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PubMed2000

Hydrodynamic and Colloidal Interactions in Concentrated Charge-Stabilized Polymer Dispersions.

Hydrodynamic and colloidal interactions are explored in concentrated, charge-stabilized colloidal dispersions by measuring the dependence of rheology (e.g., low and high-shear viscosity, high-frequency viscosity, and modulus) and self-diffusivity on salt content, particle size, and concentration. Model, sulfonated polystyrene lactices of varying diameter are prepared and investigated by shear rheology, high-frequency torsional resonance, electrophoresis, titration, and dynamic light scattering. The high-frequency and high-shear viscosity both are dominated by hydrodynamic interactions, but are shown not to be identical, due to the microstructure distortion resulting from high shear rates. The short-time self-diffusion is also shown to be insensitive to direct particle interactions, but has a different concentration dependence than the high-frequency viscosity, further illustrating a predicted violation of a generalized Stokes-Einstein relationship for these properties. The apparent colloidal surface charge is extracted from the high-frequency elastic modulus measurements on concentrated dispersions. The surface charge is in good agreement with results from critical coagulation concentration measurements and perturbation theories, but disagrees with electrophoretic mobility experiments. This indicates that the effective surface charge determined by torsional high-frequency measurements is a more reliable predicter of the salt stability of charge-stabilized dispersions, in comparison to zeta-potentials determined from electrophoretic mobilities. Further, we demonstrate by direct comparison that measurements of the apparent plateau modulus by rotational rheometry underestimate the true, high-frequency modulus and provide unreliable estimates for the surface charge. Copyright 2000 Academic Press.

Journal Article↗
PubMed1994

Characterization of the tryptophan fluorescence and hydrodynamic properties of rat DNA polymerase beta.

We have examined the biophysical properties of DNA polymerase beta (beta-pol) in solution. Time-resolved and steady-state fluorescence were used to investigate the microenvironment of the lone tryptophanyl residue (Trp324), and a combination of sedimentation equilibrium, sedimentation velocity and fluorescence anisotropy decay measurements were used to study the hydrodynamic properties of the enzyme. Trp324 appears to be exposed to water as judged by the tryptophan emission and steady-state and lifetime quenching experiments. The fluorescence is easily quenched by a neutral quencher acrylamide (kq = 1.59 x 10(9)M-1S-1), and by a negatively charged ionic quencher, I- (kq = 1.60 x 10(9) M-1S-1), but not by a positively charged ionic quencher, Cs+ (kq = 0.2 x 10(9) M-1S-1). The fluorescence lifetime of beta-pol is best described by the sum of two exponentials with a longer lifetime component of 8.4 ns and a shorter lifetime component of 1.3 ns. Decay associated spectra (DAS) show emission maxima at 340 nm and at 345 nm for the shorter lifetime and longer lifetime components, respectively, with corresponding centers of gravity at 347 nm and 348 nm. Sedimentation equilibrium experiments show that the enzyme exists as a monomer at the KCl concentrations (> 0.05 M) studied in the absence of divalent metals. Zn2+ causes higher order aggregation, but no such aggregates are seen with Mg2+ and Mn2+. In the presence of 1 mM manganese, the average lifetime decreased approximately 10%, from 8.14 ns to 7.38 ns, with a concomitant increase of average rotational correlational time (phi) from 24 ns to 28 ns. The accessibility of the positively charged quencher (Cs+) to tryptophan also decreases approximately 50%, indicating alteration of the tryptophan microenvironment. By contrast, Mg2+ causes minor changes in fluorescence properties. The hydrodynamic shape of the intact enzyme and its single-stranded (8 kDa) and double-stranded (31 kDa) DNA binding domains were further investigated by sedimentation velocity measurements. The value of S0(20),W for the intact enzyme is 2.97 S, and the calculated axial ratio is 5.0. In contrast to the 8 kDa domain, which has a less asymmetric shape with an axial ratio of 2.3, the 31 kDa domain shows an elongated structure with an axial ratio of 5.5. These data suggest that the axial ratio of the intact enzyme may be the result of marked bending of the molecule at the flexible hinge region between the two domains.

