Isotropic Membrane Research Articles

On the Role of Curved Membrane Nanodomains, and Passive and Active Skeleton Forces in the Determination of Cell Shape and Membrane Budding.

Biological membranes are composed of isotropic and anisotropic curved nanodomains. Anisotropic membrane components, such as Bin/Amphiphysin/Rvs (BAR) superfamily protein domains, could trigger/facilitate the growth of membrane tubular protrusions, while isotropic curved nanodomains may induce undulated (necklace-like) membrane protrusions. We review the role of isotropic and anisotropic membrane nanodomains in stability of tubular and undulated membrane structures generated or stabilized by cyto- or membrane-skeleton. We also describe the theory of spontaneous self-assembly of isotropic curved membrane nanodomains and derive the critical concentration above which the spontaneous necklace-like membrane protrusion growth is favorable. We show that the actin cytoskeleton growth inside the vesicle or cell can change its equilibrium shape, induce higher degree of segregation of membrane nanodomains or even alter the average orientation angle of anisotropic nanodomains such as BAR domains. These effects may indicate whether the actin cytoskeleton role is only to stabilize membrane protrusions or to generate them by stretching the vesicle membrane. Furthermore, we demonstrate that by taking into account the in-plane orientational ordering of anisotropic membrane nanodomains, direct interactions between them and the extrinsic (deviatoric) curvature elasticity, it is possible to explain the experimentally observed stability of oblate (discocyte) shapes of red blood cells in a broad interval of cell reduced volume. Finally, we present results of numerical calculations and Monte-Carlo simulations which indicate that the active forces of membrane skeleton and cytoskeleton applied to plasma membrane may considerably influence cell shape and membrane budding.

Rayleigh–Plateau instability of anisotropic interfaces. Part 1. An analytical and numerical study of fluid interfaces

Abstract

Minimizing isotropic and deviatoric membrane energy - An unifying formation mechanism of different cellular membrane nanovesicle types.

Tiny membrane-enclosed cellular fragments that can mediate interactions between cells and organisms have recently become a subject of increasing attention. In this work the mechanism of formation of cell membrane nanovesicles (CNVs) was studied experimentally and theoretically. CNVs were isolated by centrifugation and washing of blood cells and observed by optical microscopy and scanning electron microscopy. The shape of the biological membrane in the budding process, as observed in phospholipid vesicles, in erythrocytes and in CNVs, was described by an unifying model. Taking the mean curvature h and the curvature deviator d of the membrane surface as the relevant parameters, the shape and the distribution of membrane constituents were determined theoretically by minimization of membrane free energy. Considering these results and previous results on vesiculation of red blood cells it was interpreted that the budding processes may lead to formation of different types of CNVs as regards the compartment (exo/endovesicles), shape (spherical/tubular/torocytic) and composition (enriched/depleted in particular kinds of molecules). It was concluded that the specificity of pinched off nanovesicles derives from the shape of the membrane constituents and not primarily from their chemical identity, which explains evidences on great heterogeneity of isolated extracellular vesicles with respect to composition.

A review of methods for the removal of penicillins from water

Penicillins (PENs) are β-lactam antibiotics with significant environmental toxicology. This review aimed to synthesise the research efforts on the removal of PENs via a variety of separation, degradation and biological processes. It was observed that isotropic microporous microfiltration membranes are not effective for rejecting PENs, due to their large uniform pore size distribution. Researchers favoured the application of Nanofiltration membrane and adsorption as separation technologies. Carbon-based adsorbents were the most efficient class of adsorbents for PENs removal from water. Lewis acid-base interactions, hydrogen bonding, electrostatic attraction and π – π interactions were the main adsorption mechanisms. Generally, the ultraviolet irradiation assisted-advanced oxidation processes (AOPs) and the Fenton-like processes outperformed the electrochemical and ultrasonic assisted-AOPs for PENs degradation. AOPs must be incorporated with other methods of treatment to minimise potential costs in terms of energy, time, equipment, and chemicals. For biological processes for PENs removal, anaerobic treatment processes were observed to be more efficient for the removal of PENs than aerobic processes. With the exception of microfiltration and electrocoagulation, most other processes were found to be effective for the removal of PENs from water, albeit with some disadvantages. From the review, it can be surmised that there has been great research progress on the subject and many new findings have been obtained in recent times though there is still much work to be done.

