scholarly journals Role of Electrostatic Interactions on Supramolecular Organization in Calf-Thymus DNA Solutions under Flow

Polymers ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1204 ◽  
Author(s):  
L. Bravo-Anaya ◽  
Denis Roux ◽  
J. Soltero Martínez ◽  
Francisco Carvajal Ramos ◽  
Frédéric Pignon ◽  
...  
Keyword(s):  
Shear Rate ◽  
Salt Concentration ◽  
Liquid Crystalline ◽  
Rheological Parameters ◽  
Supramolecular Organization ◽  
High Shear ◽  
Electrostatic Forces ◽  
Shear Rates ◽  
Rheological Experiments ◽  
Low Shear

Previous investigations were conducted on two concentrations of DNA solution: 4 mg/mL, for which it has been shown that no supramolecular organization is induced under flow at low shear rates; and 10 mg/mL, in which a liquid crystalline-type texture is formed under flow at low shear rates, attesting to an orientation of pre-organized chains. Rheological experiments are discussed and their results supported by small-angle X-ray scattering (SAXS) and flow birefringence visualization experiments. Scattering from polyelectrolytes has a characteristic signal, which is here observed in SAXS, showing a strong correlation peak between charged chains in water, for both concentrations. This peak is weaker in the presence of 0.01 M NaCl and suppressed in salt excess at 0.1 M NaCl. No plateau in the σ( γ ˙ ) plot was observed in analysis of rheological experiments on low DNA concentration (4 mg/mL). As typically observed in polyelectrolyte systems both the dynamic moduli and shear viscosity were higher in water as electrostatic forces dominate, than in the presence of salt, especially at low shear rates. The rheological results for concentrations of 0.01 M NaCl are lower than in water as expected due to partial screening of electrostatic repulsions. Rheological data for concentrations of 0.1 M NaCl are unexpected. Electrostatic forces are partially screened in the low salt concentration, leading to a drop in the rheological values. For high salt concentration there are no longer interchain repulsions and so steric interactions dominate within the entangled network leading to the subsequent increase in rheological parameters. Regardless of the solvent, at high shear rates the solutions are birefringent. In the 10 mg/mL case, under flow, textures are formed at relatively low shear rate before all the chains align going to a pseudonematic liquid crystalline phase at high shear rate. The electrostatic repulsion between semi-rigid chains induces a correlation between the chains leading to an electrostatic pseudo-gel in water and loosely in 0.01 M NaCl at low stress applied. To the best of our knowledge, this is the first time that such behavior is observed. In 0.1 M NaCl, DNA behavior resembles the corresponding neutral polymer as expected for polyelectrolyte in salt excess, exhibiting a yield stress. When texture appears in water and in 0.01 M NaCl, a critical transition is observed in rheological curves, where the viscosity decreases sharply at a given critical shear stress corresponding to a plateau in the σ( γ ˙ ) plot also observed in creep transient experiment.

Whole blood viscosity in the evaluation of thrombogenic milieu in mitral stenosis

2021 ◽  
Vol 15 (3) ◽  
pp. 181-190
Author(s):  
Elif H Ozcan Cetin ◽  
Mehmet S Cetin ◽  
Mustafa B Ozbay ◽  
Hasan C Könte ◽  
Nezaket M Yaman ◽  
...  
Keyword(s):  
Shear Rate ◽  
Blood Viscosity ◽  
Whole Blood ◽  
Mitral Stenosis ◽  
High Shear Rate ◽  
High Shear ◽  
Whole Blood Viscosity ◽  
Spontaneous Echo Contrast ◽  
Shear Rates ◽  
Low Shear

Aim: We aimed to assess the association of whole blood with thromboembolic milieu in significant mitral stenosis patients. Methodology & results: We included 122 patients and classified patients into two groups as having thrombogenic milieu, thrombogenic milieu (+), otherwise patients without thrombogenic milieu, thrombogenic milieu (-). Whole blood viscosity (WBV) in both shear rates were higher in thrombogenic milieu (+) group comparing with thrombogenic milieu (-). WBV at high shear rate and WBV at low shear rate parameters were moderately correlated with grade of spontaneous echo contrast. Adjusted with other parameters, WBV parameters at both shear rates were associated with presence of thrombogenic milieu. Discussion & conclusion: We found that extrapolated WBV at both shear rates was significantly associated with the thrombogenic milieu in mitral stenosis. This easily available parameter may provide additional perspective about thrombogenic diathesis.

