Membrane Transport Model Research Articles

Transport Characteristics of Asymmetric Cellulose Triacetate Hemodialysis Membranes

Aims: The objective of this study was to compare the transport characteristics of highly asymmetric cellulose triacetate (ATA™) membranes with that of both symmetric cellulose triacetate and asymmetric polysulfone membranes. Methods: Data were obtained for solute clearance and sieving coefficients of vitamin B₁₂ and a range of polydisperse dextrans using ATA™ SOLACEA-25H and Optiflux F250NR polysulfone dialyzers. Results for these, and the CT190 symmetric cellulose triacetate dialyzer, were analyzed using available membrane transport models. Results: The ATA™ had the largest solute clearance, although the homogeneous CT190 dialyzer had the highest sieving coefficients. These differences were a direct result of the differences in the underlying membrane morphology, with the asymmetric ATA™ membrane providing much higher diffusive transport rates (and thus higher solute clearance). Conclusions: These results demonstrate the importance of membrane morphology on dialyzer transport and provide important insights into the effective clinical performance observed with the highly asymmetric ATA™ dialyzers.

On negative rejection of uncharged organic solutes in forward osmosis

Negative rejection of 7 alcohols in Forward Osmosis (FO) is reported. The alcohols used in this study are uncharged, hydrophilic organic solutes. It is shown that current membrane transport models are not capable of reproducing the rejection pattern presented here, and consequently, a new model is developed. The model relies on adsorption of the solutes to the membrane followed by coupled transport. Adsorption is caused by salting out of the solutes, while coupled transport is caused by their small size and hydrophilicity, yielding comparatively strong water-solute interactions. It is calculated that the solutes are enriched 4–5 times in the membrane compared to the feed solution. Coupled transport is also demonstrated using the same membrane and solutes in RO mode. The novel model yields an excellent fit, and model parameters are discussed.

Quantitative study of RNA transmission through ultrafiltration membranes

Nucleic acid-based therapies have the potential to treat a wide range of diseases through their ability to silence and/or regulate gene expression. Strategies for the large-scale purification of RNA are still being developed, creating a need for more fundamental understanding of the behavior of RNA in different separation systems. The objective of this work was to evaluate RNA transmission through a series of composite regenerated cellulose and polyethersulfone ultrafiltration membranes with different molecular weight cutoffs. Data were obtained using Torula yeast RNA, with the size distribution evaluated by both dynamic light scattering and agarose gel electrophoresis. Results with dilute RNA solutions were strongly influenced by RNA adsorption to the composite regenerated cellulose membrane; this effect was not seen with the polyethersulfone membranes. Data for the polyethersulfone membranes were analyzed using the concentration polarization model, which describes the affects of bulk mass transfer on RNA transmission, in combination with available hydrodynamic models for membrane transport. The results provide important insights into the factors controlling RNA transmission and the potential for using ultrafiltration for the purification of nucleic acid therapeutics.

Reverse osmosis desalination modules containing corrugated membranes – Computational study

Computational fluid dynamics simulation was carried out for three-dimensional desalination modules containing triangular and square ribs attached to the membrane surface. The solution-diffusion membrane transport model was applied along the surface of the corrugated membrane. The membrane flux model which couples the water permeation rate with local salt concentration impose a selective removal of components in the feed channel. The local water flux, salt concentration, wall shear stress, and Sherwood number were monitored over the surface of membranes to determine effects of eddy promoter corrugations on mitigation of concentration polarization and the total water flux. Simulations are conducted using a laminar model for Reynolds number of 100 and k-ω SST turbulence model for Reynolds number of 400 and 1000. Mathematical model and numerical methods employed are validated by comparing predictions against measurements reported earlier. Predicted results agree quantitatively and qualitatively with previous experimental results for membranes with semi-circular cross-sectioned ribs. The results show that corrugated membranes especially triangular chevrons enhance membrane performance profoundly at all flow rates. Water permeation rate is increased, concentration polarization is alleviated, and the potential fouling in the module is reduced by introducing corrugated membranes.

The Membrane Transport System of the Guard Cell and Its Integration for Stomatal Dynamics.

