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At least 973 records · Page 54Linked to original sources
PubMed2003

Vesicles in haptotaxis with hydrodynamical dissipation.

We analyze the problem of vesicle migration in haptotaxis (a motion directed by an adhesion gradient), though most of the reasoning applies to chemotaxis as well as to a variety of driving forces. A brief account has been published on this topic. We present an extensive analysis of this problem and provide a basic discussion of most of the relevant processes of migration. The problem allows for an arbitrary shape evolution which is compatible with the full hydrodynamical flow in the Stokes limit. The problem is solved within the boundary integral formulation based on the Oseen tensor. For the sake of simplicity we confine ourselves to 2D flows in the numerical analysis. There are basically two regimes (i) the tense regime where the vesicle behaves as a "droplet" with an effective contact angle. In that case the migration velocity is given by the Stokes law. (ii) The flask regime where the vesicle has a significant (on the scale of the vesicle size) contact curvature. In that case we obtain a new migration law which substantially differs from the Stokes law. We develop general arguments in order to extract analytical laws of migration. These are in good agreement with the full numerical analysis. Finally we mention several important future issues and open questions.

Adsorption↗
PubMed2003

Hydrodynamic instabilities in ferronematics.

In the hydrodynamic description of ferronematics there are various dynamic magnetic-field effects, linear in the field strength, that are negligible in usual nematics, but can play a role in ferronematics. Here, we investigate theoretically the influence of these new terms on the thermal convection (Rayleigh-Bénard) and the viscous fingering (Saffman-Taylor) instability in ferronematics in the presence of a strong magnetic field. We find that the instabilities are qualitatively changed due to the occurrence of a finite vorticity component--a feature that is known from simple liquids in the case of a superimposed mechanical rotation. We suggest to use the additional effects (cross-flow within convection rolls, oblique rolls, rotating fingers) for measuring the phenomenological coefficients involved.

Journal Article↗
PubMed2004

Dynamics of simple liquids at heterogeneous surfaces: molecular-dynamics simulations and hydrodynamic description.

In this paper we consider the effect of surface heterogeneity on the slippage of fluid, using two complementary approaches. First, MD simulations of a corrugated hydrophobic surface have been performed. A dewetting transition, leading to a super-hydrophobic state, is observed for pressure below a "capillary" pressure. Conversely, a very large slippage of the fluid on this composite interface is found in this super-hydrophobic state. Second, we propose a macroscopic estimate of the effective slip length on the basis of continuum hydrodynamics, in order to rationalize the previous MD results. This calculation allows to estimate the effect of a heterogeneous slip length pattern at the composite interface. Comparison between the two approaches shows that they are in good agreement at low pressure, but highlights the role of the exact shape of the liquid-vapor interface at higher pressure. These results confirm that small variations in the roughness of a surface can lead to huge differences in the slip effect. On the basis of these results, we propose some guidelines to design highly slippery surfaces, motivated by potential applications in microfluidics.

Journal Article↗
PubMed2006

Molecular-dynamics simulations with explicit hydrodynamics II: on the collision of polymers with molecular obstacles.

We present a study of the dynamics of single polymers colliding with molecular obstacles using Molecular-dynamics simulations. In concert with these simulations we present a generalized polymer-obstacle collision model which is applicable to a number of collision scenarios. The work focusses on three specific problems: i) a polymer driven by an external force colliding with a fixed microscopic post; ii) a polymer driven by a (plug-like) fluid flow colliding with a fixed microscopic post; and iii) a polymer driven by an external force colliding with a free polymer. In all three cases, we present a study of the length-dependent dynamics of the polymers involved. The simulation results are compared with calculations based on our generalized collision model. The generalized model yields analytical results in the first two instances (cases i) and ii)), while in the polymer-polymer collision example (case iii)) we obtain a series solution for the system dynamics. For the case of a polymer-polymer collision we find that a distinct V-shaped state exists as seen in experimental systems, though normally associated with collisions with multiple polymers. We suggest that this V-shaped state occurs due to an effective hydrodynamic counter flow generated by a net translational motion of the two-chain system.

Adsorption↗
PubMed2004

Hydrodynamic analysis of waveforms induced by vibrational stimuli at meridian and non-meridian points.