Animals↗
PubMed2000

HYDRONMR: prediction of NMR relaxation of globular proteins from atomic-level structures and hydrodynamic calculations.

The heteronuclear NMR relaxation of globular proteins depends on the anisotropic rotational diffusion tensor. Using our previous developments for prediction of hydrodynamic properties of arbitrarily shaped particles, by means of bead models, we have constructed a computational procedure to calculate the rotational diffusion tensor and other properties of proteins from their detailed, atomic-level structure. From the atomic coordinates file used to build the bead model, the orientation of the pertinent dipoles can be extracted and combined with the hydrodynamic information to predict, for each residue in the protein, the relaxation times. All of these developments have been implemented in a computer program, HYDRONMR, which will be of public domain.

Algorithms↗
PubMed2001

Morphological models of radiate accretive growth and the influence of hydrodynamics.

In many marine sessile organisms (for example sponges and stony corals) the skeleton is formed by an accretive growth process, where layers of material are secreted on top of each other in a surface normal deposition process. In many of these organisms the growth process exhibits a strong morphological plasticity due to differences in exposure to water movement. In general, many of these organisms tend to form thin-branching growth forms under sheltered conditions, while the growth form gradually transforms into a more compact shape when the exposure of water movement increases. In this paper, we investigate this phenomenon by combining a three-dimensional simulation model of radiate accretive growth driven by the local availability of simulated food particles and a model, based on the lattice Boltzmann method, for simulating food particle distributions caused by a combination of flow and diffusion. In the simulations two different models of a suspension feeder with accretive growth were compared. In the first model, the deposition process is exclusively driven by the local availability of food particles, in the second model the deposition process was determined by the combination of local amount of contact to the environment and availability of food particles. In the simulations it was found that hydrodynamics has a strong impact on the overall morphologies which develop in the accretive growth process. In the model exclusively driven by the local availability of food particles, column-shaped objects emerged under diffusion conditions, while more spherical and lobed object were found for the flow-dominated case. In the simulations, the Péclet number was varied independently from the Reynolds number, which was kept at a relatively low constant value. In a range of increasing Péclet numbers, indicating an increasing influence of hydrodynamics, the simulated morphologies gradually transformed from thin-branching ones into more spherical and compact morphologies in the model where deposition was controlled by the local availability of food particles and the local amount of contact with the environment.

Animal Nutritional Physiological Phenomena↗
PubMed1994

A hydrodynamic interpretation of crisis in sickle cell anemia.

The occurrence of crisis events in patients with sickle cell disease is associated with an increase in blood plasma viscosity, the hydrodynamic consequences of which are examined here. A mathematical model of the flow of sickle cells in capillaries predicts that for moderate increases in plasma viscosity, a regime of multivalued solutions for blood velocities is encountered, and the likely physical response is a precipitous drop to the lowest velocity solution. This behavior results from the coupling of the hydrodynamics with sickle erythrocyte rheology and oxygen transport to the surrounding tissue; no such catastrophe is predicted for normal erythrocytes. The type of velocity changes predicted by the model strongly suggest that plasma viscosity changes may play an important role in initiating or exacerbating crisis.

Anemia, Sickle Cell↗
PubMed1998

The possible role of CSF hydrodynamic parameters following in management of SAH patients.

It is suggested that reduced intracranial compliance may be present even when measured ICP is normal and may precede clinical deterioration. Our findings reflect a decompensation of hydrodynamic parameters more pronounced 4-7 postictal days, when compliance is reduced not only in patients with poor clinical condition, but also in patients with Hunt-Hess grade I-III. Increased CSF outflow resistance in the first few days is not surprising; it is thought to be due to the blockage of flow of CSF through the basal subarachnoid cisterns and clogging of the arachnoid villi with erythrocytes and fibrin. Enlargement of ventricles seen on CT scan at the same time suggests the development of acute hydrocephalus. During the first days after SAH, our data reflects evidence of ventricular enlargement in patients presenting with both poor and better clinical condition. We conclude that the monitoring of ICP and dynamic measuring of CSF hydrodynamic parameters is important for longer than the generally accepted few days for selected cases after SAH.