Stomatal guard cells are widely recognized as the premier plant cell model for membrane transport, signaling, and homeostasis. This recognition is rooted in half a century of research into ion transport across the plasma and vacuolar membranes of guard cells that drive stomatal movements and the signaling mechanisms that regulate them. Stomatal guard cells surround pores in the epidermis of plant leaves, controlling the aperture of the pore to balance CO2 entry into the leaf for photosynthesis with water loss via transpiration. The position of guard cells in the epidermis is ideally suited for cellular and subcellular research, and their sensitivity to endogenous signals and environmental stimuli makes them a primary target for physiological studies. Stomata underpin the challenges of water availability and crop production that are expected to unfold over the next 20 to 30 years. A quantitative understanding of how ion transport is integrated and controlled is key to meeting these challenges and to engineering guard cells for improved water use efficiency and agricultural yields.

Quantitative Modeling of Membrane Transport and Anisogamy by Small Groups Within a Large-Enrollment Organismal Biology Course.

Quantitative modeling is not a standard part of undergraduate biology education, yet is routine in the physical sciences. Because of the obvious biophysical aspects, classes in anatomy and physiology offer an opportunity to introduce modeling approaches to the introductory curriculum. Here, we describe two in-class exercises for small groups working within a large-enrollment introductory course in organismal biology. Both build and derive biological insights from quantitative models, implemented using spreadsheets. One exercise models the evolution of anisogamy (i.e., small sperm and large eggs) from an initial state of isogamy. Groups of four students work on Excel spreadsheets (from one to four laptops per group). The other exercise uses an online simulator to generate data related to membrane transport of a solute, and a cloud-based spreadsheet to analyze them. We provide tips for implementing these exercises gleaned from two years of experience.

Substantial Changes in the Transport Model of Reverse Osmosis and Nanofiltration by Incorporating Accurate Activity Data of Electrolytes

The transport model for reverse-osmosis membranes and nanofiltration membranes was reformulated to include the large changes in the chemical activity of solutes in solutions employed to test these membranes. The approach presented herein uses a solution-diffusion model for membrane transport and a more accurate representation of the test solution and the partitioning of the solutes into the membrane. This approach corrects the simplifying assumption in the Merten model of highly diluted solutions and predicts the large changes in the passage of solutes due to increased solute concentration. These changes are due to the large changes in the activity coefficients of the solutes outside the very dilute regions. These changes can significantly influence salt- and water-transport coefficients (e.g., A- and B-values).

Evaluation of non-commercial ceramic SiO2-ZrO2 and organosilica BTESE membranes in a highly oxidative medium: Performance in hydrogen peroxide

The development of robust membranes able to withstand harsh environments such as oxidative conditions would improve the sustainability of several separation processes. Therefore, organosilica and ceramic non-commercial membranes were characterized and their performances were compared before and after contact with hydrogen peroxide. The organosilica membrane showed a high level of solute rejection coefficients (0.928 for NaCl and 0.969 for MgCl2), but low permeability (5.04·10–13m3/m2sPa, equivalent to 0.181L/m2hbar). The ceramic membrane, however, showed low solute rejection (0.187 for NaCl and 0.649 for MgSO4), but high membrane permeability (7.05·10–12m3/m2sPa, equivalent to 2.538L/m2hbar). While the organosilica membrane was quite sensitive to the presence of hydrogen peroxide, the chemical stability of the ceramic membrane in 30% hydrogen peroxide solution was very satisfactory. A Kedem-Katchalsky membrane transport model and a logistic decay model were applied to successfully test the performance of the membranes and to characterize the evolution of the organosilica membrane, respectively.

Open Markov Processes: A Compositional Perspective on Non-Equilibrium Steady States in Biology

In recent work, Baez, Fong and the author introduced a framework for describing Markov processes equipped with a detailed balanced equilibrium as open systems of a certain type. These “open Markov processes” serve as the building blocks for more complicated processes. In this paper, we describe the potential application of this framework in the modeling of biological systems as open systems maintained away from equilibrium. We show that non-equilibrium steady states emerge in open systems of this type, even when the rates of the underlying process are such that a detailed balanced equilibrium is permitted. It is shown that these non-equilibrium steady states minimize a quadratic form which we call “dissipation”. In some circumstances, the dissipation is approximately equal to the rate of change of relative entropy plus a correction term. On the other hand, Prigogine’s principle of minimum entropy production generally fails for non-equilibrium steady states. We use a simple model of membrane transport to illustrate these concepts.

