Membrane Electrical Properties Research Articles

Effect of SPEEK content on the morphological and electrical properties of PES/SPEEK blend nanofiltration membranes

Polyethersulfone (PES)/poly (ether ether ketone) (SPEEK) blends nanofiltration membrane at different SPEEK contents were prepared using a simple dry-jet wet spinning technique. The SPEEK polymer with fixed sulfonation degree was used for membrane preparation and characterized using FTIR and nuclear magnetic resonance (NMR) spectrometer. The morphological and electrical properties of the blends membrane were deduced based on the combination of irreversible thermodynamic model, steric-hindrance pore model (SHP) and Teorell–Meyer–Sievers model (TMS). The modeling results have been analyzed and discussed. The effect of SPEEK content on the blend properties was further studied in detail by FTIR, DSC and TGA and the results were discussed.

Micro-Electro-Mechanical Switch Based on Suspended Horizontal Dense Mat of CNTs by FIB Nanomanipulation

The paper presents the carbon nanotubes (CNTs) alignment and length dependence with respect to the catalyst pattern design, the fabrication of a CNT MEM switch, nanomanipulating a CNT array by FIB and the electrical characterization of the device to evaluate the electrical and mechanical properties of the CNT membrane. The catalyst design permits to obtain, during the same growth process, both vertical and horizontal aligned nanotubes. The high density guaranties to the CNT mat to act as a compact and flexible material that could be manipulated to make MEM devices. DC electrical measurements of the CNT MEM switch show an equivalent resistivity of 0.08Ωcm and a Young Modulus of 160MPa that permit to have low actuation voltage devices in the downscaling process.

Zebrafish Motor Neuron Subtypes Differ Electrically Prior to Axonal Outgrowth

Different muscle targets and transcription factor expression patterns reveal the presence of motor neuron subtypes. However, it is not known whether these subtypes also differ with respect to electrical membrane properties. To address this question, we studied primary motor neurons (PMNs) in the spinal cord of zebrafish embryos. PMN genesis occurs during gastrulation and gives rise to a heterogeneous set of motor neurons that differ with respect to transcription factor expression, muscle targets, and soma location within each spinal cord segment. The unique subtype-specific soma locations and axonal trajectories of two PMNs-MiP (middle) and CaP (caudal)-allowed their identification in situ as early as 17 h postfertilization (hpf), prior to axon genesis. Between 17 and 48 hpf, CaPs and MiPs displayed subtype-specific electrical membrane properties. Voltage-dependent inward and outward currents differed significantly between MiPs and CaPs. Moreover, by 48 hpf, CaPs and MiPs displayed subtype-specific firing behaviors. Our results demonstrate that motor neurons that differ with respect to muscle targets and transcription factor expression acquire subtype-specific electrical membrane properties. Moreover, the differences are evident prior to axon genesis and persist to the latest stage studied, 2 days postfertilization.

Everything You Always Wanted to Know about Sachs' Seals

Everything You Always Wanted to Know about Sachs' Seals

Multiple forms of activity‐dependent intrinsic plasticity in layer V cortical neurones in vivo

Synaptic plasticity is classically considered as the neuronal substrate for learning and memory. However, activity-dependent changes in neuronal intrinsic excitability have been reported in several learning-related brain regions, suggesting that intrinsic plasticity could also participate to information storage. Compared to synaptic plasticity, there has been little exploration of the properties of induction and expression of intrinsic plasticity in an intact brain. Here, by the means of in vivo intracellular recordings in the rat we have examined how the intrinsic excitability of layer V motor cortex pyramidal neurones is altered following brief periods of repeated firing. Changes in membrane excitability were assessed by modifications in the discharge frequency versus injected current (F-I) curves. Most (approximately 64%) conditioned neurones exhibited a long-lasting intrinsic plasticity, which was expressed either by selective changes in the current threshold or in the slope of the F-I curve, or by concomitant changes in both parameters. These modifications in the neuronal input-output relationship led to a global increase or decrease in intrinsic excitability. Passive electrical membrane properties were unaffected by the intracellular conditioning, indicating that intrinsic plasticity resulted from modifications of voltage-gated ion channels. These results demonstrate that neocortical pyramidal neurones can express in vivo a bidirectional use-dependent intrinsic plasticity, modifying their sensitivity to weak inputs and/or the gain of their input-output function. These multiple forms of experience-dependent intrinsic changes, which expand the computational abilities of individual neurones, could shape new network dynamics and thus might participate in the formation of mnemonic motor engrams.