Modelling of frictionless Signorini problem for a linear elastic membrane shell

ABSTRACT The purpose of this paper is the study of the asymptotic modeling of a linearly thin elastic isotropic membrane shell which is subjected to frictionless contact with a rigid obstacle on part of the boundary. Using the formal asymptotic expansions method, we obtain a two dimensional Signorini membrane shell model, then we justify the result by convergence theorem.

High performance isotropic polyethersulfone membranes for heavy oil-in-water emulsion separation

Isotropic polyethersulfone (PES) membrane for separation of oil-in-water nanoemulsion was successfully developed using non-solvent vapor-induced phase separation (VIPS). The surface and structural properties of the fabricated PES membranes were thoroughly characterized using various techniques. The membrane separation performance was evaluated in terms of permeate flux, oil rejection, antifouling capability, and water flux recovery. Remarkably improved surface hydrophilicity for isotropic PES membrane (contact angle, CA = 39°) compared to anisotropic PES membrane (CA = 70°), resulting in superior pure water permeance, attaining 4721 L/h⋅m2⋅bar at operating pressure of 0.5 bar. The isotropic PES membrane achieved superior crude oil-in-water nanoemulsion separation (permeance of 713 L/h⋅m2⋅bar and 100% rejection) at oil concentration of 1 g/L. At extremely high oil concentration of 50 g/L, the PES membrane was not completely fouled and showed permeance of 65 L/h⋅m2⋅bar and 98.2% rejection. Moreover, the flux recovery of the fouled isotropic PES membrane exceeded 59.5% over three subsequent cycles of filtration and back-washing with water. Overall, this study might provide substantial guidance for large-scale manufacturing and application of isotropic PES membrane in treating practically challenging emulsified oil-in-water nanoemulsion under harsh conditions.

Об одной термодинамически согласованной модели разбухания глинистого сланца

Модифицированный вариант линейной теории пороупругости, описываемый тремя упругими параметрами, применяется к математическому моделированию сланцевого разбухания с водным электролитом. Предполагается, что сланец ведет себя как изотропная идеальная ионная мембрана, и в этом случае разбухание зависит только от полного напряжения и от химического потенциала воды в порах горной породы. Получена формула для коэффициента Пуассона, выражающаяся тремя упругими параметрами, физическими плотностями насыщенной жидкостью пористой среды, а также коэффициентом пористости. Показано, что коэффициент диффузии является функцией коэффициента межфазного трения (проницаемости) и обратно пропорционален коэффициенту пористости. Получены формулы для анализа плоской деформации вокруг ствола скважины. A modified version of the linear poroelasticity theory described by three elastic parameters is applied to the mathematical modeling of shale swelling with an aqueous electrolyte. It is assumed that the shale behaves as an isotropic ideal ionic membrane, and in this case, swelling depends only on the total stress and on the chemical water potential in pores of the rock. A formula is obtained for the Poisson coefficient in terms of three elastic parameters, the physical densities of the saturated fluid of the porous medium, and the porosity coefficient. It is shown that the diffusion coefficient is a function of the coefficient of interfacial friction (permeability) and is inversely proportional to the coefficient of porosity. The formulas for the flat strain analysis around the wellbore were obtained.

A unified adaptive approach for membrane structures: Form finding and large deflection isogeometric analysis

Different from large deflection analyses of plates and shells, for analysis of an isotropic membrane structure a form finding procedure is first performed to find the new geometry of membrane. With this new geometry, large deflection analysis is conducted and the membrane works in a pure membrane state. In the conventionally numerical approaches for analysis of membranes, form finding and large deflection analysis are performed separately and quite complexly by different techniques. To overcome this difficulty, this paper proposes a unified adaptive approach (UAA) for analysis of membranes in the framework of isogeometric analysis (IGA). In UAA, both form finding and large deflection analysis are simultaneously and simply performed based on a modified Riks (M-R) nonlinear solver. As another advantage of UAA, it can be applied to various types of structures without any limitation or modification. For membranes, the proposed approach performs both form finding and large deflection analysis naturally. It is convenient that UAA automatically performs large deflection analysis without form finding when plates or shells are considered. Based on the adaptation of UAA, nonlinear responses of plates/shells and membranes are first obtained at the same time in this paper. Especially, a new type of equilibrium path of membranes is first proposed via UAA. The path includes two parts: one is obtained by form finding and another is from large deflection analysis. High accuracy and efficiency of the proposed approach and the present formulation are verified via some benchmark problems. Effects of slenderness ratio, curvature and boundary condition on form finding and nonlinear responses of membranes are rigorously investigated. Some new equilibrium paths of square and cylindrical membranes are first provided.

