Osmotic pressure control in response to a specific ion signal at physiological temperature using a molecular recognition ion gating membrane

A molecular recognition gating ion membrane was prepared by graft copolymerization of N-isopropylacrylamide and benzo[18]crown-6-acrylamide onto the pore surface of porous polyethylene film. This membrane captured Ba2+ with its crown ether receptors and generated osmotic pressure in response to Ba2+ autonomously and reversibly. However, the membrane never generated osmotic pressure in response to Ca2+. In addition, the concentration gradient of both the ion and other solute such as dextran could be used as the driving force; using a dextran concentration gradient, we can control the critical concentration and the duration time of the osmosis response.     

The effect of membrane potential on the development of chemical osmotic pressure in compacted clay

When clay soils are subjected to salt concentration gradients, various interrelated processes come into play. It is known that chemical osmosis induces a water flow and that a membrane potential difference develops that counteracts diffusive flow of solutes and osmotic flow of water. In this paper, we present the results of experiments on the influence of membrane potential on chemical osmotic flow and diffusion of solutes and we show how we are able to derive the membrane potential value from theory. Moreover, the simultaneous development of water pressure, salt concentration and membrane potential difference are simulated using a model for combined chemico-electroosmosis in clays. A new method for short-circuiting the clay sample is employed to assess the influence of electrical effects on flow of water and transport of solutes.     

Molecular dynamics simulations of osmosis and reverse osmosis in solutions

Computer simulation studies using the method of molecular dynamics have been carried out to investigate osmosis and reverse osmosis in solutions separated by semi-permeable membranes. The method has been used to study the dynamic approach to equilibrium in such systems from their initial nonequilibrium state. In addition density profiles of both the solute and solvent molecules have been investigated, especially near the walls for adsorption effects. Finally the diffusion coefficients and osmotic pressure have also been measured.Our results show both osmosis and reverse osmosis, as well as a smooth transition between the two when either the solution concentration is changed, or the density (pressure) difference between the solvent and solution compartments is varied. We believe this new method can be used to improve our understanding of these two important phenomena at the molecular level.     

Osmotic behavior of a Nafion membrane in methanol-water electrolyte solutions

In this paper, an experimental study was carried out in order to investigate the osmotic transport of methanol-water electrolyte solutions through a Nafion membrane. The experimental data indicated that the Nafion membrane showed the typical anomalous osmotic behavior of charged membranes. The influence of some relevant parameters, such as electrolyte concentration difference, weight fraction of methanol on solution, and nature of cation was considered. The results showed that the osmotic volume flow was decreased with the presence of methanol on solvent, but did not alter the anomalous osmotic behavior of the membrane.     

Differential sorption in viscoelastic fluids

The diffusion of organic solvents in concentrated polymer solutions often deviates from the predictions of Fick's second law, especially when the solution is in the glassy state; such behavior is called anomalous or non-Fickian. This paper analyzes the one-dimensional sorption of a solvent into a concentrated polymer solution under a small driving force. The treatment includes the effect of an entanglement network on the process as postulated by Thomas and Windle. The deformation of the entanglement network during sorption creates a normal stress on the solvent equivalent to an osmotic pressure. Including the osmotic pressure gradient in the driving force for solvent diffusion leads to a linear, third-order partial differential equation for solvent concentration distributions. By evaluating the physical constants in the theory for the system methyl acetate/poly(methyl methacrylate) at 30°C the treatment is shown to predict the anomalous characteristics found experimentally.     

