffen; McClelland, Michael; Pierson, Duane L.; Nickerson, Cheryl A.

    2002-01-01

    We have previously demonstrated that low-shear modeled microgravity (low-shear MMG) serves to enhance the virulence of a bacterial pathogen, Salmonella enterica serovar Typhimurium. The Salmonella response to low-shear MMG involves a signaling pathway that we have termed the low-shear MMG stimulon, though the identities of the low-shear MMG stimulon genes and regulatory factors are not known. RpoS is the primary sigma factor required for the expression of genes that are induced upon exposure to different environmental-stress signals and is essential for virulence in mice. Since low-shear MMG induces a Salmonella acid stress response and enhances Salmonella virulence, we reasoned that RpoS would be a likely regulator of the Salmonella low-shear MMG response. Our results demonstrate that low-shear MMG provides cross-resistance to several environmental stresses in both wild-type and isogenic rpoS mutant strains. Growth under low-shear MMG decreased the generation time of both strains in minimal medium and increased the ability of both strains to survive in J774 macrophages. Using DNA microarray analysis, we found no evidence of induction of the RpoS regulon by low-shear MMG but did find that other genes were altered in expression under these conditions in both the wild-type and rpoS mutant strains. Our results indicate that, under the conditions of these studies, RpoS is not required for transmission of the signal that induces the low-shear MMG stimulon. Moreover, our studies also indicate that low-shear MMG can be added to a short list of growth conditions that can serve to preadapt an rpoS mutant for resistance to multiple environmental stresses.

  15. Steady and transient fluid shear stress stimulate NO release in osteoblasts through distinct biochemical pathways

    NASA Technical Reports Server (NTRS)

    McAllister, T. N.; Frangos, J. A.

    1999-01-01

    Fluid flow has been shown to be a potent stimulus in osteoblasts and osteocytes and may therefore play an important role in load-induced bone remodeling. The objective of this study was to investigate the characteristics of flow-activated pathways. Previously we reported that fluid flow stimulates rapid and continuous release of nitric oxide (NO) in primary rat calvarial osteoblasts. Here we demonstrate that flow-induced NO release is mediated by shear stress and that this response is distinctly biphasic. Transients in shear stress associated with the onset of flow stimulated a burst in NO production (8.2 nmol/mg of protein/h), while steady flow stimulated sustained NO production (2.2 nmol/mg of protein/h). Both G-protein inhibition and calcium chelation abolished the burst phase but had no effect on sustained production. Activation of G-proteins stimulated dose-dependent NO release in static cultures of both calvarial osteoblasts and UMR-106 osteoblast-like cells. Pertussis toxin had no effect on NO release. Calcium ionophore stimulated low levels of NO production within 15 minutes but had no effect on sustained production. Taken together, these data suggest that fluid shear stress stimulates NO release by two distinct pathways: a G-protein and calcium-dependent phase sensitive to flow transients, and a G-protein and calcium-independent pathway stimulated by sustained flow.

  16. Efforts to reduce mortality to hydroelectric turbine-passed fish: locating and quantifying damaging shear stresses.

    PubMed

    Cada, Glenn; Loar, James; Garrison, Laura; Fisher, Richard; Neitzel, Duane

    2006-06-01

    Severe fluid forces are believed to be a source of injury and mortality to fish that pass through hydroelectric turbines. A process is described by which laboratory bioassays, computational fluid dynamics models, and field studies can be integrated to evaluate the significance of fluid shear stresses that occur in a turbine. Areas containing potentially lethal shear stresses were identified near the stay vanes and wicket gates, runner, and in the draft tube of a large Kaplan turbine. However, under typical operating conditions, computational models estimated that these dangerous areas comprise less than 2% of the flow path through the modeled turbine. The predicted volumes of the damaging shear stress zones did not correlate well with observed fish mortality at a field installation of this turbine, which ranged from less than 1% to nearly 12%. Possible reasons for the poor correlation are discussed. Computational modeling is necessary to develop an understanding of the role of particular fish injury mechanisms, to compare their effects with those of other sources of injury, and to minimize the trial and error previously needed to mitigate those effects. The process we describe is being used to modify the design of hydroelectric turbines to improve fish passage survival. PMID:16485161

  17. Mass Transport and Shear Stress as Mediators of Flow Effects on Atherosclerotic Plaque Origin and Growth

    NASA Astrophysics Data System (ADS)

    Gorder, Riley; Aliseda, Alberto

    2009-11-01

    The carotid artery bifurcation (CAB) is one of the leading site for atherosclerosis, a major cause of mortality and morbidity in the developed world. The specific mechanisms by which perturbed flow at the bifurcation and in the carotid bulge promotes plaque formation and growth are not fully understood. Shear stress, mass transport, and flow residence times are considered dominant factors. Shear stress causes restructuring of endothelial cells at the arterial wall which changes the wall's permeability. Long residence times are associated with enhanced mass transport through increased diffusion of lipids and white blood cells into the arterial wall. Although momentum and mass transfer are traditionally coupled by correlations similar to Reynolds Analogy, the complex flow patterns present in this region due to the pulsatile, transitional, detached flow associated with the complex geometry makes the validity of commonly accepted assumptions uncertain. We create solid models of the CAB from MRI or ultrasound medical images, build flow phantoms on clear polyester resin and use an IOR matching, blood mimicking, working fluid. Using PIV and dye injection techniques the shear stress and scalar transport are experimentally investigated. Our goal is to establish a quantitative relationship between momentum and mass transfer under a wide range of physiologically normal and pathological conditions.

  18. Activation of the Caenorhabditis elegans Degenerin Channel by Shear Stress Requires the MEC-10 Subunit.

    PubMed

    Shi, Shujie; Luke, Cliff J; Miedel, Mark T; Silverman, Gary A; Kleyman, Thomas R

    2016-07-01

    Mechanotransduction in Caenorhabditis elegans touch receptor neurons is mediated by an ion channel formed by MEC-4, MEC-10, and accessory proteins. To define the role of these subunits in the channel's response to mechanical force, we expressed degenerin channels comprising MEC-4 and MEC-10 in Xenopus oocytes and examined their response to laminar shear stress (LSS). Shear stress evoked a rapid increase in whole cell currents in oocytes expressing degenerin channels as well as channels with a MEC-4 degenerin mutation (MEC-4d), suggesting that C. elegans degenerin channels are sensitive to LSS. MEC-10 is required for a robust LSS response as the response was largely blunted in oocytes expressing homomeric MEC-4 or MEC-4d channels. We examined a series of MEC-10/MEC-4 chimeras to identify specific domains (amino terminus, first transmembrane domain, and extracellular domain) and sites (residues 130-132 and 134-137) within MEC-10 that are required for a robust response to shear stress. In addition, the LSS response was largely abolished by MEC-10 mutations encoded by a touch-insensitive mec-10 allele, providing a correlation between the channel's responses to two different mechanical forces. Our findings suggest that MEC-10 has an important role in the channel's response to mechanical forces. PMID:27189943

  19. Sensor for Direct Measurement of the Boundary Shear Stress in Fluid Flow

    NASA Technical Reports Server (NTRS)

    Bao, Xiaoqi; Badescu, Mircea; Bar-Cohen, Yoseph; Lih, Shyh-Shiuh; Sherrit, Stewart; Chang, Zensheu; Chen, Beck; Widholm, Scott; Ostlund, Patrick

    2011-01-01

    The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear and normal stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear and normal stress and their fluctuations are attractive alternatives. However, this approach is a challenging one especially for high spatial resolution and high fidelity measurements. The authors designed and fabricated a prototype miniature shear stress sensor including an EDM machined floating plate and a high-resolution laser optical encoder. Tests were performed both in air as well as operation in water with controlled flow. The sensor sensitivity, stability and signal-to-noise level were measured and evaluated. The detailed test results and a discussion of future work will be presented in this paper.

