1: Magnetic Particles: Preparation, Properties and Applications: M. Ozaki. 2: Maghemite (gamma-Fe2O3): A Versatile Magnetic Colloidal Material C.J. Serna, M.P. Morales. 3: Dynamics of Adsorption and Oxidation of Organic Molecules on Illuminated Titanium Dioxide Particles Immersed in Water M.A. Blesa, R.J. Candal, S.A. Bilmes. 4: Colloidal Aggregation in Two-Dimensions A. Moncho-Jorda, F. Martinez-Lopez, M.A. Cabrerizo-Vilchez, R. Hidalgo Alvarez, M. Quesada-PMerez. 5: Kinetics of Particle and Protein Adsorption Z. Adamczyk.

Surface and Colloid Science

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

/pdf/effects-of-disturbed-flow-on-vascular-endothelium-m0k6yyxo71.pdf

Effects of Disturbed Flow on Vascular Endothelium: Pathophysiological Basis and Clinical Perspectives

Surface-tension-driven flows and, in particular, their tendency to decay spontaneously into drops have long fascinated naturalists, the earliest systematic experiments dating back to the beginning of the 19th century. Linear stability theory governs the onset of breakup and was developed by Rayleigh, Plateau, and Maxwell. However, only recently has attention turned to the nonlinear behavior in the vicinity of the singular point where a drop separates. The increased attention is due to a number of recent and increasingly refined experiments, as well as to a host of technological applications, ranging from printing to mixing and fiber spinning. The description of drop separation becomes possible because jet motion turns out to be effectively governed by one-dimensional equations, which still contain most of the richness of the original dynamics. In addition, an attraction for physicists lies in the fact that the separation singularity is governed by universal scaling laws, which constitute an asymptotic solution of the Navier-Stokes equation before and after breakup. The Navier-Stokes equation is thus continued uniquely through the singularity. At high viscosities, a series of noise-driven instabilities has been observed, which are a nested superposition of singularities of the same universal form. At low viscosities, there is rich scaling behavior in addition to aesthetically pleasing breakup patterns driven by capillary waves. The author reviews the theoretical development of this field alongside recent experimental work, and outlines unsolved problems.

/pdf/nonlinear-dynamics-and-breakup-of-free-surface-flows-2oabav2z0g.pdf

Nonlinear dynamics and breakup of free-surface flows

Jets, ie collimated streams of matter, occur from the microscale up to the large-scale structure of the universe Our focus will be mostly on surface tension effects, which result from the cohesive properties of liquids Paradoxically, cohesive forces promote the breakup of jets, widely encountered in nature, technology and basic science, for example in nuclear fission, DNA sampling, medical diagnostics, sprays, agricultural irrigation and jet engine technology Liquid jets thus serve as a paradigm for free-surface motion, hydrodynamic instability and singularity formation leading to drop breakup In addition to their practical usefulness, jets are an ideal probe for liquid properties, such as surface tension, viscosity or non-Newtonian rheology They also arise from the last but one topology change of liquid masses bursting into sprays Jet dynamics are sensitive to the turbulent or thermal excitation of the fluid, as well as to the surrounding gas or fluid medium The aim of this review is to provide a unified description of the fundamental and the technological aspects of these subjects

Physics of liquid jets

Discrete particle simulation of particulate systems: Theoretical developments

Uptake studies with labeled tracer molecules have convincingly demonstrated that the endothelial cell layer is the principal resistance barrier in the transport of macromolecules across the artery wall [1,2]. In vivo experiments with pig aorta have shown that there are localized regions of enhanced macromolecule permeability [3]. These regions which stain more readily with protein binding Evans Blue dye than the unstained “white” areas have also been shown to exhibit a significant increase in cell turnover [4]. The authors have hypothesized that the localized increase in uptake observed in these in vivo experiments is due to one of the following mechanisms: (a) increase in permeability of the endothelial junctions, (b) changes in the vesicular transport rate and (c) increase in endothelial permeability due to enhanced cell turnover. The likelihood of each of these mechanisms will be examined with the aid of mathematical models and supporting laboratory experiments described by our collegue Dr. Shu Chien in a companion paper on this program.

The Endothelium as a Mediating Factor in Transport Across the Arterial Wall

In this two part study we shall quantitatively explose the hypothesis that fully open 20 nm intercellular clefts between widenly scattered mitotic endithelial cell are main pathway of macromolecules through endothelial. In the resent analysis, the authors heve quantitatively demonstrated that this open junction pathway could also account for the localized differences in measured macromolecular permeability in mammalian arteries in so called blue areas. In part 1 of the study we shall present a model to predict the short time labeling of the leaky junction and the local subendothelial space in the first few minutes following the introduction of the tracer molecules in order to guide experiment. In part 2 of the study, we shall present a model to describe the longer time labeling of arterial media and the transiant approch to study state behavior. We have solved the mathematical problem and obtained calculating results for different parameters.