Tumor vascular area correlates with photosensitizer uptake: analysis of verteporfin microvascular delivery in the Dunning rat prostate tumor

The parameters that limit supply of photosensitizer to the cancer cells in a solid tumor were systematically analyzed with the use of microvascular transport modeling and histology data from frozen sections. In particular, the vascular permeability transport coefficient and the effective interstitial diffusion coefficient were quantified for Verteporfin-for-Injection delivery of benzoporphyrin derivative (BPD). Orthotopic tumors had higher permeability and diffusion coefficients (Pd = 0.036 microm/s and D = 1.6 microm(2)/s, respectively) as compared to subcutaneously grown tumors (Pd = 0.025 microm/s and D = 0.9 microm2/s, respectively), likely due to the fact that the vessel patterns are more homogeneous orthotopically. In general, large intersubject and intratumor variability exist in the verteporfin concentration, in the range of 25% in plasma concentration and in the range of 20% for tissue concentrations, predominantly due to these microregional variations in transport. However, the average individual uptake of photosensitizer in tumor tissue was only correlated to the total vascular area within the tumor (R2 = 64.1%, P < 0.001). The data are consistent with a view that microregional variation in the vascular permeability and interstitial diffusion rate contribute the spatial heterogeneity observed in verteporfin uptake, but that average supply to the tissue is limited by the total area of perfused blood vessels. This study presents a method to systematically analyze micro-heterogeneity as well as possible methods to increase delivery and homogeneity of photosensitizer within tumor tissue.     

Optimal strategy to model the electrodialytic recovery of a strong electrolyte

In this work, mostly Nernst–Planck derived relationships were used to simulate the electrodialytic recovery of a strong electrolyte, namely sodium chloride. To this end, it was set up a five-step experimental procedure consisting of zero-current leaching, osmosis, and dialysis, electro-osmosis, desalination, current–voltage and validation tests. The contribution of leaching and solute diffusion across the electro-membranes was found to be negligible with respect to the electro-migration. On the contrary, solvent diffusion tended to be important as the solute concentration difference at the membrane sides increased or current density was reduced. The electro-osmosis and desalination tests yielded the water and solute transport numbers.

By performing several limiting current tests at different solute concentrations and feed flow rates using anionic or cationic membranes, it was possible to determine simultaneously the limiting current intensity, the ratio of the differences between the counter-ion transport numbers in the anion- and cation-exchange membranes and solution, the overall resistance of the electro-membranes, the effective membrane surface area, and the solute mass transfer coefficient.

All these process and design parameters allowed the time course of the solute concentration in the concentrating (C) and diluting (D) compartments, as well as the voltage applied to the electrodes, to be reconstructed quite accurately without any further correction factors. The capability of the above parameters to simulate the performance of the electrodialysis (ED) unit was checked by resorting to a few validation tests, that were performed in quite different operating conditions from those used in the training tests, that is by filling tank C with a low feed volume with a low solute concentration and applying a constant current intensity to magnify the effect of electro-osmosis or by changing the current intensity step-wisely to simulate the continuous-mode operation of a multistage ED unit. Finally, a parameter sensitivity analysis made the different contribution of the process and design parameters to be assessed, thus yielding a straightforward procedure for designing or optimising accurately ED desalination units up to a final salt concentration of about 1.7 kmol m⁻³.     

Gradient generation by an osmotic pump and the behavior of human mesenchymal stem cells under the fetal bovine serum concentration gradient

This paper describes a method to generate a concentration gradient using an osmosis-driven pump, without the need for bulky peripheral devices, such as an electric syringe pump or a pneumatic pump. By the osmosis, the flow in the microfluidic channel can be controlled even to a very slow speed (nanolitre scale), which enables its application to generate the stable and wide (width = 4 mm) concentration gradient profile, even within a short flow path. A computational simulation was also performed to predict the local distribution of the solute concentration and velocity-pressure profile in the microfluidic chip. The performance of the osmosis-driven pump was evaluated by culturing human mesenchymal stem cells within the concentration gradient of fetal bovine serum. The effects of the gradient on attachment, viability and morphology of the cells were analyzed and quantified. The cell density in a higher serum concentration region was twice greater than that in the pure culture media. The compact, cost-effective, self-powered and osmosis-based gradient generation system can be useful for biomedical and chemical applications.     