Arachnoid↗
PubMed1998

Hydrodynamic properties of hydrocephalus shunts.

Hydrodynamic properties of hydrocephalus shunts are not always properly characterized by the manufacturer. Therefore, the choice of the shunt should be made, by matching performance of the shunt to the disturbed profile of CSF circulation of a given patient. The aim of the present shunt evaluation study is to evaluates all types of shunts presently in use in the U.K. and make this information available to neurosurgeons. Ten most common models of valves have been tested to date: Medtronik PS Medical: Delta Valve, Flow Control Valves and Lumbo-Peritoneal Shunt, Heyer-Schulte: In-line, Low Profile and Pudenz Flushing Valve, Codman: Medos-Programmable, Hakim-Precision, Sophy Programmable Valve, Cordis Orbis-Sigma. Our results show the majority of valves have low hydrodynamic resistance (exception: PS Lumboperitoneal, Orbis-Sigma), which increase by 100-200% after connection of a long distal catheter. A few shunts with siphon-preventing mechanism (Delta, Hayer-Schulte Low Profile, Pudenz-Flushing) offer reasonable resistance to negative outlet pressures, however, these valves may be blocked by raised subcutaneous pressure. All programmable valves are susceptible to siphoning. Programmed settings may be changed by external magnetic field.

Cerebrospinal Fluid Pressure↗
PubMed1994

Hydrodynamics of segmentally flexible macromolecules.

Segmentally flexible macromolecules are composed of a few rigid subunits linked by joints which are more or less flexible. The dynamics in solution of this type of macromolecule present special aspects that are reviewed here. Three alternative approaches are described. One is the rigid-body treatment, which is shown to be valid for overall dynamic properties such as translational diffusion and intrinsic viscosity. Another approach is the Harvey-Wegener treatment, which is particularly suited for rotational diffusion. The simplest version of this treatment, which ignores hydrodynamic interaction (HI) effects, is found to be quite accurate when compared to a more rigorous version including HI. A third approach is the Brownian dynamics simulation that, albeit at some computational cost, might describe rigorously cases of arbitrary complexity. This technique has been used to test the approximations in the rigid-body and Harvey-Wegener treatments, thus allowing a better understanding of their validity. Brownian trajectories of simplified models such as the trumbbell and the broken rod have been simulated. The comparison of the decay rates of some correlation functions with the predictions of the two treatments leads to a general conclusion: the Harvey-Wegener treatment determines the initial rate, while the long-time behavior is dominated by the rigid-body relaxation time. As an example of application to a specific biological macromolecule, we present a simulation of an immunoglobulin molecule, showing how Brownian Dynamics can be used to predict rotational and internal dynamics. Another typical example is myosin. Literature data of hydrodynamic properties of whole myosin and the myosin rod are compared with predictions from the Harvey-Wegener and rigid-body treatments. The present situation of the problem on myosin flexibility is analyzed, and some indications are given for future experimental and simulation work.

Biopolymers↗
PubMed1992

Hydrodynamics in vein of Galen malformations.