Multi-scale modelling of OSN batch concentration with spiral-wound membrane modules using OSN Designer

Three commercial spiral-wound membrane modules of different sizes, from 1.8″×12″ to 4.0″×40″, are used to concentrate a solution of sucrose octaacetate in ethyl acetate under different operating conditions. A mathematical model to describe the batch concentration process is developed, based on a combination of the classical solution diffusion membrane transport model and the film theory, to account for the mass transfer effects. The model was implemented using the “OSN Designer” software tool. The membrane transport model parameters as well as all parameters in the pressure drop and mass transfer correlations for the spiral-wound modules were obtained from regression on a limited number of experimental data at steady state conditions. Excellent agreement was found between the experimental and multi-scale modelling performance data under various operating conditions. The results illustrate that the performance of a large scale batch concentration process with spiral-wound membrane modules can be predicted based on laboratory crossflow flat sheet test data when the fluid dynamics and mass transfer characteristics in the module, and the necessary channel geometry are known. In addition, the effects of concentration polarisation, pressure drop through feed and permeate channels, and thermodynamic non-ideality of the solution at large scale batch concentration are also investigated.

Membrane reactors for isoamyl acetate production

In our previous paper (Chem. Eng. Process., 76 (2014) 70), a comprehensive study of conventional and hybrid membrane processes for isoamyl acetate synthesis, using experimentally certified models, was presented. Here, as an extension of that previous work, the performance of membrane reactors was analyzed, using the same thermodynamic, kinetic, and membrane transport models. Two different configurations were investigated by simulation using ASPEN Plus® together with a homemade Excel®-MatLab® interface for membrane reactor modules simulation. The goal was to gain more insight into the isoamyl acetate synthesis using membrane reactors, as a prelude to a detailed experimental research. The analysis procedure includes both the optimization of membrane reactor performance and the minimization of process energy consumption, including the energetic integration using the pinch point methodology. Total annualized costs were estimated and compared with the conventional and hybrid membrane schemes.

New Sensitizers Developed on a Methylpheophorbide a Platform for Photodynamic Therapy: Synthesis, Singlet Oxygen Generation and Modeling of Passive Membrane Transport

This study focuses on the behavior of new potential sensitizers for photodynamic therapy of cancer developed on a chlorophyll a platform. Pheophorbide a 17-(3) methylester and its two glycol derivatives have been synthesized from chlorophyll and identified via visible, UV-, NMR- and MS-spectra. The behavior of photosensitizers in solutions has been studied with various experimental techniques. They are found to generate singlet oxygen with a sufficient quantum yield and reveal a tendency to effectively penetrate into cell membranes due to high lipophilicity. Thermodynamic analysis indicates that the sensitizer transfer from a water-like to a lipid-like medium is controlled by a large and negative enthalpic term excepting the case of the most polar solute, where for phosphate saline buffer the favorable entropic term dominates. Our study highlights the important feature dealing with the temperature dependence of partition coefficients between saline buffer and 1-octanol which is found to be surprisingly strong for hydrophobic solutes and temperature independent for the species containing both H-donor and H-acceptor groups.

Optimization of reverse osmosis networks with split partial second pass design

This study proposes an optimal study of reverse osmosis (RO) seawater desalination system based on the split partial second pass (SPSP) design in order to fully utilize better quality and higher flux for the permeate at the front of the pressure vessel (PV). Differential equations in the membrane transport model are solved by finite difference method, which considers the longitudinal variation of the superficial velocity, the pressure and the salinity inside the PV. Superstructure optimization is adopted to determine optimal flow structure, appropriate membrane type, and operation conditions. Firstly, single product RO system has been optimized, cost breakdown and sensitive analysis reveal that membrane with large active area and high salt rejection is favored for SPSP. System recovery, pressure, and split ratio for the permeate of pass 1 should be adjusted with time in order to decrease total annualized cost. Secondly, multiple product RO system has been studied. Three-pass RO configuration with permeate re-processed and brine recycled is favored for the system with two permeate products. The optimal RO configuration with three permeate products is influenced by flow rates and required permeate concentrations. In general, SPSP could provide lower cost, lower energy consumption, and smaller system size than normal design.