Influence of polymer structure inhomogeneity on oxygen quenching of phenanthrene phosphorescence in poly(methyl methacrylate)

Decay kinetics of phenanthrene phosphorescence in atactic poly(methyl methacrylate) have been studied at 130–170 K in the presence of dissolved oxygen. The kinetics show anomalous behavior and cannot be described in terms of homogeneous diffusion of oxygen. Analysis of the dependence of the kinetics on oxygen concentration shows that such behavior is well accounted for by a polychromatic model assuming a dispersion of diffusion coefficients due to the inhomogeneity of the polymer structure. Possible errors in determining the diffusion coefficient from the phosphorescence quantum yield on the assumption of homogeneous diffusion are discussed. © 1992 John Wiley & Sons, Inc.     

Concentration effects on distribution of macromolecules in small pores

The interactions between two particles and between one particle and a rigid boundary are examined to study the effect of particle concentration on partitioning, stress and flow in microporous media. Because the particle—particle and particle—wall interactions occur over comparable length scales, their effects are not additive and lead to non-uniform particle concentration stress (“surface pressure”) in the vicinity of the boundary. A particle concentration gradient parallel to the boundary creates a gradient in surface pressure which drives a viscous flow of the solvent toward regions of higher concentration. Such flows are termed “osmosis”, and the effect of particle interactions is to reduce the osmotic velocity.     

Drug transport in responding lipid membranes can be regulated by an external osmotic gradient

In this paper, we demonstrate, for the first time, how an external osmotic gradient can be used to regulate diffusion of solutes across a lipid membrane. We present experimental and theoretical studies of the transport of different solutes across a monoolein membrane in the presence of an external osmotic gradient. The osmotic gradient introduces phase transformations in the membrane, and it causes nonlinear transport behavior. The external gradient can thus act as a kind of switch for diffusive transport in the skin and in controlled release drug formulations.     

Separation of aromatic substances from aqueous solutions using a reverse osmosis technique with thin,dense cellulose acetate membranes

Investigations were made of the water flux rate and rejection characteristics of aromatic substances in aqueous solutions using a thin, dense cellulose acetate membrane in reverse osmosis experiments. The aromatic substances used were phenol, aniline, hydroquinone and p-chlorophenol. The permeate became more enriched in aromatic compounds as compared to the feed solution as the water content of the membrane increased. By considering both the effects of pressure on the chemical potential of a component and the contribution of viscous flow to the overall transport of that component in the hydrated membrane, a theoretical relationship was developed to predict the negative solute rejection of the membrane. Based on this proposed theory, the permeability coefficients of water and organic solute were estimated from experimental solute rejection data, including negative values. The permeability coefficients of components were in good agreement with previously established correlations in measurements of partition and diffusion coefficients.     

Electrohydrodynamic transport of non‐symmetric electrolyte through porous wall of a microtube

Transport of salt through the wall of porous microtube is relevant in various physiological microcirculation systems. Transport phenomena based modeling of such system is undertaken in the present study considering a combined driving force consisting of pressure gradient and external electric field. Transport of salt is modeled in two domains, in the flow conduit and in the pores of porous wall of the microtube. The solute transport in the microtube is presented by convective‐diffusive mass balance and it is solved using integral method under the framework of boundary layer analysis. The wall of the microtube is considered to be consisting of series of straight parallel cylindrical pores with charged inner surface. The solute transport through the pores is considered to be composed of diffusive, convective and electric potential gradient governed by Nernst‐Planck equation. Transport in the microtube and pores is coupled through the osmotic pressure model for the solvent and Donnan equilibrium distribution for the solute. The simulated results agree remarkably well with the experimental data conducted by in‐house experimental set up. The charge density of the porous wall is estimated through the minimization of errors involved between the experimental and simulated data for different operating conditions.     