Meridian theory is an important part of traditional Chinese medicine (TCM). Although acupuncture has been accepted in many countries, the nature of the meridian theory and the principles of acupuncture are still unclear in the modern scientific view. The purpose of this study was to determine the differences in wave propagation of mechanical vibrations (optimal stimulator frequency of 40 Hz) through the pericardium meridian [EH-4 (Chieh-Men) and EH-5 (Chien-Shih)] and adjacent control regions in 20 subjects using hydrodynamic analysis. The mean transfer speed was significantly lower in the meridian (4 m/s) than in the adjacent control region (8.5 m/s, P < 0.001). There were also significant differences between the meridian and control points in the attenuation rate (P < 0.001) and peak amplitude (P < 0.001). In conclusion, these results imply that the substance of the meridian differs from that of the adjacent control regions.

Acupuncture Points↗
PubMed2005

Characteristics of new Staphylococcus aureus-RBC adhesion mechanism independent of fibrinogen and IgG under hydrodynamic shear conditions.

Staphylococcus aureus infection begins when bacterial cells circulating in blood adhere to components of the extracellular matrix or endothelial cells of the host and initiate colonization. S. aureus is known to exhibit extensive interactions with platelets. S. aureus is also known to bind to red blood cells (RBCs) in the presence of plasma proteins, such as fibrinogen and IgG. Herein we report a new binding mechanism of S. aureus to RBC independent of those plasma proteins. To characterize the new adhesion mechanism, we experimentally examine the binding kinetics and molecular constituents mediating the new adhesive interactions between S. aureus and RBCs under defined shear conditions. The results demonstrate that the receptors for fibrinogen (clumping factor A) and IgG (protein A) of S. aureus are not involved in the adhesion. S. aureus binds to RBCs with maximal adhesion at the shear rate 100 s(-1) and decreasing adhesion with increasing shear. The heteroaggregates formed after shear are stable when subjected to the shear rate 2,000 s(-1), indicating that intercellular contact time rather than shear forces controls the adhesion at high shear. S. aureus binding to RBC requires plasma, and 10% plasma is sufficient for maximal adhesion. Plasma proteins involved in the cell-cell adhesion, such as fibrinogen, fibronectin, von Willebrand factor, IgG, thrombospondin, laminin, and vitronectin are not involved in the observed adhesion. The extent of heteroaggregation is dramatically reduced on RBC treatment with trypsin, chymotrypsin, or neuraminidase, suggesting that the receptor(s) mediating the heteroaggregation process is a sialylated glycoprotein on RBC surface. Adhesion is divalent cation dependent and also blocked by heparin. This work demonstrates a new mechanism of S. aureus-RBC binding under hydrodynamic shear conditions via unknown RBC sialoglycoprotein(s). The binding requires plasma protein(s) other than fibrinogen or IgG and does not involve the S. aureus adhesins clumping factor A or protein A.

Bacterial Adhesion↗
PubMed2004

Distinct role of hydrodynamic shear in leukocyte-facilitated tumor cell extravasation.

Previously, we found polymorphonuclear neutrophils (PMNs) increased melanoma cell extravasation under flow conditions (Intl J Cancer 106: 713-722, 2003). In this study, we characterized the effect of hydrodynamic shear on PMN-facilitated melanoma extravasation using a novel flow-migration assay. The effect of shear stress and shear rate on PMN-facilitated melanoma extravasation was studied by increasing the medium viscosity with dextran to increase shear stress independently of shear rate. Under fixed shear rate conditions, melanoma cell extravasation did not change significantly. In contrast, the extravasation level increased at a fixed shear stress but with a decreasing shear rate. PMN-melanoma aggregation and adhesion to the endothelium via beta(2)-integrin/intracellular adhesion molecule-1 (ICAM-1) interactions were also studied. Lymphocyte function-associated molecule-1 (LFA-1; CD11a/CD18) influenced the capture phase of PMN binding to both melanoma cells and the endothelium, whereas Mac-1 (CD11b/CD18) affected prolonged PMN-melanoma aggregation. Blockage of E-selectin or ICAM-1 on the endothelium or ICAM-1 on the melanoma surface reduced PMN-facilitated melanoma extravasation. We have found PMN-melanoma adhesion is correlated with the inverse of shear rate, whereas the PMN-endothelial adhesion correlated with shear stress. Interleukin-8 (IL-8) also influenced PMN-melanoma cell adhesion. Functional blocking of the PMN IL-8 receptors, CXCR1 and CXCR2, decreased the level of Mac-1 upregulation on PMNs while in contact with melanoma cells and reduced melanoma extravasation. We have found PMN-facilitated melanoma adhesion to be a complex multistep process that is regulated by both microfluid mechanics and biology.