Transient electrical response of ion-exchange membranes with fixed-charge due to ion adsorption. A network simulation approach

The transient electrical properties of ion-exchange membranes with inhomogeneous fixed-charge distributions due to ion adsorption processes, have been investigated using the network simulation method. A network model is proposed for the Nernst–Planck and Poisson equations describing the transport of a binary electrolyte through an ion-exchange membrane and the two diffusion boundary layers on both sides of the membrane. An electric circuit simulation program is used to solve the network model in order to obtain the transient electrical properties of a system where the fixed-charge concentration of the membrane is due to an anion adsorption process. The chronoamperometric and chronopotentiometric responses of the whole membrane system have been simulated for the case of a membrane with surface charge described by a Langmuir kinetics.

Theoretical studies on structural and electrical properties of PES/SPEEK blend nanofiltration membrane

AbstractPolyethersulfone (PES) nanofiltration membranes were prepared using a simple dry‐jet wet spinning technique with different contents of sulfonated poly(ether ether ketone) (SPEEK) ranging from 0 to 4 wt %. The structural parameters (rp and Ak/Δx) and electrostatic properties (ξ and X) of the blend membranes were deduced by employing the combination of irreversible thermodynamic model, steric hindrance pore (SHP) model, and Teorell‐Meyer‐Sievers (TMS) model. The modeling results obtained have been analyzed and discussed. The mean pore radius and pore size distribution of the blends were also determined based on the theoretical models. The results showed that pore radius increased with increasing the concentration of SPEEK from 0 to 2 wt % but decreased with a further increase in SPEEK content. The water flux, however, showed a systematically increase with increasing SPEEK content. The SPEEK also showed significant effect on membrane electrical properties. Both effective charge density and ratio of effective charge density to electrolyte solution increased with increasing concentration of SPEEK in the dope solution, reaching a value of −21.02 and −2.29, respectively. The pore radius which was determined by using different transport models has also been analyzed and discussed. It is found that the addition of SPEEK into dope solution is one of the paramount parameters in developing the negatively charged nanofiltration membrane with enhanced water flux while retaining the pore radius in the nanometer range. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Influence of feed conditions on the rejection of salt and dye in aqueous solution by different characteristics of hollow fiber nanofiltration membranes

Three different characteristics of self-made hollow fiber nanofiltration (NF) membranes with different structural and electrical properties were evaluated for their suitability for removing salt and colour as a function of feed conditions. Results showed that NF achieved promising dye retention for the reactive dyes used at different concentrations and varied slightly with pH. The retention of salt was found to be dependent on feed properties and membrane electrical properties where higher retentions were achieved under alkaline condition and by using the most negatively charged NF membrane. The enhancement in the membrane negative surface charge resulting from the addition of sulfonated poly (ether ether ketone) (SPEEK) during membrane preparation had also made the NF less fouling-sensitive to dye absorption and improving the economic viability of the treatment process.