Accurate and fast evaluation of orthotropic thermal diffusivity within a membrane: A theoretical approach

In this paper, we propose a theoretical investigation of several configurations based on the infrared photothermal radiometry in order to estimate the thermal diffusivity of isotropic and orthotropic membranes. The front-face and rear-face experimental configurations are considered and show complementary results. Analytical approximations based on characteristic values of the simulated variations of the observed physical quantities, such as the phase or the amplitude, as well as the geometrical parameters are presented. Those approximations are reliable on a large range of thermal properties that make them useful for a large variety of applications. The case of semi-transparent membranes is also treated theoretically, which requires the implementation of non-linear least square minimization to estimate the in-plane thermal diffusivity.

Bicelles Rich in both Sphingolipids and Cholesterol and Their Use in Studies of Membrane Proteins.

How the distinctive lipid composition of mammalian plasma membranes impacts membrane protein structure is largely unexplored, partly because of the dearth of isotropic model membrane systems that contain abundant sphingolipids and cholesterol. This gap is addressed by showing that sphingomyelin and cholesterol-rich (SCOR) lipid mixtures with phosphatidylcholine can be cosolubilized by n-dodecyl-β-melibioside to form bicelles. Small-angle X-ray and neutron scattering, as well as cryo-electron microscopy, demonstrate that these assemblies are stable over a wide range of conditions and exhibit the bilayered-disc morphology of ideal bicelles even at low lipid-to-detergent mole ratios. SCOR bicelles are shown to be compatible with a wide array of experimental techniques, as applied to the transmembrane human amyloid precursor C99 protein in this medium. These studies reveal an equilibrium between low-order oligomer structures that differ significantly from previous experimental structures of C99, providing an example of how ordered membranes alter membrane protein structure.

Kearsley-type instabilities in finite deformations of transversely isotropic and incompressible hyperelastic materials

We assume that the strain energy density, W, for a transversely isotropic and incompressible hyperelastic solid is a complete quadratic function of components of the right Cauchy-Green strain tensor, C. We first discuss restrictions on the seven material parameters appearing in the expression for W. It is shown that for the reference configuration to be stress-free, both terms linear in (I4 − 1) and (I5 − 1) must simultaneously appear in the expression for W where I4 = A • CA, I5 = A • C2A, and A is a unit vector along the axis of transverse isotropy. Subsequently, we show that for a prismatic body comprised of this material deformed either in dead-load or displacement-controlled uniaxial tension/compression along A, depending upon the sign of the material parameter h14 multiplying the term (I1 − 3)(I4 − 1) in the expression for W, the two lateral stretches may bifurcate from being equal to being unequal for a stable solution defined as the one that has lower free energy. Here I1 = tr(C) where tr is the trace operator. This is similar to Kearsley's instability in an isotropic square Mooney-Rivlin membrane deformed with equal biaxial dead loads on the edges for which the stable deformed configuration shifts from having equal to unequal biaxial stretches.

Stress-Strain State of Sealing Rubber Membranes at Large Deformations

This paper describes a stress state of membranes of variable thickness at large deformations, namely the deformation of round continuous anisotropic and isotropic membranes of initial variable thickness, which are under the action of a uniformly distributed load. It is assumed that the membrane materials are elastic, and generalized Hooke’s law is used to describe their behavior. This problem is solved using the equation of equilibrium of the membrane element. True principal strains are expressed through dimensionless radial, annular, and normal stresses. An equation that describes the shape of the membrane after deformation and the corresponding boundary conditions are obtained. The dimensionless stresses and the shape of the membrane after deformation are determined. Numerical calculations are carried out for various parameters of the problem.

Power Generation from Concentration Gradient by Reverse Electrodialysis in Anisotropic Nanoporous Anodic Aluminum Oxide Membranes

In this study, reverse electrodialysis power generation using an anisotropic anodic aluminum oxide membrane with nanopores of two different pore diameters is proposed and experimentally investigated for the first time. A number of experiments were carried out for various combinations of concentrations to show that the anisotropic anodic aluminum oxide membrane is superior to the conventional isotropic membrane. As a result, the highest power density that was measured from the anisotropic membrane was 15.0 mW/m2, and it was 7.2 times higher than that from the isotropic membrane. The reasons why the anisotropic membrane is superior to the isotropic membrane are explained in detail. The experiments on the anisotropic membranes with various active layer lengths and pore diameters were also conducted for exploring the effects of these engineering parameters on the power generation performance. As a result, it was shown that the length of the active layer is a more important engineering parameter than the pore diameter of the active layer. Additionally, it was also shown that a low concentration solution should be brought into contact with the active layer side of the membrane whenever an anisotropic membrane is used for reverse electrodialysis.