Cell Adhesion↗
PubMed2003

Normalization of growth in hypophysectomized mice using hydrodynamic transfer of the human growth hormone gene.

Nonviral gene transfer was investigated as a potential treatment of growth hormone deficiency (GHD) using hypophysectomized mice as a model. After a single hydrodynamic administration of naked plasmid DNA containing the human growth hormone (hGH) gene controlled by an ubiquitin promoter, sustained elevation of circulating hGH was observed the entire observation period (68 days), with a concomitant normalization of circulating insulin-like growth factor I (IGF-I) and IGF-binding protein-3. Furthermore, longitudinal growth was corrected in terms of normalization of tibia length, tail length, and body weight gain. Liver, spleen, and lung weights were normalized, whereas heart weight was normalized partly. hGH mRNA was expressed exclusively in liver tissue. In conclusion, we showed that nonviral hGH gene transfer normalizes longitudinal growth in hypophysectomized mice, indicating that this method potentially could be relevant as a new therapeutic tool in the clinical handling of GHD.

Animals↗
PubMed1990

Gastric emptying of nondigestible solids in dogs: a hydrodynamic correlation.

The influence of particle size, particle density, fluid viscosity, and fluid flow rate on the gastric emptying of nondigestible solids was investigated in five dogs with chronically placed fistulas. Six hundred and fifty particles of 13 different size and density combinations were administered simultaneously with 500 ml of either normal saline or low-, medium-, or high-viscosity polymer solutions. The canine stomach was found to discriminate between these solids on the basis of size and density at all levels of viscosity above saline. The observed patterns of emptying are consistent with the hypothesis that gastric emptying of nondigestible solids is governed in part by hydrodynamics and correlate well with the gastric-emptying coefficient (GEC), a dimensionless grouping of variables that takes the form GEC = (Dpy/Dp) [g(rho f - rho p)Dp2]/[eta (nu)] where [g(rho f - rho p)] is particle buoyancy consisting of fluid (rho f) and particle (rho p) densities and g, the gravitational constant; (Dp) is the particle diameter, (Dpy) the estimated pyloric diameter, eta the fluid viscosity, and (nu) the average linear velocity of fluid exiting the stomach.

Animals↗
PubMed1981

Hydrodynamic features of pulmonary air embolism: a model study.

To elucidate the hydrodynamic events during pulmonary air embolism, experiments were conducted in a branching-tube apparatus and in small vessels. It was found that, as long as there existed an elevation differential between the two branches of a bifurcation, the vast majority of air bubbles always entered the higher branch. This finding is explained in terms of buoyancy, shear forces, and liquid flow velocity and is consistent with the in vivo finding of increased blood perfusion in the dependent lung regions during air embolization (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 51: 211-217, 1981). The pressures required to drive air bubbles through various small vessels were determined using three aqueous solutions of different surface tensions. Based on these measurements and a theoretical analysis, the diameter of air bubbles that could not pass through the pulmonary vessels was calculated to be 20-30 micrometers, agreeing well with a recent in vivo measurement (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47: 537-543, 1979).

Capillaries↗
PubMed1988

Neutrophil retention in model capillaries: deformability, geometry, and hydrodynamic forces.

The initial retention of neutrophils within the pulmonary microvascular bed occurs in both physiological and pathological states, yet the factors responsible for this retention are poorly understood. Because the diameter of the neutrophil is approximately 7.03 micron and the mean pulmonary capillary diameter is 5.5 micron, we postulated that geometric constraints imposed by the microvascular bed, the deformability of the neutrophil, and the hydrodynamic characteristics of blood were important determinants of neutrophil retention. We used a filtration system wherein 111In-labeled human neutrophils (111In-N) suspended in a serum-containing buffer were passed through Nuclepore filters of known pore size. Compared with 99mTc-labeled erythrocytes (99mTc-RBC), the passage of 111In-N was delayed and a higher percentage was retained within the filter. Because the neutrophil and RBC are approximately equal in diameter, the deformability of the neutrophil must be less than that of RBC. As the flow rate increased, retention in the filters decreased logarithmically from 72 +/- 5% (flow rate 0.5 ml/min) to 15 +/- 4% (10.0 ml/min). As the number of RBC in the buffer increased, neutrophil retention in 5-micron filters decreased in a linear fashion from 65 +/- 6% at hematocrit of 0 to 33 +/- 2% at hematocrit of 10. The perfusion pressure and shear stress were of critical importance, and there was a logarithmic relationship between retention and perfusion pressure or shear stress (tau), whether the increase in pressure or tau was generated by increasing flow or by increasing the hematocrit of the perfusate. As the pore size of the filter increased, the retention of neutrophils decreased in a logarithmic fashion: from 75 +/- 5% in the 3-micron filter to 4 +/- 1.3% in the 12-micron filter.(ABSTRACT TRUNCATED AT 250 WORDS)

Biophysical Phenomena↗
PubMed1987

The hydrodynamically balanced system: a novel principle of controlled drug release.

