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Sample records for cell membranes analytic

  1. Molecular motion in cell membranes: Analytic study of fence-hindered random walks

    NASA Astrophysics Data System (ADS)

    Kenkre, V. M.; Giuggioli, L.; Kalay, Z.

    2008-05-01

    A theoretical calculation is presented to describe the confined motion of transmembrane molecules in cell membranes. The study is analytic, based on Master equations for the probability of the molecules moving as random walkers, and leads to explicit usable solutions including expressions for the molecular mean square displacement and effective diffusion constants. One outcome is a detailed understanding of the dependence of the time variation of the mean square displacement on the initial placement of the molecule within the confined region. How to use the calculations is illustrated by extracting (confinement) compartment sizes from experimentally reported published observations from single particle tracking experiments on the diffusion of gold-tagged G -protein coupled μ -opioid receptors in the normal rat kidney cell membrane, and by further comparing the analytical results to observations on the diffusion of phospholipids, also in normal rat kidney cells.

  2. An analytical model and parametric study of electrical contact resistance in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Wu, Zhiliang; Wang, Shuxin; Zhang, Lianhong; Hu, S. Jack

    This paper presents an analytical model of the electrical contact resistance between the carbon paper gas diffusion layers (GDLs) and the graphite bipolar plates (BPPs) in a proton exchange membrane (PEM) fuel cell. The model is developed based on the classical statistical contact theory for a PEM fuel cell, using the same probability distributions of the GDL structure and BPP surface profile as previously described in Wu et al. [Z. Wu, Y. Zhou, G. Lin, S. Wang, S.J. Hu, J. Power Sources 182 (2008) 265-269] and Zhou et al. [Y. Zhou, G. Lin, A.J. Shih, S.J. Hu, J. Power Sources 163 (2007) 777-783]. Results show that estimates of the contact resistance compare favorably with experimental data by Zhou et al. [Y. Zhou, G. Lin, A.J. Shih, S.J. Hu, J. Power Sources 163 (2007) 777-783]. Factors affecting the contact behavior are systematically studied using the analytical model, including the material properties of the two contact bodies and factors arising from the manufacturing processes. The transverse Young's modulus of chopped carbon fibers in the GDL and the surface profile of the BPP are found to be significant to the contact resistance. The factor study also sheds light on the manufacturing requirements of carbon fiber GDLs for a better contact performance in PEM fuel cells.

  3. Analytical Investigation and Improvement of Performance of a Proton Exchange Membrane (Pem) Fuel Cell in Mobile Applications

    NASA Astrophysics Data System (ADS)

    Khazaee, I.

    2015-05-01

    In this study, the performance of a proton exchange membrane fuel cell in mobile applications is investigated analytically. At present the main use and advantages of fuel cells impact particularly strongly on mobile applications such as vehicles, mobile computers and mobile telephones. Some external parameters such as the cell temperature (Tcell ) , operating pressure of gases (P) and air stoichiometry (λair ) affect the performance and voltage losses in the PEM fuel cell. Because of the existence of many theoretical, empirical and semi-empirical models of the PEM fuel cell, it is necessary to compare the accuracy of these models. But theoretical models that are obtained from thermodynamic and electrochemical approach, are very exact but complex, so it would be easier to use the empirical and smi-empirical models in order to forecast the fuel cell system performance in many applications such as mobile applications. The main purpose of this study is to obtain the semi-empirical relation of a PEM fuel cell with the least voltage losses. Also, the results are compared with the existing experimental results in the literature and a good agreement is seen.

  4. Comprehensive one-dimensional, semi-analytical, mathematical model for liquid-feed polymer electrolyte membrane direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Kareemulla, D.; Jayanti, S.

    Polymer electrolyte membrane direct methanol fuel cells (PEM-DMFCs) have several advantages over hydrogen-fuelled PEM fuel cells; but sluggish methanol electrochemical oxidation and methanol crossover from the anode to the cathode through the PEM are two major problems with these cells. In the present work, a comprehensive one-dimensional, single phase, isothermal mathematical model is developed for a liquid-feed PEM-DMFC, taking into account all the necessary mass transport and electrochemical phenomena. Diffusion and convective effects are considered for methanol transport on the anode side and in the PEM, whereas only diffusional transport of species is considered on the cathode side. A multi-step reaction mechanism is used to describe the electrochemical oxidation of methanol at the anode. Stefan-Maxwell equations are used to describe multi-component diffusion on the cathode side and Tafel type of kinetics is used to describe the simultaneous methanol oxidation and oxygen reduction reactions at the cathode. The model fully accounts for the mixed potential effect caused by methanol crossover at the cathode. It shows excellent agreement with literature data of the limiting current density for different low methanol feed concentrations at different operating temperatures. At high methanol feed concentrations, oxygen depletion on the cathode side, due to excessive methanol crossover, results in mass-transport limitations. The model can be used to optimize the geometric and physical parameters with a view to extracting the highest current density while still keeping a tolerably low methanol crossover.

  5. Composite fuel cell membranes

    DOEpatents

    Plowman, K.R.; Rehg, T.J.; Davis, L.W.; Carl, W.P.; Cisar, A.J.; Eastland, C.S.

    1997-08-05

    A bilayer or trilayer composite ion exchange membrane is described suitable for use in a fuel cell. The composite membrane has a high equivalent weight thick layer in order to provide sufficient strength and low equivalent weight surface layers for improved electrical performance in a fuel cell. In use, the composite membrane is provided with electrode surface layers. The composite membrane can be composed of a sulfonic fluoropolymer in both core and surface layers.

  6. Composite fuel cell membranes

    DOEpatents

    Plowman, Keith R.; Rehg, Timothy J.; Davis, Larry W.; Carl, William P.; Cisar, Alan J.; Eastland, Charles S.

    1997-01-01

    A bilayer or trilayer composite ion exchange membrane suitable for use in a fuel cell. The composite membrane has a high equivalent weight thick layer in order to provide sufficient strength and low equivalent weight surface layers for improved electrical performance in a fuel cell. In use, the composite membrane is provided with electrode surface layers. The composite membrane can be composed of a sulfonic fluoropolymer in both core and surface layers.

  7. Evaluating focused ion beam and ultramicrotome sample preparation for analytical microscopies of the cathode layer of a polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    de A. Melo, Lis G.; Hitchcock, Adam P.; Berejnov, Viatcheslav; Susac, Darija; Stumper, Juergen; Botton, Gianluigi A.

    2016-04-01

    Optimizing the structure of the porous electrodes of polymer electrolyte membrane fuel cells (PEM-FC) can improve device power and durability. Analytical microscopy techniques are important tools for measuring the electrode structure, thereby providing guidance for structural optimization. Transmission Electron Microscopy (TEM), with either Energy Dispersive X-Ray (EDX) or Electron Energy Loss Spectroscopy (EELS) analysis, and Scanning Transmission X-Ray Microscopy (STXM) are complementary methods which, together, provide a powerful approach for PEM-FC electrode analysis. Both TEM and STXM require thin (50-200 nm) samples, which can be prepared either by Focused Ion Beam (FIB) milling or by embedding and ultramicrotomy. Here we compare TEM and STXM spectromicroscopy analysis of FIB and ultramicrotomy sample preparations of the same PEM-FC sample, with focus on how sample preparation affects the derived chemical composition and spatial distributions of carbon support and ionomer. The FIB lamella method, while avoiding pore-filling by embedding media, had significant problems. In particular, in the FIB sample the carbon support was extensively amorphized and the ionomer component suffered mass loss and structural damage. Although each sample preparation technique has a role to play in PEM-FC optimization studies, it is important to be aware of the limitations of each method.

  8. Membrane in cancer cells

    SciTech Connect

    Galeotti, T.; Cittadini, A.; Neri, G.; Scarpa, A.

    1988-01-01

    This book contains papers presented at a conference on membranes in cancer cells. Topics covered include Oncogenies, hormones, and free-radical processes in malignant transformation in vitro and Superoxide onion may trigger DNA strand breaks in human granulorytes by acting as a membrane target.

  9. Analytical Applications of Transport Through Bulk Liquid Membranes.

    PubMed

    Diaconu, Ioana; Ruse, Elena; Aboul-Enein, Hassan Y; Bunaciu, Andrei A

    2016-07-03

    This review discusses the results of research in the use of bulk liquid membranes in separation processes and preconcentration for analytical purposes. It includes some theoretical aspects, definitions, types of liquid membranes, and transport mechanism, as well as advantages of using liquid membranes in laboratory studies. These concepts are necessary to understand fundamental principles of liquid membrane transport. Due to the multiple advantages of liquid membranes several studies present analytical applications of the transport through liquid membranes in separation or preconcentration processes of metallic cations and some organic compounds, such as phenol and phenolic derivatives, organic acids, amino acids, carbohydrates, and drugs. This review presents coupled techniques such as separation through the liquid membrane coupled with flow injection analysis.

  10. Membrane Cells for Brine Electrolysis.

    ERIC Educational Resources Information Center

    Tingle, M.

    1982-01-01

    Membrane cells were developed as alternatives to mercury and diaphragm cells for the electrolysis of brine. Compares the three types of cells, focusing on the advantages and disadvantages of membrane cells. (JN)

  11. The potential of carbon nanotube membranes for analytical separations.

    PubMed

    López-Lorente, A I; Simonet, B M; Valcárcel, M

    2010-07-01

    Advances in nanotechnology have enabled the development of nanoporous membranes based on carbon nanotubes, which, by virtue of their exceptional properties, constitute excellent supports for analytical processes, including the selective separation of some molecules.

  12. Membrane-based microextraction techniques in analytical chemistry: A review.

    PubMed

    Carasek, Eduardo; Merib, Josias

    2015-06-23

    The use of membrane-based sample preparation techniques in analytical chemistry has gained growing attention from the scientific community since the development of miniaturized sample preparation procedures in the 1990s. The use of membranes makes the microextraction procedures more stable, allowing the determination of analytes in complex and "dirty" samples. This review describes some characteristics of classical membrane-based microextraction techniques (membrane-protected solid-phase microextraction, hollow-fiber liquid-phase microextraction and hollow-fiber renewal liquid membrane) as well as some alternative configurations (thin film and electromembrane extraction) used successfully for the determination of different analytes in a large variety of matrices, some critical points regarding each technique are highlighted.

  13. Analytical characterization of beet root vacuole membrane

    SciTech Connect

    Marty, F.; Branton, D.

    1980-10-01

    Vacuoles from beet root (Beta vulgaris L. var. esculenta Gurke) isolated by a mechanical procedure were osmotically lysed to separate the membrane and sap components for analysis. Approximately 62% of the vacuole proteins, 70% of the nondialyzable carbohydrates and almost all of the phospholipids and sterols were recovered in the membrane fraction. The vacuole membrane had a phospholipid:protein ratio of 0.68 and a sterol:phospholipid ratio of 0.21. Seventeen complex polar lipids including phosphatides ad glycolipids have been tentatively identified. Phosphatidylcholine (54%) and phosphatidylethanolamine (24%) were the most prominant phosphoglycerides besides phosphatidylserine, phosphatidylglycerol, phosphatidylinositol, and phosphatidic acid (1, 4, 5, and 12%, respectively. A putative sulfoglycoside and two major ceramide glycoside-like lipids, resembling those of animal lysosomes, were identified by thin-layer chromatography. High-resolution SDS-acrylamide gel electrophoresis of the polypeptides from the vacuole revealed 15 major bands with apparent molecular weights ranging from 91,000 to 12,000. Selective elution experiments delineated those polypeptides that were peripheral membrane proteins or sap proteins adsorbed to the membrane, and those that exhibited hydrophobic interaction with the lipid core. Lectin labeling results indicated that most of the polypeptides from the membrane and from the sap were glycoproteins probably of the high-mannose type characteristic of lysosomal enzymes that have undergone several stages of posttranslational modification.

  14. Fuel cell membrane humidification

    DOEpatents

    Wilson, Mahlon S.

    1999-01-01

    A polymer electrolyte membrane fuel cell assembly has an anode side and a cathode side separated by the membrane and generating electrical current by electrochemical reactions between a fuel gas and an oxidant. The anode side comprises a hydrophobic gas diffusion backing contacting one side of the membrane and having hydrophilic areas therein for providing liquid water directly to the one side of the membrane through the hydrophilic areas of the gas diffusion backing. In a preferred embodiment, the hydrophilic areas of the gas diffusion backing are formed by sewing a hydrophilic thread through the backing. Liquid water is distributed over the gas diffusion backing in distribution channels that are separate from the fuel distribution channels.

  15. Biological Fuel Cells and Membranes.

    PubMed

    Ghassemi, Zahra; Slaughter, Gymama

    2017-01-17

    Biofuel cells have been widely used to generate bioelectricity. Early biofuel cells employ a semi-permeable membrane to separate the anodic and cathodic compartments. The impact of different membrane materials and compositions has also been explored. Some membrane materials are employed strictly as membrane separators, while some have gained significant attention in the immobilization of enzymes or microorganisms within or behind the membrane at the electrode surface. The membrane material affects the transfer rate of the chemical species (e.g., fuel, oxygen molecules, and products) involved in the chemical reaction, which in turn has an impact on the performance of the biofuel cell. For enzymatic biofuel cells, Nafion, modified Nafion, and chitosan membranes have been used widely and continue to hold great promise in the long-term stability of enzymes and microorganisms encapsulated within them. This article provides a review of the most widely used membrane materials in the development of enzymatic and microbial biofuel cells.

  16. Biological Fuel Cells and Membranes

    PubMed Central

    Ghassemi, Zahra; Slaughter, Gymama

    2017-01-01

    Biofuel cells have been widely used to generate bioelectricity. Early biofuel cells employ a semi-permeable membrane to separate the anodic and cathodic compartments. The impact of different membrane materials and compositions has also been explored. Some membrane materials are employed strictly as membrane separators, while some have gained significant attention in the immobilization of enzymes or microorganisms within or behind the membrane at the electrode surface. The membrane material affects the transfer rate of the chemical species (e.g., fuel, oxygen molecules, and products) involved in the chemical reaction, which in turn has an impact on the performance of the biofuel cell. For enzymatic biofuel cells, Nafion, modified Nafion, and chitosan membranes have been used widely and continue to hold great promise in the long-term stability of enzymes and microorganisms encapsulated within them. This article provides a review of the most widely used membrane materials in the development of enzymatic and microbial biofuel cells. PMID:28106711

  17. The First Cell Membranes

    NASA Astrophysics Data System (ADS)

    Deamer, David; Dworkin, Jason P.; Sandford, Scott A.; Bernstein, Max P.; Allamandola, Louis J.

    2002-12-01

    Organic compounds are synthesized in the interstellar medium and can be delivered to planetary surfaces such as the early Earth, where they mix with endogenous species. Some of these compounds are amphiphilic, having polar and nonpolar groups on the same molecule. Amphiphilic compounds spontaneously self-assemble into more complex structures such as bimolecular layers, which in turn form closed membranous vesicles. The first forms of cellular life required self-assembled membranes that were likely to have been produced from amphiphilic compounds on the prebiotic Earth. Laboratory simulations show that such vesicles readily encapsulate functional macromolecules, including nucleic acids and polymerases. The goal of future investigations will be to fabricate artificial cells as models of the origin of life.

  18. The First Cell Membranes

    NASA Technical Reports Server (NTRS)

    Deamer, David; Dworkin, Jason P.; Sandford, Scott A.; Bernstein, Max P.; Allamandola, Louis J.

    2004-01-01

    Organic compounds are synthesized in the interstellar medium and can be delivered to planetary surfaces such as the early Earth, where they mix with endogenous organic mixtures. Some of these compounds are amphiphilic, having polar and non-polar groups on the same molecule. Amphiphilic compounds spontaneously self-assembly into more complex structures such as bimolecular layers, which in turn form closed membranous vesicles. The first forms of cellular life required self-assembled membranes that were likely to be available on the prebiotic Earth. Laboratory simulations show that such vesicles readily encapsulate functional macromolecules, including nucleic acids and polymerases. A goal of future investigations is to fabricate artificial cells as models of the origin of life.

  19. Cell Membrane Softening in Cancer Cells

    NASA Astrophysics Data System (ADS)

    Schmidt, Sebastian; Händel, Chris; Käs, Josef

    Biomechanical properties are useful characteristics and regulators of the cell's state. Current research connects mechanical properties of the cytoskeleton to many cellular processes but does not investigate the biomechanics of the plasma membrane. We evaluated thermal fluctuations of giant plasma membrane vesicles, directly derived from the plasma membranes of primary breast and cervical cells and observed a lowered rigidity in the plasma membrane of malignant cells compared to non-malignant cells. To investigate the specific role of membrane rigidity changes, we treated two cell lines with the Acetyl-CoA carboxylase inhibitor Soraphen A. It changed the lipidome of cells and drastically increased membrane stiffness by up regulating short chained membrane lipids. These altered cells had a decreased motility in Boyden chamber assays. Our results indicate that the thermal fluctuations of the membrane, which are much smaller than the fluctuations driven by the cytoskeleton, can be modulated by the cell and have an impact on adhesion and motility.

  20. Fuel cell with ionization membrane

    NASA Technical Reports Server (NTRS)

    Hartley, Frank T. (Inventor)

    2007-01-01

    A fuel cell is disclosed comprising an ionization membrane having at least one area through which gas is passed, and which ionizes the gas passing therethrough, and a cathode for receiving the ions generated by the ionization membrane. The ionization membrane may include one or more openings in the membrane with electrodes that are located closer than a mean free path of molecules within the gas to be ionized. Methods of manufacture are also provided.

  1. Analytical pyrolysis of cells and cell fragments

    SciTech Connect

    Faix, O.; Bertelt, E.

    1995-12-01

    Wood of spruce, beech and birch was disintegrated without chemical pretreatment after 10 minutes of steaming at 110{degrees}C in a laboratory defibrator. Fibers, vessels, and fragments of secondary wall were separated by wet screening. A hydrocylon was used for separation of middle lamellae. By using analytical pyrolysis-GC/MS, parenchymatic cells were found to be richer in lignin than the other cells. The lignin content of middle lamellae was 35% (beech, spruce) and 39% (birch). In agreement with the literature, the S/G ratios of the vessels and middle lamellae was lower than those of the other cells and cell fragments.

  2. The Molecules of the Cell Membrane.

    ERIC Educational Resources Information Center

    Bretscher, Mark S.

    1985-01-01

    Cell membrane molecules form a simple, two-dimensional liquid controlling what enters and leaves the cell. Discusses cell membrane molecular architecture, plasma membranes, epithelial cells, cycles of endocytosis and exocytosis, and other topics. Indicates that some cells internalize, then recycle, membrane area equivalent to their entire surface…

  3. Electron-beam direct processing on living cell membrane

    SciTech Connect

    Hoshino, Takayuki; Morishima, Keisuke

    2011-10-24

    We demonstrated a direct processing on a living Hep G2 cell membrane in conventional cultivation conditions using an electron beam. Electron beam-induced deposition from liquid precursor 3,4-ethylenedioxythiophene and ablation was performed on the living cells. The 2.5-10 keV electron beam which was irradiated through a 100-nm-thick SiN nanomembrane could induce a deposition pattern and a ablation on a living cell membrane. This electron beam direct processing can provide simple in-situ cell surface modification for an analytical method of living cell membrane dynamic.

  4. Corrugated Membrane Fuel Cell Structures

    SciTech Connect

    Grot, Stephen

    2013-09-30

    One of the most challenging aspects of traditional PEM fuel cell stacks is the difficulty achieving the platinum catalyst utilization target of 0.2 gPt/kWe set forth by the DOE. Good catalyst utilization can be achieved with state-of-the-art catalyst coated membranes (CCM) when low catalyst loadings (<0.3 mg/cm2) are used at a low current. However, when low platinum loadings are used, the peak power density is lower than conventional loadings, requiring a larger total active area and a larger bipolar plate. This results in a lower overall stack power density not meeting the DOE target. By corrugating the fuel cell membrane electrode structure, Ion Power?s goal is to realize both the Pt utilization targets as well as the power density targets of the DOE. This will be achieved by demonstrating a fuel cell single cell (50 cm2) with a twofold increase in the membrane active area over the geometric area of the cell by corrugating the MEA structure. The corrugating structure must be able to demonstrate the target properties of < 10 mOhm-cm2 electrical resistance at > 20 psi compressive strength over the active area, in combination with offering at least 80% of power density that can be achieved by using the same MEA in a flat plate structure. Corrugated membrane fuel cell structures also have the potential to meet DOE power density targets by essentially packaging more membrane area into the same fuel cell volume as compared to conventional stack constructions.

  5. Fatty Acids in Membranes as Homeostatic, Metabolic and Nutritional Biomarkers: Recent Advancements in Analytics and Diagnostics

    PubMed Central

    Ferreri, Carla; Masi, Annalisa; Sansone, Anna; Giacometti, Giorgia; Larocca, Anna Vita; Menounou, Georgia; Scanferlato, Roberta; Tortorella, Silvia; Rota, Domenico; Conti, Marco; Deplano, Simone; Louka, Maria; Maranini, Anna Rosaria; Salati, Arianna; Sunda, Valentina; Chatgilialoglu, Chryssostomos

    2016-01-01

    Fatty acids, as structural components of membranes and inflammation/anti-inflammatory mediators, have well-known protective and regulatory effects. They are studied as biomarkers of pathological conditions, as well as saturated and unsaturated hydrophobic moieties in membrane phospholipids that contribute to homeostasis and physiological functions. Lifestyle, nutrition, metabolism and stress—with an excess of radical and oxidative processes—cause fatty acid changes that are examined in the human body using blood lipids. Fatty acid-based membrane lipidomics represents a powerful diagnostic tool for assessing the quantity and quality of fatty acid constituents and also for the follow-up of the membrane fatty acid remodeling that is associated with different physiological and pathological conditions. This review focuses on fatty acid biomarkers with two examples of recent lipidomic research and health applications: (i) monounsaturated fatty acids and the analytical challenge offered by hexadecenoic fatty acids (C16:1); and (ii) the cohort of 10 fatty acids in phospholipids of red blood cell membranes and its connections to metabolic and nutritional status in healthy and diseased subjects. PMID:28025506

  6. Strategies for cell membrane functionalization

    PubMed Central

    Armstrong, James PK

    2016-01-01

    The ability to rationally manipulate and augment the cytoplasmic membrane can be used to overcome many of the challenges faced by conventional cellular therapies and provide innovative opportunities when combined with new biotechnologies. The focus of this review is on emerging strategies used in cell functionalization, highlighting both pioneering approaches and recent developments. These will be discussed within the context of future directions in this rapidly evolving field. PMID:27229904

  7. Lateral organization of membranes and cell shapes.

    PubMed Central

    Markin, V S

    1981-01-01

    The relations among membrane structure, mechanical properties, and cell shape have been investigated. The fluid mosaic membrane models used contains several components that move freely in the membrane plane. These components interact with each other and determine properties of the membrane such as curvature and elasticity. A free energy equation is postulated for such a multicomponent membrane and the condition of free energy minimum is used to obtain differential equations relating the distribution of membrane components and the local membrane curvature. The force that moves membrane components along the membrane in a variable curvature field is calculated. A change in the intramembrane interactions can bring about phase separation or particle clustering. This, in turn, may strongly affect the local curvature. The numerical solution of the set of equations for the two dimensional case allows determination of the cell shape and the component distribution along the membrane. The model has been applied to describe certain erythrocytes shape transformations. PMID:7284547

  8. Fuel-Cell Structure Prevents Membrane Drying

    NASA Technical Reports Server (NTRS)

    Mcelroy, J.

    1986-01-01

    Embossed plates direct flows of reactants and coolant. Membrane-type fuel-cell battery has improved reactant flow and heat removal. Compact, lightweight battery produces high current and power without drying of membranes.

  9. Actinide transport across cell membranes.

    PubMed

    Bulman, R A; Griffin, R J

    1980-01-01

    Protactinium uptake into the normal liver does not exceed 3%, but when the phospholipid levels in the liver are elevated by administration of thioacetamide this uptake increases to 31%. Phosphatidic acid, which is absent from the normal liver, has been shown to extract protactinium into organic solvents. However, phosphatidylserine, a component of normal liver cell membranes, does not extract protactinium. It might be conjectured that this is why so little protactinium is taken up by the normal liver. The hypothesis is advanced that phosphatidylserine, which is known to complex plutonium, americium and curium, may regulate the uptake of these elements by liver.

  10. Analytical and numerical studies on the nonlinear dynamic response of orthotropic membranes under impact load

    NASA Astrophysics Data System (ADS)

    Liu, Changjiang; Zheng, Zhoulian; Yang, Xiaoyan

    2016-12-01

    Orthotropic membrane components and structures are widely used in building structures, instruments and meters, electronic engineering, space and aeronautics, etc., because of their light weights. However, the same lightweight combined with low stiffness make membranes prone to vibration under dynamic loads, and in some cases the vibration may lead to structural failure. Herein, the undamped nonlinear vibration response of pretension rectangular orthotropic membrane structures subjected to impact loading is studied by analytical and numerical methods. The analytical solution is obtained by solving the governing equations by the Bubnov-Galerkin method and the Lindstedt-Poincaré perturbation method. Numerical analysis has also been carried out based on the same theoretical model. The analytical and numerical results have been compared and analyzed, and the influence of various model parameters on membrane vibration discussed. The results obtained herein provide some theoretical basis for the vibration control and dynamic design of orthotropic membrane components and structures.

  11. Chemical degradation mechanisms of membranes for alkaline membrane fuel cells

    SciTech Connect

    Choe, Yoong-Kee; Henson, Neil J.; Kim, Yu Seung

    2015-12-31

    Chemical degradation mechanisms of membranes for alkaline membrane fuel cells have been investigated using density functional theory (DFT). We have elucidated that the aryl-ether moiety of membranes is one of the weakest site against attack of hydroxide ions. The results of DFT calculations for hydroxide initiated aryl-ether cleavage indicated that the aryl-ether cleavage occurred prior to degradation of cationic functional group. Such a weak nature of the aryl-ether group arises from the electron deficiency of the aryl group as well as the low bond dissociation energy. The DFT results suggests that removal of the aryl-ether group in the membrane should enhance the stability of membranes under alkaline conditions. In fact, an ether fee poly(phenylene) membrane exhibits excellent stability against the attack from hydroxide ions.

  12. In-membrane micro fuel cell

    DOEpatents

    Omosebi, Ayokunle; Besser, Ronald

    2016-09-06

    An in-membrane micro fuel cell comprises an electrically-insulating membrane that is permissive to the flow of cations, such as protons, and a pair of electrodes deposited on channels formed in the membrane. The channels are arranged as conduits for fluids, and define a membrane ridge between the channels. The electrodes are porous and include catalysts for promoting the liberation of a proton and an electron from a chemical species and/or or the recombination of a proton and an electron with a chemical specie. The fuel cell may be provided a biosensor, an electrochemical sensor, a microfluidic device, or other microscale devices fabricated in the fuel cell membrane.

  13. Membrane tether formation from blebbing cells.

    PubMed Central

    Dai, J; Sheetz, M P

    1999-01-01

    Membrane tension has been proposed to be important in regulating cell functions such as endocytosis and cell motility. The apparent membrane tension has been calculated from tether forces measured with laser tweezers. Both membrane-cytoskeleton adhesion and membrane tension contribute to the tether force. Separation of the plasma membrane from the cytoskeleton occurs in membrane blebs, which could remove the membrane-cytoskeleton adhesion term. In renal epithelial cells, tether forces are significantly lower on blebs than on membranes that are supported by cytoskeleton. Furthermore, the tether forces are equal on apical and basolateral blebs. In contrast, tether forces from membranes supported by the cytoskeleton are greater in apical than in basolateral regions, which is consistent with the greater apparent cytoskeletal density in the apical region. We suggest that the tether force on blebs primarily contains only the membrane tension term and that the membrane tension may be uniform over the cell surface. Additional support for this hypothesis comes from observations of melanoma cells that spontaneously bleb. In melanoma cells, tether forces on blebs are proportional to the radius of the bleb, and as large blebs form, there are spikes in the tether force in other cell regions. We suggest that an internal osmotic pressure inflates the blebs, and the pressure calculated from the Law of Laplace is similar to independent measurements of intracellular pressures. When the membrane tension term is subtracted from the apparent membrane tension over the cytoskeleton, the membrane-cytoskeleton adhesion term can be estimated. In both cell systems, membrane-cytoskeleton adhesion was the major factor in generating the tether force. PMID:10585959

  14. A membrane reservoir at the cell surface

    PubMed Central

    Figard, Lauren; Sokac, Anna Marie

    2014-01-01

    Cell surface expansion is a necessary part of cell shape change. One long-standing hypothesis proposes that membrane for this expansion comes from the flattening out of cell surface projections such as microvilli and membrane folds. Correlative EM data of cells undergoing phagocytosis, cytokinesis, and morphogenesis has hinted at the existence of such an unfolding mechanism for decades; but unfolding has only recently been confirmed using live-cell imaging and biophysical approaches. Considering the wide range of cells in which plasma membrane unfolding has now been reported, it likely represents a fundamental mechanism of cell shape change. PMID:24844289

  15. Polymer electrolyte membrane assembly for fuel cells

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S. (Inventor); Kindler, Andrew (Inventor); Yavrouian, Andre (Inventor); Halpert, Gerald (Inventor)

    2000-01-01

    An electrolyte membrane for use in a fuel cell can contain sulfonated polyphenylether sulfones. The membrane can contain a first sulfonated polyphenylether sulfone and a second sulfonated polyphenylether sulfone, wherein the first sulfonated polyphenylether and the second sulfonated polyphenylether sulfone have equivalent weights greater than about 560, and the first sulfonated polyphenylether and the second sulfonated polyphenylether sulfone also have different equivalent weights. Also, a membrane for use in a fuel cell can contain a sulfonated polyphenylether sulfone and an unsulfonated polyphenylether sulfone. Methods for manufacturing a membrane electrode assemblies for use in fuel cells can include roughening a membrane surface. Electrodes and methods for fabricating such electrodes for use in a chemical fuel cell can include sintering an electrode. Such membranes and electrodes can be assembled into chemical fuel cells.

  16. Polymer electrolyte membrane assembly for fuel cells

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S. (Inventor); Kindler, Andrew (Inventor); Yavrouian, Andre (Inventor); Halpert, Gerald (Inventor)

    2002-01-01

    An electrolyte membrane for use in a fuel cell can contain sulfonated polyphenylether sulfones. The membrane can contain a first sulfonated polyphenylether sulfone and a second sulfonated polyphenylether sulfone, wherein the first sulfonated polyphenylether and the second sulfonated polyphenylether sulfone have equivalent weights greater than about 560, and the first sulfonated polyphenylether and the second sulfonated polyphenylether sulfone also have different equivalent weights. Also, a membrane for use in a fuel cell can contain a sulfonated polyphenylether sulfone and an unsulfonated polyphenylether sulfone. Methods for manufacturing a membrane electrode assemblies for use in fuel cells can include roughening a membrane surface. Electrodes and methods for fabricating such electrodes for use in a chemical fuel cell can include sintering an electrode. Such membranes and electrodes can be assembled into chemical fuel cells.

  17. [Germ cell membrane lipids in spermatogenesis].

    PubMed

    Wang, Ting; Shi, Xiao; Quan, Song

    2016-05-01

    Spermatogenesis is a complex developmental process in which a diploid progenitor germ cell transforms into highly specialized spermatozoa. During spermatogenesis, membrane remodeling takes place, and cell membrane permeability and liquidity undergo phase-specific changes, which are all associated with the alteration of membrane lipids. Lipids are important components of the germ cell membrane, whose volume and ratio fluctuate in different phases of spermatogenesis. Abnormal lipid metabolism can cause spermatogenic dysfunction and consequently male infertility. Germ cell membrane lipids are mainly composed of cholesterol, phospholipids and glycolipids, which play critical roles in cell adhesion and signal transduction during spermatogenesis. An insight into the correlation of membrane lipids with spermatogenesis helps us to better understand the mechanisms of spermatogenesis and provide new approaches to the diagnosis and treatment of male infertility.

  18. Fuel cell ion-exchange membrane investigation

    NASA Technical Reports Server (NTRS)

    Toy, M. S.

    1972-01-01

    The present deficiencies in the fluorocarbon sulfonic acid membrane used as the solid polymer electrolyte in the H2/O2 fuel cell are studied. Considered are: Adhesives selection, elastomeric formulations, scavenger exploration, and membrane characterization. The significant data are interpreted and recommendations are given for both short and long range further investigations in two of the four major areas: membrane adhesives and membrane stabilization.

  19. Measurement of Cell Membrane Fluidity by Laurdan GP: Fluorescence Spectroscopy and Microscopy.

    PubMed

    Scheinpflug, Kathi; Krylova, Oxana; Strahl, Henrik

    2017-01-01

    Membrane fluidity is a critical parameter of cellular membranes which cells continuously strive to maintain within a viable range. An interference with the correct membrane fluidity state can strongly inhibit cell function. Triggered changes in membrane fluidity have been postulated to contribute to the mechanism of action of membrane targeting antimicrobials, but the corresponding analyses have been hampered by the absence of readily available analytical tools. Here, we provide detailed protocols that allow straightforward measurement of antibiotic compound-triggered changes in membrane fluidity both in vivo and in vitro.

  20. Fuel cell and membrane therefore

    SciTech Connect

    Aindow, Tai-Tsui

    2016-08-09

    A fuel cell includes first and second flow field plates, and an anode electrode and a cathode electrode between the flow field plates. A polymer electrolyte membrane (PEM) is arranged between the electrodes. At least one of the flow field plates influences, at least in part, an in-plane anisotropic physical condition of the PEM that varies in magnitude between a high value direction and a low value direction. The PEM has an in-plane physical property that varies in magnitude between a high value direction and a low value direction. The PEM is oriented with its high value direction substantially aligned with the high value direction of the flow field plate.

  1. Proton Exchange Membranes for Fuel Cells

    SciTech Connect

    Devanathan, Ramaswami

    2010-11-01

    Proton exchange membrane, also known as polymer electrolyte membrane, fuel cells (PEMFCs) offer the promise of efficient conversion of chemical energy of fuel, such as hydrogen or methanol, into electricity with minimal pollution. Their widespread use to power zero-emission automobiles as part of a hydrogen economy can contribute to enhanced energy security and reduction in greenhouse gas emissions. However, the commercial viability of PEMFC technology is hindered by high cost associated with the membrane electrode assembly (MEA) and poor membrane durability under prolonged operation at elevated temperature. Membranes for automotive fuel cell applications need to perform well over a period comparable to the life of an automotive engine and under heavy load cycling including start-stop cycling under sub-freezing conditions. The combination of elevated temperature, changes in humidity levels, physical stresses and harsh chemical environment contribute to membrane degradation. Perfluorinated sulfonic acid (PFSA)-based membranes, such as Nafion®, have been the mainstay of PEMFC technology. Their limitations, in terms of cost and poor conductivity at low hydration, have led to continuing research into membranes that have good proton conductivity at elevated temperatures above 120 °C and under low humidity conditions. Such membranes have the potential to avoid catalyst poisoning, simplify fuel cell design and reduce the cost of fuel cells. Hydrocarbon-based membranes are being developed as alternatives to PFSA membranes, but concerns about chemical and mechanical stability and durability remain. Novel anhydrous membranes based on polymer gels infused with protic ionic liquids have also been recently proposed, but considerable fundamental research is needed to understand proton transport in novel membranes and evaluate durability under fuel cell operating conditions. In order to advance this promising technology, it is essential to rationally design the next generation

  2. Analytical strategies for studying stem cell metabolism

    PubMed Central

    Arnold, James M.; Choi, William T.; Sreekumar, Arun

    2015-01-01

    Owing to their capacity for self-renewal and pluripotency, stem cells possess untold potential for revolutionizing the field of regenerative medicine through the development of novel therapeutic strategies for treating cancer, diabetes, cardiovascular and neurodegenerative diseases. Central to developing these strategies is improving our understanding of biological mechanisms responsible for governing stem cell fate and self-renewal. Increasing attention is being given to the significance of metabolism, through the production of energy and generation of small molecules, as a critical regulator of stem cell functioning. Rapid advances in the field of metabolomics now allow for in-depth profiling of stem cells both in vitro and in vivo, providing a systems perspective on key metabolic and molecular pathways which influence stem cell biology. Understanding the analytical platforms and techniques that are currently used to study stem cell metabolomics, as well as how new insights can be derived from this knowledge, will accelerate new research in the field and improve future efforts to expand our understanding of the interplay between metabolism and stem cell biology. PMID:26213533

  3. Analytical strategies for studying stem cell metabolism.

    PubMed

    Arnold, James M; Choi, William T; Sreekumar, Arun; Maletić-Savatić, Mirjana

    2015-04-01

    Owing to their capacity for self-renewal and pluripotency, stem cells possess untold potential for revolutionizing the field of regenerative medicine through the development of novel therapeutic strategies for treating cancer, diabetes, cardiovascular and neurodegenerative diseases. Central to developing these strategies is improving our understanding of biological mechanisms responsible for governing stem cell fate and self-renewal. Increasing attention is being given to the significance of metabolism, through the production of energy and generation of small molecules, as a critical regulator of stem cell functioning. Rapid advances in the field of metabolomics now allow for in-depth profiling of stem cells both in vitro and in vivo, providing a systems perspective on key metabolic and molecular pathways which influence stem cell biology. Understanding the analytical platforms and techniques that are currently used to study stem cell metabolomics, as well as how new insights can be derived from this knowledge, will accelerate new research in the field and improve future efforts to expand our understanding of the interplay between metabolism and stem cell biology.

  4. Functional dynamics of cell surface membrane proteins

    NASA Astrophysics Data System (ADS)

    Nishida, Noritaka; Osawa, Masanori; Takeuchi, Koh; Imai, Shunsuke; Stampoulis, Pavlos; Kofuku, Yutaka; Ueda, Takumi; Shimada, Ichio

    2014-04-01

    Cell surface receptors are integral membrane proteins that receive external stimuli, and transmit signals across plasma membranes. In the conventional view of receptor activation, ligand binding to the extracellular side of the receptor induces conformational changes, which convert the structure of the receptor into an active conformation. However, recent NMR studies of cell surface membrane proteins have revealed that their structures are more dynamic than previously envisioned, and they fluctuate between multiple conformations in an equilibrium on various timescales. In addition, NMR analyses, along with biochemical and cell biological experiments indicated that such dynamical properties are critical for the proper functions of the receptors. In this review, we will describe several NMR studies that revealed direct linkage between the structural dynamics and the functions of the cell surface membrane proteins, such as G-protein coupled receptors (GPCRs), ion channels, membrane transporters, and cell adhesion molecules.

  5. Effect of BCD Plasma on a Bacteria Cell Membrane

    NASA Astrophysics Data System (ADS)

    Nasrin, Navabsafa; Hamid, Ghomi; Maryam, Nikkhah; Soheila, Mohades; Hossein, Dabiri; Saeed, Ghasemi

    2013-07-01

    Abstract Cell membrane rupture is considered to be one of the probable mechanisms for bacterial inactivation using barrier corona discharge (BCD) plasma. In this paper, the effect of the BCD plasma on the Escherichia coli (E. coli) bacteria cell wall was investigated through two analytical methods; Adenosine-5'-triphosphate (ATP) assay and Atomic Force Microscopy (AFM). The ATP assay results indicate an increase in the ATP content of samples which were exposed to the BCD plasma. This implies the bacteria cell rupture. Moreover, AFM images confirm a serious damage of the bacteria cell wall under the influence of the bactericidal agents of the plasma.

  6. Menin localization in cell membrane compartment

    PubMed Central

    He, Xin; Wang, Lei; Yan, Jizhou; Yuan, Chaoxing; Witze, Eric S.; Hua, Xianxin

    2016-01-01

    ABSTRACT Menin is encoded by the MEN1 gene, which is mutated in an inherited human syndrome, multiple endocrine neoplasia type 1(MEN1). Menin is primarily nuclear protein, acting as a tumor suppressor in endocrine organs, but as an oncogenic factor in the mixed lineage leukemia, in a tissue-specific manner. Recently, the crystal structures of menin with different binding partners reveal menin as a key scaffold protein that functionally interacts with various partners to regulate gene transcription in the nucleus. However, outside the nucleus, menin also regulates multiple signaling pathways that traverse the cell surface membrane. The precise nature regarding to how menin associates with the membrane fraction is poorly understood. Here we show that a small fraction of menin associates with the cell membrane fraction likely via serine palmitoylation. Moreover, the majority of the membrane-associated menin may reside inside membrane vesicles, as menin is protected from trypsin-mediated proteolysis, but disruption of the membrane fraction using detergent abolishes the detection. Consistently, cellular staining for menin also reveals the distribution of menin in the cell membrane and the punctate-like cell organelles. Our findings suggest that part of intracellular menin associates with the cell membrane peripherally as well as resides within the membrane vesicles. PMID:26560942

  7. Red cell membrane: past, present, and future

    PubMed Central

    Gallagher, Patrick G.

    2008-01-01

    As a result of natural selection driven by severe forms of malaria, 1 in 6 humans in the world, more than 1 billion people, are affected by red cell abnormalities, making them the most common of the inherited disorders. The non-nucleated red cell is unique among human cell type in that the plasma membrane, its only structural component, accounts for all of its diverse antigenic, transport, and mechanical characteristics. Our current concept of the red cell membrane envisions it as a composite structure in which a membrane envelope composed of cholesterol and phospholipids is secured to an elastic network of skeletal proteins via transmembrane proteins. Structural and functional characterization of the many constituents of the red cell membrane, in conjunction with biophysical and physiologic studies, has led to detailed description of the way in which the remarkable mechanical properties and other important characteristics of the red cells arise, and of the manner in which they fail in disease states. Current studies in this very active and exciting field are continuing to produce new and unexpected revelations on the function of the red cell membrane and thus of the cell in health and disease, and shed new light on membrane function in other diverse cell types. PMID:18988878

  8. Red cell membrane: past, present, and future.

    PubMed

    Mohandas, Narla; Gallagher, Patrick G

    2008-11-15

    As a result of natural selection driven by severe forms of malaria, 1 in 6 humans in the world, more than 1 billion people, are affected by red cell abnormalities, making them the most common of the inherited disorders. The non-nucleated red cell is unique among human cell type in that the plasma membrane, its only structural component, accounts for all of its diverse antigenic, transport, and mechanical characteristics. Our current concept of the red cell membrane envisions it as a composite structure in which a membrane envelope composed of cholesterol and phospholipids is secured to an elastic network of skeletal proteins via transmembrane proteins. Structural and functional characterization of the many constituents of the red cell membrane, in conjunction with biophysical and physiologic studies, has led to detailed description of the way in which the remarkable mechanical properties and other important characteristics of the red cells arise, and of the manner in which they fail in disease states. Current studies in this very active and exciting field are continuing to produce new and unexpected revelations on the function of the red cell membrane and thus of the cell in health and disease, and shed new light on membrane function in other diverse cell types.

  9. Mass-Sensitive Biosensor Systems to Determine the Membrane Interaction of Analytes.

    PubMed

    Hoß, Sebastian G; Bendas, Gerd

    2017-01-01

    Biosensors are devices that transform a biological interaction into a readout signal, which is evaluable for analytical purposes. The general strength of biosensor approaches is the avoidance of time-consuming and cost-intensive labeling procedures of the analytes. In this chapter, we give insight into a mass-sensitive surface-acoustic wave (SAW) biosensor, which represents an elegant and highly sensitive method to investigate binding events at a molecular level. The principle of SAW technology is based on the piezoelectric properties of the sensors, so as to binding events and their accompanied mass increase at the sensor surface are detectable by a change in the oscillation of the surface acoustic wave. In combination with model membranes, transferred to the sensor surface, the analytical value of SAW biosensors has strongly been increased and extended to different topics of biomedical investigations, including antibiotic research. The interaction with the bacterial membrane or certain target structures therein is the essential mode of action for various antibacterial compounds. Beside targeted interaction, an unspecific membrane binding or membrane insertion of drugs can contribute to the antibacterial activity by changing the lateral order of membrane constituents or by interfering with the membrane barrier function. Those pleiotropic effects are hardly to illustrate in the bacterial systems and need a detailed view at the in vitro level. Here, we illustrate the usefulness of a SAW biosensor in combination with model membranes to investigate the mode of membrane interaction of antibiotic active peptides. Using two different peptides we exemplary describe the interaction analysis in a two-step gain of information: (1) a binding intensity or affinity by analyzing the phase changes of oscillation, and (2) mode of membrane interaction, i.e., surface binding or internalization of the peptide by following the amplitude of oscillation.

  10. Membrane Stability during Biopreservation of Blood Cells

    PubMed Central

    Stoll, Christoph; Wolkers, Willem F.

    2011-01-01

    Summary Storage methods, which can be taken into consideration for red blood cells and platelets, include liquid storage, cryopreservation and freeze-drying. Red blood cells can be hypothermically stored at refrigerated temperatures, whereas platelets are chilling sensitive and therefore cannot be stored at temperatures below 20 °C. Here we give an overview of available cryopreservation and freeze-drying procedures for blood cells and discuss the effects of these procedures on cells, particularly on cellular membranes. Cryopreservation and freeze-drying may result in chemical and structural modifications of cellular membranes. Membranes undergo phase and permeability changes during freezing and drying. Cryo- and lyoprotective agents prevent membrane damage by different mechanisms. Cryoprotective agents are preferentially excluded from membrane surfaces. They decrease the activation energy for water transport during freezing and control the rate of cellular dehydration. Lyoprotectants are thought to stabilize membranes during drying by forming direct hydrogen bonding interactions with phospholipid head groups. In addition, lyoprotectants can form a glassy state at room temperature. Recently liposomes have been investigated to stabilize blood cells during freezing and freeze-drying. Liposomes modify the composition of cellular membranes by lipid and cholesterol transfer, which can stabilize or destabilize the low temperature response of cells. PMID:21566710

  11. Proton conducting membrane for fuel cells

    DOEpatents

    Colombo, Daniel G.; Krumpelt, Michael; Myers, Deborah J.; Kopasz, John P.

    2005-12-20

    An ion conducting membrane comprising dendrimeric polymers covalently linked into a network structure. The dendrimeric polymers have acid functional terminal groups and may be covalently linked via linking compounds, cross-coupling reactions, or copolymerization reactions. The ion conducting membranes may be produced by various methods and used in fuel cells.

  12. Proton conducting membrane for fuel cells

    DOEpatents

    Colombo, Daniel G.; Krumpelt, Michael; Myers, Deborah J.; Kopasz, John P.

    2007-03-27

    An ion conducting membrane comprising dendrimeric polymers covalently linked into a network structure. The dendrimeric polymers have acid functional terminal groups and may be covalently linked via linking compounds, cross-coupling reactions, or copolymerization reactions. The ion conducting membranes may be produced by various methods and used in fuel cells.

  13. Membrane elastic properties and cell function.

    PubMed

    Pontes, Bruno; Ayala, Yareni; Fonseca, Anna Carolina C; Romão, Luciana F; Amaral, Racκele F; Salgado, Leonardo T; Lima, Flavia R; Farina, Marcos; Viana, Nathan B; Moura-Neto, Vivaldo; Nussenzveig, H Moysés

    2013-01-01

    Recent studies indicate that the cell membrane, interacting with its attached cytoskeleton, is an important regulator of cell function, exerting and responding to forces. We investigate this relationship by looking for connections between cell membrane elastic properties, especially surface tension and bending modulus, and cell function. Those properties are measured by pulling tethers from the cell membrane with optical tweezers. Their values are determined for all major cell types of the central nervous system, as well as for macrophage. Astrocytes and glioblastoma cells, which are considerably more dynamic than neurons, have substantially larger surface tensions. Resting microglia, which continually scan their environment through motility and protrusions, have the highest elastic constants, with values similar to those for resting macrophage. For both microglia and macrophage, we find a sharp softening of bending modulus between their resting and activated forms, which is very advantageous for their acquisition of phagocytic functions upon activation. We also determine the elastic constants of pure cell membrane, with no attached cytoskeleton. For all cell types, the presence of F-actin within tethers, contrary to conventional wisdom, is confirmed. Our findings suggest the existence of a close connection between membrane elastic constants and cell function.

  14. Membrane Elastic Properties and Cell Function

    PubMed Central

    Pontes, Bruno; Ayala, Yareni; Fonseca, Anna Carolina C.; Romão, Luciana F.; Amaral, Racκele F.; Salgado, Leonardo T.; Lima, Flavia R.; Farina, Marcos; Viana, Nathan B.; Moura-Neto, Vivaldo; Nussenzveig, H. Moysés

    2013-01-01

    Recent studies indicate that the cell membrane, interacting with its attached cytoskeleton, is an important regulator of cell function, exerting and responding to forces. We investigate this relationship by looking for connections between cell membrane elastic properties, especially surface tension and bending modulus, and cell function. Those properties are measured by pulling tethers from the cell membrane with optical tweezers. Their values are determined for all major cell types of the central nervous system, as well as for macrophage. Astrocytes and glioblastoma cells, which are considerably more dynamic than neurons, have substantially larger surface tensions. Resting microglia, which continually scan their environment through motility and protrusions, have the highest elastic constants, with values similar to those for resting macrophage. For both microglia and macrophage, we find a sharp softening of bending modulus between their resting and activated forms, which is very advantageous for their acquisition of phagocytic functions upon activation. We also determine the elastic constants of pure cell membrane, with no attached cytoskeleton. For all cell types, the presence of F-actin within tethers, contrary to conventional wisdom, is confirmed. Our findings suggest the existence of a close connection between membrane elastic constants and cell function. PMID:23844071

  15. Advanced membrane electrode assemblies for fuel cells

    SciTech Connect

    Kim, Yu Seung; Pivovar, Bryan S

    2014-02-25

    A method of preparing advanced membrane electrode assemblies (MEA) for use in fuel cells. A base polymer is selected for a base membrane. An electrode composition is selected to optimize properties exhibited by the membrane electrode assembly based on the selection of the base polymer. A property-tuning coating layer composition is selected based on compatibility with the base polymer and the electrode composition. A solvent is selected based on the interaction of the solvent with the base polymer and the property-tuning coating layer composition. The MEA is assembled by preparing the base membrane and then applying the property-tuning coating layer to form a composite membrane. Finally, a catalyst is applied to the composite membrane.

  16. Advanced membrane electrode assemblies for fuel cells

    SciTech Connect

    Kim, Yu Seung; Pivovar, Bryan S.

    2012-07-24

    A method of preparing advanced membrane electrode assemblies (MEA) for use in fuel cells. A base polymer is selected for a base membrane. An electrode composition is selected to optimize properties exhibited by the membrane electrode assembly based on the selection of the base polymer. A property-tuning coating layer composition is selected based on compatibility with the base polymer and the electrode composition. A solvent is selected based on the interaction of the solvent with the base polymer and the property-tuning coating layer composition. The MEA is assembled by preparing the base membrane and then applying the property-tuning coating layer to form a composite membrane. Finally, a catalyst is applied to the composite membrane.

  17. A novel bioactive membrane by cell electrospinning.

    PubMed

    Chen, Haiping; Liu, Yuanyuan; Hu, Qingxi

    2015-11-01

    Electrospinning permits fabrication of biodegradable matrices that can resemble the both scale and mechanical behavior of the native extracellular matrix. However, achieving high-cellular density and infiltration of cells within matrices with traditional technique remain challenging and time consuming. The cell electrospinning technique presented in this paper can mitigate the problems associated with these limitations. Cells encapsulated by the material in the cell electrospinning technique survived well and distributed homogenously within the nanofibrous membrane, and their vitality was improved to 133% after being cultured for 28 days. The electrospun nanofibrous membrane has a certain degradation property and favorable cell-membrane interaction that supports the active biocompatibility of the membrane. Its properties are helpful for supporting cell attachment and growth, maintaining phenotypic shape, and secreting an ample amount of extracellular matrix (ECM). This novel membrane may be a potential application within the field of tissue engineering. The ability of cell electrospinning to microintegrate cells into a biodegradable fibrous matrix embodies a novel tissue engineering approach that could be applied to fabricate a high cell density elastic tissue mimetic.

  18. Cell-cell adhesion interface: rise of the lateral membrane

    PubMed Central

    Tang, Vivian

    2017-01-01

    The lateral membrane plays an important role in the mechanical stability of epithelial cell sheet in steady state. In addition, the lateral membrane is continuously remodeled during dynamic processes such as cell extrusion, cytokinesis, and intercellular cell movement. In wound healing, the lateral membrane must be built from flat and spread cells that had crawled into the area of the wound. Thus, forming the lateral membrane is a phenomenon that occurs not only in development but also during homeostatic maintenance and regeneration of differentiated epithelial tissues. PMID:28357057

  19. Spherical indentation of a freestanding circular membrane revisited: Analytical solutions and experiments

    NASA Astrophysics Data System (ADS)

    Jin, Congrui; Davoodabadi, Ali; Li, Jianlin; Wang, Yanli; Singler, Timothy

    2017-03-01

    Due to the development of novel micro-fabrication techniques to produce ultra-thin materials and increasing interest in thin biological membranes, in recent years, the mechanical characterization of thin films has received a significant amount of attention. To provide a more accurate solution for the relationship among contact radius, load and deflection, the fundamental and widely applicable problem of spherical indentation of a freestanding circular membrane have been revisited. The work presented here significantly extends the previous contributions by providing an exact analytical solution to the governing equations of Föppl-Hecky membrane indented by a frictionless spherical indenter. In this study, experiments of spherical indentation has been performed, and the exact analytical solution presented in this paper is compared against experimental data from existing literature as well as our own experimental results.

  20. Spherical indentation of a freestanding circular membrane revisited: Analytical solutions and experiments

    DOE PAGES

    Jin, Congrui; Davoodabadi, Ali; Li, Jianlin; ...

    2017-01-11

    Because of the development of novel micro-fabrication techniques to produce ultra-thin materials and increasing interest in thin biological membranes, in recent years, the mechanical characterization of thin films has received a significant amount of attention. To provide a more accurate solution for the relationship among contact radius, load and deflection, the fundamental and widely applicable problem of spherical indentation of a freestanding circular membrane have been revisited. The work presented here significantly extends the previous contributions by providing an exact analytical solution to the governing equations of Föppl–Hecky membrane indented by a frictionless spherical indenter. In this study, experiments ofmore » spherical indentation has been performed, and the exact analytical solution presented in this article is compared against experimental data from existing literature as well as our own experimental results.« less

  1. A membrane reservoir at the cell surface: unfolding the plasma membrane to fuel cell shape change.

    PubMed

    Figard, Lauren; Sokac, Anna Marie

    2014-01-01

    Cell surface expansion is a necessary part of cell shape change. One long-standing hypothesis proposes that membrane for this expansion comes from the flattening out of cell surface projections such as microvilli and membrane folds. Correlative EM data of cells undergoing phagocytosis, cytokinesis, and morphogenesis has hinted at the existence of such an unfolding mechanism for decades; but unfolding has only recently been confirmed using live-cell imaging and biophysical approaches. Considering the wide range of cells in which plasma membrane unfolding has now been reported, it likely represents a fundamental mechanism of cell shape change.

  2. Durability of PEM Fuel Cell Membranes

    NASA Astrophysics Data System (ADS)

    Huang, Xinyu; Reifsnider, Ken

    Durability is still a critical limiting factor for the commercialization of polymer electrolyte membrane (PEM) fuel cells, a leading energy conversion technology for powering future hydrogen fueled automobiles, backup power systems (e.g., for base transceiver station of cellular networks), portable electronic devices, etc. Ionic conducting polymer (ionomer) electrolyte membranes are the critical enabling materials for the PEM fuel cells. They are also widely used as the central functional elements in hydrogen generation (e.g., electrolyzers), membrane cell for chlor-alkali production, etc. A perfluorosulfonic acid (PFSA) polymer with the trade name Nafion® developed by DuPont™ is the most widely used PEM in chlor-alkali cells and PEM fuel cells. Similar PFSA membranes have been developed by Dow Chemical, Asahi Glass, and lately Solvay Solexis. Frequently, such membranes serve the dual function of reactant separation and selective ionic conduction between two otherwise separate compartments. For some applications, the compromise of the "separation" function via the degradation and mechanical failure of the electrolyte membrane can be the life-limiting factor; this is particularly the case for PEM in hydrogen/oxygen fuel cells.

  3. Long-lived anomalous thermal diffusion induced by elastic cell membranes on nearby particles

    NASA Astrophysics Data System (ADS)

    Daddi-Moussa-Ider, Abdallah; Guckenberger, Achim; Gekle, Stephan

    2016-01-01

    The physical approach of a small particle (virus, medical drug) to the cell membrane represents the crucial first step before active internalization and is governed by thermal diffusion. Using a fully analytical theory we show that the stretching and bending of the elastic membrane by the approaching particle induces a memory in the system, which leads to anomalous diffusion, even though the particle is immersed in a purely Newtonian liquid. For typical cell membranes the transient subdiffusive regime extends beyond 10 ms and can enhance residence times and possibly binding rates up to 50%. Our analytical predictions are validated by numerical simulations.

  4. Vaccinia virus interactions with the cell membrane studied by new chromatic vesicle and cell sensor assays.

    PubMed

    Orynbayeva, Z; Kolusheva, S; Groysman, N; Gavrielov, N; Lobel, L; Jelinek, R

    2007-02-01

    The potential danger of cross-species viral infection points to the significance of understanding the contributions of nonspecific membrane interactions with the viral envelope compared to receptor-mediated uptake as a factor in virus internalization and infection. We present a detailed investigation of the interactions of vaccinia virus particles with lipid bilayers and with epithelial cell membranes using newly developed chromatic biomimetic membrane assays. This analytical platform comprises vesicular particles containing lipids interspersed within reporter polymer units that emit intense fluorescence following viral interactions with the lipid domains. The chromatic vesicles were employed as membrane models in cell-free solutions and were also incorporated into the membranes of epithelial cells, thereby functioning as localized membrane sensors on the cell surface. These experiments provide important insight into membrane interactions with and fusion of virions and the kinetic profiles of these processes. In particular, the data emphasize the significance of cholesterol/sphingomyelin domains (lipid rafts) as a crucial factor promoting bilayer insertion of the viral particles. Our analysis of virus interactions with polymer-labeled living cells exposed the significant role of the epidermal growth factor receptor in vaccinia virus infectivity; however, the data also demonstrated the existence of additional non-receptor-mediated mechanisms contributing to attachment of the virus to the cell surface and its internalization.

  5. Activated Membrane Patches Guide Chemotactic Cell Motility

    PubMed Central

    Hecht, Inbal; Skoge, Monica L.; Charest, Pascale G.; Ben-Jacob, Eshel; Firtel, Richard A.; Loomis, William F.; Levine, Herbert; Rappel, Wouter-Jan

    2011-01-01

    Many eukaryotic cells are able to crawl on surfaces and guide their motility based on environmental cues. These cues are interpreted by signaling systems which couple to cell mechanics; indeed membrane protrusions in crawling cells are often accompanied by activated membrane patches, which are localized areas of increased concentration of one or more signaling components. To determine how these patches are related to cell motion, we examine the spatial localization of RasGTP in chemotaxing Dictyostelium discoideum cells under conditions where the vertical extent of the cell was restricted. Quantitative analyses of the data reveal a high degree of spatial correlation between patches of activated Ras and membrane protrusions. Based on these findings, we formulate a model for amoeboid cell motion that consists of two coupled modules. The first module utilizes a recently developed two-component reaction diffusion model that generates transient and localized areas of elevated concentration of one of the components along the membrane. The activated patches determine the location of membrane protrusions (and overall cell motion) that are computed in the second module, which also takes into account the cortical tension and the availability of protrusion resources. We show that our model is able to produce realistic amoeboid-like motion and that our numerical results are consistent with experimentally observed pseudopod dynamics. Specifically, we show that the commonly observed splitting of pseudopods can result directly from the dynamics of the signaling patches. PMID:21738453

  6. Vesicle trafficking and cell surface membrane patchiness.

    PubMed Central

    Tang, Q; Edidin, M

    2001-01-01

    Membrane proteins and lipids often appear to be distributed in patches on the cell surface. These patches are often assumed to be membrane domains, arising from specific molecular associations. However, a computer simulation (Gheber and Edidin, 1999) shows that membrane patchiness may result from a combination of vesicle trafficking and dynamic barriers to lateral mobility. The simulation predicts that the steady-state patches of proteins and lipids seen on the cell surface will decay if vesicle trafficking is inhibited. To test this prediction, we compared the apparent sizes and intensities of patches of class I HLA molecules, integral membrane proteins, before and after inhibiting endocytic vesicle traffic from the cell surface, either by incubation in hypertonic medium or by expression of a dominant-negative mutant dynamin. As predicted by the simulation, the apparent sizes of HLA patches increased, whereas their intensities decreased after endocytosis and vesicle trafficking were inhibited. PMID:11423406

  7. Development of an analytical method coupling cell membrane chromatography with gas chromatography-mass spectrometry via microextraction by packed sorbent and its application in the screening of volatile active compounds in natural products.

    PubMed

    Li, Miao; Wang, Sicen; He, Langchong

    2015-01-01

    Natural products (NPs) are important sources of lead compounds in modern drug discovery. To facilitate the screening of volatile active compounds in NPs, we have developed a new biochromatography method that uses rat vascular smooth muscle cells (VSMC), which are rich in L-type calcium channels (LCC), to prepare the stationary phase. This integrated method, which couples cell membrane chromatography (CMC) with gas chromatography-mass spectrometry (GC-MS) via microextraction by packed sorbent (MEPS) technology, has been termed VSMC/CMC-MEPS-GC-MS. Methodological validation confirmed its specificity, reliability and convenience. Screening results for Radix Angelicae Dahuricae and Fructus Cnidii obtained using VSMC/CMC-MEPS-GC-MS were consistent with those obtained using VSMC/CMC-offline-GC-MS. MEPS connection plays as simplified solid-phase extraction and replaces the uncontrollable evaporation operation in reported offline connections, so our new method is supposed to be more efficient and reliable than the offline ones, especially for compounds that are volatile, thermally unstable or difficult to purify. In application, senkyunolide A and ligustilide were preliminary identified as the volatile active components in Rhizoma Chuanxiong. We have thus confirmed the suitability of VSMC/CMC-MEPS-GC-MS for volatile active compounds screening in NP.

  8. Stretching micropatterned cells on a PDMS membrane.

    PubMed

    Carpi, Nicolas; Piel, Matthieu

    2014-01-22

    Mechanical forces exerted on cells and/or tissues play a major role in numerous processes. We have developed a device to stretch cells plated on a PolyDiMethylSiloxane (PDMS) membrane, compatible with imaging. This technique is reproducible and versatile. The PDMS membrane can be micropatterned in order to confine cells or tissues to a specific geometry. The first step is to print micropatterns onto the PDMS membrane with a deep UV technique. The PDMS membrane is then mounted on a mechanical stretcher. A chamber is bound on top of the membrane with biocompatible grease to allow gliding during the stretch. The cells are seeded and allowed to spread for several hours on the micropatterns. The sample can be stretched and unstretched multiple times with the use of a micrometric screw. It takes less than a minute to apply the stretch to its full extent (around 30%). The technique presented here does not include a motorized device, which is necessary for applying repeated stretch cycles quickly and/or computer controlled stretching, but this can be implemented. Stretching of cells or tissue can be of interest for questions related to cell forces, cell response to mechanical stress or tissue morphogenesis. This video presentation will show how to avoid typical problems that might arise when doing this type of seemingly simple experiment.

  9. Analytical Chemistry in Microenvironments: Single Nerve Cells.

    DTIC Science & Technology

    1992-03-16

    AD-A251 491 * - OFFICE OF NAVAL RESEARCH GRANT or CONTRACT N00014-90-J-1161 R & T Code 4133030 Technical Report No. 012 Analytical Chemistry in...AGENCY USE ONLY (Leave oldnk) 2. REPORT DATE 1. R EP O R T T Y P E AND DATES COVERED 4. TITLE AND SUBTITLE S. FUNDING NUMBERS Analytical Chemistry in...CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT unclassified unclassified unclassified ANALYTICAL CHEMISTRY IN

  10. Fuel cell subassemblies incorporating subgasketed thrifted membranes

    DOEpatents

    Iverson, Eric J.; Pierpont, Daniel M.; Yandrasits, Michael A.; Hamrock, Steven J.; Obradovich, Stephan J.; Peterson, Donald G.

    2016-03-01

    A fuel cell roll good subassembly is described that includes a plurality of individual electrolyte membranes. One or more first subgaskets are attached to the individual electrolyte membranes. Each of the first subgaskets has at least one aperture and the first subgaskets are arranged so the center regions of the individual electrolyte membranes are exposed through the apertures of the first subgaskets. A second subgasket comprises a web having a plurality of apertures. The second subgasket web is attached to the one or more first subgaskets so the center regions of the individual electrolyte membranes are exposed through the apertures of the second subgasket web. The second subgasket web may have little or no adhesive on the subgasket surface facing the electrolyte membrane.

  11. Fuel cell subassemblies incorporating subgasketed thrifted membranes

    DOEpatents

    Iverson, Eric J; Pierpont, Daniel M; Yandrasits, Michael A; Hamrock, Steven J; Obradovich, Stephan J; Peterson, Donald G

    2014-01-28

    A fuel cell roll good subassembly is described that includes a plurality of individual electrolyte membranes. One or more first subgaskets are attached to the individual electrolyte membranes. Each of the first subgaskets has at least one aperture and the first subgaskets are arranged so the center regions of the individual electrolyte membranes are exposed through the apertures of the first subgaskets. A second subgasket comprises a web having a plurality of apertures. The second subgasket web is attached to the one or more first subgaskets so the center regions of the individual electrolyte membranes are exposed through the apertures of the second subgasket web. The second subgasket web may have little or no adhesive on the subgasket surface facing the electrolyte membrane.

  12. Mechanical tension drives cell membrane fusion.

    PubMed

    Kim, Ji Hoon; Ren, Yixin; Ng, Win Pin; Li, Shuo; Son, Sungmin; Kee, Yee-Seir; Zhang, Shiliang; Zhang, Guofeng; Fletcher, Daniel A; Robinson, Douglas N; Chen, Elizabeth H

    2015-03-09

    Membrane fusion is an energy-consuming process that requires tight juxtaposition of two lipid bilayers. Little is known about how cells overcome energy barriers to bring their membranes together for fusion. Previously, we have shown that cell-cell fusion is an asymmetric process in which an "attacking" cell drills finger-like protrusions into the "receiving" cell to promote cell fusion. Here, we show that the receiving cell mounts a Myosin II (MyoII)-mediated mechanosensory response to its invasive fusion partner. MyoII acts as a mechanosensor, which directs its force-induced recruitment to the fusion site, and the mechanosensory response of MyoII is amplified by chemical signaling initiated by cell adhesion molecules. The accumulated MyoII, in turn, increases cortical tension and promotes fusion pore formation. We propose that the protrusive and resisting forces from fusion partners put the fusogenic synapse under high mechanical tension, which helps to overcome energy barriers for membrane apposition and drives cell membrane fusion.

  13. Cell membrane softening in human breast and cervical cancer cells

    NASA Astrophysics Data System (ADS)

    Händel, Chris; Schmidt, B. U. Sebastian; Schiller, Jürgen; Dietrich, Undine; Möhn, Till; Kießling, Tobias R.; Pawlizak, Steve; Fritsch, Anatol W.; Horn, Lars-Christian; Briest, Susanne; Höckel, Michael; Zink, Mareike; Käs, Josef A.

    2015-08-01

    Biomechanical properties are key to many cellular functions such as cell division and cell motility and thus are crucial in the development and understanding of several diseases, for instance cancer. The mechanics of the cellular cytoskeleton have been extensively characterized in cells and artificial systems. The rigidity of the plasma membrane, with the exception of red blood cells, is unknown and membrane rigidity measurements only exist for vesicles composed of a few synthetic lipids. In this study, thermal fluctuations of giant plasma membrane vesicles (GPMVs) directly derived from the plasma membranes of primary breast and cervical cells, as well as breast cell lines, are analyzed. Cell blebs or GPMVs were studied via thermal membrane fluctuations and mass spectrometry. It will be shown that cancer cell membranes are significantly softer than their non-malignant counterparts. This can be attributed to a loss of fluid raft forming lipids in malignant cells. These results indicate that the reduction of membrane rigidity promotes aggressive blebbing motion in invasive cancer cells.

  14. Basement Membranes: Cell Scaffoldings and Signaling Platforms

    PubMed Central

    Yurchenco, Peter D.

    2011-01-01

    Basement membranes are widely distributed extracellular matrices that coat the basal aspect of epithelial and endothelial cells and surround muscle, fat, and Schwann cells. These extracellular matrices, first expressed in early embryogenesis, are self-assembled on competent cell surfaces through binding interactions among laminins, type IV collagens, nidogens, and proteoglycans. They form stabilizing extensions of the plasma membrane that provide cell adhesion and that act as solid-phase agonists. Basement membranes play a role in tissue and organ morphogenesis and help maintain function in the adult. Mutations adversely affecting expression of the different structural components are associated with developmental arrest at different stages as well as postnatal diseases of muscle, nerve, brain, eye, skin, vasculature, and kidney. PMID:21421915

  15. Alternate Fuel Cell Membranes for Energy Independence

    SciTech Connect

    Storey, Robson, F.; Mauritz, Kenneth, A.; Patton, Derek, L.; Savin, Daniel, A.

