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PubMed2006

Exploring the evaluation of net charge, hydrodynamic size and shape of peptides through experimental electrophoretic mobilities obtained from CZE.

This work explores the validity of simple CZE models to analyze the electrophoretic mobilities of 102 peptides reported in literature. These models are based mainly on fundamental physicochemical theories providing analytical expressions amenable to relatively simple numerical analysis. Thus, the Linderstrøm-Lang capillary electrophoresis model (LLCEM) and its perturbed version (PLLCEM), proposed and applied previously to the CZE of globular proteins, are adapted and used here for peptides. Also the effects of pK-shifts on net charge, hydration and hydrodynamic size and shape of peptides are analyzed and discussed. Emphasis is placed on the fact that these parameters are physically coupled, and thus a variation in the net charge may produce an appreciable change in the hydrodynamic size of peptides. Within the framework of CZE, peptides may be assumed as having a hydrodynamic volume associated with either spherical or spheroidal particles. The effects on peptide net charge and hydrodynamic size, of electrostatic interaction between a pair of charged groups in the chain and electrical permitivitty around the peptide domain are studied. The predictions of the PLLCEM and LLCEM are in good agreement with results reported previously in the literature. Several limitations concerning these models and some needs for further research are also described.

Amino Acid Sequence↗
PubMed2006

Hydrodynamic compression of young and adult rat osteoblast-like cells on titanium fiber mesh.

Living bone cells are responsive to mechanical loading. Consequently, numerous in vitro models have been developed to examine the application of loading to cells. However, not all systems are suitable for the fibrous and porous three-dimensional materials, which are preferable for tissue repair purposes, or for the production of tissue engineering scaffolds. For three-dimensional applications, mechanical loading of cells with either fluid flow systems or hydrodynamic pressure systems has to be considered. Here, we aimed to evaluate the response of osteoblast-like cells to hydrodynamic compression, while growing in a three-dimensional titanium fiber mesh scaffolding material. For this purpose, a custom hydrodynamic compression chamber was built. Bone marrow cells were obtained from the femora of young (12-day-old) or old (1-year-old) rats, and precultured in the presence of dexamethasone and beta-glycerophosphate to achieve an osteoblast-like phenotype. Subsequently, cells were seeded onto the titanium mesh scaffolds, and subjected to hydrodynamic pressure, alternating between 0.3 to 5.0 MPa at 1 Hz, at 15-min intervals for a total of 60 min per day for up to 3 days. After pressurization, cell viability was checked. Afterward, DNA levels, alkaline phosphatase (ALP) activity, and extracellular calcium content were measured. Finally, all specimens were observed with scanning electron microscopy. Cell viability studies showed that the applied pressure was not harmful to the cells. Furthermore, we found that cells were able to detect the compression forces, because we did see evident effects on the cell numbers of the cells derived from old animals. However, there were no other changes in the cells under pressure. Finally, it was also noticeable that cells from old animals did not express ALP activity, but did show similar calcified extracellular matrix formation to the cells from young animals. In conclusion, the difference in DNA levels as reaction toward pressure, and the difference in ALP levels, suggest that the osteogenic properties of bone marrow-derived osteoblast-like cells are different with respect to the age of the donor.

Aging↗
PubMed1999

Hydrodynamic Instability of Liquid Films on Moving Fibers.

The stability of liquid films on moving fibers is studied with a focus on effects caused by film-solid adhesion interactions and hydrodynamic interactions between the film and the surrounding gas. We show that at high fiber velocities (large Reynolds numbers) the film-gas hydrodynamic interactions induce instability in films, which would, otherwise, be stabilized by the adhesion interactions at static conditions. Two types of unstable modes caused by hydrodynamic factors are found: the first corresponds to the Kelvin-Helmholtz waves induced by inertia effects; the second, induced by viscosity effects, is observed at smaller (yet still large) Reynolds numbers when the Kelvin-Helmholtz instability is suppressed. Linear stability analysis of the system of coupled hydrodynamic equations of film and gas flow is performed by the method of normal modes. We derive the general dispersion relation as an implicit equation with respect to the mode frequency. In the limit of vanishing fiber velocities, the obtained equation provides the dispersion equation for motionless fibers. The conditions of film stability and unstable modes are analyzed in terms of two dimensionless parameters, the adhesion factor, which quantifies the intensity of film-fiber interactions, and the Weber number, which quantifies the intensity of film-gas interactions. The Reynolds number determines the regions of validity of the inviscid and viscous regimes of film instability. The results are illustrated by estimates of the stability conditions for moving fibers in terms of the stability diagram, the critical film thickness, the fastest unstable mode, and the corresponding characteristic break-up time. Although the methods developed are applicable for any type of liquid-solid interaction, the estimates were made for the long-range van der Waals interactions. Practical applications include various technologies related to fabrication and chemical modifications of fibers and fiber products, e.g., spin finishing and lubrication. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Hydrodynamic Interactions and Mean Settling Velocity of Porous Particles in a Dilute Suspension.

