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PubMed2002

Kinematics and hydrodynamics of an invertebrate undulatory swimmer: the damsel-fly larva.

The kinematics and hydrodynamics of free-swimming larvae of Enallagma cyathigerum were investigated using videography combined with a simple wake visualisation technique (tracer dyes). Damsel-fly larvae are undulatory swimmers with two distinct styles of movement: 'slow' swimming, in which body undulation is assisted by paddling of the legs, and 'fast' swimming, in which the legs are inactive. In both cases, the wake consists of discrete ring vortices shed from the caudal fin at the end of each half-stroke. The vortices propagate away from the mid-line, alternately to one side of the body then the other, at an angle of 67 degrees from dead aft. There is no aft-flowing jet such as that observed in the wakes of continuously swimming fish that use caudal fin propulsion. The estimated momentum within the vortices, and the resultant thrust on the body are in tolerable agreement with calculations based on the large-amplitude bulk momentum model of fish locomotion. However, the drag on the body is not known, so it cannot be concluded with certainty that a force balance exists. The agreement between experiment and prediction gives confidence to the idea that most, if not all, of the vorticity generated by the swimming larva is located within the observable wake elements.

Animals↗

PubMed1975

Applicability of hydrodynamic analyses of spermatozoan motion.

This paper investigates the applicability of a simple hydrodynamics theory due to Gray & Hancock (1955), and extended by Brokaw (1970), to the analysis of the motions of sea urchin, rabbit, and bull spermatozoa. Experimental procedures for filming and analysing the swimming motions are presented. A detailed discussion of the agreement between the experimental and theoretical results is given, and the limitations of the theory in analysing the motion of mammalian spermatozoa are discussed.

Animals↗

PubMed2001

In vitro release of metoclopramide from hydrophobic matrix tablets. influence of hydrodynamic conditions on kinetic release parameters.

There has been growing interest in the subject of drug delivery and the design and evaluation of controlled-release systems. The simplest way to control the release of an active agent is to disperse it in an inert polymeric matrix. Controlled-release systems are of interest because they are technologically simple, relatively cheap, and practically unaffected by physiological changes. In this study, a new matrix system was formed by an active principle, metoclopramide hydrochloride, scattered into a biocompatible hydrophobic polymerical mesh, polyamide 12, to achieve sustained and controlled delivery of metoclopramide hydrochloride. This research was conducted to investigate the in vitro drug release behavior from these new inert polymeric matrix tablets. The drug release process was investigated both experimentally and by means of mathematical models. Different models were applied for the evaluation of drug release data. On the basis of our results, a biexponential equation was proposed, Q=Qfast(1)(1 - e(-Kfast t)) + Qslow(2)(1 - e(-Kslow t)), in an attempt to explain the mechanism responsible for the release process. Additionally, the influence of the experimental conditions of the dissolution devices, such as rate of flow and pH of dissolution medium, on the parameters that characterize the release mechanism was studied, and it was found that the main factor was the hydrodynamic condition of rate of flow.

Algorithms↗

PubMed1995

[Visco-elasticity of transplanted menisci in rabbits. A correlative histological and hydrodynamical studies].

The purpose of this study is to investigate the visco-elasticity, histology and hydrodynamics of transplanted menisci following transplantation. Experiments to examine visco-elasticity are performed on 30 rabbits, to examine NMR on 20 rabbits and on 12 rabbits respectively for histological study. Under intravenous general anesthesia the medial meniscus was completely resected, and a cryopreserved allograft meniscus was implanted. The rabbits are sacrificed 1, 2, 3 and 5 months post-operatively, and the implanted menisci are removed for examination. One month after surgery, dynamic stiffness is markedly lower in the implanted menisci than in the controls. Thereafter, it gradually increased. Three months after surgery, there is no significant difference between the transplanted menisci and the controls. However the value of tan delta which serves as indicator of dynamic visco-elasticity is larger in the implanted menisci than in the control specimens throughout the experiment. The water content was higher in the transplanted menisci throughout. The 1H-NMR relaxation time (T2) was markedly prolonged 1 month post-operatively, but shortened rapidly after that. Nevertheless, it is still longer than in the control specimen after 5 months. In the histological study, no chondrocytes are observed in the transplanted menisci, and the matrix was poorly stained with Eosin 1 month after surgery. Thereafter, granulomatous tissues proliferated in the menisci, and by 5 months after surgery, the chondrocytes appear to be almost normal. However, matrix was weakly stained with Eosin. These results suggest that the interactions between high molecular weight matrix and water in transplanted menisci are different from those in normal menisci, and that therefore the viscosity of transplanted menisci is higher.