Modulation of drug transport properties by multicomponent diffusion in surfactant aqueous solutions

Diffusion coefficients of drug compounds are crucial parameters used for modeling transport processes. Interestingly, diffusion of a solute can be generated not only by its own concentration gradient but also by concentration gradients of other solutes. This phenomenon is known as multicomponent diffusion. A multicomponent diffusion study on drug-surfactant-water ternary mixtures is reported here. Specifically, high-precision Rayleigh interferometry was used to determine multicomponent diffusion coefficients for the hydrocortisone-tyloxapol-water system at 25 degrees C. For comparison, diffusion measurements by dynamic light scattering were also performed. In addition, drug solubility was measured as a function of tyloxapol concentration, and drug-surfactant thermodynamic interactions using the two-phase partitioning model were characterized. The diffusion results are in agreement with a proposed coupled multicomponent diffusion model for ternary mixtures relevant to nonionic drug and surfactant molecules. Theoretical examination of diffusion-based drug transport in the presence of concentration gradients of micelles shows that drug fluxes and drug concentration profiles are significantly affected by coupled multicomponent diffusion. This work provides guidance for the development of accurate models of diffusion-based controlled release in multicomponent systems and for the applications of micelle concentration gradients to the modulation of diffusion-based drug transport.     

Oscillations with a long periodical time observed in solute transport by diffusion combined with convection through a single hollow-fiber membrane

Solute transport by diffusion combined with convection through a single hollow-fiber membrane fixed on an axis of a circular tube was studied precisely. Purified water and an aqueous solution of a solute were fed at constant flow rates into the circular tube and the lumen of the membrane, respectively, and oscillations with a long periodical time were observed in the concentration of solution discharged from the lumen. Results obtained with varying experimental conditions (different solutes, membranes and flow rates at the lumen inlet and outlet) suggest that the oscillations are related to solute transport caused by convection flow through the membranes.     

Forward Osmosis Membranes for Water Reclamation

This review addressed the fundamental principles, advantages and challenges of forward osmosis (FO) membrane processes. FO is receiving more and more research attractions because it can concurrently produce clean water with low energy input and generate hydraulic energy (pressure retarded osmosis). FO typically requires zero or low hydraulic driving pressure, therefore the fouling potential of the FO membranes is much lower than conventional pressure-driven membrane processes. However, concentration polarization (CP), especially the internal CP significantly reduces the effective osmotic pressure across the FO membrane, the major driving force for the filtration process. As a result, innovative FO membrane materials like electrospun nanofibers have been explored to make low tortuosity, high porosity, and thin FO membranes with a high rejection rate of solutes and low or zero diffusion of the draw solute. The orientation of the FO membrane with active layer-facing-feed solution has less fouling than active layer-facing-draw solution. In addition, to further decrease the fouling potential, a hydrophilic and more negatively charged membrane is preferred when filtration of natural organic matter (NOM) or alginate in the absence of multivalent cations.     

Effect of carrier concentration on the facilitated oxygen transport in a polymer membrane

Facilitated transport of oxygen in a solid Polymer membrane containing cobaltporphyrin (CoP) which carries oxygen specifically and reversibly, leads to permselectivity of oxygen against nitrogen in the membrane. The increase in concentration of the CoP carrier is expected to enhance the oxygen transport. The membranes of poly(octylmethacrylate-co-vinylimidazole) containing 0.8 ～ 10 wt% CoP were prepared, and the effects of the CoP-concentration on the transport and the diffusion constants of oxygen are studied. Although the induction period before the steady state of oxygen permeation was prolonged with the CoP concentration in the polymer membrane, the glass transition temperature (T_g) of the membrane was increased and the diffusion constants of oxygen were decreased with the CoP concentration to yield unexpected reduction of the oxygen permeation in the highly CoP loaded membrane.     

Osmotic flow in charged membranes

Summary The osmotic flow through a porous charged membrane separating electrolyte solutions of different concentrations but at a constant temperature is studied theoretically, using a capillary model for the membrane. The assumptions used are that theDebye-Hückel approximation is applicable for the ion distribution in the double layer formed near the fixed charges on the capillary wall, and that the thickness of the double layer is much smaller than the capillary radius. The steady state solutions of the differential equations derived are obtained subject to the external conditions that the concentrations of the outer solutions are maintained constant and no pressure head is applied across the membrane. It is shown that the volume rate of osmotic flow is the sum of two terms, one arising from the fact that the membrane is electrically charged and the other being independent of the membrane charge and thus observable commonly both in charged and uncharged membranes. The former corresponds to whatGrim andSollner have referred to as the true anomalous osmosis. The plot of this electric part of osmosis against the logarithm of the concentration of one outer solution gives a bell-shaped curve, when the concentration ratio of the outer solutions is fixed. This theoretical curve follows well theGrim-Sollner data of the true anomalous osmosis for various aqueous electrolyte solutions. The true anomalous osmosis is an electro-osmotic flow caused by the electric field which is set up inside the membrane so that no net transport of electric charge occurs from one solution compartment to the other. The dependence of the electroosmotic coefficient on salt concentration is responsible for the characteristic behavior of the osmotic flow rates through charged membranes.