A theoretical investigation is conducted to study hydrodynamic interactions among porous spheres under creeping flow conditions. The particles may differ in size and permeability. Based on the Brinkman equation governing the fluid flow inside the particle, the flow field, and the drag force and torque on the particle are calculated numerically using a boundary collocation method. The results show that the hydrodynamic interaction increases with decreasing permeability. An important feature is that unlike the singular force and torque for two touching identical impermeable spheres undergoing certain motions with planar symmetry, the force and torque always remain finite for the case of two porous spheres. Using the resulting hydrodynamic interactions, the average sedimentation velocity of porous spheres suspended in a bounded fluid is also evaluated to determine the leading order effect of the particle concentration. Because of weaker hydrodynamic interactions among porous spheres, the hindrance coefficient is smaller than that for impermeable particles. When the porous spheres carry charge, the hindrance effect is augmented by increasing the double layer thickness. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Effects of hydrodynamic and interfacial forces on plant cell suspension systems.

Plant cells are perceived to be sensitive to the hydrodynamic environment in conventional bioreactors. Heightened sensitivity, relative to most bacterial cultures, is frequently attributed to larger plant cell sizes, extensive vacuolization and aggregation patterns. Early studies of shear sensitivity focused on cell lysis and/or loss of viability. More recently, an extensive array of sub-lethal responses has been identified. A fuller understanding of these sub-lytic effects may assist in the optimization of large-scale cultivation conditions. This paper reviews recent work on the hydrodynamic shear sensitivity of plant cell systems, under cultivation conditions and in purpose-built shearing devices. The relevance of different approaches to the characterization of the intensity of a given hydrodynamic environment is discussed. Indicators of cell response to hydrodynamic stress are evaluated. The potential significance of cellular defense mechanisms, observed in response to mechanical stimulants, is identified.

Bioreactors↗
PubMed2000

Disorders of CSF hydrodynamics.

This article reviews the range of hydrodynamic disorders affecting the CSF circulation. Initially consideration is given to questions of definition and classification. A scheme for the practical, clinical analysis for the diagnosis of such disorders is then presented. The physiology and pathophysiology of the CSF circulation is reviewed, with particular emphasis on issues that remain unresolved. This provides a background to consideration of the adverse consequences of abnormal CSF hydrodynamics, again focusing on areas where further information is required. Methods of clinical investigation of CSF hydrodynamics are reviewed, followed by general considerations of treatment. Finally, each of the main, clinically important, forms of disordered CSF hydrodynamics is briefly considered, with particular emphasis, again, on areas where current knowledge is deficient. The conditions considered include hydrocephalus of various forms (childhood, adult, arrested, multi-compartment), infantile macrocephaly, arachnoid and glioependymal cysts, syringo- and hydromyelia, pseudotumour cerebri, impaired cranial venous outflow, altered CSF composition, shunt obstruction without ventricular enlargement and low-CSF-pressure states.

Adolescent↗
PubMed1990

Translational diffusion and intrinsic viscosity of globular proteins. Theoretical predictions using hydrated hydrodynamic models. Application to BPTI.

In this paper, we present a way to make hydrodynamic models of globular proteins, including the hydration shell associated with them in aqueous solutions. Theoretical calculations using these models are made in order to determine the hydrodynamic properties of these proteins, employing rigorous and approximate methods of calculation. These will be applied to the bovine pancreatic trypsin inhibitor, BPTI. Several hydrodynamic models are constructed: the A-model for the unhydrated protein BPTI and a set of H-models for hydrated protein with different hydration degrees. Theoretical results for the translational diffusion coefficient Dt and the intrinsic viscosity [eta] are obtained from different models. From the analysis of the A-model and hydrodynamic properties, there is not a clear assignation of an ellipsoidal shape to this protein molecule. An amount of approximately 0.5 g H2O/g protein could be assigned to the BPTI.

Animals↗
PubMed1993

A flow cytometric study of hydrodynamic damage to mammalian cells.