Animals↗

PubMed2004

Static and dynamic removal rates of a new hydrodynamic polishing tool.

A new tool for hydrodynamic radial polishing, HyDra, allows for the local polishing of optical surfaces with a controllable wear rate. The results of the removal rate for different polisher types and sizes, applied air pressures for slurry expulsion, and tool height with respect to the working surface, are reported. We present a numerical analysis of the volumetric removal rate for the dynamic experiments as well as a comparison with a similar technique.

Journal Article↗

PubMed2004

Characterization of the overall rotational diffusion of a protein from 15N relaxation measurements and hydrodynamic calculations.

In this chapter, we discuss experimental and theoretical methods for characterizing the overall rotational diffusion of molecules in solution. The methods are illustrated for the B3 domain of protein G, a small protein with rotational anisotropy of Dpar/Dperp = 1.4. The rotational diffusion tensor of the protein is determined directly from 15N relaxation measurements. The experimental data are treated assuming various possible models for the overall tumbling: isotropic, axially symmetric, and fully anisotropic, and the results of these analyses are compared to determine an adequate diffusion model for the protein. These experimentally derived characteristics of the protein are compared with the results of theoretical calculations of the diffusion tensor using various hydrodynamic models, to find optimal models and parameter sets for theoretical predictions. We also derive model-free characteristics of internal backbone motions in the protein, to show that different models for the overall motion can result in significantly different pictures of motion. This emphasizes the necessity of accurately characterizing the overall tumbling of a molecule to determine its local dynamics.

Binding Sites↗

PubMed2006

Structural dynamics of the acetylcholine binding protein: hydrodynamic and fluorescence anisotropy decay analyses.

Recently, several crystal structures have become available for the acetylcholine binding protein (AChBP), a soluble nicotinic receptor extracellular domain (ECD) surrogate in its unliganded state, as well as in complex with agonists and antagonists. In these studies we sought to better understand how the dynamic receptor ECD surrogate from Lymnaea stagnalis behaves in solution, with and without ligand present. To accomplish this, we studied first the overall size and shape of the macromolecule, using hydrodynamic (sedimentation) techniques, and how these parameters were perturbed by the binding of various ligands. Analysis of sedimentation and frictional coefficients indicated that bound alpha-bungarotoxin (a three-fingered peptide toxin) is not oriented as a rigid body extending radially from the cylinder of the protein but, rather, that the toxin has inherent segmental flexibility such that it has a limited effect on the frictional coefficient of the pentamer. These results were supported by anisotropy decay studies of segmental motion of the toxin when free in solution and bound to AChBP. We selected the C-loop of AChBP, a region where ligand-elicited changes in conformation are substantial, and studied neighboring regions at higher resolution in terms of alpha-carbon backbone flexibility by decay of fluorescence anisotropy. Several single cysteine substitutions were labeled selectively with the fluorescent probe MTS-4-fluorescein. The covalently conjugated mutants, at two sites on the C-loop (S182C, D194C), and one on the opposing side of the subunit interface (Y164C), revealed similar alpha-carbon backbone flexibility with no ligand present but underwent distinctive changes in backbone mobility after ligand binding. At the sites we studied on the C-loop, agonists always segregated together in terms of their effects on backbone mobility; however antagonists did not reveal a similarly conserved pattern. At Y164C, however, we did observe segregating effects on backbone flexibility between agonists and antagonists. As a structural and functional surrogate of the nicotinic acetylcholine receptor, the AChBP reveals ligand-mediated changes in conformation, mimicking that of the receptor.

Animals↗

PubMed2004

The hydrodynamic radii of macromolecules and their effect on red blood cell aggregation.

The effects of nonionic polymers on human red blood cell (RBC) aggregation were investigated. The hydrodynamic radius (Rh) of individual samples of dextran, polyvinylpyrrolidone, and polyoxyethylene over a range of molecular weights (1,500-2,000,000) were calculated from their intrinsic viscosities using the Einstein viscosity relation and directly measured by quasi-elastic light scattering, and the effect of each polymer sample on RBC aggregation was studied by nephelometry and low-shear viscometry. For all three polymers, despite their different structures, samples with Rh <4 nm were found to inhibit aggregation, whereas those with Rh >4 nm enhanced aggregation. Inhibition increased with Rh and was maximal at approximately 3 nm; above 4 nm the pro-aggregant effect increased with Rh. For comparison, the Rh of 12 plasma proteins were calculated from literature values of intrinsic viscosity or diffusion coefficient. Each protein known to promote RBC aggregation had Rh >4 nm, whereas those with Rh <4 nm either inhibited or had no effect on aggregation. These results suggest that the influence of a nonionic polymer or plasma protein on RBC aggregation is simply a consequence of its size in an aqueous environment, and that the specific type of macromolecule is of minor importance.