Myosin-dependent targeting of transmembrane proteins to neuronal dendrites

The distinct electrical properties of axonal and dendritic membranes are largely a result of specific transport of vesicle-bound membrane proteins to each compartment. How this specificity arises is unclear because kinesin motors that transport vesicles cannot autonomously distinguish dendritically projecting microtubules from those projecting axonally. We hypothesized that interaction with a second motor might enable vesicles containing dendritic proteins to preferentially associate with dendritically projecting microtubules and avoid those that project to the axon. Here we show that in rat cortical neurons, localization of several distinct transmembrane proteins to dendrites is dependent on specific myosin motors and an intact actin network. Moreover, fusion with a myosin-binding domain from Melanophilin targeted Channelrhodopsin-2 specifically to the somatodendritic compartment of neurons in mice in vivo. Together, our results suggest that dendritic transmembrane proteins direct the vesicles in which they are transported to avoid the axonal compartment through interaction with myosin motors.

Influence of M cations on structural, thermal and electrical properties of new oxygen selective membranes based on SrCo 0.95M 0.05O 3− δ perovskite

In this work, various M cations like Bi 5+, Zr 4+, Ce 4+, Sc 3+, La 3+, Y 3+, Al 3+ and Zn 2+ were incorporated into SrCoO 3− δ (SC) lattices one by one via doping strategy to form a series of new SrCo 0.95M 0.05O 3− δ (SCM) mixed oxides for membrane separation. In general, the M cations have significant effects on the crystal structure, electrical conductivity, sintering behavior and the oxygen permeability of the SCM membranes even though only 5% of Co ions are exchanged. The phase structure of SCMs in the air atmosphere is seemingly determined by the electron configuration in the outer orbits of M cation. In the current cases, the doping of M cation with d 10 configuration results in 2H-hexagonal structure while that with p 6 gives rise to a cubic perovskite or brownmillerite. The formation of cubic perovskite induced by M cation increases the electrical conductivity and the oxygen permeability by 1–2 orders of magnitude due to the high density of oxygen vacancy. In particular, disk-shaped perovskite SrCo 0.95Sc 0.05O 3− δ membrane demonstrates the highest oxygen flux and theoretical analysis indicates that the oxygen permeation process is rate-determined by the surface reactions.

Physiology of Membrane Oestrogen Receptor Signalling in Reproduction

The best characterised oestrogen receptors (ERs) that are responsible for membrane-initiated oestradiol signalling are the classic ERs, ERalpha and ERbeta. When in the nucleus, these proteins are oestradiol activated transcription factors but, when trafficked to the cell membrane, ERalpha and ERbeta rapidly activate protein kinase pathways, alter membrane electrical properties, modulate ion flux and can mediate long-term effects through gene expression. To initiate cell signalling, membrane ERs transactivate metabotropic glutamate receptors (mGluRs) to stimulate Gq signalling through pathways using PKC and calcium. In this review, we discuss the interaction of membrane ERalpha with metabotropic glutamate receptor 1a (mGluR1a) to initiate rapid oestradiol cell signalling and its critical roles in female reproduction: sexual behaviour and oestrogen positive feedback of the luteinising hormone (LH) surge. Although long considered to be regulated by the long-term actions of oestradiol on gene transcription, recent results indicate that membrane oestradiol cell signalling is vital for a full display of sexual receptivity. Similarly, the source of pre-ovulatory progesterone necessary for initiating the LH surge is hypothalamic astrocytes. Oestradiol rapidly amplifies progesterone synthesis through the release of intracellular calcium stores. The ERalpha-mGluR1a interaction is necessary for critical calcium flux. These two examples provide support for the hypothesis that membrane ERs are not themselves G-protein receptors; rather, they use mGluRs to signal.

Theoretical studies on the morphological and electrical properties of blended PES/SPEEK nanofiltration membranes using different sulfonation degree of SPEEK

Sulfonated poly(ether ether ketone)s (SPEEKs) with different sulfonation degrees (DS) were synthesized and characterized using FTIR and NMR for the preparation of blend nanofiltration (NF) membranes. Blends of polyethersulfone and SPEEK at various SPEEK concentrations and various DS were prepared by a simple dry-jet wet spinning technique. The changes in the morphological and electrical properties of the blend membranes were deduced by employing the combination of irreversible thermodynamic model, Steric-Hindrance Pore (SHP) model and Teorell–Meyer–Sievers (TMS) model and the modeling results have been analyzed and discussed in detail. The results showed that the membrane water flux, pore size and surface charge were dependent on the content and DS of SPEEK used. FESEM–EDX results also provided supporting evidence for the trends observed for the morphological and electrical studies.