Flow cytometry has been used to study the mechanisms of damage to mammalian cells by hydrodynamic forces. Cell damage resulted from the stresses created both by bubble entrainment and by bubble bursting caused by vortex formation in highly agitated culture. Damage to the antigen molecules on the cell surface together with increasing leakage and passive transport were observed. Pluronic F-68 reduced the efflux of fluorescein out of cells suggesting the possibility of plugging damaged parts of the membrane or change in membrane molecular organisation. Surface-associated immunoglobulin molecules were also protected by Pluronic F-68. The loss of plasma membrane integrity was followed by the destruction of cytoplasmic matrix. The nuclei were last to be destroyed. The fraction of metabolically active cells was drastically decreased by the intense hydrodynamic forces. However the mitochondrial transmembrane potential, which is linked to the ATP requirements of cells was well as the mean cell size of the live cell population, remained unaffected by the stressful hydrodynamic conditions. F-Actin content peaked during the early exponential phase and declined during the mid and late exponential and death phases of batch culture. The increase of actin during exponential phase was faster in stationary culture than in agitated culture. The increase was associated with the proliferative rate. Furthermore, the response to hydrodynamic forces was not related either to cell size difference or to the stage in the cell cycle.

Actins↗
PubMed2006

Conditional gene modification in mouse liver using hydrodynamic delivery of plasmid DNA encoding Cre recombinase.

The success of Cre-mediated conditional gene targeting in liver of mice has until now depended on the generation of Cre recombinase transgenic mice or on viral-mediated transduction. Here, we sought to establish the feasibility of using hydrodynamic gene delivery of Cre recombinase into liver, using a ROSA26 EGFP mouse. The expression of EGFP and beta-galactosidase was exclusively detected in the liver of mice treated with hydrodynamic gene delivery of Cre recombinase, as assessed with fluorescence microscopy and X-Gal staining, respectively; Southern blotting also showed that Cre mediated recombination occurred specifically in the liver and not in other organs. The Cre mediated recombination reached about 61% of hepatocytes of mouse after repeated injection, as analyzed by flow cytometry. These results demonstrate that Cre recombinase can be transferred to the liver of mice through a simple hydrodynamic gene-delivery approach and can mediate efficient recombination in hepatocytes. Thus, hydrodynamic gene delivery of the Cre recombinase provides a valuable approach for Cre-loxP-mediated conditional gene modification in the liver of mice.

Animals↗
PubMed2000

Coupling of hydrodynamic and electric interactions in adsorption of colloidal particles.

The role of the coupling between hydrodynamic and electric interactions in adsorption of colloid particles is reviewed. First the general formulation of the problem of fluid motion connected with the macroscopic suspension flow as well as microscopic particle motion is presented together with the general description of the colloid particle adsorption. Then two limiting cases are considered: motion of uncharged particles and electric interactions of stationary particles. The theoretical consideration are supported by illustrative experimental results. Next the electrokinetic effects in particle adsorption process are considered and the theoretical background for the description of these effects is given. The effect of the electroviscous drag on the particle aggregation and adsorption kinetics is discussed. Also the electrokinetic lift force, which is an example of the non-linear electrokinetic effect, is considered and the possible implications on particle adsorption are examined. In the following part of the review the influence of electro-hydrodynamic coupling on the particle transport to the interface is considered. First the 'inverse salt effect' for the initial adsorption flux when the interface is not covered by adsorbed particles is examined. Then, the electro-hydrodynamic scattering effect which occurs when the interface is partially covered by particles is considered and its experimental evidence concerning the adsorption kinetics and the local structure of adsorbate is considered. Also a novel application of the scattering effect to measure interparticle forces the 'colloid particle collider' is presented and some experimental results obtained using this technique are shown. All results reported in this review suggest strong coupling of the hydrodynamic and electric forces and their pronounced influence on colloid particle adsorption.

Adsorption↗
PubMed2003

Effects of leptin gene expression in mice in vivo by electroporation and hydrodynamics-based gene delivery.

In vivo electroporation and hydrodynamics-based gene delivery were utilized to test the effect of leptin gene transfer on food intake, and body and fat weights of mice. Gene transfer of pVRmob by electroporation caused a significant reduction in body weight compared with the control counterpart (p<0.05), although a lesser effect was found in food intake, and the weights of interscapular brown and epididymal fat by electroporation. As might be expected, the hydrodynamics-based transfection method significantly reduced body weight over 1 week post-transfection (p<0.05). Furthermore, epididymal fat was decreased by 50% at 1 week after gene transfer (p<0.001). These results suggest that both electroporation and hydrodynamics-based gene delivery may be effective approaches for systemic delivery of recombinant leptin to the central nervous system, and that the efficiency of gene transfer in hydrodynamics-based gene delivery was markedly higher than that in electroporation at least within the first week after transfection.