Predictive membrane transport models for Organic Solvent Nanofiltration: How complex do we need to be?

From feasibility tests at laboratory scale to large industrial scale processes, modelling can be applied to Organic Solvent Nanofiltration (OSN) for two purposes: (i) parameter estimation, when experimental data for standard solute + solvent systems are available, and it is desired to estimate relevant parameters for as yet uncharacterised systems, and (ii) prediction, when the model parameters for the solvent–solute are available, and modelling can be applied to describe the performance of a different solute + solvent system or operations at a different process scale. Both estimation and prediction require the choice of a transport model, to carry out regression and simulation, respectively. This paper reports a systematic comparison of a range of different transport models (irreversible thermodynamics, solution–diffusion, pore-flow and transient transport models, such as the solution–diffusion with imperfections model) using selected experimental data for various solutes and solvents through polymeric OSN membranes with different physico-chemical properties. Commercial integrally skinned asymmetric polyimide (PI, glassy) and thin film composite silicone-coated PI (rubbery) membranes from Evonik® MET were systematically tested in this study, with styrene oligomers and Safranin-O dye in different organic solvents under uniform operating conditions (temperature, pressure, cross-flow velocity and solute concentration). In addition, experimental data from the literature were taken for non-commercial thin film composite silicone-coated PI, glassy poly[1-(trimethylsilyl)-1-propyne] (PTMSP) and poly[4methyl2pentyne] (PMP) membranes, to include a broad spectrum of positive and negative rejection values. The different transport models were used to perform regression of experimental data and prediction at different pressure values, based on the regressed model parameters. The models were then compared in terms of regression performance and experimental/numerical effort required to use them for parameter estimation. Negative rejection data was used to further discriminate among the models. Solution–diffusion-based models gave a better description of permeation through flexible-chain glassy membranes than pore-flow models. On the other hand, pore-flow-based models gave a better description of permeation through glassy PTMSP and PMP membranes. For integrally skinned asymmetric PI membranes, the prediction of a concentration process using the best performing regression models (i.e. the Maxwell–Stefan and the classical solution–diffusion model) was also performed. Interestingly, no significant difference was observed between the two models for both a membrane with complete solute rejection (Duramem® 200) and a membrane with partial solute rejection (Duramem® 500). Process modelling by accounting for a classical solution–diffusion-type transport mechanism is therefore sufficient to obtain a reliable transport description for this membrane family.

A novel membrane transport model for polymer electrolyte fuel cell simulations

This work presents the development of a 1D model describing water and charge transport through the polymer electrolyte membrane (PEM) in the fuel cell. The considered driving forces are electrical potential, concentration and pressure gradients. The membrane properties such as water diffusion and electro-osmotic coefficients, water sorption and ionic conductivity are treated as temperature dependent functions. The dependencies of diffusion and electro-osmotic coefficients on the membrane water concentration are described by linear functions. The membrane conductivity is computed in the framework of the percolation theory under consideration that the conducting phase in the PEM is formed by a hydrated functional groups and absorbed water. This developed membrane model was implemented in the CFD code AVL FIRE using 1D/3D coupling. The simulated polarization curves at various humidification of the cathode are found in good agreement with the experiments thus confirming the validity of the model.

Fishing with flies, worms and bacteria: emerging models for mammalian membrane transport and trafficking