  20. Quantifying Uncertainty in Inferred Viscosity and Basal Shear Stress Over Ice Streams

    NASA Astrophysics Data System (ADS)

    Lilien, D.; Joughin, I.; Smith, B. E.

    2015-12-01

    Basal friction and ice viscosity are both essential controls on glacier motion that cannot be measured by remote sensing. In order to initialize models, it is common practice to use inverse methods to determine the basal shear stress over grounded ice and the viscosity of floating ice. It is difficult to quantify the uncertainty in the inferred parameters due to the computational expense of the procedure, the choice of regularization parameter, and the errors in the various measurements used as input, as well as differences in inversion method. Various methods can be used to perform the inversion, and these differing procedures cause discrepancies in the inferred properties of the ice streams. Additionally, the inferred parameters depend on the sophistication of the approximation for ice flow that is used, e.g. full-Stokes or the shallow-shelf approximation. We analyze the impact the choices of modeling procedure and inversion method have on inferred ice properties. To do this we perform a number of inversions for basal shear stress and for ice shelf viscosity over Smith, Pope, and Kohler Glaciers in West Antarctica and assess the sensitivity to modelers' choices. We use both a three dimensional full-Stokes model and a two dimensional shallow-shelf model, with both Robin and adjoint type inversion procedures, to infer basal shear stress and ice viscosity. We compare the results of these different methods and evaluate their implication on uncertainty in the unknown parameters.

  1. Nerve growth factor translates stress response and subsequent murine abortion via adhesion molecule-dependent pathways.

    PubMed

    Tometten, Mareike; Blois, Sandra; Kuhlmei, Arne; Stretz, Anna; Klapp, Burghard F; Arck, Petra C

    2006-04-01

    Spontaneous abortion is a frequent threat affecting 10%-25% of human pregnancies. Psychosocial stress has been suggested to be attributable for pregnancy losses by challenging the equilibrium of systems mandatory for pregnancy maintenance, including the nervous, endocrine, and immune system. Strong evidence indicates that stress-triggered abortion is mediated by adhesion molecules, i.e., intercellular adhesion molecule 1 (ICAM1) and leukocyte function associated molecule 1, now being referred to as integrin alpha L (ITGAL), which facilitate recruitment of inflammatory cells to the feto-maternal interface. The neurotrophin beta-nerve growth factor (NGFB), which has been shown to be upregulated in response to stress in multiple experimental settings including in the uterine lining (decidua) during pregnancy, increases ICAM1 expression on endothelial cells. Here, we investigated whether and how NGFB neutralization has a preventive effect on stress-triggered abortion in the murine CBA/J x DBA/2J model. We provide experimental evidence that stress exposure upregulates the frequency of abortion and the expression of uterine NGFB. Further, adhesion molecules ICAM1 and selectin platelet (SELP, formerly P-Selectin) and their ligands ITGAL and SELP ligand (SELPL, formerly P selectin glycoprotein ligand 1) respectively increase in murine deciduas in response to stress. Subsequently, decidual cytokines are biased toward a proinflammatory and abortogenic cytokine profile. Additionally, a decrease of pregnancy protective CD8alpha(+) decidual cells is present. Strikingly, all such uterine stress responses are abrogated by NGFB neutralization. Hence, NGFB acts as a proximal mediator in the hierarchical network of immune rejection by mediating an abortogenic environment comprised of classical signs of neurogenic inflammation. PMID:16371592

  2. Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

    NASA Technical Reports Server (NTRS)

    Bassani, J. L.; Erdogan, F.

    1978-01-01

    The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks was considered. For the semi-infinite crack the problem was solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses were calculated. For finite cracks the problem was reduced to a pair of integral equations. Numerical results were obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

  3. Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

    NASA Technical Reports Server (NTRS)

    Bassani, J. L.; Erdogan, F.

    1979-01-01

    The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks is considered. For the semi-infinite crack the problem is solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses are calculated. For finite cracks the problem is reduced to a pair of integral equations. Numerical results are obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

  4. Hemodynamic analysis in an idealized artery tree: differences in wall shear stress between Newtonian and non-Newtonian blood models.

    PubMed

    Weddell, Jared C; Kwack, JaeHyuk; Imoukhuede, P I; Masud, Arif

    2015-01-01

    Development of many conditions and disorders, such as atherosclerosis and stroke, are dependent upon hemodynamic forces. To accurately predict and prevent these conditions and disorders hemodynamic forces must be properly mapped. Here we compare a shear-rate dependent fluid (SDF) constitutive model, based on the works by Yasuda et al in 1981, against a Newtonian model of blood. We verify our stabilized finite element numerical method with the benchmark lid-driven cavity flow problem. Numerical simulations show that the Newtonian model gives similar velocity profiles in the 2-dimensional cavity given different height and width dimensions, given the same Reynolds number. Conversely, the SDF model gave dissimilar velocity profiles, differing from the Newtonian velocity profiles by up to 25% in velocity magnitudes. This difference can affect estimation in platelet distribution within blood vessels or magnetic nanoparticle delivery. Wall shear stress (WSS) is an important quantity involved in vascular remodeling through integrin and adhesion molecule mechanotransduction. The SDF model gave a 7.3-fold greater WSS than the Newtonian model at the top of the 3-dimensional cavity. The SDF model gave a 37.7-fold greater WSS than the Newtonian model at artery walls located immediately after bifurcations in the idealized femoral artery tree. The pressure drop across arteries reveals arterial sections highly resistive to flow which correlates with stenosis formation. Numerical simulations give the pressure drop across the idealized femoral artery tree with the SDF model which is approximately 2.3-fold higher than with the Newtonian model. In atherosclerotic lesion models, the SDF model gives over 1 Pa higher WSS than the Newtonian model, a difference correlated with over twice as many adherent monocytes to endothelial cells from the Newtonian model compared to the SDF model. PMID:25897758

  5. Hemodynamic Analysis in an Idealized Artery Tree: Differences in Wall Shear Stress between Newtonian and Non-Newtonian Blood Models

    PubMed Central

    Weddell, Jared C.; Kwack, JaeHyuk; Imoukhuede, P. I.; Masud, Arif

    2015-01-01

    Development of many conditions and disorders, such as atherosclerosis and stroke, are dependent upon hemodynamic forces. To accurately predict and prevent these conditions and disorders hemodynamic forces must be properly mapped. Here we compare a shear-rate dependent fluid (SDF) constitutive model, based on the works by Yasuda et al in 1981, against a Newtonian model of blood. We verify our stabilized finite element numerical method with the benchmark lid-driven cavity flow problem. Numerical simulations show that the Newtonian model gives similar velocity profiles in the 2-dimensional cavity given different height and width dimensions, given the same Reynolds number. Conversely, the SDF model gave dissimilar velocity profiles, differing from the Newtonian velocity profiles by up to 25% in velocity magnitudes. This difference can affect estimation in platelet distribution within blood vessels or magnetic nanoparticle delivery. Wall shear stress (WSS) is an important quantity involved in vascular remodeling through integrin and adhesion molecule mechanotransduction. The SDF model gave a 7.3-fold greater WSS than the Newtonian model at the top of the 3-dimensional cavity. The SDF model gave a 37.7-fold greater WSS than the Newtonian model at artery walls located immediately after bifurcations in the idealized femoral artery tree. The pressure drop across arteries reveals arterial sections highly resistive to flow which correlates with stenosis formation. Numerical simulations give the pressure drop across the idealized femoral artery tree with the SDF model which is approximately 2.3-fold higher than with the Newtonian model. In atherosclerotic lesion models, the SDF model gives over 1 Pa higher WSS than the Newtonian model, a difference correlated with over twice as many adherent monocytes to endothelial cells from the Newtonian model compared to the SDF model. PMID:25897758

