Semipermeable Walls Research Articles

Vascular network-inspired fluidic system (VasFluidics) with spatially functionalizable membranous walls

In vascular networks, the transport across different vessel walls regulates chemical compositions in blood over space and time. Replicating such trans-wall transport with spatial heterogeneity can empower synthetic fluidic systems to program fluid compositions spatiotemporally. However, it remains challenging as existing synthetic channel walls are typically impermeable or composed of homogeneous materials without functional heterogeneity. This work presents a vascular network-inspired fluidic system (VasFluidics), which is functionalizable for spatially different trans-wall transport. Facilitated by embedded three-dimensional (3D) printing, elastic, ultrathin, and semipermeable walls self-assemble electrostatically. Physicochemical reactions between fluids and walls are localized to vary the trans-wall molecules among separate regions, for instance, by confining solutions or locally immobilizing enzymes on the outside of channels. Therefore, fluid compositions can be regulated spatiotemporally, for example, to mimic blood changes during glucose absorption and metabolism. Our VasFluidics expands opportunities to replicate biofluid processing in nature, providing an alternative to traditional fluidics.

Injection driven flow in a dilating or contracting filter chamber with parabolic left inlet velocity

Filter design is an essential aspect of the development of industrial machines. This study investigates and analyses an injection-driven flow in a dilating or contracting filter chamber with weak permeable walls. The design is such that an opening allows influx into the filter channel with parabolic velocity and another opening that serves as an outlet for the filtrates. The model follows the mass conservation, incompressible Navier–Stokes and the energy conservation equations. The study seeks steady-state operation to understand a stable filtration process. The solutions of the dependent variables are then approximated using the spectral-based paired quasilinearization technique. We found, among other results, that in the region where the flow is developing due to the inflow velocity, the axial flow when the chamber compresses is greater than the velocity when the filter chamber expands. Further, there is more average wall friction in the current design than the filter chamber design with two outlets because more fluid is present in the current filter design due to injection through the semi-permeable walls and the inflow through the left inlet. This high average wall friction causes a delay in the transition of the flow and consequently retard the outflow of the filtrates.

Numerical Modeling of the Leak through Semipermeable Walls for 2D/3D Stokes Flow: Experimental Scalability of Dual Algorithms

The paper deals with the Stokes flow subject to the threshold leak boundary conditions in two and three space dimensions. The velocity–pressure formulation leads to the inequality type problem that is approximated by the P1-bubble/P1 mixed finite elements. The resulting algebraic system is nonsmooth. It is solved by the path-following variant of the interior point method, and by the active-set implementation of the semi-smooth Newton method. Inner linear systems are solved by the preconditioned conjugate gradient method. Numerical experiments illustrate scalability of the algorithms. The novelty of this work consists in applying dual strategies for solving the problem.

Viscous energy dissipation in slender channels with porous or semipermeable walls.

We study the viscous dissipation in pipe flows in long channels with porous or semipermeable walls, taking into account both the dissipation in the bulk of the channel and in the pores. We give simple closed-form expressions for the dissipation in terms of the axially varying flow rate Q(x) and the pressure p(x), generalizing the well-known expression W[over ̇]=QΔp=RQ^{2} for the case of impenetrable walls with constant Q, pressure difference Δp between the ends of the pipe and resistance R. When the pressure p_{0} outside the pipe is constant, the result is the straightforward generalization W[over ̇]=Δ[(p-p_{0})Q]. Finally, applications to osmotic flows are considered.

3D investigation shows walls and wall-like structures around human germinal centres, probably regulating T- and B-cell entry and exit.