Madopar HBS (125 mg) is a controlled-release dosage form with 100 mg L-dopa and 25 mg benserazide. The 'hydrodynamically balanced system' (HBS) used for this novel dosage form of Madopar is a dosage form which, when in contact with gastric fluid and after dissolution of the gelatine shell of the capsule, forms a mucous body and a bulk density of less than 1 and releases the drug(s) at a desired rate whereas the dosage form remains in the stomach for a prolonged period of time. Drugs--in the present case L-dopa and benserazide--are released through the hydrated layer by diffusion principle. This system is valuable for drugs which are soluble at lower pH. By varying the composition of the excipients, desired release rates can be achieved. The in vitro dissolution rate of Madopar HBS formulation is as follows: L-dopa t75% = about 6 h and benserazide t75% = about 4 h. The floating behavior was tested in an in vitro test. These in vitro floating properties could be confirmed in man and were investigated in 10 healthy volunteers by means of gamma camera measurements using a poly-marker technique carried out in connection with a Valium CR study. It is expected that this novel drug delivery system proffers a valuable dosage form which delivers the drug at a specific rate allowing a better control of fluctuations in parkinsonian patients.

Administration, Oral↗
PubMed1977

Hydrodynamic factors in Dandy-Walker and Arnold-Chiari malformations.

The Dandy-Walker malformation (DWM) is hydrocephalus that primarily affects the fourth ventricle, whose overdistention involves also the aqueduct and third ventricle. However, just the opposite is true in the Arnold-Chiari malformation (ACM) since the hydrocephalus is limited to the lateral ventricles which squeeze the third ventricle between them and compress the aqueduct and fourth ventricle. The evidence indicates that both result from hydrodynamic stresses in embryonal and early fetal life. This communication is offered in rebuttal to some statements in an otherwise authoritative and comprehensive article.

Arnold-Chiari Malformation↗
PubMed1993

A hydrodynamic model of rabbit corpus cavernosum pressure responses to vasodilators.

The intracavernosal pressure changes induced by 3 vasodilating drugs, diazoxide, glyceryltrinitrate and verapamil were investigated during autologous extracorporeal penile blood perfusion in an experimental rabbit model. In order to separate the arterial and venous components the experiments were performed with both intact and interrupted penile arterial inflow. The major hemodynamic effect of these drugs was an increased outflow resistance from the corpora cavernosa, probably effected through relaxation of the corporal smooth muscle. However, the intracorporeal pressure responses only reflected a part of the drug-induced smooth muscle relaxation. A theory is presented, according to which the corpora cavernosa are 'accumulating' smooth muscle relaxation, without direct reflection in an increased cavernosal pressure. At the moment when sufficient smooth muscle relaxation is achieved, a sudden increase in cavernosal pressure will appear and lead to an erection. This concept was generated through an approximation of corpora cavernosa to an elastic cylinder following the elastic law of Laplace in combination with the hydrodynamic law of Poiseuilles.

Animals↗
PubMed1979

In vitro hydrodynamic comparison of mitral valve bioprostheses.

With the use of the pulse duplicator built in our laboratory, the hydrodynamic characteristics of three sizes of the four commercially available mitral bioprostheses, Hancock, Carpentier-Edwards, Angell-Shiley, and Ionescu-Shiley, were studied and compared. A wide range of performance was found: for example, during pulsatile testing, at peak flow of 15 1/min (corresonding to a normal resting cardiac output) transvalvular gradients varied from as high as 20 mm Hg (Angell-Shiley) to 5 mm Hg(Ionescu-Shiley) in the 25 mm mounting diameter size. Effective orifice areas (EOA) are significantly different in valves of the same mounting size, e.g., at peak flows of 20 1/min, the Ionescu-Shiley 25 provides an EOA of 1.7 cm2 while the Angell-Shiley provides only 1.17 cm2. The EOAs of all bioprostheses have been found to increase with increasing flow (e.g., from 10--30 1/min peak flow, the Hancock 25 changed from 1.25 cm2 to 1.50 cm2). The Gorlin formula, as constituted for calculating the area of stenotic mitral valves, is inappropriate for prosthetic valves. But the discharge coefficients of the bioprostheses have been found to be around 1 when the planimetered area of the open valve orifice is determined at a given flow. By using this discharge coefficient, the Gorlin formula will give an excellent estimate of the true orifice area of mitral bioprostheses.