  6. The effect of turbulent viscous shear stress on red blood cell hemolysis.

    PubMed

    Yen, Jen-Hong; Chen, Sheng-Fu; Chern, Ming-Kai; Lu, Po-Chien

    2014-06-01

    Non-physiologic turbulent flow occurs in medical cardiovascular devices resulting in hemodynamic stresses that may damage red blood cells (RBC) and cause hemolysis. Hemolysis was previously thought to result from Reynolds shear stress (RSS) in turbulent flows. A more recent hypothesis suggests that turbulent viscous shear stresses (TVSS) at spatial scales similar in size to RBCs are related to their damage. We applied two-dimensional digital particle image velocimetry to measure the flow field of a free-submerged axisymmetric jet that was utilized to hemolyze porcine RBCs in selected locations. Assuming a dynamic equilibrium for the sub-grid scale (SGS) energy flux between the resolved and the sub-grid scales, the SGS energy flux was calculated from the strain rate tensor computed from the resolved velocity fields. The SGS stress was determined by the Smagorinsky model, from which the turbulence dissipation rate and then TVSS were estimated. Our results showed the hemolytic threshold of the Reynolds stresses was up to 517 Pa, and the TVSSs were at least an order of magnitude less than the RSS. The results provide further insight into the relationship between turbulence and RBC damage.

  7. Effect of the glycocalyx layer on transmission of interstitial flow shear stress to embedded cells.

    PubMed

    Tarbell, John M; Shi, Zhong-Dong

    2013-01-01

    In this paper, a simple theoretical model is developed to describe the transmission of force from interstitial fluid flow to the surface of a cell covered by a proteoglycan / glycoprotein layer (glycocalyx) and embedded in an extracellular matrix. Brinkman equations are used to describe flow through the extracellular matrix and glycocalyx layers and the solid mechanical stress developed in the glycocalyx by the fluid flow loading is determined. Using reasonable values for the Darcy permeability of extracellular matrix and glycocalyx layers and interstitial flow velocity, we are able to estimate the fluid and solid shear stresses imposed on the surface of embedded vascular, cartilage and tumor cells in vivo and in vitro. The principal finding is that the surface solid stress is typically one to two orders of magnitude larger than the surface fluid stress. This indicates that interstitial flow shear stress can be sensed by the cell surface glycocalyx, supporting numerous recent observations that interstitial flow can induce mechanotransduction in embedded cells. This study may contribute to understanding of interstitial flow-related mechanobiology in embryogenesis, tumorigenesis, tissue physiology and diseases and has implications in tissue engineering.

  8. Shear Bond Strength of MDP-Containing Self-Adhesive Resin Cement and Y-TZP Ceramics: Effect of Phosphate Monomer-Containing Primers

    PubMed Central

    Ahn, Jin-Soo; Yi, Young-Ah; Lee, Yoon; Seo, Deog-Gyu

    2015-01-01

    Purpose. This study was conducted to evaluate the effects of different phosphate monomer-containing primers on the shear bond strength between yttria-tetragonal zirconia polycrystal (Y-TZP) ceramics and MDP-containing self-adhesive resin cement. Materials and Methods. Y-TZP ceramic surfaces were ground flat with #600-grit SiC paper and divided into six groups (n = 10). They were treated as follows: untreated (control), Metal/Zirconia Primer, Z-PRIME Plus, air abrasion, Metal/Zirconia Primer with air abrasion, and Z-PRIME Plus with air abrasion. MDP-containing self-adhesive resin cement was applied to the surface-treated Y-TZP specimens. After thermocycling, a shear bond strength test was performed. The surfaces of the Y-TZP specimens were analyzed under a scanning electron microscope. The bond strength values were statistically analyzed using one-way analysis of variance and the Student–Newman–Keuls multiple comparison test (P < 0.05). Results. The Z-PRIME Plus treatment combined with air abrasion produced the highest bond strength, followed by Z-PRIME Plus application, Metal/Zirconia Primer combined with air abrasion, air abrasion alone, and, lastly, Metal/Zirconia Primer application. The control group yielded the lowest results (P < 0.05). Conclusion. The application of MDP-containing primer resulted in increased bond strength between Y-TZP ceramics and MDP-containing self-adhesive resin cements. PMID:26539485

  9. Recent Developments in the Use of Liquid Crystal Coatings for Full-Surface Shear Stress Vector Measurements

    NASA Technical Reports Server (NTRS)

    Reda, D. C.; Wilder, M. C.; Zilliac, G.; Hu, K. C.; Whitney, D. J.; Deardorff, D. G.; Moffat, R. J.; Farina, D. J.; Danek, C.; Martinez, R.; Davis, Sanford S. (Technical Monitor)

    1995-01-01

    Under normal white-light illumination and oblique observation, liquid crystal coating (LCC) color-change response to shear depends on both shear stress magnitude as well as the direction of the applied shear relative to the observer's line of sight. These color-change responses were quantified by subjecting a LCC to a wall-jet shear flow and measuring scattered-light spectra using a fiber optic probe and spectrophotometer. At any fixed shear stress magnitude, the maximum color change was measured when the shear vector was aligned with and directed away from the observer; changes in the relative in-plane view angle to either side of this vector/observer aligned position resulted in symmetric Gaussian reductions in measured color change. For this vector/observer aligned orientation, color change was found to scale linearly with increasing shear stress magnitude over an eight-fold range. Based on these results, a surface shear stress vector measurement methodology, involving multiple oblique-view observations of the test surface, was formulated. In the present paper, the experimental approach and data analysis procedure required to extend this vector measurement methodology to full-surface applications will be outlined and progress towards demonstrating this areal capability will be reviewed.

  10. Caveolin-1 regulates shear stress-dependent activation of extracellular signal-regulated kinase

    NASA Technical Reports Server (NTRS)

    Park, H.; Go, Y. M.; Darji, R.; Choi, J. W.; Lisanti, M. P.; Maland, M. C.; Jo, H.

    2000-01-01

    Fluid shear stress activates a member of the mitogen-activated protein (MAP) kinase family, extracellular signal-regulated kinase (ERK), by mechanisms dependent on cholesterol in the plasma membrane in bovine aortic endothelial cells (BAEC). Caveolae are microdomains of the plasma membrane that are enriched with cholesterol, caveolin, and signaling molecules. We hypothesized that caveolin-1 regulates shear activation of ERK. Because caveolin-1 is not exposed to the outside, cells were minimally permeabilized by Triton X-100 (0.01%) to deliver a neutralizing, polyclonal caveolin-1 antibody (pCav-1) inside the cells. pCav-1 then bound to caveolin-1 and inhibited shear activation of ERK but not c-Jun NH(2)-terminal kinase. Epitope mapping studies showed that pCav-1 binds to caveolin-1 at two regions (residues 1-21 and 61-101). When the recombinant proteins containing the epitopes fused to glutathione-S-transferase (GST-Cav(1-21) or GST-Cav(61-101)) were preincubated with pCav-1, only GST-Cav(61-101) reversed the inhibitory effect of the antibody on shear activation of ERK. Other antibodies, including m2234, which binds to caveolin-1 residues 1-21, had no effect on shear activation of ERK. Caveolin-1 residues 61-101 contain the scaffolding and oligomerization domains, suggesting that binding of pCav-1 to these regions likely disrupts the clustering of caveolin-1 or its interaction with signaling molecules involved in the shear-sensitive ERK pathway. We suggest that caveolae-like domains play a critical role in the mechanosensing and/or mechanosignal transduction of the ERK pathway.

  11. Aeolian Shear Stress Ratio Measurements within Mesquite-Dominated Landscapes of the Chihuahuan Desert, New Mexico, USA

    NASA Technical Reports Server (NTRS)

    King, James; Nickling, W. G.; Gilliles, J. A.