On the transient diffusion of macromolecules through leaky junctions and their subendothelial spread - model and observations

Using porous hollow fiber membranes, systems/methods for continuously synthesizing polymer-coated particles by anti-solvent crystallization are provided. The disclosed systems/methods provide for synthesis of polymer-coated drug particles/crystals from solutions of the polymer and the drug particles in suspension by exposing the solution to an anti-solvent through a porous hollow fiber device. A feed solution of a coating polymer with suspended drug particles can be exposed to an anti-solvent through hollow fiber pores, thereby causing the polymer to precipitate on and coat the drug particles. In addition, a feed solution of a coating polymer with drug in solution can be exposed to an anti-solvent through hollow fiber pores, thereby causing the drug to crystallize from the solution and the polymer to precipitate/coat the drug. Results indicate that a uniformly coated, free-flowing product may be developed in this advantageous porous hollow fiber anti-solvent crystallization method. The coated drug particles can be used for controlled release of the drug, and the molecule and the crystal structure are not affected by the process.

Porous Hollow Fiber Anti-Solvent Crystallization-Based Continuous Method of Polymer Coating on Submicron and Nanoparticles

Experiments concerned with the rate of fall of two prolate spheroids (needle-like objects) in close proximity to each other are described in this paper. Quantitative agreement with S. Wakiya's theoretical predictions is obtained for the case in which two prolate spheroids are settling, one above the other, in the direction perpendicular to their axis of symmetry and for the case in which two prolate spheroids are settling end to end in the same horizontal plane in the direction perpendicular to their axis of symmetry.



These experiments and this theoretical treatment apply only in the creeping motion region. At higher velocities, inertial effects would become significant.



On decrit dans ce travail des experiences sur la vilesse de chute de deux spheroides allonges (objets ressemblant a des aiguilles) qui sont proches l'un de l'autre. On obtient une concordance quantitative avec les predictions theoriques de S. Wakiya dans le cas ou deux spheroides allonges reposent l'un sur l'autre, dans une direction perpendiculaire a leur axe de symetrie, ainsi qui dans le cas ou deux spheroides allonges sont places bout a bout dans le meme plan horizontal, dans une direction perpendiculaire a leur axe de symetrie. Les dites experiences et theories ne s'appliquent que dans la region ou le mouvement est ascendant. A des velocites plus grandes, les effets d'inertie deviendraient notables.

Sedimentation of two prolate spheroids in close proximity

Much of the existing theory for the hydrodynamic interaction between particles or between particles and boundaries has been based on an iterative series solution technique usually referred to as the method of reflections. The mathematical difficulty with this technique, and with creeping motion flow in general, is that the fundamental solution for three-dimensional disturbances decays as 1 / r . Thus, an iterative series solution will converge very slowly for closely spaced particles and boundaries unless special measures are taken to treat the simultaneous interaction between boundaries in the lowest order, or generating terms of the series. In the past decade, integral equation, finite element, and boundary collocation methods have been introduced for treating strongly interacting particle and boundary problems at low Reynolds number. We first describe the advantages of each technique for different flow problems. The integral equation approach is the most efficient method for describing flow past an isolated body of arbitrary shape or the motion of a slender body near infinite planar boundaries. In this approach, the kernel of the integral equation is the solution for the Stokeslet plus Rotlet, which satisfies the no-slip boundary conditions on all other boundaries in the flow field. The finite element method has, thus far, only been used in periodic bounded axisymmetric flow problems such as an infinite chain of equally spaced particles moving along the center line of a circular cylinder. Techniques have not yet been developed for treating either threedimensional motions or flows of infinite extent that are not periodic. We will then describe the recent development of the third technique, the boundary collection method, for bounded and unbounded multidimensional flow problems. This technique is, at present, the only available method for treating the strong interaction between closely spaced nonslender objects and boundaries. Since the application of the boundary collocation technique depends on an orthogonal natural coordinate expansion for each object, the technique is limited to spheroidal bodies when other boundaries are present. The principal difference between the integral equation method and the boundary collocation method for bounded flows is that, in the integral equation method, the fundamental singularity, or Green's function, used to construct the body must already satisfy the viscous flow boundary conditions for all other boundaries in the flow, while, in the boundary collocation method, the internal singularities

Robert Pfeffer

Papers

The Endothelium as a Mediating Factor in Transport Across the Arterial Wall

On the transient diffusion of macromolecules through leaky junctions and their subendothelial spread - model and observations

Porous Hollow Fiber Anti-Solvent Crystallization-Based Continuous Method of Polymer Coating on Submicron and Nanoparticles

Sedimentation of two prolate spheroids in close proximity

Strong interaction between particles and boundaries at low reynolds numbers