Forty-three patients with vein of Galen aneurysmal malformations (VGAM) referred to us for endovascular treatment between 1985 and 1990 and 335 additional cases published in the literature were reviewed with particular attention to the presence of ventricular enlargement and outcome after shunting. Hydrocephalus was the second most frequent symptom (46.8%); it is more frequent in infants (73%) than in children, adults (30%) or neonates (15%). Of the patients reported in the literature, 17.9% had undergone shunting. Within the shunted population there was an overall morbidity of 41% and a mortality of 10% (especially in the infant group). In our series 17 patients (39.5%) were shunted and a significant difference in the clinical outcome was noted between the shunted and the nonshunted group. Of the nonshunted patients, 66.6% were free of any neurological deficit or mental retardation and fewer than 5% presented with significant mental retardation. On the other hand, only 33.3% of the shunted patients had a favorable outcome and more than 15% developed significant mental retardation. Among the various causes of hydrocephalus in patients with VGAMs, such as obstruction of the aqueduct, subarachnoid hemorrhage, or ex vacuo hydrocephalus, high venous pressure may be of particular importance. In this article a physiopathological interpretation of the hydrodynamics in VGAMs is developed and a speculative explanation for CSF disorders related to ventricular shunting proposed. Treatment of hydrocephalus in VGAMs can be achieved through obliteration of the malformation or at least diminishing the venous pressure; surgical ventricular shunting does not have to be the first treatment of hydrodynamic disorders associated with VGAMs, especially in infants.

Brain Damage, Chronic↗
PubMed1988

Physicochemical characterization of gamma-crystallins from bovine lens--hydrodynamic and biochemical properties.

A detailed hydrodynamic study has been made on the gamma-crystallin of the bovine lens. Sedimentation study indicates that gamma-crystallin shows a nearly gaussian peak throughout the course of sedimentation at high speed, using a synthetic boundary cell. The diffusion and sedimentation coefficients are 10.3 x 10(-7) cm2/sec and 2.51 S, respectively. The weight-average molecular weight of the unfractionated gamma-crystallin calculated from sedimentation equilibrium is 21,800. The four major subfractions of gamma-crystallin show similar hydrodynamic properties with an intrinsic viscosity of 2.50 ml/g and a Stokes radius of 21 A. The distinct electrophoretic mobilities exhibited by the four subfractions show gel-concentration dependence and similar slopes in the Ferguson plot, indicative of being charge isomers of the same molecular species. Amino acid analysis of these four subfractions corroborated the conclusions that these gamma-crystallin polypeptides are closely related and comprise a multigene family of crystallins. Based on the sedimentation and intrinsic viscosity data, gamma-crystallin can be modeled as a prolate ellipsoid with an axial ratio of approximately 3.0 and a hydration factor of 0.27 g water per gram protein. The circular dichroism data for gamma-crystallins showed a minimum at about 217 nm, characteristic of a beta-sheet conformation. These structural characteristics are in good accord with those derived from X-ray diffraction data for gamma-crystallin II.

Amino Acid Sequence↗
PubMed1984

Effect of cranioplasty on cerebrospinal fluid hydrodynamics in patients with the syndrome of the trephined.

Forty patients with cranial bone defects after craniectomy underwent extensive cerebrospinal fluid (CSF) hydrodynamic investigations by means of a CSF infusion test before and after cranioplasty. The results of these investigations were related to the clinical signs of the patients before and after cranioplasty and to the size and location of the skull bone defect. Twenty-two patients were considered to have "the syndrome of the trephined" (ST). The remaining patients were either free of symptoms or had symptoms not related to ST. CSF hydrodynamic variables that were changed before and normalized after cranioplasty include the following: Resting pressure, sagittal sinus pressure, buffer volume, elastance at resting pressure and pulse variations at resting pressure. The changes were statistically significant mainly in ST patients who were also relieved of their symptoms after cranioplasty.

Adult↗
PubMed1988

A mathematical study of human intracranial hydrodynamics. Part 2--Simulation of clinical tests.

The mathematical model of human intracranial hydrodynamics proposed in a previous paper is here used to simulate the results of some dynamical tests of great clinical and physiological value and to analyze the blood flow pattern in the intracranial human basal arteries (especially in the internal carotid artery). Peak to peak amplitude of the blood flow waveform in the intracranial basal arteries, computed through the model, shows a significant increase at intracranial pressure levels above 50-60 mmHg, in accordance with recent experimental data. Moreover, diastolic blood flow appears to be largely sensitive to intracranial pressure changes during severe intracranial hypertension, whereas systolic blood flow is only slightly affected in this condition. The response of intracranial pressure to typical saline injection (volume-pressure response, steady state infusion and bolus injection tests) and to an abrupt obstruction in the extracranial venous drainage pathway is also well reproduced by the model. Finally, alterations in these responses, due to changes in some significant intracranial hydrodynamical parameters (i.e., the intracranial elastance coefficient and CSF outflow resistance) are presented.