    2012-12-18

    The overall objective of this project was the development and evaluation of novel hydrocarbon fuel cell (FC) membranes that possess high temperature performance and long term chemical/mechanical durability in proton exchange membrane (PEM) fuel cells (FC). The major research theme was synthesis of aromatic hydrocarbon polymers of the poly(arylene ether sulfone) (PAES) type containing sulfonic acid groups tethered to the backbone via perfluorinated alkylene linkages and in some cases also directly attached to the phenylene groups along the backbone. Other research themes were the use of nitrogen-based heterocyclics instead of acid groups for proton conduction, which provides high temperature, low relative humidity membranes with high mechanical/thermal/chemical stability and pendant moieties that exhibit high proton conductivities in the absence of water, and synthesis of block copolymers consisting of a proton conducting block coupled to poly(perfluorinated propylene oxide) (PFPO) blocks. Accomplishments of the project were as follows: 1) establishment of a vertically integrated program of synthesis, characterization, and evaluation of FC membranes, 2) establishment of benchmark membrane performance data based on Nafion for comparison to experimental membrane performance, 3) development of a new perfluoroalkyl sulfonate monomer, N,N-diisopropylethylammonium 2,2-bis(p-hydroxyphenyl) pentafluoropropanesulfonate (HPPS), 4) synthesis of random and block copolymer membranes from HPPS, 5) synthesis of block copolymer membranes containing high-acid-concentration hydrophilic blocks consisting of HPPS and 3,3'-disulfonate-4,4'-dichlorodiphenylsulfone (sDCDPS), 6) development of synthetic routes to aromatic polymer backbones containing pendent 1H-1,2,3-triazole moieties, 7) development of coupling strategies to create phase-separated block copolymers between hydrophilic sulfonated prepolymers and commodity polymers such as PFPO, 8) establishment of basic performance

  16. Modification and evaluation of fuel cell membranes

    NASA Astrophysics Data System (ADS)

    Nalawade, Amol Prataprao

    The primary goals of this study were modification of existing NafionRTM membranes and characterization of newly developed hydrocarbon-based membranes for high temperature fuel cell applications. Various NafionRTM/silicate nanocomposites were formulated via in situ sol-gel reactions for tetraethylorthosilicate. Different silicate composition profiles generated across membrane cross-sections were investigated by EDAX/ESEM. Composite water uptake, proton conductivity and fuel cell performance were comparable to that of unmodified Nafion RTM. Tafel analysis showed better electrode kinetics for composites having more silicate in the middle and less or no silicate at electrolyte-electrode interfaces. All composites showed reduced fuel cross-over and superior mechanical as well as chemical durability than unmodified NafionRTM. Poly(cyclohexadiene) (PCHD) materials were characterized in the interest of developing alternative low-cost proton exchange membranes. All cross-linked sulfonated (xsPCHD) membranes showed significantly higher water uptake at 80 °C and higher proton conductivity at 120 °C at all relative humidities (RH), compared to the current benchmark membrane, NafionRTM. A xsPCHD-poly(ethylene glycol) (PEG) copolymer and a xsPCHD-PEG blend surpassed the DOE target by exhibiting proton conductivities of 141.44 and 322.40 mS/cm, respectively, at 50 % RH. Although the PCHD-based PEMs exhibited thermal stability up to 150 °C, they showed poor mechanical properties which would cause poor membrane durability during fuel cell operation. Atomic force microscopy studies demonstrated nanophase separated morphology of xsPCHD having a higher degree of connectedness of hydrophilic domains in the copolymer and blends relative to the xsPCHD homopolymer. Broadband dielectric spectroscopy (BDS) was used to study sub-Tg relaxations in annealed poly(2,5-benzimidazole) (ABPBI) fuel cell precursor materials. A trend in degree of connectivity of charge migration pathways and

  17. Hereditary spherocytosis, elliptocytosis, and other red cell membrane disorders.

    PubMed

    Da Costa, Lydie; Galimand, Julie; Fenneteau, Odile; Mohandas, Narla

    2013-07-01

    Hereditary spherocytosis and elliptocytosis are the two most common inherited red cell membrane disorders resulting from mutations in genes encoding various red cell membrane and skeletal proteins. Red cell membrane, a composite structure composed of lipid bilayer linked to spectrin-based membrane skeleton is responsible for the unique features of flexibility and mechanical stability of the cell. Defects in various proteins involved in linking the lipid bilayer to membrane skeleton result in loss in membrane cohesion leading to surface area loss and hereditary spherocytosis while defects in proteins involved in lateral interactions of the spectrin-based skeleton lead to decreased mechanical stability, membrane fragmentation and hereditary elliptocytosis. The disease severity is primarily dependent on the extent of membrane surface area loss. Both these diseases can be readily diagnosed by various laboratory approaches that include red blood cell cytology, flow cytometry, ektacytometry, electrophoresis of the red cell membrane proteins, and mutational analysis of gene encoding red cell membrane proteins.

  18. Membrane fluidity sensoring microbial fuel cell.

    PubMed

    Choi, Youngjin; Jung, Eunkyoung; Kim, Sunghyun; Jung, Seunho

    2003-04-01

    A study has been performed to examine the effect of temperature and ethanolic stresses on the coulombic efficiency of a microbial fuel cell. The conventional-type fuel cell containing Gram-negative bacteria, Proteus vulgaris, was investigated as a model system. From current output measurements, it was found that the coulombic yields were altered by environmental stresses such as temperature shock or ethanol treatment to the bacteria. While high-temperature or ethanolic shock led to a remarkable decrement in coulombic output, the low-temperature shock induced a slight increase in microbial fuel cell efficiency. These results indicate that the membrane fluidity is affected considerably by environmental stress, which in turn affects the electron transfer process through the bacterial cell membrane to and from the electrode. This interpretation was confirmed by the cyclic voltammetric study of a mediator on an electrode surface modified with the lipids extracted from the membrane of P. vulgaris under the given stress. Markedly different electrochemical behaviors were observed depending on the environmental stress. A reciprocal relationship between coulomb output and the ratio of saturation/unsaturation of fatty acids has been observed. This is the first report, to our knowledge, that the structural adaptation of membrane fatty acids in response to the environmental shock can regulate the coulombic efficiency of a microbial fuel cell.

  19. Pattern formation in cell membrane adhesion

    NASA Astrophysics Data System (ADS)

    Discher, Dennis; Hategan, A.; Sengupta, K.; Sackmann, E.

    2004-03-01

    Strong adhesion of highly active cells often nucleates focal adhesions or related structures that are, over time, reinforced by cytoskeleton (actin, etc.). Red cells lack such complex adhesion systems, but they are shown here to also exhibit complex spatial patterns within an adhesive contact zone. While strong adhesion and spreading of the red cell to a dense poly-L-lysine surface appears complete in < 1 s by reflective interference microscopy, over longer times of 10-15 min or more distinct patterns in fluorescently labeled membrane components emerge. The fluorescent lipid Fl-PE (fluorescein phosphoethanolamine), in particular, is seen to diffuse and reorganize (eg. worm-like domains of <500 nm) within the contact zone, independent of whether the cell is intact or ruptured. Lipid patterns are accompanied by visible perturbations in band 3 distribution and weaker perturbations in membrane skeleton actin. Although fluorescent poly-L-lysine is shown to be uniform under cells, pressing down on the membrane quenches the lipid patterns and reveals the topographical basis for pattern formation. Regions of strong contact are thus separated by regions where the membrane is more distant from the surface.

  20. Cell or Cell Membrane-Based Drug Delivery Systems

    PubMed Central

    Tan, Songwei; Wu, Tingting; Zhang, Dan; Zhang, Zhiping

    2015-01-01

    Natural cells have been explored as drug carriers for a long period. They have received growing interest as a promising drug delivery system (DDS) until recently along with the development of biology and medical science. The synthetic materials, either organic or inorganic, are found to be with more or less immunogenicity and/or toxicity. The cells and extracellular vesicles (EVs), are endogenous and thought to be much safer and friendlier. Furthermore, in view of their host attributes, they may achieve different biological effects and/or targeting specificity, which can meet the needs of personalized medicine as the next generation of DDS. In this review, we summarized the recent progress in cell or cell membrane-based DDS and their fabrication processes, unique properties and applications, including the whole cells, EVs and cell membrane coated nanoparticles. We expect the continuing development of this cell or cell membrane-based DDS will promote their clinic applications. PMID:26000058

  1. Membrane electrode assembly for a fuel cell

    NASA Technical Reports Server (NTRS)

    Prakash, Surya (Inventor); Narayanan, Sekharipuram R. (Inventor); Atti, Anthony (Inventor); Olah, George (Inventor); Smart, Marshall C. (Inventor)

    2006-01-01

    A catalyst ink for a fuel cell including a catalytic material and poly(vinylidene fluoride). The ink may be applied to a substrate to form an electrode, or bonded with other electrode layers to form a membrane electrode assembly (MEA).

  2. Artificial Red Cells with Polyhemoglobin Membranes.

    DTIC Science & Technology

    1981-09-01

    preparing emulsions and ejecting cells from the oil phase. IX. REFERENCES 1. Wallace, H. W., Asher, W. J., and Li, N. N. Liquid - liquid oxygenation: a...1S. KEY WORDS (Continue, an reverse side if naceoay mnd identify by block number) Artificial Blood, Hemoglobin, Polyhemoglobin, Biotonometry Liquid ...cell-size microdroplets containing 30% of hemoglobin were held in liquid membrane capsules and treated with glutaralddhyde that cross linked the

  3. The mechanism of facilitated cell membrane resealing.

    PubMed

    Togo, T; Alderton, J M; Bi, G Q; Steinhardt, R A

    1999-03-01

    Disruption of the plasma membrane evokes an exocytotic response that is required for rapid membrane resealing. We show here in Swiss 3T3 fibroblasts that a second disruption at the same site reseals more rapidly than the initial wound. This facilitated response of resealing was inhibited by both low external Ca2+ concentration and specific protein kinase C (PKC) inhibitors, bisindolylmaleimide I (BIS) and Gö-6976. In addition, activation of PKC by phorbol ester facilitated the resealing of a first wound. BIS and Gö-6976 suppressed the effect of phorbol ester on resealing rate. Fluorescent dye loss from a FM1-43 pre-labeled endocytotic compartment was used to investigate the relationship between exocytosis, resealing and the facilitation of resealing. Exocytosis of endocytotic compartments near the wounding site was correlated with successful resealing. The destaining did not occur when exocytosis and resealing were inhibited by low external Ca2+ concentration or by injected tetanus toxin. When the dye loaded cells were wounded twice, FM1-43 destaining at the second wound was less than at the first wound. Less destaining was also observed in cells pre-treated with phorbol ester, suggesting newly formed vesicles, which were FM1-43 unlabeled, were exocytosed in the resealing at repeated woundings. Facilitation was also blocked by brefeldin A (BFA), a fungal metabolite that inhibits vesicle formation at the Golgi apparatus. Lowering the temperature below 20 degrees C also blocked facilitation as expected from a block of Golgi function. BFA had no effect on the resealing rate of an initial wound. The facilitation of the resealing by phorbol ester was blocked by pre-treatment with BFA. These results suggest that at first wounding the cell used the endocytotic compartment to add membrane necessary for resealing. At a second wounding, PKC, activated by Ca2+ entry at the first wound, stimulated vesicle formation from the Golgi apparatus, resulting in more rapid resealing

  4. Selectivity of Direct Methanol Fuel Cell Membranes.

    PubMed

    Aricò, Antonino S; Sebastian, David; Schuster, Michael; Bauer, Bernd; D'Urso, Claudia; Lufrano, Francesco; Baglio, Vincenzo

    2015-11-24

    Sulfonic acid-functionalized polymer electrolyte membranes alternative to Nafion(®) were developed. These were hydrocarbon systems, such as blend sulfonated polyetheretherketone (s-PEEK), new generation perfluorosulfonic acid (PFSA) systems, and composite zirconium phosphate-PFSA polymers. The membranes varied in terms of composition, equivalent weight, thickness, and filler and were investigated with regard to their methanol permeation characteristics and proton conductivity for application in direct methanol fuel cells. The behavior of the membrane electrode assemblies (MEA) was investigated in fuel cell with the aim to individuate a correlation between membrane characteristics and their performance in a direct methanol fuel cell (DMFC). The power density of the DMFC at 60 °C increased according to a square root-like function of the membrane selectivity. This was defined as the reciprocal of the product between area specific resistance and crossover. The power density achieved at 60 °C for the most promising s-PEEK-based membrane-electrode assembly (MEA) was higher than the benchmark Nafion(®) 115-based MEA (77 mW·cm(-2) vs. 64 mW·cm(-2)). This result was due to a lower methanol crossover (47 mA·cm(-2) equivalent current density for s-PEEK vs. 120 mA·cm(-2) for Nafion(®) 115 at 60 °C as recorded at OCV with 2 M methanol) and a suitable area specific resistance (0.15 Ohm cm² for s-PEEK vs. 0.22 Ohm cm² for Nafion(®) 115).

  5. Selectivity of Direct Methanol Fuel Cell Membranes

    PubMed Central

    Aricò, Antonino S.; Sebastian, David; Schuster, Michael; Bauer, Bernd; D’Urso, Claudia; Lufrano, Francesco; Baglio, Vincenzo

    2015-01-01

    Sulfonic acid-functionalized polymer electrolyte membranes alternative to Nafion® were developed. These were hydrocarbon systems, such as blend sulfonated polyetheretherketone (s-PEEK), new generation perfluorosulfonic acid (PFSA) systems, and composite zirconium phosphate–PFSA polymers. The membranes varied in terms of composition, equivalent weight, thickness, and filler and were investigated with regard to their methanol permeation characteristics and proton conductivity for application in direct methanol fuel cells. The behavior of the membrane electrode assemblies (MEA) was investigated in fuel cell with the aim to individuate a correlation between membrane characteristics and their performance in a direct methanol fuel cell (DMFC). The power density of the DMFC at 60 °C increased according to a square root-like function of the membrane selectivity. This was defined as the reciprocal of the product between area specific resistance and crossover. The power density achieved at 60 °C for the most promising s-PEEK-based membrane-electrode assembly (MEA) was higher than the benchmark Nafion® 115-based MEA (77 mW·cm−2 vs. 64 mW·cm−2). This result was due to a lower methanol crossover (47 mA·cm−2 equivalent current density for s-PEEK vs. 120 mA·cm−2 for Nafion® 115 at 60 °C as recorded at OCV with 2 M methanol) and a suitable area specific resistance (0.15 Ohm cm2 for s-PEEK vs. 0.22 Ohm cm2 for Nafion® 115). PMID:26610582

  6. Catalytic membranes for fuel cells

    SciTech Connect

    Liu, Di-Jia; Yang, Junbing; Wang, Xiaoping

    2011-04-19

    A fuel cell of the present invention comprises a cathode and an anode, one or both of the anode and the cathode including a catalyst comprising a bundle of longitudinally aligned graphitic carbon nanotubes including a catalytically active transition metal incorporated longitudinally and atomically distributed throughout the graphitic carbon walls of said nanotubes. The nanotubes also include nitrogen atoms and/or ions chemically bonded to the graphitic carbon and to the transition metal. Preferably, the transition metal comprises at least one metal selected from the group consisting of Fe, Co, Ni, Mn, and Cr.

  7. Microfluidic microbial fuel cells: from membrane to membrane free

    NASA Astrophysics Data System (ADS)

    Yang, Yang; Ye, Dingding; Li, Jun; Zhu, Xun; Liao, Qiang; Zhang, Biao

    2016-08-01

    Microfluidic microbial fuel cells (MMFCs) are small carbon-neutral devices that use self-organized bacteria to degrade organic substrates and harness energy from the waste water. Conventional MMFCs have made great strides in the past decade and have overcome some limitations, such as high capital costs and low energy output. A co-laminar flow MFC has been first proposed in 2011 with the potential to be an attractively power source to niche applications. Co-laminar MFCs typically operate without any physical membranes separating the reactants, and bacterial ecosystems can be easily manipulated by regulating the inlet conditions. This paper highlights recent accomplishments in the development of co-laminar MFCs, emphasizing basic principles, mass transport and fluid dynamics including boundary layer theory, entrance conditions and mixing zone issues. Furthermore, the development of current techniques, major challenges and the potential research directions are discussed.

  8. Interaction of peptides with cell membranes: insights from molecular modeling

    NASA Astrophysics Data System (ADS)

    Li, Zhen-lu; Ding, Hong-ming; Ma, Yu-qiang

    2016-03-01

    The investigation of the interaction of peptides with cell membranes is the focus of active research. It can enhance the understanding of basic membrane functions such as membrane transport, fusion, and signaling processes, and it may shed light on potential applications of peptides in biomedicine. In this review, we will present current advances in computational studies on the interaction of different types of peptides with the cell membrane. Depending on the properties of the peptide, membrane, and external environment, the peptide-membrane interaction shows a variety of different forms. Here, on the basis of recent computational progress, we will discuss how different peptides could initiate membrane pores, translocate across the membrane, induce membrane endocytosis, produce membrane curvature, form fibrils on the membrane surface, as well as interact with functional membrane proteins. Finally, we will present a conclusion summarizing recent progress and providing some specific insights into future developments in this field.

  9. Sputter-deposited fuel cell membranes and electrodes

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram R. (Inventor); Jeffries-Nakamura, Barbara (Inventor); Chun, William (Inventor); Ruiz, Ron P. (Inventor); Valdez, Thomas I. (Inventor)

    2001-01-01

    A method for preparing a membrane for use in a fuel cell membrane electrode assembly includes the steps of providing an electrolyte membrane, and sputter-depositing a catalyst onto the electrolyte membrane. The sputter-deposited catalyst may be applied to multiple sides of the electrolyte membrane. A method for forming an electrode for use in a fuel cell membrane electrode assembly includes the steps of obtaining a catalyst, obtaining a backing, and sputter-depositing the catalyst onto the backing. The membranes and electrodes are useful for assembling fuel cells that include an anode electrode, a cathode electrode, a fuel supply, and an electrolyte membrane, wherein the electrolyte membrane includes a sputter-deposited catalyst, and the sputter-deposited catalyst is effective for sustaining a voltage across a membrane electrode assembly in the fuel cell.

  10. Analytical study of microsomes and isolated subcellular membranes from rat liver VIII. Subfractionation of preparations enriched with plasma membranes, outer mitochondrial membranes, or Golgi complex membranes

    PubMed Central

    1981-01-01

    Preparations enriched with plasmalemmal, outer mitochondrial, or Golgi complex membranes from rat liver were subfractionated by isopycnic centrifugation, without or after treatment with digitonin, to establish the subcellular distribution of a variety of enzymes. The typical plasmalemmal enzymes 5'-nucleotidase, alkaline phosphodiesterase I, and alkaline phosphatase were markedly shifted by digitonin toward higher densities in all three preparations. Three glycosyltransferases, highly purified in the Golgi fraction, were moderately shifted by digitonin in both this Golgi complex preparation and the microsomal fraction. The outer mitochondrial membrane marker, monoamine oxidase, was not affected by digitonin in the outer mitochondrial membrane marker, monoamine oxidase, was not affected by digitonin in the out mitochondrial membrane preparation, in agreement wit its behavior in microsomes. With the exception of NADH cytochrome c reductase (which was concentrated in the outer mitochondrial membrane preparation), typical microsomal enzymes (glucose-6-phosphatase, esterase, and NADPH cytochrome c reductase) displayed low specific activities in the three preparations; except for part of the glucose-6-phosphatase activity in the plasma membrane preparation, their density distributions were insensitive to digitonin, as they were in microsomes. The influence of digitonin on equilibrium densities was correlated with its morphological effects. Digitonin induced pseudofenestrations in plasma membranes. In Golgi and outer mitochondrial membrane preparations, a few similarly altered membranes were detected in subfractions enriched with 5'-nucleotidase and alkaline phosphodiesterase I. The alterations of Golgi membranes were less obvious and seemingly restricted to some elements in the Golgi preparation. No morphological modification was detected in digitonin-treated outer mitochondrial membranes. These results indicate that each enzyme is associated with the same membrane

  11. Fuel cell membranes and crossover prevention

    DOEpatents

    Masel, Richard I.; York, Cynthia A.; Waszczuk, Piotr; Wieckowski, Andrzej

    2009-08-04

    A membrane electrode assembly for use with a direct organic fuel cell containing a formic acid fuel includes a solid polymer electrolyte having first and second surfaces, an anode on the first surface and a cathode on the second surface and electrically linked to the anode. The solid polymer electrolyte has a thickness t:.gtoreq..times..times..times..times. ##EQU00001## where C.sub.f is the formic acid fuel concentration over the anode, D.sub.f is the effective diffusivity of the fuel in the solid polymer electrolyte, K.sub.f is the equilibrium constant for partition coefficient for the fuel into the solid polymer electrolyte membrane, I is Faraday's constant n.sub.f is the number of electrons released when 1 molecule of the fuel is oxidized, and j.sub.f.sup.c is an empirically determined crossover rate of fuel above which the fuel cell does not operate.

  12. Interaction of Inorganic Nanoparticles With Cell Membranes

    DTIC Science & Technology

    2008-10-20

    explain the change in the Zeta-potential of the beads we studied the adsorption of protein on Chitosan coated SPIONs. The particles were incubated in...protein adsorption which enables us understand better the pathway of our particles through the membrane and inside the cell. Combined with...investigation regarding the protein adsorption and their influence on the colloidal stability we have now the tools to investigate and perhaps to understand

  13. Virus-Mimetic Fusogenic Exosomes for Direct Delivery of Integral Membrane Proteins to Target Cell Membranes.

    PubMed

    Yang, Yoosoo; Hong, Yeonsun; Nam, Gi-Hoon; Chung, Jin Hwa; Koh, Eunee; Kim, In-San

    2017-02-06

    An efficient system for direct delivery of integral membrane proteins is successfully developed using a new biocompatible exosome-based platform. Fusogenic exosomes harboring viral fusogen, vascular stomatitis virus (VSV)-G protein, can fuse with and modify plasma membranes in a process called "membrane editing." This can facilitate the transfer of biologically active membrane proteins into the target cell membranes both in vitro and in vivo.

  14. Membrane catalyst layer for fuel cells

    DOEpatents

    Wilson, Mahlon S.

    1993-01-01

    A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 .mu.m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm.sup.2. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. Alternatively, the catalyst layer is formed by applying a Na.sup.+ form of a perfluorosulfonate ionomer directly to the membrane, drying the film at a high temperature, and then converting the film back to the protonated form of the ionomer. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

  15. A review of radiation-grafted polymer electrolyte membranes for alkaline polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Zhou, Tianchi; Shao, Rong; Chen, Song; He, Xuemei; Qiao, Jinli; Zhang, Jiujun

    2015-10-01

    The past two decades have witnessed many efforts to develop radiation-grafted alkaline membranes for alkaline PEM fuel cell applications, as such membranes have certain advantages over other kinds of alkaline membranes, including well-controlled composition, functionality, and other promising properties. To facilitate research and development in this area, the present paper reviews radiation-grafted alkaline membranes. We examine their synthesis/fabrication/characterization, membrane material selection, and theoretical approaches for fundamental understanding. We also present detailed examinations of their application in fuel cell in terms of the working principles of the radiation grafting process, the fabrication of MEAs using radiation-grafted membranes, the membranes' corresponding performance in alkaline PEM fuel cells, as well as performance optimization. The paper also summarizes the challenges and mitigation strategies for radiation-grafted alkaline membranes and their application in PEM fuel cells, presenting an overall picture of the technology as it presently stands.

  16. Cell bioprocessing in space - Applications of analytical cytology

    NASA Technical Reports Server (NTRS)

    Todd, P.; Hymer, W. C.; Goolsby, C. L.; Hatfield, J. M.; Morrison, D. R.

    1988-01-01

    Cell bioprocessing experiments in space are reviewed and the development of on-board cell analytical cytology techniques that can serve such experiments is discussed. Methods and results of experiments involving the cultivation and separation of eukaryotic cells in space are presented. It is suggested that an advanced cytometer should be developed for the quantitative analysis of large numbers of specimens of suspended eukaryotic cells and bioparticles in experiments on the Space Station.

  17. Fuel cell membrane hydration and fluid metering

    DOEpatents

    Jones, Daniel O.; Walsh, Michael M.

    2003-01-01

    A hydration system includes fuel cell fluid flow plate(s) and injection port(s). Each plate has flow channel(s) with respective inlet(s) for receiving respective portion(s) of a given stream of reactant fluid for a fuel cell. Each injection port injects a portion of liquid water directly into its respective flow channel. This serves to hydrate at least corresponding part(s) of a given membrane of the corresponding fuel cell(s). The hydration system may be augmented by a metering system including flow regulator(s). Each flow regulator meters an injecting at inlet(s) of each plate of respective portions of liquid into respective portion(s) of a given stream of fluid by corresponding injection port(s).

  18. Fuel cell membrane hydration and fluid metering

    DOEpatents

    Jones, Daniel O.; Walsh, Michael M.

    1999-01-01

    A hydration system includes fuel cell fluid flow plate(s) and injection port(s). Each plate has flow channel(s) with respective inlet(s) for receiving respective portion(s) of a given stream of reactant fluid for a fuel cell. Each injection port injects a portion of liquid water directly into its respective flow channel in order to mix its respective portion of liquid water with the corresponding portion of the stream. This serves to hydrate at least corresponding part(s) of a given membrane of the corresponding fuel cell(s). The hydration system may be augmented by a metering system including flow regulator(s). Each flow regulator meters an injecting at inlet(s) of each plate of respective portions of liquid into respective portion(s) of a given stream of fluid by corresponding injection port(s).

  19. Membrane Purification Cell for Aluminum Recycling

    SciTech Connect

    David DeYoung; James Wiswall; Cong Wang

    2011-11-29

    Recycling mixed aluminum scrap usually requires adding primary aluminum to the scrap stream as a diluent to reduce the concentration of non-aluminum constituents used in aluminum alloys. Since primary aluminum production requires approximately 10 times more energy than melting scrap, the bulk of the energy and carbon dioxide emissions for recycling are associated with using primary aluminum as a diluent. Eliminating the need for using primary aluminum as a diluent would dramatically reduce energy requirements, decrease carbon dioxide emissions, and increase scrap utilization in recycling. Electrorefining can be used to extract pure aluminum from mixed scrap. Some example applications include producing primary grade aluminum from specific scrap streams such as consumer packaging and mixed alloy saw chips, and recycling multi-alloy products such as brazing sheet. Electrorefining can also be used to extract valuable alloying elements such as Li from Al-Li mixed scrap. This project was aimed at developing an electrorefining process for purifying aluminum to reduce energy consumption and emissions by 75% compared to conventional technology. An electrolytic molten aluminum purification process, utilizing a horizontal membrane cell anode, was designed, constructed, operated and validated. The electrorefining technology could also be used to produce ultra-high purity aluminum for advanced materials applications. The technical objectives for this project were to: - Validate the membrane cell concept with a lab-scale electrorefining cell; - Determine if previously identified voltage increase issue for chloride electrolytes holds for a fluoride-based electrolyte system; - Assess the probability that voltage change issues can be solved; and - Conduct a market and economic analysis to assess commercial feasibility. The process was tested using three different binary alloy compositions (Al-2.0 wt.% Cu, Al-4.7 wt.% Si, Al-0.6 wt.% Fe) and a brazing sheet scrap composition (Al-2

  20. Polymer synthesis toward fuel cell membrane materials

    NASA Astrophysics Data System (ADS)

    Rebeck, Nathaniel T.

    Fuel cells are a promising technology that will be part of the future energy landscape. New membranes for alkaline and proton exchange membrane fuel cells are needed to improve the performance, simplify the system, and reduce cost. Polymer chemistry can be applied to develop new polymers and to assemble polymers into improved membranes that need less water, have increased performance and are less expensive, thereby removing the deficiencies of current membranes. Nucleophilic aromatic substitution polymerization typically produces thermally stable engineering polymers that can be easily functionalized. New functional monomers were developed to explore new routes to novel functional polymers. Sulfonamides were discovered as new activating groups for polymerization of high molecular weight thermooxidatively stable materials with sulfonic acid latent functionality. While the sulfonamide functional polymers could be produced, the sulfonamide group proved to be too stable to convert into a sulfonic acid after reaction. The reactivity of 2-aminophenol was investigated to search for a new class of ion conducting polymer materials. Both the amine and the phenol groups are found to be reactive in a nucleophilic aromatic substitution, however not to the extent to allow the formation of high molecular weight polymer materials. Layer-by-layer films were assembled from aqueous solutions of poly(styrene sulfonate) and trimethylammonium functionalized poly(phenylene oxide). The deposition conditions were adjusted to increase the free charge carrier content, and chloride conductivites reached almost 30 mS/cm for the best films. Block and random poly(phenylene oxide) copolymers were produced from 2,6-dimethylphenol and 2,6-diphenylphenol and the methyl substituted repeat units were functionalized with trimethylammonium bromide. The block copolymers displayed bromide conductivities up to 26 mS/cm and outperformed the random copolymers, indicating that morphology has an effect on ion

  1. Resolution of Viable and Membrane-Compromised Bacteria in Freshwater and Marine Waters Based on Analytical Flow Cytometry and Nucleic Acid Double Staining

    PubMed Central

    Grégori, Gérald; Citterio, Sandra; Ghiani, Alessandra; Labra, Massimo; Sgorbati, Sergio; Brown, Spencer; Denis, Michel

    2001-01-01

    The membrane integrity of a cell is a well-accepted criterion for characterizing viable (active or inactive) cells and distinguishing them from damaged and membrane-compromised cells. This information is of major importance in studies of the function of microbial assemblages in natural environments, in order to assign bulk activities measured by various methods to the very active cells that are effectively responsible for the observations. To achieve this task for bacteria in freshwater and marine waters, we propose a nucleic acid double-staining assay based on analytical flow cytometry, which allows us to distinguish viable from damaged and membrane-compromised bacteria and to sort out noise and detritus. This method is derived from the work of S. Barbesti et al. (Cytometry 40:214–218, 2000) which was conducted on cultured bacteria. The principle of this approach is to use simultaneously a permeant (SYBR Green; Molecular Probes) and an impermeant (propidium iodide) probe and to take advantage of the energy transfer which occurs between them when both probes are staining nucleic acids. A full quenching of the permeant probe fluorescence by the impermeant probe will point to cells with a compromised membrane, a partial quenching will indicate cells with a slightly damaged membrane, and a lack of quenching will characterize intact membrane cells identified as viable. In the present study, this approach has been adapted to bacteria in freshwater and marine waters of the Mediterranean region. It is fast and easy to use and shows that a large fraction of bacteria with low DNA content can be composed of viable cells. Admittedly, limitations stem from the unknown behavior of unidentified species present in natural environments which may depart from the established permeability properties with respect to the fluorescing dyes. PMID:11571170

  2. Origin of subdiffusion of water molecules on cell membrane surfaces

    PubMed Central

    Yamamoto, Eiji; Akimoto, Takuma; Yasui, Masato; Yasuoka, Kenji

    2014-01-01

    Water molecules play an important role in providing unique environments for biological reactions on cell membranes. It is widely believed that water molecules form bridges that connect lipid molecules and stabilize cell membranes. Using all-atom molecular dynamics simulations, we show that translational and rotational diffusion of water molecules on lipid membrane surfaces exhibit subdiffusion and aging. Moreover, we provide evidence that both divergent mean trapping time (continuous-time random walk) and long-correlated noise (fractional Brownian motion) contribute to this subdiffusion. These results suggest that subdiffusion on cell membranes causes the water retardation, an enhancement of cell membrane stability, and a higher reaction efficiency. PMID:24739933

  3. Microfabrication of High-Resolution Porous Membranes for Cell Culture

    PubMed Central

    Kim, Monica Y.; Li, David Jiang; Pham, Long K.; Wong, Brandon G.

    2014-01-01

    Microporous membranes are widely utilized in cell biology to study cell-cell signaling and cell migration. However, the thickness and low porosity of commercial track-etched membranes limit the quality of cell imaging and the degree of cell-cell contact that can be achieved on such devices. We employ photolithography-based microfabrication to achieve porous membranes with pore diameter as small as 0.9 μm, up to 40% porosity, and less than 5% variation in pore size. Through the use of a soap release layer, membranes as thin as 1 μm can be achieved. The thin membranes minimally disrupt contrast enhancement optics, thus allowing good quality imaging of unlabeled cells under white light, unlike commercial membranes. In addition, the polymer membrane materials display low autofluorescence even after patterning, facilitating high quality fluorescence microscopy. Finally, confocal imaging suggests that substantial cell-cell contact is possible through the pores of these thin membranes. This membrane technology can enhance existing uses of porous membranes in cell biology as well as enable new types of experiments. PMID:24567663

  4. Membrane tension feedback on shape and motility of eukaryotic cells

    NASA Astrophysics Data System (ADS)

    Winkler, Benjamin; Aranson, Igor S.; Ziebert, Falko

    2016-04-01

    In the framework of a phase field model of a single cell crawling on a substrate, we investigate how the properties of the cell membrane affect the shape and motility of the cell. Since the membrane influences the cell dynamics on multiple levels and provides a nontrivial feedback, we consider the following fundamental interactions: (i) the reduction of the actin polymerization rate by membrane tension; (ii) area conservation of the cell's two-dimensional cross-section vs. conservation of the circumference (i.e. membrane inextensibility); and (iii) the contribution from the membrane's bending energy to the shape and integrity of the cell. As in experiments, we investigate two pertinent observables - the cell's velocity and its aspect ratio. We find that the most important effect is the feedback of membrane tension on the actin polymerization. Bending rigidity has only minor effects, visible mostly in dynamic reshaping events, as exemplified by collisions of the cell with an obstacle.

  5. Polybenzimidazole-multiwall carbon nanotubes composite membranes for polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Guerrero Moreno, Nayibe; Gervasio, Dominic; Godínez García, Andrés; Pérez Robles, Juan Francisco

    2015-12-01

    Polymer membranes are prepared as a composite of polybenzimidazole and non-functionalized multiwall carbon nanotubes (PBI-CNT) and polybenzimidazole (PBI) only. Each is doped with H3PO4 (PA) and used as a proton exchange membrane (PEM) as the electrolyte in a fuel cell. The proton conductivities at 180 °C for the doped PBI membrane (PBIPA) and the doped PBI-CNT membrane (PBICNTPA) are 6.3 × 10-2 and 7.4 × 10-2 Scm-1 respectively. A single fuel cell having these membranes as electrolyte has a Pt catalyzed hydrogen gas fed anode and a similar oxygen cathode without humidification of feed gases; the cell with the PBICNTPA membrane has higher open circuit voltage (0.96 V) than that with a PBIPA membrane (0.8 V) at 180 °C. The mechanical stability of the membrane improves with CNTs addition. The tensile strength of the composite PBI-CNT membrane with 1 wt.% CNTs loading is 32% higher and the Young's Modulus is 147% higher than the values for a membrane of PBI alone. The improvement in conductivity and mechanical properties in the composite membrane due to the CNT addition indicates that a PBI-CNT membrane is a good alternative as a membrane electrolyte in a PEMFC.

  6. An analytical approach for solid oxide cell electrode geometric design

    NASA Astrophysics Data System (ADS)

    Nelson, George J.

    2015-12-01

    An analytical model for gas distributions in porous solid oxide cell electrodes is applied to develop dimensionless metrics that describe electrode performance. These metrics include two forms of a dimensionless reactant depletion current density and a geometry sensitive Damköhler number used to assess electrode catalytic effectiveness. The first dimensionless depletion current density defines when reducing electrode thickness no longer benefits mass transfer performance for a given cell geometry. The second dimensionless depletion current density provides a gage of deviation from the limiting current behavior predicted using button-cell experimental and modeling approaches. The Damköhler number and related catalytic effectiveness quantify two-dimensional transport effects under non-depleted operating conditions, providing a means of generalizing insights from reactant depletion behavior for typical cell operating conditions. A finite element solution for gas transport based on the dusty-gas model is used as a benchmark for the analytical model and dimensionless metrics. Estimates of concentration polarization based on analytical and numerical models compare well to published experimental data. Analytical performance predictions provide clear demonstration of the influence of two-dimensional electrode geometry on solid oxide cell performance. These results agree with finite element predictions and suggest that reduction of electrode thickness does not exclusively benefit cell performance.

  7. Dynamic multiple-target tracing to probe spatiotemporal cartography of cell membranes.

    PubMed

    Sergé, Arnauld; Bertaux, Nicolas; Rigneault, Hervé; Marguet, Didier

    2008-08-01

    Although the highly dynamic and mosaic organization of the plasma membrane is well-recognized, depicting a resolved, global view of this organization remains challenging. We present an analytical single-particle tracking (SPT) method and tool, multiple-target tracing (MTT), that takes advantage of the high spatial resolution provided by single-fluorophore sensitivity. MTT can be used to generate dynamic maps at high densities of tracked particles, thereby providing global representation of molecular dynamics in cell membranes. Deflation by subtracting detected peaks allows detection of lower-intensity peaks. We exhaustively detected particles using MTT, with performance reaching theoretical limits, and then reconnected trajectories integrating the statistical information from past trajectories. We demonstrate the potential of this method by applying it to the epidermal growth factor receptor (EGFR) labeled with quantum dots (Qdots), in the plasma membrane of live cells. We anticipate the use of MTT to explore molecular dynamics and interactions at the cell membrane.

  8. Mathematical and Computational Modeling of Polymer Exchange Membrane Fuel Cells

    NASA Astrophysics Data System (ADS)

    Ulusoy, Sehribani

    results showed that the fuel performance can be improved by using flow field designs alleviating the reactant depletion along the channels and supplying more uniform reactant distribution. Stepped flow field was found to show better performance when compared to straight and tapered ones. ANSYS FLUENT model is evaluated in terms of predicting the two phase flow in the fuel cell components. It is proposed that it is not capable of predicting the entire fuel cell polarization due to the lack of agglomerate catalyst layer modeling and well-established two-phase flow modeling. Along with the comprehensive modeling efforts, also an analytical model has been computed by using MathCAD and it is found that this simpler model is able to predict the performance in a general trend according to the experimental data obtained for a new novel membrane. Therefore, it can be used for robust prediction of the cell performance at different operating conditions such as temperature and pressure, and the electrochemical properties such as the catalyst loading, the exchange current density and the diffusion coefficients of the reactants. In addition to the modeling efforts, this thesis also presents a very comprehensive literature review on the models developed in the literature so far, the modeling efforts in fuel cell sandwich including membrane, catalyst layer and gas diffusion layer and fuel cell model properties. Moreover, a summary of possible directions of research in fuel cell analysis and computational modeling has been presented.

  9. Focus on membrane differentiation and membrane domains in the prokaryotic cell.

    PubMed

    Boekema, Egbert J; Scheffers, Dirk-Jan; van Bezouwen, Laura S; Bolhuis, Henk; Folea, I Mihaela

    2013-01-01

    A summary is presented of membrane differentiation in the prokaryotic cell, with an emphasis on the organization of proteins in the plasma/cell membrane. Many species belonging to the Eubacteria and Archaea have special membrane domains and/or membrane proliferation, which are vital for different cellular processes. Typical membrane domains are found in bacteria where a specific membrane protein is abundantly expressed. Lipid rafts form another example. Despite the rareness of conventional organelles as found in eukaryotes, some bacteria are known to have an intricate internal cell membrane organization. Membrane proliferation can be divided into curvature and invaginations which can lead to internal compartmentalization. This study discusses some of the clearest examples of bacteria with such domains and internal membranes. The need for membrane specialization is highest among the heterogeneous group of bacteria which harvest light energy, such as photosynthetic bacteria and halophilic archaea. Most of the highly specialized membranes and domains, such as the purple membrane, chromatophore and chlorosome, are found in these autotrophic organisms. Otherwise the need for membrane differentiation is lower and variable, except for those structures involved in cell division. Microscopy techniques have given essential insight into bacterial membrane morphology. As microscopy will further contribute to the unraveling of membrane organization in the years to come, past and present technology in electron microscopy and light microscopy is discussed. Electron microscopy was the first to unravel bacterial morphology because it can directly visualize membranes with inserted proteins, which no other technique can do. Electron microscopy techniques developed in the 1950s and perfected in the following decades involve the thin sectioning and freeze fractioning of cells. Several studies from the golden age of these techniques show amazing examples of cell membrane morphology

  10. Training the next generation analyst using red cell analytics

    NASA Astrophysics Data System (ADS)

    Graham, Meghan N.; Graham, Jacob L.

    2016-05-01

    We have seen significant change in the study and practice of human reasoning in recent years from both a theoretical and methodological perspective. Ubiquitous communication coupled with advances in computing and a plethora of analytic support tools have created a push for instantaneous reporting and analysis. This notion is particularly prevalent in law enforcement, emergency services and the intelligence community (IC), where commanders (and their civilian leadership) expect not only a birds' eye view of operations as they occur, but a play-by-play analysis of operational effectiveness. This paper explores the use of Red Cell Analytics (RCA) as pedagogy to train the next-gen analyst. A group of Penn State students in the College of Information Sciences and Technology at the University Park campus of The Pennsylvania State University have been practicing Red Team Analysis since 2008. RCA draws heavily from the military application of the same concept, except student RCA problems are typically on non-military in nature. RCA students utilize a suite of analytic tools and methods to explore and develop red-cell tactics, techniques and procedures (TTPs), and apply their tradecraft across a broad threat spectrum, from student-life issues to threats to national security. The strength of RCA is not always realized by the solution but by the exploration of the analytic pathway. This paper describes the concept and use of red cell analytics to teach and promote the use of structured analytic techniques, analytic writing and critical thinking in the area of security and risk and intelligence training.

  11. Intravacuolar Membranes Regulate CD8 T Cell Recognition of Membrane-Bound Toxoplasma gondii Protective Antigen.

    PubMed

    Lopez, Jodie; Bittame, Amina; Massera, Céline; Vasseur, Virginie; Effantin, Grégory; Valat, Anne; Buaillon, Célia; Allart, Sophie; Fox, Barbara A; Rommereim, Leah M; Bzik, David J; Schoehn, Guy; Weissenhorn, Winfried; Dubremetz, Jean-François; Gagnon, Jean; Mercier, Corinne; Cesbron-Delauw, Marie-France; Blanchard, Nicolas

    2015-12-15

    Apicomplexa parasites such as Toxoplasma gondii target effectors to and across the boundary of their parasitophorous vacuole (PV), resulting in host cell subversion and potential presentation by MHC class I molecules for CD8 T cell recognition. The host-parasite interface comprises the PV limiting membrane and a highly curved, membranous intravacuolar network (IVN) of uncertain function. Here, using a cell-free minimal system, we dissect how membrane tubules are shaped by the parasite effectors GRA2 and GRA6. We show that membrane association regulates access of the GRA6 protective antigen to the MHC I pathway in infected cells. Although insertion of GRA6 in the PV membrane is key for immunogenicity, association of GRA6 with the IVN limits presentation and curtails GRA6-specific CD8 responses in mice. Thus, membrane deformations of the PV regulate access of antigens to the MHC class I pathway, and the IVN may play a role in immune modulation.

  12. The Dielectric Behavior of Nonspherical Biological Cell Suspensions: An Analytic Approach

    PubMed Central

    Di Biasio, A.; Ambrosone, L.; Cametti, C.

    2010-01-01

    Abstract The influence of the cell shape on the dielectric and conductometric properties of biological cell suspensions has been investigated from a theoretical point of view presenting an analytical solution of the electrostatic problem in the case of prolate and oblate spheroidal geometries. The model, which extends to spheroidal geometries the approach developed by other researchers in the case of a spherical geometry, takes explicitly into account the charge distributions at the cell membrane interfaces. The presence of these charge distributions, which govern the trans-membrane potential ΔV, produces composite dielectric spectra with two contiguous relaxation processes, known as the α-dispersion and the β-dispersion. By using this approach, we present a series of dielectric spectra for different values of the different electrical parameters (the permittivity ɛ and the electrical conductivity σ, together with the surface conductivity γ due to the surface charge distribution) that define the whole behavior of the system. In particular, we analyze the interplay between the parameters governing the α-dispersion and those influencing the β-dispersion. Even if these relaxation processes generally occur in well-separated frequency ranges, it is worth noting that, for certain values of the membrane conductivity, the high-frequency dispersion attributed to the Maxwell-Wagner effect is influenced not only by the bulk electrical parameters of the different adjacent media, but also by the surface conductivity at the two membrane interfaces. PMID:20655844

  13. The three dimensionality of cell membranes: lamellar to cubic membrane transition as investigated by electron microscopy.

    PubMed

    Chong, Ketpin; Deng, Yuru

    2012-01-01

    Biological membranes are generally perceived as phospholipid bilayer structures that delineate in a lamellar form the cell surface and intracellular organelles. However, much more complex and highly convoluted membrane organizations are ubiquitously present in many cell types under certain types of stress, states of disease, or in the course of viral infections. Their occurrence under pathological conditions make such three-dimensionally (3D) folded and highly ordered membranes attractive biomarkers. They have also stimulated great biomedical interest in understanding the molecular basis of their formation. Currently, the analysis of such membrane arrangements, which include tubulo-reticular structures (TRS) or cubic membranes of various subtypes, is restricted to electron microscopic methods, including tomography. Preservation of membrane structures during sample preparation is the key to understand their true 3D nature. This chapter discusses methods for appropriate sample preparations to successfully examine and analyze well-preserved highly ordered membranes by electron microscopy. Processing methods and analysis conditions for green algae (Zygnema sp.) and amoeba (Chaos carolinense), mammalian cells in culture and primary tissue cells are described. We also discuss methods to identify cubic membranes by transmission electron microscopy (TEM) with the aid of a direct template matching method and by computer simulation. A 3D analysis of cubic cell membrane topology by electron tomography is described as well as scanning electron microscopy (SEM) to investigate surface contours of isolated mitochondria with cubic membrane arrangement.

  14. Multiscale modeling of mechanosensing channels on vesicles and cell membranes in 3D constricted flows and shear flows

    NASA Astrophysics Data System (ADS)

    Peng, Zhangli; Pak, On Shun; Young, Yuan-Nan; Liu, Allen; Stone, Howard

    2015-11-01

    We investigate the gating of mechanosensing channels (Mscls) on vesicles and cell membranes under different flow conditions using a multiscale approach. At the cell level (microns), the membrane tension is calculated using a 3D two-component whole-cell membrane model based on dissipative particle dynamics (DPD), including the cortex cytoskeleton and its interactions with the lipid bilayer. At the Mscl level (nanometers), we predict the relation between channel gating and the membrane tension obtained from a cell-level model using a semi-analytical model based on the bilayer hydrophobic mismatch energy. We systematically study the gating of Mscls of vesicles and cell membranes in constricted channel flows and shear flows, and explore the dependence of the gating on flow rate, cell shape and size. The results provide guidance for future experiments in inducing Mscl opening for various purposes such as drug delivery.

  15. Analytical modeling of organic solar cells and photodiodes

    NASA Astrophysics Data System (ADS)

    Altazin, S.; Clerc, R.; Gwoziecki, R.; Pananakakis, G.; Ghibaudo, G.; Serbutoviez, C.

    2011-10-01

    An analytical and physically based expression of organic solar cell I-V characteristic under dark and illuminated conditions has been derived. This model has been found in very good agreement with both experimental data and drift-diffusion numerical simulations accounting for the coupling with Poisson equation and optical propagation.

  16. Synthesis of Nanogels via Cell Membrane-Templated Polymerization

    PubMed Central

    Zhang, Jianhua; Gao, Weiwei; Fang, Ronnie H.; Dong, Anjie

    2015-01-01

    The synthesis of biomimetic hydrogel nanoparticles coated with natural cell membrane is described. Compared to existing strategy of wrapping cell membrane onto pre-formed nanoparticle substrates, this new approach forms the cell membrane-derived vesicles first, followed by growing nanoparticle cores in situ. It adds significant controllability over the nanoparticle properties and opens unique opportunities for a broad range of biomedical applications. PMID:26044721

  17. Cell Adhesion and Growth on the Anodized Aluminum Oxide Membrane.

    PubMed

    Park, Jeong Su; Moon, Dalnim; Kim, Jin-Seok; Lee, Jin Seok

    2016-03-01

    Nanotopological cues are popular tools for in vivo investigation of the extracellular matrix (ECM) and cellular microenvironments. The ECM is composed of multiple components and generates a complex microenvironment. The development of accurate in vivo methods for the investigation of ECM are important for disease diagnosis and therapy, as well as for studies on cell behavior. Here, we fabricated anodized aluminum oxide (AAO) membranes using sulfuric and oxalic acid under controlled voltage and temperature. The membranes were designed to possess three different pore and interpore sizes, AAO-1, AAO-2, and AAO-3 membranes, respectively. These membranes were used as tools to investigate nanotopology-signal induced cell behavior. Cancerous cells, specifically, the OVCAR-8 cell-line, were cultured on porous AAO membranes and the effects of these membranes on cell shape, proliferation, and viability were studied. AAO-1 membranes bearing small sized pores were found to maintain the spreading shape of the cultured cells. Cells cultured on AAO-2 and AAO-3 membranes, bearing large pore-sized AAO membranes, changed shape from spreading to rounding. Furthermore, cellular area decreased when cells were cultured on all three AAO membranes that confirmed decreased levels of focal adhesion kinase (FAK). Additionally, OVCAR-8 cells exhibited increased proliferation on AAO membranes possessing various pore sizes, indicating the importance of the nanosurface structure in regulating cell behaviors, such as cell proliferation. Our results suggest that porous-AAO membranes induced nanosurface regulated cell behavior as focal adhesion altered the intracellular organization of the cytoskeleton. Our results may find potential applications as tools in in vivo cancer research studies.

  18. Cell membrane modulation as adjuvant in cancer therapy.

    PubMed

    Zalba, Sara; Ten Hagen, Timo L M

    2017-01-01

    Cancer is a complex disease involving numerous biological processes, which can exist in parallel, can be complementary, or are engaged when needed and as such can replace each other. This redundancy in possibilities cancer cells have, are fundamental to failure of therapy. However, intrinsic features of tumor cells and tumors as a whole provide also opportunities for therapy. Here we discuss the unique and specific makeup and arrangement of cell membranes of tumor cells and how these may help treatment. Interestingly, knowledge on cell membranes and associated structures is present already for decades, while application of membrane modification and manipulation as part of cancer therapy is lagging. Recent developments of scientific tools concerning lipids and lipid metabolism, opened new and previously unknown aspects of tumor cells and indicate possible differences in lipid composition and membrane function of tumor cells compared to healthy cells. This field, coined Lipidomics, demonstrates the importance of lipid components in cell membrane in several illnesses. Important alterations in cancer, and specially in resistant cancer cells compared to normal cells, opened the door to new therapeutic strategies. Moreover, the ability to modulate membrane components and/or properties has become a reality. Here, developments in cancer-related Lipidomics and strategies to interfere specifically with cancer cell membranes and how these affect cancer treatment are discussed. We hypothesize that combination of lipid or membrane targeted strategies with available care to improve chemotherapy, radiotherapy and immunotherapy will bring the much needed change in treatment in the years to come.

  19. Molecular interactions between amantadine and model cell membranes.

    PubMed

    Wu, Fu-Gen; Yang, Pei; Zhang, Chi; Li, Bolin; Han, Xiaofeng; Song, Minghu; Chen, Zhan

    2014-07-22

    Sum frequency generation (SFG) vibrational spectroscopy was applied to study molecular interactions between amantadine and substrate supported lipid bilayers serving as model cell membranes. Both isotopically asymmetric and symmetric lipid bilayers were used in the research. SFG results elucidated how the water-soluble drug, amantadine, influenced the packing state of each leaflet of a lipid bilayer and how the drugs affected the lipid flip-flop process. It is difficult to achieve such detailed molecular-level information using other analytical techniques. Especially, from the flip-flop rate change of isotopically asymmetric lipid bilayer induced by amantadine, important information on the drug-membrane interaction mechanism can be derived. The results show that amantadine can be associated with zwitterionic PC bilayers but has a negligible influence on the flip-flop behavior of PC molecules unless at high concentrations. Different effects of amantadine on the lipid bilayer were observed for the negatively charged DPPG bilayer; low concentration amantadine (e.g., 0.20 mM) in the subphase could immediately disturb the outer lipid leaflet and then the lipid associated amantadine molecules gradually reorganize to cause the outer leaflet to return to the original orderly packed state. Higher concentration amantadine (e.g., 5.0 mM) immediately disordered the packing state of the outer lipid leaflet. For both the high and low concentration cases, amantadine molecules only bind to the outer PG leaflet and cannot translocate to the inner layer. The presence of amantadine within the negatively charged lipid layers has certain implications for using liposomes as drug delivery carriers for amantadine. Besides, by using PC or PG bilayers with both leaflets deuterated, we were able to examine how amantadine is distributed and/or oriented within the lipid bilayer. The present work demonstrates that SFG results can provide an in-depth understanding of the molecular mechanisms of

  20. Hydrocarbon-based polymer electrolyte cerium composite membranes for improved proton exchange membrane fuel cell durability

    NASA Astrophysics Data System (ADS)

    Lee, Hyejin; Han, Myungseong; Choi, Young-Woo; Bae, Byungchan

    2015-11-01

    Hydrocarbon-based cerium composite membranes were prepared for proton exchange membrane fuel cell applications to increase oxidative stability. Different amounts of cerium ions were impregnated in sulfonated poly(arylene ether sulfone) (SPES) membranes and their physicochemical properties were investigated according to the cerium content. Field-emission scanning electron microscopy and inductively coupled plasma analyses confirmed the presence of cerium ions in the composite membranes and 1H NMR indicated the successful coordination of sulfonic acid groups with the metal ions. Increasing amounts of cerium ions resulted in decreases in the proton conductivity and water uptake, but enhanced oxidative stability. The oxidative stability of the composite membranes was proven via a hydrogen peroxide exposure experiment which mimicked fuel cell operating conditions. In addition, more than 2200 h was achieved with the composite membrane under in situ accelerated open circuit voltage (OCV) durability testing (DOE protocol), whereas the corresponding pristine SPES membrane attained only 670 h.

  1. Impedance study of membrane dehydration and compression in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Le Canut, Jean-Marc; Latham, Ruth; Mérida, Walter; Harrington, David A.

    Electrochemical impedance spectroscopy (EIS) is used to measure drying and rehydration in proton exchange membrane fuel cells running under load. The hysteresis between forward and backward acquisition of polarization curves is shown to be largely due to changes in the membrane resistance. Drying tests are carried out with hydrogen and simulated reformate (hydrogen and carbon dioxide), and quasi-periodic drying and rehydration conditions are studied. The membrane hydration state is clearly linked to the high-frequency arc in the impedance spectrum, which increases in size for dry conditions indicating an increase in membrane resistance. Changes in impedance spectra as external compression is applied to the cell assembly show that EIS can separate membrane and interfacial effects, and that changes in membrane resistance dominate. Reasons for the presence of a capacitance in parallel with the membrane resistance are discussed.

  2. Development of composite membranes of PVA-TEOS doped KOH for alkaline membrane fuel cell

    SciTech Connect

    Haryadi, Sugianto, D.; Ristopan, E.

    2015-12-29

    Anion exchange membranes (AEMs) play an important role in separating fuel and oxygen (or air) in the Alkaline Membrane Fuel Cells. Preparation of hybrid organic inorganic materials of Polyvinylalcohol (PVA) - Tetraethylorthosilicate (TEOS) composite membrane doped KOH for direct alcohol alkaline fuel cell application has been investigated. The sol-gel method has been used to prepare the composite membrane of PVA-TEOS through crosslinking step and catalyzed by concentrated of hydrochloric acid. The gel solution was cast on the membrane plastic plate to obtain membrane sheets. The dry membranes were then doped by immersing in various concentrations of KOH solutions for about 4 hours. Investigations of the cross-linking process and the presence of hydroxyl group were conducted by FTIR as shown for frequency at about 1600 cm{sup −1} and 3300 cm{sup −1} respectively. The degree of swelling in ethanol decreased as the KOH concentration for membrane soaking process increased. The ion exchange capacity (IEC) of the membrane was 0.25meq/g. This composite membranes display significant ionic conductivity of 3.23 x 10{sup −2} S/cm in deionized water at room temperature. In addition, the morphology observation by scanning electron microscope (SEM) of the membrane indicates that soaking process of membrane in KOH increased thermal resistant.

  3. Development of composite membranes of PVA-TEOS doped KOH for alkaline membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Haryadi, Sugianto, D.; Ristopan, E.

    2015-12-01

    Anion exchange membranes (AEMs) play an important role in separating fuel and oxygen (or air) in the Alkaline Membrane Fuel Cells. Preparation of hybrid organic inorganic materials of Polyvinylalcohol (PVA) - Tetraethylorthosilicate (TEOS) composite membrane doped KOH for direct alcohol alkaline fuel cell application has been investigated. The sol-gel method has been used to prepare the composite membrane of PVA-TEOS through crosslinking step and catalyzed by concentrated of hydrochloric acid. The gel solution was cast on the membrane plastic plate to obtain membrane sheets. The dry membranes were then doped by immersing in various concentrations of KOH solutions for about 4 hours. Investigations of the cross-linking process and the presence of hydroxyl group were conducted by FTIR as shown for frequency at about 1600 cm-1 and 3300 cm-1 respectively. The degree of swelling in ethanol decreased as the KOH concentration for membrane soaking process increased. The ion exchange capacity (IEC) of the membrane was 0.25meq/g. This composite membranes display significant ionic conductivity of 3.23 x 10-2 S/cm in deionized water at room temperature. In addition, the morphology observation by scanning electron microscope (SEM) of the membrane indicates that soaking process of membrane in KOH increased thermal resistant.

  4. Nonhumidified High-Temperature Membranes Developed for Proton Exchange Membrane Fuel Cells

    NASA Technical Reports Server (NTRS)

    Kinder, James D.

    2005-01-01

    Fuel cells are being considered for a wide variety of aerospace applications. One of the most versatile types of fuel cells is the proton-exchange-membrane (PEM) fuel cell. PEM fuel cells can be easily scaled to meet the power and space requirements of a specific application. For example, small 100-W PEM fuel cells are being considered for personal power for extravehicular activity suit applications, whereas larger PEM fuel cells are being designed for primary power in airplanes and in uninhabited air vehicles. Typically, PEM fuel cells operate at temperatures up to 80 C. To increase the efficiency and power density of the fuel cell system, researchers are pursuing methods to extend the operating temperature of the PEM fuel cell to 180 C. The most widely used membranes in PEM fuel cells are Nafion 112 and Nafion 117--sulfonated perfluorinated polyethers that were developed by DuPont. In addition to their relatively high cost, the properties of these membranes limit their use in a PEM fuel cell to around 80 C. The proton conductivity of Nafion membranes significantly decreases above 80 C because the membrane dehydrates. The useful operating range of Nafion-based PEM fuel cells can be extended to over 100 C if ancillary equipment, such as compressors and humidifiers, is added to maintain moisture levels within the membrane. However, the addition of these components reduces the power density and increases the complexity of the fuel cell system.

  5. Graphene-Induced Pore Formation on Cell Membranes

    NASA Astrophysics Data System (ADS)

    Duan, Guangxin; Zhang, Yuanzhao; Luan, Binquan; Weber, Jeffrey K.; Zhou, Royce W.; Yang, Zaixing; Zhao, Lin; Xu, Jiaying; Luo, Judong; Zhou, Ruhong

    2017-02-01

    Examining interactions between nanomaterials and cell membranes can expose underlying mechanisms of nanomaterial cytotoxicity and guide the design of safer nanomedical technologies. Recently, graphene has been shown to exhibit potential toxicity to cells; however, the molecular processes driving its lethal properties have yet to be fully characterized. We here demonstrate that graphene nanosheets (both pristine and oxidized) can produce holes (pores) in the membranes of A549 and Raw264.7 cells, substantially reducing cell viability. Electron micrographs offer clear evidence of pores created on cell membranes. Our molecular dynamics simulations reveal that multiple graphene nanosheets can cooperate to extract large numbers of phospholipids from the membrane bilayer. Strong dispersion interactions between graphene and lipid-tail carbons result in greatly depleted lipid density within confined regions of the membrane, ultimately leading to the formation of water-permeable pores. This cooperative lipid extraction mechanism for membrane perforation represents another distinct process that contributes to the molecular basis of graphene cytotoxicity.

  6. Selective effect of cell membrane on synaptic neurotransmission

    NASA Astrophysics Data System (ADS)

    Postila, Pekka A.; Vattulainen, Ilpo; Róg, Tomasz

    2016-01-01

    Atomistic molecular dynamics simulations were performed with 13 non-peptidic neurotransmitters (NTs) in three different membrane environments. The results provide compelling evidence that NTs are divided into membrane-binding and membrane-nonbinding molecules. NTs adhere to the postsynaptic membrane surface whenever the ligand-binding sites of their synaptic receptors are buried in the lipid bilayer. In contrast, NTs that have extracellular ligand-binding sites do not have a similar tendency to adhere to the membrane surface. This finding is a seemingly simple yet important addition to the paradigm of neurotransmission, essentially dividing it into membrane-independent and membrane-dependent mechanisms. Moreover, the simulations also indicate that the lipid composition especially in terms of charged lipids can affect the membrane partitioning of NTs. The revised paradigm, highlighting the importance of cell membrane and specific lipids for neurotransmission, should to be of interest to neuroscientists, drug industry and the general public alike.

  7. The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells

    NASA Technical Reports Server (NTRS)

    Eisman, G. A.

    1989-01-01

    Dow Chemical's research activities in fuel cells revolve around the development of perfluorosulfonic acid membranes useful as the proton transport medium and separator. Some of the performance characteristics which are typical for such membranes are outlined. The results of tests utilizing a new experimental membrane useful in proton-exchange membrane fuel cells are presented. The high voltage at low current densities can lead to higher system efficiencies while, at the same time, not sacrificing other critical properties pertinent to membrane fuel cell operation. A series of tests to determine response times indicated that on-off cycles are on the order of 80 milliseconds to reach 90 percent of full power. The IR free voltage at 100 amps/sq ft was determined and the results indicating a membrane/electrode package resistance to be .15 ohm-sq cm at 100 amps/sq ft.

  8. Membrane fouling in microfiltration used for cell harvesting

    NASA Astrophysics Data System (ADS)

    Kaghazchi, Tahereh; Zokaee, Farzin; Zare, Abbas

    2001-03-01

    In the present study the membrane fouling in microfiltration used for cell harvesting in a deadend system has been investigated. Experimental results were analysed in terms of existing membrane filtration models and membrane resistances. The cake filtration model (CFM) and standard blocking model (SBM) have been considered in this study. Various membrane resistances were determined at different processing time, feed concentration and stirring speed. Resistances to permeation in this system include filter medium, pore blocking, adsorption, cake layer and concentration polarization.

  9. Interaction of gentamicin polycation with model and cell membranes.

    PubMed

    Kovács, Eugenia; Savopol, Tudor; Iordache, Maria-Minodora; Săplăcan, Lavinia; Sobaru, Iuliana; Istrate, Claudia; Mingeot-Leclercq, Marie-Paule; Moisescu, Mihaela-Georgeta

    2012-10-01

    The interaction of positively-charged antibiotic gentamicin with cell membranes was studied to determine if any changes in membrane organization were induced by the drug. Opossum kidney epithelia (OK) cells were used as models of eukaryotic cells. Two methods were used: laurdan fluorescence spectroscopy and fluorescence anisotropy recordings on 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate (TMA-DPH) labeled cell suspensions. Both methods showed an altered membrane hydration and fluidity of gentamicin treated cells. Liposomes prepared from dimyristoyl-phosphatidylcholine (DMPC) mixed with cardiolipin, which mimics the heterogeneous charge composition of the natural cell membrane, were used to determine the effect of gentamicin on artificial bilayers. The membrane lipid packing as revealed by generalized polarization (GP) and fluorescence anizotropy variation with increasing temperature was studied. It was found that the generalized polarization of liposomal membranes containing a negatively charged lipid (cardiolipin) is higher in the presence of gentamicin; in the membrane of living cell (OK), gentamicin induces, on the contrary, a decrease of general polarization. Considering the role of membrane organization in the function of transmembrane channels and receptors, our findings suggest hypotheses that may explain the permeation of gentamicin through the living cell membrane by using these channels.

  10. Analytical determination of critical crack size in solar cells

    NASA Technical Reports Server (NTRS)

    Chen, C. P.

    1988-01-01

    Although solar cells usually have chips and cracks, no material specifications concerning the allowable crack size on solar cells are available for quality assurance and engineering design usage. Any material specifications that the cell manufacturers use were developed for cosmetic reasons that have no technical basis. Therefore, the Applied Solar Energy Corporation (ASEC) has sponsored a continuing program for the fracture mechanics evaluation of GaAs. Fracture mechanics concepts were utilized to develop an analytical model that can predict the critical crack size of solar cells. This model indicates that the edge cracks of a solar cell are more critical than its surface cracks. In addition, the model suggests that the material specifications on the allowable crack size used for Si solar cells should not be applied to GaAs solar cells. The analytical model was applied to Si and GaAs solar cells, but it would also be applicable to the semiconductor wafers of other materials, such as a GaAs thin film on a Ge substrate, using appropriate input data.

  11. Fluorescence and polarization imaging of membrane dynamics in living cells

    NASA Astrophysics Data System (ADS)

    Wagner, M.; Weber, P.; Bruns, T.; Strauss, W. S. L.; Schneckenburger, H.

    2009-02-01

    Methods of wide field fluorescence microscopy for measuring membrane dynamics in living cells are described. These methods are based on laser pulse excitation of the membrane marker 6-dodecanoyl-2-dimethylamino naphthalene (laurdan) whose emission spectra, fluorescence decay kinetics and anisotropies are sensitive to membrane stiffness and fluidity. Plasma membranes are selected by illumination with an evanescent electromagnetic field and distinguished from intracellular membranes assessed by whole cell illumination. While fluorescence spectra of laurdan appeared red-shifted with decreasing membrane stiffness, fluorescence anisotropy and rotational relaxation times were reduced with increasing membrane fluidity. Membrane stiffness was found to increase with decreasing temperature and increasing amounts of cholesterol. In addition, membrane stiffness of the plasma membrane was always higher than that of intracellular membranes. These effects may have some influence on pathogenesis of certain diseases, uptake of pharmaceutical agents or cell aging. Present experiments are limited to fluorescence microscopy with total internal reflection (TIR) or epi-illumination, but corresponding methods can also be used for screening of larger cell collectives, e.g. in microtiter plates.

  12. Conductivity Measurements of Synthesized Heteropoly Acid Membranes for Proton Exchange Membrane Fuel Cells

    SciTech Connect

    Record, K.A.; Haley, B.T.; Turner, J.

    2006-01-01

    Fuel cell technology is receiving attention due to its potential to be a pollution free method of electricity production when using renewably produced hydrogen as fuel. In a Proton Exchange Membrane (PEM) fuel cell H2 and O2 react at separate electrodes, producing electricity, thermal energy, and water. A key component of the PEM fuel cell is the membrane that separates the electrodes. DuPont’s Nafion® is the most commonly used membrane in PEM fuel cells; however, fuel cell dehydration at temperatures near 100°C, resulting in poor conductivity, is a major hindrance to fuel cell performance. Recent studies incorporating heteropoly acids (HPAs) into membranes have shown an increase in conductivity and thus improvement in performance. HPAs are inorganic materials with known high proton conductivities. The primary objective of this work is to measure the conductivity of Nafion, X-Ionomer membranes, and National Renewable Energy Laboratory (NREL) Developed Membranes that are doped with different HPAs at different concentrations. Four-point conductivity measurements using a third generation BekkTech conductivity test cell are used to determine membrane conductivity. The effect of multiple temperature and humidification levels is also examined. While the classic commercial membrane, Nafion, has a conductivity of approximately 0.10 S/cm, measurements for membranes in this study range from 0.0030 – 0.58 S/cm, depending on membrane type, structure of the HPA, and the relative humidity. In general, the X-ionomer with H6P2W21O71 HPA gave the highest conductivity and the Nafion with the 12-phosphotungstic (PW12) HPA gave the lowest. The NREL composite membranes had conductivities on the order of 0.0013 – 0.025 S/cm.