The Journal of Physiology has a long and distinguished history of publishing original observations using non-mammalian tractable model systems that have fundamentally informed understanding of mammalian membrane transport processes. Some specific examples include a pioneering investigation of the selective barrier function of epithelia using frog skin (Waymouth Reid, 1890), an elegant illustration of ion channel and Na+–K+ pump activity in giant axons from the cuttlefish and squid (Hodgkin & Keynes, 1955) and an early demonstration of Na+-dependent sugar transport in the toad intestine (Csaky & Thale, 1960). Such physiological demonstrations of transport function have, in more recent times, been supported by the explosion in available genomic information that has, in turn, greatly improved our understanding of conserved biological functions across many species. Likewise, the high degree of similarity in protein structures from prokaryotes and eukaryotes, despite limited sequence homology, also points towards essential and sustained biological roles. Thus, prokaryotic transporter structures can provide key information concerning the way in which mammalian transport proteins are likely to function. A series of talks on the topic of emerging models for investigation of mammalian membrane transport and trafficking were presented on Sunday 21 April 2013 as part of the American Physiological Society programme of symposia at the Experimental Biology 2013 meeting. The session was held in the Boston Convention & Exhibition Center. The symposium was sponsored by The Physiological Society and The Journal of Physiology. The topics covered in this symposium emphasized the utility of so-called ‘lower organisms’ and how they can be used to improve our understanding of mammalian membrane transport and trafficking. The symposium opened with a presentation by Aravind Penmatsa on how the elucidation of the crystal structure of the amino acid transporter LeuT, from the thermophilic bacterium Aquifex aeolicus, has revolutionized our understanding of mammalian neurotransmitter transporter stucture and function (Penmatsa & Gouaux, 2014). The availability of the LeuT crystal has provided a structural basis to determine the action of antidepressants on the SLC6 family of human biogenic amine transporters (Wang et al. 2013). The next speaker, Britta Spanier, highlighted clear similarities in the mechanisms of transcriptional and functional regulation of the intestinal di/tripeptide transporter PepT1 in the gut of the nematode Caenorhabditis elegans and the commonly used cell culture model of the human small intestinal epithelium, the Caco-2 cell monolayer (Spanier, 2014). In both cases, PepT1 is regulated by the intracellular amino acid pool and functional activity of the co-expressed Na+–H+ exchanger NHE3. Tiziano Verri continued the theme of intestinal absorption of protein by providing a comprehensive review of the genomic and functional information currently available about PepT1 from a great number of studies using teleost fish (Romano et al. 2014). Intestinal protein absorption is such a fundamental biological process that modifications of the PepT1 transporter protein in different teleosts allow adaptation to extremes of temperature, pH and substrate availability. This information not only provides useful tips on how the mammalian PepT1 could be modified to enhance transport but also provides valuable information for optimization of feed for commercially valuable fish. Linda Stuart gave an elegant presentation on how animals (ranging from the fruitfly Drosophila melanogaster to mammals) sense pathogens (Stuart et al. 2013) and how phagosome acidification following phagocytosis of Gram-positive and Gram-negative bacteria takes place via distinct mechanisms (Sokolovska et al. 2013). The session was completed by a short presentation by Bill Harvey on a novel theory that considers how a K+ pump, comprising a H+ V-ATPase and a K+–H+ antiporter, originally discovered in the caterpillar midgut, might contribute to auditory mechanosensory transduction in the mammalian cochlea (Harvey & Xiang, 2012). The topics discussed in this symposium where diverse, but the common thread is clear. Our understanding of mammalian physiology is enhanced greatly by information obtained from studies of diverse organisms, including prokaryotes, fish, flies and worms.

Numerical Approach for Optimal Design of a Hollow Fiber Dialyzer System

A numerical approach for an optimal designing of a countercurrent hollow fiber dialyzer has been proposed by utilizing the membrane transport model based on the porous media theory. The three-dimensional numerical computations have been conducted to capture individual concentration fields, namely, blood, dialysate and membrane phases within a hollow fiber dialyzer. Clearances for the Creatinine and Vitamin B12 obtained from present numerical simulations are compared against available experimental date so as to examine the validity of the present method. Subsequently, the effects of housing of countercurrent hollow fiber dialyzers on the mass transfer rate have been also investigated by utilizing several types of hollow fiber dialyzers. Furthermore, a series of calculations have been carried out with variation of the number of hollow fibers so as to find the effective hollow fiber dialyzer for given pumping power. The present numerical methods based on the membrane transport model can be useful for optimization of hollow fiber dialyzer systems.