This study deals with 3D laser investigation on the border between the human lymph node T-zone and germinal centre. Only a few T-cells specific for antigen selected B-cells are allowed to enter germinal centres. This selection process is guided by sinus structures, chemokine gradients and inherent motility of the lymphoid cells. We measured gaps and wall-like structures manually, using IMARIS, a 3D image software for analysis and interpretation of microscopy datasets. In this paper, we describe alpha-actin positive and semipermeable walls and wall-like structures that may hinder T-cells and other cell types from entering germinal centres. Some clearly defined holes or gaps probably regulate lymphoid traffic between T- and B-cell areas. In lymphadenitis, the morphology of this border structure is clearly defined. However, in case of malignant lymphoma, the wall-like structure is disrupted. This has been demonstrated exemplarily in case of angioimmunoblastic T-cell lymphoma. We revealed significant differences of lengths of the wall-like structures in angioimmunoblastic T-cell lymphoma in comparison with wall-like structures in reactive tissue slices. The alterations of morphological structures lead to abnormal and less controlled T- and B-cell distributions probably preventing the immune defence against tumour cells and infectious agents by dysregulating immune homeostasis.

Transcapillary transport of water, small solutes and proteins during hemodialysis

The semipermeable capillary walls not only enable the removal of excess body water and solutes during hemodialysis (HD) but also provide an essential mechanism for maintaining cardiovascular homeostasis. Here, we investigated transcapillary transport processes on the whole-body level using the three-pore model of the capillary endothelium with large, small and ultrasmall pores. The transcapillary transport and cardiovascular response to a 4-h hemodialysis (HD) with 2 L ultrafiltration were analyzed by simulations in a virtual patient using the three-pore model of the capillary wall integrated in the whole-body compartmental model of the cardiovascular system with baroreflex mechanisms. The three-pore model revealed substantial changes during HD in the magnitude and direction of transcapillary water flows through small and ultrasmall pores and associated changes in the transcapillary convective transport of proteins and small solutes. The fraction of total capillary hydraulic conductivity attributed to ultrasmall pores was found to play an important role in the transcapillary water transport during HD thus influencing the cardiovascular response to HD. The presented model provides a novel computational framework for a detailed analysis of microvascular exchange during HD and as such may contribute to a better understanding of dialysis-induced changes in blood volume and blood pressure.

Monitoring Molecular Transport across Colloidal Membranes.

The controlled shaping and surface functionalization of colloidal particles has provided opportunities for the development of new materials and responsive particles. The possibility of creating hollow particles with semipermeable walls allows modulating molecular transport properties on colloidal length scales. While shapes and sizes can typically be observed by optical means, the underlying chemical and physical properties are often invisible. Here, we present measurements of cross-membrane transport via pulsed field gradient NMR in packings of hollow colloidal particles. The work is conducted using a systematic selection of particle sizes, wall permeabilities, and osmotic pressures and allows tracking organic molecules as well as ions. It is also shown that, while direct transport of molecules can be measured, indirect markers can be obtained for invisible species via the osmotic pressure as well. The cross-membrane transport information is important for applications in nanoconfinement, nanofiltration, nanodelivery, or nanoreactor devices.

A Pumpless Acoustofluidic Platform for Size-Selective Concentration and Separation of Microparticles.

We have designed a pumpless acoustofluidic device for the concentration and separation of different sized particles inside a single-layered straight polydimethylsiloxane (PDMS) microfluidic channel. The proposed device comprises two parallel interdigitated transducers (IDTs) positioned underneath the PDMS microchannel. The IDTs produce high-frequency surface acoustic waves that generate semipermeable virtual acoustic radiation force field walls that selectively trap and concentrate larger particles at different locations inside the microchannel and allow the smaller particles to pass through the acoustic filter. The performance of the acoustofluidic device was first characterized by injecting into the microchannel a uniform flow of suspended 9.9 μm diameter particles with various initial concentrations (as low as 10 particles/mL) using a syringe pump. The particles were trapped with ∼100% efficiency by a single IDT actuated at 73 MHz. The acoustofluidic platform was used to demonstrate the pumpless separation of 12.0, 4.8, and 2.1 μm microparticles by trapping the 12 and 4.8 μm particles using the two IDTs actuated at 73 and 140 MHz, respectively. However, most of the 2.1 μm particles flowed over the IDTs unaffected. The acoustofluidic device was capable of rapidly processing a large volume of sample fluid pumped through the microchannel using an external syringe pump. A small volume of the sample fluid was processed through the device using a capillary flow and a hydrodynamic pressure difference that did not require an external pumping device.