Rheology of Fluoride Gels

1976 ◽  
Vol 55 (3) ◽  
pp. 353-356 ◽  
Author(s):  
M. Braden ◽  
Ratna Perera
Keyword(s):  
Infrared Spectroscopy ◽  
Shear Rate ◽  
Elastic Behavior ◽  
Shear Stresses ◽  
High Shear ◽  
Shear Rates ◽  
Extreme Stress ◽  
Thickening Agents ◽  
Shear Rate Dependence ◽  
Low Shear

Six commercial fluoride gels have been studied, using a cone and plate viscometer. Also, the thickening agents have been analyzed using infrared spectroscopy. All gels showed stress thinning, which is the decrease of viscosity with shear rate. Such shear rate dependence is clinically convenient in that the gel will flow readily at the high shear stresses present when the gel is applied but will not flow readily under its own weight when on the tooth. Five materials containing hydroxyalkyl celluloses showed similar degrees of shear thinning. One material with a non-cellulosic thickener showed much more extreme stress thinning together with elastic behavior at low shear rates; such behavior may be clinically advantageous. All of the gels showed only slight temperature dependence of rheological properties.

The Simulation of Aggregated Colloids Under Flow

1992 ◽  
Vol 289 ◽  
Author(s):  
John R. Melrose
Keyword(s):  
Shear Rate ◽  
Large Scale ◽  
Shear Thinning ◽  
High Shear ◽  
Shear Rates ◽  
Rouse Model ◽  
High Shear Rates ◽  
Structural Breakdown ◽  
Large Scale Simulations ◽  
Low Shear

AbstractAn overview is given of theories of aggregates under flow. These generally assume some sort of structural breakdown as the shear rate is increased. Models vary with both the rigidity of the bonding and the level of treatment of hydrodynamics. Results are presented for simulations of a Rouse model of non-rigid, (i.e. central force) weakly bonded aggregates. In large scale simulations different structures are observed at low and high shear rates. The change from one structure to another is associated with a change in the rate of shear thinning. The model captures low shear rate features of real systems absent in previous models: this feature is ascribed to agglomerate deformations. Quantitatively, the model is two orders of magnitude out from experiment but some scaling is possible.

Transfusion Therapy Decreases Oxygen Transport to Low-Flow Vascular Beds in Sickle Cell Disease.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1518-1518
Author(s):  
Tamas Alexy ◽  
Thomas D. Coates ◽  
John C Wood ◽  
Herbert J. Meiselman ◽  
Rosalinda B Wenby ◽  
...  
Keyword(s):  
Shear Rate ◽  
Oxygen Transport ◽  
Blood Viscosity ◽  
Low Flow ◽  
High Shear ◽  
Cell Disease ◽  
Blood Samples ◽  
Shear Rates ◽  
Low Shear ◽  
High Risk Children