Adipose Tissue↗
PubMed1997

Hydrodynamic effects and receptor interactions of platelets and their aggregates in linear shear flow.

We have modeled platelet aggregation in a linear shear flow by accounting for two body collision hydrodynamics, platelet activation and receptor biology. Considering platelets and their aggregates as unequal-sized spheres with DLVO interactions (psi(platelet) = -15 mV, Hamaker constant = 10(-19) J), detailed hydrodynamics provided the flow field around the colliding platelets. Trajectory calculations were performed to obtain the far upstream cross-sectional area and the particle flux through this area provided the collision frequency. Only a fraction of platelets brought together by a shearing fluid flow were held together if successfully bound by fibrinogen cross-bridging GPIIb/IIIa receptors on the platelet surfaces. This fraction was calculated by modeling receptor-mediated aggregation using the formalism of Bell (Bell, G. I. 1979. A theoretical model for adhesion between cells mediated by multivalent ligands. Cell Biophys. 1:133-147) where the forward rate of bond formation dictated aggregation during collision and was estimated from the diffusional limited rate of lateral association of receptors multiplied by an effectiveness factor, eta, to give an apparent rate. For a value of eta = 0.0178, we calculated the overall efficiency (including both receptor binding and hydrodynamics effects) for equal-sized platelets with 50,000 receptors/platelet to be 0.206 for G = 41.9 s(-1), 0.05 for G = 335 s(-1), and 0.0086 for G = 1920 s(-1), values which are in agreement with efficiencies determined from initial platelet singlet consumption rates in flow through a tube. From our analysis, we predict that bond formation proceeds at a rate of approximately 0.1925 bonds/microm2 per ms, which is approximately 50-fold slower than the diffusion limited rate of association. This value of eta is also consistent with a colloidal stability of unactivated platelets at low shear rates. Fibrinogen was calculated to mediate aggregation quite efficiently at low shear rates but not at high shear rates. Although secondary collisions (an orbitlike trajectory) form only a small fraction of the total number of collisions, they become important at high shear rates (>750 s(-1)), as these are the only collisions that provide enough time to result in successful aggregate formation mediated by fibrinogen. The overall method provides a hydrodynamic and receptor correction of the Smoluchowski collision kernel and gives a first estimate of eta for the fibrinogen-GPIIb/IIIa cross-bridging of platelets. We also predict that secondary collisions extend the shear rate range at which fibrinogen can mediate successful aggregation.

Adenosine Diphosphate↗
PubMed1999

Hydrodynamic properties of rigid particles: comparison of different modeling and computational procedures.

The hydrodynamic properties of rigid particles are calculated from models composed of spherical elements (beads) using theories developed by Kirkwood, Bloomfield, and their coworkers. Bead models have usually been built in such a way that the beads fill the volume occupied by the particles. Sometimes the beads are few and of varying sizes (bead models in the strict sense), and other times there are many small beads (filling models). Because hydrodynamic friction takes place at the molecular surface, another possibility is to use shell models, as originally proposed by Bloomfield. In this work, we have developed procedures to build models of the various kinds, and we describe the theory and methods for calculating their hydrodynamic properties, including approximate methods that may be needed to treat models with a very large number of elements. By combining the various possibilities of model building and hydrodynamic calculation, several strategies can be designed. We have made a quantitative comparison of the performance of the various strategies by applying them to some test cases, for which the properties are known a priori. We provide guidelines and computational tools for bead modeling.

Biophysical Phenomena↗
PubMed2002

The essential role of hydrodynamic shear force in the formation of biofilm and granular sludge.

Biofilm and granular sludge processes are promising biotechnology for wastewater treatment. The formation, structure and metabolism of immobilized microbial community are associated very closely with hydrodynamic shear force in reactors. Therefore, this paper attempts to review the essential role of shear force in the formation and performance of biofilm and granular sludge. More compact, stable and denser biofilms, aerobic and anaerobic granules form at relatively higher hydrodynamic shear force. It is clearly shown that shear force has significant influences on the structure, mass transfer, production of exopolysaccharides, metabolic/genetic behaviours of biofilms, aerobic and anaerobic granules. In an engineering sense, hydrodynamic shear force can be manipulated, as a control parameter, to enhance microbial granulation process. It can be concluded that the knowledge regarding the effects of hydrodynamic shear force on biofilms and granules is far from complete and much research is still needed to fully understand the relevant mechanisms. Some of these future research niches are therefore outlined.