  13. Preparation and performance of nano silica/Nafion composite membrane for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Wang, Keping; McDermid, Scott; Li, Jing; Kremliakova, Natalia; Kozak, Paul; Song, Chaojie; Tang, Yanghua; Zhang, Jianlu; Zhang, Jiujun

    Composite membranes made from Nafion ionomer with nano phosphonic acid-functionalised silica and colloidal silica were prepared and evaluated for proton exchange membrane fuel cells (PEMFCs) operating at elevated temperature and low relative humidity (RH). The phosphonic acid-functionalised silica additive obtained from a sol-gel process was well incorporated into Nafion membrane. The particle size determined using transmission electron microscope (TEM) had a narrow distribution with an average value of approximately 11 nm and a standard deviation of ±4 nm. The phosphonic acid-functionalised silica additive enhanced proton conductivity and water retention by introducing both acidic groups and porous silica. The proton conductivity of the composite membrane with the acid-functionalised silica was 0.026 S cm -1, 24% higher than that of the unmodified Nafion membrane at 85 °C and 50% RH. Compared with the Nafion membrane, the phosphonic acid-functionalised silica (10% loading level) composite membrane exhibited 60 mV higher fuel cell performance at 1 A cm -2, 95 °C and 35% RH, and 80 mV higher at 0.8 A cm -2, 120 °C and 35% RH. The fuel cell performance of composite membrane made with 6% colloidal silica without acidic group was also higher than unmodified Nafion membrane, however, its performance was lower than the acid-functionalised silica additive composite membrane.

  14. Roles of membrane trafficking in plant cell wall dynamics

    PubMed Central

    Ebine, Kazuo; Ueda, Takashi

    2015-01-01

    The cell wall is one of the characteristic components of plant cells. The cell wall composition differs among cell types and is modified in response to various environmental conditions. To properly generate and modify the cell wall, many proteins are transported to the plasma membrane or extracellular space through membrane trafficking, which is one of the key protein transport mechanisms in eukaryotic cells. Given the diverse composition and functions of the cell wall in plants, the transport of the cell wall components and proteins that are involved in cell wall-related events could be specialized for each cell type, i.e., the machinery for cell wall biogenesis, modification, and maintenance could be transported via different trafficking pathways. In this review, we summarize the recent progress in the current understanding of the roles and mechanisms of membrane trafficking in plant cells and focus on the biogenesis and regulation of the cell wall. PMID:26539200

  15. Physical principles of membrane remodelling during cell mechanoadaptation

    PubMed Central

    Kosmalska, Anita Joanna; Casares, Laura; Elosegui-Artola, Alberto; Thottacherry, Joseph Jose; Moreno-Vicente, Roberto; González-Tarragó, Víctor; del Pozo, Miguel Ángel; Mayor, Satyajit; Arroyo, Marino; Navajas, Daniel; Trepat, Xavier; Gauthier, Nils C.; Roca-Cusachs, Pere

    2015-01-01

    Biological processes in any physiological environment involve changes in cell shape, which must be accommodated by their physical envelope—the bilayer membrane. However, the fundamental biophysical principles by which the cell membrane allows for and responds to shape changes remain unclear. Here we show that the 3D remodelling of the membrane in response to a broad diversity of physiological perturbations can be explained by a purely mechanical process. This process is passive, local, almost instantaneous, before any active remodelling and generates different types of membrane invaginations that can repeatedly store and release large fractions of the cell membrane. We further demonstrate that the shape of those invaginations is determined by the minimum elastic and adhesive energy required to store both membrane area and liquid volume at the cell–substrate interface. Once formed, cells reabsorb the invaginations through an active process with duration of the order of minutes. PMID:26073653

  16. Anatomy of the red cell membrane skeleton: unanswered questions.

    PubMed

    Lux, Samuel E

    2016-01-14

    The red cell membrane skeleton is a pseudohexagonal meshwork of spectrin, actin, protein 4.1R, ankyrin, and actin-associated proteins that laminates the inner membrane surface and attaches to the overlying lipid bilayer via band 3-containing multiprotein complexes at the ankyrin- and actin-binding ends of spectrin. The membrane skeleton strengthens the lipid bilayer and endows the membrane with the durability and flexibility to survive in the circulation. In the 36 years since the first primitive model of the red cell skeleton was proposed, many additional proteins have been discovered, and their structures and interactions have been defined. However, almost nothing is known of the skeleton's physiology, and myriad questions about its structure remain, including questions concerning the structure of spectrin in situ, the way spectrin and other proteins bind to actin, how the membrane is assembled, the dynamics of the skeleton when the membrane is deformed or perturbed by parasites, the role lipids play, and variations in membrane structure in unique regions like lipid rafts. This knowledge is important because the red cell membrane skeleton is the model for spectrin-based membrane skeletons in all cells, and because defects in the red cell membrane skeleton underlie multiple hemolytic anemias.

  17. Raman Imaging in Cell Membranes, Lipid-Rich Organelles, and Lipid Bilayers.

    PubMed

    Syed, Aleem; Smith, Emily A

    2017-03-15

    Raman-based optical imaging is a promising analytical tool for noninvasive, label-free chemical imaging of lipid bilayers and cellular membranes. Imaging using spontaneous Raman scattering suffers from a low intensity that hinders its use in some cellular applications. However, developments in coherent Raman imaging, surface-enhanced Raman imaging, and tip-enhanced Raman imaging have enabled video-rate imaging, excellent detection limits, and nanometer spatial resolution, respectively. After a brief introduction to these commonly used Raman imaging techniques for cell membrane studies, this review discusses selected applications of these modalities for chemical imaging of membrane proteins and lipids. Finally, recent developments in chemical tags for Raman imaging and their applications in the analysis of selected cell membrane components are summarized. Ongoing developments toward improving the temporal and spatial resolution of Raman imaging and small-molecule tags with strong Raman scattering cross sections continue to expand the utility of Raman imaging for diverse cell membrane studies. Expected final online publication date for the Annual Review of Analytical Chemistry Volume 10 is June 12, 2017. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

  18. Analyte loss due to membrane filter adsorption as determined by high-performance liquid chromatography.

    PubMed

    Carlson, M; Thompson, R D

    2000-02-01

    The phenomenon of membrane filter adsorption in high-performance liquid chromatography (HPLC) is investigated utilizing 16 brands of filters representing 3 polymeric materials: cellulose acetate (CA), nylon, and polyvinylidene difluoride in a variety of diameters (3, 4, 7, 13, and 25 mm). Sixteen compounds commonly encountered in drug preparations are selected as sample analytes and classified as acidic, basic, and neutral in chemical behavior. Six mobile phase/sample solvent mixtures are included: 3 with methanol-water and 3 with acetonitrile-water as major constituents. When using methanol as the mobile phase organic component, CA, nylon, and polyvinylidene difluoride (PVDF) filters exhibit negligible to moderate adsorption levels with regard to the neutral and basic drug compounds. The acidic drug test compounds are adsorbed by 50% of all 3 filter materials tested in methanol-water. In acetonitrile, neutral compounds are affected by 31.4%, basic compounds are affected by 47.0%, and acidic compounds are affected by 53.6% of the nylon and PVDF filters. CA is incompatible with acetonitrile and is excluded from the study with this solvent.

  19. Effect of EMP fields on cell membrane potentials

    SciTech Connect

    Gailey, P.C.; Easterly, C.E.

    1993-06-01

    A simple model is presented for cell membrane potentials induced during exposure to electromagnetic pulse (EMP). Using calculated values of internal electric field strength induced during EMP exposure, the model predicts that cell membrane potentials of about 100 mV may be induced for time frames on the order of 10 ns. Possible biological effects of these potentials including electroporation area discussed.

  20. Blood analyte sensing using fluorescent dye-loaded red blood cells

    NASA Astrophysics Data System (ADS)

    Ritter, Sarah C.; Shao, Xiaole; Cooley, Nicholas; Milanick, Mark A.; Glass, Timothy E.; Meissner, Kenith E.

    2014-02-01

    Measurement of blood analytes provides crucial information about a patient's health. Some such analytes, such as glucose in the case of diabetes, require long-term or near-continuous monitoring for proper disease management. However, current monitoring techniques are far from ideal: multiple-per-day finger stick tests are inconvenient and painful for the patient; implantable sensors have short functional life spans (i.e., 3-7 days). Due to analyte transporters on red blood cell (RBC) membranes that equilibrate intracellular and extracellular analyte levels, RBCs serve as an attractive alternative for encapsulating analyte sensors. Once reintroduced to the blood stream, the functionalized RBCs may continue to live for the remainder of their life span (120 days for humans). They are biodegradable and biocompatible, thereby eliminating the immune system response common for many implanted devices. The proposed sensing system utilizes the ability of the RBCs to swell in response to a decrease in the osmolarity of the extracellular solution. Just before lysis, they develop small pores on the scale of tens of nanometers. While at low temperature, analyte-sensitive dyes in the extracellular solution diffuse into the perforated RBCs and become entrapped upon restoration of temperature and osmolarity. Since the fluorescent signal from the entrapped dye reports on changes in the analyte level of the extracellular solution via the RBC transporters, interactions between the RBCs and the dye are critical to the efficacy of this technique. In this work, we study the use of a near infrared pH sensitive dye encapsulated within RBCs and assess the ability to measure dye fluorescence in vivo.

  1. Favorable effect of in-situ generated platinum in the membrane on fuel cell membrane durability

    NASA Astrophysics Data System (ADS)

    Macauley, Natalia; Wong, Ka Hung; Watson, Mark; Kjeang, Erik

    2015-12-01

    The overall lifetime of polymer electrolyte fuel cells is often determined by the membrane durability. Platinum, which may dissolve from the catalyst layers during fuel cell operation and deposit in the membrane, has been shown to have both positive and negative effects on membrane stability. In the present work, we analyze what specific conditions are required in order to reach a favorable, membrane stabilizing effect with the controlled use of platinum in the membrane. Using accelerated membrane durability testing, field operated membrane samples, and electron microscopy, we demonstrate that a high platinum concentration with specific particle shapes and sizes is essential for enhanced membrane stability. Specifically, star shaped and dendritic particles with high particle density and high surface area are shown to be preferable. These particles contain high levels of Pt(111) and are expected to have high catalytic activity toward peroxide quenching and crossover gas consumption, thereby mitigating chemical membrane degradation. On the other hand, small, dispersed cubic particles are found to have no effect or the opposite, negative effect on membrane stability.

  2. Radiation-Grafted Polymer Electrolyte Membranes for Water Electrolysis Cells: Evaluation of Key Membrane Properties.

    PubMed

    Albert, Albert; Barnett, Alejandro O; Thomassen, Magnus S; Schmidt, Thomas J; Gubler, Lorenz

    2015-10-14

    Radiation-grafted membranes can be considered an alternative to perfluorosulfonic acid (PFSA) membranes, such as Nafion, in a solid polymer electrolyte electrolyzer. Styrene, acrylonitrile, and 1,3-diisopropenylbenzene monomers are cografted into preirradiated 50 μm ethylene tetrafluoroethylene (ETFE) base film, followed by sulfonation to introduce proton exchange sites to the obtained grafted films. The incorporation of grafts throughout the thickness is demonstrated by scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analysis of the membrane cross-sections. The membranes are analyzed in terms of grafting kinetics, ion-exchange capacity (IEC), and water uptake. The key properties of radiation-grafted membranes and Nafion, such as gas crossover, area resistance, and mechanical properties, are evaluated and compared. The plot of hydrogen crossover versus area resistance of the membranes results in a property map that indicates the target areas for membrane development for electrolyzer applications. Tensile tests are performed to assess the mechanical properties of the membranes. Finally, these three properties are combined to establish a figure of merit, which indicates that radiation-grafted membranes obtained in the present study are promising candidates with properties superior to those of Nafion membranes. A water electrolysis cell test is performed as proof of principle, including a comparison to a commercial membrane electrode assembly (MEA).

  3. Durability of symmetrically and asymmetrically porous polybenzimidazole membranes for high temperature proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Jheng, Li-Cheng; Chang, Wesley Jen-Yang; Hsu, Steve Lien-Chung; Cheng, Po-Yang

    2016-08-01

    Two types of porous polybenzimidazole (PBI) membranes with symmetric and asymmetric morphologies were fabricated by the template-leaching method and characterized by scanning electron microscope (SEM). Their physicochemical properties were compared in terms of acid-doping level, proton conductivity, mechanical strength, and oxidative stability. The durability of fuel cell operation is one of the most challenging for the PBI based membrane electrode assembly (MEA) used in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). In the present work, we carried out a long-term steady-state fuel cell test to compare the effect of membrane structure on the cell voltage degradation. It has also been demonstrated that the asymmetrically porous PBI could bring some notable improvements on the durability of fuel cell operation, the fuel crossover problem, and the phosphoric acid leakage.

  4. Studying the Nucleated Mammalian Cell Membrane by Single Molecule Approaches

    PubMed Central

    Wang, Feng; Wu, Jiazhen; Gao, Jing; Liu, Shuheng; Jiang, Junguang; Jiang, Shibo; Wang, Hongda

    2014-01-01

    The cell membrane plays a key role in compartmentalization, nutrient transportation and signal transduction, while the pattern of protein distribution at both cytoplasmic and ectoplasmic sides of the cell membrane remains elusive. Using a combination of single-molecule techniques, including atomic force microscopy (AFM), single molecule force spectroscopy (SMFS) and stochastic optical reconstruction microscopy (STORM), to study the structure of nucleated cell membranes, we found that (1) proteins at the ectoplasmic side of the cell membrane form a dense protein layer (4 nm) on top of a lipid bilayer; (2) proteins aggregate to form islands evenly dispersed at the cytoplasmic side of the cell membrane with a height of about 10–12 nm; (3) cholesterol-enriched domains exist within the cell membrane; (4) carbohydrates stay in microdomains at the ectoplasmic side; and (5) exposed amino groups are asymmetrically distributed on both sides. Based on these observations, we proposed a Protein Layer-Lipid-Protein Island (PLLPI) model, to provide a better understanding of cell membrane structure, membrane trafficking and viral fusion mechanisms. PMID:24806512

  5. In-situ membrane hydration measurement of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Lai, Yeh-Hung; Fly, Gerald W.; Clapham, Shawn

    2015-01-01

    Achieving proper membrane hydration control is one of the most critical aspects of PEM fuel cell development. This article describes the development and application of a novel 50 cm2 fuel cell device to study the in-situ membrane hydration by measuring the through-thickness membrane swelling via an array of linear variable differential transducers. Using this setup either as an air/air (dummy) cell or as a hydrogen/air (operating) cell, we performed a series of hydration and dehydration experiments by cycling the RH of the inlet gas streams at 80 °C. From the linear relationship between the under-the-land swelling and the over-the-channel water content, the mechanical constraint within the fuel cell assembly can suppress the membrane water uptake by 11%-18%. The results from the air/air humidity cycling test show that the membrane can equilibrate within 120 s for all RH conditions and that membrane can reach full hydration at a RH higher than 140% in spite of the use of a liquid water impermeable Carbel MP30Z microporous layer. This result confirms that the U.S. DOE's humidity cycling mechanical durability protocol induces sufficient humidity swings to maximize hygrothermal mechanical stresses. This study shows that the novel experimental technique can provide a robust and accurate means to study the in-situ hydration of thin membranes subject to a wide range of fuel cell conditions.

  6. Axially resolved polarisation microscopy of membrane dynamics in living cells

    NASA Astrophysics Data System (ADS)

    Wagner, Michael; Weber, Petra; Schneckenburger, Herbert

    2007-07-01

    Membrane dynamics has a large impact on cellular uptake and release of various metabolites or pharmaceutical agents. For a deeper understanding of the cellular processes involved, we used U373-MG human glioblastoma cells as a model system. As conventional microscopy does not permit to investigate individual layers in living cells, we used structured illumination techniques and total internal reflection fluorescence microscopy (TIRFM) to analyse the plasma membrane and intracellular membranes of living cells selectively. Optical image sections provide a high resolution and the possibility of 3D reconstruction. Membranes of living cells were characterized by the membrane marker 6-dodecanoyl-2-dimethylamino naphthalene (laurdan). Due to its spectral and kinetic properties this fluorescence marker appears appropriate for measuring membrane stiffness and fluidity. After excitation with linearly polarized laser pulses, membrane fluidity of human glioblastoma cells was determined by measurements of steady-state and time-resolved fluorescence anisotropy r(t), since with increasing viscosity of the environment, the rotation of an excited molecule is impeded. The corresponding time constant τ r of molecular relaxation decreased with temperature and increased with the amount of cholesterol. In addition, fluorescence anisotropy r(t) values of the plasma membrane were larger than the values of intracellular membranes for all temperatures in the range of 16°C<=T<=41°C.

  7. Empirical membrane lifetime model for heavy duty fuel cell systems

    NASA Astrophysics Data System (ADS)

    Macauley, Natalia; Watson, Mark; Lauritzen, Michael; Knights, Shanna; Wang, G. Gary; Kjeang, Erik

    2016-12-01

    Heavy duty fuel cells used in transportation system applications such as transit buses expose the fuel cell membranes to conditions that can lead to lifetime-limiting membrane failure via combined chemical and mechanical degradation. Highly durable membranes and reliable predictive models are therefore needed in order to achieve the ultimate heavy duty fuel cell lifetime target of 25,000 h. In the present work, an empirical membrane lifetime model was developed based on laboratory data from a suite of accelerated membrane durability tests. The model considers the effects of cell voltage, temperature, oxygen concentration, humidity cycling, humidity level, and platinum in the membrane using inverse power law and exponential relationships within the framework of a general log-linear Weibull life-stress statistical distribution. The obtained model is capable of extrapolating the membrane lifetime from accelerated test conditions to use level conditions during field operation. Based on typical conditions for the Whistler, British Columbia fuel cell transit bus fleet, the model predicts a stack lifetime of 17,500 h and a membrane leak initiation time of 9200 h. Validation performed with the aid of a field operated stack confirmed the initial goal of the model to predict membrane lifetime within 20% of the actual operating time.

  8. Revealing the Dynamics of Thylakoid Membranes in Living Cyanobacterial Cells

    DOE PAGES

    Stingaciu, Laura-Roxana; O’Neill, Hugh; Liberton, Michelle; ...

    2016-01-21

    Cyanobacteria are photosynthetic prokaryotes that make major contributions to the production of the oxygen in the Earth atmosphere. The photosynthetic machinery in cyanobacterial cells is housed in flattened membrane structures called thylakoids. The structural organization of cyanobacterial cells and the arrangement of the thylakoid membranes in response to environmental conditions have been widely investigated. However, there is limited knowledge about the internal dynamics of these membranes in terms of their flexibility and motion during the photosynthetic process. We present a direct observation of thylakoid membrane undulatory motion in vivo and show a connection between membrane mobility and photosynthetic activity. High-resolutionmore » inelastic neutron scattering experiments on the cyanobacterium Synechocystis sp. PCC 6803 assessed the flexibility of cyanobacterial thylakoid membrane sheets and the dependence of the membranes on illumination conditions. We observed softer thylakoid membranes in the dark that have three-to four fold excess mobility compared to membranes under high light conditions. We find our analysis indicates that electron transfer between photosynthetic reaction centers and the associated electrochemical proton gradient across the thylakoid membrane result in a significant driving force for excess membrane dynamics. Lastly, these observations provide a deeper understanding of the relationship between photosynthesis and cellular architecture.« less

  9. Revealing the Dynamics of Thylakoid Membranes in Living Cyanobacterial Cells

    SciTech Connect

    Stingaciu, Laura-Roxana; O’Neill, Hugh; Urban, Volker S.; Ohl, Michael

    2016-01-21

    Cyanobacteria are photosynthetic prokaryotes that make major contributions to the production of the oxygen in the Earth atmosphere. The photosynthetic machinery in cyanobacterial cells is housed in flattened membrane structures called thylakoids. The structural organization of cyanobacterial cells and the arrangement of the thylakoid membranes in response to environmental conditions have been widely investigated. However, there is limited knowledge about the internal dynamics of these membranes in terms of their flexibility and motion during the photosynthetic process. We present a direct observation of thylakoid membrane undulatory motion in vivo and show a connection between membrane mobility and photosynthetic activity. High-resolution inelastic neutron scattering experiments on the cyanobacterium Synechocystis sp. PCC 6803 assessed the flexibility of cyanobacterial thylakoid membrane sheets and the dependence of the membranes on illumination conditions. We observed softer thylakoid membranes in the dark that have three-to four fold excess mobility compared to membranes under high light conditions. We find our analysis indicates that electron transfer between photosynthetic reaction centers and the associated electrochemical proton gradient across the thylakoid membrane result in a significant driving force for excess membrane dynamics. Lastly, these observations provide a deeper understanding of the relationship between photosynthesis and cellular architecture.

  10. Revealing the Dynamics of Thylakoid Membranes in Living Cyanobacterial Cells

    NASA Astrophysics Data System (ADS)

    Stingaciu, Laura-Roxana; O’Neill, Hugh; Liberton, Michelle; Urban, Volker S.; Pakrasi, Himadri B.; Ohl, Michael

    2016-01-01

    Cyanobacteria are photosynthetic prokaryotes that make major contributions to the production of the oxygen in the Earth atmosphere. The photosynthetic machinery in cyanobacterial cells is housed in flattened membrane structures called thylakoids. The structural organization of cyanobacterial cells and the arrangement of the thylakoid membranes in response to environmental conditions have been widely investigated. However, there is limited knowledge about the internal dynamics of these membranes in terms of their flexibility and motion during the photosynthetic process. We present a direct observation of thylakoid membrane undulatory motion in vivo and show a connection between membrane mobility and photosynthetic activity. High-resolution inelastic neutron scattering experiments on the cyanobacterium Synechocystis sp. PCC 6803 assessed the flexibility of cyanobacterial thylakoid membrane sheets and the dependence of the membranes on illumination conditions. We observed softer thylakoid membranes in the dark that have three-to four fold excess mobility compared to membranes under high light conditions. Our analysis indicates that electron transfer between photosynthetic reaction centers and the associated electrochemical proton gradient across the thylakoid membrane result in a significant driving force for excess membrane dynamics. These observations provide a deeper understanding of the relationship between photosynthesis and cellular architecture.

  11. Proteomics and Phosphoproteomics Analysis of Human Lens Fiber Cell Membranes

    PubMed Central

    Wang, Zhen; Han, Jun; David, Larry L.; Schey, Kevin L.

    2013-01-01

    Purpose. The human lens fiber cell insoluble membrane fraction contains important membrane proteins, cytoskeletal proteins, and cytosolic proteins that are strongly associated with the membrane. The purpose of this study was to characterize the lens fiber cell membrane proteome and phosphoproteome from human lenses. Methods. HPLC-mass spectrometry–based multidimensional protein identification technology (MudPIT), without or with phosphopeptide enrichment, was applied to study the proteome and phosphoproteome of lens fiber cell membranes, respectively. Results. In total, 951 proteins were identified, including 379 integral membrane and membrane-associated proteins. Enriched gene categories and pathways based on the proteomic analysis include carbohydrate metabolism (glycolysis/gluconeogenesis, pentose phosphate pathway, pyruvate metabolism), proteasome, cell-cell signaling and communication (GTP binding, gap junction, focal adhesion), glutathione metabolism, and actin regulation. The combination of TiO2 phosphopeptide enrichment and MudPIT analysis revealed 855 phosphorylation sites on 271 proteins, including 455 phosphorylation sites that have not been previously identified. PKA, PKC, CKII, p38MAPK, and RSK are predicted as the major kinases for phosphorylation on the sites identified in the human lens membrane fraction. Conclusions. The results presented herein significantly expand the characterized proteome and phosphoproteome of the human lens fiber cell and provide a valuable reference for future research in studies of lens development and disease. PMID:23349431

  12. ISOLATION OF PLASMA MEMBRANE FRAGMENTS FROM HELA CELLS

    PubMed Central

    Boone, Charles W.; Ford, Lincoln E.; Bond, Howard E.; Stuart, Donald C.; Lorenz, Dianne

    1969-01-01

    A method for isolating plasma membrane fragments from HeLa cells is described. The procedure starts with the preparation of cell membrane "ghosts," obtained by gentle rupture of hypotonically swollen cells, evacuation of most of the cell contents by repeated washing, and isolation of the ghosts on a discontinuous sucrose density gradient. The ghosts are then treated by minimal sonication (5 sec) at pH 8.6, which causes the ghost membranes to pinch off into small vesicles but leaves any remaining larger intracellular particulates intact and separable by differential centrifugation. The ghost membrane vesicles are then subjected to isopycnic centrifugation on a 20–50% w/w continuous sucrose gradient in tris-magnesium buffer, pH 8.6. A band of morphologically homogeneous smooth vesicles, derived principally from plasma membrane, is recovered at 30–33% (peak density = 1.137). The plasma membrane fraction contained a Na-K-activated ATPase activity of 1.5 µmole Pi/hr per mg, 3% RNA, and 13.8% of the NADH-cytochrome c reductase activity of a heavier fraction from the same gradient which contained mitochondria and rough endoplasmic vesicles. The plasma membranes of viable HeLa cells were marked with 125I-labeled horse antibody and followed through the isolation procedure. The specific antibody binding of the plasma membrane vesicle fraction was increased 49-fold over that of the original whole cells. PMID:4239370

  13. Membrane potential perturbations induced in tissue cells by pulsed electric fields

    SciTech Connect

    Cooper, M.S.

    1995-09-01

    Pulsed electric fields directly influence the electrophysiology of tissue cells by transiently perturbing their transmembrane potential. To determine the magnitude and time course of this interaction, electronic cable theory was used to calculate the membrane potential perturbations induced in tissue cells by a spatially uniform, pulsed electric field. Analytic solutions were obtained that predict shifts in membrane potential along the length of cells as a function of time in response to an electrical pulse. For elongated tissue cells, or groups of tissue cells that are couple electronically by gap junctions, significant hyperpolarizations and depolarizations can result form millisecond applications of electric fields with strengths on the order of 10--100 mV/cm. The results illustrate the importance of considering cellular cable parameters in assessing the effects of transient electric fields on biological systems, as well as in predicting the efficacy of pulsed electric fields in medical treatments.

  14. Detecting Nanodomains in Living Cell Membrane by Fluorescence Correlation Spectroscopy

    NASA Astrophysics Data System (ADS)

    He, Hai-Tao; Marguet, Didier

    2011-05-01

    Cell membranes actively participate in numerous cellular functions. Inasmuch as bioactivities of cell membranes are known to depend crucially on their lateral organization, much effort has been focused on deciphering this organization on different length scales. Within this context, the concept of lipid rafts has been intensively discussed over recent years. In line with its ability to measure diffusion parameters with great precision, fluorescence correlation spectroscopy (FCS) measurements have been made in association with innovative experimental strategies to monitor modes of molecular lateral diffusion within the plasma membrane of living cells. These investigations have allowed significant progress in the characterization of the cell membrane lateral organization at the suboptical level and have provided compelling evidence for the in vivo existence of raft nanodomains. We review these FCS-based studies and the characteristic structural features of raft nanodomains. We also discuss the findings in regards to the current view of lipid rafts as a general membrane-organizing principle.

  15. Photocatalytic Degradation of Cell Membrane Coatings for Controlled Drug Release.

    PubMed

    Rao, Lang; Meng, Qian-Fang; Huang, Qinqin; Liu, Pei; Bu, Lin-Lin; Kondamareddy, Kiran Kumar; Guo, Shi-Shang; Liu, Wei; Zhao, Xing-Zhong

    2016-06-01

    Biomimetic cell-membrane-camouflaged particles with desirable features have been widely used for various biomedical applications. However, there are few reports on employing these particles for cancer drug delivery due to the failure of the membrane coatings to be efficiently degraded in the tumor microenvironment which hampers the drug release. In this work, core-shell SiO2 @TiO2 nanoparticles with enhanced photocatalytic activity are used for controlled degradation of surface erythrocyte membrane coatings. The antitumor drug docetaxel is encapsulated into nanocarriers to demonstrate the controlled drug release under ultraviolet irradiation, and the drug-loaded nanoparticles are further used for enhanced cancer cell therapy. Here, a simple but practical method for degradation of cell membrane coatings is presented, and a good feasibility of using cell membrane-coated nanocarriers for controlled drug delivery is demonstrated.

  16. Cell Membranes Under Hydrostatic Pressure Subjected to Micro-Injection

    NASA Astrophysics Data System (ADS)

    Vassilev, Vassil M.; Kostadinov, Kostadin G.; Mladenov, Ivaïlo M.; Shulev, Assen A.; Stoilov, Georgi I.; Djondjorov, Peter A.

    2011-04-01

    The work is concerned with the determination of the mechanical behaviour of cell membranes under uniform hydrostatic pressure subject to micro-injections. For that purpose, assuming that the shape of the deformed cell membrane is axisymmetric a variational statement of the problem is developed on the ground of the so-called spontaneous curvature model. In this setting, the cell membrane is regarded as an axisymmetric surface in the three-dimensional Euclidean space providing a stationary value of the shape energy functional under the constraint of fixed total area and fixed enclosed volume. The corresponding Euler-Lagrange equations and natural boundary conditions are derived, analyzed and used to express the forces and moments in the membrane. Several examples of such surfaces representing possible shapes of cell membranes under pressure subjected to micro injection are determined numerically.

  17. How the antimicrobial peptides destroy bacteria cell membrane: Translocations vs. membrane buckling

    NASA Astrophysics Data System (ADS)

    Golubovic, Leonardo; Gao, Lianghui; Chen, Licui; Fang, Weihai

    2012-02-01

    In this study, coarse grained Dissipative Particle Dynamics simulation with implementation of electrostatic interactions is developed in constant pressure and surface tension ensemble to elucidate how the antimicrobial peptide molecules affect bilayer cell membrane structure and kill bacteria. We find that peptides with different chemical-physical properties exhibit different membrane obstructing mechanisms. Peptide molecules can destroy vital functions of the affected bacteria by translocating across their membranes via worm-holes, or by associating with membrane lipids to form hydrophilic cores trapped inside the hydrophobic domain of the membranes. In the latter scenario, the affected membranes are strongly corrugated (buckled) in accord with very recent experimental observations [G. E. Fantner et al., Nat. Nanotech., 5 (2010), pp. 280-285].

  18. Exploring the inhibitory effect of membrane tension on cell polarization

    PubMed Central

    Wang, Jing; Yang, Gen; Ouyang, Qi; Wang, Yugang; Zhang, Lei

    2017-01-01

    Cell polarization toward an attractant is influenced by both physical and chemical factors. Most existing mathematical models are based on reaction-diffusion systems and only focus on the chemical process occurring during cell polarization. However, membrane tension has been shown to act as a long-range inhibitor of cell polarization. Here, we present a cell polarization model incorporating the interplay between Rac GTPase, filamentous actin (F-actin), and cell membrane tension. We further test the predictions of this model by performing single cell measurements of the spontaneous polarization of cancer stem cells (CSCs) and non-stem cancer cells (NSCCs), as the former have lower cell membrane tension. Based on both our model and the experimental results, cell polarization is more sensitive to stimuli under low membrane tension, and high membrane tension improves the robustness and stability of cell polarization such that polarization persists under random perturbations. Furthermore, our simulations are the first to recapitulate the experimental results described by Houk et al., revealing that aspiration (elevation of tension) and release (reduction of tension) result in a decrease in and recovery of the activity of Rac-GTP, respectively, and that the relaxation of tension induces new polarity of the cell body when a cell with the pseudopod-neck-body morphology is severed. PMID:28135277

  19. The Flocculating Cationic Polypetide from Moringa oleifera Seeds Damages Bacterial Cell Membranes by Causing Membrane Fusion.

    PubMed

    Shebek, Kevin; Schantz, Allen B; Sines, Ian; Lauser, Kathleen; Velegol, Stephanie; Kumar, Manish

    2015-04-21

    A cationic protein isolated from the seeds of the Moringa oleifera tree has been extensively studied for use in water treatment in developing countries and has been proposed for use in antimicrobial and therapeutic applications. However, the molecular basis for the antimicrobial action of this peptide, Moringa oleifera cationic protein (MOCP), has not been previously elucidated. We demonstrate here that a dominant mechanism of MOCP antimicrobial activity is membrane fusion. We used a combination of cryogenic electron microscopy (cryo-EM) and fluorescence assays to observe and study the kinetics of fusion of membranes in liposomes representing model microbial cells. We also conducted cryo-EM experiments on E. coli cells where MOCP was seen to fuse the inner and outer membranes. Coarse-grained molecular dynamics simulations of membrane vesicles with MOCP molecules were used to elucidate steps in peptide adsorption, stalk formation, and fusion between membranes.

  20. Membrane curvature in cell biology: An integration of molecular mechanisms.

    PubMed

    Jarsch, Iris K; Daste, Frederic; Gallop, Jennifer L

    2016-08-15

    Curving biological membranes establishes the complex architecture of the cell and mediates membrane traffic to control flux through subcellular compartments. Common molecular mechanisms for bending membranes are evident in different cell biological contexts across eukaryotic phyla. These mechanisms can be intrinsic to the membrane bilayer (either the lipid or protein components) or can be brought about by extrinsic factors, including the cytoskeleton. Here, we review examples of membrane curvature generation in animals, fungi, and plants. We showcase the molecular mechanisms involved and how they collaborate and go on to highlight contexts of curvature that are exciting areas of future research. Lessons from how membranes are bent in yeast and mammals give hints as to the molecular mechanisms we expect to see used by plants and protists.

  1. Membrane curvature in cell biology: An integration of molecular mechanisms

    PubMed Central

    Daste, Frederic

    2016-01-01

    Curving biological membranes establishes the complex architecture of the cell and mediates membrane traffic to control flux through subcellular compartments. Common molecular mechanisms for bending membranes are evident in different cell biological contexts across eukaryotic phyla. These mechanisms can be intrinsic to the membrane bilayer (either the lipid or protein components) or can be brought about by extrinsic factors, including the cytoskeleton. Here, we review examples of membrane curvature generation in animals, fungi, and plants. We showcase the molecular mechanisms involved and how they collaborate and go on to highlight contexts of curvature that are exciting areas of future research. Lessons from how membranes are bent in yeast and mammals give hints as to the molecular mechanisms we expect to see used by plants and protists. PMID:27528656

  2. Fuel cell using novel electrolyte membrane

    SciTech Connect

    Polak, A.J.; Beuhler, A.J.

    1986-06-10

    An apparatus is described for producing electricity from a fuel gas having a gaseous component which is capable, in the presence of a catalytic agent, of dissociating to yield hydrogen ions comprising: (a) a thin film organic-inorganic membrane which comprises a single phase blend from about 1% to about 70% by weight of a heteropoly acid and salts; (b) a membrane housing comprising a fuel gas chamber and an oxidant gas chamber separated by a substantially imporous partition comprising the membrane defined in element (a), the membrane having a first surface in communication with the fuel gas chamber and a second surface in communication with the oxidant gas chamber; (c) two separate portions of catalytic agent effective to promote dissociation and combination, one portion in contact with the first surface of the membrane and one portion in contact with the second surface of the membrane; and, (d) means for forming electrical connection in operative contact with the catalytic agent in contact with the first surface of the membrane and in operative contact with the catalytic agent in contact with the second surface of the membrane.

  3. Fluorescence imaging of cholesterol and temperature dependent cell membrane dynamics

    NASA Astrophysics Data System (ADS)

    Weber, Petra; Wagner, Michael; Strauss, Wolfgang S. L.; Schneckenburger, Herbert

    2007-07-01

    Cholesterol content is an important factor for membrane dynamics of living cells. With well defined protocols of depletion and enrichment the impact of cholesterol on membrane dynamics was examined by fluorescence microscopy. In addition, the intracellular cholesterol content was determined with biochemical methods. Changes of cholesterol amounts in cell membranes have previously been related to specific disease and may have some influence on the uptake of pharmaceutical agents. A combination of conventional and total internal reflection fluorescence microscopy was applied to the fluorescence marker laurdan, a polarity-sensitive probe, whose electronic excitation energy is different in polar and non-polar environment. Once incorporated into cell membranes, the fluorescence of laurdan shows a spectral shift towards longer wavelength when its molecules get into contact with adjacent water molecules, e.g. when a phase transition from the tightly packed gel phase to the liquid crystalline phase of membrane lipids occurs. The generalized polarization (GP, characterizing this spectral shift) as well as the fluorescence lifetime (τ) of laurdan revealed to be appropriate measures for membrane stiffness and fluidity. GP generally decreased with increasing temperature and was always higher for the plasma membrane than for intracellular membranes. Enrichment of cholesterol caused a pronounced increase, whereas depletion of cholesterol caused a decrease of GP. In addition, pronounced changes of the fluorescence lifetime pattern occurred in the subnanosecond range. GP, and τ were determined as integral values of single cells or small cell collectives and were also displayed as microscopic images.

  4. Layer-by-layer cell membrane assembly

    NASA Astrophysics Data System (ADS)

    Matosevic, Sandro; Paegel, Brian M.

    2013-11-01

    Eukaryotic subcellular membrane systems, such as the nuclear envelope or endoplasmic reticulum, present a rich array of architecturally and compositionally complex supramolecular targets that are as yet inaccessible. Here we describe layer-by-layer phospholipid membrane assembly on microfluidic droplets, a route to structures with defined compositional asymmetry and lamellarity. Starting with phospholipid-stabilized water-in-oil droplets trapped in a static droplet array, lipid monolayer deposition proceeds as oil/water-phase boundaries pass over the droplets. Unilamellar vesicles assembled layer-by-layer support functional insertion both of purified and of in situ expressed membrane proteins. Synthesis and chemical probing of asymmetric unilamellar and double-bilayer vesicles demonstrate the programmability of both membrane lamellarity and lipid-leaflet composition during assembly. The immobilized vesicle arrays are a pragmatic experimental platform for biophysical studies of membranes and their associated proteins, particularly complexes that assemble and function in multilamellar contexts in vivo.

  5. The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells

    NASA Technical Reports Server (NTRS)

    Eisman, G. A.

    1989-01-01

    Dow Chemical's research activities in fuel cell devices revolves around the development and subsequent investigation of the perfluorinated inomeric membrane separator useful in proton-exchange membrane systems. Work is currently focusing on studying the effects of equivalent weight, thickness, water of hydration, pretreatment procedures, as well as the degree of water management required for a given membrane separator in the cell. The presentation will include details of certain aspects of the above as well as some of the requirements for high and low power generation.

  6. Improved Membrane Materials for PEM Fuel Cell Application

    SciTech Connect

    Kenneth A. Mauritz; Robert B. Moore

    2008-06-30

    The overall goal of this project is to collect and integrate critical structure/property information in order to develop methods that lead to significant improvements in the durability and performance of polymer electrolyte membrane fuel cell (PEMFC) materials. This project is focused on the fundamental improvement of PEMFC membrane materials with respect to chemical, mechanical and morphological durability as well as the development of new inorganically-modified membranes.

  7. Fault detection and isolation of PEM fuel cell system based on nonlinear analytical redundancy. An application via parity space approach

    NASA Astrophysics Data System (ADS)

    Aitouche, A.; Yang, Q.; Ould Bouamama, B.

    2011-05-01

    This paper presents a procedure dealing with the issue of fault detection and isolation (FDI) using nonlinear analytical redundancy (NLAR) technique applied in a proton exchange membrane (PEM) fuel cell system based on its mathematic model. The model is proposed and simplified into a five orders state space representation. The transient phenomena captured in the model include the compressor dynamics, the flow characteristics, mass and energy conservation and manifold fluidic mechanics. Nonlinear analytical residuals are generated based on the elimination of the unknown variables of the system by an extended parity space approach to detect and isolate actuator and sensor faults. Finally, numerical simulation results are given corresponding to a faults signature matrix.

  8. Direct measurements of membrane potential and membrane resistance of human red cells

    PubMed Central

    Lassen, U. V.; Sten-Knudsen, O.

    1968-01-01

    1. In order to evaluate the membrane potentials calculated from the distribution of chloride ions in human red cells and plasma, it is desirable to have a direct measurement of the transmembrane potential of these cells. 2. A method has been devised for introducing a capillary micro-electrode into human red cells. The method allows simultaneous measurements of potential and membrane resistance with only one micro-electrode located in the cell. 3. Upon impalement of single cells in plasma, a scatter of membrane potentials and of resistance values was obtained. The potential drop never exceeded -14 mV and the maximum resistances were about 7 Ω. cm2. Positive potentials were obtained on impalement of red cell aggregates. 4. Arguments are given to support the view that it is in these cells which suffer least damage from the impalement that maximum values of membrane potentials and resistances are observed. The errors caused by the change in the liquid junction during the impalement have been estimated. 5. As judged from this study, it seems permissible under normal conditions to calculate the membrane potential of the red cell from the chloride concentrations in plasma and in intracellular water. PMID:5649641

  9. Radiation Interaction with Therapeutic Drugs and Cell Membranes

    SciTech Connect

    Martin, Diana I.; Manaila, Elena N.; Matei, Constantin I.; Iacob, Nicusor I.; Ighigeanu, Daniel I.; Craciun, Gabriela D.; Moisescu, Mihaela I.; Savopol, Tudor D.; Kovacs, Eugenia A.; Cinca, Sabin A.; Margaritescu, Irina D.

    2007-04-23

    This transient permeabilized state of the cell membrane, named the 'cell electroporation' (CE) can be used to increase cells uptake of drugs that do not readily pass cell membrane, thus enabling their cytotoxicity. The anticancer drugs, such as bleomycin (BL) and cisplatin, are the most candidates for the combined use with ionizing and non-ionizing radiation fields. The methods and installations for the cell electroporation by electron beam (EB) and microwave (MW) irradiation are presented. The viability tests of the human leukocytes under EB and MW exposure with/without the BL in the cell cultures are discussed.

  10. Investigating cell membrane structure and dynamics with TCSPC-FLIM

    NASA Astrophysics Data System (ADS)

    Le Marois, Alix; Owen, Dylan M.; Suhling, Klaus

    2015-03-01

    We report the use of Time-Correlated Single Photon Counting (TCSPC) in a polarization-resolved Fluorescence Lifetime Imaging (FLIM) setup for the investigation of cell membrane structural and dynamic properties. This technique allows us to study the orientation and mobility of fluorescent membrane dyes, namely di-4-ANEPPDHQ and DiO, in model bilayers of different lipid compositions. Dipole alignment and extent of rotational motion can be linked to membrane order and fluidity. Comparison of the time-resolved anisotropy decays of the two fluorescent dyes suggests that rotational motion of membrane constituents is restricted in liquid-ordered phases, and appears to be limited to the region of aliphatic tails in liquid-disordered phases. In living cells, understanding the membrane structure provides crucial information on its functional properties, such as exo- and endocytosis, cell mobility and signal transduction.

  11. Automated membrane test cell apparatus and method for so using

    SciTech Connect

    Yeager, H.L.; Malinsky, J.D.

    1984-11-20

    An automated electrolytic membrane test cell apparatus adaptable for the purpose of accurately measuring cationic transport and water transport numbers for membranes used in chlor-alkali cells under operating conditions similar to those used in such cells is disclosed. The apparatus comprises a test cell, said test cell being adapted to hold a permselective membrane sealingly supported therein so as to create separate anode and cathode compartments, each of said compartments having a suitable electrode, and heating electrolyte inlet and outlet means attached thereto. The apparatus further comprises means to select one of a plurality of anolyte and catholyte test solutions and control means adapted to control the electrolysis, circulation and heating of said solutions and the generation of all test samples needed to perform the measurements necessary to calculate said transport numbers. When used in conjunction with radioactive tracer techniques, considerably improvements are possible in the accuracy and ease with which transport phenomena in said membrane can be studied.

  12. Single cell wound generates electric current circuit and cell membrane potential variations that requires calcium influx.

    PubMed

    Luxardi, Guillaume; Reid, Brian; Maillard, Pauline; Zhao, Min

    2014-07-24

    Breaching of the cell membrane is one of the earliest and most common causes of cell injury, tissue damage, and disease. If the compromise in cell membrane is not repaired quickly, irreversible cell damage, cell death and defective organ functions will result. It is therefore fundamentally important to efficiently repair damage to the cell membrane. While the molecular aspects of single cell wound healing are starting to be deciphered, its bio-physical counterpart has been poorly investigated. Using Xenopus laevis oocytes as a model for single cell wound healing, we describe the temporal and spatial dynamics of the wound electric current circuitry and the temporal dynamics of cell membrane potential variation. In addition, we show the role of calcium influx in controlling electric current circuitry and cell membrane potential variations. (i) Upon wounding a single cell: an inward electric current appears at the wound center while an outward electric current is observed at its sides, illustrating the wound electric current circuitry; the cell membrane is depolarized; calcium flows into the cell. (ii) During cell membrane re-sealing: the wound center current density is maintained for a few minutes before decreasing; the cell membrane gradually re-polarizes; calcium flow into the cell drops. (iii) In conclusion, calcium influx is required for the formation and maintenance of the wound electric current circuitry, for cell membrane re-polarization and for wound healing.

  13. Membrane-electrode assemblies for electrochemical cells

    DOEpatents

    Swathirajan, Sundararajan; Mikhail, Youssef M.

    1993-01-01

    A combination, unitary, membrane and electrode assembly with a solid polymer electrolyte membrane, and first and second electrodes at least partially embedded in opposed surfaces of the membrane. The electrodes each comprise a respective group of finely divided carbon particles, very finely divided catalytic particles supported on internal and external surfaces of the carbon particles and a proton conductive material intermingled with the catalytic and carbon particles. A first group of finely divided carbon particles forming the first electrode has greater water attraction and retention properties, and is more hydrophilic than a second group of carbon particles forming the second electrode. In a preferred method, the membrane electrode assembly of the invention is prepared by forming a slurry of proton conductive material and at least one group of the carbon and catalyst particles. The slurry is applied to the opposed surfaces of the membrane and heated while being pressed to the membrane for a time and at a temperature and compressive load sufficient to embed at least a portion of the particles into the membrane.

  14. Loading of red blood cells with an analyte-sensitive dye for development of a long-term monitoring technique

    NASA Astrophysics Data System (ADS)

    Ritter, Sarah C.; Meissner, Kenith E.

    2012-03-01

    Measurement of blood analytes, such as pH and glucose, provide crucial information about a patient's health. Some such analytes, such as glucose in the case of diabetes, require long-term or near-continuous monitoring for proper disease management. However, current monitoring techniques are far from ideal: multiple-per-day finger stick tests are inconvenient and painful for the patient; implantable sensors have short functional life spans (i.e., 3-7 days). Red blood cells serve as an attractive alternative for carriers of analyte sensors. Once reintroduced to the blood stream, these carriers may continue to live for the remainder of their life span (120 days for humans). They are also biodegradable and biocompatible, thereby eliminating the immune system response common for many implanted devices. The proposed carrier system takes advantage of the ability of the red blood cells to swell in response to a decrease in the osmolarity of the extracellular solution. Just before the membranes lyse, they develop small pores on the scale of tens of nanometers. Analyte-sensitive dyes in the extracellular solution may then diffuse into the perforated red blood cells and become entrapped upon restoration of physiological temperature and osmolarity. Because the membranes contain various analyte transporters, intracellular analyte levels rapidly equilibrate to those of the extracellular solution. A fluorescent dye has been loaded inside of red blood cells using a preswelling technique. Alterations in preparation parameters have been shown to affect characteristics of the resulting dye-loaded red blood cells (e.g., intensity of fluorescence).

  15. Prism-patterned Nafion membrane for enhanced water transport in polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Kim, Sang Moon; Kang, Yun Sik; Ahn, Chiyeong; Jang, Segeun; Kim, Minhyoung; Sung, Yung-Eun; Yoo, Sung Jong; Choi, Mansoo

    2016-06-01

    Here, we report a simple and effective strategy to enhance the performance of the polymer electrolyte membrane fuel cell by imprinting prism-patterned arrays onto the Nafion membrane, which provides three combined effects directly related to the device performance. First, a locally thinned membrane via imprinted micro prism-structures lead to reduced membrane resistance, which is confirmed by electrochemical impedance spectroscopy. Second, increments of the geometrical surface area of the prism-patterned Nafion membrane compared to a flat membrane result in the increase in the electrochemical active surface area. Third, the vertically asymmetric geometry of prism structures in the cathode catalyst layer lead to enhanced water transport, which is confirmed by oxygen gain calculation. To explain the enhanced water transport, we propose a simple theoretical model on removal of water droplets existing in the asymmetric catalyst layer. These three combined effects achieved via incorporating prism patterned arrays into the Nafion membrane effectively enhance the performance of the polymer electrolyte membrane fuel cell.

  16. Adaptation of yeast cell membranes to ethanol

    SciTech Connect

    Jimenez, J.; Benitez, T.

    1987-05-01

    A highly ethanol-tolerant Saccharomyces wine strain is able, after growth in the presence of ethanol, to efficiently improve the ethanol tolerance of its membrane. A less-tolerant Saccharomyces laboratory strain, however, is unable to adapt its membrane to ethanol. Furthermore, after growth in the presence of ethanol, the membrane of the latter strain becomes increasingly sensitive, although this is a reversible process. Reversion to a higher tolerance occurs only after the addition of an energy source and does not take place in the presence of cycloheximide.

  17. Catalytic membranes for CO oxidation in fuel cells

    DOEpatents

    Sandi-Tapia, Giselle; Carrado Gregar, Kathleen; Kizilel, Riza

    2010-06-08

    A hydrogen permeable membrane, which includes a polymer stable at temperatures of about 200 C having clay impregnated with Pt or Au or Ru or Pd particles or mixtures thereof with average diameters of less than about 10 nanometers (nms) is disclosed. The membranes are useful in fuel cells or any device which requires hydrogen to be separated from carbon monoxide.

  18. Expression of basement membrane antigens in spindle cell melanoma.

    PubMed

    Prieto, V G; Woodruff, J M

    1998-07-01

    Spindle cell melanoma (SCM) is an uncommon form of melanoma that may be confused histologically with other tumors, including malignant peripheral nerve sheath tumors (MPNST). Tumors with neural differentiation and melanocytic nevi may both show basement membrane immunohistochemically and at the ultrastructural level. However, most ultrastructural studies of melanoma have failed to demonstrate well formed basement membrane around tumor cells. The presence of basement membrane has been used by some authors as evidence favoring MPNST, as opposed to SCM. To evaluate this distinction immunohistochemically, 22 primary and metastatic cutaneous melanomas having a spindle cell component (SCM) were studied using monoclonal antibodies against laminin and Type IV collagen. S100 protein and HMB45 antigen expression were also studied. All but one of the SCM were reactive for S100 protein in at least 25% of the cells. Thirteen of 20 tumors (65%) were focally reactive with HMB45. Laminin was expressed in 42% of the tumors (only membranous pattern in 3; cytoplasmic and membranous in 5). Seventeen tumors (77%) expressed type IV collagen (only membranous pattern in 7; cytoplasmic and membranous pattern in 10). Laminin and type IV collagen, known components of basement membrane, are often found in SCM. Therefore, their detection cannot be used to distinguish SCM from MPNST.

  19. Cell-Cell Communication Via Extracellular Membrane Vesicles and Its Role in the Immune Response

    PubMed Central

    Hwang, Inkyu

    2013-01-01

    The host immune response involves a variety of cell types, including specialized immune and non-immune cells. The delicate coordination among these cells via close communication is central for the proper operation of immune system. Cell-cell communication is mediated by a complex network that includes soluble factors such as cytokines, chemokines, and metabolites exported from cells, as well as membrane-bound receptors and their ligands. Cell-cell communication is also mediated by membrane vesicles (e.g., exosomes, ectosomes), which are either shed by distant cells or exchanged by cells that are making direct contact. Intercellular communication via extracellular membrane vesicles has drawn much attention recently, as they have been shown to carry various biomolecules that modulate the activities of recipient cells. In this review, I will discuss current views on cell-cell communication via extra-cellular membrane vesicles, especially shedded membrane vesicles, and their effects on the control of the immune system. PMID:23807045

  20. Monitoring of lung tumour cell growth in artificial membranes.

    PubMed

    Yang, Ying; Sulé-Suso, Josep; El Haj, Alicia J; Hoban, Paul R; Wang, Ruikang

    2004-10-15

    Morbidity of many tumour types is associated with invasion of tumour cells through the basement membrane and subsequent metastasis to vital organs. Tumour invasion is frequently detected late on as many patients present with advanced disease. The method of detecting invasion is through conventional histological staining techniques, which are time consuming and require processing of the sample. This can affect interpretation of the results. In this study, a new imaging technique, optical coherence tomography (OCT), was used to monitor lung tumour cell growth in two artificial membranes composed of either collagen type I or Matrigel. In parallel, standard histological section analysis was performed to validate the accuracy of the monitoring by OCT. Cross-sectional images from OCT revealed that lung tumour cells infiltrated only when low cell seeding density (5 x 10(5)) and low collagen concentration (1.5 mg/ml) were combined. The cells could be easily differentiated from the artificial membranes and appeared as either a brighter layer on the top of the membrane or brighter foci embedded within the darker membrane. These cell-membrane morphologies matched remarkably to the standard histological section images. Our results suggest that OCT has a great potential to become a useful tool for fast and robust imaging of cell growth in vivo and as a potential assessment of cell invasion.

  1. Sulfonated polyphosphazene-based membranes for use in direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Carter, Roy Lee

    Novel crosslinked and sulfonated poly[bis(3-methylphenoxy)phosphazene] blended proton exchange membranes were fabricated for use as the solid polymer electrolyte in a direct methanol fuel cell. Three polymers, polybenzimidazole, polyacrylonitrile and polyvinylidene fluoride-co-polyhexafluoropropylene were found to be compatible for blending with sulfonated polyphosphazene. A combination of blending and crosslinking was shown to be an effective method of producing durable, low water swelling films with acceptable proton conductivity. A novel tracer-diffusion 1H NMR method was developed and used to measure the mutual diffusion of methanol in non-crosslinked and crosslinked membranes composed of sulfonated polyphosphazene. The technique measures the growth of a solute NMR signal in the bulk (external) solution as it diffuses out of a thin film membrane. The transient increase in methanol peak height during analyte (methanol) desorption was fitted to a simple theoretical diffusion model using the methanol diffusion coefficient as an adjustable parameter. This method was found to be fast, reproducible, and accurate to within about +/-20%. Diffusion coefficients at 25°C were in the range of 1.0 x 10-8 cm2/s to 4.0 x 10-7 cm2/s for methanol concentrations of 1.0--5.0 M and were significantly smaller than those reported for a NafionRTM perfluorosulfonic acid membrane. Direct liquid methanol fuel cell tests were performed with membrane electrode assemblies (MEAs) fabricated with polyphosphazene-based proton-exchange membranes. MEAs worked best when high ion-exchange capacity (high conductivity) polyphosphazene membrane contacted the electrodes, in which case the fuel cell power output was nearly the same as that with Nafion 117 (for current densities ≤0.15 A/cm2), but the methanol crossover was three times lower than that of Nafion. The electrochemical performance of single-membrane MEAs with low conductivity S-POP/PAN films was poor, although the methanol crossover was

  2. A macroscopic model of proton transport through the membrane-ionomer interface of a polymer electrolyte membrane fuel cell.

    PubMed

    Kumar, Milan; Edwards, Brian J; Paddison, Stephen J

    2013-02-14

    The membrane-ionomer interface is the critical interlink of the electrodes and catalyst to the polymer electrolyte membrane (PEM); together forming the membrane electrode assembly in current state-of-the-art PEM fuel cells. In this paper, proton conduction through the interface is investigated to understand its effect on the performance of a PEM fuel cell. The water containing domains at this interface were modeled as cylindrical pores/channels with the anionic groups (i.e., -SO(3)(-)) assumed to be fixed on the pore wall. The interactions of each species with all other species and an applied external field were examined. Molecular-based interaction potential energies were computed in a small test element of the pore and were scaled up in terms of macroscopic variables. Evolution equations of the density and momentum of the species (water molecules and hydronium ions) were derived within a framework of nonequilibrium thermodynamics. The resulting evolution equations for the species were solved analytically using an order-of-magnitude analysis to obtain an expression for the proton conductivity. Results show that the conductivity increases with increasing water content and pore radius, and strongly depends on the separation distance between the sulfonate groups and their distribution on the pore wall. It was also determined that the conductivity of two similar pores of different radii in series is limited by the pore with the smaller radius.

  3. A macroscopic model of proton transport through the membrane-ionomer interface of a polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Kumar, Milan; Edwards, Brian J.; Paddison, Stephen J.

    2013-02-01

    The membrane-ionomer interface is the critical interlink of the electrodes and catalyst to the polymer electrolyte membrane (PEM); together forming the membrane electrode assembly in current state-of-the-art PEM fuel cells. In this paper, proton conduction through the interface is investigated to understand its effect on the performance of a PEM fuel cell. The water containing domains at this interface were modeled as cylindrical pores/channels with the anionic groups (i.e., -SO3-) assumed to be fixed on the pore wall. The interactions of each species with all other species and an applied external field were examined. Molecular-based interaction potential energies were computed in a small test element of the pore and were scaled up in terms of macroscopic variables. Evolution equations of the density and momentum of the species (water molecules and hydronium ions) were derived within a framework of nonequilibrium thermodynamics. The resulting evolution equations for the species were solved analytically using an order-of-magnitude analysis to obtain an expression for the proton conductivity. Results show that the conductivity increases with increasing water content and pore radius, and strongly depends on the separation distance between the sulfonate groups and their distribution on the pore wall. It was also determined that the conductivity of two similar pores of different radii in series is limited by the pore with the smaller radius.

  4. Sulfated Titania-Silica Reinforced Nafion Nanocomposite Membranes for Proton Exchange Membrane Fuel Cells.

    PubMed

    Abu Sayeed, M D; Kim, Hee Jin; Gopalan, A I; Kim, Young Ho; Lee, Kwang-Pill; Choi, Sang-June

    2015-09-01

    Sulfated titania-silica (SO4(2-)-/TiO2-SiO2) composites were prepared by a sol-gel method with sulfate reaction and characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The nanometric diameter and geometry of the sulfated titania-silica (STS) was investigated by transmission electron microscopy (TEM). A small amount of the STS composite in the range of 0.5-3 wt% was then added as reinforcing into the Nafion membrane by water-assisted solution casting method to prepare STS reinforced Nafion nanocomposite membranes (STS-Nafion nanocomposite membranes). The additional functional groups, sulfate groups, of the nanocomposite membrane having more surface oxygenated groups enhanced the fuel cell membrane properties. The STS-Nafion nanocomposite membranes exhibited improved water uptake compared to that of neat Nafion membranes, whereas methanol uptake values were decreased dramatically improved thermal property of the prepared nanocomposite membranes were measured by thermogravimetric analysis (TGA). Furthermore, increased ion exchange capacity values were obtained by thermoacidic pretreatment of the nanocomposite membranes.

  5. CO2 permeability of cell membranes is regulated by membrane cholesterol and protein gas channels.

    PubMed

    Itel, Fabian; Al-Samir, Samer; Öberg, Fredrik; Chami, Mohamed; Kumar, Manish; Supuran, Claudiu T; Deen, Peter M T; Meier, Wolfgang; Hedfalk, Kristina; Gros, Gerolf; Endeward, Volker

    2012-12-01

    Recent observations that some membrane proteins act as gas channels seem surprising in view of the classical concept that membranes generally are highly permeable to gases. Here, we study the gas permeability of membranes for the case of CO(2), using a previously established mass spectrometric technique. We first show that biological membranes lacking protein gas channels but containing normal amounts of cholesterol (30-50 mol% of total lipid), e.g., MDCK and tsA201 cells, in fact possess an unexpectedly low CO(2) permeability (P(CO2)) of ∼0.01 cm/s, which is 2 orders of magnitude lower than the P(CO2) of pure planar phospholipid bilayers (∼1 cm/s). Phospholipid vesicles enriched with similar amounts of cholesterol also exhibit P(CO2) ≈ 0.01 cm/s, identifying cholesterol as the major determinant of membrane P(CO2). This is confirmed by the demonstration that MDCK cells depleted of or enriched with membrane cholesterol show dramatic increases or decreases in P(CO2), respectively. We demonstrate, furthermore, that reconstitution of human AQP-1 into cholesterol-containing vesicles, as well as expression of human AQP-1 in MDCK cells, leads to drastic increases in P(CO2), indicating that gas channels are of high functional significance for gas transfer across membranes of low intrinsic gas permeability.

  6. Cell-free system for synthesizing membrane proteins cell free method for synthesizing membrane proteins

    DOEpatents

    Laible, Philip D; Hanson, Deborah K

    2013-06-04

    The invention provides an in vitro method for producing proteins, membrane proteins, membrane-associated proteins, and soluble proteins that interact with membrane-associated proteins for assembly into an oligomeric complex or that require association with a membrane for proper folding. The method comprises, supplying intracytoplasmic membranes from organisms; modifying protein composition of intracytoplasmic membranes from organism by modifying DNA to delete genes encoding functions of the organism not associated with the formation of the intracytoplasmic membranes; generating appropriate DNA or RNA templates that encode the target protein; and mixing the intracytoplasmic membranes with the template and a transcription/translation-competent cellular extract to cause simultaneous production of the membrane proteins and encapsulation of the membrane proteins within the intracytoplasmic membranes.

  7. Low Crossover Polymer Electrolyte Membranes for Direct Methanol Fuel Cells

    NASA Technical Reports Server (NTRS)

    Prakash, G. K. Surya; Smart, Marshall; Atti, Anthony R.; Olah, George A.; Narayanan, S. R.; Valdez, T.; Surampudi, S.

    1996-01-01

    Direct Methanol Fuel Cells (DMFC's) using polymer electrolyte membranes are promising power sources for portable and vehicular applications. State of the art technology using Nafion(R) 117 membranes (Dupont) are limited by high methanol permeability and cost, resulting in reduced fuel cell efficiencies and impractical commercialization. Therefore, much research in the fuel cell field is focused on the preparation and testing of low crossover and cost efficient polymer electrolyte membranes. The University of Southern California in cooperation with the Jet Propulsion Laboratory is focused on development of such materials. Interpenetrating polymer networks are an effective method used to blend polymer systems without forming chemical links. They provide the ability to modify physical and chemical properties of polymers by optimizing blend compositions. We have developed a novel interpenetrating polymer network based on poly (vinyl - difluoride)/cross-linked polystyrenesulfonic acid polymer composites (PVDF PSSA). Sulfonation of polystyrene accounts for protonic conductivity while the non-polar, PVDF backbone provides structural integrity in addition to methanol rejection. Precursor materials were prepared and analyzed to characterize membrane crystallinity, stability and degree of interpenetration. USC JPL PVDF-PSSA membranes were also characterized to determine methanol permeability, protonic conductivity and sulfur distribution. Membranes were fabricated into membrane electrode assemblies (MEA) and tested for single cell performance. Tests include cell performance over a wide range of temperatures (20 C - 90 C) and cathode conditions (ambient Air/O2). Methanol crossover values are measured in situ using an in-line CO2 analyzer.

  8. Selectivity of biopolymer membranes using HepG2 cells.

    PubMed

    Lü, Dongyuan; Gao, Yuxin; Luo, Chunhua; Lü, Shouqian; Wang, Qian; Xu, Xianghong; Sun, Shujin; Wang, Chengzhi; Long, Mian

    2015-03-01

    Bioartificial liver (BAL) system has emerged as an alternative treatment to bridge acute liver failure to either liver transplantation or liver regeneration. One of the main reasons that the efficacy of the current BAL systems was not convincing in clinical trials is attributed to the lack of friendly interface between the membrane and the hepatocytes in liver bioreactor, the core unit of BAL system. Here, we systematically compared the biological responses of hepatosarcoma HepG2 cells seeded on eight, commercially available biocompatible membranes made of acetyl cellulose-nitrocellulose mixed cellulose (CA-NC), acetyl cellulose (CA), nylon (JN), polypropylene (PP), nitrocellulose (NC), polyvinylidene fluoride (PVDF), polycarbonate (PC) and polytetrafluoroethylene (PTFE). Physicochemical analysis and mechanical tests indicated that CA, JN and PP membranes yield high adhesivity and reasonable compressive and/or tensile features with friendly surface topography for cell seeding. Cells prefer to adhere on CA, JN, PP or PTFE membranes with high proliferation rate in spheriod-like shape. Actin, albumin and cytokeratin 18 expressions are favorable for cells on CA or PP membrane, whereas protein filtration is consistent among all the eight membranes. These results further the understandings of cell growth, morphology and spreading, as well as protein filtration on distinct membranes in designing a liver bioreactor.

  9. Drug Delivery via Cell Membrane Fusion Using Lipopeptide Modified Liposomes

    PubMed Central

    2016-01-01

    Efficient delivery of drugs to living cells is still a major challenge. Currently, most methods rely on the endocytotic pathway resulting in low delivery efficiency due to limited endosomal escape and/or degradation in lysosomes. Here, we report a new method for direct drug delivery into the cytosol of live cells in vitro and invivo utilizing targeted membrane fusion between liposomes and live cells. A pair of complementary coiled-coil lipopeptides was embedded in the lipid bilayer of liposomes and cell membranes respectively, resulting in targeted membrane fusion with concomitant release of liposome encapsulated cargo including fluorescent dyes and the cytotoxic drug doxorubicin. Using a wide spectrum of endocytosis inhibitors and endosome trackers, we demonstrate that the major site of cargo release is at the plasma membrane. This method thus allows for the quick and efficient delivery of drugs and is expected to have many invitro, ex vivo, and invivo applications. PMID:27725960

  10. Decreasing Outer Hair Cell Membrane Cholesterol Increases Cochlear Electromechanics

    NASA Astrophysics Data System (ADS)

    Brownell, William E.; Jacob, Stefan; Hakizimana, Pierre; Ulfendahl, Mats; Fridberger, Anders

    2011-11-01

    The effect of decreasing membrane cholesterol on the mechanical response of the cochlea to acoustic and/or electrical stimulation was monitored using laser interferometry. In contrast to pharmacological interventions that typically decrease cochlear electromechanics, reducing membrane cholesterol increased the response. The electromechanical response in untreated preparations was asymmetric with greater displacements in response to positive currents and cholesterol depletion increased the asymmetry. The results confirm that outer hair cell electromotility is enhanced by low membrane cholesterol. The asymmetry of the response indicates the outer hair cell resting membrane potential is hyperpolarized relative to the voltage of maximum gain for the outer hair cell voltage-displacement function. The magnitude of the response increase suggests a non-uniform distribution of cholesterol along the lateral wall of normal adult outer hair cells.

  11. Apparatus measures swelling of membranes in electrochemical cells

    NASA Technical Reports Server (NTRS)

    Hennigan, T. J.

    1965-01-01

    Apparatus consisting of a pressure plate unit, four springs of known spring constant and a micrometer measures the swelling and force exerted by the polymer membranes of alkaline electrochemical cells.

  12. Membrane Composition Tunes the Outer Hair Cell Motor

    NASA Astrophysics Data System (ADS)

    Rajagopalan, L.; Sfondouris, J.; Oghalai, J. S.; Pereira, F. A.; Brownell, W. E.

    2009-02-01

    Cholesterol and docosahexaenoic acid (DHA), an ω-3 fatty acid, affect membrane mechanical properties in different ways and modulate the function of membrane proteins. We have probed the functional consequence of altering cholesterol and DHA levels in the membranes of OHCs and prestin expressing HEK cells. Large, dynamic and reversible changes in prestin-associated charge movement and OHC motor activity result from altering the concentration of membrane cholesterol. Increasing membrane cholesterol shifts the q/V function ~ 50 mV in the hyperpolarizing direction, possibly a response related to increases in membrane stiffness. The voltage shift is linearly related to total membrane cholesterol. Increasing cholesterol also decreases the total charge moved in a linear fashion. Decreasing membrane cholesterol shifts the q/V function ~ 50 mV in the depolarizing direction with little or no effect on the amount of charge moved. In vivo increases in membrane cholesterol transiently increase but ultimately lead to decreases in DPOAE. Docosahexaenoic acid shifts the q/V function in the hyperpolarizing direction < 15 mV and increases total charge moved. Tuning of cochlear function by membrane cholesterol contributes to the exquisite temporal and frequency processing of mammalian hearing by optimizing the cochlear amplifier.

  13. Penetration of Cell Membranes and Synthetic Lipid Bilayers by Nanoprobes

    PubMed Central

    Angle, Matthew R.; Wang, Andrew; Thomas, Aman; Schaefer, Andreas T.; Melosh, Nicholas A.