Abstract Abstract 1518 Poster Board I-541 Introduction Chronic blood transfusions are commonly used as therapy for sickle cell disease (SCD, HbSS) in order to improve oxygen delivery and minimize complications such as stroke in high-risk children. Vaso-occlusive crises can occur in regions of high shear flow (e.g., major cerebral artery occlusions) or regions of low shear flow (e.g., marrow infarct) leading to acute ischemia and, if severe, to necrosis of affected tissues. Transfusion with normal (AA) RBC causes an increase of hematocrit (H) that is complicated by two opposing factors: increased hematocrit (H) causes a linear increase of oxygen carrying capacity and also an exponential increase of blood viscosity (η). As a consequence, the calculated oxygen transport effectiveness, defined as the ratio of H to η (H/η), is a biphasic function of hematocrit: H/η initially increases with H, reaches a maximum at an optimal H value, and then declines with further increases of H. At equal H and shear rate, sickle (SS) blood has significantly higher viscosity than AA and hence part of the strategy for transfusing SCD patients is to reduce η so as to improve H/η. Viscosity studies at high shear rates indicate that an optimum H can be demonstrated for AA-SS RBC mixtures prepared by adding AA RBC to SS blood to simulate transfusion. In marked contrast, low shear rate results for AA-SS mixtures indicate that there is no optimum hematocrit and H/η always decreases with increasing H (Transfusion 46:912-918, 2006). In order to extend these previous in vitro observations to SCD patients, we have measured blood viscosity and hematocrit using whole blood samples acquired prior to and following routine therapeutic transfusion; H/η was calculated over a wide, physiologically relevant shear rate range. Methods All subjects (n= 8, mean age =18.7 years) had homozygous HbSS disease, were crisis-free for > 4 weeks, and were enrolled in a chronic transfusion protocol designed to yield < 30% HbS and a post-transfusion H of 30-35%. Blood samples were obtained pre- and within 120 hours post-transfusion. A computer-controller tube viscometer was used to determine blood viscosity (37 °C, 40 mm Hg oxygen tension) over a shear rate range of 1 – 1,000 1/s. Results 1) As anticipated, blood viscosity and the degree of non-Newtonian flow behavior increased with H (24.7% pre-transfusion, 34.6% post-transfusion); 2) the change of H/η from pre- to post- transfusion was markedly affected by shear rate (Figure). As indicated, there is a large adverse effect at low shear (i.e., H/η reduced by 20-25% following transfusion), a neutral effect at about 50-100 1/s, and an improved H/η at high shear (Figure). That is, transfusion with AA RBC to obtain a lower percent SS RBC and a higher H actually impairs oxygen transport effectiveness at low shear and is only beneficial at high shear. Conclusions Clinical experience suggests that transfusion regimens aimed a keeping HbS at 30-50% are effective in preventing recurrent strokes in high-risk children. However, our new in vivo transfusion data suggest that at low shear rates, %HbS must be reduced further for H/η to surpass pre-transfusion levels. We interpret these findings as being consistent with our previous data for AA-SS RBC mixtures. They are also consistent with clinical results indicating lack of efficacy for transfusion in low flow areas (e.g., bone marrow during acute crisis) but highly beneficial effects in high flow regions (e.g., cerebral arteries). Our results thus suggest that benefits of transfusion may vary depending on local flow rates (i.e., shear rates) and organ-specific hemodynamics. Disclosures No relevant conflicts of interest to declare.

Changes in Whole Blood Viscosity at Low Shear Rates Correlate with Intravascular Volume Changes during Hemodialysis

2012 ◽  
Vol 35 (6) ◽  
pp. 425-434 ◽  
Author(s):  
Won Kim ◽  
Sung Kwang Park ◽  
Kyung Pyo Kang ◽  
Dong Hwan Lee ◽  
Sam Yeon Kim ◽  
...  
Keyword(s):  
Shear Rate ◽  
Blood Volume ◽  
Blood Viscosity ◽  
Whole Blood ◽  
High Shear ◽  
Whole Blood Viscosity ◽  
Shear Rates ◽  
Before And After ◽  
The Relationship ◽  
Low Shear