Multi-objective optimization of reverse osmosis networks by lexicographic optimization and augmented epsilon constraint method

This study proposes a multi-objective optimization (MOO) of reverse osmosis (RO) networks for seawater desalination. The membrane transport model takes into consideration of the longitudinal variation of the velocity, the pressure, and the concentration in the membrane modules. The RO network with three type energy recovery device options (pressure exchanger (PX), Hydraulic Turbocharger, and turbine) is introduced. Lexicographic optimization (for calculation of a more effective payoff table) and augmented ε-constraint method (to avoid inefficient Pareto solutions) are proposed to solve the MOO problem. A fuzzy decision maker is introduced to derive the most efficient solution among Pareto-optimal solutions. Firstly, different energy recovery option studies show that using PX is seen to be the most profitable option. Exergy analysis is used to evaluate the contribution of the equipments in energy degradation. Secondly, the proposed multi-objective framework simultaneously optimizes the total annualized cost (TAC) and energy consumption. With the increases of weighting for the main objective function: TAC, the most efficient solution moves to lower TAC direction. Finally, system recovery rate is added as the third objective function. It is reasonable to stay at the appropriate system recovery rather than to increase up to its limit and generating high energetic losses.

Membrane permeability of the human granulocyte to water, dimethyl sulfoxide, glycerol, propylene glycol and ethylene glycol

Granulocytes are currently transfused as soon as possible after collection because they rapidly deteriorate after being removed from the body. This short shelf life complicates the logistics of granulocyte collection, banking, and safety testing. Cryopreservation has the potential to significantly increase shelf life; however, cryopreservation of granulocytes has proven to be difficult. In this study, we investigate the membrane permeability properties of human granulocytes, with the ultimate goal of using membrane transport modeling to facilitate development of improved cryopreservation methods. We first measured the equilibrium volume of human granulocytes in a range of hypo- and hypertonic solutions and fit the resulting data using a Boyle-van’t Hoff model. This yielded an isotonic cell volume of 378μm3 and an osmotically inactive volume of 165μm3. To determine the permeability of the granulocyte membrane to water and cryoprotectant (CPA), cells were injected into well-mixed CPA solution while collecting volume measurements using a Coulter Counter. These experiments were performed at temperatures ranging from 4 to 37°C for exposure to dimethyl sulfoxide, glycerol, ethylene glycol, and propylene glycol. The best-fit water permeability was similar in the presence of all of the CPAs, with an average value at 21°C of 0.18μmatm−1min−1. The activation energy for water transport ranged from 41 to 61kJ/mol. The CPA permeability at 21°C was 6.4, 1.0, 8.4, and 4.0μm/min for dimethyl sulfoxide, glycerol, ethylene glycol, and propylene glycol, respectively, and the activation energy for CPA transport ranged between 59 and 68kJ/mol.

130 Membrane permeability properties of human granulocytes

Granulocytes are a type of circulating white blood cell with high medical relevance because of their potential use in the treatment of infections and possibly even for treatment of cancer. However, granulocytes rapidly deteriorate after being removed from the body. As a result, granulocytes are typically collected from the donor on site and used in a transfusion shortly afterwards. Cryopreservation has the potential to significantly increase shelf life, which would facilitate granulocyte collection, banking and safety testing. However, cryopreservation of granulocytes has proven to be difficult. In this study, we investigate the membrane permeability properties of human granulocytes, with the ultimate goal of using membrane transport modeling to facilitate development of improved cryopreservation methods. We first measured the equilibrium volume of human granulocytes in a range of hypo- and hypertonic solutions and fit the resulting data using a Boyle-van’t Hoff model. This yielded an isotonic cell volume of 378 μ m 3 and an osmotically inactive volume of 165 μ m 3 . To determine the permeability of the granulocyte membrane to water and cryoprotectant (CPA), cells were injected into well-mixed CPA solution while collecting volume measurements using a Coulter counter. These experiments were performed at temperatures ranging from 4 to 37 °C for exposure to dimethyl sulfoxide, glycerol, ethylene glycol and propylene glycol. The best-fit water permeability was similar in the presence of all of the CPAs, with an average value at 20 °C of 0.17 μ m atm −1 min −1 . The activation energy for water transport ranged from 41 to 61 kJ/mol. The CPA permeability at 20 °C was 5.9, 0.95, 7.7 and 3.6 μ m/min for dimethyl sulfoxide, glycerol, ethylene glycol and propylene glycol, respectively, and the activation energy for CPA transport ranged between 59 and 68 kJ/mol. Source of funding: National Science Foundation Grant #1150861. Conflict of interest: None declared. adam.higgins@oregonstate.edu