    2006-01-01

    A field study was conducted to ascertain the amount of protection that mesquite-dominated communities provide to the surface from wind erosion. The dynamics of the locally accelerated evolution of a mesquite/coppice dune landscape and the undetermined spatial dependence of potential erosion by wind from a shear stress partition model were investigated. Sediment transport and dust emission processes are governed by the amount of protection that can be provided by roughness elements. Although shear stress partition models exist that can describe this, their accuracy has only been tested against a limited dataset because instrumentation has previously been unable to provide the necessary measurements. This study combines the use of meteorological towers and surface shear stress measurements with Irwin sensors to measure the partition of shear stress in situ. The surface shear stress within preferentially aligned vegetation (within coppice dune development) exhibited highly skewed distributions, while a more homogenous surface stress was recorded at a site with less developed coppice dunes. Above the vegetation, the logarithmic velocity profile deduced roughness length (based on 10-min averages) exhibited a distinct correlation with compass direction for the site with vegetation preferentially aligned, while the site with more homogenously distributed vegetation showed very little variation in the roughness length. This distribution in roughness length within an area, defines a distribution of a resolved shear stress partitioning model based on these measurements, ultimately providing potential closure to a previously uncorrelated model parameter.

  12. Pressure and shear stress in trabecular bone marrow during whole bone loading.

    PubMed

    Metzger, Thomas A; Schwaner, Stephen A; LaNeve, Anthony J; Kreipke, Tyler C; Niebur, Glen L

    2015-09-18

    Skeletal adaptation to mechanical loading is controlled by mechanobiological signaling. Osteocytes are highly responsive to applied strains, and are the key mechanosensory cells in bone. However, many cells residing in the marrow also respond to mechanical cues such as hydrostatic pressure and shear stress, and hence could play a role in skeletal adaptation. Trabecular bone encapsulates marrow, forming a poroelastic solid. According to the mechanical theory, deformation of the pores induces motion in the fluid-like marrow, resulting in pressure and velocity gradients. The latter results in shear stress acting between the components of the marrow. To characterize the mechanical environment of trabecular bone marrow in situ, pore pressure within the trabecular compartment of whole porcine femurs was measured with miniature pressure transducers during stress-relaxation and cyclic loading. Pressure gradients ranging from 0.013 to 0.46 kPa/mm were measured during loading. This range was consistent with calculated pressure gradients from continuum scale poroelastic models with the same permeability. Micro-scale computational fluid dynamics models created from computed tomography images were used to calculate the micromechanical stress in the marrow using the measured pressure differentials as boundary conditions. The volume averaged shear stress in the marrow ranged from 1.67 to 24.55 Pa during cyclic loading, which exceeds the mechanostimulatory threshold for mesenchymal lineage cells. Thus, the loading of bone through activities of daily living may be an essential component of bone marrow health and mechanobiology. Additional studies of cell-level interactions during loading in healthy and disease conditions will provide further incite into marrow mechanobiology.

  13. Mechanotransduction of shear stress occurs through changes in VE-cadherin and PECAM-1 tension: implications for cell migration.

    PubMed

    Conway, Daniel E; Schwartz, Martin A

    2015-01-01

    Recent work has shown that cadherins at cell-cell junctions bear tensile forces. Using novel FRET-based tension sensors, we showed first that in response to shear stress, endothelial cells rapidly reduce mechanical tension on vascular endothelial (VE)-cadherin. Second, we observed a simultaneous increase in tension on platelet endothelial cell adhesion molecule (PECAM)-1, induced by an interaction with vimentin. In this commentary, we discuss how our results fit with existing data on cadherins as important mediators of mechanotransduction, in particular, in cell migration where mechanical tension across cadherins may communicate the direction of movement. The ability of PECAM-1 to bear mechanical tension may also be important in other PECAM-1 functions, such as leukocyte transmigration through the endothelium. Additionally, our observation that vimentin expression was required for PECAM-1 tension and mechanotransduction of fluid flow suggests that intermediate filaments are capable of transmitting tension. Overall, our results argue against models where an external force is passively transferred across the cytoskeleton, and instead suggest that cells actively respond to extracellular forces by modulating tension across junctional proteins.

  14. Side-implanted piezoresistive shear stress sensor for turbulent boundary layer measurement

    NASA Astrophysics Data System (ADS)

    Li, Yawei

    In this dissertation, I discuss the device modeling, design optimization, fabrication, packaging and characterization of a micromachined floating element piezoresistive shear stress sensor for the time-resolved, direct measurement of fluctuating wall shear stress in a turbulent flow. This device impacts a broad range of applications from fundamental scientific research to industrial flow control and biomedical applications. The sensor structure integrates side-implanted, diffused resistors into the silicon tethers for piezoresistive detection. Temperature compensation is enabled by integrating a fixed, dummy Wheatstone bridge adjacent to the active shear-stress sensor. A theoretical nonlinear mechanical model is combined with a piezoresistive sensing model to determine the electromechanical sensitivity. Lumped element modeling (LEM) is used to estimate the resonant frequency. Finite element modeling is employed to verify the quasi-static and dynamic models. Two dominant electrical noise sources in the piezoresistive shear stress sensor, 1/f noise and thermal noise, and amplifier noise were considered to determine the noise floor. These models were then leveraged to obtain optimal sensor designs for several sets of specifications. The cost function, minimum detectable shear stress (MDS) formulated in terms of sensitivity and noise floor, is minimized subject to nonlinear constraints of geometry, linearity, bandwidth, power, resistance, and manufacturing limitations. The optimization results indicate a predicted optimal device performance with a MDS of O(0.1 mPa) and a dynamic range greater than 75 dB. A sensitivity analysis indicates that the device performance is most responsive to variations in tether width. The sensors are fabricated using an 8-mask, bulk micromachining process on a silicon wafer. An n-well layer is formed to control the space-charge layer thickness of reverse-biased p/n junction-isolated piezoresistors. The sensor geometry is realized using

  15. Evaluation of bioprosthetic heart valve failure using a matrix-fibril shear stress transfer approach.

    PubMed

    Anssari-Benam, Afshin; Barber, Asa H; Bucchi, Andrea

    2016-02-01

    A matrix-fibril shear stress transfer approach is devised and developed in this paper to analyse the primary biomechanical factors which initiate the structural degeneration of the bioprosthetic heart valves (BHVs). Using this approach, the critical length of the collagen fibrils l c and the interface shear acting on the fibrils in both BHV and natural aortic valve (AV) tissues under physiological loading conditions are calculated and presented. It is shown that the required critical fibril length to provide effective reinforcement to the natural AV and the BHV tissue is l c  = 25.36 µm and l c  = 66.81 µm, respectively. Furthermore, the magnitude of the required shear force acting on fibril interface to break a cross-linked fibril in the BHV tissue is shown to be 38 µN, while the required interfacial force to break the bonds between the fibril and the surrounding extracellular matrix is 31 µN. Direct correlations are underpinned between these values and the ultimate failure strength and the failure mode of the BHV tissue compared with the natural AV, and are verified against the existing experimental data. The analyses presented in this paper explain the role of fibril interface shear and critical length in regulating the biomechanics of the structural failure of the BHVs, for the first time. This insight facilitates further understanding into the underlying causes of the structural degeneration of the BHVs in vivo. PMID:26715134

  16. Predicting equilibrium states with Reynolds stress closures in channel flow and homogeneous shear flow

    NASA Technical Reports Server (NTRS)

    Abid, R.; Speziale, C. G.

    1992-01-01

    Turbulent channel flow and homogeneous shear flow have served as basic building block flows for the testing and calibration of Reynolds stress models. A direct theoretical connection is made between homogeneous shear flow in equilibrium and the log-layer of fully-developed turbulent channel flow. It is shown that if a second-order closure model is calibrated to yield good equilibrium values for homogeneous shear flow it will also yield good results for the log-layer of channel flow provided that the Rotta coefficient is not too far removed from one. Most of the commonly used second-order closure models introduce an ad hoc wall reflection term in order to mask deficient predictions for the log-layer of channel flow that arise either from an inaccurate calibration of homogeneous shear flow or from the use of a Rotta coefficient that is too large. Illustrative model calculations are presented to demonstrate this point which has important implications for turbulence modeling.