Background: Elevated blood viscosity has been shown to be independently correlated with cardiovascular risk factors and associated with increased risk of major cardiovascular events, including death and acute myocardial infarction. The aim of the present study was to investigate changes in whole blood viscosity (WBV) at shear rates of 1, 5, and 300 s-1 before and after hemodialysis in patients with end-stage renal disease (ESRD). We also examined the relationship between the changes of WBV and intravascular blood volume. Methods: 43 patients with ESRD receiving maintenance hemodialysis were enrolled. WBV was measured using a scanning capillary tube viscometer pre- and post-dialysis to quantify dialytic viscosity surges. Body weight, blood pressure, and hematocrit were also measured before and after hemodialysis, as was the fluid removed during the session. Results: Hemodialysis had a 3 times greater impact on the low-shear WBV at a shear rate of 1 s-1 (i.e., 44.1% change) than on the high-shear WBV at a shear rate of 300 s-1 (i.e., 15.9% change). Changes in the low-shear WBV obtained at shear rates of 1 and 5 s-1 during hemodialysis were significantly correlated with changes in hematocrit. The intravascular blood volume reduction during hemodialysis was positively correlated with the changes in both high-shear and low-shear WBVs. Conclusions: These results suggest that the WBV parameter may hold additional information beyond hemoconcentration. Further research is needed to evaluate the relationship between low-shear WBV surges and increased morbidity in the patient population with ESRD.

Comparison of antithrombotic efficacy between edoxaban, a direct factor Xa inhibitor, and fondaparinux, an indirect factor Xa inhibitor under low and high shear rates

2011 ◽  
Vol 106 (12) ◽  
pp. 1062-1068 ◽  
Author(s):  
Naoki Tsuji ◽  
Yuko Honda ◽  
Chikako Kamisato ◽  
Yoshiyuki Morishima ◽  
Toshiro Shibano ◽  
...  
Keyword(s):  
Shear Rate ◽  
Arterial Thrombosis ◽  
Factor Xa ◽  
High Shear ◽  
Shear Rates ◽  
Thrombosis Model ◽  
Perfusion Chamber ◽  
High Shear Rates ◽  
Antithrombotic Effects ◽  
Antithrombotic Efficacy

SummaryEdoxaban is an oral, direct factor Xa (FXa) inhibitor under late-phase clinical development. This study compared the antithrombotic efficacy of edoxaban with that of an indirect FXa inhibitor, fondaparinux, in in vivo venous and arterial thrombosis models and in ex vivo perfusion chamber thrombosis model under low and high shear rates in rats. Venous and arterial thrombi were induced by platinum wire insertion into the inferior vena cava and by application of FeCl3 to the carotid artery, respectively. The perfusion chamber thrombus was formed by blood perfusion into a collagen-coated capillary at 150 s-1 (low shear rate) and 1,600 s-1 (high shear rate). Effective doses of edoxaban that reduced thrombus formation by 50% (ED50) in venous and arterial thrombosis models were 0.076 and 0.093 mg/kg/h, respectively. In contrast, ED50 of fondaparinux in the arterial thrombosis model (>10 mg/kg/h) was markedly higher compared to ED50 in the venous thrombosis model (0.021 mg/kg/h). In the perfusion chamber thrombosis model, the ratio of ED50 under high shear rate (1.13 mg/kg/h) to that under low shear rate (0.63 mg/kg/h) for edoxaban was 1.9, whereas that for fondaparinux was more than 66. While the efficacy of fondaparinux markedly decreased in arterial thrombosis and in a high-shear state, edoxaban exerted consistent antithrombotic effects regardless of flow conditions. These results suggest that shear rate is a key factor in different antithrombotic effects between edoxaban and fondaparinux.

scholarly journals Platelet von Willebrand factor: evidence for its involvement in platelet adhesion to collagen

Blood ◽  
1987 ◽  
Vol 70 (4) ◽  
pp. 1214-1217
Author(s):  
E Fressinaud ◽  
D Baruch ◽  
C Rothschild ◽  
HR Baumgartner ◽  
D Meyer
Keyword(s):  
Shear Rate ◽  
Von Willebrand Factor ◽  
Platelet Adhesion ◽  
Von Willebrand Disease ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Von Willebrand ◽  
Willebrand Factor