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Zusammenfassung Der osmotische Flu\ durch eine poröse geladene Membran, die die Elektrolytlösungen verschiedener Konzentrationen, doch von konstanter Temperatur trennt, wird theoretisch untersucht unter Anwendung eines Kapillarmodells für die Membran. Die verwendeten Annahmen sind die, da\Debye-Hückel-NÄherung für die Ionenverteilung in der Doppelschicht, die sich in der NÄhe der fixierten Ladungen an der Kapillarwand bildet, verwendet werden kann und da\ die Dicke dieser Doppelschicht viel kleiner als der Kapillarradius ist. Die stationÄren Lösungen der abgeleiteten Differentialgleichungen werden unter der Bedingung erhalten, da\ die Konzentrationen der Äu\eren Lösungen konstant sind und keine Druckdifferenz über die Membran existiert. Es wird gezeigt, da\ die Volumendurchtritts-geschwindigkeit des osmotischen Flusses aus zwei Anteilen besteht, der eine auf Grund der Tatsache, da\ die Membran elektrisch geladen ist, der andere unabhÄngig von der Membranladung, und da\ gewöhnlich beide in geladenen und ungeladenen Membranen beobachtet werden können. Erstere entspricht dem, wasGrim undSollner als wahre anomale Osmose bezeichnen. Die Auftragung dieses elektrischen Teils gegen den Logarithmus der Konzentration der einen Äu\eren Lösung gibt eine Glockenkurve, wenn das KonzentrationsverhÄltnis der Äu\eren Lösungen fixiert ist. Diese theoretische Kurve folgt gut den Ergebnissen vonGrim-Sollner für die wahre anomale Osmose für verschiedene wÄ\rige Elektrolytlösungen. Die wahre anomale Osmose ist ein elektro-osmotischer Strom auf Grund des elektrischen Feldes, das innerhalb der Membran aufgebaut wird, so da\ kein Nettotransport elektrischer Ladungen von einer Lösung zur anderen stattfindet. Die AbhÄngigkeit des elektro-osmotischen Koeffizienten von der Salzkonzentration ist für das charakteristische Verhalten osmotischer Flie\geschwindigkeiten durch die geladene Membran verantwortlich.

     

Concentration Polarization of Interacting Solute Particles in Cross-Flow Membrane Filtration

A theoretical approach for predicting the influence of interparticle interactions on concentration polarization and the ensuing permeate flux decline during cross-flow membrane filtration of charged solute particles is presented. The Ornstein-Zernike integral equation is solved using appropriate closures corresponding to hard-spherical and long-range solute-solute interactions to predict the radial distribution function of the solute particles in a concentrated solution (dispersion). Two properties of the solution, namely the osmotic pressure and the diffusion coefficient, are determined on the basis of the radial distribution function at different solute concentrations. Incorporation of the concentration dependence of these two properties in the concentration polarization model comprising the convective-diffusion equation and the osmotic-pressure governed permeate flux equation leads to the coupled prediction of the solute concentration profile and the local permeate flux. The approach leads to a direct quantitative incorporation of solute-solute interactions in the framework of a standard theory of concentration polarization. The developed model is used to study the effects of ionic strength and electrostatic potential on the variations of solute diffusivity and osmotic pressure. Finally, the combined influence of these two properties on the permeate flux decline behavior during cross-flow membrane filtration of charged solute particles is predicted. Copyright 1999 Academic Press.