A Theoretical Study of Circular Orthotropic Membrane Under Concentrated Load: The Relation of Load and Deflection

In this study, the deformation of circular orthotropic membranes subjected to a central concentrated force is investigated. An orthotropic membrane equation indicating load-deflection behavior based on Foppl-von Karman membrane theory is obtained and the numerical solutions are gotten by using MATLAB. A variable k, which is the most influential parameter on the load-deflection behavior, is proposed. In isotropic membrane, the change of material parameters mainly influences the deflection of membranes subjected to a concentrated force; however, when studying for orthotropic membrane, the shape of membrane after deformation can be controlled by changing the value of xk. Only change in elastic modulus and Poisson's ratio, with k constant, mainly influence the deflection of curves, instead of the shape of curves. Then, four numerical simulations by ABAQUS are conducted and the membrane element M3D4R is used to set up a finite-element model. By comparing these simulation results with the solutions from orthotropic membrane equation, it is shown that the orthotropic membrane equation gives a good estimation of load-deflection behavior.

Sub-100 nm carbon molecular sieve membranes from a polymer of intrinsic microporosity precursor: Physical aging and near-equilibrium gas separation properties

Challenging molecular separation tasks continue to drive the need for advanced membranes, which could combine high productivity and selectivity with outstanding chemical resistance and mechanical robustness. Here, ultra-thin, sub-100 nm carbon molecular sieve (CMS) membranes based on a polymer of intrinsic microporosity precursor were fabricated and characterized with respect to their separation performance for six gases, He, H2, N2, O2, CO2 and CH4. The rarely reported in thin CMS membranes physical aging was tracked until near-equilibrium was reached. The use of commercially available, small pore size (2–5 nm) γ-alumina-coated α-alumina ceramic supports allowed for an easy membrane precursor fabrication by a simple solution coating process. The subsequent application of a protective polydimethylsiloxane layer, as often done in research and membrane production, assured excellent defect control and produced CMS composite membranes with very high membrane permselectivities (e.g. CO2/CH4 = 84.5, H2/CH4 = 360). No significant deviations from bulk properties in terms of the chemical decomposition were discovered in the film thickness range of 60–300 nm. However, a surprisingly massive acceleration of the physical aging in comparison to the bulk was detected in all sub-100 nm membranes including the precursor polymer. All CMS membranes reached near-equilibrium gas transport properties within 1–1.5 months providing a rare opportunity to study aging-stabilized performance. For the aging-stabilized sub-100 nm membranes a decrease in gas permeabilities of up to 3 orders of magnitude was detected. Remarkably, sub-100 nm CMS membranes showed significantly increased selectivities typical to thick isotropic CMS membranes pyrolyzed at 100–200 °C higher temperatures. A clear aging-related shift to more significant size sieving behavior occurred for the majority of the studied CMS membranes throughout the aging period. Overall, our study provides an important observation that excessive reduction of the selective layer thickness, especially in initially highly microporous materials (PIMs, CMS etc.), may not present the best strategy for the optimization of the long-term membrane performance.

Approximation Method for Evaluation of Strains and Forces in LTP Reinforcement of Embankments on Columns

This article presents a method of approximate finding of forces and strains resulting from the so-called membrane effect in the reinforcement of the transmission layer of embankments located on a soft soil improved by columns (rigid inclusions). The model task needed to determine the characteristic values in geosynthetic reinforcement supported on rigid columns was formulated. The reinforcement is treated as an isotropic membrane, in which the strains are determined using the formula for the length of the curve, i.e. it deviates from the assumptions of the small strain theory. Spatial problems are reduced to equivalent one-dimensional static tasks for analysis using the isotropic membrane theory. The closed form solution of this task exists only in the case of uniform load. For other types of loads, it is necessary to approximate the formula for the length of the curve occurring in the expression defining the strains in the membrane, e.g. using the Taylor series, and then solving the strongly non-linear equation in which the membrane tension force is unknown. The article presents the analysis of the effect of the length curve approximation with usage of the Taylor series on the accuracy of the results obtained. The presented analysis is very important from the point of view of standard engineering calculations needed to design the reinforcement of the transmission layer in the case of embankments located on soft soil reinforced with rigid inclusions.