Blood Viscosity↗

PubMed2006

Pulsed laser microbeam-induced cell lysis: time-resolved imaging and analysis of hydrodynamic effects.

Time-resolved imaging was used to examine the use of pulsed laser microbeam irradiation to produce cell lysis. Lysis was accomplished through the delivery of 6 ns, lambda=532 nm laser pulses via a 40x, 0.8 NA objective to a location 10 microm above confluent monolayers of PtK2 cells. The process dynamics were examined at cell surface densities of 600 and 1000 cells/mm2 and pulse energies corresponding to 0.7x, 1x, 2x, and 3x the threshold for plasma formation. The cell lysis process was imaged at times of 0.5 ns to 50 micros after laser pulse delivery and revealed the processes of plasma formation, pressure wave propagation, and cavitation bubble dynamics. Cavitation bubble expansion was the primary agent of cell lysis with the zone of lysed cells fully established within 600 ns of laser pulse delivery. The spatial extent of cell lysis increased with pulse energy but decreased with cell surface density. Hydrodynamic analysis indicated that cells subject to transient shear stresses in excess of a critical value were lysed while cells exposed to lower shear stresses remained adherent and viable. This critical shear stress is independent of laser pulse energy and varied from approximately 60-85 kPa for cell monolayers cultured at a density of 600 cells/mm2 to approximately 180-220 kPa for a surface density of 1000 cells/mm2. The implications for single cell lysis and microsurgery are discussed.

Animals↗

PubMed2003

In vitro assessment of the plaque-removing ability of hydrodynamic shear forces produced beyond the bristles by 2 electric toothbrushes.

BACKGROUND: The aim of this study was to compare the efficacy of interproximal plaque removal by the hydrodynamic shear forces produced by 2 electric toothbrushes (toothbrush A, Sonicare Plus and toothbrush B, Braun Oral B) using laboratory-grown plaque biofilms in an anatomically correct in vitro brushing model. METHODS: In vitro oral biofilms were grown in a constant-depth film fermenter on hydroxyapatite (HA) discs. Brushing experiments were conducted in a specially constructed machine designed to simulate the brushing of interproximal plaque between mandibular molar teeth; the bristles of the toothbrush did not make contact with the biofilm at any time. The load force between the brushes and teeth were in accordance with typical use and an exposure time of 5 seconds was used throughout. The efficacy of brushing was assessed by enumeration of the percentage of viable bacteria removed from the HA discs. These experiments were conducted with the electronic effect of the toothbrushes either activated or inactivated. RESULTS: Activation of toothbrush A significantly (P = 0.004) increased the median percentage of bacteria removed from 0.47% to 48.45%. Likewise, activation of toothbrush B significantly (P = 0.015) increased the median percentage of bacteria removed from 2.85% to 15.86%. The median percentage of plaque bacteria removed by the active toothbrush A was significantly (P = 0.009) greater than that removed by toothbrush B in this model system. CONCLUSION: These data imply that toothbrush A would be more effective than toothbrush B at removing interproximal dental plaque in vivo.

Adult↗

PubMed2004

Counting and behavior of an individual fluorescent molecule without hydrodynamic flow, immobilization, or photon count statistics.