    2014-01-01

    Nanoscale devices have been proposed as tools for measuring and controlling intracellular activity by providing electrical and/or chemical access to the cytosol. Unfortunately, nanostructures with diameters of 50–500 nm do not readily penetrate the cell membrane, and rationally optimizing nanoprobes for cell penetration requires real-time characterization methods that are capable of following the process of membrane penetration with nanometer resolution. Although extensive work has examined the rupture of supported synthetic lipid bilayers, little is known about the applicability of these model systems to living cell membranes with complex lipid compositions, cytoskeletal attachment, and membrane proteins. Here, we describe atomic force microscopy (AFM) membrane penetration experiments in two parallel systems: live HEK293 cells and stacks of synthetic lipid bilayers. By using the same probes in both systems, we were able to clearly identify membrane penetration in synthetic bilayers and compare these events with putative membrane penetration events in cells. We examined membrane penetration forces for three tip geometries and 18 chemical modifications of the probe surface, and in all cases the median forces required to penetrate cellular and synthetic lipid bilayers with nanoprobes were greater than 1 nN. The penetration force was sensitive to the probe's sharpness, but not its surface chemistry, and the force did not depend on cell surface or cytoskeletal properties, with cells and lipid stacks yielding similar forces. This systematic assessment of penetration under various mechanical and chemical conditions provides insights into nanoprobe-cell interactions and informs the design of future intracellular nanoprobes. PMID:25418094

  14. Effect of Chemicals on the Cell Membrane Transport of Nucleosides.

    DTIC Science & Technology

    1983-08-01

    lipid synthesis , a direct inhibition of the purine carrier by PFDA would not be expected. When efflux of AP from L5178Y cells was estimated with PFDA in...turnover of the carrier protein. PFDA may be an inhibitor -of carrier protein synthesis in the cell membrane. Another hypothesis suggests that the...inactive form. The activity level *may be controlled through inhibition of protein synthesis or the interaction 4between the carrier and the membrane

  15. Live cell imaging of membrane/cytoskeleton interactions and membrane topology.

    PubMed

    Chierico, Luca; Joseph, Adrian S; Lewis, Andrew L; Battaglia, Giuseppe

    2014-09-10

    We elucidate the interaction between actin and specific membrane components, using real time live cell imaging, by delivering probes that enable access to components, that cannot be accessed genetically. We initially investigated the close interplay between Phosphatidylinositol 4,5-bisphosphate (PIP2) and the F-actin network. We show that, during the early stage of cell adhesion, PIP2 forms domains within the filopodia membrane. We studied these domains alongside cell spreading and observed that these very closely follow the actin tread-milling. We show that this mechanism is associated with an active transport of PIP2 rich organelles from the cell perinuclear area to the edge, along actin fibers. Finally, mapping other phospholipids and membrane components we observed that the PIP2 domains formation is correlated with sphingosine and cholesterol rafts.

  16. Modelling the structure of the red cell membrane.

    PubMed

    Burton, Nicholas M; Bruce, Lesley J

    2011-04-01

    The red cell membrane has long been the focus of extensive study. The macromolecules embedded within the membrane carry the blood group antigens and perform many functions including the vital task of gas exchange. Links between the intramembrane macromolecules and the underlying cytoskeleton stabilize the biconcave morphology of the red cell and allow deformation during microvascular transit. Much is now known about the proteins of the red cell membrane and how they are organised. In many cases we have an understanding of which proteins are expressed, the number of each protein per cell, their oligomeric state(s), and how they are collected in large multi-protein complexes. However, our typical view of these structures is as cartoon shapes in schematic figures. In this study we have combined knowledge of the red cell membrane with a wealth of protein structure data from crystallography, NMR, and homology modelling to generate the first, tentative models of the complexes which link the membrane to the cytoskeleton. Measurement of the size of these complexes and comparison with known cytoskeletal distance parameters suggests the idea of interaction between the membrane complexes, which may have profound implications for understanding red cell function and deformation.

  17. Controlled permeation of cell membrane by single bubble acoustic cavitation.

    PubMed

    Zhou, Y; Yang, K; Cui, J; Ye, J Y; Deng, C X

    2012-01-10

    Sonoporation is the membrane disruption generated by ultrasound and has been exploited as a non-viral strategy for drug and gene delivery. Acoustic cavitation of microbubbles has been recognized to play an important role in sonoporation. However, due to the lack of adequate techniques for precise control of cavitation activities and real-time assessment of the resulting sub-micron process of sonoporation, limited knowledge has been available regarding the detail processes and correlation of cavitation with membrane disruption at the single cell level. In the current study, we developed a combined approach including optical, acoustical, and electrophysiological techniques to enable synchronized manipulation, imaging, and measurement of cavitation of single bubbles and the resulting cell membrane disruption in real-time. Using a self-focused femtosecond laser and high frequency ultrasound (7.44MHz) pulses, a single microbubble was generated and positioned at a desired distance from the membrane of a Xenopus oocyte. Cavitation of the bubble was achieved by applying a low frequency (1.5MHz) ultrasound pulse (duration 13.3 or 40μs) to induce bubble collapse. Disruption of the cell membrane was assessed by the increase in the transmembrane current (TMC) of the cell under voltage clamp. Simultaneous high-speed bright field imaging of cavitation and measurements of the TMC were obtained to correlate the ultrasound-generated bubble activities with the cell membrane poration. The change in membrane permeability was directly associated with the formation of a sub-micrometer pore from a local membrane rupture generated by bubble collapse or bubble compression depending on ultrasound amplitude and duration. The impact of the bubble collapse on membrane permeation decreased rapidly with increasing distance (D) between the bubble (diameter d) and the cell membrane. The effective range of cavitation impact on membrane poration was determined to be D/d=0.75. The maximum mean

  18. Spray deposition of Nafion membranes: Electrode-supported fuel cells

    NASA Astrophysics Data System (ADS)

    Bayer, Thomas; Pham, Hung Cuong; Sasaki, Kazunari; Lyth, Stephen Matthew

    2016-09-01

    Fuel cells are a key technology for the successful transition towards a hydrogen society. In order to accelerate fuel cell commercialization, improvements in performance are required. Generally, polymer electrolyte membrane fuel cells (PEFCs) are membrane-supported; the electrocatalyst layer is sprayed onto both sides of the membrane, and sandwiched between carbon-based gas diffusion layers (GDLs). In this work we redesign the membrane electrode assembly (MEA) and fabricate an electrode-supported PEFC. First the electrocatalyst layer is sprayed onto the GDL, and then Nafion dispersion is sprayed over the top of this to form a thin membrane. This method has the advantage of simplifying the fabrication process, allowing the fabrication of extremely thin electrolyte layers (down to ∼10 μm in this case), and reducing the amount of ionomer required in the cell. Electrode-supported PEFCs operate at significantly increased power density compared to conventional membrane-supported PEFCs, with a maximum of 581 mW/cm2 at 80 °C (atmospheric pressure, air at the cathode). Impedance spectroscopy confirmed that the origin of the improved performance was an 80% reduction in the membrane resistance due the thinner Nafion layer. This novel fabrication method is a step towards cheaper, thinner, fully printable PEFCs with high power density and efficiency.

  19. Proton conducting membranes for high temperature fuel cells with solid state water free membranes

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram R. (Inventor); Yen, Shiao-Pin S. (Inventor)

    2006-01-01

    A water free, proton conducting membrane for use in a fuel cell is fabricated as a highly conducting sheet of converted solid state organic amine salt, such as converted acid salt of triethylenediamine with two quaternized tertiary nitrogen atoms, combined with a nanoparticulate oxide and a stable binder combined with the converted solid state organic amine salt to form a polymeric electrolyte membrane. In one embodiment the membrane is derived from triethylenediamine sulfate, hydrogen phosphate or trifiate, an oxoanion with at least one ionizable hydrogen, organic tertiary amine bisulfate, polymeric quaternized amine bisulfate or phosphate, or polymeric organic compounds with quaternizable nitrogen combined with Nafion to form an intimate network with ionic interactions.

  20. Catalyst layers for proton exchange membrane fuel cells prepared by electrospray deposition on Nafion membrane

    NASA Astrophysics Data System (ADS)

    Chaparro, A. M.; Ferreira-Aparicio, P.; Folgado, M. A.; Martín, A. J.; Daza, L.

    The electrospray deposition method has been used for preparation of catalyst layers for proton exchange membrane fuel cells (PEMFC) on Nafion membrane. Deposition of Pt/C + ionomer suspensions on Nafion 212 gives rise to layers with a globular morphology, in contrast with the dendritic growth observed for the same layers when deposited on the gas diffusion layer, GDL (microporous carbon black layer on carbon cloth) or on metallic Al foils. Such a change is discussed in the light of the influence of the Nafion substrate on the electrospray deposition process. Nafion, which is a proton conductor and electronic insulator, gives rise to the discharge of particles through proton release and transport towards the counter electrode, compared with the direct electron transfer that takes place when depositing on an electronic conductor. There is also a change in the electric field distribution in the needle to counter-electrode gap due to the presence of Nafion, which may alter conditions for the electrospray effect. If discharging of particles is slow enough, for instances with a low membrane protonic conductivity, the Nafion substrate may be charged positively yielding a change in the electric field profile and, with it, in the properties of the film. Single cell characterization is carried out with Nafion 212 membranes catalyzed by electrospray on the cathode side. It is shown that the internal resistance of the cell decreases with on-membrane deposited cathodic catalyst layers, with respect to the same layers deposited on GDL, giving rise to a considerable improvement in cell performance. The lower internal resistance is due to higher proton conductivity at the catalyst layer-membrane interface resulting from on-membrane deposition. On the other hand, electroactive area and catalyst utilization appear little modified by on-membrane deposition, compared with on-GDL deposition.

  1. Hydrogen Gas Driven Permeation through Asymmetric Membranes in Diffusion Limited and Surface Limited Regimes: Interplay between Analytical and Numerical Calculations

    NASA Astrophysics Data System (ADS)

    Pisarev, A.; Bacherov, A.

    Validity of analytical solutions for the gas driven permeation of H in the Diffusion Limited Regime (DLR) and Surface Limited Regime (SLR) is analyzed by comparison with numerical calculations. Margins for analytical formulas have been established in terms of the permeation factors W = KLSp1/2/D on the inlet (W1) and outlet (W2) sides of the membrane. The DLR analytical formula gives perfect result (error less than 0.5%) if both W2 ≥ 104 and W1 ≥ 102 conditions are satisfied simultaneously. Decrease of both margins by two orders of magnitude leads to 10% error. The SLR analytical formula gives a very good result (error less than 0.5%) if both W1 ≤ 10-2 and W2W1 ≤ 10-3 conditions are satisfied simultaneously. Increase of both margins by two orders of magnitude leads to 10% error. It has been shown that the inlet side and the outlet side conditions are different in their importance for validity of the analytical formulas. In DLR the condition is softer on the inlet side and more rigid on the outlet side, while in SLR the condition is softer on the outlet side and more rigid on the inlet side.

  2. Nanomaterials for Polymer Electrolyte Membrane Fuel Cells; Materials Challenges Facing Electrical Energy Storate

    SciTech Connect

    Gopal Rao, MRS Web-Editor; Yury Gogotsi, Drexel University; Karen Swider-Lyons, Naval Research Laboratory

    2010-08-05

    Symposium T: Nanomaterials for Polymer Electrolyte Membrane Fuel Cells Polymer electrolyte membrane (PEM) fuel cells are under intense investigation worldwide for applications ranging from transportation to portable power. The purpose of this seminar is to focus on the nanomaterials and nanostructures inherent to polymer fuel cells. Symposium topics will range from high-activity cathode and anode catalysts, to theory and new analytical methods. Symposium U: Materials Challenges Facing Electrical Energy Storage Electricity, which can be generated in a variety of ways, offers a great potential for meeting future energy demands as a clean and efficient energy source. However, the use of electricity generated from renewable sources, such as wind or sunlight, requires efficient electrical energy storage. This symposium will cover the latest material developments for batteries, advanced capacitors, and related technologies, with a focus on new or emerging materials science challenges.

  3. Membrane protein production in Escherichia coli cell-free lysates.

    PubMed

    Henrich, Erik; Hein, Christopher; Dötsch, Volker; Bernhard, Frank

    2015-07-08

    Cell-free protein production has become a core technology in the rapidly spreading field of synthetic biology. In particular the synthesis of membrane proteins, highly problematic proteins in conventional cellular production systems, is an ideal application for cell-free expression. A large variety of artificial as well as natural environments for the optimal co-translational folding and stabilization of membrane proteins can rationally be designed. The high success rate of cell-free membrane protein production allows to focus on individually selected targets and to modulate their functional and structural properties with appropriate supplements. The efficiency and robustness of lysates from Escherichia coli strains allow a wide diversity of applications and we summarize current strategies for the successful production of high quality membrane protein samples.

  4. Anhydrous Proton-Conducting Membranes for Fuel Cells

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram; Yen, Shiao-Pin S.

    2005-01-01

    Polymeric electrolyte membranes that do not depend on water for conduction of protons are undergoing development for use in fuel cells. Prior polymeric electrolyte fuel-cell membranes (e.g., those that contain perfluorosulfonic acid) depend on water and must be limited to operation below a temperature of 125 C because they retain water poorly at higher temperatures. In contrast, the present developmental anhydrous membranes are expected to function well at temperatures up to 200 C. The developmental membranes exploit a hopping-and-reorganization proton- conduction process that can occur in the solid state in organic amine salts and is similar to a proton-conduction process in a liquid. This process was studied during the 1970s, but until now, there has been no report of exploiting organic amine salts for proton conduction in fuel cells.

  5. Effect of gas diffusion layer and membrane properties in an annular proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Khazaee, I.; Ghazikhani, M.; Esfahani, M. Nasr

    2012-01-01

    A complete three-dimensional and single phase computational dynamics model for annular proton exchange membrane (PEM) fuel cell is used to investigate the effect of changing gas diffusion layer and membrane properties on the performances, current density and gas concentration. The proposed model is a full cell model, which includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain; therefore no interfacial boundary condition is required at the internal boundaries between cell components. This computational fluid dynamics code is used as the direct problem solver, which is used to simulate the two-dimensional mass, momentum and species transport phenomena as well as the electron- and proton-transfer process taking place in a PEMFC that cannot be investigated experimentally. The results show that by increasing the thickness and decreasing the porosity of GDL the performance of the cell enhances that it is different with planner PEM fuel cell. Also the results show that by decreasing the thickness of the membrane the performance of the cell increases.

  6. Protein diffusion in plant cell plasma membranes: the cell-wall corral

    PubMed Central

    Martinière, Alexandre; Runions, John

    2013-01-01

    Studying protein diffusion informs us about how proteins interact with their environment. Work on protein diffusion over the last several decades has illustrated the complex nature of biological lipid bilayers. The plasma membrane contains an array of membrane-spanning proteins or proteins with peripheral membrane associations. Maintenance of plasma membrane microstructure can be via physical features that provide intrinsic ordering such as lipid microdomains, or from membrane-associated structures such as the cytoskeleton. Recent evidence indicates, that in the case of plant cells, the cell wall seems to be a major player in maintaining plasma membrane microstructure. This interconnection / interaction between cell-wall and plasma membrane proteins most likely plays an important role in signal transduction, cell growth, and cell physiological responses to the environment. PMID:24381579

  7. Cytotoxicity of bovine and porcine collagen membranes in mononuclear cells.

    PubMed

    Moura, Camilla Christian Gomes; Soares, Priscilla Barbosa Ferreira; Carneiro, Karine Fernandes; Souza, Maria Aparecida de; Magalhães, Denildo

    2012-01-01

    This study compared the cytotoxicity and the release of nitric oxide induced by collagen membranes in human mononuclear cells. Peripheral blood was collected from each patient and the separation of mononuclear cells was performed by Ficoll. Then, 2x10(5) cells were plated in 48-well culture plates under the membranes in triplicate. The polystyrene surface was used as negative control. Cell viability was assessed by measuring mitochondrial activity (MTT) at 4, 12 and 24 h, with dosage levels of nitrite by the Griess method for the same periods. Data had non-normal distribution and were analyzed by the Kruskal-Wallis test (p<0.05). Statistically significant differences (p<0.05) were observed between the membranes and the control in the experimental period, although there was a significant reduction in viability over time (p<0.01). At 4 and 12 h, the porcine membrane induced a higher release of nitrite compared with the control and bovine membrane, respectively (p<0.01), and this difference was maintained at 24 h (p<0.05). This in vitro study showed that the porcine collagen membrane induces an increased production of proinflammatory mediators by mononuclear cells in the first hours of contact, decreasing with time.

  8. Graphene-Induced Pore Formation on Cell Membranes

    PubMed Central

    Duan, Guangxin; Zhang, Yuanzhao; Luan, Binquan; Weber, Jeffrey K.; Zhou, Royce W.; Yang, Zaixing; Zhao, Lin; Xu, Jiaying; Luo, Judong; Zhou, Ruhong

    2017-01-01

    Examining interactions between nanomaterials and cell membranes can expose underlying mechanisms of nanomaterial cytotoxicity and guide the design of safer nanomedical technologies. Recently, graphene has been shown to exhibit potential toxicity to cells; however, the molecular processes driving its lethal properties have yet to be fully characterized. We here demonstrate that graphene nanosheets (both pristine and oxidized) can produce holes (pores) in the membranes of A549 and Raw264.7 cells, substantially reducing cell viability. Electron micrographs offer clear evidence of pores created on cell membranes. Our molecular dynamics simulations reveal that multiple graphene nanosheets can cooperate to extract large numbers of phospholipids from the membrane bilayer. Strong dispersion interactions between graphene and lipid-tail carbons result in greatly depleted lipid density within confined regions of the membrane, ultimately leading to the formation of water-permeable pores. This cooperative lipid extraction mechanism for membrane perforation represents another distinct process that contributes to the molecular basis of graphene cytotoxicity. PMID:28218295

  9. Membrane Targeting of P-type ATPases in Plant Cells

    SciTech Connect

    Jeffrey F. Harper, Ph.D.

    2004-06-30

    How membrane proteins are targeted to specific subcellular locations is a very complex and poorly understood area of research. Our long-term goal is to use P-type ATPases (ion pumps), in a model plant system Arabidopsis, as a paradigm to understand how members of a family of closely related membrane proteins can be targeted to different subcellular locations. The research is divided into two specific aims. The first aim is focused on determining the targeting destination of all 10 ACA-type calcium pumps (Arabidopsis Calcium ATPase) in Arabidopsis. ACAs represent a plant specific-subfamily of plasma membrane-type calcium pumps. In contrast to animals, the plant homologs have been found in multiple membrane systems, including the ER (ACA2), tonoplast (ACA4) and plasma membrane (ACA8). Their high degree of similarity provides a unique opportunity to use a comparative approach to delineate the membrane specific targeting information for each pump. One hypothesis to be tested is that an endomembrane located ACA can be re-directed to the plasma membrane by including targeting information from a plasma membrane isoform, ACA8. Our approach is to engineer domain swaps between pumps and monitor the targeting of chimeric proteins in plant cells using a Green Fluorescence Protein (GFP) as a tag. The second aim is to test the hypothesis that heterologous transporters can be engineered into plants and targeted to the plasma membrane by fusing them to a plasma membrane proton pump. As a test case we are evaluating the targeting properties of fusions made between a yeast sodium/proton exchanger (Sod2) and a proton pump (AHA2). This fusion may potentially lead to a new strategy for engineering salt resistant plants. Together these aims are designed to provide fundamental insights into the biogenesis and function of plant cell membrane systems.

  10. Crosstalk between adjacent nanopores in a solid-state membrane array for multi-analyte high-throughput biomolecule detection

    NASA Astrophysics Data System (ADS)

    Raza, Muhammad Usman; Saleem, Sajid; Ali, Waqas; Iqbal, Samir M.

    2016-08-01

    Single nanopores are used to detect a variety of biological molecules. The modulations in ionic current under applied bias across the nanopore contain important information about translocating species, thus providing single analyte detection. These systems are, however, challenged in practical situations where multiple analytes have to be detected at high throughput. This paper presents the analysis of a multi-nanopore system that can be used for the detection of analytes with high throughput. As a scalable model, two nanopores were simulated in a single solid-state membrane. The interactions of the electric fields at the mouths of the individual nanopores were analyzed. The data elucidated the electrostatic properties of the nanopores from a single membrane and provided a framework to calculate the -3 dB distance, akin to the Debye length, from one nanopore to the other. This distance was the minimum distance between the adjacent nanopores such that their individual electric fields did not significantly interact with one another. The results can help in the optimal experimental design to construct solid-state nanopore arrays for any given nanopore size and applied bias.

  11. Polyarylenethioethersulfone Membranes for Fuel Cells (Postprint)

    DTIC Science & Technology

    2007-09-01

    precipitated copolymer was washed several times with deionized water in an attempt to completely remove the salts and then soxhlet - extracted in methanol...mation such as membrane resistance, charge-transfer resistance, and pore resistance was extracted from impedance plots using Nafion- and SPTES-50

  12. Fuel cell electrolyte membrane with basic polymer

    DOEpatents

    Larson, James M.; Pham, Phat T.; Frey, Matthew H.; Hamrock, Steven J.; Haugen, Gregory M.; Lamanna, William M.

    2012-12-04

    The present invention is an electrolyte membrane comprising an acid and a basic polymer, where the acid is a low-volatile acid that is fluorinated and is either oligomeric or non-polymeric, and where the basic polymer is protonated by the acid and is stable to hydrolysis.

  13. Fuel cell electrolyte membrane with basic polymer

    DOEpatents

    Larson, James M.; Pham, Phat T.; Frey, Matthew H.; Hamrock, Steven J.; Haugen, Gregory M.; Lamanna, William M.

    2010-11-23

    The present invention is an electrolyte membrane comprising an acid and a basic polymer, where the acid is a low-volatile acid that is fluorinated and is either oligomeric or non-polymeric, and where the basic polymer is protonated by the acid and is stable to hydrolysis.

  14. A Journey of Cytolethal Distending Toxins through Cell Membranes

    PubMed Central

    Boesze-Battaglia, Kathleen; Alexander, Desiree; Dlakić, Mensur; Shenker, Bruce J.

    2016-01-01

    The multifunctional role of lipids as structural components of membranes, signaling molecules, and metabolic substrates makes them an ideal partner for pathogens to hijack host cell processes for their own survival. The properties and composition of unique membrane micro-domains such as membrane rafts make these regions a natural target for pathogens as it affords them an opportunity to hijack cell signaling and intracellular trafficking pathways. Cytolethal distending toxins (Cdts), members of the AB2 family of toxins are comprised of three subunits, the active, CdtB unit, and the binding, CdtA-CdtC unit. Cdts are cyclomodulins leading to cell cycle arrest and apoptosis in a wide variety of cell types. Cdts from several species share a requirement for membrane rafts, and often cholesterol specifically for cell binding and CdtB mediated cytotoxicity. In this review we focus on how host–cell membrane bilayer organization contributes to the cell surface association, internalization, and action of bacteria derived cytolethal distending toxins (Cdts), with an emphasis on Aggregatibacter actinomycetemcomitans Cdt. PMID:27559534

  15. Gradiently crosslinked polymer electrolyte membranes in fuel cells

    NASA Astrophysics Data System (ADS)

    An, De; Wu, Bin; Zhang, Genlei; Zhang, Wen; Wang, Yuxin

    2016-01-01

    Polymer electrolyte membranes in fuel cells should be high in both ionic conductivity and mechanical strength. However, the two are often exclusive to each other. To solve this conundrum, a novel strategy is proposed in this paper, with extensively researched sulfonated poly (ether ether ketone) (SPEEK) membrane as a paradigm. A SPEEK membrane of high sulfonation degree is simply post-treated with NaBH4 and H2SO4 solution at ambient temperature for a certain time to afford the membrane with a gradient crosslinking structure. Measurements via 1H NMR, ATR-FTIR and SEM-EDS are conducted to verify such structural changes. The gradient crosslinks make practically no damage to proton conductance, but effectively restrain the membrane from over swelling and greatly enhance its tensile strength. A H2-O2 fuel cell with the gradiently crosslinked SPEEK membrane shows a maximal power density of 533 mW cm-2 at 80 °C, whereas the fuel cell with the pristine SPEEK membrane cannot be operated beyond 30 °C.

  16. Improving dynamic performance of proton-exchange membrane fuel cell system using time delay control

    NASA Astrophysics Data System (ADS)

    Kim, Young-Bae

    Transient behaviour is a key parameter for the vehicular application of proton-exchange membrane (PEM) fuel cell. The goal of this presentation is to construct better control technology to increase the dynamic performance of a PEM fuel cell. The PEM fuel cell model comprises a compressor, an injection pump, a humidifier, a cooler, inlet and outlet manifolds, and a membrane-electrode assembly. The model includes the dynamic states of current, voltage, relative humidity, stoichiometry of air and hydrogen, cathode and anode pressures, cathode and anode mass flow rates, and power. Anode recirculation is also included with the injection pump, as well as anode purging, for preventing anode flooding. A steady-state, isothermal analytical fuel cell model is constructed to analyze the mass transfer and water transportation in the membrane. In order to prevent the starvation of air and flooding in a PEM fuel cell, time delay control is suggested to regulate the optimum stoichiometry of oxygen and hydrogen, even when there are dynamical fluctuations of the required PEM fuel cell power. To prove the dynamical performance improvement of the present method, feed-forward control and Linear Quadratic Gaussian (LQG) control with a state estimator are compared. Matlab/Simulink simulation is performed to validate the proposed methodology to increase the dynamic performance of a PEM fuel cell system.

  17. Direct visualization of membrane architecture of myelinating cells in transgenic mice expressing membrane-anchored EGFP.

    PubMed

    Deng, Yaqi; Kim, BongWoo; He, Xuelian; Kim, Sunja; Lu, Changqing; Wang, Haibo; Cho, Ssang-Goo; Hou, Yiping; Li, Jianrong; Zhao, Xianghui; Lu, Q Richard

    2014-04-01

    Myelinogenesis is a complex process that involves substantial and dynamic changes in plasma membrane architecture and myelin interaction with axons. Highly ramified processes of oligodendrocytes in the central nervous system (CNS) make axonal contact and then extrapolate to wrap around axons and form multilayer compact myelin sheathes. Currently, the mechanisms governing myelin sheath assembly and axon selection by myelinating cells are not fully understood. Here, we generated a transgenic mouse line expressing the membrane-anchored green fluorescent protein (mEGFP) in myelinating cells, which allow live imaging of details of myelinogenesis and cellular behaviors in the nervous systems. mEGFP expression is driven by the promoter of 2'-3'-cyclic nucleotide 3'-phosphodiesterase (CNP) that is expressed in the myelinating cell lineage. Robust mEGFP signals appear in the membrane processes of oligodendrocytes in the CNS and Schwann cells in the peripheral nervous system (PNS), wherein mEGFP expression defines the inner layers of myelin sheaths and Schmidt-Lanterman incisures in adult sciatic nerves. In addition, mEGFP expression can be used to track the extent of remyelination after demyelinating injury in a toxin-induced demyelination animal model. Taken together, the membrane-anchored mEGFP expression in the new transgenic line would facilitate direct visualization of dynamic myelin membrane formation and assembly during development and process remodeling during remyelination after various demyelinating injuries.

  18. Analytical coupled vibroacoustic modeling of membrane-type acoustic metamaterials: plate model.

    PubMed

    Chen, Yangyang; Huang, Guoliang; Zhou, Xiaoming; Hu, Gengkai; Sun, Chin-Teh

    2014-12-01

    By considering the elastic membrane's dissipation, the membrane-type acoustic metamaterial (MAM) has been demonstrated to be a super absorber for low-frequency sound. In the paper, a theoretical vibroacoustic plate model is developed to reveal the sound energy absorption mechanism within the MAM under a plane normal incidence. Based on the plate model in conjunction with the point matching method, the in-plane strain energy of the membrane due to the resonant and antiresonant motion of the attached masses can be accurately captured by solving the coupled vibroacoustic integrodifferential equation. The sound absorption ability of the MAM is quantitatively determined, which is also in good agreement with the prediction from the finite element method. In particular, microstructure effects including eccentricity of the attached masses, the depth, thickness, and loss factor of the membrane on sound absorption peak values are discussed.

  19. Performance of cell-penetrating peptide-linked polymers physically mixed with poorly membrane-permeable molecules on cell membranes.

    PubMed

    Sakuma, Shinji; Suita, Masaya; Yamamoto, Takafumi; Masaoka, Yoshie; Kataoka, Makoto; Yamashita, Shinji; Nakajima, Noriko; Shinkai, Norihiro; Yamauchi, Hitoshi; Hiwatari, Ken-Ichiro; Hashizume, Akio; Tachikawa, Hiroyuki; Kimura, Ryoji; Ishimaru, Yuki; Kasai, Atsushi; Maeda, Sadaaki

    2012-05-01

    We are investigating a new class of penetration enhancers that enable poorly membrane-permeable molecules physically mixed with them to effectively penetrate cell membranes without their concomitant cellular uptake. Since we previously revealed that poly(N-vinylacetamide-co-acrylic acid) modified with d-octaarginine, which is a typical cell-penetrating peptide, significantly enhanced the nasal absorption of insulin, we examined the performance of the polymers on cell membranes. When Caco-2 cells were incubated with 5(6)-carboxyfluorescein (CF) for 30 min, approximately 0.1% of applied CF was internalized into the cells. This poor membrane permeability was dramatically enhanced by d-octaarginine-linked polymers; a 25-fold increase in the cellular uptake of CF was observed when the polymer concentration was adjusted to 0.2mg/mL. None of the individual components, for example, d-octaarginine, had any influence on CF uptake, demonstrating that only d-octaarginine anchored chemically to the polymeric platform enhanced the membrane permeation of CF. The polymer-induced CF uptake was consistently high even when the incubation time was extended to 120 min. Confocal laser scanning microphotographs of cells incubated with d-octaarginine-linked polymers bearing rhodamine red demonstrated that the cell outline was stained with red fluorescence. The polymer-induced CF uptake was significantly suppressed by 5-(N-ethyl-N-isopropyl)amiloride, which is an inhibitor of macropinocytosis. Results indicated that d-octaarginine-linked polymers remained on the cell membrane and poorly membrane-permeable CF was continuously internalized into cells mainly via macropinocytosis repeated for the individual peptidyl branches in the polymer backbone.

  20. Distance Measurement on an Endogenous Membrane Transporter in E. coli Cells and Native Membranes Using EPR Spectroscopy.

    PubMed

    Joseph, Benesh; Sikora, Arthur; Bordignon, Enrica; Jeschke, Gunnar; Cafiso, David S; Prisner, Thomas F

    2015-05-18

    Membrane proteins may be influenced by the environment, and they may be unstable in detergents or fail to crystallize. As a result, approaches to characterize structures in a native environment are highly desirable. Here, we report a novel general strategy for precise distance measurements on outer membrane proteins in whole Escherichia coli cells and isolated outer membranes. The cobalamin transporter BtuB was overexpressed and spin-labeled in whole cells and outer membranes and interspin distances were measured to a spin-labeled cobalamin using pulse EPR spectroscopy. A comparative analysis of the data reveals a similar interspin distance between whole cells, outer membranes, and synthetic vesicles. This approach provides an elegant way to study conformational changes or protein-protein/ligand interactions at surface-exposed sites of membrane protein complexes in whole cells and native membranes, and provides a method to validate outer membrane protein structures in their native environment.

  1. Graphene microsheets enter cells through spontaneous membrane penetration at edge asperities and corner sites.

    PubMed

    Li, Yinfeng; Yuan, Hongyan; von dem Bussche, Annette; Creighton, Megan; Hurt, Robert H; Kane, Agnes B; Gao, Huajian

    2013-07-23

    Understanding and controlling the interaction of graphene-based materials with cell membranes is key to the development of graphene-enabled biomedical technologies and to the management of graphene health and safety issues. Very little is known about the fundamental behavior of cell membranes exposed to ultrathin 2D synthetic materials. Here we investigate the interactions of graphene and few-layer graphene (FLG) microsheets with three cell types and with model lipid bilayers by combining coarse-grained molecular dynamics (MD), all-atom MD, analytical modeling, confocal fluorescence imaging, and electron microscopic imaging. The imaging experiments show edge-first uptake and complete internalization for a range of FLG samples of 0.5- to 10-μm lateral dimension. In contrast, the simulations show large energy barriers relative to kBT for membrane penetration by model graphene or FLG microsheets of similar size. More detailed simulations resolve this paradox by showing that entry is initiated at corners or asperities that are abundant along the irregular edges of fabricated graphene materials. Local piercing by these sharp protrusions initiates membrane propagation along the extended graphene edge and thus avoids the high energy barrier calculated in simple idealized MD simulations. We propose that this mechanism allows cellular uptake of even large multilayer sheets of micrometer-scale lateral dimension, which is consistent with our multimodal bioimaging results for primary human keratinocytes, human lung epithelial cells, and murine macrophages.

  2. Optical Detection of Aqueous Phase Analytes via Host-Guest Interactions on a Lipid Membrane Surface

    SciTech Connect

    Sasaki, D.Y.; Waggoner, T.A.

    1999-01-11

    The organization and assembly of molecules in cellular membranes is orchestrated through the recognition and binding of specific chemical signals. A simplified version of the cellular membrane system has been developed using a synthetically prepared membrane receptor incorporated into a biologically derived lipid bilayer. Through an interplay of electrostatic and van der Wards interactions, aggregation or dispersion of molecular components could be executed on command using a specific chemical signal. A pyrene fluorophore was used as an optical probe to monitor the aggregational state of the membrane receptors in the bilayer matrix. The pyrene excimer emission to monomer emission (E/M) intensity ratio gave a relative assessment of the local concentration of receptors in the membrane. Bilayers were prepared with receptors selective for the divalent metal ions of copper, mercury, and lead. Addition of the metal ions produced a rapid dispersion of aggregated receptor components at nano- to micro-molar concentrations. The process was reversible by sequestering the metal ions with EDTA. Receptors for proteins and polyhistidine were also prepared and incorporated into phosphatidylcholine lipid bilayers. In this case, the guest molecules bound to the membrane through multiple points of interaction causing aggregation of initially dispersed receptor molecules. The rapid, selective, and sensitive fluorescence optical response of these lipid assemblies make them attractive in sensor applications for aqueous phase metal ions and polypeptides.

  3. Tight binding of proteins to membranes from older human cells.

    PubMed

    Truscott, Roger J W; Comte-Walters, Susana; Ablonczy, Zsolt; Schwacke, John H; Berry, Yoke; Korlimbinis, Anastasia; Friedrich, Michael G; Schey, Kevin L

    2011-12-01

    The lens is an ideal model system for the study of macromolecular aging and its consequences for cellular function, since there is no turnover of lens fibre cells. To examine biochemical processes that take place in the lens and that may also occur in other long-lived cells, membranes were isolated from defined regions of human lenses that are synthesised at different times during life, and assayed for the presence of tightly bound cytosolic proteins using quantitative iTRAQ proteomics technology. A majority of lens beta crystallins and all gamma crystallins became increasingly membrane bound with age, however, the chaperone proteins alpha A and alpha B crystallin, as well as the thermally-stable protein, βB2 crystallin, did not. Other proteins such as brain-associated signal protein 1 and paralemmin 1 became less tightly bound in the older regions of the lens. It is evident that protein-membrane interactions change significantly with age. Selected proteins that were formerly cytosolic become increasingly tightly bound to cell membranes with age and are not removed even by treatment with 7 M urea. It is likely that such processes reflect polypeptide denaturation over time and the untoward binding of proteins to membranes may alter membrane properties and contribute to impairment of communication between older cells.

  4. 3D visualization of membrane failures in fuel cells

    NASA Astrophysics Data System (ADS)

    Singh, Yadvinder; Orfino, Francesco P.; Dutta, Monica; Kjeang, Erik

    2017-03-01

    Durability issues in fuel cells, due to chemical and mechanical degradation, are potential impediments in their commercialization. Hydrogen leak development across degraded fuel cell membranes is deemed a lifetime-limiting failure mode and potential safety issue that requires thorough characterization for devising effective mitigation strategies. The scope and depth of failure analysis has, however, been limited by the 2D nature of conventional imaging. In the present work, X-ray computed tomography is introduced as a novel, non-destructive technique for 3D failure analysis. Its capability to acquire true 3D images of membrane damage is demonstrated for the very first time. This approach has enabled unique and in-depth analysis resulting in novel findings regarding the membrane degradation mechanism; these are: significant, exclusive membrane fracture development independent of catalyst layers, localized thinning at crack sites, and demonstration of the critical impact of cracks on fuel cell durability. Evidence of crack initiation within the membrane is demonstrated, and a possible new failure mode different from typical mechanical crack development is identified. X-ray computed tomography is hereby established as a breakthrough approach for comprehensive 3D characterization and reliable failure analysis of fuel cell membranes, and could readily be extended to electrolyzers and flow batteries having similar structure.

  5. Synaptic and Golgi membrane recycling in cochlear hair cells.

    PubMed

    Siegel, J H; Brownell, W E

    1986-06-01

    Membrane recycling in the mechanoreceptive sensory cells of the mammalian cochlea was studied by observing membrane-bound horseradish peroxidase (HRP) reaction product following brief in vivo exposure to the enzyme. In the inner hair cell (IHC), peroxidase was taken up into coated vesicles and became incorporated into synaptic vesicles surrounding presynaptic bodies, but much HRP was also transported to the apical zone where reaction product appeared in all components of the Golgi complex. Neither the subsurface cisternae nor a tubular network associated with clusters of mitochondria were labelled. Outer hair cells (OHCs) showed considerably less membrane-bound reaction product than IHCs, indicating less rapid plasmalemmal recycling. Most membrane-bound reaction product was contained in coated vesicles and small vacuoles in the synaptic zone, but was occasionally seen in multivesicular bodies in the most apical zone. No labelled organelles were detected in the large central region of the OHC. A diffuse staining of the cytoplasm, particularly pronounced in OHCs, often interfered with the evaluation of membrane-bound reaction product in OHCs. This staining pattern could be qualitatively reproduced in both IHCs and OHCs by incubating fixed segments of the organ of Corti in oxidized diaminobenzidine. The presence of labelled synaptic vesicles associated with presynaptic bodies of IHCs and OHCs suggests that they are formed from membrane retrieved from the plasmalemma. We found no evidence that the subsurface cisternae of IHCs or the laminated cisternae of OHCs are derived from the cell surface as they never contained reaction product.

  6. Effects of Extracellular Calcium on Cell Membrane Resealing during Sonoporation

    NASA Astrophysics Data System (ADS)

    Zhou, Yun; Cui, Jianmin; Deng, Cheri X.

    2006-05-01

    Sonoporation has been exploited as a novel strategy for intracellular drug and gene delivery. In sonoporation, ultrasound application generates transient pores or openings in the cell membrane that allow entry of extracellular agents normally not permeable to the cell membrane. In order to improve the sonoporation outcome, we seek to obtain improved understanding of the sonoporation mechanism and investigate the factors affecting sonoporation process. We established a voltage clamp technique for real time measurement of sonoporation at single cell level using Xenopus oocytes as a model system. As both cell survival and intracellular delivery efficiency of drug or genes depend on the sonoporation dynamic process, and Calcium plays important roles in cellular processes, we focus on studying of the effect of extracellular Calcium concentration on the formation, extension, and resealing of membrane pores in sonoporation. We obtained experimental results demonstrating that the cell membrane reseals in the order of seconds in the presence of physiological level of extracellular [Ca]. We measured the resealing as function of extracellular [Ca] (0-1.8mM) and observed that the resealing rate decreases as extracellular [Ca] decreases from normal physiological level. No resealing was demonstrated when 1mM EGTA was added in the extracellular medium to chelate the [Ca] extracellularly. Our experimental findings suggest that extracellular Calcium plays an important role in controlling membrane resealing in sonoporation and thus the sonoporation outcome such as cell survival and delivery efficiency.

  7. Anion selective membrane. [ion exchange resins and ion exchange membrane electrolytes for electrolytic cells

    NASA Technical Reports Server (NTRS)

    Alexander, S. S.; Geoffroy, R. R.; Hodgdon, R. B.

    1975-01-01

    Experimental anion permselective membranes were prepared and tested for their suitability as cell separators in a chemical redox power storage system being developed at NASA-Lewis Research Center. The goals of long-term (1000 hr) oxidative and thermal stability at 80 C in FeCl3 and CrCl3 electrolytes were met by most of the weak base and strong base amino exchange groups considered in the program. Good stability is exhibited by several of the membrane substrate resins. These are 'styrene' divinylbenzene copolymer and PVC film. At least four membrane systems produce strong flexible films with electrochemical properties (resistivity, cation transfer) superior to those of the 103QZL, the most promising commercial membrane. The physical and chemical properties of the resins are listed.

  8. Cell Membrane-Cloaked Nanoparticles for Targeted Therapeutics

    NASA Astrophysics Data System (ADS)

    Luk, Brian Tsengchi

    The advent of nanoparticle-based delivery systems has made a significant impact on clinical patient outcomes. In recent decades, myriad nanoparticle-based therapeutic agents have been developed for the treatment and management of ailments such as cancer, diabetes, pain, bacterial infections, and asthma, among many others. Nanotherapeutics offer many distinct advantages over conventional free drug formulations. For example, nanoparticles are able to accumulate at tumor sites by extravasation through leaky vasculature at tumor sites via the enhanced permeability and retention (EPR) effect; nanoparticles can also be tailored to have desirable characteristics, such as prolonged circulation in the blood stream, improved drug encapsulation, and sustained or triggered drug release. Currently, a growing number of nanoformulations with favorable pharmacological profiles and promising efficacy are being used in clinical trials for the treatment of various cancers. Building on the success of these encouraging clinical results, new engineering strategies have emerged that combine synthetic nanoparticles with natural biomaterials to create nature-inspired biomimetic delivery systems. The work presented in this dissertation focuses on the biointerfacing between synthetic and natural materials, namely in the manifestation of cell membrane-coated nanoparticles. By exploiting the natural functionalities of source cell membranes, cell membrane-cloaked nanoparticles have huge potential in the delivery of therapeutic agents for a variety of applications. The first portion of this thesis will focus on understanding the fundamentals underlying cell membrane coating on synthetic nanoparticles. First introduced in 2011, cell membrane-cloaked nanoparticles showed immediate promise in drug delivery applications, but further understanding was necessary to be able to harness the full potential of the membrane coating platform. The first section provides further insight into the interfacial

  9. Surface-enhanced Raman imaging of cell membrane by a highly homogeneous and isotropic silver nanostructure

    NASA Astrophysics Data System (ADS)

    Zito, Gianluigi; Rusciano, Giulia; Pesce, Giuseppe; Dochshanov, Alden; Sasso, Antonio

    2015-04-01

    scattering (SERS) in confocal microscopy, but requires engineering plasmonic architectures with a spatially invariant SERS enhancement factor G(x, y) = G. To this end, we exploit a self-assembled isotropic nanostructure with characteristics of homogeneity typical of the so-called near-hyperuniform disorder. The resulting highly dense, homogeneous and isotropic random pattern consists of clusters of silver nanoparticles with limited size dispersion. This nanostructure brings together several advantages: very large hot spot density (~104 μm-2), superior spatial reproducibility (SD < 1% over 2500 μm2) and single-molecule sensitivity (Gav ~ 109), all on a centimeter scale transparent active area. We are able to reconstruct the label-free SERS-based chemical map of live cell membranes with confocal resolution. In particular, SERS imaging is here demonstrated on red blood cells in vitro in order to use the Raman-resonant heme of the cell as a contrast medium to prove spectroscopic detection of membrane molecules. Numerical simulations also clarify the SERS characteristics of the substrate in terms of electromagnetic enhancement and distance sensitivity range consistently with the experiments. The large SERS-active area is intended for multi-cellular imaging on the same substrate, which is important for spectroscopic comparative analysis of complex organisms like cells. This opens new routes for in situ quantitative surface analysis and dynamic probing of living cells exposed to membrane-targeting drugs. Electronic supplementary information (ESI) available: Additional details of the methods, further experimental data and data analysis, Raman assignment with additional references. Further sections: Basis Analysis (for two-analyte statistics), substrate oxidation, long-term stability and nanotoxicity issues. See DOI: 10.1039/c5nr01341k

  10. The use of Permeation Liquid Membrane (PLM) as an analytical tool for trace metal speciation studies in natural waters

    NASA Astrophysics Data System (ADS)

    Parthasarathy, N.; Pelletier, M.; Buffle, J.

    2003-05-01

    Permeation liquid membrane (PLM) based on liquid-liquid extraction principles is an emerging analytical tool for making in situ trace metal speciation measurements. A PLM comprising didecyl 1, 10 diaza crown etherlauric acid in phenylhexane/toluene has been developed for measuring free metal ions (e.g. Cu, Pb, Cd and Zn) concentration under natural water conditions. The capability of PLM for making speciation studies has been demonstrated using synthetic and natural ligands. Application of in situ preconcentration of trace metals in diverse waters using specially designed hollow fibre PLM are reported.

  11. Interaction of injectable neurotropic drugs with the red cell membrane.

    PubMed

    Reinhart, Walter H; Lubszky, Szabina; Thöny, Sandra; Schulzki, Thomas

    2014-10-01

    The normal red blood cell (RBC) shape is a biconcave discocyte. An intercalation of a drug in the outer half of the membrane lipid bilayer leads to echinocytosis, an intercalation in the inner half to stomatocytosis. We have used the shape transforming capacity of RBCs as a model to analyse the membrane interaction potential of various neurotropic drugs. Chlorpromazine, clomipramine, citalopram, clonazepam, and diazepam induced a reversible stomatocytosis, phenytoin induced echinocytosis, while the anticonvulsants levetiracetam, valproic acid and phenobarbital had no effect. This diversity of RBC shape transformations suggests that the pharmacological action is not linked to the membrane interaction. We conclude that this simple RBC shape transformation assay could be a useful tool to screen for potential drug interactions with cell membranes.

  12. Direct Cytoskeleton Forces Cause Membrane Softening in Red Blood Cells

    PubMed Central

    Rodríguez-García, Ruddi; López-Montero, Iván; Mell, Michael; Egea, Gustavo; Gov, Nir S.; Monroy, Francisco

    2015-01-01

    Erythrocytes are flexible cells specialized in the systemic transport of oxygen in vertebrates. This physiological function is connected to their outstanding ability to deform in passing through narrow capillaries. In recent years, there has been an influx of experimental evidence of enhanced cell-shape fluctuations related to metabolically driven activity of the erythroid membrane skeleton. However, no direct observation of the active cytoskeleton forces has yet been reported to our knowledge. Here, we show experimental evidence of the presence of temporally correlated forces superposed over the thermal fluctuations of the erythrocyte membrane. These forces are ATP-dependent and drive enhanced flickering motions in human erythrocytes. Theoretical analyses provide support for a direct force exerted on the membrane by the cytoskeleton nodes as pulses of well-defined average duration. In addition, such metabolically regulated active forces cause global membrane softening, a mechanical attribute related to the functional erythroid deformability. PMID:26083919

  13. A new material concept for the red cell membrane.

    PubMed

    Evans, E A

    1973-09-01

    The proposition is made that the red cell membrane is a two-dimensional, incompressible material and a general stress-strain law is developed for finite deformations. In the linear form, the character of such a material is analogous to a two-dimensional Mooney material (e.g., rubber), indicating that the molecular structure in the plane of the membrane would consist of long chains, randomly kinked and cross-linked in the natural state. The loose network could be provided by the protein component and the lipid phase could exist interstitially as a liquid bilayer, giving the membrane its two-dimensional incompressibility. The material provides the capability of large deformations exhibited by the discocyte and yet the rigidity associated with the osmotic spherocyte state. It is demonstrated that a membrane of this type can form a sphere at constant area. An illustrative example of the application to single cell discocyte-to-osmotic spherocyte transformations is presented.

  14. Attachment of killed Mycoplasma gallisepticum cells and membranes to erythrocytes

    SciTech Connect

    Banai, M.; Kahane, I.; Feldner, J.; Razin, S.

    1981-11-01

    To correlate viability with attachment capacity, Mycoplasma gallisepticum cells harvested at different growth phases and treated by various agents were tested for their capacity to attach to human erythrocytes. The results show that viability per se is not essential for M. gallisepticum attachment to erythrocytes, as cells killed by ultraviolet irradiation and membranes isolated by lysing M. gallisepticum cells by various means retained attachment capacity. However, treatment of the mycoplasmas by protein-denaturing agents, such as heart, glutaraldehyde, or prolonged exposure to low pH, drastically affected or even abolished attachment, supporting the protein nature of the mycoplasma membrane components responsible for specific binding to the sialoglycoprotein receptors on the erythrocytes.

  15. Coating nanofiber scaffolds with beta cell membrane to promote cell proliferation and function

    NASA Astrophysics Data System (ADS)

    Chen, Wansong; Zhang, Qiangzhe; Luk, Brian T.; Fang, Ronnie H.; Liu, Younian; Gao, Weiwei; Zhang, Liangfang

    2016-05-01

    The cell membrane cloaking technique has emerged as an intriguing strategy in nanomaterial functionalization. Coating synthetic nanostructures with natural cell membranes bestows the nanostructures with unique cell surface antigens and functions. Previous studies have focused primarily on development of cell membrane-coated spherical nanoparticles and the uses thereof. Herein, we attempt to extend the cell membrane cloaking technique to nanofibers, a class of functional nanomaterials that are drastically different from nanoparticles in terms of dimensional and mechanophysical characteristics. Using pancreatic beta cells as a model cell line, we demonstrate successful preparation of cell membrane-coated nanofibers and validate that the modified nanofibers possess an antigenic exterior closely resembling that of the source beta cells. When such nanofiber scaffolds are used to culture beta cells, both cell proliferation rate and function are significantly enhanced. Specifically, glucose-dependent insulin secretion from the cells is increased by near five-fold compared with the same beta cells cultured in regular, unmodified nanofiber scaffolds. Overall, coating cell membranes onto nanofibers could add another dimension of flexibility and controllability in harnessing cell membrane functions and offer new opportunities for innovative applications.

  16. Phytosphingosine kills Candida albicans by disrupting its cell membrane.

    PubMed

    Veerman, Enno C I; Valentijn-Benz, Marianne; van't Hof, Wim; Nazmi, Kamran; van Marle, Jan; Amerongen, Arie V Nieuw

    2010-01-01

    The mechanism of action of phytosphingosine (PHS), a member of the sphingosine family which has candidacidal activity when added externally, was investigated. Previously, it has been reported that the fungicidal activity of PHS is based on the induction of caspase-independent apoptosis. In contrast, we found that addition of PHS causes a direct permeabilization of the plasma membrane of yeast, highlighted by the influx of the membrane probe propidium iodide, and the efflux of small molecules (i.e., adenine nucleotides) as well as large cellular constituents such as proteins. Freeze-fracture electron microscopy revealed that PHS treatment causes severe damage of the plasma membrane of the cell, which seems to have lost its integrity completely. We also found that PHS reverts the azide-induced insensitivity to histatin 5 (Hst5) of Candida albicans. In a previous study, we had found that the decreased sensitivity to Hst5 of energy-depleted cells is due to rigidification of the plasma membrane, which could be reverted by the membrane fluidizer benzyl alcohol. In line with the increased membrane permeabilization and ultrastructural damage, this reversal of the azide-induced insensitivity by PHS also points to a direct interaction between PHS and the cytoplasmic membrane of C. albicans.

  17. Mechanical degradation of fuel cell membranes under fatigue fracture tests

    NASA Astrophysics Data System (ADS)

    Khorasany, Ramin M. H.; Sadeghi Alavijeh, Alireza; Kjeang, Erik; Wang, G. G.; Rajapakse, R. K. N. D.

    2015-01-01

    The effects of cyclic stresses on the fatigue and mechanical stability of perfluorosulfonic acid (PFSA) membranes are experimentally investigated under standard fuel cell conditions. The experiments are conducted ex-situ by subjecting membrane specimens to cyclic uniaxial tension at controlled temperature and relative humidity. The fatigue lifetime is measured in terms of the number of cycles until ultimate fracture. The results indicate that the membrane fatigue lifetime is a strong function of the applied stress, temperature, and relative humidity. The fatigue life increases exponentially with reduced stresses in all cases. The effect of temperature is found to be more significant than that of humidity, with reduced fatigue life at high temperatures. The maximum membrane strain at fracture is determined to decrease exponentially with increasing membrane lifetime. At a given fatigue life, a membrane exposed to fuel cell conditions is shown to accommodate more plastic strain before fracture than one exposed to room conditions. Overall, the proposed ex-situ membrane fatigue experiment can be utilized to benchmark the fatigue lifetime of new materials in a fraction of the time and cost associated with conventional in-situ accelerated stress testing methods.

  18. Epidermal cells adhere preferentially to type IV (basement membrane) collagen

    PubMed Central

    1979-01-01

    Epidermal cells from adult guinea pig skin attach and differentiate preferentially on substrates of type IV (basement membrane) collagen, compared to those of types I--III collagen. In contrast, guinea pig dermal fibroblasts attach equally well to all four collagen substrates. Fibronectin mediates the attachment of fibroblasts but not of epidermal cells to collagen. PMID:422650

  19. Membrane proteins of dense lysosomes from Chinese hamster ovary cells

    SciTech Connect

    Chance, S.C.

    1987-01-01

    In this work membrane proteins from lysosomes were studied in order to gain more information on the biogenesis and intracellular sorting of this class of membrane proteins. Membrane proteins were isolated from a purified population of lysosomes. These proteins were then examined for various co- and post-translational modifications which could serve as potential intracellular sorting signals. Biochemical analysis using marker enzymatic activities detected no plasma membrane, Golgi, endoplasmic reticulum, peroxisomes, mitochondria, or cytosol. Analysis after incorporation of ({sup 3}H)thymidine or ({sup 3}H)uridine detected no nuclei or ribosomes. A fraction containing integral membrane proteins was obtained from the dense lysosomes by extraction with Triton X-114. Twenty-three polypeptides which incorporated both ({sup 35}S)methionine and ({sup 3}H)leucine were detected by SDS PAGE in this membrane fraction, and ranged in molecular weight from 30-130 kDa. After incorporation by cells of various radioactive metabolic precursors, the membrane fraction from dense lysosomes was examined and was found to be enriched in mannose, galactose, fucose, palmitate, myristate, and sulfate, but was depleted in phosphate. The membrane fraction from dense lysosomes was then analyzed by SDS PAGE to determine the apparent molecular weights of modified polypepties.

  20. Numerical modeling transport phenomena in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Suh, DongMyung

    To study the coupled phenomena occurring in proton exchange membrane fuel cells, a two-phase, one-dimensional, non-isothermal model is developed in the chapter 1. The model includes water phase change, proton transport in the membrane and electro-osmotic effect. The thinnest, but most complex layer in the membrane electrode assembly, catalyst layer, is considered an interfacial boundary between the gas diffusion layer and the membrane. Mass and heat transfer and electro-chemical reaction through the catalyst layer are formulated into equations, which are applied to boundary conditions for the gas diffusion layer and the membrane. Detail accounts of the boundary equations and the numerical solving procedure used in this work are given. The polarization curve is calculated at different oxygen pressures and compared with the experimental results. When the operating condition is changed along the polarization curve, the change of physicochemical variables in the membrane electrode assembly is studied. In particular, the over-potential diagram presents the usage of the electrochemical energy at each layer of the membrane electrode assembly. Humidity in supplying gases is one of the most important factors to consider for improving the performance of PEMFE. Both high and low humidity conditions can result in a deteriorating cell performance. The effect of humidity on the cell performance is studied in the chapter 2. First, a numerical model based on computational fluid dynamics is developed. Second, the cell performances are simulated, when the relative humidity is changed from 0% to 100% in the anode and the cathode channel. The simulation results show how humidity in the reactant gases affects the water content distribution in the membrane, the over-potential at the catalyst layers and eventually the cell performance. In particular, the rapid enhancement in the cell performance caused by self-hydrating membrane is captured by the simulation. Fully humidifying either H2

  1. Scalable nanostructured membranes for solid-oxide fuel cells.

    PubMed

    Tsuchiya, Masaru; Lai, Bo-Kuai; Ramanathan, Shriram

    2011-05-01

    The use of oxide fuel cells and other solid-state ionic devices in energy applications is limited by their requirement for elevated operating temperatures, typically above 800°C (ref. 1). Thin-film membranes allow low-temperature operation by reducing the ohmic resistance of the electrolytes. However, although proof-of-concept thin-film devices have been demonstrated, scaling up remains a significant challenge because large-area membranes less than ~ 100 nm thick are susceptible to mechanical failure. Here, we report that nanoscale yttria-stabilized zirconia membranes with lateral dimensions on the scale of millimetres or centimetres can be made thermomechanically stable by depositing metallic grids on them to function as mechanical supports. We combine such a membrane with a nanostructured dense oxide cathode to make a thin-film solid-oxide fuel cell that can achieve a power density of 155 mW cm⁻² at 510 °C. We also report a total power output of more than 20 mW from a single fuel-cell chip. Our large-area membranes could also be relevant to electrochemical energy applications such as gas separation, hydrogen production and permeation membranes.

  2. Performance equations for a polymer electrolyte membrane fuel cell with unsaturated cathode feed

    NASA Astrophysics Data System (ADS)

    Hsuen, Hsiao-Kuo; Yin, Ken-Ming

    A mathematical formulation for the cathode of a membrane electrode assembly of a polymer electrolyte membrane fuel cell is proposed, in which the effect of unsaturated vapor feed in the cathode is considered. This mechanistic model formulates the water saturation front within the gas diffusion layer with an explicit analytical expression as a function of operating conditions. The multi-phase flows of gaseous species and liquid water are correlated with the established capillary pressure equilibrium in the medium. In addition, less than fully hydrated water contents in the polymer electrolyte and catalyst layers are considered, and are integrated with the relevant liquid and vapor transfers in the gas diffusion layer. The developed performance equations take into account the influences of all pertinent material properties on cell performance using first principles. The mathematical approach is logical and concise in terms of revealing the underlying physical significance in comparison with many other empirical data fitting models.

  3. Understanding the transport processes in polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Cheah, May Jean

    Polymer electrolyte membrane (PEM) fuel cells are energy conversion devices suitable for automotive, stationary and portable applications. An engineering challenge that is hindering the widespread use of PEM fuel cells is the water management issue, where either a lack of water (resulting in membrane dehydration) or an excess accumulation of liquid water (resulting in fuel cell flooding) critically reduces the PEM fuel cell performance. The water management issue is addressed by this dissertation through the study of three transport processes occurring in PEM fuel cells. Water transport within the membrane is a combination of water diffusion down the water activity gradient and the dragging of water molecules by protons when there is a proton current, in a phenomenon termed electro-osmotic drag, EOD. The impact of water diffusion and EOD on the water flux across the membrane is reduced due to water transport resistance at the vapor/membrane interface. The redistribution of water inside the membrane by EOD causes an overall increase in the membrane resistance that regulates the current and thus EOD, thereby preventing membrane dehydration. Liquid water transport in the PEM fuel cell flow channel was examined at different gas flow regimes. At low gas Reynolds numbers, drops transitioned into slugs that are subsequently pushed out of the flow channel by the gas flow. The slug volume is dependent on the geometric shape, the surface wettability and the orientation (with respect to gravity) of the flow channel. The differential pressure required for slug motion primarily depends on the interfacial forces acting along the contact lines at the front and the back of the slug. At high gas Reynolds number, water is removed as a film or as drops depending on the flow channel surface wettability. The shape of growing drops at low and high Reynolds number can be described by a simple interfacial energy minimization model. Under flooding conditions, the fuel cell local current

  4. Accumulation of Multipotent Progenitor Cells on Polymethylpentene Membranes During Extracorporeal Membrane Oxygenation.

    PubMed

    Lehle, Karla; Friedl, Lucas; Wilm, Julius; Philipp, Alois; Müller, Thomas; Lubnow, Matthias; Schmid, Christof

    2016-06-01

    Multipotent progenitor cells were mobilized during pediatric extracorporeal membrane oxygenation (ECMO). We hypothesize that these cells also adhered onto polymethylpentene (PMP) fibers within the membrane oxygenator (MO) during adult ECMO support. Mononuclear cells were removed from the surface of explanted PMP-MOs (n = 16). Endothelial-like outgrowth and mesenchymal-like cells were characterized by flow cytometric analysis using different surface markers. Spindle-shaped attaching cells were identified early, but without proliferative activity. After long-term cultivation palisading type or cobblestone-type outgrowth cells with high proliferative activity appeared and were characterized as (i) leukocytoid CD45+/CD31+ (CD133+/VEGFR-II+/CD90+/CD14+/CD146dim/CD105dim); (ii) endothelial-like CD45-/CD31+ (VEGF-RII+/CD146+/CD105+/CD133-/CD14-/CD90-); and (iii) mesenchymal-like cells CD45-/CD31- (CD105+/CD90+/CD133dim/VEGFR-II-/CD146-/CD14-). The distribution of the cell populations depended on the MO and cultivation time. Endothelial-like cells formed capillary-like structures and did uptake Dil-acetylated low-density lipoprotein. Endothelial- and mesenchymal-like cells adhered on the surface of PMP-MOs. Further research is needed to identify the clinical relevance of these cells.

  5. Corona discharge in electroporation of cell membranes

    NASA Astrophysics Data System (ADS)

    Cramariuc, R.; Tudorache, A.; Popa, M. E.; Branduse, E.; Nisiparu, L.; Mitelut, A.; Turtoi, M. O.; Fotescu, L.

    2008-12-01

    The objective of the present work is to demonstrate that electrical corona discharge is very efficient in cellular membrane electroporation due to current pulses with sharp front (2-5 ns) and to the fact that corona discharge is associated with UV radiation and micro particles emission. A comparison between DC and AC at 800 Hz and a special waveform to corona application is presented. The comparison is analyzed by means of applying all these in the maceration process (electroplasmolysis) of red wine production and in the processes of different types of the microbes.

  6. Development of membrane electrode assembly for high temperature proton exchange membrane fuel cell by catalyst coating membrane method

    NASA Astrophysics Data System (ADS)

    Liang, Huagen; Su, Huaneng; Pollet, Bruno G.; Pasupathi, Sivakumar

    2015-08-01

    Membrane electrode assembly (MEA), which contains cathode and anode catalytic layer, gas diffusion layers (GDL) and electrolyte membrane, is the key unit of a PEMFC. An attempt to develop MEA for ABPBI membrane based high temperature (HT) PEMFC is conducted in this work by catalyst coating membrane (CCM) method. The structure and performance of the MEA are examined by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and I-V curve. Effects of the CCM preparation method, Pt loading and binder type are investigated for the optimization of the single cell performance. Under 160 °C and atmospheric pressure, the peak power density of the MEA, with Pt loading of 0.5 mg cm-2 and 0.3 mg cm-2 for the cathode and the anode, can reach 277 mW cm-2, while a current density of 620 A cm-2 is delivered at the working voltage of 0.4 V. The MEA prepared by CCM method shows good stability operating in a short term durability test: the cell voltage maintained at ∼0.45 V without obvious drop when operated at a constant current density of 300 mA cm-2 and 160 °C under ambient pressure for 140 h.

  7. Resolving the challenge of measuring ligand binding to membrane proteins by combining analytical ultracentrifugation and light scattering photometry.

    PubMed

    Doran, J D; Mohanty, A K; Fox, T

    2012-01-01

    Membrane proteins are attractive therapeutic targets, however the presence of detergents complicates biophysical binding measurements. Difficulties in determining quantitative dissociation constants for problematic membrane proteins were addressed by combining analytical ultracentrifugation and classical light scattering techniques. Validation of the algorithm used to calculate dissociation constants from sedimentation equilibrium experiments was demonstrated by analyzing binding data of the inhibitor Y-27632 to rho-kinase (ROCK). Kd's of 1.3 ± 0.7 and 52 ± 27 µM were calculated for ROCK constructs (S6-R415) and (M71-E379) respectively, consistent with previously published Ki's of 1.4 ± 0.1 and > 30 µM. Extension of the algorithm to membrane proteins required the collection of light scattering data to determine the partial specific volume, ν, for the membrane protein-detergent complex. Vitamin B12 binding to the bacterial protein btuB in octyl β-D-glucopyranoside (β-OG) illustrates the applicability of the method. A ν of 0.781 ml/g was determined for the btuB-β-OG complex. Incorporating this value into the algorithm generated a Kd of 7.0 ± 1.5 µM for the vitamin B12-btuB affinity. A Kd of 9.7 ± 2.7 µM was determined by equilibrium dialysis under similar experimental conditions. Successfully applying AUC to quantifying small-molecule ligand affinities to membrane proteins represents a significant advance to the field.

  8. Extensive determination of glycan heterogeneity reveals an unusual abundance of high mannose glycans in enriched plasma membranes of human embryonic stem cells.

    PubMed

    An, Hyun Joo; Gip, Phung; Kim, Jaehan; Wu, Shuai; Park, Kun Wook; McVaugh, Cheryl T; Schaffer, David V; Bertozzi, Carolyn R; Lebrilla, Carlito B

    2012-04-01

    Most cell membrane proteins are known or predicted to be glycosylated in eukaryotic organisms, where surface glycans are essential in many biological processes including cell development and differentiation. Nonetheless, the glycosylation on cell membranes remains not well characterized because of the lack of sensitive analytical methods. This study introduces a technique for the rapid profiling and quantitation of N- and O-glycans on cell membranes using membrane enrichment and nanoflow liquid chromatography/mass spectrometry of native structures. Using this new method, the glycome analysis of cell membranes isolated from human embryonic stem cells and somatic cell lines was performed. Human embryonic stem cells were found to have high levels of high mannose glycans, which contrasts with IMR-90 fibroblasts and a human normal breast cell line, where complex glycans are by far the most abundant and high mannose glycans are minor components. O-Glycosylation affects relatively minor components of cell surfaces. To verify the quantitation and localization of glycans on the human embryonic stem cell membranes, flow cytometry and immunocytochemistry were performed. Proteomics analyses were also performed and confirmed enrichment of plasma membrane proteins with some contamination from endoplasmic reticulum and other membranes. These findings suggest that high mannose glycans are the major component of cell surface glycosylation with even terminal glucoses. High mannose glycans are not commonly presented on the surfaces of mammalian cells or in serum yet may play important roles in stem cell biology. The results also mean that distinguishing stem cells from other mammalian cells may be facilitated by the major difference in the glycosylation of the cell membrane. The deep structural analysis enabled by this new method will enable future mechanistic studies on the biological significance of high mannose glycans on stem cell membranes and provide a general tool to examine

  9. Adenosine deaminase in cell transformation. Biophysical manifestation of membrane dynamics.

    PubMed

    Porat, N; Gill, D; Parola, A H

    1988-10-15

    Cell transformation is associated with a dramatic collapse of a graphic fingerprint characteristic of normal cells, as measured by phase fluorimetry. This is demonstrated on adenosine deaminase (ADA, EC 3.5.4.4), an established malignancy marker. ADA activity is known to decrease markedly in chick embryo fibroblasts (CEF) transformed by Rous sarcoma virus. The high affinity between the catalytic small subunit ADA (SS-ADA) and its membranal complexing protein (ADCP) (which abounds on the plasma membrane of CEF) allowed the hybridization of fluorescent labeled SS-ADA with native ADCP on CEF. Multifrequency differential phase fluorimetry responded remarkably to the state of this hybrid membrane protein. The transformation process is shown to have led to increased membrane fluidity and rotational mobility of ADCP as well as to its reduced availability to SS-ADA binding. The hypothesis of protein vertical sinking into the lipid core of the membrane is now given support by our spectroscopic data. Additional models are considered. A regulatory role is thus suggested for the complexing protein, which may also account for (a) reduced ADA activity in transformed cells and (b) detachment, exclusive to normal cells, upon addition of SS-ADA in excess.

  10. Electrochemical detection of intracellular and cell membrane redox systems in Saccharomyces cerevisiae

    NASA Astrophysics Data System (ADS)

    Rawson, Frankie J.; Downard, Alison J.; Baronian, Keith H.

    2014-06-01

    Redox mediators can interact with eukaryote cells at a number of different cell locations. While cell membrane redox centres are easily accessible, the redox centres of catabolism are situated within the cytoplasm and mitochondria and can be difficult to access. We have systematically investigated the interaction of thirteen commonly used lipophilic and hydrophilic mediators with the yeast Saccharomyces cerevisiae. A double mediator system is used in which ferricyanide is the final electron acceptor (the reporter mediator). After incubation of cells with mediators, steady state voltammetry of the ferri/ferrocyanide redox couple allows quantitation of the amount of mediator reduced by the cells. The plateau current at 425 mV vs Ag/AgCl gives the analytical signal. The results show that five of the mediators interact with at least three different trans Plasma Membrane Electron Transport systems (tPMETs), and that four mediators cross the plasma membrane to interact with cytoplasmic and mitochondrial redox molecules. Four of the mediators inhibit electron transfer from S. cerevisiae. Catabolic inhibitors were used to locate the cellular source of electrons for three of the mediators.

  11. Electrochemical detection of intracellular and cell membrane redox systems in Saccharomyces cerevisiae

    PubMed Central

    Rawson, Frankie J.; Downard, Alison J.; Baronian, Keith H.

    2014-01-01

    Redox mediators can interact with eukaryote cells at a number of different cell locations. While cell membrane redox centres are easily accessible, the redox centres of catabolism are situated within the cytoplasm and mitochondria and can be difficult to access. We have systematically investigated the interaction of thirteen commonly used lipophilic and hydrophilic mediators with the yeast Saccharomyces cerevisiae. A double mediator system is used in which ferricyanide is the final electron acceptor (the reporter mediator). After incubation of cells with mediators, steady state voltammetry of the ferri/ferrocyanide redox couple allows quantitation of the amount of mediator reduced by the cells. The plateau current at 425 mV vs Ag/AgCl gives the analytical signal. The results show that five of the mediators interact with at least three different trans Plasma Membrane Electron Transport systems (tPMETs), and that four mediators cross the plasma membrane to interact with cytoplasmic and mitochondrial redox molecules. Four of the mediators inhibit electron transfer from S. cerevisiae. Catabolic inhibitors were used to locate the cellular source of electrons for three of the mediators. PMID:24910017

  12. Boron Induces Hyperpolarization of Sunflower Root Cell Membranes and Increases Membrane Permeability to K+1

    PubMed Central

    Schon, Mary K.; Novacky, Anton; Blevins, Dale G.