Although it is well established that plasma von Willebrand Factor (vWF) is essential to platelet adhesion to subendothelium at high shear rates, the role of platelet vWF is less clear. We studied the respective role of both plasma and platelet vWF in mediating platelet adhesion to fibrillar collagen in a parallel-plate perfusion chamber. Reconstituted blood containing RBCs, various mixtures of labeled washed platelets and plasma from controls or five patients with severe von Willebrand disease (vWD), was perfused through the chamber for five minutes at a shear rate of 1,600 s-1. Platelet-collagen interactions were estimated by counting the radioactivity in deposited platelets and by quantitative morphometry. When the perfusate consisted of normal platelets suspended in normal plasma, platelet deposition on the collagen was 24.7 +/- 3.6 X 10(6)/cm2 (mean +/- SEM, n = 6). Significantly less deposition (16 +/- 2.3) was observed when vWD platelets were substituted for normal platelets. In mixtures containing vWD plasma, significantly greater deposition (9 +/- 2.2) was obtained with normal than with vWD platelets (1 +/- 0.4) demonstrating a role for platelet vWF in mediating the deposition of platelets on collagen. Morphometric analysis confirmed these data. Our findings indicate that platelet, as well as plasma, vWF mediates platelet-collagen interactions at a high shear rate.

scholarly journals Shear-Thinning Effect of the Spinning Disc Mixer on Starch Nanoparticle Precipitation

Processes ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 1622
Author(s):  
Sahr Sana ◽  
Vladimir Zivkovic ◽  
Kamelia Boodhoo
Keyword(s):  
Shear Rate ◽  
Shear Thinning ◽  
Solute Concentration ◽  
Liquid Films ◽  
High Shear ◽  
Shear Rates ◽  
Disc Surface ◽  
Particle Characteristics ◽  
Thinning Effect ◽  
Spinning Disc

Spinning disc technology is capable of achieving intensified micromixing within thin liquid films created through large shear rates, typically of the order of 103 s−1, generated by means of fast disc surface rotation. In this study the effect of the high shear on solvent–antisolvent mixing and starch nanoparticle precipitation is reported. Rheological studies of starch solutions at 2% w/v and 4% w/v have demonstrated their shear-thinning behaviour at the large shear rates experienced on the spinning disc surface. The effect of such high shear rate on starch nanoparticle precipitation is investigated alongside solute concentration and several other operating parameters such as flow rate, disc rotational speed, and solvent/antisolvent ratio. A reduction in nanoparticle size has been observed with an increase in starch concentration, although agglomeration was found to be more prevalent amongst these smaller particles particularly at larger flow rates and disc rotational speeds. Micromixing time, estimated on the basis of an engulfment mechanism, has been correlated against shear rate. With fast micromixing of the order of 1 ms observed at higher shear rates, and which are practically unaffected by the starch concentrations used, micromixing is not thought to be influential in determining the particle characteristics highlighted in this work.

Flow instability due to coupling of shear-gradients with concentration: non-uniform flow of (hard-sphere) glasses

Soft Matter ◽  
2014 ◽  
Vol 10 (47) ◽  
pp. 9470-9485 ◽  
Author(s):  
Howon Jin ◽  
Kyongok Kang ◽  
Kyung Hyun Ahn ◽  
Jan K. G. Dhont
Keyword(s):  
Shear Rate ◽  
Hard Sphere ◽  
Flow Instability ◽  
Microscopic Theory ◽  
Shear Rates ◽  
Spatial Gradients ◽  
Flow Profiles ◽  
Mass Fluxes ◽  
Glassy Systems ◽  
Low Shear

A microscopic theory explains the origin of mass fluxes induced by spatial gradients in the shear rate, and leads to an expression for the corresponding transport coefficient. The resulting instability gives rise to banded flow profiles in glassy systems for low shear rates.