Biofilms↗
PubMed2001

A unified picture of protein hydration: prediction of hydrodynamic properties from known structures.

Hydration is essential for the structural and functional integrity of globular proteins. How much hydration water is required for that integrity? A number of techniques such as X-ray diffraction, nuclear magnetic resonance (NMR) spectroscopy, calorimetry, infrared spectroscopy, and molecular dynamics (MD) simulations indicate that the hydration level is 0.3-0.5 g of water per gram of protein for medium sized proteins. Hydrodynamic properties, when accounted for by modeling proteins as ellipsoids, appear to give a wide range of hydration levels. In this paper we describe an alternative numerical technique for hydrodynamic calculations that takes account of the detailed protein structures. This is made possible by relating hydrodynamic properties (translational and rotational diffusion constants and intrinsic viscosity) to electrostatic properties (capacitance and polarizability). We show that the use of detailed protein structures in predicting hydrodynamic properties leads to hydration levels in agreement with other techniques. A unified picture of protein hydration emerges. There are preferred hydration sites around a protein surface. These sites are occupied nearly all the time, but by different water molecules at different times. Thus, though a given water molecule may have a very short residence time (approximately 100-500 ps from NMR spectroscopy and MD simulations) in a particular site, the site appears fully occupied in experiments in which time-averaged properties are measured.

Nuclear Magnetic Resonance, Biomolecular↗
PubMedDate not supplied

Influence of hydrodynamic conditions on biofilm behavior in a methanogenic inverse turbulent bed reactor.

This paper presents a study about the influence of gas velocity on a methanogenic biofilm in an inverse turbulent bed reactor. Experimental results indicate a dynamic response of the growing attached biomass to the changes of hydrodynamic conditions, mainly attrition constraints. Short but intensive increases of gas velocity (U(g)) are shown to induce more detachment than a high but constant gas flow rate. Hydrodynamic conditions control the composition of the growing biofilm in terms of cells and exocellular polymeric substances (EPS). The cell fraction within the biofilm (R(cell)) was found to be inversely proportional to the gas velocity. The specific activity expressed in methane production rate or COD removal rate is higher in biofilms formed under high hydrodynamic constraints. The control of the hydrodynamic conditions in a biofilm reactor should make it possible to obtain a resistant and active biofilm.

Bacteria, Anaerobic↗
PubMed2006

Ecological consequences of major hydrodynamic disturbances on coral reefs.

A recent tsunami and an apparent increase in the frequency of severe tropical storms underscore the need to understand and predict the ecological consequences of major hydrodynamic disturbances. Reef corals provide the habitat structure that sustains the high biodiversity of tropical reefs, and thus provide the foundation for the ecosystem goods and services that are critical to many tropical societies. Here we integrate predictions from oceanographic models with engineering theory, to predict the dislodgement of benthic reef corals during hydrodynamic disturbances. This generalizes earlier work, by incorporating colonies of any shape and by explicitly examining the effects of hydrodynamic gradients on coral assemblage structure. A field test shows that this model accurately predicts changes in the mechanical vulnerability of coral colonies, and thus their size and shape, with distance from the reef crest. This work provides a general framework for understanding and predicting the effects of hydrodynamic disturbances on coral reef communities; such disturbances have a major role in determining species zonation and coexistence on coral reefs, and are critical determinants of how coral assemblages will respond to changes in the frequency and intensity of tropical storms associated with a changing climate.

Animals↗
PubMed2002

Mechanism of hydrodynamic separation of biological objects in microchannel devices.

In this study, the separation mechanism employed in hydrodynamic chromatography in microchannel devices is analyzed. The main purpose of this work is to provide a methodology to develop a predictive model for hydrodynamic chromatography for biological macromolecules in microchannels and to assess the importance of various phenomenological coefficients. A theoretical model for the hydrodynamic chromatography of particles in a microchannel is investigated herein. A fully developed concentration profile for non-reactive particles in a microchannel was obtained to elucidate the hydrodynamic chromatography of these particles. The external forces acting on the particles considered in this model include the van der Waals attractive force, double-layer force as well as the gravitational force. The surface forces, such as van der Waals attractive force as well as the double-layer repulsive force, can either enhance or hinder the average velocity of the macromolecular particles. The average velocity of the particles decreases with the molecular radius because the van der Waals attractive force increases the concentration of the particles near the channel surface, which is the low-velocity region. The transport velocity of the particles is dominated by the gravity and the higher density enlarges the effect caused by gravity.

Chromatography, Liquid↗