    1990-01-01

    Although many studies have alluded to a role for boron (B) in membrane function, there is little evidence for a direct effect of B on the plasmalemma of higher plant cells. These studies were conducted to demonstrate, by electrophysiological techniques, a direct effect of B on the membrane potential (Em) of sunflower (Helianthus annuus [L.], cv Mammoth Grey Stripe) root tip cells and to determine if the response to B occurs rapidly enough to account for the previously observed effects of B on ion uptake. By inserting a glass microelectrode into an individual cell in the root tip, the Em of the cell was determined in basal salt medium (BSM), pH 6.0. The perfusion solution surrounding the root tissue was then changed to BSM + 50 micromolar H3BO3, pH 6.0. The exposure to B induced a significant plasmalemma hyperpolarization in sunflower root cells within 20 minutes. After just 3 minutes of exposure to B, the change in Em was already significantly different from the negligible change in Em observed over time in root cells never exposed to B. Membrane hyperpolarization could be caused by a stimulation of the proton pump or by a change in the conductance of one or more permeable ions. Since B has been shown to affect K+ uptake by plants, the electrophysiological techniques described above were used to determine if B has an effect on membrane permeability to K+, and could thereby lead to an increased diffusion potential. When sunflower root tips were pretreated in 50 micromolar B for 2 hours, cell membranes exhibited a significantly greater depolarization with each 10-fold increase in external [K+] than minus-B cells. Subsequent studies demonstrated that the depolarization due to increased external [K+] was also significantly greater when tissue was exposed to B at the same time as the 10-fold increase in [K+], indicating that the effect of B on K+ permeability was immediate. Analysis of sunflower root tips demonstrated that treatment in 50 micromolar B caused a

  13. Analytical method development using functionalized polysulfone membranes for the determination of chlorinated hydrocarbons in water.

    PubMed

    Nuhu, Abdulmumin A; Basheer, Chanbasha; Abu-Thabit, Nedal Y; Alhooshani, Khalid; Al-Arfaj, Abdul Rahman

    2011-12-15

    In this study, functionalized polysulfone membrane has been utilized as a sorbent for the extraction of chlorinated hydrocarbons (CHCs) in water samples. Two different functionalized polysulfones (i) phosphonic acid functionalized polysulfone (PPSU-A) with different forms (cross-linked and non cross-linked) membranes and (ii) phosphonic ester functionalized polysulfone (PPSU-E) with different forms (cross-linked and non cross-linked) were evaluated for the extraction of CHCs in water. A 10 ml of spiked water sample was extracted with 50mg piece of the functionalized membrane. After extraction, the membrane was desorbed by organic solvent and the extract was analyzed by gas chromatography-mass spectrometry. Eight CHCs, 1,3,5-trichlorobenzene (1,3,5-TCB), 1,2,3-trichlorobenzene (1,2,3-TCB), 1,1,2,3,4,4-hexachloro-1,3-butadiene (HCBD), 1,2,4-trichloro-3-methylbenzene (TCMB), 1,2,3,4-tetrachlorobenzene (1,2,3,4-TeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), pentachlorobenzene (PeCB) and hexachlorobenzene (HCB) were used as model compounds. Experimental parameters such as extraction time, desorption time, types of polymer membrane as well the nature of desorption solvent were optimized. Using optimum extraction conditions calibration curves were linear with coefficients of determination between 0.9954 and 0.9999 over wide range of concentrations (0.05-100 μgl(-1)). The method detection limits (at a signal-to-noise ratio of 3) were in the range of 0.4-3.9 ng l(-1). The proposed method was evaluated for the determination of CHCs in drinking water samples.

  14. A membrane bending model of outer hair cell electromotility.

    PubMed Central

    Raphael, R M; Popel, A S; Brownell, W E

    2000-01-01

    We propose a new mechanism for outer hair cell electromotility based on electrically induced localized changes in the curvature of the plasma membrane (flexoelectricity). Electromechanical coupling in the cell's lateral wall is modeled in terms of linear constitutive equations for a flexoelectric membrane and then extended to nonlinear coupling based on the Langevin function. The Langevin function, which describes the fraction of dipoles aligned with an applied electric field, is shown to be capable of predicting the electromotility voltage displacement function. We calculate the electrical and mechanical contributions to the force balance and show that the model is consistent with experimentally measured values for electromechanical properties. The model rationalizes several experimental observations associated with outer hair cell electromotility and provides for constant surface area of the plasma membrane. The model accounts for the isometric force generated by the cell and explains the observation that the disruption of spectrin by diamide reduces force generation in the cell. We discuss the relation of this mechanism to other proposed models of outer hair cell electromotility. Our analysis suggests that rotation of membrane dipoles and the accompanying mechanical deformation may be the molecular mechanism of electromotility. PMID:10827967

  15. Transport parameters in the human red cell membrane: solute-membrane interactions of amides and ureas.

    PubMed

    Toon, M R; Solomon, A K

    1991-04-02

    We have studied the permeability of a series of hydrophilic amides and ureas through the red cell membrane by determining the three phenomenological coefficients which describe solute-membrane interaction: the hydraulic permeability (Lp), the phenomenological permeability coefficient (omega i) and the reflection coefficient (sigma i). In 55 experiments on nine solutes, we have determined that the reflection coefficient (after a small correction for solute permeation by membrane dissolution) is significantly less than 1.0 (P less than 0.003, t-test), which provides very strong evidence that solute and water fluxes are coupled as they cross the red cell membrane. It is proposed that the aqueous channel is a tripartite assembly, comprising H-bond exchange regions at both faces of the membrane, joined by a narrower sieve-specific region which crosses the lipid. The solutes bind to the H-bond exchange regions to exchange their solvation shell with the H-bonds of the channel; the existence of these regions is confirmed by the finding that the permeation of all the amides and ureas requires binding to well-characterized sites with Km values of 0.1-0.5 M. The sieve-specific regions provide the steric restraints which govern the passage of the solutes according to their size; their existence is shown by the findings that: (1) the reflection coefficient (actually the function [1-corrected sigma i]) is linearly dependent upon the solute molecular diameter; and (2) the permeability coefficient is linearly dependent upon solute molar volume. These several observations, taken together, provide strong arguments which lead to the conclusion that the amides and urea cross the red cell membrane in an aqueous pore.

  16. Plasma membrane associated membranes (PAM) from Jurkat cells contain STIM1 protein is PAM involved in the capacitative calcium entry?

    PubMed

    Kozieł, Katarzyna; Lebiedzinska, Magdalena; Szabadkai, Gyorgy; Onopiuk, Marta; Brutkowski, Wojciech; Wierzbicka, Katarzyna; Wilczyński, Grzegorz; Pinton, Paolo; Duszyński, Jerzy; Zabłocki, Krzysztof; Wieckowski, Mariusz R

    2009-12-01

    A proper cooperation between the plasma membrane, the endoplasmic reticulum and the mitochondria seems to be essential for numerous cellular processes involved in Ca(2+) signalling and maintenance of Ca(2+) homeostasis. A presence of microsomal and mitochondrial proteins together with those characteristic for the plasma membrane in the fraction of the plasma membrane associated membranes (PAM) indicates a formation of stabile interactions between these three structures. We isolated the plasma membrane associated membranes from Jurkat cells and found its significant enrichment in the plasma membrane markers including plasma membrane Ca(2+)-ATPase, Na(+), K(+)-ATPase and CD3 as well as sarco/endoplasmic reticulum Ca(2+) ATPase as a marker of the endoplasmic reticulum membranes. In addition, two proteins involved in the store-operated Ca(2+) entry, Orai1 located in the plasma membrane and an endoplasmic reticulum protein STIM1 were found in this fraction. Furthermore, we observed a rearrangement of STIM1-containing protein complexes isolated from Jurkat cells undergoing stimulation by thapsigargin. We suggest that the inter-membrane compartment composed of the plasma membrane and the endoplasmic reticulum, and isolated as a stabile plasma membrane associated membranes fraction, might be involved in the store-operated Ca(2+) entry, and their formation and rebuilding have an important regulatory role in cellular Ca(2+) homeostasis.

  17. Membrane Mechanics of Endocytosis in Cells with Turgor

    PubMed Central

    Dmitrieff, Serge; Nédélec, François

    2015-01-01

    Endocytosis is an essential process by which cells internalize a piece of plasma membrane and material from the outside. In cells with turgor, pressure opposes membrane deformations, and increases the amount of force that has to be generated by the endocytic machinery. To determine this force, and calculate the shape of the membrane, we used physical theory to model an elastic surface under pressure. Accurate fits of experimental profiles are obtained assuming that the coated membrane is highly rigid and preferentially curved at the endocytic site. The forces required from the actin machinery peaks at the onset of deformation, indicating that once invagination has been initiated, endocytosis is unlikely to stall before completion. Coat proteins do not lower the initiation force but may affect the process by the curvature they induce. In the presence of isotropic curvature inducers, pulling the tip of the invagination can trigger the formation of a neck at the base of the invagination. Hence direct neck constriction by actin may not be required, while its pulling role is essential. Finally, the theory shows that anisotropic curvature effectors stabilize membrane invaginations, and the loss of crescent-shaped BAR domain proteins such as Rvs167 could therefore trigger membrane scission. PMID:26517669

  18. Membrane Mechanics of Endocytosis in Cells with Turgor.

    PubMed

    Dmitrieff, Serge; Nédélec, François

    2015-10-01

    Endocytosis is an essential process by which cells internalize a piece of plasma membrane and material from the outside. In cells with turgor, pressure opposes membrane deformations, and increases the amount of force that has to be generated by the endocytic machinery. To determine this force, and calculate the shape of the membrane, we used physical theory to model an elastic surface under pressure. Accurate fits of experimental profiles are obtained assuming that the coated membrane is highly rigid and preferentially curved at the endocytic site. The forces required from the actin machinery peaks at the onset of deformation, indicating that once invagination has been initiated, endocytosis is unlikely to stall before completion. Coat proteins do not lower the initiation force but may affect the process by the curvature they induce. In the presence of isotropic curvature inducers, pulling the tip of the invagination can trigger the formation of a neck at the base of the invagination. Hence direct neck constriction by actin may not be required, while its pulling role is essential. Finally, the theory shows that anisotropic curvature effectors stabilize membrane invaginations, and the loss of crescent-shaped BAR domain proteins such as Rvs167 could therefore trigger membrane scission.

  19. Red Blood Cell Membrane-Cloaked Nanoparticles For Drug Delivery

    NASA Astrophysics Data System (ADS)

    Carpenter, Cody Westcott

    Herein we describe the development of the Red Blood Cell coated nanoparticle, RBC-NP. Purified natural erythrocyte membrane is used to coat drug-loaded poly(lacticco-glycolic acid) (PLGA). Synthetic PLGA co-polymer is biocompatible and biodegradable and has already received US FDA approval for drug-delivery and diagnostics. This work looks specifically at the retention of immunosuppressive proteins on RBC-NPs, right-sidedness of natural RBC membranes interfacing with synthetic polymer nanoparticles, sustained and retarded drug release of RBC-NPs as well as further surface modification of RBC-NPs for increased targeting of model cancer cell lines.

  20. Microstructured Electrolyte Membranes to Improve Fuel Cell Performance

    NASA Astrophysics Data System (ADS)

    Wei, Xue

    Fuel cells, with the advantages of high efficiency, low greenhouse gas emission, and long lifetime are a promising technology for both portable power and stationary power sources. The development of efficient electrolyte membranes with high ionic conductivity, good mechanical durability and dense structure at low cost remains a challenge to the commercialization of fuel cells. This thesis focuses on exploring novel composite polymer membranes and ceramic electrolytes with the microstructure engineered to improve performance in direct methanol fuel cells (DMFCs) and solid oxide fuel cells (SOFCs), respectively. Polymer/particle composite membranes hold promise to meet the demands of DMFCs at lower cost. The structure of composite membranes was controlled by aligning proton conducting particles across the membrane thickness under an applied electric field. The field-induced structural changes caused the membranes to display an enhanced water uptake, proton conductivity, and methanol permeability in comparison to membranes prepared without an applied field. Although both methanol permeability and proton conductivity are enhanced by the applied field, the permeability increase is relatively lower than the proton conductivity improvement, which results in enhanced proton/methanol selectivity and improved DMFC performance. Apatite ceramics are a new class of fast ion conductors being studied as alternative SOFC electrolytes in the intermediate temperature range. An electrochemical/hydrothermal deposition method was developed to grow fully dense apatite membranes containing well-developed crystals with c-axis alignment to promote ion conductivity. Hydroxyapatite seed crystals were first deposited onto a metal substrate electrochemically. Subsequent ion substitution during the hydrothermal growth process promoted the formation of dense, fully crystalline films with microstructure optimal for ion transport. The deposition parameters were systematically investigated, such as

  1. New High-Temperature Membranes Developed for Proton Exchange Membrane Fuel Cells

    NASA Technical Reports Server (NTRS)

    Kinder, James D.

    2004-01-01

    Fuel cells are receiving a considerable amount of attention for potential use in a variety of areas, including the automotive industry, commercial power generation, and personal electronics. Research at the NASA Glenn Research Center has focused on the development of fuel cells for use in aerospace power systems for aircraft, unmanned air vehicles, and space transportation systems. These applications require fuel cells with higher power densities and better durability than what is required for nonaerospace uses. In addition, membrane cost is a concern for any fuel cell application. The most widely used membrane materials for proton exchange membrane (PEM) fuel cells are based on sulfonated perfluorinated polyethers, typically Nafion 117, Flemion, or Aciplex. However, these polymers are costly and do not function well at temperatures above 80 C. At higher temperatures, conventional membrane materials dry out and lose their ability to conduct protons, essential for the operation of the fuel cell. Increasing the operating temperature of PEM fuel cells from 80 to 120 C would significantly increase their power densities and enhance their durability by reducing the susceptibility of the electrode catalysts to carbon monoxide poisoning. Glenn's Polymers Branch has focused on developing new, low-cost membranes that can operate at these higher temperatures. A new series of organically modified siloxane (ORMOSIL) polymers were synthesized for use as membrane materials in a high-temperature PEM fuel cell. These polymers have an organic portion that can allow protons to transport through the polymer film and a cross-linked silica network that gives the polymers dimensional stability. These flexible xerogel polymer films are thermally stable, with decomposition onset as high as 380 C. Two types of proton-conducting ORMOSIL films have been produced: (1) NASA-A, which can coordinate many highly acid inorganic salts that facilitate proton conduction and (2) NASA-B, which has been

  2. Highly Water Resistant Anion Exchange Membrane for Fuel Cells.

    PubMed

    Yang, Zhengjin; Hou, Jianqiu; Wang, Xinyu; Wu, Liang; Xu, Tongwen

    2015-07-01

    For anion exchange membranes (AEMs), achieving efficient hydroxide conductivity without excessive hydrophilicity presents a challenge. Hence, new strategies for constructing mechanically strengthened and hydroxide conductive (especially at controlled humidity) membranes are critical for developing better AEMs. Macromolecular modification involving ylide chemistry (Wittig reaction) for the fabrication of novel AEMs with an interpenetrating polymer network structure is reported. The macromolecular modification is cost effective, facile, and based on a one-pot synthesis. AEM water uptake is reduced to 3.6 wt% and a high hydroxide conductivity (69.7 mS cm(-1) , 90 °C) is achieved simultaneously. More importantly, the membrane exhibits similar tensile strength (>35 MPa) and comparable flexibility in both dry and wet states. These AEMs could find further applications within anion exchange membrane fuel cells with low humidity or photoelectric assemblies.

  3. Mapping Cd²⁺-induced membrane permeability changes of single live cells by means of scanning electrochemical microscopy.

    PubMed

    Filice, Fraser P; Li, Michelle S M; Henderson, Jeffrey D; Ding, Zhifeng

    2016-02-18

    Scanning Electrochemical Microscopy (SECM) is a powerful, non-invasive, analytical methodology that can be used to investigate live cell membrane permeability. Depth scan SECM imaging allowed for the generation of 2D current maps of live cells relative to electrode position in the x-z or y-z plane. Depending on resolution, one depth scan image can contain hundreds of probe approach curves (PACs). Individual PACs were obtained by simply extracting vertical cross-sections from the 2D image. These experimental PACs were overlaid onto theoretically generated PACs simulated at specific geometry conditions. Simulations were carried out using 3D models in COMSOL Multiphysics to determine the cell membrane permeability coefficients at different locations on the surface of the cells. Common in literature, theoretical PACs are generated using a 2D axially symmetric geometry. This saves on both compute time and memory utilization. However, due to symmetry limitations of the model, only one experimental PAC right above the cell can be matched with simulated PAC data. Full 3D models in this article were developed for the SECM system of live cells, allowing all experimental PACs over the entire cell to become usable. Cd(2+)-induced membrane permeability changes of single human bladder (T24) cells were investigated at several positions above the cell, displaced from the central axis. The experimental T24 cells under study were incubated with Cd(2+) in varying concentrations. It is experimentally observed that 50 and 100 μM Cd(2+) caused a decrease in membrane permeability, which was uniform across all locations over the cell regardless of Cd(2+) concentration. The Cd(2+) was found to have detrimental effects on the cell, with cells shrinking in size and volume, and the membrane permeability decreasing. A mapping technique for the analysis of the cell membrane permeability under the Cd(2+) stress is realized by the methodology presented.

  4. Lactic acid fermentation in cell-recycle membrane bioreactor.

    PubMed

    Choudhury, B; Swaminathan, T

    2006-02-01

    Traditional lactic acid fermentation suffers from low productivity and low product purity. Cell-recycle fermentation has become one of the methods to obtain high cell density, which results in higher productivity. Lactic acid fermentation was investigated in a cell-recycle membrane bioreactor at higher substrate concentrations of 100 and 120 g/dm3. A maximum cell density of 145 g/dm3 and a maximum productivity of 34 g/(dm3.h) were achieved in cell-recycle fermentation. In spite of complete consumption of substrate, there was a continuous increase in cell density in cell-recycle fermentation. Control of cell density in cell-recycle fermentation was attempted by cell bleeding and reduction in yeast extract concentration.

  5. Membrane patterned by pulsed laser micromachining for proton exchange membrane fuel cell with sputtered ultra-low catalyst loadings

    NASA Astrophysics Data System (ADS)

    Cuynet, S.; Caillard, A.; Kaya-Boussougou, S.; Lecas, T.; Semmar, N.; Bigarré, J.; Buvat, P.; Brault, P.

    2015-12-01

    Proton exchange membranes were nano- and micro-patterned on their cathode side by pressing them against stainless steel molds previously irradiated by a Ti:Sapphire femtosecond laser. The membranes were associated to ultra-low loaded thin catalytic layers (25 μgPt cm-2) prepared by plasma magnetron sputtering. The Pt catalyst was sputtered either on the membrane or on the porous electrode. The fuel cell performance in dry conditions were found to be highly dependent on the morphology of the membrane surface. When nanometric ripples covered by a Pt catalyst were introduced on the surface of the membrane, the fuel cell outperformed the conventional one with a flat membrane. By combining nano- and micro-patterns (nanometric ripples and 11-24 μm deep craters), the performance of the cells was clearly enhanced. The maximum power density achieved by the fuel cell was multiplied by a factor of 3.6 (at 50 °C and 3 bar): 438 mW cm-2 vs 122 mW cm-2. This improvement is due to high catalyst utilization with a high membrane conductivity. When Pt is sputtered on the porous electrode (and not on the membrane), the contribution of the patterned membrane to the fuel cell efficiency was less significant, except in the presence of nanometric ripples. This result suggests that the patterning of the membrane must be consistent with the way the catalyst is synthesized, on the membrane or on the porous electrode.

  6. Radiation effects on membranes - 1. Cellular permeability and cell survival

    SciTech Connect

    Khare, S.; Jayakumar, A.; Trivedi, A.; Kesavan, P.C.; Prasad, R.

    1982-05-01

    The effect of various doses of ..gamma.. radiation (5-60 krad) on the membrane permeability and cell survival of Candida albicans, a pathogenic yeast, was investigated. A reduction in the cell survival and in the accumulation of amino acids (proline, glycine, lysine, and glutamic acid) was observed following irradiation. The rate of oxygen uptake, which is often associated with transport, was also reduced. There was no damage to available sulfhydryl groups following the exposure of cells to various doses of ..gamma.. radiation. The membrane lipid composition of C. albicans cells can be altered by growing them in alkanes of varying chain lengths. The effects of such altered lipid composition on radiosensitivity was examined. It was observed that C. albicans cells with altered lipid content acquire resistance to ..gamma.. radiation.

  7. Preparation, Characterization, and Analytical Application of Ramipril Membrane-Based Ion-Selective Electrode

    PubMed Central

    Arida, Hassan; Ahmed, Mona; Ali, Abdallah

    2009-01-01

    The fabrication and electrochemical evaluation of two PVC membrane-based Ion-Selective electrodes responsive for ramipril drug have been proposed. The sensitive membranes were prepared using ramipril-phosphomolibdate and ramipril-tetraphenylborate ion-pair complexes as electroactive sensing materials in plasticized PVC support. The electrodes based on these materials provide near-Nernestian response (sensitivity of 53 ± 0.5–54 ± 0.5 mV/concentration decade) covering the concentration range of 1.0 × 10−2–1.0 × 10−5 mol L−1 with a detection limit of 3.0 × 10−6–4.0 × 10−6 mol L−1. The suggested electrodes have been successfully used in the determination of ramipril drug in some pharmaceutical formulations using direct potentiometry with average recovery of >96% and mean standard deviation of <3% (n = 5). PMID:20140081

  8. Evidence for Bidirectional Endocannabinoid Transport across Cell Membranes*

    PubMed Central

    Chicca, Andrea; Marazzi, Janine; Nicolussi, Simon; Gertsch, Jürg

    2012-01-01

    Despite extensive research on the trafficking of anandamide (AEA) across cell membranes, little is known about the membrane transport of other endocannabinoids, such as 2-arachidonoylglycerol (2-AG). Previous studies have provided data both in favor and against a cell membrane carrier-mediated transport of endocannabinoids, using different methodological approaches. Because AEA and 2-AG undergo rapid and almost complete intracellular hydrolysis, we employed a combination of radioligand assays and absolute quantification of cellular and extracellular endocannabinoid levels. In human U937 leukemia cells, 100 nm AEA and 1 μm 2-AG were taken up through a fast and saturable process, reaching a plateau after 5 min. Employing differential pharmacological blockage of endocannabinoid uptake, breakdown, and interaction with intracellular binding proteins, we show that eicosanoid endocannabinoids harboring an arachidonoyl chain compete for a common membrane target that regulates their transport, whereas other N-acylethanolamines did not interfere with AEA and 2-AG uptake. By combining fatty acid amide hydrolase or monoacyl glycerol lipase inhibitors with hydrolase-inactive concentrations of the AEA transport inhibitors UCM707 (1 μm) and OMDM-2 (5 μm), a functional synergism on cellular AEA and 2-AG uptake was observed. Intriguingly, structurally unrelated AEA uptake inhibitors also blocked the cellular release of AEA and 2-AG. We show, for the first time, that UCM707 and OMDM-2 inhibit the bidirectional movement of AEA and 2-AG across cell membranes. Our findings suggest that a putative endocannabinoid cell membrane transporter controls the cellular AEA and 2-AG trafficking and metabolism. PMID:22879589

  9. Cell cycle dependent changes in the plasma membrane organization of mammalian cells.

    PubMed

    Denz, Manuela; Chiantia, Salvatore; Herrmann, Andreas; Mueller, Peter; Korte, Thomas; Schwarzer, Roland

    2017-03-01

    Lipid membranes are major structural elements of all eukaryotic and prokaryotic organisms. Although many aspects of their biology have been studied extensively, their dynamics and lateral heterogeneity are still not fully understood. Recently, we observed a cell-to-cell variability in the plasma membrane organization of CHO-K1 cells (Schwarzer et al., 2014). We surmised that cell cycle dependent changes of the individual cells from our unsynchronized cell population account for this phenomenon. In the present study, this hypothesis was tested. To this aim, CHO-K1 cells were arrested in different cell cycle phases by chemical treatments, and the order of their plasma membranes was determined by various fluorescent lipid analogues using fluorescence lifetime imaging microscopy. Our experiments exhibit significant differences in the membrane order of cells arrested in the G2/M or S phase compared to control cells. Our single-cell analysis also enabled the specific selection of mitotic cells, which displayed a significant increase of the membrane order compared to the control. In addition, the lipid raft marker GPImYFP was used to study the lateral organization of cell cycle arrested cells as well as mitotic cells and freely cycling samples. Again, significant differences were found between control and arrested cells and even more pronounced between control and mitotic cells. Our data demonstrate a direct correlation between cell cycle progression and plasma membrane organization, underlining that cell-to-cell heterogeneities of membrane properties have to be taken into account in cellular studies especially at the single-cell level.

  10. Electronic circuit model for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Yu, Dachuan; Yuvarajan, S.

    The proton exchange membrane (PEM) fuel cell is being investigated as an alternate power source for various applications like transportation and emergency power supplies. The paper presents a novel circuit model for a PEM fuel cell that can be used to design and analyze fuel cell power systems. The PSPICE-based model uses bipolar junction transistors (BJTs) and LC elements available in the PSPICE library with some modification. The model includes the phenomena like activation polarization, ohmic polarization, and mass transport effect present in a PEM fuel cell. The static and dynamic characteristics obtained through simulation are compared with experimental results obtained on a commercial fuel cell module.

  11. PIG7 promotes leukemia cell chemosensitivity via lysosomal membrane permeabilization

    PubMed Central

    Niu, Ting; Wu, Yu; Li, Jianjun; Wang, Fangfang; Zheng, Yuhuan; Liu, Ting

    2016-01-01

    PIG7 localizes to lysosomal membrane in leukemia cells. Our previous work has shown that transduction of pig7 into a series of leukemia cell lines did not result in either apoptosis or differentiation of most tested cell lines. Interestingly, it did significantly sensitize these cell lines to chemotherapeutic drugs. Here, we further investigated the mechanism underlying pig7-induced improved sensitivity of acute leukemia cells to chemotherapy. Our results demonstrated that the sensitization effect driven by exogenous pig7 was more effective in drug-resistant leukemia cell lines which had lower endogenous pig7 expression. Overexpression of pig7 did not directly activate the caspase apoptotic pathway, but decreased the lysosomal stability. The expression of pig7 resulted in lysosomal membrane permeabilization (LMP) and lysosomal protease (e.g. cathepsin B, D, L) release. Moreover, we also observed increased reactive oxygen species (ROS) and decreased mitochondrial membrane potential (ΔΨm) induced by pig7. Some autophagy markers such as LC3I/II, ATG5 and Beclin-1, and necroptosis maker MLKL were also stimulated. However, intrinsic antagonism such as serine/cysteine protease inhibitors Spi2A and Cystatin C prevented downstream effectors from triggering leukemia cells, which were only on the “verge of apoptosis”. When combined with chemotherapy, LMP increased and more proteases were released. Once this process was beyond the limit of intrinsic antagonism, it induced programmed cell death cooperatively via caspase-independent and caspase-dependent pathways. PMID:26716897

  12. PIG7 promotes leukemia cell chemosensitivity via lysosomal membrane permeabilization.

    PubMed

    Liu, Jiazhuo; Peng, Leiwen; Niu, Ting; Wu, Yu; Li, Jianjun; Wang, Fangfang; Zheng, Yuhuan; Liu, Ting

    2016-01-26

    PIG7 localizes to lysosomal membrane in leukemia cells. Our previous work has shown that transduction of pig7 into a series of leukemia cell lines did not result in either apoptosis or differentiation of most tested cell lines. Interestingly, it did significantly sensitize these cell lines to chemotherapeutic drugs. Here, we further investigated the mechanism underlying pig7-induced improved sensitivity of acute leukemia cells to chemotherapy. Our results demonstrated that the sensitization effect driven by exogenous pig7 was more effective in drug-resistant leukemia cell lines which had lower endogenous pig7 expression. Overexpression of pig7 did not directly activate the caspase apoptotic pathway, but decreased the lysosomal stability. The expression of pig7 resulted in lysosomal membrane permeabilization (LMP) and lysosomal protease (e.g. cathepsin B, D, L) release. Moreover, we also observed increased reactive oxygen species (ROS) and decreased mitochondrial membrane potential (ΔΨm) induced by pig7. Some autophagy markers such as LC3I/II, ATG5 and Beclin-1, and necroptosis maker MLKL were also stimulated. However, intrinsic antagonism such as serine/cysteine protease inhibitors Spi2A and Cystatin C prevented downstream effectors from triggering leukemia cells, which were only on the "verge of apoptosis". When combined with chemotherapy, LMP increased and more proteases were released. Once this process was beyond the limit of intrinsic antagonism, it induced programmed cell death cooperatively via caspase-independent and caspase-dependent pathways.

  13. Lipids that determine detergent resistance of MDCK cell membrane fractions.

    PubMed

    Manni, Marco M; Cano, Ainara; Alonso, Cristina; Goñi, Félix M

    2015-10-01

    A comparative lipidomic study has been performed of whole Madin-Darby canine kidney epithelial cells and of the detergent-resistant membrane fraction (DRM) obtained after treating the cells with the non-ionic detergent Triton X-100. The DRM were isolated following a standard procedure that is extensively used in cell biology studies. Significant differences were found in the lipid composition of the whole cells and of DRM. The latter were enriched in all the analyzed sphingolipid classes: sphingomyelins, ceramides and hexosylceramides. Diacylglycerols were also preferentially found in DRM. The detergent-resistant fraction was also enriched in saturated over unsaturated fatty acyl chains, and in sn-1 acyl chains containing 16 carbon atoms, over the longer and shorter ones. The glycerophospholipid species phosphatidylethanolamines and phosphatidylinositols, that were mainly unsaturated, did not show a preference for DRM. Phosphatidylcholines were an intermediate case: the saturated, but not the unsaturated species were found preferentially in DRM. The question remains on whether these DRM, recovered from detergent-membrane mixtures by floatation over a sucrose gradient, really correspond to membrane domains existing in the cell membrane prior to detergent treatment.

  14. The role of cell membranes in the regulation of lignification in pine cells

    NASA Technical Reports Server (NTRS)

    Hendrix, D. L.

    1978-01-01

    The identity of pine cell membranes bearing PAL enzyme activity, the isolation of a plasma membrane preparation from pine cells for testing as a regulatory barrier in lignification, and the measurement of the geopotential effect in pine stems are presented. A model to describe and predict the interaction of gravity and lignification of higher plants was developed.

  15. Membrane with internal passages to permit fluid flow and an electrochemical cell containing the same

    NASA Technical Reports Server (NTRS)

    Cisar, Alan J. (Inventor); Gonzalez-Martin, Anuncia (Inventor); Hitchens, G. Duncan (Inventor); Murphy, Oliver J. (Inventor)

    1997-01-01

    The invention provides an improved proton exchange membrane for use in electrochemical cells having internal passages parallel to the membrane surface, an apparatus and process for making the membrane, membrane and electrode assemblies fabricated using the membrane, and the application of the membrane and electrode assemblies to a variety of devices, both electrochemical and otherwise. The passages in the membrane extend from one edge of the membrane to another and allow fluid flow through the membrane and give access directly to the membrane for purposes of hydration.

  16. Macrophages engulf endothelial cell membrane particles preceding pupillary membrane capillary regression.

    PubMed

    Poché, Ross A; Hsu, Chih-Wei; McElwee, Melissa L; Burns, Alan R; Dickinson, Mary E

    2015-07-01

    Programmed capillary regression and remodeling are essential developmental processes. However, the cellular and molecular mechanisms that regulate vessel regression are only the beginning to be understood. Here, using in vivo, dynamic, confocal imaging of mouse transgenic reporters as well as static confocal and electron microscopy, we studied the embryonic development and postnatal regression of the transient mouse pupillary membrane (PM) vasculature. This approach allowed us to directly observe the precise temporal sequence of cellular events preceding and during the elimination of the PM from the mouse eye. Imaging of Tcf/Lef-H2B::GFP Wnt-reporter mice uncovered that, unlike the hyaloid vasculature of the posterior eye, a PM endothelial cell (EC) Wnt/β-catenin response is unlikely to be part of the regression mechanism. Live imaging of EC and macrophage dynamics revealed highly active Csf1r-GFP+ macrophages making direct contact with the Flk1-myr::mCherry+ vessel surface and with membrane protrusions or filopodia extending from the ECs. Flk1-myr::mCherry+ EC membrane particles were observed on and around ECs as well as within macrophages. Electron microscopy studies confirmed that they were in phagosomes within macrophages, indicating that the macrophages engulfed the membrane particles. Interestingly, EC plasma membrane uptake by PM macrophages did not correlate with apoptosis and was found shortly after vessel formation at mid-gestation stages in the embryo; long before vessel regression begins during postnatal development. Additionally, genetic ablation of macrophages showed that EC membrane particles were still shed in the absence of macrophages suggesting that macrophages do not induce the formation or release of EC microparticles. These studies have uncovered a novel event during programmed capillary regression in which resident macrophages scavenge endothelial cell microparticles released from the PM vessels. This finding suggests that there may be an

  17. Durable, Low-cost, Improved Fuel Cell Membranes

    SciTech Connect

    Chris Roger; David Mountz; Wensheng He; Tao Zhang

    2011-03-17

    The development of low cost, durable membranes and membranes electrode assemblies (MEAs) that operate under reduced relative humidity (RH) conditions remain a critical challenge for the successful introduction of fuel cells into mass markets. It was the goal of the team lead by Arkema, Inc. to address these shortages. Thus, this project addresses the following technical barriers from the fuel cells section of the Hydrogen Fuel Cells and Infrastructure Technologies Program Multi-Year Research, Development and Demonstration Plan: (A) Durability (B) Cost Arkema’s approach consisted of using blends of polyvinylidenefluoride (PVDF) and proprietary sulfonated polyelectrolytes. In the traditional approach to polyelectrolytes for proton exchange membranes (PEM), all the required properties are “packaged” in one macromolecule. The properties of interest include proton conductivity, mechanical properties, durability, and water/gas transport. This is the case, for example, for perfluorosulfonic acid-containing (PFSA) membranes. However, the cost of these materials is high, largely due to the complexity and the number of steps involved in their synthesis. In addition, they suffer other shortcomings such as mediocre mechanical properties and insufficient durability for some applications. The strength and originality of Arkema’s approach lies in the decoupling of ion conductivity from the other requirements. Kynar® PVDF provides an exceptional combination of properties that make it ideally suited for a membrane matrix (Kynar® is a registered trademark of Arkema Inc.). It exhibits outstanding chemical resistance in highly oxidative and acidic environments. In work with a prior grant, a membrane known as M41 was developed by Arkema. M41 had many of the properties needed for a high performance PEM, but had a significant deficiency in conductivity at low RH. In the first phase of this work, the processing parameters of M41 were explored as a means to increase its proton

  18. Single cell electric impedance topography: mapping membrane capacitance.

    PubMed

    Dharia, Sameera; Ayliffe, Harold E; Rabbitt, Richard D

    2009-12-07

    Single-cell electric impedance topography (sceTopo), a technique introduced here, maps the spatial distribution of capacitance (i.e. displacement current) associated with the membranes of isolated, living cells. Cells were positioned in the center of a circular recording chamber surrounded by eight electrodes. Electrodes were evenly distributed on the periphery of the recording chamber. Electric impedance measured between adjacent electrode pairs (10 kHz-5 MHz) was used to construct topographical maps of the spatial distribution of membrane capacitance. Xenopus Oocytes were used as a model cell to develop sceTopo because these cells consist of two visually distinguishable hemispheres, each with distinct membrane composition and structure. Results showed significant differences in the imaginary component of the impedance between the two oocyte hemispheres. In addition, the same circumferential array was used to map the size of the extracellular electrical shunt path around the cell, providing a means to estimate the location and shape of the cell in the recording chamber.

  19. Single cell electric impedance topography: Mapping membrane capacitance

    PubMed Central

    Dharia, Sameera; Ayliffe, Harold E.

    2010-01-01

    Single-cell electric impedance topography (sceTopo), a technique introduced here, maps the spatial distribution of capacitance (i.e. displacement current) associated with the membranes of isolated, living cells. Cells were positioned in the center of a circular recording chamber surrounded by eight electrodes. Electrodes were evenly distributed on the periphery of the recording chamber. Electric impedance measured between adjacent electrode pairs (10 kHz–5 MHz) was used to construct topographical maps of the spatial distribution of membrane capacitance. Xenopus Oocytes were used as a model cell to develop sceTopo because these cells consist of two visually distinguishable hemispheres, each with distinct membrane composition and structure. Results showed significant differences in the imaginary component of the impedance between the two oocyte hemispheres. In addition, the same circumferential array was used to map the size of the extracellular electrical shunt path around the cell, providing a means to estimate the location and shape of the cell in the recording chamber. PMID:19904403

  20. Binding of white spot syndrome virus to Artemia sp. cell membranes.

    PubMed

    Feng, Shuying; Li, Guangda; Feng, Wenpo; Huang, Jie

    2013-10-01

    Using differential velocity centrifugation, cell membranes of Artemia sp. were prepared, and their binding to white spot syndrome virus (WSSV) was analyzed in vitro. The results indicated that WSSV can specifically bind to Artemia cell membranes, and that WSSV receptor very likely existed in this membrane, which suggested that Artemia sp. may be a reservoir of WSSV. This study investigated the specific WSSV binding site by performing competitive inhibition experiments using shrimp gill cell membranes to bind WSSV to Artemia cell membranes. The results showed that shrimp gill cell membranes had a distinct inhibition effect on the specific binding of Artemia cell membranes to WSSV. Thus, potentially similar WSSV receptors or binding sites existed on Artemia sp. cell membranes and shrimp gill cell membranes. Taken together, these findings may provide experimental basis for the development of an effective approach to controlling WSSV, and theoretical basis for the study of WSSV receptors.

  1. Facile and green assembly of nanocomposite membranes for fuel cells.

    PubMed

    Quartarone, Eliana; Villa, Davide Carlo; Angioni, Simone; Mustarelli, Piercarlo

    2015-02-04

    We report on a facile spray deposition method, which allows obtaining nanocomposite membranes for high-temperature polymer fuel cells characterized by high homogeneity and excellent proton conductivity. The proposed method is also green, as it requires much smaller amounts of solvents with respect to standard casting.

  2. Sulfonated Nanoplates in Proton Conducting Membranes for Fuel Cells

    SciTech Connect

    Chen, W.F.; Ni’mah, H.; Yu-Cheng Shen, Y.-C.; Kuo, P.-L.

    2011-09-29

    Surface-functionalized nanoplates are synthesized by anchoring sulfonic acid containing siloxanes on zirconium phosphate, and in turn blended with Nafion to fabricate proton conducting membranes. The effects of these sulfonated nanoplates on proton conduction, hydro-characteristics and fuel cell performance are reported.

  3. Hereditary red cell membrane disorders and laboratory diagnostic testing.

    PubMed

    King, M-J; Zanella, A

    2013-06-01

    This overview describes two groups of nonimmune hereditary hemolytic anemias caused by defects in membrane proteins located in distinct layers of the red cell membrane. Hereditary spherocytosis (HS), hereditary elliptocytosis (HE), and hereditary pyropoikilocytosis (HPP) represent disorders of the red cell cytoskeleton. Hereditary stomatocytoses represents disorders of cation permeability in the red cell membrane. The current laboratory screening tests for HS are the osmotic fragility test, acid glycerol lysis time test (AGLT), cryohemolysis test, and eosin-5'-maleimide (EMA)-binding test. For atypical HS, SDS-polyacrylamide gel electrophoresis of erythrocyte membrane proteins is carried out to confirm the diagnosis. The diagnosis of HE/HPP is based on abnormal red cell morphology and the detection of protein 4.1R deficiency or spectrin variants using gel electrophoresis. None of screening tests can detect all HS cases. Some testing centers (a survey of 25 laboratories) use a combination of tests (e.g., AGLT and EMA). No specific screening test for hereditary stomatocytoses is available. The preliminary diagnosis is based on presenting a compensated hemolytic anemia, macrocytosis, and a temperature or time dependent pseudohyperkalemia in some patients. Both the EMA-binding test and the osmotic fragility test may help in differential diagnosis of HS and hereditary stomatocytosis.

  4. Monocyte cell membrane-derived nanoghosts for targeted cancer therapy

    NASA Astrophysics Data System (ADS)

    Krishnamurthy, S.; Gnanasammandhan, M. K.; Xie, C.; Huang, K.; Cui, M. Y.; Chan, J. M.

    2016-03-01

    Core-shell type `nanoghosts' were synthesized with a drug-loaded biodegradable PLGA core and a monocyte cell membrane-derived shell. The nanoghosts were monodisperse with an average size <200 nm, and showed good serum stability for 120 h. Doxorubicin-loaded nanoghosts showed greater cellular uptake and cytotoxicity compared to non-coated nanoparticle controls in metastatic MCF-7 breast cancer cell lines.Core-shell type `nanoghosts' were synthesized with a drug-loaded biodegradable PLGA core and a monocyte cell membrane-derived shell. The nanoghosts were monodisperse with an average size <200 nm, and showed good serum stability for 120 h. Doxorubicin-loaded nanoghosts showed greater cellular uptake and cytotoxicity compared to non-coated nanoparticle controls in metastatic MCF-7 breast cancer cell lines. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07588b

  5. Mitochondria and cell death: outer membrane permeabilization and beyond.

    PubMed

    Tait, Stephen W G; Green, Douglas R

    2010-09-01

    Mitochondrial outer membrane permeabilization (MOMP) is often required for activation of the caspase proteases that cause apoptotic cell death. Various intermembrane space (IMS) proteins, such as cytochrome c, promote caspase activation following their mitochondrial release. As a consequence, mitochondrial outer membrane integrity is highly controlled, primarily through interactions between pro- and anti-apoptotic members of the B cell lymphoma 2 (BCL-2) protein family. Following MOMP by pro-apoptotic BCL-2-associated X protein (BAX) or BCL-2 antagonist or killer (BAK), additional regulatory mechanisms govern the mitochondrial release of IMS proteins and caspase activity. MOMP typically leads to cell death irrespective of caspase activity by causing a progressive decline in mitochondrial function, although cells can survive this under certain circumstances, which may have pathophysiological consequences.

  6. How to Evaluate the Electric Noise in a Cell Membrane?

    NASA Astrophysics Data System (ADS)

    Bier, M.

    2006-05-01

    There has been considerable public anxiety about possible health effects of electromagnetic radiation emitted by high voltage power lines. Power frequencies (60 Hz in the US, 50 Hz in many other countries) are sufficiently slow for the associated electric fields to distribute themselves across the highly resistive cell membranes. To assess the ambient power frequency fields, researchers have compared the voltage that these fields induce across cell membranes to the strength of the electric noise that the membranes generate themselves through Brownian motion. However, there has been disagreement among researchers on how to evaluate this equilibrium membrane electric noise. I will review the different approaches and present an {ITALIC ab initio} modeling of membrane electric fields. I will show that different manifestations of Brownian noise lead to an electric noise intensity that is many times larger than what conventional estimates have yielded. Next, the legitimacy of gauging a nonequilibrium external signal against internal equilibrium noise is questioned and a more meaningful criterion is proposed. Finally, an estimate will be derived of the nonequilibrium noise intensity due to the driven ion traffic through randomly opening and closing ion channels.

  7. A prototype biosensor: artificial cell membrane on porous silicon

    NASA Astrophysics Data System (ADS)

    Retamal, Maria Jose; Cisternas, Marcelo; Busch, Mark; Gutierrez, Sebastian; Huber, Patrick; Perez-Acle, Tomas; Kappl, Michael; Volkmann, Ulrich

    2014-03-01

    Biosensors have been studied in recent years because they are powerful instruments to detect physical or chemical parameters as, e.g., intracellular interactions. What we propose is a prototype biosensor based on an artificial cell membrane (DPPC) on porous silicon. Porous silicon is used as a sponge-like substrate to absorb water by capillarity and keep the membrane hydrated, which is essential for the membrane not to denature when performing temperature cycles. Thus, one can observe the phase changes of the cell membrane with temperature using optical and surface scanning methods. In this research we used the technique of Very High Resolution Ellipsometry (VHRE) to observe changes in the ellipsometric angles during temperature ramps, which are attributed to different lipid phase transitions. Imaging ellipsometry (IE) was used to observe surface changes at the microscopic level and Atomic Force Microscopy (AFM) to observe changes in the topography of the membrane at the nanoscale. This work was supported by Fondecyt 1100882, DAAD-Conicyt PCCI 044, Conicyt Scholarship and Project Anillo ACT 1107.

  8. Alternative Sources of Adult Stem Cells: Human Amniotic Membrane

    NASA Astrophysics Data System (ADS)

    Wolbank, Susanne; van Griensven, Martijn; Grillari-Voglauer, Regina; Peterbauer-Scherb, Anja

    Human amniotic membrane is a highly promising cell source for tissue engineering. The cells thereof, human amniotic epithelial cells (hAEC) and human amniotic mesenchymal stromal cells (hAMSC), may be immunoprivileged, they represent an early developmental status, and their application is ethically uncontroversial. Cell banking strategies may use freshly isolated cells or involve in vitro expansion to increase cell numbers. Therefore, we have thoroughly characterized the effect of in vitro cultivation on both phenotype and differentiation potential of hAEC. Moreover, we present different strategies to improve expansion including replacement of animal-derived supplements by human platelet products or the introduction of the catalytic subunit of human telomerase to extend the in vitro lifespan of amniotic cells. Characterization of the resulting cultures includes phenotype, growth characteristics, and differentiation potential, as well as immunogenic and immunomodulatory properties.

  9. Chemical Imaging of the Cell Membrane by NanoSIMS

    SciTech Connect

    Weber, P K; Kraft, M L; Frisz, J F; Carpenter, K J; Hutcheon, I D

    2010-02-23

    The existence of lipid microdomains and their role in cell membrane organization are currently topics of great interest and controversy. The cell membrane is composed of a lipid bilayer with embedded proteins that can flow along the two-dimensional surface defined by the membrane. Microdomains, known as lipid rafts, are believed to play a central role in organizing this fluid system, enabling the cell membrane to carry out essential cellular processes, including protein recruitment and signal transduction. Lipid rafts are also implicated in cell invasion by pathogens, as in the case of the HIV. Therefore, understanding the role of lipid rafts in cell membrane organization not only has broad scientific implications, but also has practical implications for medical therapies. One of the major limitations on lipid organization research has been the inability to directly analyze lipid composition without introducing artifacts and at the relevant length-scales of tens to hundreds of nanometers. Fluorescence microscopy is widely used due to its sensitivity and specificity to the labeled species, but only the labeled components can be observed, fluorophores can alter the behavior of the lipids they label, and the length scales relevant to imaging cell membrane domains are between that probed by fluorescence resonance energy transfer (FRET) imaging (<10 nm) and the diffraction limit of light. Topographical features can be imaged on this length scale by atomic force microscopy (AFM), but the chemical composition of the observed structures cannot be determined. Immuno-labeling can be used to study the distribution of membrane proteins at high resolution, but not lipid composition. We are using imaging mass spectrometry by secondary ion mass spectrometry (SIMS) in concert with other high resolution imaging methods to overcome these limitations. The experimental approach of this project is to combine molecule-specific stable isotope labeling with high-resolution SIMS using a

  10. Durability aspects of polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Sethuraman, Vijay Anand

    In order for the successful adoption of proton exchange membrane (PEM) fuel cell technology, it is imperative that durability is understood, quantified and improved. A number of mechanisms are known to contribute to PEMFC membrane electrode assembly (MEA) performance degradation. In this dissertation, we show, via experiments, some of the various processes that degrade the proton exchange membrane in a PEM fuel cell; and catalyst poisoning due to hydrogen sulfide (H2S) and siloxane. The effect of humidity on the chemical stability of two types of membranes, [i.e., perfluorosulfonic acid type (PFSA, NafionRTM 112) and biphenyl sulfone hydrocarbon type, (BPSH-35)] was studied by subjecting the MEAs to open-circuit voltage (OCV) decay and potential cycling tests at elevated temperatures and low inlet gas relative humidities. The BPSH-35 membranes showed poor chemical stability in ex situ Fenton tests compared to that of NafionRTM membranes. However, under fuel cell conditions, BPSH-35 MEAs outperformed NafionRTM 112 MEAs in both the OCV decay and potential cycling tests. For both membranes, (i) at a given temperature, membrane degradation was more pronounced at lower humidities and (ii) at a given relative humidity operation, increasing the cell temperature accelerated membrane degradation. Mechanical stability of these two types of membranes was also studied using relative humidity (RH) cycling. Hydrogen peroxide (H2O2) formation rates in a proton exchange membrane (PEM) fuel cell were estimated by studying the oxygen reduction reaction (ORR) on a rotating ring disc electrode (RRDE). Fuel cell conditions were replicated by depositing a film of Pt/Vulcan XC-72 catalyst onto the disk and by varying the temperature, dissolved O2 concentration and the acidity levels in HClO4. The HClO4 acidity was correlated to ionomer water activity and hence fuel cell humidity. H 2O2 formation rates showed a linear dependence on oxygen concentration and square dependence on water

  11. Membrane protein synthesis in cell-free systems: from bio-mimetic systems to bio-membranes.

    PubMed

    Sachse, Rita; Dondapati, Srujan K; Fenz, Susanne F; Schmidt, Thomas; Kubick, Stefan

    2014-08-25

    When taking up the gauntlet of studying membrane protein functionality, scientists are provided with a plethora of advantages, which can be exploited for the synthesis of these difficult-to-express proteins by utilizing cell-free protein synthesis systems. Due to their hydrophobicity, membrane proteins have exceptional demands regarding their environment to ensure correct functionality. Thus, the challenge is to find the appropriate hydrophobic support that facilitates proper membrane protein folding. So far, various modes of membrane protein synthesis have been presented. Here, we summarize current state-of-the-art methodologies of membrane protein synthesis in biomimetic-supported systems. The correct folding and functionality of membrane proteins depend in many cases on their integration into a lipid bilayer and subsequent posttranslational modification. We highlight cell-free systems utilizing the advantages of biological membranes.

  12. Process analytical technology (PAT) in insect and mammalian cell culture processes: dielectric spectroscopy and focused beam reflectance measurement (FBRM).

    PubMed

    Druzinec, Damir; Weiss, Katja; Elseberg, Christiane; Salzig, Denise; Kraume, Matthias; Pörtner, Ralf; Czermak, Peter

    2014-01-01

    Modern bioprocesses demand for a careful definition of the critical process parameters (CPPs) already during the early stages of process development in order to ensure high-quality products and satisfactory yields. In this context, online monitoring tools can be applied to recognize unfavorable changes of CPPs during the production processes and to allow for early interventions in order to prevent losses of production batches due to quality issues. Process analytical technologies such as the dielectric spectroscopy or focused beam reflectance measurement (FBRM) are possible online monitoring tools, which can be applied to monitor cell growth as well as morphological changes. Since the dielectric spectroscopy only captures cells with intact cell membranes, even information about dead cells with ruptured or leaking cell membranes can be derived. The following chapter describes the application of dielectric spectroscopy on various virus-infected and non-infected cell lines with respect to adherent as well as suspension cultures in common stirred tank reactors. The adherent mammalian cell lines Vero (African green monkey kidney cells) and hMSC-TERT (telomerase-immortalized human mesenchymal stem cells) are thereby cultured on microcarrier, which provide the required growth surface and allow the cultivation of these cells even in dynamic culture systems. In turn, the insect-derived cell lines S2 and Sf21 are used as examples for cells typically cultured in suspension. Moreover, the FBRM technology as a further monitoring tool for cell culture applications has been included in this chapter using the example of Drosophila S2 insect cells.

  13. Block copolymers for alkaline fuel cell membrane materials

    NASA Astrophysics Data System (ADS)

    Li, Yifan

    Alkaline fuel cells (AFCs) using anion exchange membranes (AEMs) as electrolyte have recently received considerable attention. AFCs offer some advantages over proton exchange membrane fuel cells, including the potential of non-noble metal (e.g. nickel, silver) catalyst on the cathode, which can dramatically lower the fuel cell cost. The main drawback of traditional AFCs is the use of liquid electrolyte (e.g. aqueous potassium hydroxide), which can result in the formation of carbonate precipitates by reaction with carbon dioxide. AEMs with tethered cations can overcome the precipitates formed in traditional AFCs. Our current research focuses on developing different polymer systems (blend, block, grafted, and crosslinked polymers) in order to understand alkaline fuel cell membrane in many aspects and design optimized anion exchange membranes with better alkaline stability, mechanical integrity and ionic conductivity. A number of distinct materials have been produced and characterized. A polymer blend system comprised of poly(vinylbenzyl chloride)-b-polystyrene (PVBC-b-PS) diblock copolymer, prepared by nitroxide mediated polymerization (NMP), with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) or brominated PPO was studied for conversion into a blend membrane for AEM. The formation of a miscible blend matrix improved mechanical properties while maintaining high ionic conductivity through formation of phase separated ionic domains. Using anionic polymerization, a polyethylene based block copolymer was designed where the polyethylene-based block copolymer formed bicontinuous morphological structures to enhance the hydroxide conductivity (up to 94 mS/cm at 80 °C) while excellent mechanical properties (strain up to 205%) of the polyethylene block copolymer membrane was observed. A polymer system was designed and characterized with monomethoxy polyethylene glycol (mPEG) as a hydrophilic polymer grafted through substitution of pendent benzyl chloride groups of a PVBC

  14. Reticulated lipid probe fluorescence reveals MDCK cell apical membrane topography.

    PubMed

    Colarusso, Pina; Spring, Kenneth R

    2002-02-01

    High spatial resolution confocal microscopy of young MDCK cells stained with the lipophilic probe 1,1'-dihexadecyl-3,3,3',3'- tetramethylindocarbocyanine perchlorate (DiIC(16)) revealed a reticulated fluorescence pattern on the apical membrane. DiIC(16) was delivered as crystals to live cells to minimize possible solvent perturbations of the membrane lipids. The ratio of the integrated fluorescence intensities in the bright versus dim regions was 1.6 +/- 0.1 (n = 13). Deconvolved images of the cells were consistent with exclusive plasma membrane staining. Multi-spectral and fluorescence anisotropy microscopy did not reveal differences between bright and dim regions. Bright regions coincided with microvilli and microridges observed by differential interference contrast microscopy and were stable for several minutes. Fluorescence recovery after photobleaching yielded similar diffusion coefficients (pooled D = 1.5 +/- 0.6 x 10(-9) cm(2)/s, n = 40) for both bright and dim regions. Line fluorescence recovery after photobleaching showed that the reticulated pattern was maintained as the fluorescence recovered in the bleached areas. Cytochalasin D did not affect the staining pattern, but the pattern was eliminated by cholesterol depletion with methyl-beta-cyclodextrin. We conclude that the reticulated fluorescence pattern was caused by increased optical path lengths through the microvilli and microridges compared with the flat areas on the apical membrane.

  15. Reticulated lipid probe fluorescence reveals MDCK cell apical membrane topography.

    PubMed Central

    Colarusso, Pina; Spring, Kenneth R

    2002-01-01

    High spatial resolution confocal microscopy of young MDCK cells stained with the lipophilic probe 1,1'-dihexadecyl-3,3,3',3'- tetramethylindocarbocyanine perchlorate (DiIC(16)) revealed a reticulated fluorescence pattern on the apical membrane. DiIC(16) was delivered as crystals to live cells to minimize possible solvent perturbations of the membrane lipids. The ratio of the integrated fluorescence intensities in the bright versus dim regions was 1.6 +/- 0.1 (n = 13). Deconvolved images of the cells were consistent with exclusive plasma membrane staining. Multi-spectral and fluorescence anisotropy microscopy did not reveal differences between bright and dim regions. Bright regions coincided with microvilli and microridges observed by differential interference contrast microscopy and were stable for several minutes. Fluorescence recovery after photobleaching yielded similar diffusion coefficients (pooled D = 1.5 +/- 0.6 x 10(-9) cm(2)/s, n = 40) for both bright and dim regions. Line fluorescence recovery after photobleaching showed that the reticulated pattern was maintained as the fluorescence recovered in the bleached areas. Cytochalasin D did not affect the staining pattern, but the pattern was eliminated by cholesterol depletion with methyl-beta-cyclodextrin. We conclude that the reticulated fluorescence pattern was caused by increased optical path lengths through the microvilli and microridges compared with the flat areas on the apical membrane. PMID:11806917

  16. Capacitance-Voltage Measurement of Transporting Function at Cell Membrane

    NASA Astrophysics Data System (ADS)

    Sakata, Toshiya; Miyahara, Yuji

    In this paper, we report the detection of transporting function at cell membrane using capacitance-voltage (CV) measurement. The detection principle of our devices is based on the field-effect of electrostatic interaction between charged species at cell membrane in solution and surface electrons in silicon crystal through the gate insulator of Si3N4/SiO2 thin double-layer. We designed an oocyte-based field-effect capacitor, on which a Xenopus laevis oocyte was fixed. The transporter of human organic anion transporting peptide C (hOATP-C) was expressed at oocyte membrane by induction of cRNA. The electrical phenomena such as ion or molecular charge flux at the interface between cell membrane and gate surface could be detected as the change of flat band voltage in CV characteristics. The flat band voltage shift decreased with incubation time after introduction of substrate into the oocyte-based field-effect capacitor. The electrical signal is due to the change of charge flux from the oocyte at the gate surface inspired by transporter-substrate binding. The platform based on the oocyte-based field-effect capacitor is suitable for a simple and non-invasive detection system in order to analyze function of transporters related to drug efficacy.

  17. A Novel Unitized Regenerative Proton Exchange Membrane Fuel Cell

    NASA Technical Reports Server (NTRS)

    Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

    1996-01-01

    A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel single cell unitized regenerative fuel cell and results obtained on testing it are presented.

  18. Construction and analytical applications of plastic membrane electrode for oxymetazoline hydrochloride.

    PubMed

    Issa, Y M; Zayed, S I M

    2004-02-01

    A new oxymetazoline (OM) ion-selective PVC membrane electrode based on the ion associate of OM with phosphotungstic acid was prepared. The electrode exhibits a linear response with a mean calibration graph slope of 57.16 mV decade(-1) at 25 degrees C within the concentration range of 1.96 x 10(-5) - 1 x 10(-2) M OMCl. The change in the pH within the range of 1.0 - 9.4 did not affect the electrode performance. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode (-0.001233 V). The electrode showed a very good selectivity for OM with respect to a large number of inorganic cations and compounds. The standard addition method and potentiometric titration were applied to the determination of (OM) with RSD not exceeding 1.19%.

  19. Mass Spectrometry of Polymer Electrolyte Membrane Fuel Cells

    PubMed Central

    Ostroverkh, Anna; Fiala, Roman; Rednyk, Andrii; Matolín, Vladimír

    2016-01-01

    The chemical analysis of processes inside fuel cells under operating conditions in either direct or inverted (electrolysis) mode and their correlation with potentiostatic measurements is a crucial part of understanding fuel cell electrochemistry. We present a relatively simple yet powerful experimental setup for online monitoring of the fuel cell exhaust (of either cathode or anode side) downstream by mass spectrometry. The influence of a variety of parameters (composition of the catalyst, fuel type or its concentration, cell temperature, level of humidification, mass flow rate, power load, cell potential, etc.) on the fuel cell operation can be easily investigated separately or in a combined fashion. We demonstrate the application of this technique on a few examples of low-temperature (70°C herein) polymer electrolyte membrane fuel cells (both alcohol- and hydrogen-fed) subjected to a wide range of conditions. PMID:28042492

  20. Mass Spectrometry of Polymer Electrolyte Membrane Fuel Cells.

    PubMed

    Johánek, Viktor; Ostroverkh, Anna; Fiala, Roman; Rednyk, Andrii; Matolín, Vladimír

    2016-01-01

    The chemical analysis of processes inside fuel cells under operating conditions in either direct or inverted (electrolysis) mode and their correlation with potentiostatic measurements is a crucial part of understanding fuel cell electrochemistry. We present a relatively simple yet powerful experimental setup for online monitoring of the fuel cell exhaust (of either cathode or anode side) downstream by mass spectrometry. The influence of a variety of parameters (composition of the catalyst, fuel type or its concentration, cell temperature, level of humidification, mass flow rate, power load, cell potential, etc.) on the fuel cell operation can be easily investigated separately or in a combined fashion. We demonstrate the application of this technique on a few examples of low-temperature (70°C herein) polymer electrolyte membrane fuel cells (both alcohol- and hydrogen-fed) subjected to a wide range of conditions.

  1. Morphological features (defects) in fuel cell membrane electrode assemblies

    NASA Astrophysics Data System (ADS)

    Kundu, S.; Fowler, M. W.; Simon, L. C.; Grot, S.

    Reliability and durability issues in fuel cells are becoming more important as the technology and the industry matures. Although research in this area has increased, systematic failure analysis, such as a failure modes and effects analysis (FMEA), are very limited in the literature. This paper presents a categorization scheme of causes, modes, and effects related to fuel cell degradation and failure, with particular focus on the role of component quality, that can be used in FMEAs for polymer electrolyte membrane (PEM) fuel cells. The work also identifies component defects imparted on catalyst-coated membranes (CCM) by manufacturing and proposes mechanisms by which they can influence overall degradation and reliability. Six major defects have been identified on fresh CCM materials, i.e., cracks, orientation, delamination, electrolyte clusters, platinum clusters, and thickness variations.

  2. Gold Nanoparticles-Enhanced Proton Exchange Membrane (PEM) Fuel Cell

    NASA Astrophysics Data System (ADS)

    Li, Hongfei; Pan, Cheng; Liu, Ping; Zhu, Yimei; Adzic, Radoslav; Rafailovich, Miriam

    Proton exchange membrane fuel cells have drawn great attention and been taken as a promising alternated energy source. One of the reasons hamper the wider application of PEM fuel cell is the catalytic poison effect from the impurity of the gas flow. Haruta has predicted that gold nanoparticles that are platelet shaped and have direct contact with the metal oxide substrate to be the perfect catalysts of the CO oxidization, yet the synthesis method is difficult to apply in the Fuel Cell. In our approach, thiol-functionalized gold nanoparticles were synthesized through two-phase method developed by Brust et al. We deposit these Au particles with stepped surface directly onto the Nafion membrane in the PEM fuel cell by Langmuir-Blodgett method, resulting in over 50% enhancement of the efficiency of the fuel cell. DFT calculations were conducted to understand the theory of this kind of enhancement. The results indicated that only when the particles were in direct surface contact with the membrane, where AuNPs attached at the end of the Nafion side chains, it could reduce the energy barrier for the CO oxidation that could happen at T<300K.

  3. Investigation of Anion-Exchange and Immunoaffinity Particle-Loaded Membranes for the Isolation of Charged Organic Analytes from Water

    USGS Publications Warehouse

    Dombrowski, T.R.; Wilson, G.S.; Thurman, E.M.

    1998-01-01

    Anion-exchange and immunoaffinity particle loaded membranes (PLMs) were investigated as a mechanism for the isolation of charged organic analytes from water. Kinetic properties determined theoretically included dynamic capacity, pressure drop (??P), residence and diffusion times (Tr, Td), and total membrane porosity (???T). These properties were confirmed through experimental evaluation, and the PLM method showed significant improvement over conventional solid-phase extraction (SPE) and ion-exchange formats. Recoveries of more than 90% were observed for a variety of test compounds at flow rates up to 70 mL/min (equipment-limited maximum flow rate). A fast-flow immunoaffinity column was developed using antibodies (Abs) attached to the PLMs. Reproducible recoveries (88% ?? 4%) were observed at flow rates up to 70 mL/min for the antibody (Ab)-loaded PLMs. Findings indicate increased selectivity over anion-exchange PLMs and conventional SPE or ion-exchange methods and rapid Ab-antigen binding rates given the excellent mass-transfer characteristics of the PLMs.

  4. Analytical Models for Predicting Mechanical Properties of Self-Expandable Metal Stents with Cover Membrane

    DTIC Science & Technology

    2007-11-02

    compressed, it elongates in its longitudinal direction. Consider the deformation of parallelogram cell as shown in Fig. 4(A). When the points A, B, and...the cell maintains a parallelogram shape during compression. The length between A and B of uncompressed stent is N klL wireAB 0 sin2 β= (14...Expansive pressure- deformation curve for bare type stent. 8 10 12 14 16 0 4 8 12 16 Experiments Pbare Pcoat Pcoated stent

  5. Incorporating photon recycling into the analytical drift-diffusion model of high efficiency solar cells

    SciTech Connect

    Lumb, Matthew P.; Steiner, Myles A.; Geisz, John F.; Walters, Robert J.

    2014-11-21

    The analytical drift-diffusion formalism is able to accurately simulate a wide range of solar cell architectures and was recently extended to include those with back surface reflectors. However, as solar cells approach the limits of material quality, photon recycling effects become increasingly important in predicting the behavior of these cells. In particular, the minority carrier diffusion length is significantly affected by the photon recycling, with consequences for the solar cell performance. In this paper, we outline an approach to account for photon recycling in the analytical Hovel model and compare analytical model predictions to GaAs-based experimental devices operating close to the fundamental efficiency limit.

  6. Deoxygenation affects tyrosine phosphoproteome of red cell membrane from patients with sickle cell disease.

    PubMed

    Siciliano, Angela; Turrini, Franco; Bertoldi, Mariarita; Matte, Alessandro; Pantaleo, Antonella; Olivieri, Oliviero; De Franceschi, Lucia

    2010-04-15

    Sickle cell disease (SCD) is a worldwide distributed hereditary red cell disorder related to the production of a defective form of hemoglobin, hemoglobin S (HbS). One of the hallmarks of SCD is the presence of dense, dehydrate highly adhesive sickle red blood cells (RBCs) that result from persistent membrane damage associated with HbS polymerization, abnormal activation of membrane cation transports and generation of distorted and rigid red cells with membrane perturbation and cytoskeleton dysfunction. Although modulation of phosphorylation state of the proteins from membrane and cytoskeleton networks has been proposed to participate in red cell homeostasis, much still remains to be investigated in normal and diseased red cells. Here, we report that tyrosine (Tyr-) phosphoproteome of sickle red cells was different from normal controls and was affected by deoxygenation. We found proteins, p55 and band 4.1, from the junctional complex, differently Tyr-phosphorylated in SCD RBCs compared to normal RBCs under normoxia and modulated by deoxygenation, while band 4.2 was similarly Tyr-phosphorylated in both conditions. In SCD RBCs we identified the phosphopeptides for protein 4.1R located in the protein FERM domain (Tyr-13) and for alpha-spectrin located near or in a linker region (Tyr-422 and Tyr-1498) involving protein areas crucial for their functions in the context of red cell membrane properties, suggesting that Tyr-phosphorylation may be part of the events involved in maintaining membrane mechanical stability in SCD red cells.

  7. Creating Transient Cell Membrane Pores Using a Standard Inkjet Printer

    PubMed Central

    Owczarczak, Alexander B.; Shuford, Stephen O.; Wood, Scott T.; Deitch, Sandra; Dean, Delphine

    2012-01-01

    Bioprinting has a wide range of applications and significance, including tissue engineering, direct cell application therapies, and biosensor microfabrication.1-10 Recently, thermal inkjet printing has also been used for gene transfection.8,9 The thermal inkjet printing process was shown to temporarily disrupt the cell membranes without affecting cell viability. The transient pores in the membrane can be used to introduce molecules, which would otherwise be too large to pass through the membrane, into the cell cytoplasm.8,9,11 The application being demonstrated here is the use of thermal inkjet printing for the incorporation of fluorescently labeled g-actin monomers into cells. The advantage of using thermal ink-jet printing to inject molecules into cells is that the technique is relatively benign to cells.8, 12 Cell viability after printing has been shown to be similar to standard cell plating methods1,8. In addition, inkjet printing can process thousands of cells in minutes, which is much faster than manual microinjection. The pores created by printing have been shown to close within about two hours. However, there is a limit to the size of the pore created (~10 nm) with this printing technique, which limits the technique to injecting cells with small proteins and/or particles. 8,9,11 A standard HP DeskJet 500 printer was modified to allow for cell printing.3, 5, 8 The cover of the printer was removed and the paper feed mechanism was bypassed using a mechanical lever. A stage was created to allow for placement of microscope slides and coverslips directly under the print head. Ink cartridges were opened, the ink was removed and they were cleaned prior to use with cells. The printing pattern was created using standard drawing software, which then controlled the printer through a simple print command. 3T3 fibroblasts were grown to confluence, trypsinized, and then resuspended into phosphate buffered saline with soluble fluorescently labeled g-actin monomers. The

  8. A novel unitized regenerative proton exchange membrane fuel cell

    NASA Technical Reports Server (NTRS)

    Murphy, O. J.; Cisar, A. J.; Gonzalez-Martin, A.; Salinas, C. E.; Simpson, S. F.

    1995-01-01

    A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed in work performed at Lynntech. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel unitized regenerative fuel cell and results obtained on testing it will be presented.