Accuracy of Föppl–von Karman membrane theory for determining elastic constants of monolayer graphene

For interpreting results of an indentation test on a single-layer graphene sheet (SLGS), it is frequently modeled as an elastic, isotropic, and homogeneous membrane. With a small thickness (∼10−10 m) as compared to a characteristic length (∼10−6 m) of specimens used in experiments, the non-dimensional von-Karman factor (vKf ∼ 108) for a SLGS predicts negligible flexural rigidity (D ∼ 10−19 Nm). Since the membrane undergoes large deformations under a small force, a direct relationship between the resulting force-displacement curves and elasticities of the graphene sheet is still elusive. Here we compare predicted load-displacement curves for nanoindentation of a SLGS by using a full non-linear theory with St. Venant–Kirchhoff material, and the Föppl–von Karman nonlinear equations with a Hookean material. The nonlinear governing equations in each formulation are numerically integrated by the shooting method. Even though the radial variations of the membrane deflections computed with the two theories differ by at most 1.5%, the stresses, the declination angles, the curvatures and the strain energy densities may reach differences as high as 6.4%, 7.4%, 70% and 25%, respectively. These differences are significant enough to reexamine using the FvK derived solutions to find elastic constants from the test data.

Scattering analysis of a partitioned wave-bearing cavity containing different material properties

The scattering analysis of acoustic waves through a wave-bearing cavity containing parallel partitioning is presented. The modeled physical configuration comprises an elastic membrane-bounded expansion chamber separated by horizontal plates. The bounding wall conditions of the splitting plates can be chosen to acoustically rigid, soft or an absorbent lining. The governing boundary value problem is solved by using Mode-Matching technique. The low frequency approximation is used and validated in a low frequency regime via the Mode-Matching solution. It is seen that scattering energies and the transmission loss is significantly affected by the variations of material properties of isotropic membranes and the bounding wall conditions. The considered configuration can be opted for the reactive as well as passive control measure of sound.

Magnetoelastic deformation of a circular membrane: Wrinkling and limit point instabilities

We study the inflation of a weakly magnetizable isotropic incompressible circular membrane in the presence of magnetic field generated by a magnetic dipole. Following the approach in recent papers by Reddy and Saxena (Int. J. Sol. Struct. 136, 203–219, 2018; Int. J. Non-Lin. Mech. 95, 248–263, 2017) we start with a variational formulation, solving the resulting governing equations to determine the equilibria and checking the second variation condition for stability. Conjecture of possibility of multiple equilibria under a single coupled load, and attaining elastic and magnetic limit points made in the above two papers is confirmed in the present work for a circular membrane. Another main focus of this work is on the determination of wrinkling instability in the membrane due to magnetoelastic stresses. Wrinkles along one or both in-plane directions of membrane appear in a majority of loading scenarios due to compressive Maxwell stresses. Our computations demonstrate that wrinkles arise in the central region when dipole and inflation are in the same direction and in the annular region close to the edges when the dipole and inflation are in opposite directions.

Permeabilities and selectivities in anisotropic planar membranes for gas separations

The use of membrane technologies for separation processes is an alternative approach to reduce the environmental impact and energy demand of separations. The development of new membrane materials plays a central role to overcome the limitations of membranes in terms of selectivity, permeability, and stability. Most membrane materials in the past have been engineered to control the relative magnitude of the flux of the species diffusing through the membrane. However, mass flux is a vector and controlling its direction can open new opportunities to design separation processes. In this paper we characterize the separation capabilities of metamaterial-inspired anisotropic planar membranes by studying the development of spatially dependent permeabilities and selectivities as a consequence of manipulating the flux direction within the membrane. Specifically, we show how the performance of anisotropic planar membranes for separations can be characterized in terms of permeability, selectivity, and the collected permeate proportion. In contrast to isotropic membrane materials, we show how the selectivity under single stage operation can be increased beyond the selectivities of the constituent materials by reducing the permeate proportion that is collected. Our work provides new opportunities for the design of alternative separation processes that take advantage of flux directional control within membrane materials.