Many theoretical models of molecular interactions, biochemical and chemical reactions are described on the single-molecule level, although our knowledge about the biochemical/chemical structure and dynamics primarily originates from the investigation of many-molecule systems. At present, there are four experimental platforms to observe the movement and the behavior of single fluorescent molecules: wide-field epi-illumination, near-field optical scanning, and laser scanning confocal and multiphoton microscopy. The platforms are combined with analytical methods such as fluorescence resonance energy transfer (FRET), fluorescence auto-or two-color cross-correlation spectroscopy (FCS), fluorescence polarizing anisotropy, fluorescence quenching and fluorescence lifetime measurements. The original contribution focuses on counting and characterization of freely diffusing single molecules in a single-phase like a solution or a membrane without hydrodynamic flow, immobilization or burst size analysis of intensity traces. This can be achieved, for example, by Fluorescence auto- or two-color cross-Correlation Spectroscopy as demonstrated in this original article. Three criteria (Földes-Papp (2002) Pteridines, 13, 73-82; Földes-Papp et al. (2004a) J. Immunol. Meth., 286, 1-11; Földes-Papp et al. (2004b) J. Immunol. Meth., 286, 13-20) are discussed for performing continuous measurements with one and the same single (individual) molecule, freely diffusing in a solution or a membrane, from sub-milliseconds up to severals hours. The 'algorithms' developed for single-molecule fluorescence detection are called the 'selfsame single-fluorescent-molecule regime'. An interesting application of the results found is in the field of immunology. The application of the theory to experimental results shows that the theory is consistent with the experiments. The exposition of the novel ideas on Single (Solution)-Phase Single-Molecule Fluorescence auto- or two-color cross-Correlation Spectroscopy (SPSM-FCS) are comprehensively presented. As technology continues to improve, the limits of what FCS/FCCS is being asked to do are concomitantly pushed.

Fluorescence↗

PubMedDate not supplied

Perilymphatic pressure in the cat. Description of a new method for study of inner ear hydrodynamics.

Continuous recordings of the perilymphatic (Pp), cerebrospinal fluid (PCSF), central venous (PCV) and arterial (PA) pressures have been performed on anesthetized cats. The perilymphatic space was reached by an extraural approach that leaves the ear canal and middle ear intact. A conical canal was drilled into the temporal bone down to the vestibule. The position of the canal was later confirmed histologically. A small, threaded, metallic cannula was screwed into the bone. For pressure measurements Millar microtip transducers were used, thus giving minimum measurement volume displacement. The mean PP and PCSF were found to be equal, whereas the maximum pressure during expiration was significantly higher in the CSF. not affected by the given anesthetics. Ligation of the external jugular veins had a minor and temporary effect on the PP and PCSF. The method is considered to be suitable for studies on the inner ear hydrodynamics as well as for audiophysiological measurements with an intact middle ear transmission system.

Animals↗

PubMed1983

The Björk-Shiley and Ionescu-Shiley heart valve prostheses. In vitro comparison of their hydrodynamic performance in the mitral position.

Shiley Scientific Inc., are now manufacturing six types of prosthetic heart valves. There are four different models of the Björk-Shiley and two versions of the Ionescu-Shiley pericardial heart valve. The Björk-Shiley valves are those with a spherical disc, 60 degrees and 70 degrees opening convexo-concave discs, and the latest monostrut model. The Ionescu-Shiley valves are the original titanium stent model and the latest Delrin stent low profile model. The hydrodynamic performance of these valves in the mitral position all having a tissue annulus diameter of 29 mm, has been measured. Tests were performed in a pulse duplicator simulating sinus rhythm at heart rates of 60, 80 and 120 beats per minute (BPM) with a stroke volume (SV) between 69 and 73 ml and at a heart rate of 200 BPM with SV between 27 and 34 ml. The latter test condition simulates a situation of supraventricular tachycardia. Mean transmitral pressure, regurgitation, and transmitral energy loss for each valve under each set of conditions were compared. All the Björk-Shiley valves were tested in two orientations with the major flow orifice oriented either anteriorly (A) or posteriorly (P). For all valves, it was found that the major contribution to the total transmitral energy loss, most apparent at 200 BPM, was caused by regurgitation and that at 60, 80 and 200 BPM, the forward flow phase contributed only a small amount to the total energy loss. The small intentional leakage across the Björk-Shiley valves is minor compared to closing regurgitation but is a major contributor to transmitral energy loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Output↗

PubMed1985

Effect of the skull and dura on neural axis pressure-volume relationships and CSF hydrodynamics.