  9. Sodium channels in membrane vesicles from cultured toad bladder cells

    SciTech Connect

    Asher, C.; Moran, A.; Rossier, B.C.; Garty, H. Ben Gurion Univ., Beer-Sheva Institut de Pharmacologie de l'Universite de Lausanne )

    1988-04-01

    Electrical potential-driven {sup 22}Na{sup +} fluxes were measured in membrane vesicles prepared from TBM-18(cl23) cells (a clone of the established cell line TB-M). Fifty to seventy percent of the tracer uptake in vesicles derived from cells that were cultivated on a porous support were blocked by the diuretic amiloride. The amiloride inhibition constant was <0.1 {mu}M, indicating that this flux is mediated by the apical Na{sup +}-specific channels. Vesicles prepared from cells that were not grown on a porous support exhibited much smaller amiloride-sensitive fluxes. Two Ca{sup 2+}-dependent processes that down-regulated the channel conductance and were previously identified in native epithelia were found in the cultured cells as well. Vesicles isolated from cells that were preincubated with 5 {times} 10{sup {minus}7} M aldosterone for 16-20 h exhibited higher amiloride-sensitive conductance than vesicles derived from control, steroid-depleted cells. Thus membrane derived from TBM-18(cl23) cells can be used to characterize the epithelial Na{sup +} channel and its hormonal regulation.

  10. Electro-driven extraction across a polymer inclusion membrane in a flow-through cell.

    PubMed

    See, Hong Heng; Stratz, Simone; Hauser, Peter C

    2013-07-26

    A flow-through arrangement for electrodriven extraction across a polymer inclusion membrane was developed. Sample introduction into the donor chamber was continuous, while the acceptor solution was stagnant. By adjustment of the total volume of the donor solution pumped through the cell the best compromise between enrichment factor and extraction time can be set. The enriched extract was analyzed by capillary electrophoresis with contactless conductivity detection. Membranes of 20μm thickness were employed which consisted of 60% cellulose triacetate as base polymer, 20% o-nitrophenyl octyl ether as plasticizer, and 20% Aliquat 336. By passing through 10mL of sample at a flow rate of 1mL/min the model analytes glyphosate (a common herbicide) and its major metabolite aminomethylphosphonic acid could be transported from the aqueous donor solution to the aqueous acceptor solution with efficiencies >87% in 10min at an applied voltage of 1500V. Enrichment factors of 87 and 95 and limits of detection down to 43 and 64pg/mL were obtained for glyphosate and aminomethylphosphonic acid, respectively. The intra- and interday reproducibilities for the extraction of the two compounds from spiked river water were about 6 and 7% respectively when new membranes were used for each experiment. For consecutive extractions of batches of river water with a single piece of membrane a deterioration of recovery by about 16% (after 20 runs) was noted, an effect not observed with purely aqueous standards.

  11. Membrane tether formation from outer hair cells with optical tweezers.

    PubMed Central

    Li, Zhiwei; Anvari, Bahman; Takashima, Masayoshi; Brecht, Peter; Torres, Jorge H; Brownell, William E

    2002-01-01

    Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC) plasma membrane by pulling tethers with 4.5-microm polystyrene beads. Tether formation force and tether force were measured in static and dynamic conditions. A greater force was required for tether formations from OHC lateral wall (499 +/- 152 pN) than from OHC basal end (142 +/- 49 pN). The difference in the force required to pull tethers is consistent with an extensive cytoskeletal framework associated with the lateral wall known as the cortical lattice. The apparent plasma membrane stiffness, estimated under the static conditions by measuring tether force at different tether length, was 3.71 pN/microm for OHC lateral wall and 4.57 pN/microm for OHC basal end. The effective membrane viscosity was measured by pulling tethers at different rates while continuously recording the tether force, and estimated in the range of 2.39 to 5.25 pN x s/microm. The viscous force most likely results from the viscous interactions between plasma membrane lipids and the OHC cortical lattice and/or integral membrane proteins. The information these studies provide on the mechanical properties of the OHC lateral wall is important for understanding the mechanism of OHC electromotility. PMID:11867454

  12. Modified SPEEK membranes for direct ethanol fuel cell

    NASA Astrophysics Data System (ADS)

    Maab, Husnul; Nunes, Suzana Pereira

    Membranes with low ethanol crossover were prepared aiming their application for direct ethanol fuel cell (DEFC). They were based on (1) sulfonated poly(ether ether ketone) (SPEEK) coated with carbon molecular sieves (CMS) and (2) on SPEEK/PI homogeneous blends. The membranes were characterized concerning their water and ethanol solution uptake, water and ethanol permeability in pervaporation experiments and their performance in DEFC tests. The ethanol permeabilities for the CMS-coated (180 nm and 400 nm thick layers) SPEEK were 8.5 and 3.1 × 10 -10 kg m s -1 m -2 and for the homogeneous SPEEK/PI blends membranes with 10, 20 and 30 wt.% of PI were 4.4, 1.0 and 0.4 × 10 -10 kg m s -1 m -2 respectively, which is 2- to 50-fold lower than that for plain SPEEK (19 × 10 -10 kg m s -1 m -2). Particularly the SPEEK/PI membranes had substantially better performance than Nafion 117 ® membranes in DEFC tests at 60 °C and 90 °C.

  13. Preparation and characterization of micro-cell membrane chromatographic column with silica-based porous layer open tubular capillary as cellular membrane carrier.

    PubMed

    Zhang, Fugeng; Zhao, Xinchao; Xu, Bei; Cheng, Shuai; Tang, Cheng; Duan, Hongquan; Xiao, Xuefeng; Du, Wuxun; Xu, Liang

    2016-04-01

    Cell membrane chromatography (CMC) is a powerful tool to study membrane protein interactions and to screen active compounds extracted from natural products. Unfortunately, a large amount of cells are typically required for column preparation in order to carry out analyses in an efficient manner. Micro-CMC (mCMC) has recently been developed by using a silica capillary as a membrane carrier. However, a reduced retention of analytes is generally associated with mCMC mostly due to a low ligand (cellular membrane) capacity. To solve this common problem, in this work a silica-based porous layer open tubular (PLOT) capillary was fabricated and, to the best of our knowledge, for the first time applied to mCMC. The mCMC column was prepared by physical adsorption of rabbit red blood cell (rRBC) membranes onto the inner surface of the PLOT capillary. The effects of the PLOT capillaries fabricated by different feed compositions, on the immobilization amount of cellular membranes (represented by the fluorescence intensity of the capillary immobilized with fluorescein isothiocyanate isomer-labeled cellular membranes) and on the dynamic binding capacity (DBC) of verapamil (VP, a widely used calcium antagonist which specific interacts with L-type calcium channel proteins located on cellular membrane of rRBC) have been systematically investigated. The fluorescence intensity of the mCMC column when combined with the PLOT capillary was found to be more than five times higher than the intensity using a bare capillary. This intriguing result indicates that the PLOT capillary exhibits a higher cellular membrane capacity. The DBC of VP in the PLOT column was found to be more than nine times higher than that in the bare capillary. An rRBC/CMC column was also prepared for comparative studies. As a result, mCMC provides similar chromatographic retention factors and stability with common CMC; however, the cellular membrane consumption for mCMC was found to be more than 460 times lower than

  14. Membrane phenotypic studies in B cell lymphoproliferative disorders.

    PubMed Central

    Scott, C S; Limbert, H J; MacKarill, I D; Roberts, B E

    1985-01-01

    A total of 398 cases of B cell lymphoproliferative disease were phenotypically characterised by membrane mouse red blood cell (MRBC) receptor, surface immunoglobulin, common acute lymphoblastic leukaemia (CALLA), and FMC7 and T1 monoclonal antibody studies. Relations between chronic lymphocytic leukaemia (CLL), prolymphocytic leukaemia (PLL), and "prolymphocytoid" CLL variants were examined with particular reference to the expression of FMC7. In addition, the reactivity of TU1 monoclonal antibody with B cell disorders was established. The results suggest that despite some heterogeneity most cases may be characterised by their phenotypic patterns and that these investigations provide a reproducible basis for classification. PMID:2413082

  15. Rigid proteins and softening of biological membranes-with application to HIV-induced cell membrane softening.

    PubMed

    Agrawal, Himani; Zelisko, Matthew; Liu, Liping; Sharma, Pradeep

    2016-05-06

    A key step in the HIV-infection process is the fusion of the virion membrane with the target cell membrane and the concomitant transfer of the viral RNA. Experimental evidence suggests that the fusion is preceded by considerable elastic softening of the cell membranes due to the insertion of fusion peptide in the membrane. What are the mechanisms underpinning the elastic softening of the membrane upon peptide insertion? A broader question may be posed: insertion of rigid proteins in soft membranes ought to stiffen the membranes not soften them. However, experimental observations perplexingly appear to show that rigid proteins may either soften or harden membranes even though conventional wisdom only suggests stiffening. In this work, we argue that regarding proteins as merely non-specific rigid inclusions is flawed, and each protein has a unique mechanical signature dictated by its specific interfacial coupling to the surrounding membrane. Predicated on this hypothesis, we have carried out atomistic simulations to investigate peptide-membrane interactions. Together with a continuum model, we reconcile contrasting experimental data in the literature including the case of HIV-fusion peptide induced softening. We conclude that the structural rearrangements of the lipids around the inclusions cause the softening or stiffening of the biological membranes.

  16. Effect of isosmotic removal of extracellular Na+ on cell volume and membrane potential in muscle cells.

    PubMed

    Peña-Rasgado, C; Summers, J C; McGruder, K D; DeSantiago, J; Rasgado-Flores, H

    1994-09-01

    Isosmotic removal of extracellular Na+ (Nao) is a frequently performed manipulation. With the use of isolated voltage-clamped barnacle muscle cells, the effect of this manipulation on isosmotic cell volume was studied. Replacement of Nao by tris(hydroxymethyl)aminomethane produced membrane depolarization (approximately 20 mV) and cell volume loss (approximately 14%). The membrane depolarization was verapamil insensitive but depended on extracellular Ca2+ (Cao) and was probably due to activation of intracellular Ca2+ (Cai)-dependent nonselective cation channels. The cell volume loss did not require membrane depolarization but depended on Cao. This was probably due to an increase in Cai, mediated by activation of Ca2+ influx via Na+/Ca2+ exchange. Nao replacement by Li+ also promoted membrane depolarization (approximately 20 mV) and cell volume loss (20%). Both effects were reduced (approximately 73%) but were not abolished by Cao removal. Under this condition, the remaining membrane depolarization was probably due to a higher membrane permeability of Li+ over Na+. The remaining cell volume loss was due to membrane depolarization, which probably induced Ca2+ release from intracellular stores.

  17. Muscarinic receptor size on smooth muscle cells and membranes

    SciTech Connect

    Collins, S.M.; Jung, C.Y.; Grover, A.K.

    1986-08-01

    The loss of (/sup 3/H)quinuclidinyl benzilate ((/sup 3/H)QNB) binding following high-energy radiation was used to compare the muscarinic receptor size on single smooth muscle cells isolated by collagenase digestion from the canine stomach and on plasma membranes derived from intact gastric smooth muscle without exposure to exogenous proteolysis. Radiation inactivation of galactose oxidase (68 kdaltons), yeast alcohol dehydrogenase (160 kdaltons), and pyruvate kinase (224 kdaltons) activities were used as molecular-weight standards. Radiation inactivation of (/sup 3/H)QNB binding to rat brain membranes, which gave a target size of 86 kdaltons, served as an additional control. In isolated smooth muscle cells, the calculated size of the muscarinic receptor was 80 +/- 8 kdaltons. In contrast, in a smooth muscle enriched plasma membrane preparation, muscarinic receptor size was significantly smaller at 45 +/- 3 kdaltons. Larger molecular sizes were obtained either in the presence of protease inhibitors (62 +/- 4 kdaltons) or by using a crude membrane preparation of gastric smooth muscle 86 +/- 7 kdaltons).

  18. The organochlorine herbicide chloridazon interacts with cell membranes.

    PubMed

    Suwalsky, M; Benites, M; Villena, F; Norris, B; Quevedo, L

    1998-07-01

    Chloridazon is a widely used organochlorine herbicide. In order to evaluate its perturbing effect on cell membranes it was made to interact with human erythrocytes, frog adrenergic neuroepithelial synapse and molecular models. These consisted in multilayers of dimyristoylphosphatidylethanolamine (DMPE) and of dimyristoylphosphatidyltidylcholine (DMPC), representative of phospholipid classes located in the inner and outer monolayers of the erythrocyte membrane, respectively. X-ray diffraction showed that chloridazon interacted preferentially with DMPC multilayers. Scanning electron microscopy revealed that 0.1 mM chloridazon induced erythrocyte crenation. According to the bilayer couple hypothesis, this is due to the preferential insertion of chloridazon in the phosphatidylcholine-rich external moiety of the red cell membrane. Electrophysiological measurements showed that nerve stimulation was followed immediately by a transient increase in short-circuit current (SCC) and in the potential difference (PD) of the neuroepithelial synapse. Increasing concentrations of chloridazon caused a dose-dependent and reversible decrease of the responses of both parameters to 76% of their control values. The pesticide induced a similar (28%) significant time-dependent decrease in the basal values of the SCC and of PD. These results are in accordance with a perturbing effect of chloridazon on the phospholipid moiety of the nerve fibre membrane leading to interference with total ion transport across the nerve skin junction.

  19. Membrane electrolytic cell for minimizing hypochlorite and chlorate formation

    SciTech Connect

    Fair, D. L.; Justice, D. D.; Woodard Jr., K. E.

    1985-07-09

    An electrolytic cell for the electrolysis of an alkali metal chloride brine is comprised of an anode compartment and a cathode compartment separated by a cation exchange membrane. The anode is comprised of an unflattened expanded structure of a valve metal selected from the group consisting of titanium, tantalum, niobium, and alloys thereof. At least one side of the anode has as the electrochemically active surface an electrodeposited layer of a valve metal oxide. A plurality of cracks traverse the electrodeposited layer and a coating of a platinum metal group oxide covers the electrodeposited layer and substantially fills the cracks. The cationic exchange membrane is comprised of a laminated structure having a first surface adapted to contact an anolyte in which the ion exchange groups are predominately sulfonic acid groups. The first surface is also in contact with the electrochemically active surface of the anode. A second surface of the cation exchange membrane, adapted to contact a catholyte, has ion exchange groups which are predominately carboxylic acid groups. The cathode positioned in the cathode compartment is spaced apart from the cation exchange membrane. The cell operates with both a low chlorine overvoltage and a low oxygen overvoltage. During electrolysis of alkali metal chloride brines, the formation of hypochlorite and chlorate ions is minimized and the alkali metal hydroxides produced have low chlorate concentrations and are suitable for use without further treatment in chlorate-sensitive applications. Spent brine treatment is simplified and at reduced costs.

  20. Analyte flux through chronically implanted subcutaneous polyamide membranes differs in humans and rats.

    PubMed

    Wisniewski, N; Rajamand, N; Adamsson, U; Lins, P E; Reichert, W M; Klitzman, B; Ungerstedt, U

    2002-06-01

    The rat is commonly used to evaluate physiological responses of subcutaneous tissue to implanted devices. In vivo longevity of various devices and the biocompatibility of biomaterials depend on how adjacent tissue interacts. How closely the rat model predicts the human response has not been well characterized. The objective of this study was to compare rat and human subcutaneous foreign body responses by monitoring the biochemical environment at a polymer-tissue interface over 8 days using microdialysis. Polyamide microdialysis probes were implanted subcutaneously in humans and rats (n = 12). Daily microdialysis samples were analyzed for glucose, lactate, pyruvate, glycerol, and urea. Blood glucose was also monitored. Analyte concentrations differed significantly between rats and humans at the implant-tissue interface. There were also qualitative differences in the 8-day trends. For example, over 8 days, microdialysate glucose increased two- to fourfold in humans but decreased in rats (P < 0.001). This study reveals profound physiological differences at material-tissue interfaces in rats and humans and highlights the need for caution when extrapolating subcutaneous rat biocompatibility data to humans.

  1. Sterol-Rich Membrane Domains Define Fission Yeast Cell Polarity.

    PubMed

    Makushok, Tatyana; Alves, Paulo; Huisman, Stephen Michiel; Kijowski, Adam Rafal; Brunner, Damian

    2016-05-19

    Cell polarization is crucial for the functioning of all organisms. The cytoskeleton is central to the process but its role in symmetry breaking is poorly understood. We study cell polarization when fission yeast cells exit starvation. We show that the basis of polarity generation is de novo sterol biosynthesis, cell surface delivery of sterols, and their recruitment to the cell poles. This involves four phases occurring independent of the polarity factor cdc42p. Initially, multiple, randomly distributed sterol-rich membrane (SRM) domains form at the plasma membrane, independent of the cytoskeleton and cell growth. These domains provide platforms on which the growth and polarity machinery assembles. SRM domains are then polarized by the microtubule-dependent polarity factor tea1p, which prepares for monopolar growth initiation and later switching to bipolar growth. SRM polarization requires F-actin but not the F-actin organizing polarity factors for3p and bud6p. We conclude that SRMs are key to cell polarization.

  2. Proton exchange membrane fuel cell technology for transportation applications

    SciTech Connect

    Swathirajan, S.

    1996-04-01

    Proton Exchange Membrane (PEM) fuel cells are extremely promising as future power plants in the transportation sector to achieve an increase in energy efficiency and eliminate environmental pollution due to vehicles. GM is currently involved in a multiphase program with the US Department of Energy for developing a proof-of-concept hybrid vehicle based on a PEM fuel cell power plant and a methanol fuel processor. Other participants in the program are Los Alamos National Labs, Dow Chemical Co., Ballard Power Systems and DuPont Co., In the just completed phase 1 of the program, a 10 kW PEM fuel cell power plant was built and tested to demonstrate the feasibility of integrating a methanol fuel processor with a PEM fuel cell stack. However, the fuel cell power plant must overcome stiff technical and economic challenges before it can be commercialized for light duty vehicle applications. Progress achieved in phase I on the use of monolithic catalyst reactors in the fuel processor, managing CO impurity in the fuel cell stack, low-cost electrode-membrane assembles, and on the integration of the fuel processor with a Ballard PEM fuel cell stack will be presented.

  3. Voltage- and Tension-Dependent Lipid Mobility in the Outer Hair Cell Plasma Membrane

    NASA Astrophysics Data System (ADS)

    Oghalai, John S.; Zhao, Hong-Bo; Kutz, J. Walter; Brownell, William E.

    2000-01-01

    The mechanism responsible for electromotility of outer hair cells in the ear is unknown but is thought to reside within the plasma membrane. Lipid lateral diffusion in the outer hair cell plasma membrane is a sigmoidal function of transmembrane potential and bathing media osmolality. Cell depolarization or hyposmotic challenge shorten the cell and reduce membrane fluidity by half. Changing the membrane tension with amphipathic drugs results in similar reductions. These dynamic changes in membrane fluidity represent the modulation of membrane tension by lipid-protein interactions. The voltage dependence may be associated with the force-generating motors that contribute to the exquisite sensitivity of mammalian hearing.

  4. Transient electrical field across cellular membranes: pulsed electric field treatment of microbial cells

    NASA Astrophysics Data System (ADS)

    Timoshkin, I. V.; MacGregor, S. J.; Fouracre, R. A.; Crichton, B. H.; Anderson, J. G.

    2006-02-01

    The pulsed electric field (PEF) treatment of liquid and pumpable products contaminated with microorganisms has attracted significant interest from the pulsed power and bioscience research communities particularly because the inactivation mechanism is non-thermal, thereby allowing retention of the original nutritional and flavour characteristics of the product. Although the biological effects of PEF have been studied for several decades, the physical mechanisms of the interaction of the fields with microorganisms is still not fully understood. The present work is a study of the dynamics of the electrical field both in a PEF treatment chamber with dielectric barriers and in the plasma (cell) membrane of a microbial cell. It is shown that the transient process can be divided into three physical phases, and models for these phases are proposed and briefly discussed. The complete dynamics of the time development of the electric field in a spherical dielectric shell representing the cellular membrane is then obtained using an analytical solution of the Ohmic conduction problem. It was found that the field in the membrane reaches a maximum value that could be two orders of magnitude higher than the original Laplacian electrical field in the chamber, and this value was attained in a time comparable to the field relaxation time in the chamber. Thus, the optimal duration of the field during PEF treatment should be equal to such a time.

  5. Analysis and Test of a Proton Exchange Membrane Fuel Cell Power System for Space Power Applications

    NASA Technical Reports Server (NTRS)

    Vasquez, Arturo; Varanauski, Donald; Clark, Robert, Jr.

    2000-01-01

    An effort is underway to develop a prototype Proton Exchange Membrane (PEM) Fuel Cell breadboard system for fuhlre space applications. This prototype will be used to develop a comprehensive design basis for a space-rated PEM fuel cell powerplant. The prototype system includes reactant pressure regulators, ejector-based reactant pumps, a 4-kW fuel cell stack and cooling system, and a passive, membranebased oxygen / water separator. A computer model is being developed concurrently to analytically predict fluid flow in the oxidant reactant system. Fuel cells have historically played an important role in human-rated spacecraft. The Gemini and Apollo spacecraft used fuel cells for vehicle electrical power. The Space Shuttle currently uses three Alkaline Fuel Cell Powerplants (AFCP) to generate all of the vehicle's 15-20kW electrical power. Engineers at the Johnson Space Center have leveraged off the development effort ongoing in the commercial arena to develop PEM fuel cel ls for terrestrial uses. The prototype design originated from efforts to develop a PEM fuel cell replacement for the current Space Shuttle AFCP' s. In order to improve on the life and an already excellent hi storical record of reliability and safety, three subsystems were focused on. These were the fuel cell stack itself, the reactant circulation devices, and reactant / product water separator. PEM fuel cell stack performance is already demonstrating the potential for greater than four times the useful life of the current Shuttle's AFCP. Reactant pumping for product water removal has historically been accomplished with mechanical pumps. Ejectors offer an effective means of reactant pumping as well as the potential for weight reduction, control simplification, and long life. Centrifugal water separation is used on the current AFCP. A passive, membrane-based water separator offers compatibility with the micro-gravity environment of space, and the potential for control simplification, elimination of

  6. Evaluation of stem cell components in retrocorneal membranes.

    PubMed

    Lee, Seok Hyun; Kim, Kyoung Woo; Kim, Mi Kyung; Chun, Yeoun Sook; Kim, Jae Chan

    2014-06-01

    The purpose of this study was to elucidate the origin and cellular composition of retrocorneal membranes (RCMs) associated with chemical burns using immunohistochemical staining for primitive cell markers. Six cases of RCMs were collected during penetrating keratoplasty. We examined RCMs with hematoxylin and eosin (H&E), periodic acid-Schiff (PAS) staining and immunohistochemical analysis using monoclonal antibodies against hematopoietic stem cells (CD34, CD133, c-kit), mesenchymal stem cells (beta-1-integrin, TGF-β, vimentin, hSTRO-1), fibroblasts (FGF-β, α-smooth muscle actin), and corneal endothelial cells (type IV collagen, CD133, VEGF, VEGFR1). Histologic analysis of RCMs revealed an organized assembly of spindle-shaped cells, pigment-laden cells, and thin collagenous matrix structures. RCMs were positive for markers of mesenchymal stem cells including beta-1-integrin, TGF-β, vimentin, and hSTRO-1. Fibroblast markers were also positive, including FGF-β and α-smooth muscle actin (SMA). In contrast, immunohistochemical staining was negative for hematopoietic stem cell markers including CD34, CD133 and c-kit as well as corneal endothelial cell markers such as type IV collagen, CD133 except VEGF and VEGFR1. Pigment-laden cells did not stain with any antibodies. The results of this study suggest that RCMs consist of a thin collagen matrix and fibroblast-like cells and may be a possible neogenetic structure produced from a lineage of bone marrow-derived mesenchymal stem cells.

  7. Analytical applications of microbial fuel cells. Part II: Toxicity, microbial activity and quantification, single analyte detection and other uses.

    PubMed

    Abrevaya, Ximena C; Sacco, Natalia J; Bonetto, Maria C; Hilding-Ohlsson, Astrid; Cortón, Eduardo

    2015-01-15

    Microbial fuel cells were rediscovered twenty years ago and now are a very active research area. The reasons behind this new activity are the relatively recent discovery of electrogenic or electroactive bacteria and the vision of two important practical applications, as wastewater treatment coupled with clean energy production and power supply systems for isolated low-power sensor devices. Although some analytical applications of MFCs were proposed earlier (as biochemical oxygen demand sensing) only lately a myriad of new uses of this technology are being presented by research groups around the world, which combine both biological-microbiological and electroanalytical expertises. This is the second part of a review of MFC applications in the area of analytical sciences. In Part I a general introduction to biological-based analytical methods including bioassays, biosensors, MFCs design, operating principles, as well as, perhaps the main and earlier presented application, the use as a BOD sensor was reviewed. In Part II, other proposed uses are presented and discussed. As other microbially based analytical systems, MFCs are satisfactory systems to measure and integrate complex parameters that are difficult or impossible to measure otherwise, such as water toxicity (where the toxic effect to aquatic organisms needed to be integrated). We explore here the methods proposed to measure toxicity, microbial metabolism, and, being of special interest to space exploration, life sensors. Also, some methods with higher specificity, proposed to detect a single analyte, are presented. Different possibilities to increase selectivity and sensitivity, by using molecular biology or other modern techniques are also discussed here.

  8. Interaction of Boron Nitride Nanosheets with Model Cell Membranes.

    PubMed

    Hilder, Tamsyn A; Gaston, Nicola

    2016-06-03

    Boron nitride nanomaterials have attracted attention for biomedical applications, due to their improved biocompatibility when compared with carbon nanomaterials. Recently, graphene and graphene oxide nanosheets have been shown, both experimentally and computationally, to destructively extract phospholipids from Escherichia coli. Boron nitride nanosheets (BNNSs) have exciting potential biological and environmental applications, for example the ability to remove oil from water. These applications are likely to increase the exposure of prokaryotes and eukaryotes to BNNSs. Yet, despite their promise, the interaction between BNNSs and cell membranes has not yet been investigated. Here, all-atom molecular dynamics simulations were used to demonstrate that BNNSs are spontaneously attracted to the polar headgroups of the lipid bilayer. The BNNSs do not passively cross the lipid bilayer, most likely due to the large forces experienced by the BNNSs. This study provides insight into the interaction of BNNSs with cell membranes and may aid our understanding of their improved biocompatibility.

  9. Collaboration between primitive cell membranes and soluble catalysts.

    PubMed

    Adamala, Katarzyna P; Engelhart, Aaron E; Szostak, Jack W

    2016-03-21

    One widely held model of early life suggests primitive cells consisted of simple RNA-based catalysts within lipid compartments. One possible selective advantage conferred by an encapsulated catalyst is stabilization of the compartment, resulting from catalyst-promoted synthesis of key membrane components. Here we show model protocell vesicles containing an encapsulated enzyme that promotes the synthesis of simple fatty acid derivatives become stabilized to Mg(2+), which is required for ribozyme activity and RNA synthesis. Thus, protocells capable of such catalytic transformations would have enjoyed a selective advantage over other protocells in high Mg(2+) environments. The synthetic transformation requires both the catalyst and vesicles that solubilize the water-insoluble precursor lipid. We suggest that similar modified lipids could have played a key role in early life, and that primitive lipid membranes and encapsulated catalysts, such as ribozymes, may have acted in conjunction with each other, enabling otherwise-impossible chemical transformations within primordial cells.

  10. Patterns of Nonelectrolyte Permeability in Human Red Blood Cell Membrane

    PubMed Central

    Naccache, P.; Sha'afi, R. I.

    1973-01-01

    The permeability of human red cell membrane to 90 different molecules has been measured. These solutes cover a wide spectrum of nonelectrolytes with varying chemical structure, chain length, lipid solubility, chemical reactive group, ability to form hydrogen bonds, and other properties. In general, the present study suggests that the permeability of red cell membrane to a large solute is determined by lipid solubility, its molecular size, and its hydrogen-bonding ability. The permeability coefficient increases with increasing lipid solubility and decreasing ability to form hydrogen bonds, whereas it decreases with increasing molecular size. In the case of small solutes, the predominant diffusion factor is steric hindrance augmented by lipid solubility. It is also found that replacement of a hydroxyl group by a carbonyl group or an ether linkage tends to increase permeability. On the other hand, replacement of a hydroxyl group by an amide group tends to decrease the permeability coefficient. PMID:4804758

  11. Quantitative understanding of cell signaling: The importance of membrane organization

    PubMed Central

    Radhakrishnan, Krishnan; Halász, Ádám; Vlachos, Dion; Edwards, Jeremy S.

    2010-01-01

    Systems biology modeling of signal transduction pathways traditionally employs ordinary differential equations, deterministic models based on assumptions of spatial homogeneity. However, this can be a poor approximation for certain aspects of signal transduction, especially its initial steps: the cell membrane exhibits significant spatial organization, with diffusion rates approximately two orders of magnitude slower than those in the cytosol. Thus, to unravel the complexities of signaling pathways, quantitative models must consider spatial organization as an important feature of cell signaling. Furthermore, spatial separation limits the number of molecules that can physically interact, requiring stochastic simulation methods that account for individual molecules. Herein, we discuss the need for mathematical models and experiments that appreciate the importance of spatial organization in the membrane. PMID:20829029

  12. Collaboration between primitive cell membranes and soluble catalysts

    PubMed Central

    Adamala, Katarzyna P.; Engelhart, Aaron E.; Szostak, Jack W.

    2016-01-01

    One widely held model of early life suggests primitive cells consisted of simple RNA-based catalysts within lipid compartments. One possible selective advantage conferred by an encapsulated catalyst is stabilization of the compartment, resulting from catalyst-promoted synthesis of key membrane components. Here we show model protocell vesicles containing an encapsulated enzyme that promotes the synthesis of simple fatty acid derivatives become stabilized to Mg2+, which is required for ribozyme activity and RNA synthesis. Thus, protocells capable of such catalytic transformations would have enjoyed a selective advantage over other protocells in high Mg2+ environments. The synthetic transformation requires both the catalyst and vesicles that solubilize the water-insoluble precursor lipid. We suggest that similar modified lipids could have played a key role in early life, and that primitive lipid membranes and encapsulated catalysts, such as ribozymes, may have acted in conjunction with each other, enabling otherwise-impossible chemical transformations within primordial cells. PMID:26996603

  13. Membrane associated qualitative differences in cell ultrastructure of chemically and high pressure cryofixed plant cells.

    PubMed

    Zechmann, Bernd; Müller, Maria; Zellnig, Günther

    2007-06-01

    Membrane contrast can sometimes be poor in biological samples after high pressure freezing (HPF) and freeze substitution (FS). The addition of water to the FS-medium has been shown to improve membrane contrast in animal tissue and yeast. In the present study we tested the effects of 1% and 5% water added to the FS-medium (2% osmium with 0.2% uranyl acetate in anhydrous acetone) on the quality and visibility of membranes in high pressure frozen leaf samples of Cucurbita pepo L. plants and compared them to chemically fixed cells (3% glutaraldehyde post-fixed with 1% osmium tetroxide). The addition of water to the FS-medium drastically decreased the amounts of well preserved cells and did not significantly improve the quality nor visibility of membranes. In samples that were freeze substituted in FS-media containing 1% and 5% water the width of thylakoid membranes was found to be significantly increased of about 20% and the perinuclear space was up to 76% wider in comparison to what was found in samples which were freeze substituted without water. No differences were found in the thickness of membranes between chemically and cryofixed cells that were freeze substituted in the FS-medium without water. Nevertheless, in chemically fixed cells the intrathylakoidal space was about 120% wider than in cryofixed cells that were freeze substituted with or without water. The present results demonstrate that the addition of water to the FS-medium does not improve membrane contrast but changes the width of thylakoid membranes and the perinuclear space in the present plant material. The addition of water to the FS-medium is therefore not as essential for improved membrane contrast in the investigated plant samples as it was observed in cells of animal tissues and yeast cells.

  14. Analytical cell adhesion chromatography reveals impaired persistence of metastatic cell rolling adhesion to P-selectin

    PubMed Central

    Oh, Jaeho; Edwards, Erin E.; McClatchey, P. Mason; Thomas, Susan N.

    2015-01-01

    ABSTRACT Selectins facilitate the recruitment of circulating cells from the bloodstream by mediating rolling adhesion, which initiates the cell–cell signaling that directs extravasation into surrounding tissues. To measure the relative efficiency of cell adhesion in shear flow for in vitro drug screening, we designed and implemented a microfluidic-based analytical cell adhesion chromatography system. The juxtaposition of instantaneous rolling velocities with elution times revealed that human metastatic cancer cells, but not human leukocytes, had a reduced capacity to sustain rolling adhesion with P-selectin. We define a new parameter, termed adhesion persistence, which is conceptually similar to migration persistence in the context of chemotaxis, but instead describes the capacity of cells to resist the influence of shear flow and sustain rolling interactions with an adhesive substrate that might modulate the probability of extravasation. Among cell types assayed, adhesion persistence to P-selectin was specifically reduced in metastatic but not leukocyte-like cells in response to a low dose of heparin. In conclusion, we demonstrate this as an effective methodology to identify selectin adhesion antagonist doses that modulate homing cell adhesion and engraftment in a cell-subtype-selective manner. PMID:26349809

  15. The insecticide DDT decreases membrane potential and cell input resistance of cultured human liver cells.

    PubMed

    Schefczik, K; Buff, K

    1984-10-03

    The resting membrane potential, Em, and the cell input resistance, Rinp, of cultured human Chang liver cells were measured using the single electrode 'double-pulse' current clamp technique, following exposure of the cells to the insecticide DDT (20 microM). In control (unexposed) cells, the mean Em was -24 mV, and the mean Rinp was 30 M omega. Neither parameter was significantly impaired after 1 h of cell exposure to DDT. But after 7 and 48 h, the Em was depolarized by 15 and 25 mV, respectively, in parallel with a decrease of the cell input resistance. The strongly time-delayed effect of DDT on Chang liver cell membranes may indicate a mode of interaction different from excitable membranes.

  16. Do heavy ions cause microlesions in cell membranes?

    NASA Technical Reports Server (NTRS)

    Koniarek, Jan P.; Worgul, Basil V.

    1992-01-01

    The microlesion question is investigated by monitoring the electrical potential difference across the endothelium of rat corneas in vitro before, during, and after irradiation. When the corneas were exposed to 1 Gy of Fe-56 ions (450 and 600 MeV/a.m.u.), no effect was detected on this parameter. These results suggest that direct physical damage to cell membranes, as predicted by the microlesion theory, does not take place.

  17. Interferometric tomography of fuel cells for monitoring membrane water content.

    PubMed

    Waller, Laura; Kim, Jungik; Shao-Horn, Yang; Barbastathis, George

    2009-08-17

    We have developed a system that uses two 1D interferometric phase projections for reconstruction of 2D water content changes over time in situ in a proton exchange membrane (PEM) fuel cell system. By modifying the filtered backprojection tomographic algorithm, we are able to incorporate a priori information about the object distribution into a fast reconstruction algorithm which is suitable for real-time monitoring.

  18. A micromechanic study of cell polarity and plasma membrane cell body coupling in Dictyostelium.

    PubMed Central

    Merkel, R; Simson, R; Simson, D A; Hohenadl, M; Boulbitch, A; Wallraff, E; Sackmann, E

    2000-01-01

    We used micropipettes to aspirate leading and trailing edges of wild-type and mutant cells of Dictyostelium discoideum. Mutants were lacking either myosin II or talin, or both proteins simultaneously. Talin is a plasma membrane-associated protein important for the coupling between membrane and actin cortex, whereas myosin II is a cytoplasmic motor protein essential for the locomotion of Dictyostelium cells. Aspiration into the pipette occurred above a threshold pressure only. For all cells containing talin this threshold was significantly lower at the leading edge of an advancing cell as compared to its rear end, whereas we found no such difference in cells lacking talin. Wild-type and talin-deficient cells were able to retract from the pipette against an applied suction pressure. In these cells, retraction was preceded by an accumulation of myosin II in the tip of the aspirated cell lobe. Mutants lacking myosin II could not retract, even if the suction pressures were removed after aspiration. We interpreted the initial instability and the subsequent plastic deformation of the cell surface during aspiration in terms of a fracture between the cell plasma membrane and the cell body, which may involve destruction of part of the cortex. Models are presented that characterize the coupling strength between membrane and cell body by a surface energy sigma. We find sigma approximately 0.6(1.6) mJ/m(2) at the leading (trailing) edge of wild-type cells. PMID:10920005

  19. Polymer Electrolyte Membrane (PEM) Fuel Cells Modeling and Optimization

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuqian; Wang, Xia; Shi, Zhongying; Zhang, Xinxin; Yu, Fan

    2006-11-01

    Performance of polymer electrolyte membrane (PEM) fuel cells is dependent on operating parameters and designing parameters. Operating parameters mainly include temperature, pressure, humidity and the flow rate of the inlet reactants. Designing parameters include reactants distributor patterns and dimensions, electrodes dimensions, and electrodes properties such as porosity, permeability and so on. This work aims to investigate the effects of various designing parameters on the performance of PEM fuel cells, and the optimum values will be determined under a given operating condition.A three-dimensional steady-state electrochemical mathematical model was established where the mass, fluid and thermal transport processes are considered as well as the electrochemical reaction. A Powell multivariable optimization algorithm will be applied to investigate the optimum values of designing parameters. The objective function is defined as the maximum potential of the electrolyte fluid phase at the membrane/cathode interface at a typical value of the cell voltage. The robustness of the optimum design of the fuel cell under different cell potentials will be investigated using a statistical sensitivity analysis. By comparing with the reference case, the results obtained here provide useful tools for a better design of fuel cells.

  20. Proton electrolyte membrane properties and direct methanol fuel cell performance. II. Fuel cell performance and membrane properties effects

    NASA Astrophysics Data System (ADS)

    Silva, V. S.; Schirmer, J.; Reissner, R.; Ruffmann, B.; Silva, H.; Mendes, A.; Madeira, L. M.; Nunes, S. P.

    In order to study the relationship between the properties of proton electrolyte membranes (PEMs), obtained through standard characterization methods, and the direct methanol fuel cell (DMFC) performance, inorganic-organic hybrid membranes, modified via in situ hydrolysis, were used in a membrane electrolyte assembly (MEA) for DMFC application. The membranes, the characterization of which was performed in the previous paper of this series, were based on sulfonated poly(ether ether ketone) (sPEEK) with a sulfonation degree (SD) of 87% and were loaded with different amounts of zirconium oxide (5.0, 7.5, 10.0, 12.5 wt.%). The standard characterization methods applied were impedance spectroscopy (proton conductivity), water uptake, and pervaporation (permeability to methanol). The MEAs were characterized investigating the DMFC current-voltage polarization curves, constant voltage current (CV, 35 mV), and open-circuit voltage (OCV). The fuel cell ohmic resistance (null phase angle impedance, NPAI) and CO 2 concentration in the cathode outlet were also measured. The characterization results show that the incorporation of the inorganic oxide in the polymer network decreases the DMFC current density for CV experiments, CO 2 concentration in the cathode outlet for both OCV and CV experiments and, finally, the maximum power density output. The opposite effect was verified in terms of the NPAI (ohmic resistance) for both OCV and CV experiments. A good agreement was found between the studied DMFC performance parameters and the characterization results evaluated by impedance spectroscopy, water uptake and pervaporation experiments.

  1. Latent progenitor cells as potential regulators for tympanic membrane regeneration

    NASA Astrophysics Data System (ADS)

    Kim, Seung Won; Kim, Jangho; Seonwoo, Hoon; Jang, Kyung-Jin; Kim, Yeon Ju; Lim, Hye Jin; Lim, Ki-Taek; Tian, Chunjie; Chung, Jong Hoon; Choung, Yun-Hoon

    2015-06-01

    Tympanic membrane (TM) perforation, in particular chronic otitis media, is one of the most common clinical problems in the world and can present with sensorineural healing loss. Here, we explored an approach for TM regeneration where the latent progenitor or stem cells within TM epithelial layers may play an important regulatory role. We showed that potential TM stem cells present highly positive staining for epithelial stem cell markers in all areas of normal TM tissue. Additionally, they are present at high levels in perforated TMs, especially in proximity to the holes, regardless of acute or chronic status, suggesting that TM stem cells may be a potential factor for TM regeneration. Our study suggests that latent TM stem cells could be potential regulators of regeneration, which provides a new insight into this clinically important process and a potential target for new therapies for chronic otitis media and other eardrum injuries.

  2. MECHANISM OF GLUCOSE TRANSPORT ACROSS THE YEAST CELL MEMBRANE

    PubMed Central

    Cirillo, Vincent P.

    1962-01-01

    Cirillo, Vincent P. (Seton Hall College of Medicine and Dentistry, Jersey City, N.J.). Mechanism of glucose transport across the yeast cell membrane. J. Bacteriol. 84:485–491. 1962.—The kinetics of d-glucose and l-sorbose transport was studied in Saccharomyces cerevisiae inhibited with iodoacetic acid under nitrogen to prevent glucose metabolism. d-Glucose was found to compete with l-sorbose for a common membrane transport system with an apparent affinity greater than 25 times that of sorbose. A comparison of the net rate of glucose and sorbose transport at 50 and 500 mm external concentration showed that glucose transport is greater than that of sorbose from the lower concentration, but sorbose transport is greater than glucose at the higher concentration. This reversal of transport rate of two sugars with markedly different affinities is predicted by the membrane carrier theory. A further prediction of carrier theory was confirmed by the demonstration that the rate of glucose transport into fructose-loaded cells is greater than into unloaded cells. PMID:14021412

  3. Graphene-doped electrospun nanofiber membrane electrodes and proton exchange membrane fuel cell performance

    NASA Astrophysics Data System (ADS)

    Wei, Meng; Jiang, Min; Liu, Xiaobo; Wang, Min; Mu, Shichun

    2016-09-01

    A rational electrode structure can allow proton exchange membrane (PEM) fuel cells own high performance with a low noble metal loading and an optimal transport pathway for reaction species. In this study, we develop a graphene doped polyacrylonitile (PAN)/polyvinylident fluoride (PVDF) (GPP) electrospun nanofiber electrode with improved electrical conductivity and high porosity, which could enhance the triple reaction boundary and promote gas and water transport throughout the porous electrode. Thus the increased electrochemical active surface area (ECSA) of Pt catalysts and fuel cell performance can be expected. As results, the ECSA of hot-pressed electrospun electrodes with 2 wt% graphene oxide (GO) is up to 84.3 m2/g, which is greatly larger than that of the conventional electrode (59.5 m2/g). Significantly, the GPP nanofiber electrospun electrode with Pt loading of 0.2 mg/cm2 exhibits higher fuel cell voltage output and stability than the conventional electrode.

  4. Quantitative analysis of cell surface membrane proteins using membrane-impermeable chemical probe coupled with 18O labeling.

    PubMed

    Zhang, Haizhen; Brown, Roslyn N; Qian, Wei-Jun; Monroe, Matthew E; Purvine, Samuel O; Moore, Ronald J; Gritsenko, Marina A; Shi, Liang; Romine, Margaret F; Fredrickson, James K; Pasa-Tolić, Ljiljana; Smith, Richard D; Lipton, Mary S

    2010-05-07

    We report a mass spectrometry-based strategy for quantitative analysis of cell surface membrane proteome changes. The strategy includes enrichment of surface membrane proteins using a membrane-impermeable chemical probe followed by stable isotope (18)O labeling and LC-MS analysis. We applied this strategy for enriching membrane proteins expressed by Shewanella oneidensis MR-1, a Gram-negative bacterium with known metal-reduction capability via extracellular electron transfer between outer membrane proteins and extracellular electron receptors. LC/MS/MS analysis resulted in the identification of about 400 proteins with 79% of them being predicted to be membrane localized. Quantitative aspects of the membrane enrichment were shown by peptide level (16)O and (18)O labeling of proteins from wild-type and mutant cells (generated from deletion of a type II secretion protein, GspD) prior to LC-MS analysis. Using a chemical probe labeled pure protein as an internal standard for normalization, the quantitative data revealed reduced abundances in Delta gspD mutant cells of many outer membrane proteins including the outer membrane c-type cytochromes OmcA and MtrC, in agreement with a previous report that these proteins are substrates of the type II secretion system.

  5. A review of polymer electrolyte membranes for direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Neburchilov, Vladimir; Martin, Jonathan; Wang, Haijiang; Zhang, Jiujun

    This review describes the polymer electrolyte membranes (PEM) that are both under development and commercialized for direct methanol fuel cells (DMFC). Unlike the membranes for hydrogen fuelled PEM fuel cells, among which perfluorosulfonic acid based membranes show complete domination, the membranes for DMFC have numerous variations, each has its advantages and disadvantages. No single membrane is emerging as absolutely superior to others. This review outlines the prospects of the currently known membranes for DMFC. The membranes are evaluated according to various properties, including: methanol crossover, proton conductivity, durability, thermal stability and maximum power density. Hydrocarbon and composite fluorinated membranes currently show the most potential for low cost membranes with low methanol permeability and high durability. Some of these membranes are already beginning to impact the portable fuel cell market.

  6. Fascin, an Actin-bundling Protein, Induces Membrane Protrusions and Increases Cell Motility of Epithelial Cells

    PubMed Central

    Yamashiro, Shigeko; Yamakita, Yoshihiko; Ono, Shoichiro; Matsumura, Fumio

    1998-01-01

    Fascin is an actin-bundling protein that is found in membrane ruffles, microspikes, and stress fibers. The expression of fascin is greatly increased in many transformed cells, as well as in specialized normal cells including neuronal cells and antigen-presenting dendritic cells. A morphological characteristic common to these cells expressing high levels of fascin is the development of many membrane protrusions in which fascin is predominantly present. To examine whether fascin contributes to the alterations in microfilament organization at the cell periphery, we have expressed fascin in LLC-PK1 epithelial cells to levels as high as those found in transformed cells and in specialized normal cells. Expression of fascin results in large changes in morphology, the actin cytoskeleton, and cell motility: fascin-transfected cells form an increased number of longer and thicker microvilli on apical surfaces, extend lamellipodia-like structures at basolateral surfaces, and show disorganization of cell–cell contacts. Cell migration activity is increased by 8–17 times when assayed by modified Boyden chamber. Microinjection of a fascin protein into LLC-PK1 cells causes similar morphological alterations including the induction of lamellipodia at basolateral surfaces and formation of an increased number of microvilli on apical surfaces. Furthermore, microinjection of fascin into REF-52 cells, normal fibroblasts, induces the formation of many lamellipodia at all regions of cell periphery. These results together suggest that fascin is directly responsible for membrane protrusions through reorganization of the microfilament cytoskeleton at the cell periphery. PMID:9571235

  7. Production of membrane proteins through the wheat-germ cell-free technology.

    PubMed

    Nozawa, Akira; Nanamiya, Hideaki; Tozawa, Yuzuru

    2010-01-01

    Membrane proteins play crucial roles in various processes. However, biochemical characterization of the membrane proteins remains challenging due to the difficulty in producing membrane proteins in a functional state. Here, we describe a novel method for the production of functional membrane proteins based on a wheat germ cell-free translation system. Using this method, functional membrane proteins are successfully synthesized in the presence of liposomes and a detergent. In addition, the synthesized membrane proteins are easily purified from the cell-free translation mixture as proteoliposomes by sucrose density gradient ultracentrifugation. These advantages over conventional approaches are very helpful for the clarification of the function of membrane proteins.

  8. Self-humidified proton exchange membrane fuel cells: Operation of larger cells and fuel cell stacks

    SciTech Connect

    Dhar, H.P.; Lee, J.H.; Lewinski, K.A.

    1996-12-31

    The PEM fuel cell is promising as the power source for use in mobile and stationary applications primarily because of its high power density, all solid components, and simplicity of operation. For wide acceptability of this power source, its cost has to be competitive with the presently available energy sources. The fuel cell requires continuous humidification during operation as a power source. The humidification unit however, increases fuel cell volume, weight, and therefore decreases its overall power density. Great advantages in terms of further fuel cell simplification can be achieved if the humidification process can be eliminated or minimized. In addition, cost reductions are associated with the case of manufacturing and operation. At BCS Technology we have developed a technology of self-humidified operation of PEM fuel cells based on the mass balance of the reactants and products and the ability of membrane electrode assembly (MEA) to retain water necessary for humidification under the cell operating conditions. The reactants enter the fuel cell chambers without carrying any form of water, whether in liquid or vapor form. Basic principles of self-humidified operation of fuel cells as practiced by BCS Technology, Inc. have been presented previously in literature. Here, we report the operation of larger self-humidified single cells and fuel cell stacks. Fuel cells of areas Up to 100 cm{sup 2} have been operated. We also show the self-humidified operation of fuel cell stacks of 50 and 100 cm{sup 2} electrode areas.

  9. Nanofiber Composite Membranes for Alkaline Fuel Cells: Generation of Compositional, Morphological, and Functional Property Relationships

    DTIC Science & Technology

    2015-12-01

    properties of nanofiber composite anion-exchange membranes for alkaline fuel cells. A new membrane fabrication strategy, utilizing polymer fiber...electrospinning, will be employed to make hydroxide-conducting membranes with an entirely new morphology, where one electrospun polymer provides pathways...for ion conductivity and the second electrospun polymer restricts ionomer swelling and imparts mechanical strength to the membrane. The functional

  10. Proton exchange membrane fuel cells with chromium nitridenanocrystals as electrocatalysts

    SciTech Connect

    Zhong, Hexiang; Chen, Xiaobo; Zhang, Huamin; Wang, Meiri; Mao,Samuel S.

    2007-07-01

    Polymer electrolyte membrane fuel cells (PEMFCs) are energy conversion devices that produce electricity from a supply of fuel, such as hydrogen. One of the major challenges in achieving efficient energy conversion is the development of cost-effective materials that can act as electrocatalysts for PEMFCs. In this letter, we demonstrate that, instead of conventional noble metals, such as platinum, chromium nitride nanocrystals of fcc structure exhibit attractive catalytic activity for PEMFCs. Device testing indicates good stability of nitride nanocrystals in low temperature fuel cell operational environment.

  11. Dynamic analysis of magnetic nanoparticles crossing cell membrane

    NASA Astrophysics Data System (ADS)

    Pedram, Maysam Z.; Shamloo, Amir; Ghafar-Zadeh, Ebrahim; Alasty, Aria

    2017-01-01

    Nowadays, nanoparticles (NPs) are used in a variety of biomedical applications including brain disease diagnostics and subsequent treatments. Among the various types of NPs, magnetic nanoparticles (MNPs) have been implemented by many research groups for an array of life science applications. In this paper, we studied MNPs controlled delivery into the endothelial cells using a magnetic field. Dynamics equations of MNPs were defined in the continuous domain using control theory methods and were applied to crossing the cell membrane. This study, dedicated to clinical and biomedical research applications, offers a guideline for the generation of a magnetic field required for the delivery of MNPs.

  12. A hybrid microbial fuel cell membrane bioreactor with a conductive ultrafiltration membrane biocathode for wastewater treatment.

    PubMed

    Malaeb, Lilian; Katuri, Krishna P; Logan, Bruce E; Maab, Husnul; Nunes, S P; Saikaly, Pascal E

    2013-10-15

    A new hybrid, air-biocathode microbial fuel cell-membrane bioreactor (MFC-MBR) system was developed to achieve simultaneous wastewater treatment and ultrafiltration to produce water for direct reclamation. The combined advantages of this system were achieved by using an electrically conductive ultrafiltration membrane as both the cathode and the membrane for wastewater filtration. The MFC-MBR used an air-biocathode, and it was shown to have good performance relative to an otherwise identical cathode containing a platinum catalyst. With 0.1 mm prefiltered domestic wastewater as the feed, the maximum power density was 0.38 W/m(2) (6.8 W/m(3)) with the biocathode, compared to 0.82 W/m(2) (14.5 W/m(3)) using the platinum cathode. The permeate quality from the biocathode reactor was comparable to that of a conventional MBR, with removals of 97% of the soluble chemical oxygen demand, 97% NH3-N, and 91% of total bacteria (based on flow cytometry). The permeate turbidity was <0.1 nephelometric turbidity units. These results show that a biocathode MFC-MBR system can achieve high levels of wastewater treatment with a low energy input due to the lack of a need for wastewater aeration.

  13. Fault tolerance control for proton exchange membrane fuel cell systems

    NASA Astrophysics Data System (ADS)

    Wu, Xiaojuan; Zhou, Boyang

    2016-08-01

    Fault diagnosis and controller design are two important aspects to improve proton exchange membrane fuel cell (PEMFC) system durability. However, the two tasks are often separately performed. For example, many pressure and voltage controllers have been successfully built. However, these controllers are designed based on the normal operation of PEMFC. When PEMFC faces problems such as flooding or membrane drying, a controller with a specific design must be used. This paper proposes a unique scheme that simultaneously performs fault diagnosis and tolerance control for the PEMFC system. The proposed control strategy consists of a fault diagnosis, a reconfiguration mechanism and adjustable controllers. Using a back-propagation neural network, a model-based fault detection method is employed to detect the PEMFC current fault type (flooding, membrane drying or normal). According to the diagnosis results, the reconfiguration mechanism determines which backup controllers to be selected. Three nonlinear controllers based on feedback linearization approaches are respectively built to adjust the voltage and pressure difference in the case of normal, membrane drying and flooding conditions. The simulation results illustrate that the proposed fault tolerance control strategy can track the voltage and keep the pressure difference at desired levels in faulty conditions.

  14. Cell Surface and Membrane Engineering: Emerging Technologies and Applications

    PubMed Central

    Saeui, Christopher T.; Mathew, Mohit P.; Liu, Lingshui; Urias, Esteban; Yarema, Kevin J.

    2015-01-01

    Membranes constitute the interface between the basic unit of life—a single cell—and the outside environment and thus in many ways comprise the ultimate “functional biomaterial”. To perform the many and often conflicting functions required in this role, for example to partition intracellular contents from the outside environment while maintaining rapid intake of nutrients and efflux of waste products, biological membranes have evolved tremendous complexity and versatility. This article describes how membranes, mainly in the context of living cells, are increasingly being manipulated for practical purposes with drug discovery, biofuels, and biosensors providing specific, illustrative examples. Attention is also given to biology-inspired, but completely synthetic, membrane-based technologies that are being enabled by emerging methods such as bio-3D printers. The diverse set of applications covered in this article are intended to illustrate how these versatile technologies—as they rapidly mature—hold tremendous promise to benefit human health in numerous ways ranging from the development of new medicines to sensitive and cost-effective environmental monitoring for pathogens and pollutants to replacing hydrocarbon-based fossil fuels. PMID:26096148

  15. Analytical Ultracentrifugation Sedimentation Velocity for the Characterization of Detergent-Solubilized Membrane Proteins Ca++-ATPase and ExbB

    PubMed Central

    Salvay, Andrés G.; Santamaria, Monica; le Maire, Marc

    2008-01-01

    We have investigated the potential of new methods of analysis of sedimentation velocity (SV) analytical ultracentrifugation (AUC) for the characterization of detergent-solubilized membrane proteins. We analyze the membrane proteins Ca++-ATPase and ExbB solubilized with DDM (dodecyl-β-d-maltoside). SV is extremely well suited for characterizing sample heterogeneity. DDM micelles (s20w = 3.1 S) and complexes (Ca++-ATPase: s20w = 7.3 S; ExbB: s20w = 4 S) are easily distinguished. Using different detergent and protein concentrations, SV does not detect any evidence of self-association for the two proteins. An estimate of bound detergent of 0.9 g/g for Ca++-ATPase and 1.5 g/g for ExbB is obtained from the combined analysis of SV profiles obtained using absorbance and interference optics. Combining s20w with values of the hydrodynamic radius, Rs = 5.5 nm for Ca++-ATPase or Rs = 3.4 nm for ExbB, allows the determination of buoyant molar masses, Mb. In view of their Mb and composition, Ca++-ATPase and ExbB are monomers in our experimental conditions. We conclude that one of the main advantages of SV versus other techniques is the possibility to ascertain the homogeneity of the samples and to focus on a given complex even in the presence of other impurities or aggregates. The relative rapidity of SV measurements also allows experiments on unstable samples. PMID:19669527

  16. Better Proton-Conducting Polymers for Fuel-Cell Membranes

    NASA Technical Reports Server (NTRS)

    Narayan, Sri; Reddy, Prakash

    2012-01-01

    Polyoxyphenylene triazole sulfonic acid has been proposed as a basis for development of improved proton-conducting polymeric materials for solid-electrolyte membranes in hydrogen/air fuel cells. Heretofore, the proton-conducting membrane materials of choice have been exemplified by a family of perfluorosulfonic acid-based polymers (Nafion7 or equivalent). These materials are suitable for operation in the temperature of 75 to 85 C, but in order to reduce the sizes and/or increase the energy-conversion efficiencies of fuel-cell systems, it would be desirable to increase temperatures to as high as 120 C for transportation applications, and to as high as 180 C for stationary applications. However, at 120 C and at relative humidity values below 50 percent, the loss of water from perfluorosulfonic acid-based polymer membranes results in fuel-cell power densities too low to be of practical value. Therefore, membrane electrolyte materials that have usefully high proton conductivity in the temperature range of 180 C at low relative humidity and that do not rely on water for proton conduction at 180 C would be desirable. The proposed polyoxyphenylene triazole sulfonic acid-based materials have been conjectured to have these desirable properties. These materials would be free of volatile or mobile acid constituents. The generic molecular structure of these materials is intended to exploit the fact, demonstrated in previous research, that materials that contain ionizable acid and base groups covalently attached to thermally stable polymer backbones exhibit proton conduction even in the anhydrous state.

  17. Membrane Cholesterol Modulates LOX-1 Shedding in Endothelial Cells.

    PubMed

    Gioia, Magda; Vindigni, Giulia; Testa, Barbara; Raniolo, Sofia; Fasciglione, Giovanni Francesco; Coletta, Massimiliano; Biocca, Silvia

    2015-01-01

    The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a scavenger receptor responsible for ox-LDL recognition, binding and internalization, which is up-regulated during atherogenesis. Its activation triggers endothelium dysfunction and induces inflammation. A soluble form of LOX-1 has been identified in the human blood and its presence considered a biomarker of cardiovascular diseases. We recently showed that cholesterol-lowering drugs inhibit ox-LDL binding and internalization, rescuing the ox-LDL induced apoptotic phenotype in primary endothelial cells. Here we have investigated the molecular bases of human LOX-1 shedding by metalloproteinases and the role of cell membrane cholesterol on the regulation of this event by modulating its level with MβCD and statins. We report that membrane cholesterol affects the release of different forms of LOX-1 in cells transiently and stably expressing human LOX-1 and in a human endothelial cell line (EA.hy926). In particular, our data show that i) cholesterol depletion triggers the release of LOX-1 in exosomes as a full-length transmembrane isoform and as a truncated ectodomain soluble fragment (sLOX-1); ii) endothelial cells secrete a soluble metalloproteinase which induces LOX-1 ectodomain shedding and iii) long term statins treatment enhances sLOX-1 proteolytic shedding.

  18. Membrane currents of spiking cells isolated from turtle retina.

    PubMed

    Lasater, E M; Witkovsky, P

    1990-05-01

    We examined the membrane properties of spiking neurons isolated from the turtle (Pseudemys scripta) retina. The cells were maintained in culture for 1-7 days and were studied with the whole cell patch clamp technique. We utilized cells whose perikaryal diameters were greater than 15 microns since Kolb (1982) reported that ganglion cell perikarya in Pseudemys retina are 13-25 microns, whereas amacrine perikarya are less than 14 microns in diameter. We identified 5 currents in the studied cells: (1) a transient sodium current (INa) blocked by TTX, (2) a sustained calcium current (ICa) blocked by cobalt and enhanced by Bay-K 8644, (3) a calcium-dependent potassium current (IK(Ca)), (4) an A-type transient potassium current (IA) somewhat more sensitive to 4-AP than TEA, (5) a sustained potassium current (IK) more sensitive to TEA than 4-AP. The estimated average input resistance of the cells at -70 mV was 720 +/- 440 M omega. When all active currents were blocked, the membrane resistance between -130 and +20 mV was 2.5 G omega. When examined under current clamp, some cells produced multiple spikes to depolarizing steps of 0.1-0.3 nA, whereas other cells produced only a single spike irrespective of the strength of the current pulse. Most single spikers had an outward current that rose to a peak relatively slowly, whereas multiple spikers tend to have a more rapidly activating outward current. Under current clamp, 4-AP slowed the repolarization phase of the spike thus broadening it, but did not always abolish the ability to produce multiple spikes. TEA induced a depolarized plateau following the initial spike which precluded further spikes. It thus appears that the spiking patterns of the retinal cells are shaped primarily by the kinetics of INa, IK and IA and to a lesser extent by IK(Ca).

  19. Alkaline direct alcohol fuel cells using an anion exchange membrane

    NASA Astrophysics Data System (ADS)

    Matsuoka, Koji; Iriyama, Yasutoshi; Abe, Takeshi; Matsuoka, Masao; Ogumi, Zempachi

    Alkaline direct alcohol fuel cells using an OH-form anion exchange membrane and polyhydric alcohols were studied. A high open circuit voltage of ca. 800 mV was obtained for a cell using Pt-Ru/C (anode) and Pt/C (cathode) at 323 K, which was about 100-200 mV higher than that for a DMFC using Nafion ®. The maximum power densities were in the order of ethylene glycol > glycerol > methanol > erythritol > xylitol. Silver catalysts were used as a cathode catalyst to fabricate alkaline fuel cells, since silver catalyst is almost inactive in the oxidation of polyhydric alcohols. Alkaline direct ethylene glycol fuel cells using silver as a cathode catalyst gave excellent performance because higher concentrations of fuel could be supplied to the anode.

  20. Dual Split Protein (DSP) Assay to Monitor Cell-Cell Membrane Fusion.

    PubMed

    Nakane, Shuhei; Matsuda, Zene

    2015-01-01

    Fusion between viral and cellular membranes is the essential first step in infection of enveloped viruses. This step is mediated by viral envelope glycoproteins (Env) that recognize cellular receptors. The membrane fusion between the effector cells expressing viral Env and the target cells expressing its receptors can be monitored by several methods. We have recently developed a pair of chimeric reporter protein composed of split Renilla luciferase (RL) and split GFP. We named this reporter dual split protein (DSP), since it recovers both RL and GFP activities upon self reassociation. By using DSP, pore formation and content mixing between the effector and target cells can be monitored upon the recovery of RL and GFP activities after the membrane fusion. This quick assay provides quantitative as well as spatial information about membrane fusion mediated by viral Env.

  1. Membrane potentials of epithelial cells in rat small intestine

    PubMed Central

    Barry, R. J. C.; Eggenton, Jacqueline

    1972-01-01

    1. Stripped sacs of rat jejunum in which the outer muscle layers had been removed were found to maintain substantial transport and electrical activities. 2. Mucosal and serosal membrane potentials of epithelial cells of normal and stripped everted sacs of rat jejunum were recorded in vitro together with the transmural potential difference. 3. The cell interior was negative relative to both serosal and mucosal fluids, the transmural potential being the sum of the two membrane potentials. 4. Changes in the transmural potentials in the presence of actively transferred hexoses and amino acids were entirely due to variations in the serosal potential, the mucosal potential being unchanged. 5. Serosal and transmural potential increases on the addition of galactose were consistent with Michaelis—Menten kinetics, giving apparent Km values of 14·9 and 14·1 mM respectively. 6. Phlorrhizin, ouabain, 2,4-dinitrophenol and sodium fluoroacetate inhibited serosal potential changes in the presence of galactose. 7. Osmotic potentials resulting from transmural osmotic gradients originated from the serosal layers of the tissue. 8. The results are consistent with the concept of a serosally located, electrogenic sodium pump which is stimulated by actively transferred hexoses and amino acids. The sodium-dependent entry mechanism at the mucosal membrane is non-electrogenic. ImagesPlate 1 PMID:4646578

  2. Trans-cis isomerization of lipophilic dyes probing membrane microviscosity in biological membranes and in live cells.

    PubMed

    Chmyrov, Volodymyr; Spielmann, Thiemo; Hevekerl, Heike; Widengren, Jerker

    2015-06-02

    Membrane environment and fluidity can modulate the dynamics and interactions of membrane proteins and can thereby strongly influence the function of cells and organisms in general. In this work, we demonstrate that trans-cis isomerization of lipophilic dyes is a useful parameter to monitor packaging and fluidity of biomembranes. Fluorescence fluctuations, generated by trans-cis isomerization of the thiocarbocyanine dye Merocyanine 540 (MC540), were first analyzed by fluorescence correlation spectroscopy (FCS) in different alcohol solutions. Similar isomerization kinetics of MC540 in lipid vesicles could then also be monitored, and the influence of lipid polarity, membrane curvature, and cholesterol content was investigated. While no influence of membrane curvature and lipid polarity could be observed, a clear decrease in the isomerization rates could be observed with increasing cholesterol contents in the vesicle membranes. Finally, procedures to spatially map photoinduced and thermal isomerization rates on live cells by transient state (TRAST) imaging were established. On the basis of these procedures, MC540 isomerization was studied on live MCF7 cells, and TRAST images of the cells at different temperatures were found to reliably detect differences in the isomerization parameters. Our studies indicate that trans-cis isomerization is a useful parameter for probing membrane dynamics and that the TRAST imaging technique can provide spatial maps of photoinduced isomerization as well as both photoinduced and thermal back-isomerization, resolving differences in local membrane microviscosity in live cells.

  3. Golgi and vacuolar membrane proteins reach the vacuole in vps1 mutant yeast cells via the plasma membrane.

    PubMed

    Nothwehr, S F; Conibear, E; Stevens, T H

    1995-04-01

    The Vps1 protein of Saccharomyces cerevisiae is an 80-kD GTPase associated with the Golgi apparatus. Vps1p appears to play a direct role in the retention of late Golgi membrane proteins, which are mislocalized to the vacuolar membrane in its absence. The pathway by which late Golgi and vacuolar membrane proteins reach the vacuole in vps1 delta mutants was investigated by analyzing transport of these proteins in vps1 delta cells that also contained temperature sensitive mutations in either the SEC4 or END4 genes, which are required for a late step in secretion and the internalization step of endocytosis, respectively. Not only was vacuolar transport of a Golgi membrane protein blocked in the vps1 delta sec4-ts and vps1 delta end4-ts double mutant cells at the non-permissive temperature but vacuolar delivery of the vacuolar membrane protein, alkaline phosphatase was also blocked in these cells. Moreover, both proteins expressed in the vps1 delta end4-ts cells at the elevated temperature could be detected on the plasma membrane by a protease digestion assay indicating that these proteins are transported to the vacuole via the plasma membrane in vps1 mutant cells. These data strongly suggest that a loss of Vps1p function causes all membrane traffic departing from the late Golgi normally destined for the prevacuolar compartment to instead be diverted to the plasma membrane. We propose a model in which Vps1p is required for formation of vesicles from the late Golgi apparatus that carry vacuolar and Golgi membrane proteins bound for the prevacuolar compartment.

  4. Effect of cell culture using chitosan membranes on stemness marker genes in mesenchymal stem cells.

    PubMed

    Li, Zhiqiang; Tian, Xiaojun; Yuan, Yan; Song, Zhixiu; Zhang, Lili; Wang, Xia; Li, Tong

    2013-06-01

    Mesenchymal stem cell (MSC) therapy is a promising treatment for diseases of the nervous system. However, MSCs often lose their stemness and homing abilities when cultured in conventional two‑dimensional (2D) systems. Consequently, it is important to explore novel culture methods for MSC-based therapies in clinical practice. To investigate the effect of a cell culture using chitosan membranes on MSCs, the morphology of MSCs cultured using chitosan membranes was observed and the expression of stemness marker genes was analyzed. We demonstrated that MSCs cultured using chitosan membranes form spheroids. Additionally, the expression of stemness marker genes, including Oct4, Sox2 and Nanog, increased significantly when MSCs were cultured using chitosan membranes compared with 2D culture systems. Finally, MSCs cultured using chitosan membranes were found to have an increased potential to differentiate into nerve cells and chrondrocytes. In conclusion, we demonstrated that MSCs cultured on chitosan membranes maintain their stemness and homing abilities. This finding may be further investigated for the development of novel cell-based therapies for diseases involving neuron-like cells and chondrogenesis.

  5. NREL Develops Technique to Measure Membrane Thickness and Defects in Polymer Electrode Membrane Fuel Cells (Fact Sheet)

    SciTech Connect

    Not Available

    2010-11-01

    This fact sheet describes NREL's accomplishments in fuel cell membrane electrode assembly research and development. Work was performed by the Hydrogen Technologies and Systems Center and the National Center for Photovoltaics.