Carotid Artery, Internal↗
PubMed1988

Relations between hydrodynamic and mechanical properties of a sphere.

Important hydrodynamic characteristics of a heart chamber are isometric pressures at operating distensions, compliances at operating distensions, and wall-displacement resistances at operating distensions. Wall-displacement resistance is the pressure change relative to the rate of cavity-volume change causing the pressure change. Another chamber characteristic is the dependence of wall-displacement resistance on distension. Equations were derived showing dependences of hydrodynamic characteristics on dimensions and mechanical properties of a thick-walled sphere whose inner and outer fibers are comparably stretched at operating distensions. Equations could be arranged so as to identify midwall elements whose enclosed volumes best express distension. If the appropriate midwall volume is used to express distension, then the fractional change of any intensive variable (pressure, apparent average stress, apparent midwall stress, wall-displacement resistance, volume-normalized wall-displacement resistance, apparent average viscosity, apparent midwall viscosity) depends simply on a property of the wall elements and fractional distension change or fractional rate of distension change. The apparent average stress or viscosity calculated with the assumption that the quantity is uniformly distributed is virtually the value of the quantity in the midwall element. These principles should be useful in characterizing normal and abnormal myocardium in situ.

Heart↗
PubMed1998

Role of hydrodynamic shear on activity and structure of proteins.

Proteins are important products used in industry. They may be enzymes which catalyze different reactions or they may be required for their biological activities as hormones, growth factors or therapeutics. During production and recovery, proteins are subjected to fluid forces which arise due to operations such as stirring, pumping and centrifugation. The resulting hydrodynamic shear forces may cause damage to the large molecular weight proteins, resulting in denaturation and inactivation of the protein. This is a major concern as it affects the overall efficiency of protein recovery and final yield of the product. A considerable amount of research has been devoted to studying the effects of hydrodynamic shear stress on proteins, especially with respect to the enzymes. Enzymes are subjected to shear stresses during their production in fermentors, during isolation and purification steps in downstream operations and also during their use in enzyme reactors, especially if stirred reactors are employed to perform enzyme catalysed reactions. The present review discusses the effects of fluid shear stress on proteins including enzymes. A brief description on deactivation has been included in order to understand the effect of shear on the deactivation kinetics of proteins. The model systems used to subject proteins to shear and some unit operations during protein processing or use wherein they are exposed to shear stresses have also been presented. The significance of shear effects in designing bioprocesses involving shear sensitive biocatalysts as well as suggestions for future work have also been given.

Chemical Precipitation↗
PubMed2003

Percutaneous hydrodynamic thrombectomy for femoral arterial thrombosis after arterial catheterization.

We report on a 3-year-old boy in whom a complete occlusive thrombus in the right femoral artery was removed rapidly and successfully using a hydrodynamic thrombectomy catheter. There was no bleeding complication, reocclusion, vascular injury, or loss of motor or sensory function. Hydrodynamic thrombectomy can be an important part of the treatment of thrombosis in children.

Angiography↗
PubMed1999

Linking Sediment Biofilms, Hydrodynamics, and River Bed Clogging: Evidence from a Large River.