  17. Evaluation of bioprosthetic heart valve failure using a matrix-fibril shear stress transfer approach.

    PubMed

    Anssari-Benam, Afshin; Barber, Asa H; Bucchi, Andrea

    2016-02-01

    A matrix-fibril shear stress transfer approach is devised and developed in this paper to analyse the primary biomechanical factors which initiate the structural degeneration of the bioprosthetic heart valves (BHVs). Using this approach, the critical length of the collagen fibrils l c and the interface shear acting on the fibrils in both BHV and natural aortic valve (AV) tissues under physiological loading conditions are calculated and presented. It is shown that the required critical fibril length to provide effective reinforcement to the natural AV and the BHV tissue is l c  = 25.36 µm and l c  = 66.81 µm, respectively. Furthermore, the magnitude of the required shear force acting on fibril interface to break a cross-linked fibril in the BHV tissue is shown to be 38 µN, while the required interfacial force to break the bonds between the fibril and the surrounding extracellular matrix is 31 µN. Direct correlations are underpinned between these values and the ultimate failure strength and the failure mode of the BHV tissue compared with the natural AV, and are verified against the existing experimental data. The analyses presented in this paper explain the role of fibril interface shear and critical length in regulating the biomechanics of the structural failure of the BHVs, for the first time. This insight facilitates further understanding into the underlying causes of the structural degeneration of the BHVs in vivo.

  18. Differential regulation of protease activated receptor-1 and tissue plasminogen activator expression by shear stress in vascular smooth muscle cells

    NASA Technical Reports Server (NTRS)

    Papadaki, M.; Ruef, J.; Nguyen, K. T.; Li, F.; Patterson, C.; Eskin, S. G.; McIntire, L. V.; Runge, M. S.

    1998-01-01

    Recent studies have demonstrated that vascular smooth muscle cells are responsive to changes in their local hemodynamic environment. The effects of shear stress on the expression of human protease activated receptor-1 (PAR-1) and tissue plasminogen activator (tPA) mRNA and protein were investigated in human aortic smooth muscle cells (HASMCs). Under conditions of low shear stress (5 dyn/cm2), PAR-1 mRNA expression was increased transiently at 2 hours compared with stationary control values, whereas at high shear stress (25 dyn/cm2), mRNA expression was decreased (to 29% of stationary control; P<0.05) at all examined time points (2 to 24 hours). mRNA half-life studies showed that this response was not due to increased mRNA instability. tPA mRNA expression was decreased (to 10% of stationary control; P<0.05) by low shear stress after 12 hours of exposure and was increased (to 250% of stationary control; P<0.05) after 24 hours at high shear stress. The same trends in PAR-1 mRNA levels were observed in rat smooth muscle cells, indicating that the effects of shear stress on human PAR-1 were not species-specific. Flow cytometry and ELISA techniques using rat smooth muscle cells and HASMCs, respectively, provided evidence that shear stress exerted similar effects on cell surface-associated PAR-1 and tPA protein released into the conditioned media. The decrease in PAR-1 mRNA and protein had functional consequences for HASMCs, such as inhibition of [Ca2+] mobilization in response to thrombin stimulation. These data indicate that human PAR-1 and tPA gene expression are regulated differentially by shear stress, in a pattern consistent with their putative roles in several arterial vascular pathologies.

  19. Role of xanthine oxidoreductase and NAD(P)H oxidase in endothelial superoxide production in response to oscillatory shear stress

    NASA Technical Reports Server (NTRS)

    McNally, J. Scott; Davis, Michael E.; Giddens, Don P.; Saha, Aniket; Hwang, Jinah; Dikalov, Sergey; Jo, Hanjoong; Harrison, David G.

    2003-01-01

    Oscillatory shear stress occurs at sites of the circulation that are vulnerable to atherosclerosis. Because oxidative stress contributes to atherosclerosis, we sought to determine whether oscillatory shear stress increases endothelial production of reactive oxygen species and to define the enzymes responsible for this phenomenon. Bovine aortic endothelial cells were exposed to static, laminar (15 dyn/cm2), and oscillatory shear stress (+/-15 dyn/cm2). Oscillatory shear increased superoxide (O2.-) production by more than threefold over static and laminar conditions as detected using electron spin resonance (ESR). This increase in O2*- was inhibited by oxypurinol and culture of endothelial cells with tungsten but not by inhibitors of other enzymatic sources. Oxypurinol also prevented H2O2 production in response to oscillatory shear stress as measured by dichlorofluorescin diacetate and Amplex Red fluorescence. Xanthine-dependent O2*- production was increased in homogenates of endothelial cells exposed to oscillatory shear stress. This was associated with decreased xanthine dehydrogenase (XDH) protein levels and enzymatic activity resulting in an elevated ratio of xanthine oxidase (XO) to XDH. We also studied endothelial cells lacking the p47phox subunit of the NAD(P)H oxidase. These cells exhibited dramatically depressed O2*- production and had minimal XO protein and activity. Transfection of these cells with p47phox restored XO protein levels. Finally, in bovine aortic endothelial cells, prolonged inhibition of the NAD(P)H oxidase with apocynin decreased XO protein levels and prevented endothelial cell stimulation of O2*- production in response to oscillatory shear stress. These data suggest that the NAD(P)H oxidase maintains endothelial cell XO levels and that XO is responsible for increased reactive oxygen species production in response to oscillatory shear stress.

  20. Fluid shear stress induces differentiation of Flk-1-positive embryonic stem cells into vascular endothelial cells in vitro.

    PubMed

    Yamamoto, Kimiko; Sokabe, Takaaki; Watabe, Tetsuro; Miyazono, Kohei; Yamashita, Jun K; Obi, Syotaro; Ohura, Norihiko; Matsushita, Akiko; Kamiya, Akira; Ando, Joji

    2005-04-01

    Pluripotent embryonic stem (ES) cells are capable of differentiating into all cell lineages, but the molecular mechanisms that regulate ES cell differentiation have not been sufficiently explored. In this study, we report that shear stress, a mechanical force generated by fluid flow, can induce ES cell differentiation. When Flk-1-positive (Flk-1(+)) mouse ES cells were subjected to shear stress, their cell density increased markedly, and a larger percentage of the cells were in the S and G(2)-M phases of the cell cycle than Flk-1(+) ES cells cultured under static conditions. Shear stress significantly increased the expression of the vascular endothelial cell-specific markers Flk-1, Flt-1, vascular endothelial cadherin, and PECAM-1 at both the protein level and the mRNA level, but it had no effect on expression of the mural cell marker smooth muscle alpha-actin, blood cell marker CD3, or the epithelial cell marker keratin. These findings indicate that shear stress selectively promotes the differentiation of Flk-1(+) ES cells into the endothelial cell lineage. The shear stressed Flk-1(+) ES cells formed tubelike structures in collagen gel and developed an extensive tubular network significantly faster than the static controls. Shear stress induced tyrosine phosphorylation of Flk-1 in Flk-1(+) ES cells that was blocked by a Flk-1 kinase inhibitor, SU1498, but not by a neutralizing antibody against VEGF. SU1498 also abolished the shear stress-induced proliferation and differentiation of Flk-1(+) ES cells, indicating that a ligand-independent activation of Flk-1 plays an important role in the shear stress-mediated proliferation and differentiation by Flk-1(+) ES cells. PMID:15576436

  1. Heterogeneity and the role of normal stresses during the extensional thinning of non-Brownian shear-thickening fluids.