  6. Nanocomposite membranes based on polybenzimidazole and ZrO2 for high-temperature proton exchange membrane fuel cells.

    PubMed

    Nawn, Graeme; Pace, Giuseppe; Lavina, Sandra; Vezzù, Keti; Negro, Enrico; Bertasi, Federico; Polizzi, Stefano; Di Noto, Vito

    2015-04-24

    Owing to the numerous benefits obtained when operating proton exchange membrane fuel cells at elevated temperature (>100 °C), the development of thermally stable proton exchange membranes that demonstrate conductivity under anhydrous conditions remains a significant goal for fuel cell technology. This paper presents composite membranes consisting of poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (PBI4N) impregnated with a ZrO2 nanofiller of varying content (ranging from 0 to 22 wt %). The structure-property relationships of the acid-doped and undoped composite membranes have been studied using thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, wide-angle X-ray scattering, infrared spectroscopy, and broadband electrical spectroscopy. Results indicate that the level of nanofiller has a significant effect on the membrane properties. From 0 to 8 wt %, the acid uptake as well as the thermal and mechanical properties of the membrane increase. As the nanofiller level is increased from 8 to 22 wt % the opposite effect is observed. At 185 °C, the ionic conductivity of [PBI4N(ZrO2 )0.231 ](H3 PO4 )13 is found to be 1.04×10(-1)  S cm(-1) . This renders membranes of this type promising candidates for use in high-temperature proton exchange membrane fuel cells.

  7. Influence of estrogenic pesticides on membrane integrity and membrane transfer of monosaccharide into the human red cell

    SciTech Connect

    Ingermann, R.L. )

    1989-09-01

    Some natural and synthetic estrogens inhibit carrier-mediated transport of glucose into human red blood cells and membrane vesicles from the placenta. The inhibitory action of these estrogens on transport appears to be a direct effect at the membrane and does not involve receptor binding and protein synthesis. It is not clear, however, whether such inhibition is a common feature among estrogenic agents. Several chlorinated hydrocarbon pesticides have been shown to possess estrogenic activity. These pesticides could have inhibitory effects on the human sodium-independent glucose transporter. Owing to the apparent importance of this membrane transporter in human tissues, direct interaction of hormones and xenobiotics with the glucose transporter is of fundamental significance. Some pesticides have been shown to alter membrane structure directly and alter the passive permeability of membranes. Whether the estrogenic pesticides influence passive diffusion of sugars across membranes has not been established. Finally, preliminary observations have suggested that some estrogens and pesticides have lytic effects on intact cells. Consequently, this study focuses on the ability of several estrogens and estrogenic pesticides to disrupt the cell membrane, influence the monosaccharide transporter, and alter the rate of monosaccharide permeation through the membrane by simple diffusion.

  8. High temperature polymers for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Einsla, Brian Russel

    Novel proton exchange membranes (PEMs) were investigated that show potential for operating at higher temperatures in both direct methanol (DMFC) and H 2/air PEM fuel cells. The need for thermally stable polymers immediately suggests the possibility of heterocyclic polymers bearing appropriate ion conducting sites. Accordingly, monomers and random disulfonated poly(arylene ether) copolymers containing either naphthalimide, benzoxazole or benzimidazole moieties were synthesized via direct copolymerization. The ion exchange capacity (IEC) was varied by simply changing the ratio of disulfonated monomer to nonsulfonated monomer in the copolymerization step. Water uptake and proton conductivity of cast membranes increased with IEC. The water uptake of these heterocyclic copolymers was lower than that of comparable disulfonated poly(arylene ether) systems, which is a desirable improvement for PEMs. Membrane electrode assemblies were prepared and the initial fuel cell performance of the disulfonated polyimide and polybenzoxazole (PBO) copolymers was very promising at 80°C compared to the state-of-the-art PEM (NafionRTM); nevertheless these membranes became brittle under operating conditions. Several series of poly(arylene ether)s based on disodium-3,3'-disulfonate-4,4 '-dichlorodiphenylsulfone (S-DCDPS) and a benzimidazole-containing bisphenol were synthesized and afforded copolymers with enhanced stability. Selected properties of these membranes were compared to separately prepared miscible blends of disulfonated poly(arylene ether sulfone) copolymers and polybenzimidazole (PBI). Complexation of the sulfonic acid groups with the PBI structure reduced water swelling and proton conductivity. The enhanced proton conductivity of NafionRTM membranes has been proposed to be due to the aggregation of the highly acidic side-chain sulfonic acid sites to form ion channels. A series of side-chain sulfonated poly(arylene ether sulfone) copolymers based on methoxyhydroquinone was

  9. Elastic thickness compressibilty of the red cell membrane.

    PubMed

    Heinrich, V; Ritchie, K; Mohandas, N; Evans, E

    2001-09-01

    We have used an ultrasensitive force probe and optical interferometry to examine the thickness compressibility of the red cell membrane in situ. Pushed into the centers of washed-white red cell ghosts lying on a coverglass, the height of the microsphere-probe tip relative to its closest approach on the adjacent glass surface revealed the apparent material thickness, which began at approximately 90 nm per membrane upon detection of contact (force approximately 1-2 pN). With further impingement, the apparent thickness per membrane diminished over a soft compliant regime that spanned approximately 40 nm and stiffened on approach to approximately 50 nm under forces of approximately 100 pN. The same force-thickness response was obtained on recompression after retraction of the probe, which demonstrated elastic recoverability. Scaled by circumferences of the microspheres, the forces yielded energies of compression per area which exhibited an inverse distance dependence resembling that expected for flexible polymers. Attributed to the spectrin component of the membrane cytoskeleton, the energy density only reached one thermal energy unit (k(B)T) per spectrin tetramer near maximum compression. Hence, we hypothesized that the soft compliant regime probed in the experiments represented the compressibility of the outer region of spectrin loops and that the stiff regime < 50 nm was the response of a compact mesh of spectrin backed by a hardcore structure. To evaluate this hypothesis, we used a random flight theory for the entropic elasticity of polymer loops to model the spectrin network. We also examined the possibility that additional steric repulsion and apparent thickening could arise from membrane thermal-bending excitations. Fixing the energy scale to k(B)T/spectrin tetramer, the combined elastic response of a network of ideal polymer loops plus the membrane steric interaction correlated well with the measured dependence of energy density on distance for a statistical

  10. Water free proton conducting membranes based on poly-4-vinylpyridinebisulfate for fuel cells

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram R. (Inventor); Yen, Shiao-Pin S. (Inventor)

    2007-01-01

    Disclosed are methods for forming a water-free electrolyte membrane useful in fuel cells. Also provided is a water-free electrolyte membrane comprising a quaternized amine salt including poly-4-vinylpyridinebisulfate, a poly-4-vinylpyridinebisulfate silica composite, and a combination thereof and a fuel cell comprising the membrane.

  11. Heat sources in proton exchange membrane (PEM) fuel cells

    NASA Astrophysics Data System (ADS)

    Ramousse, Julien; Lottin, Olivier; Didierjean, Sophie; Maillet, Denis

    In order to model accurately heat transfer in PEM fuel cell, a particular attention had to be paid to the assessment of heat sources in the cell. Although the total amount of heat released is easily computed from its voltage, local heat sources quantification and localization are not simple. This paper is thus a discussion about heat sources/sinks distribution in a single cell, for which many bold assumptions are encountered in the literature. The heat sources or sinks under consideration are: (1) half-reactions entropy, (2) electrochemical activation, (3) water sorption/desorption at the GDL/membrane interfaces, (4) Joule effect in the membrane and (5) water phase change in the GDL. A detailed thermodynamic study leads to the conclusion that the anodic half-reaction is exothermic (Δ Sr ev a = - 226 J mo l-1 K-1) , instead of being athermic as supposed in most of the thermal studies. As a consequence, the cathodic half-reaction is endothermic (Δ Sr ev c = + 62.8 J mo l-1 K-1) , which results in a heat sink at the cathode side, proportional to the current. In the same way, depending on the water flux through the membrane, sorption can create a large heat sink at one electrode and an equivalent heat source at the other. Water phase change in the GDL - condensation/evaporation - results in heat sources/sinks that should also be taken into account. All these issues are addressed in order to properly set the basis of heat transfer modeling in the cell.

  12. The effect of platinum in a Nafion membrane on the durability of the membrane under fuel cell conditions

    NASA Astrophysics Data System (ADS)

    Zhao, D.; Yi, B. L.; Zhang, H. M.; Liu, Meilin

    The effect of platinum on free radical generation and membrane degradation in proton exchange membrane (PEM) fuel cells is investigated using three typical cell configurations. Examinations of the fluoride emission rates (FERs) under different testing conditions indicate that platinum deposited in the membrane plays an important role as a catalytic center for the formation of H 2O 2 and HO rad free radicals, leading to PEM degradation. The chemical durability of the membranes is tested in accelerated Fenton tests. It confirms the formation of free radicals in the presence of platinum in the decomposition of H 2O 2 by colorimetric method with dimethyl sulfoxide (DMSO) as the trapping agent. In addition, structural and morphological changes of the membranes are characterized using FT-IR spectroscopy and scanning electron microscopy (SEM).

  13. Triggering of erythrocyte cell membrane scrambling by salinomycin.

    PubMed

    Bissinger, Rosi; Malik, Abaid; Jilani, Kashif; Lang, Florian

    2014-11-01

    Salinomycin, a polyether ionophore antibiotic effective against a variety of pathogens, has been shown to trigger apoptosis of cancer cells and cancer stem cells. The substance is thus considered for the treatment of malignancy. Salinomycin compromises tumour cell survival at least in part by interference with mitochondrial function. Erythrocytes lack mitochondria but may undergo apoptosis-like suicidal cell death or eryptosis, which is characterized by scrambling of the cell membrane with phosphatidylserine exposure at the erythrocyte surface. Signalling involved in the triggering of eryptosis includes activation of oxidant-sensitive Ca(2+) permeable cation channels with subsequent increase in cytosolic Ca(2+) activity ([Ca(2+)]i). This study explored whether salinomycin stimulates eryptosis. Phosphatidylserine-exposing erythrocytes were identified by measurement of annexin-V binding, cell volume was estimated from forward scatter, haemolysis determined from haemoglobin release, [Ca(2+)]i quantified utilizing Fluo3-fluorescence and oxidative stress from 2',7' dichlorodihydrofluorescein diacetate (DCFDA) fluorescence in flow cytometry. A 48-hr exposure to salinomycin (5-100 nM) was followed by a significant increase in Fluo3-fluorescence, DCFDA fluorescence and annexin-V binding, as well as a significant decrease in forward scatter (at 5-10 nM, but not at 50 and 100 nM). The annexin-V binding after salinomycin treatment was significantly blunted but not abrogated in the nominal absence of extracellular Ca(2+) or in the presence of antioxidant n-acetyl cysteine (1 mM). Salinomycin triggers cell membrane scrambling, an effect at least partially due to oxidative stress and entry of extracellular Ca(2+).

  14. ACME: automated cell morphology extractor for comprehensive reconstruction of cell membranes.

    PubMed

    Mosaliganti, Kishore R; Noche, Ramil R; Xiong, Fengzhu; Swinburne, Ian A; Megason, Sean G

    2012-01-01

    The quantification of cell shape, cell migration, and cell rearrangements is important for addressing classical questions in developmental biology such as patterning and tissue morphogenesis. Time-lapse microscopic imaging of transgenic embryos expressing fluorescent reporters is the method of choice for tracking morphogenetic changes and establishing cell lineages and fate maps in vivo. However, the manual steps involved in curating thousands of putative cell segmentations have been a major bottleneck in the application of these technologies especially for cell membranes. Segmentation of cell membranes while more difficult than nuclear segmentation is necessary for quantifying the relations between changes in cell morphology and morphogenesis. We present a novel and fully automated method to first reconstruct membrane signals and then segment out cells from 3D membrane images even in dense tissues. The approach has three stages: 1) detection of local membrane planes, 2) voting to fill structural gaps, and 3) region segmentation. We demonstrate the superior performance of the algorithms quantitatively on time-lapse confocal and two-photon images of zebrafish neuroectoderm and paraxial mesoderm by comparing its results with those derived from human inspection. We also compared with synthetic microscopic images generated by simulating the process of imaging with fluorescent reporters under varying conditions of noise. Both the over-segmentation and under-segmentation percentages of our method are around 5%. The volume overlap of individual cells, compared to expert manual segmentation, is consistently over 84%. By using our software (ACME) to study somite formation, we were able to segment touching cells with high accuracy and reliably quantify changes in morphogenetic parameters such as cell shape and size, and the arrangement of epithelial and mesenchymal cells. Our software has been developed and tested on Windows, Mac, and Linux platforms and is available

  15. Characteristics of Subfreezing Operation of Polymer Electrolyte Membrane Fuel Cells

    NASA Astrophysics Data System (ADS)

    Mishler, Jeffrey Harris

    Polymer Electrolyte Membrane (PEM) Fuel Cells are capable of high efficiency operation, and are free of NOx, SOx, and CO2 emissions when using hydrogen fuel, and ideally suited for use in transportation applications due to their high power density and low operating temperatures. However, under subfreezing conditions which may be encountered during winter seasons in some areas, product water will freeze within the membrane, cathode side catalyst layer and gas diffusion media, leading to voltage loss and operation failure. Experiments were undertaken in order to characterize the amount and location of water during fuel cell operation. First, in-situ neutron radiography was undertaken on the fuel cells at a normal operating temperature for various operating current densities, inlet relative humidities, and diffusion media hydrophobicities. It was found that more hydrophobic cathode microporous layer (MPL) or hydrophilic anode MPL may result in a larger amount of water transporting back to the anode. The water profiles along the channels were measured and the point of liquid water emergence, where two phase flow begins, was compared to previous models. Secondly, under subfreezing temperatures, neutron imaging showed that water ice product accumulates because of lack of a water removal mechanism. Water was observed under both the lands and channels, and increased almost linearly with time. It is found that most ice exists in the cathode side. With evidence from experimental observation, a cold start model was developed and explained, following existing approaches in the literature. Three stages of cold start are explained: membrane saturation, ice storage in catalyst layer pores, and then ice melting. The voltage losses due to temperature change, increased transport resistance, and reduced electrochemical surface area. The ionic conductivity of the membrane at subfreezing temperatures was modeled. Voltage evolution over time for isothermal cold starts was predicted and

  16. [The sodium-potassium-chloride cotransport of the cell membrane].

    PubMed

    Urazaev, A Kh

    1998-01-01

    Discovery and active exploration of the furosemid-sensitive derived-active co-transport of sodium-potassium-chlorine ions took place in the end of 1970-es-1980-es. This transportation mechanism was discovered in various types of cells, both of plant and of animal origin. This review describes properties of the transportation process, which was most comprehensive explored in experiments with erythrocytes, epithelium cells and muscles. The review covers the following properties: anion and cation selectivity of the chlorine transportation, its sensitivity to the specific blocking agents (furocemid, bumetanid, etc.), stoichiometry of the transportation process, etc. For energy source, the chlorine transportation is based on transmembrane electrochemical gradient for sodium ions. The article provides the most recent results of investigation of the chemical nature of the molecule of the chlorine membrane transport. Based on various studies, the molecule of this protein weighs from 120 to 200 kD, includes about 1200 amino acid residua, and forms long cytoplasmatic NH2 and COOH-termini. The gene encoding the amino acid sequence has been cloned. The article discusses the issues of regulation of the chlorine transportation. Humoral control of intensity of the chlorine transportation has been mostly studied in experiments with plain muscles, the issues related to nervous regulation--with only skeleton muscle fibers. The article provides specific data on the mechanisms of the above types of the physiological regulation of active chlorine transportation. In general, the humoral factors, which increase the intracellular concentration of cAMF stimulate chlorine transportation. On the contrary, the hormones, which increase concentration of cGMF in cytoplasm reduce its activity in plain muscles. The discussion of the mechanisms of the nervous controls of the chlorine transportation in the skeleton muscles includes the original results of the author. These results indicate that the

  17. Major outer membrane proteins unique to reproductive cells of Hyphomonas jannaschiana.

    PubMed Central

    Shen, N; Dagasan, L; Sledjeski, D; Weiner, R M

    1989-01-01

    Separation on the basis of molecular weight resolved three proteins specific to the swarmer cell of Hyphomonas jannaschiana. In the reproductive cell, 4 major proteins were identified as cytoplasmic and 10 were identified as envelope. Of these envelope proteins, one was common to both the inner and outer membranes, four were common to the inner membrane, and five were common to the outer membrane. Four of these outer membrane proteins were specific to the reproductive cell, and two of these proteins, with apparent molecular weights of 116,000 and 29,000, constituted 19% of the total cell protein and 54% of the outer membrane protein. Images PMID:2703471

  18. Process for recycling components of a PEM fuel cell membrane electrode assembly

    DOEpatents

    Shore, Lawrence [Edison, NJ

    2012-02-28

    The membrane electrode assembly (MEA) of a PEM fuel cell can be recycled by contacting the MEA with a lower alkyl alcohol solvent which separates the membrane from the anode and cathode layers of the assembly. The resulting solution containing both the polymer membrane and supported noble metal catalysts can be heated under mild conditions to disperse the polymer membrane as particles and the supported noble metal catalysts and polymer membrane particles separated by known filtration means.

  19. Differentiation of membrane IgE+ rat B cells into IgE-secreting cells.

    PubMed Central

    Vanhove, B; Bazin, H

    1993-01-01

    Rat spleen cells were stimulated with pokeweed mitogen (PWM) and the IgM and IgE responses were assessed. An enrichment of the cell suspension with IgE-bearing cells before stimulation resulted in an increase in the number of IgE-secreting cells. A decrease of the number of IgE-secreting cells was found after depletion of IgE- or IgM-bearing cells, but not those bearing IgD molecules on their membranes, before stimulation. Moreover, the stimulation of membrane IgE on B cells with anti-IgE antibodies was shown to increase the number of IgE-secreting cells after PWM-induced differentiation in vitro. In vivo, it was also observed that a single injection of anti-IgE antibodies can induce the differentiation of IgE-secreting cells. These results demonstrate the presence of IgE(+)-IgM (+)-IgD- B cells in the rat that are responsive to PWM-induced differentiation into IgE-secreting cells. They indicate a pre-commitment of these cells at a stage where they still express IgM on their surface. IgE molecules on the cell membranes play a role in their differentiation. PMID:8406582

  20. Characterization of membrane currents in dissociated adult rat pineal cells.

    PubMed Central

    Aguayo, L G; Weight, F F

    1988-01-01

    1. Membrane currents, particularly the outward components, were studied in pineal cells acutely dissociated from adult rats using the whole-cell variant of the patch-clamp technique. 2. In current clamp, outward constant current elicited a transient graded depolarizing response. A sustained membrane rectification developed within 20 ms; this phenomenon was reduced in cells internally dialysed with 120 mM-CsCl. 3. Study of the membrane current revealed the existence of a transient and a delayed outward current. These currents were virtually eliminated when the cell was internally dialysed with CsCl. 4. The delayed outward current, isolated from a holding potential of -50 mV, activated at potentials near -20 mV, reached a steady-state current amplitude within 60 ms and had little or no decay during steps up to 400 ms in duration. This component was reduced by 80% or more with the addition of 5 mM-TEA. 5. From -100 mV, the transient outward current reached a peak within 15 ms and decayed with a single-exponential time course. The mean decay time constant was 66 +/- 10 ms (at -33 mV) and it showed little voltage sensitivity. This current, which activated at potentials positive to -60 mV and displayed half-inactivation at -76 +/- 8 mV, was reduced by 50% with the addition of 5 mM-4-AP (4-amino-pyridine). 6. In the presence of external Ca2+, the current-voltage relationship for the delayed current did not display a region of negative-slope conductance (N-shape). Increasing the intracellular ionized Ca2+ concentration by varying the Ca-EGTA buffer ratio did not alter the dependence of the current on the membrane potential. 7. Block of outward currents with internal Cs+ revealed a small (less than 90 pA) inward Ca2+ current when the external Ca2+ concentration was increased to 10 mM. From a holding potential of -50 mV, it had a threshold at -30 mV and peaked at +5 mV. Evidence for an inward Na+ current was not obtained. 8. We conclude that acutely dissociated pineal cells

  1. [LIGHT-DEPENDENT SYNTHESIS OF CELL MEMBRANES IN THE Brc-1 MUTANT OF CHLAMYDOMONAS REINHARDTII].

    PubMed

    Semenova, G A; Chekunova, E M; Ladygin, V G

    2015-01-01

    The structural organization of cells of the Brc-1 mutant of the unicellular green algae Chlamydomonas reinhardtii grown in the light and in the dark has been studied. The Brc-1 mutant contains the brc-1 mutation in the nucleus gene LTS3. In the light, all membrane structures in mutant cells form normally and are well developed. In the dark under heterotrophic conditions, the mutant cells grew and divided well, however, all its cell membranes: plasmalemma, tonoplast, mitochondrial membranes, membranes of the nucleus shell and chloroplast, thylakoids, and the membranes of dictiosomes of the Golgi apparatus were not detected. In the dark under heterotrophic conditions, mutant cells well grow and divide. It were shown that a short-term (1-10 min) exposure of Brc-1 mutant cells to light leads to the restoration of all above-mentioned membrane structures. Possible reasons for the alterations of membrane structures are discussed.

  2. Cell dualism: presence of cells with alternative membrane potentials in growing populations of bacteria and yeasts.

    PubMed

    Ivanov, Volodymyr; Rezaeinejad, Saeid; Chu, Jian

    2013-10-01

    It is considered that all growing cells, for exception of acidophilic bacteria, have negatively charged inside cytoplasmic membrane (Δψ⁻-cells). Here we show that growing populations of microbial cells contain a small portion of cells with positively charged inside cytoplasmic membrane (Δψ⁺-cells). These cells were detected after simultaneous application of the fluorescent probes for positive membrane potential (anionic dye DIBAC⁻) and membrane integrity (propidium iodide, PI). We found in exponentially growing cell populations of Escherichia coli and Saccharomyces cerevisiae that the content of live Δψ⁻-cells was 93.6 ± 1.8 % for bacteria and 90.4 ± 4.0 % for yeasts and the content of live Δψ⁺-cells was 0.9 ± 0.3 % for bacteria and 2.4 ± 0.7 % for yeasts. Hypothetically, existence of Δψ⁺-cells could be due to short-term, about 1 min for bacteria and 5 min for yeasts, change of membrane potential from negative to positive value during the cell cycle. This change has been shown by the reversions of K⁺, Na⁺, and Ca²⁺ ions fluxes across the cell membrane during synchronous yeast culture. The transformation of Δψ(⁻-cells to Δψ⁺-cells can be explained by slow influx of K⁺ ions into Δψ⁻-cell to the trigger level of K⁺ concentration ("compression of potassium spring"), which is forming "alternative" Δψ⁺-cell for a short period, following with fast efflux of K⁺ ions out of Δψ⁺-cell ("release of potassium spring") returning cell to normal Δψ⁻ state. We anticipate our results to be a starting point to reveal the biological role of cell dualism in form of Δψ⁻- and Δψ⁺- cells.

  3. Ionic Liquids and New Proton Exchange Membranes for Fuel Cells

    NASA Technical Reports Server (NTRS)

    Belieres, Jean-Philippe

    2004-01-01

    There is currently a great surge of activity in fuel cell research as laboratories across the world seek to take advantage of the high energy capacity provided by &el cells relative to those of other portable electrochemical power systems. Much of this activity is aimed at high temperature fie1 cells, and a vital component of such &el cells must be the availability of a high temperature stable proton-permeable membrane. NASA Glenn Research Center is greatly involved in developing this technology. Other approaches to the high temperature fuel cell involve the use of single- component or almost-single-component electrolytes that provide a path for protons through the cell. A heavily researched case is the phosphoric acid fuel cell, in which the electrolyte is almost pure phosphoric acid and the cathode reaction produces water directly. The phosphoric acid fie1 cell delivers an open circuit voltage of 0.9 V falling to about 0.7 V under operating conditions at 170 C. The proton transport mechanism is mainly vehicular in character according to the viscosity/conductance relation. Here we describe some Proton Transfer Ionic Liquids (PTILs) with low vapor pressure and high temperature stability that have conductivities of unprecedented magnitude for non-aqueous systems. The first requirement of an ionic liquid is that, contrary to experience with most liquids consisting of ions, it must have a melting point that is not much above room temperature. The limit commonly suggested is 100 C. PTILs constitute an interesting class of non-corrosive proton-exchange electrolyte, which can serve well in high temperature (T = 100 - 250 C) fuel cell applications. We will present cell performance data showing that the open circuit voltage output, and the performance of a simple H2(g)Pt/PTIL/Pt/O2(g) fuel cell may be superior to those of the equivalent phosphoric acid electrolyte fuel cell both at ambient temperature and temperatures up to and above 200 C. My work at NASA Glenn Research

  4. Noncontact microsurgery of cell membranes using femtosecond laser pulses for optoinjection of specified substances into cells

    SciTech Connect

    Il'ina, I V; Ovchinnikov, A V; Chefonov, O V; Sitnikov, D S; Agranat, Mikhail B; Mikaelyan, A S

    2013-04-30

    IR femtosecond laser pulses were used for microsurgery of a cell membrane aimed at local and short-duration change in its permeability and injection of specified extracellular substances into the cells. The possibility of noncontact laser delivery of the propidium iodide fluorescent dye and the pEGFP plasmid, encoding the green fluorescent protein, into the cells with preservation of the cell viability was demonstrated. (extreme light fields and their applications)

  5. Molecular mechanisms of membrane polarity in renal epithelial cells.

    PubMed

    Campo, C; Mason, A; Maouyo, D; Olsen, O; Yoo, D; Welling, P A

    2005-01-01

    Exciting discoveries in the last decade have cast light onto the fundamental mechanisms that underlie polarized trafficking in epithelial cells. It is now clear that epithelial cell membrane asymmetry is achieved by a combination of intracellular sorting operations, vectorial delivery mechanisms and plasmalemma-specific fusion and retention processes. Several well-defined signals that specify polarized segregation, sorting, or retention processes have, now, been described in a number of proteins. The intracellular machineries that decode and act on these signals are beginning to be described. In addition, the nature of the molecules that associate with intracellular trafficking vesicles to coordinate polarized delivery, tethering, docking, and fusion are also becoming understood. Combined with direct visualization of polarized sorting processes with new technologies in live-cell fluorescent microscopy, new and surprising insights into these once-elusive trafficking processes are emerging. Here we provide a review of these recent advances within an historically relevant context.

  6. Percolation in a Proton Exchange Membrane Fuel Cell Catalyst Layer

    SciTech Connect

    Stacy, Stephen; Allen, Jeffrey

    2012-07-01

    Water management in the catalyst layers of proton exchange membrane fuel cells (PEMFC) is confronted by two issues, flooding and dry out, both of which result in improper functioning of the fuel cell and lead to poor performance and degradation. At the present time, the data that has been reported about water percolation and wettability within a fuel cell catalyst layer is limited. A method and apparatus for measuring the percolation pressure in the catalyst layer has been developed based upon an experimental apparatus used to test water percolation in porous transport layers (PTL). The experimental setup uses a pseudo Hele-Shaw type testing where samples are compressed and a fluid is injected into the sample. Testing the samples gives percolation pressure plots which show trends in increasing percolation pressure with an increase in flow rate. A decrease in pressure was seen as percolation occurred in one sample, however the pressure only had a rising effect in the other sample.

  7. Physical Chemistry Research Toward Proton Exchange Membrane Fuel Cell Advancement.

    PubMed

    Swider-Lyons, Karen E; Campbell, Stephen A

    2013-02-07

    Hydrogen fuel cells, the most common type of which are proton exchange membrane fuel cells (PEMFCs), are on a rapid path to commercialization. We credit physical chemistry research in oxygen reduction electrocatalysis and theory with significant breakthroughs, enabling more cost-effective fuel cells. However, most of the physical chemistry has been restricted to studies of platinum and related alloys. More work is needed to better understand electrocatalysts generally in terms of properties and characterization. While the advent of such highly active catalysts will enable smaller, less expensive, and more powerful stacks, they will require better understanding and a complete restructuring of the diffusion media in PEMFCs to facilitate faster transport of the reactants (O2) and products (H2O). Even Ohmic losses between materials become more important at high power. Such lessons from PEMFC research are relevant to other electrochemical conversion systems, including Li-air batteries and flow batteries.

  8. Direct liquid-feed fuel cell with membrane electrolyte and manufacturing thereof

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram (Inventor); Surampudi, Subbarao (Inventor); Halpert, Gerald (Inventor)

    1999-01-01

    An improved direct liquid-feed fuel cell having a solid membrane electrolyte for electrochemical reactions of an organic fuel. Improvements in interfacing of the catalyst layer and the membrane and activating catalyst materials are disclosed.

  9. Demonstrating Cell Traction--Using Hens' Egg Vitelline Membrane as Substratum.

    ERIC Educational Resources Information Center

    Downie, Roger

    1987-01-01

    Suggests ways in which hens' egg vitelline membranes can be used to demonstrate cell traction effects. Reviews procedures for using and culturing the membranes and identifies topic areas for student projects. (ML)

  10. Transcellular transport and membrane insertion of the C5b-9 membrane attack complex of complement by glomerular epithelial cells in experimental membranous nephropathy.

    PubMed

    Kerjaschki, D; Schulze, M; Binder, S; Kain, R; Ojha, P P; Susani, M; Horvat, R; Baker, P J; Couser, W G

    1989-07-15

    Deposition of the C5b-9 complex of C in glomeruli of rats with experimental membranous nephropathy (MN) is essential for the development of proteinuria. In this investigation C5b-9 was localized in the passive Heymann nephritis (PHN) by immunoelectron microscopy with a mAb specific for C5b-9(m) neoantigen. Its distribution was compared with that in another model of MN induced by successive injections of cationic human IgG and rabbit anti-human IgG into rats. In PHN C5b-9 was found: 1) in the immune deposits (ID), and on the cell membranes of foot processes close to the ID; 2) in clathrin-coated pits of the glomerular epithelial cells (GEC) close to the ID and in membrane vesicles in the cytoplasm, separated from sheep IgG and the gp330 Ag; 3) in high concentration in multivesicular bodies of GEC; and 4) in association with membrane vesicles in the urinary space which presumably are the exocytosed content of membrane vesicular bodies. By contrast, in the cationic IgG-MN model C5b-9 was found mostly in ID, but rarely within the GEC. By freeze-fracture electron microscopy we have further identified 200- to 250-A intramembrane particles in PHN in the cell membranes of the "soles" of the foot processes which resemble membrane inserted human C5b-9(m). Degradation products of C5b-9 were further detected by immunoblotting of a 100,000 x g pellet of PHN rat urine. These results indicate that, in PHN, C5b-9 is inserted into the cell membranes of GEC, and that it is selectively endocytosed and transported across GEC by a cellular mechanism which apparently protects the cell from accumulation of membrane-inserted C5b-9.

  11. The Properties of Chondrocyte Membrane Reservoirs and Their Role in Impact-Induced Cell Death

    PubMed Central

    Moo, Eng Kuan; Amrein, Matthias; Epstein, Marcelo; Duvall, Mike; Abu Osman, Noor Azuan; Pingguan-Murphy, Belinda; Herzog, Walter

    2013-01-01

    Impact loading of articular cartilage causes extensive chondrocyte death. Cell membranes have a limited elastic range of 3–4% strain but are protected from direct stretch during physiological loading by their membrane reservoir, an intricate pattern of membrane folds. Using a finite-element model, we suggested previously that access to the membrane reservoir is strain-rate-dependent and that during impact loading, the accessible membrane reservoir is drastically decreased, so that strains applied to chondrocytes are directly transferred to cell membranes, which fail when strains exceed 3–4%. However, experimental support for this proposal is lacking. The purpose of this study was to measure the accessible membrane reservoir size for different membrane strain rates using membrane tethering techniques with atomic force microscopy. We conducted atomic force spectroscopy on isolated chondrocytes (n = 87). A micron-sized cantilever was used to extract membrane tethers from cell surfaces at constant pulling rates. Membrane tethers could be identified as force plateaus in the resulting force-displacement curves. Six pulling rates were tested (1, 5, 10, 20, 40, and 80 μm/s). The size of the membrane reservoir, represented by the membrane tether surface areas, decreased exponentially with increasing pulling rates. The current results support our theoretical findings that chondrocytes exposed to impact loading die because of membrane ruptures caused by high tensile membrane strain rates. PMID:24094400

  12. Alterations of Red Cell Membrane Properties in Nneuroacanthocytosis

    PubMed Central

    Siegl, Claudia; Hamminger, Patricia; Jank, Herbert; Ahting, Uwe; Bader, Benedikt; Danek, Adrian; Gregory, Allison; Hartig, Monika; Hayflick, Susan; Hermann, Andreas; Prokisch, Holger; Sammler, Esther M.; Yapici, Zuhal; Prohaska, Rainer; Salzer, Ulrich

    2013-01-01

    Neuroacanthocytosis (NA) refers to a group of heterogenous, rare genetic disorders, namely chorea acanthocytosis (ChAc), McLeod syndrome (MLS), Huntington’s disease-like 2 (HDL2) and pantothenate kinase associated neurodegeneration (PKAN), that mainly affect the basal ganglia and are associated with similar neurological symptoms. PKAN is also assigned to a group of rare neurodegenerative diseases, known as NBIA (neurodegeneration with brain iron accumulation), associated with iron accumulation in the basal ganglia and progressive movement disorder. Acanthocytosis, the occurrence of misshaped erythrocytes with thorny protrusions, is frequently observed in ChAc and MLS patients but less prevalent in PKAN (about 10%) and HDL2 patients. The pathological factors that lead to the formation of the acanthocytic red blood cell shape are currently unknown. The aim of this study was to determine whether NA/NBIA acanthocytes differ in their functionality from normal erythrocytes. Several flow-cytometry-based assays were applied to test the physiological responses of the plasma membrane, namely drug-induced endocytosis, phosphatidylserine exposure and calcium uptake upon treatment with lysophosphatidic acid. ChAc red cell samples clearly showed a reduced response in drug-induced endovesiculation, lysophosphatidic acid-induced phosphatidylserine exposure, and calcium uptake. Impaired responses were also observed in acanthocyte-positive NBIA (PKAN) red cells but not in patient cells without shape abnormalities. These data suggest an “acanthocytic state” of the red cell where alterations in functional and interdependent membrane properties arise together with an acanthocytic cell shape. Further elucidation of the aberrant molecular mechanisms that cause this acanthocytic state may possibly help to evaluate the pathological pathways leading to neurodegeneration. PMID:24098554

  13. Biocompatible fluorescent nanocrystals for immunolabeling of membrane proteins and cells.

    PubMed

    Sukhanova, Alyona; Devy, Jérôme; Venteo, Lydie; Kaplan, Hervé; Artemyev, Mikhail; Oleinikov, Vladimir; Klinov, Dmitry; Pluot, Michel; Cohen, Jacques H M; Nabiev, Igor

    2004-01-01

    A methodology for simple convenient preparation of bright, negatively or positively charged, water-soluble CdSe/ZnS core/shell nanocrystals (NCs) and their stabilization in aqueous solution is described. Single NCs can be detected using a standard epifluorescent microscope, ensuring a detection limit of one molecule coupled with an NC. NCs solubilized in water by DL-Cys were stabilized, to avoid aggregation, by poly(allylamine) and conjugated with polyclonal anti-mouse antibodies (Abs). NC-Abs conjugates were tested in dot-blots and exhibited retention of binding capacity within several nanograms of antigen detected. We further demonstrated the advantages of NC-Abs conjugates in the immunofluorescent detection and three-dimensional (3D) confocal analysis of p-glycoprotein (p-gp), one of the main mediators of the MDR phenotype, overexpressed in the membrane of MCF7r breast adenocarcinoma cells. Immunolabeling of p-gp with NC-Abs conjugates was 4200-, 2600-, and 420-fold more resistant to photobleaching than its labeling with fluorescein isothiocyanate-Abs, R-phycoerythrin-Abs, and AlexaFluor488-Abs, respectively. The labeling of p-gp with NC-Abs conjugates was highly specific, and the data were used for confocal reconstruction of 3D images of the p-gp distribution in the MCF7r cell membrane. Finally, we demonstrated the applicability of NC-Abs conjugates obtained by the method described to specific detection of antigens in paraffin-embedded formaldehyde-fixed cancer tissue specimens, using immunostaining of cytokeratin in skin basal carcinoma as an example. We conclude that the NC-Abs conjugates may serve as easy-to-do, highly sensitive, photostable labels for immunofluorescent analysis, immunohistochemical detection, and 3D confocal studies of membrane proteins and cells.

  14. Scanning Ion Conductance Microscopy for living cell membrane potential measurement

    NASA Astrophysics Data System (ADS)

    Panday, Namuna

    Recently, the existence of multiple micro-domains of extracellular potential around individual cells have been revealed by voltage reporter dye using fluorescence microscopy. One hypothesis is that these long lasting potential patterns play a vital role in regulating important cell activities such as embryonic patterning, regenerative repair and reduction of cancerous disorganization. We used multifunctional Scanning Ion Conductance Microscopy (SICM) to study these extracellular potential patterns of single cell with higher spatial resolution. To validate this novel technique, we compared the extracellular potential distribution on the fixed HeLa cell surface and Polydimethylsiloxane (PDMS) surface and found significant difference. We then measured the extracellular potential distributions of living melanocytes and melanoma cells and found both the mean magnitude and spatial variation of extracellular potential of the melanoma cells are bigger than those of melanocytes. As compared to the voltage reporter dye based fluorescence microscope method, SICM can achieve quantitative potential measurements of non-labeled living cell membranes with higher spatial resolution.

  15. Cell Labeling via Membrane-Anchored Lipophilic MR Contrast Agents

    PubMed Central

    2015-01-01

    Cell tracking in vivo with MR imaging requires the development of contrast agents with increased sensitivity that effectively label and are retained by cells. Most clinically approved Gd(III)-based contrast agents require high incubation concentrations and prolonged incubation times for cellular internalization. Strategies to increase contrast agent permeability have included conjugating Gd(III) complexes to cell penetrating peptides, nanoparticles, and small molecules which have greatly improved cell labeling but have not resulted in improved cellular retention. To overcome these challenges, we have synthesized a series of lipophilic Gd(III)-based MR contrast agents that label cell membranes in vitro. Two of the agents were synthesized with a multiplexing strategy to contain three Gd(III) chelates (1 and 2) while the third contains a single Gd(III) chelate (3). These new agents exhibit significantly enhanced labeling and retention in HeLa and MDA-MB-231-mcherry cells compared to agents that are internalized by cells (4 and Prohance). PMID:24787689

  16. LM cell growth and membrane lipid adaptation to sterol structure.

    PubMed

    Rujanavech, C; Silbert, D F

    1986-06-05

    Using a sterol auxotroph of the LM cell mouse fibroblast, we demonstrate that relatively few cholesterol analogues can substitute for cholesterol as a growth factor. The auxotroph grows normally on desmosterol and trans-22-dehydrocholesterol and at reduced rates on dihydrocholesterol, campesterol, and 22,23-dihydrobrassicasterol. It does not grow with beta-sitosterol, stigmasterol, ergosterol, or cis-22-dehydrocholesterol when the sterol is present as sole supplement but does grow at normal rates when the analogue is supplied with suboptimal amounts of cholesterol. Two contrasting types of membrane lipid changes are observed in cells grown on cholesterol analogues. In cells grown with dihydrocholesterol, a marked increase in desaturation and elongation of fatty acids is noted. Conversely, when cells are grown with cis-22-dehydrocholesterol, desaturation and elongation of fatty acids are severely curtailed. Cells grown on alkyl sterols respond like cells grown on cis-22-dehydrocholesterol but in a less pronounced fashion. The effects of sterol substitution in mammalian cells versus in lower eukaryotes are compared, and an explanation for the secondary changes in fatty acid composition in terms of phospholipid phase behavior is suggested.

  17. Membrane electrode assembly with enhanced platinum utilization for high temperature proton exchange membrane fuel cell prepared by catalyst coating membrane method

    NASA Astrophysics Data System (ADS)

    Liang, Huagen; Su, Huaneng; Pollet, Bruno G.; Linkov, Vladimir; Pasupathi, Sivakumar

    2014-11-01

    In this work, membrane electrode assemblies (MEAs) prepared by catalyst coating membrane (CCM) method are investigated for reduced platinum (Pt) loading and improved Pt utilization of high temperature proton exchange membrane fuel cell (PEMFC) based on phosphoric acid (PA)-doped poly(2,5-benzimidazole) (AB-PBI) membrane. The results show that CCM method exhibits significantly higher cell performance and Pt-specific power density than that of MEAs prepared with conventional gas diffusion electrode (GDE) under a low Pt loading level. In-suit cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) show that the MEAs prepared by the CCM method have a higher electrochemical surface area (ECSA), low cell ohmic resistance and low charge transfer resistance as compared to those prepared with GDEs at the same Pt loading.

  18. Analysis of plasma membrane phosphoinositides from fusogenic carrot cells

    SciTech Connect

    Wheeler, J.J.; Boss, W.F.

    1987-04-01

    Phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP/sub 2/) were found to be associated with the plasma membrane-rich fractions isolated by aqueous polymer two-phase partitioning from fusogenic cells. They represented at least 5% and 0.7% of the total inositol-labeled lipids in the plasma membrane-rich fractions, respectively, and were present in a ratio of about 7:1 (PIP:PIP/sub 2/). In addition, two unidentified inositol-labeled compounds, which together were approximately 3% of the inositol-labeled lipids, were found predominantly in the plasma membrane-rich fractions and migrated between PIP/sub 2/ and PIP. The R/sub f/s of these compounds were approximately 0.31 and 0.34 in the solvent system CHCl/sub 3/:MeOH:15N NH/sub 4/OH:H/sub 2/O (90:90:7:22) using LK5 plates presoaked in 1% potassium oxalate. These compounds incorporated /sup 32/P/sub i/, (/sup 3/H)inositol and were hydrolyzed in mild base. These data suggested that they were glycero-phospholipids. Although the compounds did not comigrate with lysoPIP obtained from bovine brain (R/sub f/ approx. 0.35), when endogenous PIP was hydrolyzed to lysoPIP, the breakdown product migrated in the region of the unidentified inositol lipids.

  19. Probing red cell membrane cholesterol movement with cyclodextrin.

    PubMed

    Steck, Theodore L; Ye, Jin; Lange, Yvonne

    2002-10-01

    We probed the kinetics with which cholesterol moves across the human red cell bilayer and exits the membrane using methyl-beta-cyclodextrin as an acceptor. The fractional rate of cholesterol transfer (% s(-1)) was unprecedented, the half-time at 37 degrees C being ~1 s. The kinetics observed under typical conditions were independent of donor concentration and directly proportional to acceptor concentration. The rate of exit of membrane cholesterol fell hyperbolically to zero with increasing dilution. The energy of activation for cholesterol transfer was the same at high and low dilution; namely, 27-28 Kcal/mol. This behavior is not consistent with an exit pathway involving desorption followed by aqueous diffusion to acceptors nor with a simple one-step collision mechanism. Rather, it is that predicted for an activation-collision mechanism in which the reversible partial projection of cholesterol molecules out of the bilayer precedes their collisional capture by cyclodextrin. Because the entire membrane pool was transferred in a single first-order process under all conditions, we infer that the transbilayer diffusion (flip-flop) of cholesterol must have proceeded faster than its exit, i.e., with a half-time of <1 s at 37 degrees C.

  20. Fusion of Legionella pneumophila outer membrane vesicles with eukaryotic membrane systems is a mechanism to deliver pathogen factors to host cell membranes.

    PubMed

    Jäger, Jens; Keese, Susanne; Roessle, Manfred; Steinert, Michael; Schromm, Andra B

    2015-05-01

    The formation and release of outer membrane vesicles (OMVs) is a phenomenon observed in many bacteria, including Legionella pneumophila. During infection, this human pathogen primarily invades alveolar macrophages and replicates within a unique membrane-bound compartment termed Legionella-containing vacuole. In the current study, we analysed the membrane architecture of L. pneumophila OMVs by small-angle X-ray scattering and biophysically characterized OMV membranes. We investigated the interaction of L. pneumophila OMVs with model membranes by Förster resonance energy transfer and Fourier transform infrared spectroscopy. These experiments demonstrated the incorporation of OMV membrane material into liposomes composed of different eukaryotic phospholipids, revealing an endogenous property of OMVs to fuse with eukaryotic membranes. Cellular co-incubation experiments showed a dose- and time-dependent binding of fluorophore-labelled OMVs to macrophages. Trypan blue quenching experiments disclosed a rapid internalization of OMVs into macrophages at 37 and 4 °C. Purified OMVs induced tumour necrosis factor-α production in human macrophages at concentrations starting at 300 ng ml(-1). Experiments on HEK293-TLR2 and TLR4/MD-2 cell lines demonstrated a dominance of TLR2-dependent signalling pathways. In summary, we demonstrate binding, internalization and biological activity of L. pneumophila OMVs on human macrophages. Our data support OMV membrane fusion as a mechanism for the remote delivery of virulence factors to host cells.

  1. 2011 Alkaline Membrane Fuel Cell Workshop Final Report

    SciTech Connect

    Pivovar, B.

    2012-02-01

    A workshop addressing the current state-of-the-art in alkaline membrane fuel cells (AMFCs) was held May 8-9, 2011, at the Crystal Gateway Marriott in Arlington, Virginia. This workshop was the second of its kind, with the first being held December 11-13, 2006, in Phoenix, Arizona. The 2011 workshop and associated workshop report were created to assess the current state of AMFC technology (taking into account recent advances), investigate the performance potential of AMFC systems across all possible power ranges and applications, and identify the key research needs for commercial competitiveness in a variety of areas.

  2. Cytoskeleton confinement and tension of red blood cell membranes.

    PubMed

    Gov, N; Zilman, A G; Safran, S

    2003-06-06

    We analyze theoretically both the static and dynamic fluctuation spectra of the red blood cell in a unified manner, using a simple model of the composite membrane. In this model, the two-dimensional spectrin network that forms the cytoskeleton is treated as a rigid shell, located at a fixed, average distance from the lipid bilayer. The cytoskeleton thereby confines both the static and dynamic fluctuations of the lipid bilayer. The sparse connections of the cytoskeleton and bilayer induce a surface tension, for wavelengths larger than the bilayer persistence length. The predictions of the model give a consistent account for both the wave vector and frequency dependence of the experimental data.

  3. Visual Analytics approach for Lightning data analysis and cell nowcasting

    NASA Astrophysics Data System (ADS)

    Peters, Stefan; Meng, Liqiu; Betz, Hans-Dieter

    2013-04-01

    Thunderstorms and their ground effects, such as flash floods, hail, lightning, strong wind and tornadoes, are responsible for most weather damages (Bonelli & Marcacci 2008). Thus to understand, identify, track and predict lightning cells is essential. An important aspect for decision makers is an appropriate visualization of weather analysis results including the representation of dynamic lightning cells. This work focuses on the visual analysis of lightning data and lightning cell nowcasting which aim to detect and understanding spatial-temporal patterns of moving thunderstorms. Lightnings are described by 3D coordinates and the exact occurrence time of lightnings. The three-dimensionally resolved total lightning data used in our experiment are provided by the European lightning detection network LINET (Betz et al. 2009). In all previous works, lightning point data, detected lightning cells and derived cell tracks are visualized in 2D. Lightning cells are either displayed as 2D convex hulls with or without the underlying lightning point data. Due to recent improvements of lightning data detection and accuracy, there is a growing demand on multidimensional and interactive visualization in particular for decision makers. In a first step lightning cells are identified and tracked. Then an interactive graphic user interface (GUI) is developed to investigate the dynamics of the lightning cells: e.g. changes of cell density, location, extension as well as merging and splitting behavior in 3D over time. In particular a space time cube approach is highlighted along with statistical analysis. Furthermore a lightning cell nowcasting is conducted and visualized. The idea thereby is to predict the following cell features for the next 10-60 minutes including location, centre, extension, density, area, volume, lifetime and cell feature probabilities. The main focus will be set to a suitable interactive visualization of the predicted featured within the GUI. The developed visual

  4. The Molecular Structure of Human Red Blood Cell Membranes from Highly Oriented, Solid Supported Multi-Lamellar Membranes

    PubMed Central

    Himbert, Sebastian; Alsop, Richard J.; Rose, Markus; Hertz, Laura; Dhaliwal, Alexander; Moran-Mirabal, Jose M.; Verschoor, Chris P.; Bowdish, Dawn M. E.; Kaestner, Lars; Wagner, Christian; Rheinstädter, Maikel C.

    2017-01-01

    We prepared highly oriented, multi-lamellar stacks of human red blood cell (RBC) membranes applied on silicon wafers. RBC ghosts were prepared by hemolysis and applied onto functionalized silicon chips and annealed into multi-lamellar RBC membranes. High resolution X-ray diffraction was used to determine the molecular structure of the stacked membranes. We present direct experimental evidence that these RBC membranes consist of nanometer sized domains of integral coiled-coil peptides, as well as liquid ordered (lo) and liquid disordered (ld) lipids. Lamellar spacings, membrane and hydration water layer thicknesses, areas per lipid tail and domain sizes were determined. The common drug aspirin was added to the RBC membranes and found to interact with RBC membranes and preferably partition in the head group region of the lo domain leading to a fluidification of the membranes, i.e., a thinning of the bilayers and an increase in lipid tail spacing. Our results further support current models of RBC membranes as patchy structures and provide unprecedented structural details of the molecular organization in the different domains. PMID:28045119

  5. The Molecular Structure of Human Red Blood Cell Membranes from Highly Oriented, Solid Supported Multi-Lamellar Membranes.

    PubMed

    Himbert, Sebastian; Alsop, Richard J; Rose, Markus; Hertz, Laura; Dhaliwal, Alexander; Moran-Mirabal, Jose M; Verschoor, Chris P; Bowdish, Dawn M E; Kaestner, Lars; Wagner, Christian; Rheinstädter, Maikel C

    2017-01-03

    We prepared highly oriented, multi-lamellar stacks of human red blood cell (RBC) membranes applied on silicon wafers. RBC ghosts were prepared by hemolysis and applied onto functionalized silicon chips and annealed into multi-lamellar RBC membranes. High resolution X-ray diffraction was used to determine the molecular structure of the stacked membranes. We present direct experimental evidence that these RBC membranes consist of nanometer sized domains of integral coiled-coil peptides, as well as liquid ordered (lo) and liquid disordered (ld) lipids. Lamellar spacings, membrane and hydration water layer thicknesses, areas per lipid tail and domain sizes were determined. The common drug aspirin was added to the RBC membranes and found to interact with RBC membranes and preferably partition in the head group region of the lo domain leading to a fluidification of the membranes, i.e., a thinning of the bilayers and an increase in lipid tail spacing. Our results further support current models of RBC membranes as patchy structures and provide unprecedented structural details of the molecular organization in the different domains.

  6. The Molecular Structure of Human Red Blood Cell Membranes from Highly Oriented, Solid Supported Multi-Lamellar Membranes

    NASA Astrophysics Data System (ADS)

    Himbert, Sebastian; Alsop, Richard J.; Rose, Markus; Hertz, Laura; Dhaliwal, Alexander; Moran-Mirabal, Jose M.; Verschoor, Chris P.; Bowdish, Dawn M. E.; Kaestner, Lars; Wagner, Christian; Rheinstädter, Maikel C.

    2017-01-01

    We prepared highly oriented, multi-lamellar stacks of human red blood cell (RBC) membranes applied on silicon wafers. RBC ghosts were prepared by hemolysis and applied onto functionalized silicon chips and annealed into multi-lamellar RBC membranes. High resolution X-ray diffraction was used to determine the molecular structure of the stacked membranes. We present direct experimental evidence that these RBC membranes consist of nanometer sized domains of integral coiled-coil peptides, as well as liquid ordered (lo) and liquid disordered (ld) lipids. Lamellar spacings, membrane and hydration water layer thicknesses, areas per lipid tail and domain sizes were determined. The common drug aspirin was added to the RBC membranes and found to interact with RBC membranes and preferably partition in the head group region of the lo domain leading to a fluidification of the membranes, i.e., a thinning of the bilayers and an increase in lipid tail spacing. Our results further support current models of RBC membranes as patchy structures and provide unprecedented structural details of the molecular organization in the different domains.

  7. High-temperature proton-exchange-membrane fuel cells using an ether-containing polybenzimidazole membrane as electrolyte.

    PubMed

    Li, Jin; Li, Xiaojin; Zhao, Yun; Lu, Wangting; Shao, Zhigang; Yi, Baolian

    2012-05-01

    Herein, poly[2,2'-(p-oxydiphenylene)-5,5'-benzimidazole] (PBI) is synthesized from 3,3'-diaminobenzidine and 4,4'-oxybisbenzoic acid, and the membrane is prepared by solvent casting. The main characteristics of PBI are studied. In the preparation of the PBI/H(3) PO(4) composite membrane, the absorbing temperature of H(3) PO(4) is 120 °C, which leads to a membrane with a high content of H(3) PO(4) . Membrane electrode assemblies (MEAs) are fabricated from PBI/H(3) PO(4) membranes with the catalyst layer made of Pt/C, PBI, and polyvinylidene fluoride (230:12:7 w/w). The fabricated MEA is tested at 150 °C with dry hydrogen and oxygen gas at 0.2 MPa for both anode and cathode feeds. No degradation of voltage is seen during stability testing of the PBI/H(3) PO(4) membrane at a constant current for 100 h. The maximum power density is 1.17 W cm(-2) , and the maximum current density is 6.0 A cm(-2) with a Pt loading of 0.5 mg cm(-2) . The high performance of these membrane materials demonstrates that PBI can be regarded as an alternative membrane material for high-temperature proton-exchange-membrane fuel cells.

  8. Computational analysis of the tether pulling experiment to probe plasma membrane - cytoskeleton interaction in cells

    PubMed Central

    Schumacher, Kristopher R.; Popel, Aleksander S.; Anvari, Bahman; Brownell, William E.; Spector, Alexander A.

    2016-01-01

    Tethers are thin membrane tubes that can be formed when relatively small and localized forces are applied to cellular membranes and lipid bilayers. Tether pulling experiments have been used to better understand the fine membrane properties. These include the interaction between the plasma membrane and the underlying cytoskeleton, which is an important factor affecting membrane mechanics. We use a computational method aimed at the interpretation and design of tether pulling experiments in cells with a strong membrane-cytoskeleton attachment. In our model, we take into account the detailed information on the topology of bonds connecting the plasma membrane and the cytoskeleton. We compute the force-dependent piecewise membrane deflection and bending as well as modes of stored energy in three major regions of the system: body of the tether, membrane-cytoskeleton attachment zone, and the transition zone between the two. We apply our method to three cells: cochlear outer hair cells (OHCs), human embryonic kidney (HEK) cells, and Chinese hamster ovary (CHO) cells. OHCs have a special system of pillars connecting the membrane and the cytoskeleton, and HEK and CHO cells have a bond arrangement via bonds (e.g., PIP2) which is common to many other cells. We also present a validation of our model by using experimental data on CHO and HEK cells. The proposed method can be an effective tool in the analyses of experiments to probe the properties of cellular membranes. PMID:19905340

  9. Nanocellulose based asymmetric composite membrane for the multiple functions in cell encapsulation.

    PubMed

    Park, Minsung; Shin, Sungchul; Cheng, Jie; Hyun, Jinho

    2017-02-20

    We describe the nanocomposite membrane for cell encapsulation using nanocelluose hydrogels. One of the surfaces of bacterial cellulose (BC) pellicles was coated with collagen to enhance cell adhesion and the opposite side of the BC pellicles was coated with alginate to protect transplanted cells from immune rejection by the reduced pore size of the composite membrane. The morphology of nanocomposite membrane was observed by scanning electron microscopy and the permeability of the membrane was estimated by the release test using different molecular weights of polymer solution. The nanocomposite membrane was permeable to small molecules but impermeable to large molecules such as IgG antibodies inferring the potential use in cell implantation. In addition, the BC-based nanocomposite membrane showed a superior mechanical property due to the incorporation of compared with alginate membranes. The cells attached efficiently to the surface of BC composite membranes with a high level of cell viability as well as bioactivity. Cells grown on the BC composite membrane kit released dopamine freely to the medium through the membrane, which showed that the BC composite membrane would be a promising cell encapsulation material in implantation.

  10. Structural and functional changes in the membrane and membrane skeleton of red blood cells induced by peroxynitrite.

    PubMed

    Starodubtseva, Maria N; Tattersall, Amanda L; Kuznetsova, Tatyana G; Yegorenkov, Nicolai I; Ellory, J Clive

    2008-08-01

    The changes in passive ion permeability of the red blood cell membrane after peroxynitrite action (3 microM-3 mM) have been studied by biophysical (using radioisotopes of rubidium, sodium and sulphur (sulphate)) and electrophysiological methods. The enhancement of passive membrane permeability to cations (potassium and sodium ions) and the inhibition of anion flux through the anion exchanger in peroxynitrite-treated red blood cells were revealed. In patch-clamp experiments the whole-cell conductance after peroxynitrite (80 microM) treatment of red blood cells increased 3-3.5-fold with a shift in the reversal potential from -7.0+/-1.5 mV to -4.3+/-0.9 mV (n=7, p=0.005). The addition of cobalt and nickel ions to red blood cell suspensions before peroxynitrite treatment had no effect on the peroxynitrite-induced cation flux but zinc ions in the same condition decreased cation flux about 2-fold. Using atomic force microscopy methods we revealed an increase in red blood cell membrane stiffness and the membrane skeleton complexity after peroxynitrite action. We conclude that the peroxynitrite-induced water and ion imbalance and reorganization in membrane structure lead to crenation of red blood cells.

  11. Evidence for Transfer of Membranes from Mesenchymal Stem Cells to HL-1 Cardiac Cells.

    PubMed

    Boomsma, Robert A; Geenen, David L

    2014-01-01

    This study examined the interaction of mouse bone marrow mesenchymal stem cells (MSC) with cardiac HL-1 cells during coculture by fluorescent dye labeling and then flow cytometry. MSC were layered onto confluent HL-1 cell cultures in a 1 : 4 ratio. MSC gained gap junction permeant calcein from HL-1 cells after 4 hours which was partially reduced by oleamide. After 20 hours, 99% MSC gained calcein, unaffected by oleamide. Double-labeling HL-1 cells with calcein and the membrane dye DiO resulted in transfer of both calcein and DiO to MSC. When HL-1 cells were labeled with calcein and MSC with DiO, MSC gained calcein while HL-1 cells gained DiO. Very little fusion was observed since more than 90% Sca-1 positive MSC gained DiO from HL-1 cells while less than 9% gained gap junction impermeant CMFDA after 20 hours with no Sca-1 transfer to HL-1 cells. Time dependent transfer of membrane DiD was observed from HL-1 cells to MSC (100%) and vice versa (50%) after 20 hours with more limited transfer of CMFDA. These results demonstrate that MSC and HL-1 cells exchange membrane components which may account for some of the beneficial effect of MSC in the heart after myocardial infarction.

  12. Polymeric nanoparticles of different sizes overcome the cell membrane barrier.

    PubMed

    Lerch, Simone; Dass, Martin; Musyanovych, Anna; Landfester, Katharina; Mailänder, Volker

    2013-06-01

    Polymeric nanoparticles have tremendous potential either as carriers or markers in treatment for diseases or as diagnostics in biomedical applications. Finding the optimal conditions for effective intracellular delivery of the payload to the location of interest is still a big challenge. The particles have to overcome the barrier of the cell membrane. Here, we investigated the uptake in HeLa cells of fluorescent polystyrene particles with different size and surface charge. Particles stabilized with the nonionic surfactant Lutensol AT50® (132 nm, 180 nm, 242 nm, 816 nm, 846 nm diameter) were synthesized via dispersion polymerization. Cationic particles (120 nm, 208 nm, 267 nm, 603 nm diameter) were obtained by a combination of miniemulsion and seed dispersion polymerization using cationic surfactant (cetyltrimethylammonium chloride (CTMA-Cl). The particle uptake into HeLa cells was studied by confocal laser scanning microscopy and flow cytometry. Nonionic particles were - independent of their size - taken up by cells only at a barely detectable level, thus aggravating a quantitative comparison. The uptake of positively charged particles was substantially higher and therefore enabling further investigation keeping constant one of these parameters: either material amount or particles number or total interaction surface area. It was found that the uptake rather depends on the total amount of polymeric material present in the media than on the number of particles. The total particle's surface area does not correlate linearly with the uptake, thus indicating that there is no direct dependency between the total surface area and the cellular endocytotic process to overcome the biobarrier "cell membrane." A potentially novel uptake mechanism is found which can be described as an excavator shovel like mechanism. It is a kind of macropinocytosis dependent on actin filaments as well as dynamin, but is clathrin-independent.

  13. A novel membrane-less direct alcohol fuel cell

    NASA Astrophysics Data System (ADS)

    Yi, Qingfeng; Chen, Qinghua; Yang, Zheng

    2015-12-01

    Membrane-less fuel cell possesses such advantages as simplified design and lower cost. In this paper, a membrane-less direct alcohol fuel cell is constructed by using multi-walled carbon nanotubes (MWCNT) supported Pd and ternary PdSnNi composites as the anode catalysts and Fe/C-PANI composite, produced by direct pyrolysis of Fe-doped polyaniline precursor, as the oxygen reduction reaction (ORR) catalyst. The alcohols investigated in the present study are methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol and sec-butanol. The cathode catalyst Fe/C-PANI is electrochemically inactive to oxidation of the alcohols. The performance of the cell with various alcohols in 1 mol L-1 NaOH solution on either Pd/MWCNT or PdSnNi/MWCNT catalyst has been evaluated. In any case, the performance of the cell using the anode catalyst PdSnNi/MWCNT is considerably better than Pd/MWCNT. For the PdSnNi/MWCNT, the maximum power densities of the cell using methanol (0.5 mol L-1), ethanol (0.5 mol L-1), n-propanol (0.5 mol L-1), iso-propanol (0.5 mol L-1), n-butanol (0.2 mol L-1), iso-butanol (0.2 mol L-1) and sec-butanol (0.2 mol L-1) are 0.34, 1.03, 1.07, 0.44, 0.50, 0.31 and 0.15 mW cm-2, respectively.

  14. DEVELOPMENT OF NOVEL ELECTROCATALYST FOR PROTON EXCHANGE MEMBRANE FUEL CELLS

    SciTech Connect

    Shamsuddin Ilias

    2000-01-19

    Proton-exchange membrane fuel cell (PEMFC) is one of the strongest contenders as a power source for space & electric vehicle applications. Platinum catalyst is used for both fuel and air electrodes in PEMFCs. CO contamination of H{sub 2} greatly affects electrocatalysts used at the anode of polymer electrolyte fuel cells and decrease the cell performance. Pt-Ru catalyst had been recognized to alleviate this problem by showing better tolerance to CO poisoning than only Pt catalyst. This irreversible poisoning of the anode can be happened even in concentrations as little as a few ppm, and therefore, require expensive scrubbing to reduce the contaminant concentration to acceptable level. In order to commercialize this environmentally sound source of energy/power system, development of suitable impurity tolerant catalyst is needed. This project will develop novel electrocatalysts for the PEMFCs and demonstrate the feasibility of a H{sub 2}/O{sub 2} fuel cell base on these materials. This project, if successful, will reduce the costs due to reduce Pt catalyst loading or use non-precious metals. It will increase the PEM fuel cell performance by increasing catalyst tolerance to methanol oxidation intermediate products (CO) and fuel impurities (H{sub 2}S), which will generate substantial interest for commercialization of the PEM fuel cell technology.

  15. Experience with Dismantling of the Analytic Cell in the JRTF Decommissioning Program

    SciTech Connect

    Annoh, Akio; Nemoto, Koichi; Tajiri, Hideo; Saito, Keiichiro; Miyajima, Kazutoshi; Myodo, Masato

    2003-02-27

    The analytic cell was mainly used for process control analysis of the reprocessing process and for the measurement of fuel burn up ratio in JAERI's Reprocessing Test Facility (JRTF). The analytic cell was a heavy shielded one and equipped with a conveyor. The cell was alpha and beta(gamma)contaminated. For dismantling of analytic cells, it is very important to establish a method to remove the heavy shield safely and reduce the exposure. At first, a green house was set up to prevent the spread out of contamination, and next, the analytic cell was dismantled. Depending on the contamination condition, the workers wore protective suits such as air ventilated-suits for prevention of internal exposure and vinyl chloride aprons, lead aprons in order to reduce external exposure. From the work carried out, various data such as needed manpower for the activities, the collective dose of workers by external exposure, the amount of radioactive wastes and the relation between the weight of the shield and its dismantling efficiency were obtained and input for the database. The method of dismantling and the experience with the dismantling of the analytic cell in the JRTF, carried out during 2001 and 2002, are described in this paper.

  16. Dynamic analysis of CO₂ labeling and cell respiration using membrane-inlet mass spectrometry.

    PubMed

    Yang, Tae Hoon

    2014-01-01

    Here, we introduce a mass spectrometry-based analytical method and relevant technical details for dynamic cell respiration and CO2 labeling analysis. Such measurements can be utilized as additional information and constraints for model-based (13)C metabolic flux analysis. Dissolved dynamics of oxygen consumption and CO2 mass isotopomer evolution from (13)C-labeled tracer substrates through different cellular processes can be precisely measured on-line using a miniaturized reactor system equipped with a membrane-inlet mass spectrometer. The corresponding specific rates of physiologically relevant gases and CO2 mass isotopomers can be quantified within a short-term range based on the liquid-phase dynamics of dissolved fermentation gases.

  17. Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Wang, Z. H.; Wang, C. Y.; Chen, K. S.

    Two-phase flow and transport of reactants and products in the air cathode of proton exchange membrane (PEM) fuel cells is studied analytically and numerically. Single- and two-phase regimes of water distribution and transport are classified by a threshold current density corresponding to first appearance of liquid water at the membrane/cathode interface. When the cell operates above the threshold current density, liquid water appears and a two-phase zone forms within the porous cathode. A two-phase, multicomponent mixture model in conjunction with a finite-volume-based computational fluid dynamics (CFD) technique is applied to simulate the cathode operation in this regime. The model is able to handle the situation where a single-phase region co-exists with a two-phase zone in the air cathode. For the first time, the polarization curve as well as water and oxygen concentration distributions encompassing both single- and two-phase regimes of the air cathode are presented. Capillary action is found to be the dominant mechanism for water transport inside the two-phase zone of the hydrophilic structure. The liquid water saturation within the cathode is predicted to reach 6.3% at 1.4 A cm -2 for dry inlet air.

  18. The Effect of Platinum Electrocatalyst on Membrane Degradation in Polymer Electrolyte Fuel Cells

    PubMed Central

    Bodner, Merit; Cermenek, Bernd; Rami, Mija; Hacker, Viktor

    2015-01-01

    Membrane degradation is a severe factor limiting the lifetime of polymer electrolyte fuel cells. Therefore, obtaining a deeper knowledge is fundamental in order to establish fuel cells as competitive product. A segmented single cell was operated under open circuit voltage with alternating relative humidity. The influence of the catalyst layer on membrane degradation was evaluated by measuring a membrane without electrodes and a membrane-electrode-assembly under identical conditions. After 100 h of accelerated stress testing the proton conductivity of membrane samples near the anode and cathode was investigated by means of ex situ electrochemical impedance spectroscopy. The membrane sample near the cathode inlet exhibited twofold lower membrane resistance and a resulting twofold higher proton conductivity than the membrane sample near the anode inlet. The results from the fluoride ion analysis have shown that the presence of platinum reduces the fluoride emission rate; which supports conclusions drawn from the literature. PMID:26670258

  19. The Effect of Platinum Electrocatalyst on Membrane Degradation in Polymer Electrolyte Fuel Cells.

    PubMed

    Bodner, Merit; Cermenek, Bernd; Rami, Mija; Hacker, Viktor

    2015-12-08

    Membrane degradation is a severe factor limiting the lifetime of polymer electrolyte fuel cells. Therefore, obtaining a deeper knowledge is fundamental in order to establish fuel cells as competitive product. A segmented single cell was operated under open circuit voltage with alternating relative humidity. The influence of the catalyst layer on membrane degradation was evaluated by measuring a membrane without electrodes and a membrane-electrode-assembly under identical conditions. After 100 h of accelerated stress testing the proton conductivity of membrane samples near the anode and cathode was investigated by means of ex situ electrochemical impedance spectroscopy. The membrane sample near the cathode inlet exhibited twofold lower membrane resistance and a resulting twofold higher proton conductivity than the membrane sample near the anode inlet. The results from the fluoride ion analysis have shown that the presence of platinum reduces the fluoride emission rate; which supports conclusions drawn from the literature.

  20. HeLa cell plasma membranes. I. 5'-Nucleotidase and ouabain-sensitive ATPase as markers for plasma membranes.

    PubMed

    Johnsen, S; Stokke, T; Prydz, H

    1974-11-01

    A method for the preparation of HeLa cell plasma membrane ghosts is described. The purity of the plasma membrane fraction was examined by phase contrast and electron microscopy, by chemical analysis, and by assay of marker enzymes. Data on the composition of the plasma membrane fraction are given. It was observed that the distribution pattern of 5'-nucleotidase activity among the subcellular fractions differed from that of ouabain-sensitive ATPase. In addition, the specific activity of 5'-nucleotidase did not follow the distribution of the membrane ghosts. Thus, this enzyme would seem unsuitable as a plasma membrane marker. A complete balance sheet for marker enzyme activities during the fractionation is necessary for the calculation of increase in specific activity because the activities of both 5'-nucleotidase and ouabain-sensitive ATPase might change during the fractionation procedures.