> Abstract We investigated possible effects of the hydrodynamics at the water/sediment interface on river bed biofilms within the reservoir Freudenau (Vienna, Austria) of the Danube River during the period 1996/97. Two study sites (OBB and SSF) that differed in the magnitude of surface/subsurface water exchange were selected and intersite comparisons revealed higher organic matter, bacterial cell numbers, and esterase activity in SSF with lower horizontal outflow. Concentrations of colloidal carbohydrates and uronic acids were unaffected by hydrodynamics. The relative contribution of uronic acids to bulk colloidal carbohydrates was higher in the low-flow site SSF. The distribution patterns of this relative contribution generally matched the subsurface flow pattern. Shortly after impoundment in March 1996 and along with decreased surface flow velocity, maximal biofilm carbohydrate exopolymers concurred with minimal esterase activity in OBB. We hypothesize that this inverse relationship is due to increased diffusional resistance within the exopolymer biofilm matrix that reduces mass transfer and hydrolytic activity. These results, to our knowledge, are the first evidence for microbial participation in the clogging of a large river bed. Biofilm-associated organic carbon increased significantly by a factor of approximately 3.3 to 4.4 with progressive clogging as determined by the sediment leakage coefficient, which increased approximately 3.8 times. Concomitantly, with ongoing clogging, esterase activity exhibited increasingly higher values at the interface relatively to deeper sediment layers, which translates into steeper depth gradients. Furthermore, minimal inflow from the surface water into the river bed along with steepest esterase gradients concurred with a senescent benthic algal bloom. This suggests an important role for algae in clogging. Either algae obstruct voids mechanically, or their exudates fuel heterotrophic bacteria that in turn are involved in clogging processes. However, our data do not allow unequivocal differentiation between biogenic and physical clogging mechanisms.

Journal Article↗
PubMed2004

Hydrodynamic effects in fast AFM single-molecule force measurements.

Atomic force microscopy (AFM) allows the critical forces that unfold single proteins and rupture individual receptor-ligand bonds to be measured. To derive the shape of the energy landscape, the dynamic strength of the system is probed at different force loading rates. This is usually achieved by varying the pulling speed between a few nm/s and a few microm/s, although for a more complete investigation of the kinetic properties higher speeds are desirable. Above 10 microm/s, the hydrodynamic drag force acting on the AFM cantilever reaches the same order of magnitude as the molecular forces. This has limited the maximum pulling speed in AFM single-molecule force spectroscopy experiments. Here, we present an approach for considering these hydrodynamic effects, thereby allowing a correct evaluation of AFM force measurements recorded over an extended range of pulling speeds (and thus loading rates). To support and illustrate our theoretical considerations, we experimentally evaluated the mechanical unfolding of a multi-domain protein recorded at 30 microm/s pulling speed.

Algorithms↗
PubMed1997

Automated hydrodynamic modelling of a complex between a human IgE fragment (Fc epsilon 3-4) and the IgE high affinity receptor Fc epsilon RI alpha-chain.

The binding of IgE to its high affinity receptor Fc epsilon RI plays an important role in the allergic response. The interaction between soluble Fc epsilon RI alpha-chain (sFc epsilon RI alpha) and Fc epsilon 3-4, a fragment of IgE consisting of the C epsilon 3 and C epsilon 4 heavy chain constant domains, has been studied using analytical ultracentrifugation (Keown et al. this volume). Here we describe the development of a simple automated hydrodynamic modelling technique and its application to this interaction. This procedure utilises sphere models of the two molecules and performs an automated systematic translational search of sFc epsilon RI alpha relative to Fc epsilon 3-4. The result of this is the generation of 40,359 individual models of how the receptor can be placed relative to Fc epsilon 3-4. These are then assessed for consistency by comparing the sedimentation coefficients generated for the models to the experimentally determined sedimentation coefficients, and are displayed graphically to show allowed and disallowed complexes. From this analysis, it is clear that the complex between sFc epsilon RI alpha and Fc epsilon 3-4 is compact, with the most elongated models being excluded. In addition, sFc epsilon RI alpha appears not to interact with the C-terminal end of Fc epsilon 3-4, and probably binds either to the sides or face, observations which are consistent with other experimental data on the Fc epsilon RI alpha/IgE interaction. Automated hydrodynamic modelling also has the potential to be used for other interactions, providing a simple way of looking at a large number of models, and making rigorous studies of interacting components more feasible.

Automation↗