    PubMed

    Roché, Matthieu; Kellay, Hamid; Stone, Howard A

    2011-09-23

    We contrast the extensional and shear dynamics of non-Brownian suspensions as a function of particle concentration. We show that the thinning rate selected during the viscoelastic pinch-off of a liquid bridge is related to the shear rate at which normal stresses become positive, which differs from the shear rate at the onset of shear thickening. By tracking particles, we demonstrate that the extensional flow is heterogeneous, with local variations of the volume fraction consistent with self-dilution. This nonuniform structure is the cause of the buckling of the threads formed after breakup. PMID:22026859

  2. Inverting for Shear Stress Rate on the Northern Cascadia Megathrust Using Geodetic Data

    NASA Astrophysics Data System (ADS)

    Bruhat, L.; Segall, P.; Bradley, A. M.

    2014-12-01

    Past physics-based models of slow slip events (SSE) have shown that, when averaged over many SSE cycles, the shear stress within the SSE zone remains roughly constant. Stress accumulates between SSE, and then is released during slow slip events. However, the predicted long-term deformation rates from such models, assuming the plate boundary is locked to the top of the ETS zone, do not fit well GPS velocities and uplift rates determined from leveling and tide-gauge data. These physics-based models particularly misfit the vertical rates. At the same time, previous kinematic inversions display a gap between the down-dip limit of the locked region and the top of the ETS zone. Our inversions of geodetic data for fault slip rates exhibit a steeper slip-rate profile at the top of the ETS zone, relative to the constant shear stress model, as well as creep up dip of the ETS zone. We explore physics-based models with velocity-strengthening regions of different length up dip the ETS zone, i.e. within the "gap" identified in kinematic inversions. However, this still does not match the observations well. We therefore try a new approach: we invert for shear stress rates on the megathrust that best fit the data. We show that a small decrease in shear stress within the top of the ETS zone, reaching 5 kPa/year at a depth of ~ 30 km, is required to fit the data. Possible explanations for this include a slow decrease in normal stress with time, possibly due to an increase in pore pressure, or a reduction in fault friction. We explore these hypotheses, using 2D quasi-dynamic simulations with rate-and-state friction and isothermal v-cutoff models for generating slow slip events. The potential for creep above the top of the ETS zone has important implications for the mechanical relationship between deep slow slip and dynamic events in the locked region.

  3. Evolution of the wall shear stresses during the progressive enlargement of symmetric abdominal aortic aneurysms

    NASA Astrophysics Data System (ADS)

    Salsac, A.-V.; Sparks, S. R.; Chomaz, J.-M.; Lasheras, J. C.

    2006-08-01

    The changes in the evolution of the spatial and temporal distribution of the wall shear stresses (WSS) and gradients of wall shear stresses (GWSS) at different stages of the enlargement of an abdominal aortic aneurysm (AAA) are important in understanding the aetiology and progression of this vascular disease since they affect the wall structural integrity, primarily via the changes induced on the shape, functions and metabolism of the endothelial cells. Particle image velocimetry (PIV) measurements were performed in in vitro aneurysm models, while changing their geometric parameters systematically. It has been shown that, even at the very early stages of the disease, i.e. increase in the diameter ≤ 50%, the flow separates from the wall and a large vortex ring, usually followed by internal shear layers, is created. These lead to the generation of WSS that drastically differ in mean and fluctuating components from the healthy vessel. Inside the AAA, the mean WSS becomes negative along most of the aneurysmal wall and the magnitude of the WSS can be as low as 26% of the value in a healthy abdominal aorta.

  4. Regulation of shear stress on rolling behaviors of HL-60 cells on P-selectin

    NASA Astrophysics Data System (ADS)

    Ling, YingChen; Fang, Ying; Yang, XiaoFang; Li, QuHuan; Lin, QinYong; Wu, JianHua

    2014-10-01

    Circulating leukocytes in trafficking to the inflammatory sites, will be first tether to, and then roll on the vascular surface. This event is mediated through specific interaction of P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1), and regulated by hemodynamics. Poor data were reported in understanding P-selectin-mediated rolling. With the flow chamber technique, we herein observed HL-60 cell rolling on P-selectin with or without 3% Ficoll at various wall shear stresses from 0.05 to 0.4 dyn/cm2. The results demonstrated that force rather than transport regulated the rolling, similar to rolling on L- and E-selectin. The rolling was accelerated quickly by an increasing force below the optimal shear threshold of 0.15 dyn/cm2 first and then followed by a slowly decelerating phase starting at the optimum, showing a catch-slip transition and serving as a mechanism for the rolling. The catch-slip transition was completely reflected to the tether lifetime and other rolling parameters, such as the mean and fractional stop time. The narrow catch bond regime stabilized the rolling quickly, through steeply increasing fractional stop time to a plateau of about 0.85. Data presented here suggest that the low shear stress threshold serves as a mechanism for most cell rolling events through P-selectin.

  5. Platelet Activation Due to Hemodynamic Shear Stresses: Damage Accumulation Model and Comparison to In Vitro Measurements

    PubMed Central

    Nobili, Matteo; Sheriff, Jawaad; Morbiducci, Umberto; Redaelli, Alberto; Bluestein, Danny

    2009-01-01

    The need to optimize the thrombogenic performance of blood recirculating cardiovascular devices, e.g., prosthetic heart valves (PHV) and ventricular assist devices (VAD), is accentuated by the fact that most of them require lifelong anticoagulation therapy that does not eliminate the risk of thromboembolic complications. The formation of thromboemboli in the flow field of these devices is potentiated by contact with foreign surfaces and regional flow phenomena that stimulate blood clotting, especially platelets. With the lack of appropriate methodology, device manufacturers do not specifically optimize for thrombogenic performance. Such optimization can be facilitated by formulating a robust numerical methodology with predictive capabilities of flow-induced platelet activation. In this study, a phenomenological model for platelet cumulative damage, identified by means of genetic algorithms (GAs), was correlated with in vitro experiments conducted in a Hemodynamic Shearing Device (HSD). Platelets were uniformly exposed to flow shear representing the lower end of the stress levels encountered in devices, and platelet activity state (PAS) was measured in response to six dynamic shear stress waveforms representing repeated passages through a device, and correlated to the predictions of the damage accumulation model. Experimental results demonstrated an increase in PAS with a decrease in “relaxation” time between pulses. The model predictions were in very good agreement with the experimental results. PMID:18204318

  6. Numerical study of wall shear stress-based descriptors in the human left coronary artery.

    PubMed

    Pinto, S I S; Campos, J B L M

    2016-10-01

    The present work is about the application of wall shear stress descriptors - time averaged wall shear stress (TAWSS), oscillating shear index (OSI) and relative residence time (RRT) - to the study of blood flow in the left coronary artery (LCA). These descriptors aid the prediction of disturbed flow conditions in the vessels and play a significant role in the detection of potential zones of atherosclerosis development. Hemodynamic descriptors data were obtained, numerically, through ANSYS® software, for the LCA of a patient-specific geometry and for a 3D idealized model. Comparing both cases, the results are coherent, in terms of location and magnitude. Low TAWSS, high OSI and high RRT values are observed in the bifurcation - potential zone of atherosclerosis appearance. The dissimilarities observed in the TAWSS values, considering blood as a Newtonian or non-Newtonian fluid, releases the importance of the correct blood rheologic caracterization. Moreover, for a higher Reynolds number, the TAWSS values decrease in the bifurcation and along the LAD branch, increasing the probability of plaques deposition. Furthermore, for a stenotic LCA model, very low TAWSS and high RRT values in front and behind the stenosis are observed, indicating the probable extension, in the flow direction, of the lesion. PMID:26883291

  7. Numerical study of wall shear stress-based descriptors in the human left coronary artery.

    PubMed

    Pinto, S I S; Campos, J B L M

    2016-10-01

    The present work is about the application of wall shear stress descriptors - time averaged wall shear stress (TAWSS), oscillating shear index (OSI) and relative residence time (RRT) - to the study of blood flow in the left coronary artery (LCA). These descriptors aid the prediction of disturbed flow conditions in the vessels and play a significant role in the detection of potential zones of atherosclerosis development. Hemodynamic descriptors data were obtained, numerically, through ANSYS® software, for the LCA of a patient-specific geometry and for a 3D idealized model. Comparing both cases, the results are coherent, in terms of location and magnitude. Low TAWSS, high OSI and high RRT values are observed in the bifurcation - potential zone of atherosclerosis appearance. The dissimilarities observed in the TAWSS values, considering blood as a Newtonian or non-Newtonian fluid, releases the importance of the correct blood rheologic caracterization. Moreover, for a higher Reynolds number, the TAWSS values decrease in the bifurcation and along the LAD branch, increasing the probability of plaques deposition. Furthermore, for a stenotic LCA model, very low TAWSS and high RRT values in front and behind the stenosis are observed, indicating the probable extension, in the flow direction, of the lesion.