Effects of Optical Purity and Finite System Size on Self-Assembly of 12-Hydroxystearic Acid in Hexane: Molecular Dynamics Simulations.

12-Hydroxystearic acid (12HSA) and its derivatives are well-known organogelators, and they play critical roles in a variety of applications. The overall aggregate structure of 12HSA is sensitive to the chirality at the 12th carbon, but a fundamental understanding of this dependence is lacking. In this study, molecular dynamics simulations were conducted on microsecond long time scales for (1) (R)-12HSA, (2) (S)-12HSA, and (3) a 50/50 racemic mixture, each solvated at 12.5 wt % in explicit hexane. Self-assembly was accelerated by turning off alkyl chain dihedral gauche states and forcing the molecules to adopt an all-trans conformation. The stability of the resulting aggregates was tested by quenching them with access to gauche states restored. Ordered aggregates produced from optically pure (R)- and (S)-12HSA remained stable for at least 1 μs. The characteristic ordered structure observed is termed a "ring-of-rings" motif, and it contains two twisted six-membered ringlike bundles connected through acetic acid dimerization and surrounded by six satellite bundles. The chirality at the 12th carbon dictates the overall twist of the rings and thereby the handedness of the aggregates. Racemic mixtures did not produce stable ordered aggregates likely due to insufficient enantiomerically pure ring formation. The most prevalent finite-size effect observed was the stochastic formation of percolating aggregates, which were later avoided by using solvent-permeable, solute-impermeable, confining walls. The resulting ordered aggregates were in all important ways identical to those produced in unconfined systems. The combination of cycling off and on gauche states and the semipermeable walls may be an important new way to study the self-assembly underlying aggregation at industrially relevant concentrations of surfactants in organic solvents.

Diffusion-limited encounter rate in a three-dimensional lattice of connected compartments studied by Brownian-dynamics simulations.

We considered the rate at which a diffusing particle encounters a target in a three-dimensional lattice of compartments with semipermeable walls. This work expands a previous theory [Li et al., Phys. Rev. Lett. 113, 028303 (2014)] for the encounter rate in the dilute limit of targets to the general case of any density of targets. We also used Brownian dynamics simulations to evaluate the approximations in the analytical theory. We find that the largest errors in the analytical theory are on the order of 10%. This work therefore demonstrates an analytical theory capable of describing the encounter rates in compartmentalized environments for any level of confinement and any target density.

ChemInform Abstract: Pot‐in‐Pot Reactions: A Simple and Green Approach to Efficient Organic Synthesis

AbstractReview: 134 refs.

Controlled delivery of carvedilol nanosuspension from osmotic pump capsule: In vitro and in vivo evaluation

This study intended to develop a novel controlled delivery osmotic pump capsule of carvedilol nanosuspension. The capsule is assembled using a semi-permeable capsule shell with contents including nanosuspension drying powder, mannitol and Plasdone S-630. The physical characteristics of semi-permeable capsule walls were compared among different coating solutions under different temperature. The composition of the coating solution and drying temperature appeared to be important for the formation of the shells. Carvedilol nanosuspension was prepared by precipitation–ultrasonication technique and was further lyophilized. Response surface methodology was used to investigate the influence of factors on the responses. The optimized formulation displayed complete drug delivery and zero-order release rate. The TEM and particle size analysis indicated that the morphology of the resultant nanoparticle in the capsule was spherical shaped with a mean size of 252±19nm. The in vivo test in beagle dogs demonstrated that the relative bioavailability of the novel system was 203.5% in comparison to that of the marketed preparation. The capsule successfully controlled the release of carvedilol and the fluctuation of plasma concentration was minimized. The system is a promising strategy to improve the oral bioavailability for poorly soluble drugs and preparing it into elementary osmotic pump conveniently.