  1. Purification and differentiation of human adipose-derived stem cells by membrane filtration and membrane migration methods

    PubMed Central

    Lin, Hong Reng; Heish, Chao-Wen; Liu, Cheng-Hui; Muduli, Saradaprasan; Li, Hsing-Fen; Higuchi, Akon; Kumar, S. Suresh; Alarfaj, Abdullah A.; Munusamy, Murugan A.; Hsu, Shih-Tien; Chen, Da-Chung; Benelli, Giovanni; Murugan, Kadarkarai; Cheng, Nai-Chen; Wang, Han-Chow; Wu, Gwo-Jang

    2017-01-01

    Human adipose-derived stem cells (hADSCs) are easily isolated from fat tissue without ethical concerns, but differ in purity, pluripotency, differentiation ability, and stem cell marker expression, depending on the isolation method. We isolated hADSCs from a primary fat tissue solution using: (1) conventional culture, (2) a membrane filtration method, (3) a membrane migration method where the primary cell solution was permeated through membranes, adhered hADSCs were cultured, and hADSCs migrated out from the membranes. Expression of mesenchymal stem cell markers and pluripotency genes, and osteogenic differentiation were compared for hADSCs isolated by different methods using nylon mesh filter membranes with pore sizes ranging from 11 to 80 μm. hADSCs isolated by the membrane migration method had the highest MSC surface marker expression and efficient differentiation into osteoblasts. Osteogenic differentiation ability of hADSCs and MSC surface marker expression were correlated, but osteogenic differentiation ability and pluripotent gene expression were not. PMID:28071738

  2. Purification and differentiation of human adipose-derived stem cells by membrane filtration and membrane migration methods.

    PubMed

    Lin, Hong Reng; Heish, Chao-Wen; Liu, Cheng-Hui; Muduli, Saradaprasan; Li, Hsing-Fen; Higuchi, Akon; Kumar, S Suresh; Alarfaj, Abdullah A; Munusamy, Murugan A; Hsu, Shih-Tien; Chen, Da-Chung; Benelli, Giovanni; Murugan, Kadarkarai; Cheng, Nai-Chen; Wang, Han-Chow; Wu, Gwo-Jang

    2017-01-10

    Human adipose-derived stem cells (hADSCs) are easily isolated from fat tissue without ethical concerns, but differ in purity, pluripotency, differentiation ability, and stem cell marker expression, depending on the isolation method. We isolated hADSCs from a primary fat tissue solution using: (1) conventional culture, (2) a membrane filtration method, (3) a membrane migration method where the primary cell solution was permeated through membranes, adhered hADSCs were cultured, and hADSCs migrated out from the membranes. Expression of mesenchymal stem cell markers and pluripotency genes, and osteogenic differentiation were compared for hADSCs isolated by different methods using nylon mesh filter membranes with pore sizes ranging from 11 to 80 μm. hADSCs isolated by the membrane migration method had the highest MSC surface marker expression and efficient differentiation into osteoblasts. Osteogenic differentiation ability of hADSCs and MSC surface marker expression were correlated, but osteogenic differentiation ability and pluripotent gene expression were not.

  3. Thermal, High Pressure, and Electric Field Processing Effects on Plant Cell Membrane Integrity and Relevance to Fruit and Vegetable Quality

    PubMed Central

    Gonzalez, Maria E; Barrett, Diane M

    2010-01-01

    Advanced food processing methods that accomplish inactivation of microorganisms but minimize adverse thermal exposure are of great interest to the food industry. High pressure (HP) and pulsed electric field (PEF) processing are commercially applied to produce high quality fruit and vegetable products in the United States, Europe, and Japan. Both microbial and plant cell membranes are significantly altered following exposure to heat, HP, or PEF. Our research group sought to quantify the degree of damage to plant cell membranes that occurs as a result of exposure to heat, HP, or PEF, using the same analytical methods. In order to evaluate whether new advanced processing methods are superior to traditional thermal processing methods, it is necessary to compare them. In this review, we describe the existing state of knowledge related to effects of heat, HP, and PEF on both microbial and plant cells. The importance and relevance of compartmentalization in plant cells as it relates to fruit and vegetable quality is described and various methods for quantification of plant cell membrane integrity are discussed. These include electrolyte leakage, cell viability, and proton nuclear magnetic resonance (1H-NMR). PMID:20492210

  4. Thermal, high pressure, and electric field processing effects on plant cell membrane integrity and relevance to fruit and vegetable quality.

    PubMed

    Gonzalez, Maria E; Barrett, Diane M

    2010-09-01

    Advanced food processing methods that accomplish inactivation of microorganisms but minimize adverse thermal exposure are of great interest to the food industry. High pressure (HP) and pulsed electric field (PEF) processing are commercially applied to produce high quality fruit and vegetable products in the United States, Europe, and Japan. Both microbial and plant cell membranes are significantly altered following exposure to heat, HP, or PEF. Our research group sought to quantify the degree of damage to plant cell membranes that occurs as a result of exposure to heat, HP, or PEF, using the same analytical methods. In order to evaluate whether new advanced processing methods are superior to traditional thermal processing methods, it is necessary to compare them. In this review, we describe the existing state of knowledge related to effects of heat, HP, and PEF on both microbial and plant cells. The importance and relevance of compartmentalization in plant cells as it relates to fruit and vegetable quality is described and various methods for quantification of plant cell membrane integrity are discussed. These include electrolyte leakage, cell viability, and proton nuclear magnetic resonance (¹H-NMR).

  5. Cooperative binding of Annexin A5 to phosphatidylserine on apoptotic cell membranes

    NASA Astrophysics Data System (ADS)

    Janko, Christina; Jeremic, Ivica; Biermann, Mona; Chaurio, Ricardo; Schorn, Christine; Muñoz, Luis E.; Herrmann, Martin

    2013-12-01

    Healthy cells exhibit an asymmetric plasma membrane with phosphatidylserine (PS) located on the cytoplasmic leaflet of the plasma membrane bilayer. Annexin A5-FITC, a PS binding protein, is commonly used to evaluate apoptosis in flow cytometry. PS exposed by apoptotic cells serves as a major ‘eat-me’ signal for phagocytes. Although exposition of PS has been observed after alternative stimuli, no clearance of viable, PS exposing cells has been detected. Thus, besides PS exposure, membranes of viable and apoptotic cells might exhibit specific characteristics. Here, we show that Annexin A5 binds in a cooperative manner to different types of dead cells. Shrunken apoptotic cells thereby showed the highest Hill coefficient values. Contrarily, parafomaldehyde fixation of apoptotic cells completely abrogates the cooperativity effect seen with dead and dying cells. We tend to speculate that the cooperative binding of Annexin A5 to the membranes of apoptotic cells reflects higher fluidity of the exposed membranes facilitating PS clustering.

  6. Modeling of gaseous flows within proton exchange membrane fuel cells

    SciTech Connect

    Weisbrod, K.R.; Vanderborgh, N.E.; Grot, S.A.

    1996-12-31

    Development of a comprehensive mechanistic model has been helpful to understand PEM fuel cell performance. Both through-the-electrode and down-the-channel models have been developed to support our experimental effort to enhance fuel cell design and operation. The through-the-electrode model was described previously. This code describes the known transport properties and dynamic processes that occur within a membrane and electrode assembly. Key parameters include transport through the backing layers, water diffusion and electroosmotic transport in the membrane, and reaction electrochemical kinetics within the cathode catalyst layer. In addition, two geometric regions within the cathode layer are represented, the first region below saturation and second with liquid water present. Although processes at high gas stoichiometry are well represented by more simple codes, moderate stoichiometry processes require a two dimensional representation that include the gaseous composition and temperature along flow channel. Although usually PEM hardware utilizes serpentine flow channels, this code does not include such geometric features and thus the flow can be visualized along a single channel.

  7. Compositional Heterogeneity in Ternary Models for the Cell Membrane

    NASA Astrophysics Data System (ADS)

    Smith, Robin; Heberle, Frederick; Wu, Jing; Feigenson, Gerald

    2010-03-01

    Ternary models for the cell membrane comprised of cholesterol (Chol) plus high and low melting temperature lipids exhibit rich phase behavior as a function of temperature and composition. Of particular interest is a region of coexisting disordered and ordered fluid phases that is thought to indicate how lipids organize to promote protein function in the cell membrane. We have used fluorescence resonance energy transfer to investigate the ternary mixtures DOPC(1,2-dioleoyl-sn-glycero-3-phosphocholine)/bSM (porcine brainsphingomyelin)/Chol and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine)/bSM/Chol at high compositional resolution. We confirmed liquid coexistence for DOPC/bSM/Chol at 15 and 25C that melts by 35C, but in contrast to previous studies we detected no fluid-phase compositional heterogeneity for POPC/bSM/Chol from 5-35C. If domains exist, they must be smaller than the approximately 5 nm sensitivity provided by the fluorescent lipid analogs employed. We propose electron spin resonance and x-ray scattering for measuring whether liquid-phase compositional heterogeneity occurs for POPC/bSM/Chol. Understanding POPC/bSM/Chol phase behavior will provide a framework for investigating peptide/lipid interactions in a biologically relevant lipid mixture.

  8. Penetration of living cell membranes with fortified carbon nanotube tips.

    PubMed

    Vakarelski, Ivan U; Brown, Scott C; Higashitani, Ko; Moudgil, Brij M

    2007-10-23

    We have fabricated robust nanosurgical needles suitable for single cell operations by modifying multiwalled carbon nanotube (MCNT)-terminated atomic force microscopy (AFM) tips. Extra-long MCNT AFM tips were prepared and fortified with molecular layers of carbon to overcome mechanical instabilities and then coated with an outer shell of gold to promote chemical versatility. The terminal diameters of the final fabricated tips were approximately 30-40 nm, and the MCNT probes were several micrometers in length. We illustrate the capability of these modified MCNT tips to carry nanoparticulate payloads and to penetrate the plasma membrane of living pleural mesothelial cells at the smallest indentation depths (100-200 nm) and lowest penetration forces (100-200 pN) currently reported for these procedures.

  9. Cell-Culture Reactor Having a Porous Organic Polymer Membrane

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L. (Inventor)

    2000-01-01

    A method for making a biocompatible polymer article using a uniform atomic oxygen treatment is disclosed. The substrate may be subsequently optionally grated with a compatibilizing compound. Compatibilizing compounds may include proteins, phosphory1choline groups, platelet adhesion preventing polymers, albumin adhesion promoters, and the like. The compatibilized substrate may also have a living cell layer adhered thereto. The atomic oxygen is preferably produced by a flowing afterglow microwave discharge, wherein the substrate resides in a sidearm out of the plasma. Also, methods for culturing cells for various purposes using the various membranes are disclosed as well. Also disclosed are porous organic polymers having a distributed pore chemistry (DPC) comprising hydrophilic and hydrophobic regions, and a method for making the DPC by exposing the polymer to atomic oxygen wherein the rate of hydrophilization is greater than the rate of mass loss.

  10. Composite materials for polymer electrolyte membrane microbial fuel cells.

    PubMed

    Antolini, Ermete

    2015-07-15

    Recently, the feasibility of using composite metal-carbon, metal-polymer, polymer-carbon, polymer-polymer and carbon-carbon materials in microbial fuel cells (MFCs) has been investigated. These materials have been tested as MFC anode catalyst (microorganism) supports, cathode catalysts and membranes. These hybrid materials, possessing the properties of each component, or even with a synergistic effect, would present improved characteristics with respect to the bare components. In this paper we present an overview of the use of these composite materials in microbial fuel cells. The characteristics of the composite materials as well as their effect on MFC performance were compared with those of the individual component and/or the conventionally used materials.

  11. RELATION BETWEEN EPSTEIN-BARR VIRAL AND CELL MEMBRANE IMMUNOFLUORESCENCE OF BURKITT TUMOR CELLS

    PubMed Central

    Klein, G.; Pearson, G.; Nadkarni, J. S.; Nadkarni, J. J.; Klein, E.; Henle, G.; Henle, W.; Clifford, P.

    1968-01-01

    A comparison was made of the immunofluorescence tests for detection of cell membrane and Epstein-Barr virus antigens in cells from Burkitt tumor biopsies or continuous cultures derived therefrom. On the whole, cell membrane fluorescence in established lines appeared to depend not only upon the presence of EBV but to a considerable degree also upon the extent of the persistent viral infection. There was no constant relationship, however, between the results of the two tests and exceptions to the rule were noted. These observations indicate that different antigens are involved in the two tests. Biopsy cells in general and young cultures may reveal strong MIF activity but few, if any, EBV-positive cells. The reverse, the presence of relatively large numbers of EBV antigen-containing cells in the absence of significant MIF reactions, was also noted on occasion in a few established cultures. The possible interpretations of these findings have been discussed. PMID:4878906

  12. Structural transition of actin filament in a cell-sized water droplet with a phospholipid membrane

    NASA Astrophysics Data System (ADS)

    Hase, M.; Yoshikawa, K.

    2006-03-01

    Actin filament, F-actin, is a semiflexible polymer with a negative charge, and is one of the main constituents of cell membranes. To clarify the effect of cross talk between a phospholipid membrane and actin filaments in cells, we conducted microscopic observations on the structural changes in actin filaments in a cell-sized (several tens of micrometers in diameter) water droplet coated with a phospholipid membrane such as phosphatidylserine (PS; negatively charged head group) or phosphatidylethanolamine (PE; neutral head group) as a simple model of a living cell membrane. With PS, actin filaments are distributed uniformly in the water phase without adsorption onto the membrane surface between 2 and 6mM Mg2+, while between 6 and 12mM Mg2+, actin filaments are adsorbed onto the inner membrane surface. With PE, the actin filaments are uniformly adsorbed onto the inner membrane surface between 2 and 12mM Mg2+. With both PS and PE membranes, at Mg2+ concentrations higher than 12mM, thick bundles are formed in the bulk water droplet accompanied by the dissolution of actin filaments from the membrane surface. The attraction between actin filaments and membrane is attributable to an increase in the translational entropy of counterions accompanied by the adsorption of actin filaments onto the membrane surface. These results suggest that a microscopic water droplet coated with phospholipid can serve as an easy-to-handle model of cell membranes.

  13. Mechanisms of outer membrane vesicle entry into host cells

    PubMed Central

    O'Donoghue, Eloise J.

    2016-01-01

    Abstract Bacterial outer membrane vesicles (OMVs) are nano‐sized compartments consisting of a lipid bilayer that encapsulates periplasm‐derived, luminal content. OMVs, which pinch off of Gram‐negative bacteria, are now recognized as a generalized secretion pathway which provides a means to transfer cargo to other bacterial cells as well as eukaryotic cells. Compared with other secretion systems, OMVs can transfer a chemically extremely diverse range of cargo, including small molecules, nucleic acids, proteins, and lipids to proximal cells. Although it is well recognized that OMVs can enter and release cargo inside host cells during infection, the mechanisms of host association and uptake are not well understood. This review highlights existing studies focusing on OMV‐host cell interactions and entry mechanisms, and how these entry routes affect cargo processing within the host. It further compares the wide range of methods currently used to dissect uptake mechanisms, and discusses potential sources of discrepancy regarding the mechanism of OMV uptake across different studies. PMID:27529760

  14. DEVELOPMENT OF NOVEL ELECTROCATALYSTS FOR PROTON EXCHANGE MEMBRANE FUEL CELLS

    SciTech Connect

    Shamsuddin Ilias

    2002-06-11

    The Proton Exchange Membrane Fuel Cell (PEMFC) is one of the most promising power sources for stand-alone utility and electric vehicle applications. Platinum (Pt) Catalyst is used for both fuel and air electrodes in PEMFCs. However, carbon monoxide (CO) contamination of H{sub 2} greatly affects electro catalysts used at the anode of PEMFCs and decreases cell performance. The irreversible poisoning of the anode can occur even in CO concentrations as low as few parts per million (ppm). In this work, we have synthesized several novel elctrocatalysts (Pt/C, Pt/Ru/C, Pt/Mo/C, Pt/Ir and Pt/Ru/Mo) for PEMFCs. These catalysts have been tested for CO tolerance in the H{sub 2}/air fuel cell, using CO concentrations in the H{sub 2} fuel that varies from 10 to 100 ppm. The performance of the electrodes was evaluated by determining the cell potential against current density. The effects of catalyst composition and electrode film preparation method on the performance of PEM fuel cell were also studied. It was found that at 70 C and 3.5 atm pressure at the cathode, Pt-alloy catalyst (10 wt% Pt/Ru/C, 20 wt% Pt/Mo/C) were more CO tolerant than the 20 wt% Pt/C catalyst alone. It was also observed that spraying method was better than the brushing technique for the preparation of electrode film.

  15. Pyro-electrification of polymer membranes for cell patterning

    NASA Astrophysics Data System (ADS)

    Rega, R.; Gennari, O.; Mecozzia, L.; Grilli, S.; Pagliarulo, V.; Ferraro, P.

    2016-05-01

    In the recent years, much attention has been devoted to the possibility of charging polymer-based materials, due to their potential in developing large-scale and inexpensive flexible thin-film technology. The availability of localized electrostatic fields is in of great interest for a huge amount of applications such as distribution of biomolecules and cells from the liquid phase. Here we report a voltage-free pyro-electrification (PE) process able to induce permanent dipoles into polymer layers; the lithium niobate (LN) crystal is the key component that plays the multi-purpose role of sustaining, heating and poling the polymer layer that is then peeled-off easily in order to have a free-standing charged membrane. The results show the fascinating application for the living cell patterning. It well known that cell behaviour is affected by chemical and topographical cues of substrate. In fact, polymers, such as polystyrene (PS) and poly(methyl methacrylate) (PMMA), are naturally cytophobic and require specific functionalization treatments in order to promote cell adhesion. Through our proposal technique, it's possible to obtain spontaneous organization and a driven growth of SH-SY5Y cells that is solely dictated by the nature of the charge polymer surface, opening, in this way, the innovative chance to manipulate and transfer biological samples on a free-standing polymer layer [1].

  16. Modifications of wheat germ cell-free system for functional proteomics of plant membrane proteins.

    PubMed

    Nozawa, Akira; Tozawa, Yuzuru

    2014-01-01

    Functional proteomics of plant membrane proteins is an important approach to understand the comprehensive architecture of each metabolic pathway in plants. One bottleneck in the characterization of membrane proteins is the difficulty in producing sufficient quantities of functional protein for analysis. Here, we describe three methods for membrane protein production utilizing a wheat germ cell-free protein expression system. Owing to the open nature of cell-free synthesis reaction, protein synthesis can be modified with components necessary to produce functional protein. In this way we have developed modifications to a wheat germ cell-free system for the production of functional membrane proteins. Supplementation of liposomes or detergents allows the synthesis of functional integral membrane proteins. Furthermore, supplementation of myristic acid enables synthesis of N-myristylated peripheral membrane proteins. These modified cell-free synthesis methods facilitate the preparation and subsequent functional analyses of a wide variety of membrane proteins.

  17. Chimera proteins with affinity for membranes and microtubule tips polarize in the membrane of fission yeast cells.

    PubMed

    Recouvreux, Pierre; Sokolowski, Thomas R; Grammoustianou, Aristea; ten Wolde, Pieter Rein; Dogterom, Marileen

    2016-02-16

    Cell polarity refers to a functional spatial organization of proteins that is crucial for the control of essential cellular processes such as growth and division. To establish polarity, cells rely on elaborate regulation networks that control the distribution of proteins at the cell membrane. In fission yeast cells, a microtubule-dependent network has been identified that polarizes the distribution of signaling proteins that restricts growth to cell ends and targets the cytokinetic machinery to the middle of the cell. Although many molecular components have been shown to play a role in this network, it remains unknown which molecular functionalities are minimally required to establish a polarized protein distribution in this system. Here we show that a membrane-binding protein fragment, which distributes homogeneously in wild-type fission yeast cells, can be made to concentrate at cell ends by attaching it to a cytoplasmic microtubule end-binding protein. This concentration results in a polarized pattern of chimera proteins with a spatial extension that is very reminiscent of natural polarity patterns in fission yeast. However, chimera levels fluctuate in response to microtubule dynamics, and disruption of microtubules leads to disappearance of the pattern. Numerical simulations confirm that the combined functionality of membrane anchoring and microtubule tip affinity is in principle sufficient to create polarized patterns. Our chimera protein may thus represent a simple molecular functionality that is able to polarize the membrane, onto which additional layers of molecular complexity may be built to provide the temporal robustness that is typical of natural polarity patterns.

  18. Water-Free Proton-Conducting Membranes for Fuel Cells

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram; Yen, Shiao-Pin

    2007-01-01

    Poly-4-vinylpyridinebisulfate (P4VPBS) is a polymeric salt that has shown promise as a water-free proton-conducting material (solid electrolyte) suitable for use in membrane/electrode assemblies in fuel cells. Heretofore, proton-conducting membranes in fuel cells have been made from perfluorinated ionomers that cannot conduct protons in the absence of water and, consequently, cannot function at temperatures >100 C. In addition, the stability of perfluorinated ionomers at temperatures >100 C is questionable. However, the performances of fuel cells of the power systems of which they are parts could be improved if operating temperatures could be raised above 140 C. What is needed to make this possible is a solid-electrolyte material, such as P4VPBS, that can be cast into membranes and that both retains proton conductivity and remains stable in the desired higher operating temperature range. A family of solid-electrolyte materials different from P4VPBS was described in Anhydrous Proton-Conducting Membranes for Fuel Cells (NPO-30493), NASA Tech Briefs, Vol. 29, No. 8 (August 2005), page 48. Those materials notably include polymeric quaternized amine salts. If molecules of such a polymeric salt could be endowed with flexible chain structures, it would be possible to overcome the deficiencies of simple organic amine salts that must melt before being able to conduct protons. However, no polymeric quaternized amine salts have yet shown to be useful in this respect. The present solid electrolyte is made by quaternizing the linear polymer poly- 4-vinylpyridine (P4VP) to obtain P4VPBS. It is important to start with P4VP having a molecular weight of 160,000 daltons because P4VPBS made from lower-molecular-weight P4VP yields brittle membranes. In an experimental synthesis, P4VP was dissolved in methanol and then reacted with an excess of sulfuric acid to precipitate P4VPBS. The precipitate was recovered, washed several times with methanol to remove traces of acid, and dried to a

  19. Sampling membrane potential, membrane resistance and electrode resistance with a glass electrode impaled into a single cell.

    PubMed

    Schiebe, M; Jaeger, U

    1980-04-01

    A method is demonstrated to measure membrane resistances and membrane potentials of single cells during impalement by a single glass microelectrode. The intention was to develop a procedure which would provide data almost continuously. Therefore, a frequency-dependent voltage divider network has been chosen to represent the basic electrical properties of the electrode and cell membrane, and used to explore its voltage response to a current stimulus, consisting of two rectangular pulses of different widths. It can be shown that the resolution of the method can be improved by inverting this stimulus so that each polarization becomes a relaxation and vice versa. In order to generate, analyze and display this signal continuously, a device has been designed which has been called 'Electrophysiological Monitor, (E1M2)'. E1M2 provides a current stimulus as input into a standard bridge network and can analyze the summed response of the electrode and cell by a set of sample-hold amplifiers. It then decodes and displays the data continuously, as membrane potential (Em), input resistance of the cell (Rinp) and the electrode resistance (Re) respectively. From Rinp the membrane resistance (Rm) can be deduced. The validity of the method has been examined by measuring these parameters in frog muscle cells. Technical design considerations, the accuracy and possible pitfalls with the suggested procedure are discussed.

  20. Irvalec Inserts into the Plasma Membrane Causing Rapid Loss of Integrity and Necrotic Cell Death in Tumor Cells

    PubMed Central

    Molina-Guijarro, José M.; Macías, Álvaro; García, Carolina; Muñoz, Eva; García-Fernández, Luis F.; David, Miren; Núñez, Lucía; Martínez-Leal, Juan F.; Moneo, Victoria; Cuevas, Carmen; Lillo, M. Pilar; Villalobos Jorge, Carlos; Valenzuela, Carmen; Galmarini, Carlos M.

    2011-01-01

    Irvalec is a marine-derived antitumor agent currently undergoing phase II clinical trials. In vitro, Irvalec induces a rapid loss of membrane integrity in tumor cells, accompanied of a significant Ca2+ influx, perturbations of membrane conductivity, severe swelling and the formation of giant membranous vesicles. All these effects are not observed in Irvalec-resistant cells, or are significantly delayed by pretreating the cells with Zn2+. Using fluorescent derivatives of Irvalec it was demonstrated that the compound rapidly interacts with the plasma membrane of tumor cells promoting lipid bilayer restructuration. Also, FRET experiments demonstrated that Irvalec molecules localize in the cell membrane close enough to each other as to suggest that the compound could self-organize, forming supramolecular structures that likely trigger cell death by necrosis through the disruption of membrane integrity. PMID:21556352

  1. Enhancement of the fuel cell performance of a high temperature proton exchange membrane fuel cell running with titanium composite polybenzimidazole-based membranes

    NASA Astrophysics Data System (ADS)

    Lobato, Justo; Cañizares, Pablo; Rodrigo, Manuel A.; Úbeda, Diego; Pinar, F. Javier

    2011-10-01

    The fuel cell performance of a composite PBI-based membrane with TiO2 has been studied. The behaviour of the membrane has been evaluated by comparison with the fuel cell performance of other PBI-based membranes, all of which were cast from the same polymer with the same molecular weight. The PBI composite membrane incorporating TiO2 showed the best performance and reached 1000 mW cm-2 at 175 °C. Moreover, this new titanium composite PBI-based membrane also showed the best stability during the preliminary long-term test under our operation conditions. Thus, the slope of the increase in the ohmic resistance of the composite membrane was 0.041 mΩ cm2 h-1 and this is five times lower than that of the standard PBI membrane. The increased stability was due to the high phosphoric acid retention capacity - as confirmed during leaching tests, in which the Ti-based composite PBI membrane retained 5 mol of H3PO4/PBI r.u. whereas the PBI standard membrane only retained 1 mol H3PO4/PBI r.u. Taking into account the results obtained in this study, the TiO2-PBI based membranes are good candidates as electrolytes for high temperature PEMFCs.

  2. Development of analytical cell support for vitrification at the West Valley Demonstration Project. Topical report

    SciTech Connect

    Barber, F.H.; Borek, T.T.; Christopher, J.Z.

    1997-12-01

    Analytical and Process Chemistry (A&PC) support is essential to the high-level waste vitrification campaign at the West Valley Demonstration Project (WVDP). A&PC characterizes the waste, providing information necessary to formulate the recipe for the target radioactive glass product. High-level waste (HLW) samples are prepared and analyzed in the analytical cells (ACs) and Sample Storage Cell (SSC) on the third floor of the main plant. The high levels of radioactivity in the samples require handling them in the shielded cells with remote manipulators. The analytical hot cells and third floor laboratories were refurbished to ensure optimal uninterrupted operation during the vitrification campaign. New and modified instrumentation, tools, sample preparation and analysis techniques, and equipment and training were required for A&PC to support vitrification. Analytical Cell Mockup Units (ACMUs) were designed to facilitate method development, scientist and technician training, and planning for analytical process flow. The ACMUs were fabricated and installed to simulate the analytical cell environment and dimensions. New techniques, equipment, and tools could be evaluated m in the ACMUs without the consequences of generating or handling radioactive waste. Tools were fabricated, handling and disposal of wastes was addressed, and spatial arrangements for equipment were refined. As a result of the work at the ACMUs the remote preparation and analysis methods and the equipment and tools were ready for installation into the ACs and SSC m in July 1995. Before use m in the hot cells, all remote methods had been validated and four to eight technicians were trained on each. Fine tuning of the procedures has been ongoing at the ACs based on input from A&PC technicians. Working at the ACs presents greater challenges than had development at the ACMUs. The ACMU work and further refinements m in the ACs have resulted m in a reduction m in analysis turnaround time (TAT).

  3. Characterization of direct methanol fuel cell (DMFC) applications with H 2SO 4 modified chitosan membrane

    NASA Astrophysics Data System (ADS)

    Osifo, Peter O.; Masala, Aluwani

    Chitosan (Chs) flakes were prepared from chitin materials that were extracted from the exoskeleton of Cape rock lobsters in South Africa. The Chs flakes were prepared into membranes and the Chs membranes were modified by cross-linking with H 2SO 4. The cross-linked Chs membranes were characterized for the application in direct methanol fuel cells. The Chs membrane characteristics such as water uptake, thermal stability, proton resistance and methanol permeability were compared to that of high performance conventional Nafion 117 membranes. Under the temperature range studied 20-60 °C, the membrane water uptake for Chs was found to be higher than that of Nafion. Thermal analysis revealed that Chs membranes could withstand temperature as high as 230 °C whereas Nafion 117 membranes were stable to 320 °C under nitrogen. Nafion 117 membranes were found to exhibit high proton resistance of 284 s cm -1 than Chs membranes of 204 s cm -1. The proton fluxes across the membranes were 2.73 mol cm -2 s -1 for Chs- and 1.12 mol cm -2 s -1 Nafion membranes. Methanol (MeOH) permeability through Chs membrane was less, 1.4 × 10 -6 cm 2 s -1 for Chs membranes and 3.9 × 10 -6 cm 2 s -1 for Nafion 117 membranes at 20 °C. Chs and Nafion membranes were fabricated into membrane electrode assemblies (MAE) and their performances measure in a free-breathing commercial single cell DMFC. The Nafion membranes showed a better performance as the power density determined for Nafion membranes of 0.0075 W cm -2 was 2.7 times higher than in the case of Chs MEA.

  4. Lipid-protein interactions in plasma membranes of fiber cells isolated from the human eye lens.

    PubMed

    Raguz, Marija; Mainali, Laxman; O'Brien, William J; Subczynski, Witold K

    2014-03-01

    The protein content in human lens membranes is extremely high, increases with age, and is higher in the nucleus as compared with the cortex, which should strongly affect the organization and properties of the lipid bilayer portion of intact membranes. To assess these effects, the intact cortical and nuclear fiber cell plasma membranes isolated from human lenses from 41- to 60-year-old donors were studied using electron paramagnetic resonance spin-labeling methods. Results were compared with those obtained for lens lipid membranes prepared from total lipid extracts from human eyes of the same age group [Mainali, L., Raguz, M., O'Brien, W. J., and Subczynski, W. K. (2013) Biochim. Biophys. Acta]. Differences were considered to be mainly due to the effect of membrane proteins. The lipid-bilayer portions of intact membranes were significantly less fluid than lipid bilayers of lens lipid membranes, prepared without proteins. The intact membranes were found to contain three distinct lipid environments termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain. However, the cholesterol bilayer domain, which was detected in cortical and nuclear lens lipid membranes, was not detected in intact membranes. The relative amounts of bulk and trapped lipids were evaluated. The amount of lipids in domains uniquely formed due to the presence of membrane proteins was greater in nuclear membranes than in cortical membranes. Thus, it is evident that the rigidity of nuclear membranes is greater than that of cortical membranes. Also the permeability coefficients for oxygen measured in domains of nuclear membranes were significantly lower than appropriate coefficients measured in cortical membranes. Relationships between the organization of lipids into lipid domains in fiber cells plasma membranes and the organization of membrane proteins are discussed.

  5. Lipid-Protein Interactions in Plasma Membranes of Fiber Cells Isolated from the Human Eye Lens

    PubMed Central

    Raguz, Marija; Mainali, Laxman; O’Brien, William J.; Subczynski, Witold K.

    2014-01-01

    The protein content in human lens membranes is extremely high, increases with age, and is higher in the nucleus as compared with the cortex, which should strongly affect the organization and properties of the lipid bilayer portion of intact membranes. To assess these effects, the intact cortical and nuclear fiber cell plasma membranes isolated from human lenses from 41- to 60-year-old donors were studied using electron paramagnetic resonance spin-labeling methods. Results were compared with those obtained for lens lipid membranes prepared from total lipid extracts from human eyes of the same age group [Mainali,L., Raguz, M., O’Brien, W. J., and Subczynski, W. K. (2013) Biochim. Biophys. Acta]. Differences were considered to be mainly due to the effect of membrane proteins. The lipid-bilayer portions of intact membranes were significantly less fluid than lipid bilayers of lens lipid membranes, prepared without proteins. The intact membranes were found to contain three distinct lipid environments termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain. However, the cholesterol bilayer domain, which was detected in cortical and nuclear lens lipid membranes, was not detected in intact membranes. The relative amounts of bulk and trapped lipids were evaluated. The amount of lipids in domains uniquely formed due to the presence of membrane proteins was greater in nuclear membranes than in cortical membranes. Thus, it is evident that the rigidity of nuclear membranes is greater than that of cortical membranes. Also the permeability coefficients for oxygen measured in domains of nuclear membranes were significantly lower than appropriate coefficients measured in cortical membranes. Relationships between the organization of lipids into lipid domains in fiber cells plasma membranes and the organization of membrane proteins are discussed. PMID:24486794

  6. Development of a new three-phase membrane-assisted liquid-phase microextraction method: determination of nitrite in tap water samples as model analytical application.

    PubMed

    Pedrón, Isabel; Chisvert, Alberto; March, Juan G; Salvador, Amparo; Benedé, Juan L

    2011-04-01

    A novel and simple device for membrane-assisted liquid-phase microextraction is used for the first time in a three-phase system. The device consists of a glass vial containing the aqueous acceptor phase, whose septum of its screw stopper has been replaced by a sized piece of polytetrafluoroethylene membrane impregnated with n-decane. The vial is assembled to a volumetric flask containing the aqueous donor phase, and the membrane comes in contact alternatively with both donor and acceptor aqueous phases by orbital agitation. The device has been tested for the determination of nitrite in tap water samples, which is extensively carried out in routine analysis, as model analytical application. Experimental variables, such as the organic solvent used to form the supported liquid membrane, the volumes of both donor and acceptor phases, the orbital agitation rate, and the extraction time were studied and optimized in terms of enrichment factor. Under the selected working conditions, the analytical figures of merit for nitrite determination were a linearity range up to 50 ng mL(-1), limits of detection and quantification of 0.15 and 0.50 ng mL(-1), respectively, and a good repeatability (RSD < 10%). The method has been applied to four tap water samples of different origins, and accurate and precise results were achieved. Besides, the very low volume of organic solvent used, its low cost and the no-risk of cross-contamination are significant operational advantages.

  7. Direct deposit of catalyst on the membrane of direct feed fuel cells

    NASA Technical Reports Server (NTRS)

    Chun, William (Inventor); Narayanan, Sekharipuram R. (Inventor); Jeffries-Nakamura, Barbara (Inventor); Valdez, Thomas I. (Inventor); Linke, Juergen (Inventor)

    2001-01-01

    An improved direct liquid-feed fuel cell having a solid membrane electrolyte for electrochemical reactions of an organic fuel. Catalyst utilization and catalyst/membrane interface improvements are disclosed. Specifically, the catalyst layer is applied directly onto the membrane electrolyte.

  8. Circulating cell membrane microparticles transfer heme to endothelial cells and trigger vasoocclusions in sickle cell disease.

    PubMed

    Camus, Stéphane M; De Moraes, João A; Bonnin, Philippe; Abbyad, Paul; Le Jeune, Sylvain; Lionnet, François; Loufrani, Laurent; Grimaud, Linda; Lambry, Jean-Christophe; Charue, Dominique; Kiger, Laurent; Renard, Jean-Marie; Larroque, Claire; Le Clésiau, Hervé; Tedgui, Alain; Bruneval, Patrick; Barja-Fidalgo, Christina; Alexandrou, Antigoni; Tharaux, Pierre-Louis; Boulanger, Chantal M; Blanc-Brude, Olivier P

    2015-06-11

    Intravascular hemolysis describes the relocalization of heme and hemoglobin (Hb) from erythrocytes to plasma. We investigated the concept that erythrocyte membrane microparticles (MPs) concentrate cell-free heme in human hemolytic diseases, and that heme-laden MPs have a physiopathological impact. Up to one-third of cell-free heme in plasma from 47 patients with sickle cell disease (SCD) was sequestered in circulating MPs. Erythrocyte vesiculation in vitro produced MPs loaded with heme. In silico analysis predicted that externalized phosphatidylserine (PS) in MPs may associate with and help retain heme at the cell surface. Immunohistology identified Hb-laden MPs adherent to capillary endothelium in kidney biopsies from hyperalbuminuric SCD patients. In addition, heme-laden erythrocyte MPs adhered and transferred heme to cultured endothelial cells, inducing oxidative stress and apoptosis. In transgenic SAD mice, infusion of heme-laden MPs triggered rapid vasoocclusions in kidneys and compromised microvascular dilation ex vivo. These vascular effects were largely blocked by heme-scavenging hemopexin and by the PS antagonist annexin-a5, in vitro and in vivo. Adversely remodeled MPs carrying heme may thus be a source of oxidant stress for the endothelium, linking hemolysis to vascular injury. This pathway might provide new targets for the therapeutic preservation of vascular function in SCD.

  9. High cell-surface density of HER2 deforms cell membranes

    PubMed Central

    Chung, Inhee; Reichelt, Mike; Shao, Lily; Akita, Robert W.; Koeppen, Hartmut; Rangell, Linda; Schaefer, Gabriele; Mellman, Ira; Sliwkowski, Mark X.

    2016-01-01

    Breast cancers (BC) with HER2 overexpression (referred to as HER2 positive) progress more aggressively than those with normal expression. Targeted therapies against HER2 can successfully delay the progression of HER2-positive BC, but details of how this overexpression drives the disease are not fully understood. Using single-molecule biophysical approaches, we discovered a new effect of HER2 overexpression on disease-relevant cell biological changes in these BC. We found HER2 overexpression causes deformation of the cell membranes, and this in turn disrupts epithelial features by perturbing cell–substrate and cell–cell contacts. This membrane deformation does not require receptor signalling activities, but results from the high levels of HER2 on the cell surface. Our finding suggests that early-stage morphological alterations of HER2-positive BC cells during cancer progression can occur in a physical and signalling-independent manner. PMID:27599456

  10. Analytic study of three-dimensional single cell migration with and without proteolytic enzymes

    PubMed Central

    Chisholm, Rebecca H.; Hughes, Barry D.; Landman, Kerry A.; Zaman, Muhammad H.

    2012-01-01

    Cell motility is a fundamental physiological process that regulates cellular fate in healthy and diseased systems. Cells cultured in 3D environments often exhibit biphasic dependence of migration speed with cell adhesion. Much is not understood about this very common behavior. A phenomenological model for 3D single-cell migration that exhibits biphasic behavior and highlights the important role of steric hindrance is developed and studied analytically. Changes in the biphasic behavior in the presence of proteolytic enzymes are investigated. Our methods produce a framework to determine analytic formulae for the mean cell speed, allowing general statements in terms of parameters to be explored, which will be useful when interpreting future experimental results. Our formula for mean cell speed as a function of ligand concentration generalizes and extends previous computational models that have shown good agreement with in vitro experiments. PMID:24348878

  11. DEVELOPMENT OF NOVEL ELECTROCATALYSTS FOR PROTON EXCHANGE MEMBRANE FUEL CELLS

    SciTech Connect

    Shamsuddin Ilias

    2003-04-24

    Fuel cells are electrochemical devices that convert the available chemical free energy directly into electrical energy, without going through heat exchange process. Of all different types of fuel cells, the Proton Exchange Membrane Fuel Cell (PEMFC) is one of the most promising power sources for stand-alone utility and electric vehicle applications. Platinum (Pt) Catalyst is used for both fuel and air electrodes in PEMFCs. However, carbon monoxide (CO) contamination of H{sub 2} greatly affects electro catalysts used at the anode of PEMFCs and decreases cell performance. The irreversible poisoning of the anode can occur even in CO concentrations as low as few parts per million (ppm). In this work, we have synthesized several novel elctrocatalysts (Pt/C, Pt/Ru/C, Pt/Mo/C, Pt/Ir and Pt/Ru/Mo) for PEMFCs. These catalysts have been tested for CO tolerance in the H{sub 2}/air fuel cell, using CO concentrations in the H{sub 2} fuel that varies from 10 to 100 ppm. The performance of the electrodes was evaluated by determining the cell potential against current density. The effects of catalyst composition and electrode film preparation method on the performance of PEM fuel cell were also studied. It was found that at 70 C and 3.5 atm pressure at the cathode, Pt-alloy catalyst (10 wt% Pt/Ru/C, 20 wt% Pt/Mo/C) were more CO tolerant than the 20 wt% Pt/C catalyst alone. It was also observed that spraying method was better than the brushing technique for the preparation of electrode film.

  12. Acetylcholine Receptor Organization in Membrane Domains in Muscle Cells

    PubMed Central

    Piguet, Joachim; Schreiter, Christoph; Segura, Jean-Manuel; Vogel, Horst; Hovius, Ruud

    2011-01-01

    Nicotinic acetylcholine receptors (nAChR) in muscle fibers are densely packed in the postsynaptic region at the neuromuscular junction. Rapsyn plays a central role in directing and clustering nAChR during cellular differentiation and neuromuscular junction formation; however, it has not been demonstrated whether rapsyn is the only cause of receptor immobilization. Here, we used single-molecule tracking methods to investigate nAChR mobility in plasma membranes of myoblast cells during their differentiation to myotubes in the presence and absence of rapsyn. We found that in myoblasts the majority of nAChR were immobile and that ∼20% of the receptors showed restricted diffusion in small domains of ∼50 nm. In myoblasts devoid of rapsyn, the fraction of mobile nAChR was considerably increased, accompanied by a 3-fold decrease in the immobile population of nAChR with respect to rapsyn-expressing cells. Half of the mobile receptors were confined to domains of ∼120 nm. Measurements performed in heterologously transfected HEK cells confirmed the direct immobilization of nAChR by rapsyn. However, irrespective of the presence of rapsyn, about one-third of nAChR were confined in 300-nm domains. Our results show (i) that rapsyn efficiently immobilizes nAChR independently of other postsynaptic scaffold components; (ii) nAChR is constrained in confined membrane domains independently of rapsyn; and (iii) in the presence of rapsyn, the size of these domains is strongly reduced. PMID:20978122

  13. Membrane Cholesterol Regulates Lysosome-Plasma Membrane Fusion Events and Modulates Trypanosoma cruzi Invasion of Host Cells

    PubMed Central

    Hissa, Bárbara; Duarte, Jacqueline G.; Kelles, Ludmila F.; Santos, Fabio P.; del Puerto, Helen L.; Gazzinelli-Guimarães, Pedro H.; de Paula, Ana M.; Agero, Ubirajara; Mesquita, Oscar N.; Guatimosim, Cristina; Chiari, Egler; Andrade, Luciana O.

    2012-01-01

    Background Trypomastigotes of Trypanosoma cruzi are able to invade several types of non-phagocytic cells through a lysosomal dependent mechanism. It has been shown that, during invasion, parasites trigger host cell lysosome exocytosis, which initially occurs at the parasite-host contact site. Acid sphingomyelinase released from lysosomes then induces endocytosis and parasite internalization. Lysosomes continue to fuse with the newly formed parasitophorous vacuole until the parasite is completely enclosed by lysosomal membrane, a process indispensable for a stable infection. Previous work has shown that host membrane cholesterol is also important for the T. cruzi invasion process in both professional (macrophages) and non-professional (epithelial) phagocytic cells. However, the mechanism by which cholesterol-enriched microdomains participate in this process has remained unclear. Methodology/Principal Finding In the present work we show that cardiomyocytes treated with MβCD, a drug able to sequester cholesterol from cell membranes, leads to a 50% reduction in invasion by T. cruzi trypomastigotes, as well as a decrease in the number of recently internalized parasites co-localizing with lysosomal markers. Cholesterol depletion from host membranes was accompanied by a decrease in the labeling of host membrane lipid rafts, as well as excessive lysosome exocytic events during the earlier stages of treatment. Precocious lysosomal exocytosis in MβCD treated cells led to a change in lysosomal distribution, with a reduction in the number of these organelles at the cell periphery, and probably compromises the intracellular pool of lysosomes necessary for T. cruzi invasion. Conclusion/Significance Based on these results, we propose that cholesterol depletion leads to unregulated exocytic events, reducing lysosome availability at the cell cortex and consequently compromise T. cruzi entry into host cells. The results also suggest that two different pools of lysosomes are

  14. A rapid method for the evaluation of the ionic permeabilities across epithelial cell membranes.

    PubMed

    Movileanu, L

    1999-02-08

    This short note presents a recipe for the calculation of the ionic permeabilities across epithelial cell membranes. The method requires the Goldman-Hodgkin-Katz formalism as well as the consideration of the equivalent electrical circuit for an epithelial cell. The equivalent electrical circuit is solved in terms of the equivalent electromotive forces coupled in series with the ionic resistances of both cell membranes (apical and basolateral). The present procedure is feasible for any leaky epithelial cell membrane with the condition that this membrane (apical or basolateral) does not contain primary or secondary mechanisms for active transport.

  15. Single cell analytic tools for drug discovery and development

    PubMed Central

    Heath, James R.; Ribas, Antoni; Mischel, Paul S.

    2016-01-01

    The genetic, functional, or compositional heterogeneity of healthy and diseased tissues presents major challenges in drug discovery and development.1-3 In cancers, heterogeneity may be essential for tumor stability,4 but its precise role in tumor biology is poorly resolved. This challenges the design of accurate disease models for use in drug development, and can confound the interpretation of biomarker levels, and of patient responses to specific therapies. The complex nature of heterogeneous tissues has motivated the development of tools for single cell genomic, transcriptomic, and multiplex proteomic analysis. We review these tools, assess their advantages and limitations, and explore their potential applications in drug discovery and development. PMID:26669673

  16. Characterisation of cell-wall polysaccharides from mandarin segment membranes.

    PubMed

    Coll-Almela, Luis; Saura-López, Domingo; Laencina-Sánchez, José; Schols, Henk A; Voragen, Alfons G J; Ros-García, José María

    2015-05-15

    In an attempt to develop a process of enzymatic peeling of mandarin segments suitable for use on an industrial scale, the cell wall fraction of the segment membrane of Satsuma mandarin fruits was extracted to obtain a chelating agent-soluble pectin fraction (ChSS), a dilute sodium hydroxide-soluble pectin fraction (DASS), a 1M sodium hydroxide-soluble hemicellulose fraction (1MASS), a 4M sodium hydroxide-soluble hemicellulose fraction (4MASS) and a cellulose-rich residue (3.1, 0.9, 0.4, 0.7 and 1.6%w/w of fresh membrane, respectively). The ChSS pectin consisted mainly of galacturonic acid followed by arabinose and galactose. The DASS fraction contained less galacturonic acid and more neutral sugars than ChSS. Eighty-nine percent of the galacturonic acid present in the segment membranes was recovered in the above two pectin fractions. The two hemicellulosic fractions consisted of two different molecular weight populations, which also differed in their sugar composition. Arabinose, xylose, mannose, galactose and glucose were the main sugar constituents of these hemicellulose fractions. In addition to an (arabino)xylan and a xyloglucan, the presence of an arabinogalactan is suggested by the sugar composition of both hemicelluloses. The pectin fractions were also characterised by their degradability by the pectic enzymes polygalacturonase, pectinmethylesterase and rhamnogalacturonan hydrolase. However the degree of degradation of the pectin fractions by enzymes differed, and the amount of the polymeric materials resistant to further degradation and the oligomeric products also differed. Using pectic enzymes it is possible to obtain peeled mandarin segments ready to eat or for canning.

  17. Infectious rotavirus enters cells by direct cell membrane penetration, not by endocytosis

    SciTech Connect

    Kaljot, K.T.; Shaw, R.D.; Greenberg, H.B. Palo Alto Veterans Administration Medical Center, CA ); Rubin, D.H. )

    1988-04-01

    Rotaviruses are icosahedral viruses with a segmented, double-stranded RNA genome. They are the major cause of severe infantile infectious diarrhea. Rotavirus growth in tissue culture is markedly enhanced by pretreatment of virus with trypsin. Trypsin activation is associated with cleavage of the viral hemagglutinin (viral protein 3 (VP3); 88 kilodaltons) into two fragments (60 and 28 kilodaltons). The mechanism by which proteolytic cleavage leads to enhanced growth is unknown. To determine whether trypsin treatment affected rotavirus internalization, the authors studied the kinetics of entry of infectious rhesus rotavirus (RRV) into MA104 cells. Trypsin-activated RRV was internalized with a half-time of 3 to 5 min, while nonactivated virus disappeared from the cell surface with a half-time of 30 to 50 min. In contrast to trypsin-activated RRV, loss of nonactivated RRV from the cell surface did not result in the appearance of infection, as measured by plaque formation. Purified trypsin-activated RRV added to cell monolayers at pH 7.4 mediated {sup 51}Cr, ({sup 14}C)choline, and ({sup 3}H)inositol released from prelabeled MA104 cells. This release could be specifically blocked by neutralizing antibodies to VP3. These results suggest that MA104 cell infection follows the rapid entry of trypsin-activated RRV by direct cell membrane penetration. Cell membrane penetration of infectious RRV is initiated by trypsin cleavage of VP3. Neutralizing antibodies can inhibit this direct membrane penetration.

  18. Rapid micropatterning of cell lines and human pluripotent stem cells on elastomeric membranes.

    PubMed

    Paik, Isha; Scurr, David J; Morris, Bryan; Hall, Graham; Denning, Chris; Alexander, Morgan R; Shakesheff, Kevin M; Dixon, James E

    2012-10-01

    Tissue function during development and in regenerative medicine completely relies on correct cell organization and patterning at micro and macro scales. We describe a rapid method for patterning mammalian cells including human embryonic stem cells (HESCs) and induced pluripotent stem cells (iPSCs) on elastomeric membranes such that micron-scale control of cell position can be achieved over centimeter-length scales. Our method employs surface engineering of hydrophobic polydimethylsiloxane (PDMS) membranes by plasma polymerization of allylamine. Deposition of plasma polymerized allylamine (ppAAm) using our methods may be spatially restricted using a micro-stencil leaving faithful hydrophilic ppAAm patterns. We employed airbrushing to create aerosols which deposit extracellular matrix (ECM) proteins (such as fibronectin and Matrigel™) onto the same patterned ppAAm rich regions. Cell patterns were created with a variety of well characterized cell lines (e.g., NIH-3T3, C2C12, HL1, BJ6, HESC line HUES7, and HiPSC line IPS2). Individual and multiple cell line patterning were also achieved. Patterning remains faithful for several days and cells are viable and proliferate. To demonstrate the utility of our technique we have patterned cells in a variety of configurations. The ability to rapidly pattern cells at high resolution over macro scales should aid future tissue engineering efforts for regenerative medicine applications and in creating in vitro stem cell niches.

  19. Novel Polyoxometalate Containing Membranes for PEM Fuel Cells

    SciTech Connect

    Mason K. Harrup; Frederick F. Stewart; Thomas A Luther; Tammy Trowbridge

    2009-03-01

    Current proton exchange membrane (PEM) technologies are inadequate to address the projected needs for fuel cell performance above 80 ºC. Continuing research into traditional ion carriers in novel membrane materials offers the promise of marginal improvement, representing only an evolutionary increase in performance. This conclusion is supported by the role of water in conduction. Thus, the key to better PEMs is not to eliminate water, but to change the role of water by developing ion carriers that will bind water more tightly than traditional sulfur or phosphorus based carriers resulting in materials that will conduct at higher temperatures. This change entails having a carrier structure that interacts more intimately with water and by increasing the ion carrier anionic charge to result in more tightly held inner shell protonated waters of hydration. Both of these factors synergistically act to maintain a critical water concentration at the carrier necessary for conduction. In this work, polyoxometalate (POM) clusters were selected to serve as these different proton carriers.

  20. An approach to estimate spatial distribution of analyte within cells using spectrally-resolved fluorescence microscopy

    NASA Astrophysics Data System (ADS)

    Sharma, Dharmendar Kumar; Irfanullah, Mir; Basu, Santanu Kumar; Madhu, Sheri; De, Suman; Jadhav, Sameer; Ravikanth, Mangalampalli; Chowdhury, Arindam

    2017-03-01

    While fluorescence microscopy has become an essential tool amongst chemists and biologists for the detection of various analyte within cellular environments, non-uniform spatial distribution of sensors within cells often restricts extraction of reliable information on relative abundance of analytes in different subcellular regions. As an alternative to existing sensing methodologies such as ratiometric or FRET imaging, where relative proportion of analyte with respect to the sensor can be obtained within cells, we propose a methodology using spectrally-resolved fluorescence microscopy, via which both the relative abundance of sensor as well as their relative proportion with respect to the analyte can be simultaneously extracted for local subcellular regions. This method is exemplified using a BODIPY sensor, capable of detecting mercury ions within cellular environments, characterized by spectral blue-shift and concurrent enhancement of emission intensity. Spectral emission envelopes collected from sub-microscopic regions allowed us to compare the shift in transition energies as well as integrated emission intensities within various intracellular regions. Construction of a 2D scatter plot using spectral shifts and emission intensities, which depend on the relative amount of analyte with respect to sensor and the approximate local amounts of the probe, respectively, enabled qualitative extraction of relative abundance of analyte in various local regions within a single cell as well as amongst different cells. Although the comparisons remain semi-quantitative, this approach involving analysis of multiple spectral parameters opens up an alternative way to extract spatial distribution of analyte in heterogeneous systems. The proposed method would be especially relevant for fluorescent probes that undergo relatively nominal shift in transition energies compared to their emission bandwidths, which often restricts their usage for quantitative ratiometric imaging in

  1. Purinergically induced membrane fluidization in ciliary cells: characterization and control by calcium and membrane potential.

    PubMed

    Alfahel, E; Korngreen, A; Parola, A H; Priel, Z

    1996-02-01

    To examine the role of membrane dynamics in transmembrane signal transduction, we studied changes in membrane fluidity in mucociliary tissues from frog palate and esophagus epithelia stimulated by extracellular ATP. Micromolar concentrations of ATP induced strong changes in fluorescence polarization, possibly indicating membrane fluidization. This effect was dosage dependent, reaching a maximum at 10-microM ATP. It was dependent on the presence of extracellular Ca2+ (or Mg2+), though it was insensitive to inhibitors of voltage-gated calcium channels. It was inhibited by thapsigargin and by ionomycin (at low extracellular Ca2+ concentration), both of which deplete Ca2+ stores. It was inhibited by the calcium-activated potassium channel inhibitors quinidine, charybdotoxin, and apamine and was reduced considerably by replacement of extracellular Na+ with K+. Hyperpolarization, or depolarization, of the mucociliary membrane induced membrane fluidization. The degree of membrane fluidization depended on the degree of hyperpolarization or depolarization of the ciliary membrane potential and was considerably lower than the effect induced by extracellular ATP. These results indicate that appreciable membrane fluidization induced by extracellular ATP depends both on an increase in intracellular Ca2+, mainly from its internal stores, and on hyperpolarization of the membrane. Calcium-dependent potassium channels couple the two effects. In light of recent results on the enhancement of ciliary beat frequency, it would appear that extracellular ATP-induced changes both in ciliary beat frequency and in membrane fluidity are triggered by similar signal transduction pathways.

  2. S4(13)-PV cell-penetrating peptide induces physical and morphological changes in membrane-mimetic lipid systems and cell membranes: implications for cell internalization.

    PubMed

    Cardoso, Ana M S; Trabulo, Sara; Cardoso, Ana L; Lorents, Annely; Morais, Catarina M; Gomes, Paula; Nunes, Cláudia; Lúcio, Marlene; Reis, Salette; Padari, Kärt; Pooga, Margus; Pedroso de Lima, Maria C; Jurado, Amália S

    2012-03-01

    The present work aims to gain insights into the role of peptide-lipid interactions in the mechanisms of cellular internalization and endosomal escape of the S4(13)-PV cell-penetrating peptide, which has been successfully used in our laboratory as a nucleic acid delivery system. A S4(13)-PV analogue, S4(13)-PVscr, displaying a scrambled amino acid sequence, deficient cell internalization and drug delivery inability, was used in this study for comparative purposes. Differential scanning calorimetry, fluorescence polarization and X-ray diffraction at small and wide angles techniques showed that both peptides interacted with anionic membranes composed of phosphatidylglycerol or a mixture of this lipid with phosphatidylethanolamine, increasing the lipid order, shifting the phase transition to higher temperatures and raising the correlation length between the bilayers. However, S4(13)-PVscr, in contrast to the wild-type peptide, did not promote lipid domain segregation and induced the formation of an inverted hexagonal lipid phase instead of a cubic phase in the lipid systems assayed. Electron microscopy showed that, as opposed to S4(13)-PVscr, the wild-type peptide induced the formation of a non-lamellar organization in membranes of HeLa cells. We concluded that lateral phase separation and destabilization of membrane lamellar structure without compromising membrane integrity are on the basis of the lipid-driven and receptor-independent mechanism of cell entry of S4(13)-PV peptide. Overall, our results can contribute to a better understanding of the role of peptide-lipid interactions in the mechanisms of cell-penetrating peptide membrane translocation, helping in the future design of more efficient cell-penetrating peptide-based drug delivery systems.

  3. [Cell membrane electroporator with digital generation of random shaped pulses].

    PubMed

    Iakovenko, S A; Trubitsin, B V

    2003-01-01

    A Digital Poration System (DPS), a versatile device for electrotreatment of biological objects by electric field pulses; was designed, constructed, and implemented. A feature distinguishing DPS from the currently available electroporators based on capacitor discharge through the load is the use of a digital-to-analog converter card as a generator of pulses applied for electroporation of biological membranes, with further amplification of the pulse by both voltage and current. The shape of pulses, including bipolar pulses, is arbitrarily programmable in DPS unlike other electroporators providing exponentially decaying and square-wave pulses only. Thus, the application area of DPS is substantially extended. In DPS, many of the drawbacks inherent in capacitor electroporators are removed, including the need for an additional external pulse analyzer monitoring and logging the electroporation processes, the necessity to recharge the capacitor before any new pulse, a poor precision of setting and measuring the pulse parameters, the need for an additional generator of long-lasting low-voltage signals for electrophoresis of ions into the porated object, the need for additional AC generators for the alignment of cells before, after, and during electroporation, and the need for an additional microprocessor to control multi-pulse and/or repetitive protocols. DPS provides a slew rate of about 1 V/1 ns required for the electroporation of most mammalian somatic cells, with +/- 250 V output voltage and 500 Ohm load resistance. The application area of DPS is much wider than for the available porators. It includes electrochemotherapy, cell electrofusion, oocyte activation by mimicking calcium waves (the latter two are the crucial components of mammalian organism cloning technology), dielectrophoretic bunching and orientation ordering of cells, sorting of cells, and electrophoresis of charged species into the cells.

  4. Stem cells from fetal membranes and amniotic fluid: markers for cell isolation and therapy.

    PubMed

    Pozzobon, Michela; Piccoli, Martina; De Coppi, Paolo

    2014-06-01

    Stem cell therapy is in constant need of new cell sources to conceive regenerative medicine approaches for diseases that are still without therapy. Scientists drew the attention toward amniotic membrane and amniotic fluid stem cells, since these sources possess many advantages: first of all as cells can be extracted from discarded foetal material it is inexpensive, secondly abundant stem cells can be obtained and finally, these stem cell sources are free from ethical considerations. Many studies have demonstrated the differentiation potential in vitro and in vivo toward mesenchymal and non-mesenchymal cell types; in addition the immune-modulatory properties make these cells a good candidate for allo- and xenotransplantation. This review offers an overview on markers characterisation and on the latest findings in pre-clinical or clinical setting of the stem cell populations isolated from these sources.

  5. Cell invasion through basement membrane: the anchor cell breaches the barrier.

    PubMed

    Hagedorn, Elliott J; Sherwood, David R

    2011-10-01

    Cell invasion through basement membrane (BM) is a specialized cellular behavior critical to many normal developmental events, immune surveillance, and cancer metastasis. A highly dynamic process, cell invasion involves a complex interplay between cell-intrinsic elements that promote the invasive phenotype, and cell-cell and cell-BM interactions that regulate the timing and targeting of BM transmigration. The intricate nature of these interactions has made it challenging to study cell invasion in vivo and model in vitro. Anchor cell invasion in Caenorhabditis elegans is emerging as an important experimental paradigm for comprehensive analysis of BM invasion, revealing the gene networks that specify invasive behavior and the interactions that occur at the cell-BM interface.

  6. Manipulation of cell membrane using carbon nanotube scaffold as a photoresponsive stimuli generator

    PubMed Central

    Sada, Takao; Fujigaya, Tsuyohiko; Nakashima, Naotoshi

    2014-01-01

    We describe, for the first time, the perforation of the cell membrane in the targeted single cell based on the nanosecond pulsed near-infrared (NIR) laser irradiation of a thin film of carbon nanotubes that act as an effective photon absorber as well as stimuli generator. When the power of NIR laser is over 17.5 μJ/pulse, the cell membrane after irradiation is irreversibly disrupted and results in cell death. In sharp contrast, the perforation of the cell membrane occurs at suitable laser power (∼15 μJ/pulse) without involving cell termination. PMID:27877703

  7. Shock Wave-Induced Damage and Poration in Eukaryotic Cell Membranes.

    PubMed

    López-Marín, Luz M; Millán-Chiu, Blanca E; Castaño-González, Karen; Aceves, Carmen; Fernández, Francisco; Varela-Echavarría, Alfredo; Loske, Achim M

    2017-02-01

    Shock waves are known to permeabilize eukaryotic cell membranes, which may be a powerful tool for a variety of drug delivery applications. However, the mechanisms involved in shock wave-mediated membrane permeabilization are still poorly understood. In this study, the effects on both the permeability and the ultrastructural features of two human cell lineages were investigated after the application of underwater shock waves in vitro. Scanning Electron Microscopy of cells derived from a human embryo kidney (HEK)-293 and Michigan Cancer Foundation (MCF)-7 cells, an immortalized culture derived from human breast adenocarcinoma, showed a small amount of microvilli (as compared to control cells), the presence of hole-like structures, and a decrease in cell size after shock wave exposure. Interestingly, these effects were accompanied by the permeabilization of acid and macromolecular dyes and gene transfection. Trypan blue exclusion assays indicated that cell membranes were porated during shock wave treatment but resealed after a few seconds. Deformations of the cell membrane lasted for at least 5 min, allowing their observation in fixed cells. For each cell line, different shock wave parameters were needed to achieve cell membrane poration. This difference was correlated to successful gene transfection by shock waves. Our results demonstrate, for the first time, that shock waves induce transient micro- and submicrosized deformations at the cell membrane, leading to cell transfection and cell survival. They also indicate that ultrastructural analyses of cell surfaces may constitute a useful way to match the use of shock waves to different cells and settings.

  8. S-layer and cytoplasmic membrane - exceptions from the typical archaeal cell wall with a focus on double membranes.

    PubMed

    Klingl, Andreas

    2014-01-01

    The common idea of typical cell wall architecture in archaea consists of a pseudo-crystalline proteinaceous surface layer (S-layer), situated upon the cytoplasmic membrane. This is true for the majority of described archaea, hitherto. Within the crenarchaea, the S-layer often represents the only cell wall component, but there are various exceptions from this wall architecture. Beside (glycosylated) S-layers in (hyper)thermophilic cren- and euryarchaea as well as halophilic archaea, one can find a great variety of other cell wall structures like proteoglycan-like S-layers (Halobacteria), glutaminylglycan (Natronococci), methanochondroitin (Methanosarcina) or double layered cell walls with pseudomurein (Methanothermus and Methanopyrus). The presence of an outermost cellular membrane in the crenarchaeal species Ignicoccus hospitalis already gave indications for an outer membrane similar to Gram-negative bacteria. Although there is just limited data concerning their biochemistry and ultrastructure, recent studies on the euryarchaeal methanogen Methanomassiliicoccus luminyensis, cells of the ARMAN group, and the SM1 euryarchaeon delivered further examples for this exceptional cell envelope type consisting of two membranes.

  9. S-layer and cytoplasmic membrane – exceptions from the typical archaeal cell wall with a focus on double membranes

    PubMed Central

    Klingl, Andreas

    2014-01-01

    The common idea of typical cell wall architecture in archaea consists of a pseudo-crystalline proteinaceous surface layer (S-layer), situated upon the cytoplasmic membrane. This is true for the majority of described archaea, hitherto. Within the crenarchaea, the S-layer often represents the only cell wall component, but there are various exceptions from this wall architecture. Beside (glycosylated) S-layers in (hyper)thermophilic cren- and euryarchaea as well as halophilic archaea, one can find a great variety of other cell wall structures like proteoglycan-like S-layers (Halobacteria), glutaminylglycan (Natronococci), methanochondroitin (Methanosarcina) or double layered cell walls with pseudomurein (Methanothermus and Methanopyrus). The presence of an outermost cellular membrane in the crenarchaeal species Ignicoccus hospitalis already gave indications for an outer membrane similar to Gram-negative bacteria. Although there is just limited data concerning their biochemistry and ultrastructure, recent studies on the euryarchaeal methanogen Methanomassiliicoccus luminyensis, cells of the ARMAN group, and the SM1 euryarchaeon delivered further examples for this exceptional cell envelope type consisting of two membranes. PMID:25505452

  10. Cross-linked high conductive membranes based on water soluble ionomer for high performance proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Jiang, Hao; Guo, Xin; Zhang, Gang; Ni, Jing; Zhao, Chengji; Liu, Zhongguo; Zhang, Liyuan; Li, Mingyu; Xu, Shuai; Na, Hui

    2013-11-01

    In this paper, a series of proton exchange membranes prepared by “Click Reaction” are reported. The cross-linked membranes are based on water soluble sulfonated poly (ether ether ketone) containing dipropenyl groups (SDPEEK-nE/nH). Compared with self-crosslinked membranes (SDPEEK-nS), this “Click” cross-linked membranes using 1,2-Ethanedithiol and 1,6-Hexanedithiol as the cross-linker exhibit extremely reduced water uptake and swelling ratio. The lowest proton conductivity at 80 °C of the “Click” cross-linked membranes reaches to 0.168 S cm-1, and the highest methanol permeability of the “Click” cross-linked SDPEEK-8E is only 4.13 × 10-7 cm2 s-1, which is 5 times lower than that of Nafion 117 membrane. All the results imply that the cross-linked membranes with novel thiol cross-linker are promising alternative material for fuel cell application.

  11. Towards fuel cell membranes with improved lifetime: Aquivion® Perfluorosulfonic Acid membranes containing immobilized radical scavengers

    NASA Astrophysics Data System (ADS)

    D'Urso, C.; Oldani, C.; Baglio, V.; Merlo, L.; Aricò, A. S.

    2014-12-01

    A facile synthesis, based on a wet impregnation technique and a thermal treatment, of a novel silica-supported cerium-oxide-based radical scavenger bearing sulfonic acid functionalities is presented. This material is loaded as a filler in ePTFE reinforced membranes (called R79-02S) prepared starting from Aquivion® Perfluoro-Sulfonic Acid (PFSA) dispersions. The aim is to mitigate the peroxy radicals attack to the polymeric membrane under fuel cell operating conditions. These membranes show much longer (7 times more) life-time in Accelerated Stress Tests (AST) and reduced fluoride release (about one half) in Fenton's tests than the radical scavenger-free membrane without any loss in electrochemical performance. Scavenger-free Aquivion® PFSA-based membrane durability is about 200 h in AST whereas the same membrane containing the newly developed radical scavenger exceeds 1400 h. These results confirm the stability of the modified membranes and the excellent activity of the composite scavenger in mitigating the polymer electrolyte degradation.

  12. Cross-linked anion exchange membranes with pendent quaternary pyrrolidonium salts for alkaline polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Lan, Chunhua; Fang, Jun; Guan, Yingjie; Zhou, Huili; Zhao, Jinbao

    2015-11-01

    Novel anion-exchange membranes based on two kinds of pyrrolidonium type ionic liquids, N-methyl-N-vinyl-pyrrolidonium (NVMP) and N-ethyl-N-vinyl-pyrrolidonium (NVEP), have been synthesized via polymerization and crosslinking treatment, followed by membrane casting. The covalent cross-linked structures of these membranes are confirmed by FT-IR. The obtained membranes are also characterized in terms of water uptake, ion exchange capacity (IEC), ionic conductivity as well as thermal, dimensional and chemical stability. The membranes display hydroxide conductivity of above 10-2 S cm-1 at 25 °C. Excellent thermal stability with onset degradation temperature above 235 °C, good alkaline stability in 6 mol L-1 NaOH at 60 °C for 168 h and remarkable dimensional stability of the resulting membranes have been proved. H2/air single fuel cells employed membrane M3 and N3 show the open-circuit voltage (OCV) of 0.953 V and 0.933 V, and the maximum power density of 88.90 mW cm-2 and 81.90 mW cm-2 at the current density of 175 mA cm-2 and 200 mA cm-2 at 65 °C, respectively.

  13. Meninges: from protective membrane to stem cell niche

    PubMed Central

    Decimo, Ilaria; Fumagalli, Guido; Berton, Valeria; Krampera, Mauro; Bifari, Francesco

    2012-01-01

    Meninges are a three tissue membrane primarily known as coverings of the brain. More in depth studies on meningeal function and ultrastructure have recently changed the view of meninges as a merely protective membrane. Accurate evaluation of the anatomical distribution in the CNS reveals that