  8. Effects of shear stress pattern and magnitude on mesenchymal transformation and invasion of aortic valve endothelial cells

    PubMed Central

    Mahler, Gretchen J.; Frendl, Christopher M.; Cao, Qingfeng; Butcher, Jonathan T.

    2015-01-01

    Understanding the role of mechanical forces on cell behavior is critical for tissue engineering, regenerative medicine, and disease initiation studies. Current hemodynamic bioreactors are largely limited to 2D substrates or the application of general flow conditions at a tissue level, which eliminates the investigation of some essential physiological and pathological responses. One example is the mesenchymal transformation of endothelial cells in response to shear stress. Endothelial to mesenchymal transformation (EndMT) is a valve morphogenic mechanism associated with aortic valve disease initiation. The aortic valve experiences oscillatory shear on the disease-susceptible fibrosa, and the role of hemodynamics on adult EndMT is unknown. The goal of this work was to develop and characterize a microfluidic bioreactor that applies physiologically relevant laminar or oscillatory shear stresses to endothelial cells and permits the quantitative analysis of 3D cell-extracellular matrix (ECM) interactions. In this study, porcine aortic valve endothelial cells were seeded onto 3D collagen I gels and exposed to different magnitudes of steady or oscillatory shear stress for 48 hours. Cells elongated and aligned perpendicular to laminar, but not oscillatory shear. Low steady shear stress (2 dyne/cm2) and oscillatory shear stress upregulated EndMT- (ACTA2, Snail, TGFB1) and inflammation- (ICAM1, NFKB1) related gene expression, EndMT-related (αSMA) protein expression, and matrix invasion when compared with static controls or cells exposed to high steady shear (10 and 20 dyne/cm2). Our system enables direct testing of the role of shear stress on endothelial cell mesenchymal transformation in a dynamic, 3D environment and shows that hemodynamics regulate EndMT in adult valve endothelial cells. PMID:24898772

  9. Spatially and temporally resolved quantification of endothelial cell modification in response to shear stress

    NASA Astrophysics Data System (ADS)

    Lambert, Lori; Pipinos, Iraklis; Baxter, Timothy; Leighton, Richard; Wei, Timothy

    2015-11-01

    This talk contains a resport on in vivo measurements made over a confluent layer of bovine endothelial cells in a microchannel. The ultimate goal of the experiments is to understand and model cellular response to fluid stresses and the ensuing transport across the endothelial layer. High resolution μ PTV measurements were made to quantify the cellular response to steady shear rates of 5, 10 and 20 dynes/cm2. Surface topography, shear and pressure distributions were calculated from sets of velocity fields made in planes parallel to the wall. For each experiment, measurements were made in three-hour intervals for eighteen hours. To validate the methodology, the pH of the medium was varied so that the health of the cells would vary. Clear differences in topography and cell orientation were found. Implications for future experiments and research will be discussed.

  10. Interfacial shear stress distribution in model composites. I - A Kevlar 49 fibre in an epoxy matrix

    SciTech Connect

    Jahankhani, H.; Galiotis, C. )

    1991-05-01

    The technique of Laser Raman Spectroscopy has been applied in the study of aramid fibers, such as Kevlar 49, and aramid/epoxy interfaces. A linear relationship has been found between Raman frequencies and strain upon loading a single Kevlar 49 filament in air. Model composites of single Kevlar 49 fibers embedded in epoxy resins have been fabricated and subjected to various degrees of mechanical deformation. The transfer lengths for reinforcement have been measured at various levels of applied tensile load and the dependence of transfer length upon applied matrix strain has been established. Finally, by balancing the tensile and the shear forces acting along the interface, the interfacial shear stress (ISS) distribution along the embedded fiber was obtained. 52 refs.

  11. Behavior of Three Metallic Alloys under Combined Axial-Shear Stresses at Elevated Temperature

    NASA Technical Reports Server (NTRS)

    Colaiuta, J. F.; Lissenden, C. J.; Lerch, B. A.

    2003-01-01

    Type 316 stainless steel, Haynes 188, and Inconel 718 samples were subjected to an axial-shear strain controlled loading history while the specimen temperature was held at 650 C to quantify the evolution of material state under a complex biaxial load path when the material is in the viscoplastic domain. Yield surfaces were constructed in the axial-shear stress plane using a sensitive, 30 x 10(exp -6)m/m, equivalent offset strain definition for the yield strain. Subsequent yield surfaces were constructed at various points along the strain path to define the material evolution. These subsequent yield surface translated, expanded, and distorted relative to the initial yield surface. Each of these very different materials exhibited components of isotropic, kinematic and distortional hardening. Furthermore, subsequent yield surfaces for each material have a very well defined front face and a poorly defined, flattened, back side.

  12. Biological effects of dynamic shear stress in cardiovascular pathologies and devices

    PubMed Central

    Girdhar, Gaurav; Bluestein, Danny

    2010-01-01

    Altered and highly dynamic shear stress conditions have been implicated in endothelial dysfunction leading to cardiovascular disease, and in thromboembolic complications in prosthetic cardiovascular devices. In addition to vascular damage, the pathological flow patterns characterizing cardiovascular pathologies and blood flow in prosthetic devices induce shear activation and damage to blood constituents. Investigation of the specific and accentuated effects of such flow-induced perturbations on individual cell-types in vitro is critical for the optimization of device design, whereby specific design modifications can be made to minimize such perturbations. Such effects are also critical in understanding the development of cardiovascular disease. This review addresses limitations to replicate such dynamic flow conditions in vitro and also introduces the idea of modified in vitro devices, one of which is developed in the authors' laboratory, with dynamic capabilities to investigate the aforementioned effects in greater detail. PMID:18331179

  13. Wall shear stress variations and unsteadiness of pulsatile blood-like flows in 90-degree bifurcations.

    PubMed

    van Wyk, Stevin; Prahl Wittberg, Lisa; Fuchs, Laszlo

    2013-09-01

    Complex and slow interaction of different mechanical and biochemical processes in hemodynamics is believed to govern atherogenesis. Over the last decades studies have shown that fluid mechanical factors such as the Wall Shear Stress (WSS) and WSS gradients can play an important role in the pathological changes of the endothelium. This study provides further indications that the effects of fluid mechanical aspects are correlated with the diseased regions of the larger arteries. Unsteady high temporal WSS gradients (TWSSG), a function of the shear-thinning property of the non-Newtonian viscosity, move with the separation bubble. Red Blood Cell (RBC) dilution due to the secondary flows determines the magnitudes of the WSS and TWSSG. The results indicate that the focal nature of the TWSSG may have implications on the response of the endothelium.

  14. Analysis of structure and orientation of adsorbed polymers in solution subject to a dynamic shear stress

    SciTech Connect

    Smith, G.; Baker, S.; Toprakcioglu, C.