Exact and Approximate Solutions for Seepage through Semipermeable Cutoff Walls

AbstractAn explicit analytical solution is developed for the problem of steady, two-dimensional seepage in the vertical plane through a fully penetrating, semipermeable cutoff wall. The flow is driven by a head drop across an overlying dam, whose width is equal to the width of the wall. Results including the discharge beneath the dam, the differential head across the wall, the hydraulic efficiency of the wall, and the exit gradient along the bed of the downstream reservoir are presented as dimensionless charts. Rigorous comparisons are made with solutions obtained by approximate methods, which are applicable to more-general problems. The analytical solutions and approximate methods are used to estimate the discharge and the differential head at the Shikwamkwa Dam in Ontario, Canada, and to assess the need for more-detailed seepage modeling.

Attractors for Navier–Stokes flows with multivalued and nonmonotone subdifferential boundary conditions

We consider two-dimensional nonstationary Navier–Stokes shear flow with multivalued and nonmonotone boundary conditions on a part of the boundary of the flow domain. We prove the existence of global in time solutions of the considered problem which is governed by a partial differential inclusion with a multivalued term in the form of Clarke subdifferential. Then we prove the existence of a trajectory attractor and a weak global attractor for the associated multivalued semiflow.This research is motivated by control problems for fluid flows in domains with semipermeable walls and membranes.

Efficiency of osmotic pipe flows

We present experiments and theory for flows of sugar or salt solutions in cylindrical tubes with semipermeable walls (hollow fiber membranes) immersed in water, quantifying the strength of the osmotic driving force in relation to the dimensionless parameters that specify the system. The pumping efficiency of these flows is limited by the presence of "unstirred" concentration boundary layers near the tube walls, and our primary aim is to understand and quantify these layers and their effect on the flow. We measure the outlet flow rate Q(out) while varying the inlet flow rate Q(*), concentration c(*), and tube length L, and map out the dependence of the flow rate gain γ=Q(out)/Q(*)-1 on these parameters. A theoretical analysis based on (1) the known velocity field for slow flow in cylindrical porous tubes and (2) a parabolic concentration profile allows us to compute analytically how the flow gain depends on the relative magnitude of radial diffusion and advection as well as the ratio of the osmotic velocity to pumping velocity, in very good agreement with experiments and with no adjustable parameters. Our analysis provides criteria that are useful for optimizing osmotic flow processes in, e.g., water purification devices.

Transition of velocity distributions in collapsing self-gravitatingN-body systems

By means of N-body simulations, we study the evolution of gravity-dominated systems from an early relaxation to a collapse, focusing on the velocity distributions and thermodynamic properties. To simulate the dynamical evolution, we consider self-gravitating small N-body systems enclosed in a spherical container with adiabatic or semipermeable walls. It is demonstrated that in the early relaxation process, the velocity distribution is non-Gaussian and q-Gaussian, since the system is in quasiequilibrium states (here q is the Tsallis entropic parameter). Thereafter, the velocity distribution undergoes higher non-Gaussian distributions, especially when the core forms rapidly in the collapse process; i.e., q tends to be larger than that for the quasiequilibrium state, since the velocity distribution further deviates from Gaussian. However, after the core forms sufficiently, the velocity distribution gradually relaxes toward a Gaussian-like distribution. Accordingly, the velocity distribution evolves from a non-Gaussian distribution through a higher non-Gaussian distribution to a Gaussian-like distribution; i.e., the velocity distribution does not monotonically relax toward a Gaussian-like distribution in our collapse simulations. We clearly show such a transition of the velocity distribution, based not only on the Tsallis entropic parameter but also on the ratio of velocity moments. We also find that a negative specific heat occurs in a collapse process with mass and energy loss (such as the escape of stars from globular clusters), even if the velocity distribution is Gaussian-like.