The pressure-volume index (PVI) technique of bolus manipulation of cerebrospinal fluid (CSF) was used to measure changes of neural axis volume buffering-capacity and CSF dynamics produced by different conditions of the skull and dura. Twenty-eight cats were studied in the intact state, after bilateral craniectomy, and with the dura opened. At each stage of altering the container of the brain, the following parameters were obtained: steady-state intracranial pressure (ICP), sagittal sinus venous pressure, PVI, and the resistance to the absorption of CSF. The resistance to absorption of CSF was determined using both the bolus injection and the continuous infusion of fluid. After craniectomy, PVI increased from 0.76 +/- 0.04 to 1.3 +/- 0.07 ml (+/- standard error of the mean) (p less than 0.001) and increased further to 3.6 +/- 0.17 ml (p less than 0.001) after opening the dura. The resistance to absorption of CSF (Ro), determined by bolus injection, decreased after craniectomy from 91.3 +/- 7.5 to 56.3 +/- 6.2 mm Hg/ml/min (p less than 0.001) and decreased further to 8.9 +/- 0.66 mm Hg/ml/min (p less than 0.001) after opening the dura. Although resistance determined by constant infusion was similar, results were dependent on the rate of infusion. Despite these changes of resistance and PVI, steady-state ICP and sagittal sinus venous pressure were similar in all three conditions of the skull and dura. These studies indicate that changes of the container of the brain affect pressure-volume relationships within the neural axis. However, the changes of resistance to absorption of CSF are in a direction that preserves a steady-state hydrodynamic equilibrium.

Absorption↗

PubMed1984

Hydrodynamic and mechanical aspects of endothelial permeability.

The passive transport of water through the endothelial cell layer junctions is considered from the standpoint of hydrodynamic theories based on ultrastructural information. The local geometry of tight junctions based on molecular level forces and elastic membrane properties has been modeled and leads to estimates of the hydraulic resistance of the clefts. It is shown that the large resistance measured experimentally can be accounted for in this model. The transport of large macromolecules via vesicles which diffuse across the endothelial cell has been developed, but recent experimental data do not appear to support this mechanism as a primary pathway. Fused vesicles forming an open channel appear to be rare. Leaky junctions, such as around dying endothelial cells or produced by cytoskeletal changes within the cells, may be important in control of endothelial permeability. Another kind of model is a fiber matrix model of the endocapillary layer, extending into the intercellular clefts which can also account for the molecular seiving properties of the endothelial cell layer but may produce a large resistance to water flux.

Biological Transport↗

PubMed1984

Macromolecular architecture and hydrodynamic properties of human cervical mucins.

Cervical mucus glycoproteins (mucins) were extracted by using slow stirring in 6M-guanidinium chloride supplemented with proteinase inhibitors. Subsequent purification was achieved by isopycnic density-gradient centrifugation in CsCl/guanidinium chloride. The whole mucins (Mr 10 X 10(6) - 15 X 10(6)) were degraded into subunits (Mr 2 X 10(6) - 3 X 10(6)) by reduction. Trypsin digestion of subunits afforded glycopeptides (T-domains) with Mr 0.4 X 10(6). The relationship between the intrinsic viscosity and Mr for the whole mucins and the fragments suggests that cervical mucins are linear flexible macromolecules. This view is supported by hydrodynamic data.

Cervix Mucus↗

PubMed1989

Hydrodynamics of arterial branching--the effect of arterial branching on distal blood supply.

A study was conducted to investigate the hydrodynamics of branching flow in relation to the blood supply to the basal part of the brain. A series of measurements of the branching loss-coefficients under laminar steady flow were conducted using model branches with various geometries, and the effect of branching on blood supply to distal areas was described using a lumped-parameter model of the vascular structure. It was revealed that in the blood circulation, branching loss is important where a small artery divides off with a large branching angle from a large trunk. It was also indicated that the effect of such branching on the distal blood supply might become more significant when the peripheral resistance is reduced, thereby increasing the blood velocity in the trunk.

Animals↗

PubMedDate not supplied

Gardner's hydrodynamic theory of syringomyelia revisited.

Several theories have been put forth to explain the pathogenesis of syringomyelia, the formation of longitudinal, fluid-filled cavities within the spinal cord. Chief among them is Gardner's hydrodynamic theory, widely accepted for more than two decades. Gardner attributed the genesis of syringomyelia to craniospinal pressure differentials in the setting of fourth ventricular outlet obstruction; these differentials favor cerebrospinal fluid shifts from the fourth ventricle of the brain through the central canal of the spinal cord. Gardner's theory has been questioned, and several alternative theories of syringomyelia have been proposed. Physiological data and new information from magnetic resonance imaging support many of Gardner's concepts; however, a more comprehensive elucidation of the pathophysiologic mechanisms of syringomyelia requires incorporating facets of the other theories. We propose a unified theory of the pathogenesis of syringomyelia based on recent experience with magnetic resonance imaging, and on elements of other current theories.

Cerebrospinal Fluid Pressure↗