    1996-09-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Polymer-based separation techniques rely on the ability of a binding portion of the polymer to interact with a specific molecule in a solution flowing past the polymer. The location of the binding site within or out of the entangled polymer chains is thus crucial to the effectiveness of these methods. For this reason, the details of flow induced deformation of the polymer chains is important in such applications as exclusion chromatography, waste water treatment, ultrafiltration, enhanced oil recovery and microbial adhesion. Few techniques exist to examine the structure and orientation of polymeric materials, and even fewer to examine systems in a dynamic fluid flow. The goal of this project was to understand the molecular structure and orientation of adsorbed polymers with and without active binding ligands as a function of solvent shear rate, solvent power, polymer molecular weight, surface polymer coverage and heterogeneity of the surface polymer chains by neutron reflectometry in a newly designed shear cell. Geometrical effects on binding of molecules in the flow was also studied subject to the same parameters.

  15. B-Raf Regulation of Integrin α4β1-mediated Resistance to Shear Stress through Changes in Cell Spreading and Cytoskeletal Association in T Cells*

    PubMed Central

    Brown, Wells S.; Khalili, Jahan S.; Rodriguez-Cruz, Tania G.; Lizee, Greg; McIntyre, Bradley W.

    2014-01-01

    The regulation of integrin-mediated adhesion is of vital importance to adaptive and innate immunity. Integrins are versatile proteins and mediate T cell migration and trafficking by binding to extracellular matrix or other cells as well as initiating intracellular signaling cascades promoting survival or activation. The MAPK pathway is known to be downstream from integrins and to regulate survival, differentiation, and motility. However, secondary roles for canonical MAPK pathway members are being discovered. We show that chemical inhibition of RAF by sorafenib or shRNA-mediated knockdown of B-Raf reduces T cell resistance to shear stress to α4β1 integrin ligands vascular cell adhesion molecule 1 (VCAM-1) and fibronectin, whereas inhibition of MEK/ERK by U0126 had no effect. Microscopy showed that RAF inhibition leads to significant inhibition of T cell spreading on VCAM-1. The association of α4β1 integrin with the actin cytoskeleton was shown to be dependent on B-Raf activity or expression, whereas α4β1 integrin affinity for soluble VCAM-1 was not. These effects were shown to be specific for α4β1 integrin and not other integrins, such as α5β1 or LFA-1, or a variety of membrane proteins. We demonstrate a novel role for B-Raf in the selective regulation of α4β1 integrin-mediated adhesion. PMID:24936068

  16. In vitro bond strength and fatigue stress test evaluation of different adhesive cements used for fixed space maintainer cementation

    PubMed Central

    Cantekin, Kenan; Delikan, Ebru; Cetin, Secil

    2014-01-01

    Objective: The purposes of this research were to (1) compare the shear-peel bond strength (SPBS) of a band of a fixed space maintainer (SM) cemented with five different adhesive cements; and (2) compare the survival time of bands of SM with each cement type after simulating mechanical fatigue stress. Materials and Methods: Seventy-five teeth were used to assess retentive strength and another 50 teeth were used to assess the fatigue survival time. SPBS was determined with a universal testing machine. Fatigue testing was conducted in a ball mill device. Results: The mean survival time of bands cemented with R & D series Nova Glass-LC (6.2 h), Transbond Plus (6.7 h), and R & D series Nova Resin (6.8 h) was significantly longer than for bands cemented with Ketac-Cem (5.4 h) and GC Equia (5.2 h) (P < 0.05). Conclusion: Although traditional glass ionomer cement (GIC) cement presented higher retentive strength than resin-based cements (resin, resin modified GIC, and compomer cement), resin based cements, especially dual cure resin cement (nova resin cement) and compomer (Transbond Plus), can be expected to have lower failure rates for band cementation than GIC (Ketac-Cem) in the light of the results of the ball mill test. PMID:25202209

  17. Shear stress enhances microcin B17 production in a rotating wall bioreactor, but ethanol stress does not

    NASA Technical Reports Server (NTRS)

    Gao, Q.; Fang, A.; Pierson, D. L.; Mishra, S. K.; Demain, A. L.

    2001-01-01

    Stress, including that caused by ethanol, has been shown to induce or promote secondary metabolism in a number of microbial systems. Rotating-wall bioreactors provide a low stress and simulated microgravity environment which, however, supports only poor production of microcin B17 by Escherichia coli ZK650, as compared to production in agitated flasks. We wondered whether the poor production is due to the low level of stress and whether increasing stress in the bioreactors would raise the amount of microcin B17 formed. We found that applying shear stress by addition of a single Teflon bead to a rotating wall bioreactor improved microcin B17 production. By contrast, addition of various concentrations of ethanol to such bioreactors (or to shaken flasks) failed to increase microcin B17 production. Ethanol stress merely decreased production and, at higher concentrations, inhibited growth. Interestingly, cells growing in the bioreactor were much more resistant to the growth-inhibitory and production-inhibitory effects of ethanol than cells growing in shaken flasks.

  18. Shear stress enhances microcin B17 production in a rotating wall bioreactor, but ethanol stress does not.

    PubMed

    Gao, Q; Fang, A; Pierson, D L; Mishra, S K; Demain, A L

    2001-08-01

    Stress, including that caused by ethanol, has been shown to induce or promote secondary metabolism in a number of microbial systems. Rotating-wall bioreactors provide a low stress and simulated microgravity environment which, however, supports only poor production of microcin B17 by Escherichia coli ZK650, as compared to production in agitated flasks. We wondered whether the poor production is due to the low level of stress and whether increasing stress in the bioreactors would raise the amount of microcin B17 formed. We found that applying shear stress by addition of a single Teflon bead to a rotating wall bioreactor improved microcin B17 production. By contrast, addition of various concentrations of ethanol to such bioreactors (or to shaken flasks) failed to increase microcin B17 production. Ethanol stress merely decreased production and, at higher concentrations, inhibited growth. Interestingly, cells growing in the bioreactor were much more resistant to the growth-inhibitory and production-inhibitory effects of ethanol than cells growing in shaken flasks.

  19. Shear stress and flow dynamics of the femoral vein among obese patients who qualify for bariatric surgery.

    PubMed

    Wiewiora, Maciej; Piecuch, Jerzy; Glűck, Marek; Slowinska-Lozynska, Ludmila; Sosada, Krystyn

    2013-01-01

    The aim of this study was to evaluate the effects of obesity on wall shear stress and its relationship to erythrocyte aggregation. We studied 35 morbidly obese patients who were qualified for bariatric surgery. The control group consisted of 20 non-obese people. Blood rheological measurements were performed using the Laser-assisted Optical Rotational Cell Analyzer (Mechatronics, the Netherlands) and a cone-plate viscometer (Brookfield DV-II). The venous flow dynamics were assessed using a duplex ultrasound. The shear rate was estimated from the measured blood flow velocity and the diameter of the femoral vein. Venous wall shear stress was calculated from the whole blood viscosity and the shear rate. The shear rate (P < 0.005) and the venous wall shear stress (P < 0.05) were significantly lower in obese patients compared with the controls. The aggregation index (P < 0.001), syllectogram amplitude - AMP (P < 0.05) and Tslow (P < 0.001) were significantly higher in the obese patients; the aggregation half-time (P < 0.001) and Tfast (P < 0.001) were decreased compared with the control group. Multivariate regression analyses found waist circumference (β -0.31, P < 0.05), thigh circumference (β 0.33, P < 0.05) and Tslow (β -0.47, P < 0.005) to be variables that independently influenced the shear rate. Nevertheless, the AMP (β 0.34, P < 0.05) and Tslow (β -0.47, P < 0.01) were independent predictors that influenced the wall shear stress. This study indicates that there is a relationship between wall shear stress in the femoral vein and the rheological impairment of the RBC among obese patients, but further studies are necessary to confirm this suggestion.

  20. Effect of mesh distortion on the accuracy of transverse shear stresses and their sensitivity coefficients in multilayered composites

    NASA Technical Reports Serve