Bioprosthesis↗
PubMed2006

A novel in vitro model to study staphylococcal biofilm formation on intraocular lenses under hydrodynamic conditions.

PURPOSE: To develop a novel in vitro model to study the formation of Staphylococcus epidermidis biofilm on intraocular lenses (IOLs) from the primary-attachment phase to the biofilm-accumulation phase. The model was designed to replicate intraocular conditions especially by taking into account intraocular hydrodynamics. METHODS: The model consisted of Tygon tubing connected to a vial containing acrylic hydrophobic IOLs. Three septa, placed along the tubing, allowed, respectively, the artificial aqueous humor's arrival and its elimination and the bacterial suspension's inoculation. A first pump allowed the aqueous humor's movement along the circuit, whereas a second one regulated the flow at which the nutritive environment was regenerated. The whole circuit was placed in a 34 degrees C water bath. Every 2 to 4 hours, lenses were taken from this environment. Bound bacteria were removed by scraping of optical faces and counted. All data are presented as the mean, SD, and coefficient of variation (CV). Comparisons among experiments were performed by one-way analysis of variance (ANOVA). RESULTS: Calculated CVs were close to 30, showing that biofilm formation was homogeneous. Differences between experiments were nonsignificant for each removal time. The model provided the full kinetics of S. epidermidis biofilm growth on acrylic hydrophobic IOLs, with a stationary phase reached after 28 hours of incubation. CONCLUSIONS: Biofilm development is modulated by many variables, including environmental factors. The findings in the present study of bacterial colonization of IOLs under intraocular physiological conditions allow understanding and more accurate targeting of biomedical device-related infections such as endophthalmitis.

Acrylic Resins↗
PubMed1996

Neutrophil-neutrophil interactions under hydrodynamic shear stress involve L-selectin and PSGL-1. A mechanism that amplifies initial leukocyte accumulation of P-selectin in vitro.

Leukocytes attach to and roll on inflamed endothelium and on leukocyte monolayers that form on the endothelial cells. Leukocyte-leukocyte interactions occurring under hydrodynamic shear stress are mediated by binding of L-selectin to unknown sialomucin-like glycoproteins. We show that purified neutrophil PSGL-1, a sialomucin glycoprotein that serves as a ligand for both P- and E-selectin, can also support the attachment and rolling of free flowing neutrophils in vitro. Neutrophil rolling on PSGL-1 was abolished by the anti-L-selectin mAb DREG200 and by the anti-PSGL-1 mAb PL1, indicating that L-selectin can interact directly with PSGL-1. Neutrophil rolling on neutrophil monolayers was also blocked by PL1 (60 +/- 9% SEM inhibition); however, DREG200 blocked more efficiently (93 +/- 7% SEM inhibition), suggesting that other L-selectin ligands may exist on the neutrophil surface. These studies demonstrate that PSGL-1 on the neutrophil surface is a major functional ligand for L-selectin. The avidity of this L-selectin-dependent adhesion event was sufficient to allow individual neutrophils rolling on P-selectin to capture free flowing neutrophils, which progressed to form linear strings and discrete foci of rolling neutrophils. Neutrophil accumulation on P-selectin accelerated with time as a result of neutrophil-assisted capture of free flowing neutrophils. When neutrophil-neutrophil interactions were blocked by DREG200, neutrophils accumulated on P-selectin in a random pattern and at a uniform rate. Thus, leukocyte-assisted capture of flowing leukocytes may play an important role in amplifying the rate of initial leukocyte recruitment at sites of inflammation.

Antibodies, Monoclonal↗
PubMed1975

Relative flow measured by roentgen videodensitometry in hydrodynamic model.

The behaviour of injected iodine contrast medium in a pulsative hydrodynamic model was recorded on videotape in television fluoroscopy and measured by roentgen videodensitometry. By a simple relationship between the integrated densitometric area, the amount of injected contrast medium, and the flow at the site of the injection, it was possible to compare the flow in two different cross-sections of the circulatory system with high accuracy.

Absorptiometry, Photon↗