Spatial Regulation of Platelet Aggregation and Physiology Under Flow

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 3300-3300
Author(s):  
Reginald Tran ◽  
Byungwook AHN ◽  
David R Myers ◽  
Yongzhi Qiu ◽  
Yumiko Sakurai
Keyword(s):  
Platelet Aggregation ◽  
Shear Rate ◽  
Platelet Function ◽  
Microfluidic Channel ◽  
Geometric Constraints ◽  
High Shear ◽  
Spatial Cues ◽  
Shear Rates ◽  
Spatial Regulation ◽  
Aggregation Of Platelets

Abstract Abstract 3300 Background: Hemostasis is an important physiologic process that requires the aggregation of platelets at distinct sites of vascular injury to promote clot formation and prevent blood loss. Platelet response to soluble agonists and shear stress has been studied extensively, but little is known of how microenvironmental geometry affects platelet function. As platelets must quickly adhere to, aggregate, and initiate coagulation only at the affected areas, spatial cues must at some level regulate this process. This aspect of spatial regulation has been investigated under static conditions by our group and others (Kita et al., 2011; Van de Walle et al., 2012). Understanding this aspect of platelet function is vital for better understanding the process of hemostasis and pathophysiological conditions such as thrombosis. Here, we directly examine how spatial cues affect platelet aggregation and physiology under variable shear conditions by flowing heparinized whole blood over micropatterned collagen in a microfluidic channel. This system allows us to assess platelet aggregate morphology under different geometric constraints and shear rates, as well as evaluate platelet physiology at the single cell level by measuring calcium signaling using fluorogenic dyes. Results: A microfluidic channel was bonded to a glass coverslip stamped with FITC-conjugated Type I collagen using a novel technique combining microcontact printing and the stamp-stick bonding technique (Satyanarayana et al., 2005). Before flowing, each chamber was incubated with 1% bovine serum albumin (BSA) blocking solution for 1.5 hours. Whole heparinized blood was then flowed through the chamber at shear rates of 100, 1000, and 10000 s−1. Platelets were labeled with Fura Red, and time lapse confocal imaging was performed for 10 minutes to monitor the aggregation of platelets at the start of flow. The flow chambers were then flushed with Tyrode's buffer with 0.1% BSA using the same experimental shear rates until the chamber was cleared of red blood cells. Image analysis was conducted using ImageJ (to calculate the percentage of platelet coverage on the collagen stamps at different shear rates. Platelets initially adhere to the distal edge of the collagen micropatterns for all shear rates (Fig. 1), indicating that platelets may require a priming region before forming a stable adhesion. As shear rate increased, platelet coverage of the collagen stamps decreased. However, aggregates also grew without conforming to the geometric constraints imposed by the collagen micropatterns more frequently at those higher shear rates (Fig. 1). Though platelet tethers generally aligned in the direction of the flow, increased tether lengths could be seen when platelets were exposed to higher shear, which may explain why platelets were able to span larger gaps and aggregate in a less spatially constrained manner at high shear rates. Image analysis shows that 51.5% of the collagen was covered by platelet aggregates for a shear rate of 100 s−1 with some platelets forming tethers to span gaps (Fig. 2). When the shear rate was increased to 1000 s−1, platelet coverage of the collagen microstamp drastically dropped to 18.5% (Fig. 2). At a pathophysiological shear rate of 10000 s−1, the percentage of collagen covered by platelets dropped further to 12.8% and adopted a linear shape, although a large portion of the aggregate can be seen spanning gaps between the collagen microstamp (Fig. 1 and 2). Conclusions and Ongoing Efforts: Ours is the first reported study of the spatial regulation of platelet aggregation under variable shear in a microfluidic channel. We have found that platelets are more spatially regulated under low shear conditions compared to high shear, which has implications for thrombosis and other clotting disorders. Future studies will incorporate the simultaneous use of ratiometric fluorgenic calcium signaling dyes to investigate the role of spatial regulation in Ca2+ signaling. Finally, we have developed a method to culture endothelial cells around a collagen micropattern to study this spatial regulation of platelet function under more physiological conditions (Fig. 3). Disclosures: No relevant conflicts of interest to declare.

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