Iron-Sulfide-Bearing Chimneys as Potential Catalytic Energy Traps at Life's Emergence

The concept that life emerged where alkaline hydrogen-bearing submarine hot springs exhaled into the most ancient acidulous ocean was used as a working hypothesis to investigate the nature of precipitate membranes. Alkaline solutions at 25-70°C and pH between 8 and 12, bearing HS(-)±silicate, were injected slowly into visi-jars containing ferrous chloride to partially simulate the early ocean on this or any other wet and icy, geologically active rocky world. Dependent on pH and sulfide content, fine tubular chimneys and geodal bubbles were generated with semipermeable walls 4-100 μm thick that comprised radial platelets of nanometric mackinawite [FeS]±ferrous hydroxide [∼Fe(OH)(2)], accompanied by silica and, at the higher temperature, greigite [Fe(3)S(4)]. Within the chimney walls, these platelets define a myriad of micropores. The interior walls of the chimneys host iron sulfide framboids, while, in cases where the alkaline solution has a pH>11 or relatively low sulfide content, their exteriors exhibit radial flanges with a spacing of ∼4 μm that comprise microdendrites of ferrous hydroxide. We speculate that this pattern results from outward and inward radial flow through the chimney walls. The outer Fe(OH)(2) flanges perhaps precipitate where the highly alkaline flow meets the ambient ferrous iron-bearing fluid, while the intervening troughs signal where the acidulous iron-bearing solutions could gain access to the sulfidic and alkaline interior of the chimneys, thereby leading to the precipitation of the framboids. Addition of soluble pentameric peptides enhances membrane durability and accentuates the crenulations on the chimney exteriors. These dynamic patterns may have implications for acid-base catalysis and the natural proton motive force acting through the matrix of the porous inorganic membrane. Thus, within such membranes, steep redox and pH gradients would bear across the nanometric platelets and separate the two counter-flowing solutions, a condition that may have led to the onset of an autotrophic metabolism through the reduction of carbon dioxide.

Complex phase behavior of a fluid in slits with semipermeable walls modified with tethered chains

We study the phase behavior of a two-component fluid in a pore with the walls modified by tethered chains. The walls are completely permeable for one component of the fluid and completely impenetrable for the second component. The fluid is perfectly mixed in a bulk phase. We have found that depending on the details of the model the fluid undergoes capillary condensation inside the pore and wetting and layering transitions at the outer walls. Moreover, we have found transitions connected with the change of symmetry of the distribution of chains and fluid inside the pore.

Removing Heat and Conceptual Loops from the Definition of Entropy

A rigorous and general logical scheme is presented, which provides an operative non-statistical definition of entropy valid also in the nonequilibrium domain and free of the usual conceptual loops and unnecessary assumptions that restrict the traditional definition of entropy to the equilibrium domain. The scheme is based on carefully worded operative definitions for all the fundamental concepts employed, including those of system, state of a system, isolated system, separable system, systems uncorrelated form each other, environment of a system, process and reversible process. The treatment considers also systems with movable internal walls and/or semipermeable walls, with chemical reactions and and/or external force fields, and with small numbers of particles. The definition of entropy involves neither the concept of heat nor that of quasistatic process; it applies to both equilibrium and nonequilibrium states. Simple and rigorous proofs of the additivity of entropy and of the principle of entropy nondecrease complete the logical framework.

Osmotically driven pipe flows and their relation to sugar transport in plants

In plants, osmotically driven flows are believed to be responsible for translocation of sugar in the pipe-like phloem cell network, spanning the entire length of the plant – the so-called Münch mechanism. In this paper, we present an experimental and theoretical study of transient osmotically driven flows through pipes with semi-permeable walls. Our aim is to understand the dynamics and structure of a ‘sugar front’, i.e. the transport and decay of a sudden loading of sugar in a water-filled pipe which is closed in both ends. In the limit of low axial resistance (valid in our experiments as well as in many cases in plants) we show that the equations of motion for the sugar concentration and the water velocity can be solved exactly by the method of characteristics, yielding the entire flow and concentration profile along the tube. The concentration front decays exponentially in agreement with the results of Eschrich, Evert & Young (Planta (Berl.), vol. 107, 1972, p. 279). In the opposite case of very narrow channels, we obtain an asymptotic solution for intermediate times showing a decay of the front velocity as M−1/3t−2/3 with time t and dimensionless number M ~ ηκL2r−3 for tubes of length L, radius r, permeability κ and fluid viscosity η. The experiments (which are in the small M regime) are in good quantitative agreement with the theory. The applicability of our results to plants is discussed and it is shown that it is probable that the Münch mechanism can account only for the short distance transport of sugar in plants.