Effect of glucose-6-phosphate dehydrogenase deficiency on some biophysical properties of human erythrocytes

The most widespread erythrocyte enzyme defect throughout the world is glucose-6-phosphate dehydrogenase (G-6-PD) deficiency. The diagnosis of G-6-PD deficiency may be missed during an acute hemolytic episode due to increased young red blood cells which have good enzyme activity. However this might be detected at a later stage when the patient is asymptomatic. This calls for a detailed investigation of the patient with an acute attack of hemolysis at a later stage. Blood samples were obtained from 45 G-6-PD deficient male patients with previously diagnosed disease [25 subjects were during hemolytic attack (Gp1) while the rest was outside acute hemolytic crisis (Gp2)] and 20 healthy male subjects. The effect of G-6-PD deficiency on the erythrocytes of the above groups was investigated by scanning electron microscope (SEM) complemented with dielectric spectroscopy. The quantification of the morphological shape changes revealed that Gp1 had a significant increase in spheroechinocytes as well as in the morphological index in comparison with those of all other groups. The overall electrical and morphological properties of the red cell membrane of these subjects modified to a great extent during hemolytic attack. This may have important diagnostic and research implications. Thus the combined application of dielectric spectroscopy and SEM can be used as an efficient manner for monitoring abnormalities in blood and erythrocytes due to G-6-PD deficiency.

Cell Membrane Electrical And Order Properties Under Microwaves Irradiation

The degree of packing and mobility of phospholipidic molecules within a biological membrane are crucial for the latter to accomplish its physiological functions (e.g. transport across membrane, signaling processes etc). Consequently, any physical and/or chemical factor which affects the membrane order, may affect also its function.We studied the effect of 2.45 GHz microwaves irradiation on both biological and model membranes (dimiristoyl phosphatidyl choline liposomes), monitoring the following parameters:- membrane fluidity, by fluorescence depolarization of TMA-DPH,- membrane generalized polarization, by modifications of emission spectra of Laurdan,- membrane potential, by fluorescence quenching of DiSC3(5).The irradiation was performed directly in the spectrofluorometer, with a specially designed antenna and the temperature was continuously monitored using an optical fiber thermometer. Membrane fluidity, generalized polarization and potential were measured continuously during the irradiation.In parallel experiments the same thermal evolution of the system as in the case of microwave irradiation was simulated by means of a computer controlled Peltier thermostat.The dependency of the monitored parameters on the temperature in both cases (MW irradiation and “thermal” heating) was analyzed.In the case of liposomes we observed a rising of the transition temperature by a few degrees centigrade, depending on the applied microwaves power.The results are interpreted in terms of membrane destabilization by water penetration in the lipidic bilayer above the critical temperature, which seems to be affected by the presence of the electromagnetic field. The effects are very clear in the case of model membrane, but less evident and much more complex in the case of living cells.

Decreased Skeletal Muscle Intramembrane Charge Movement And Contractile Activation In S100A1 Knock Out Mice

S100A1, a calcium binding protein expressed in skeletal and cardiac muscle, modulates Ca2+ signaling. We have previously shown that isolated flexor digitorum brevis (FDB) skeletal muscle fibers from S100A1 knock out (ko) mice exhibit reduced Ca2+ transients with delayed onset in response to single action potentials compared to wild type (wt) FDB fibers (Prosser et al, 2008). Utilizing the potentiometric dye di-8-ANEPPS, we now show no differences in action potential properties between wt and ko fibers. Using whole cell voltage clamp of single isolated fibers we examined surface and transverse tubule membrane electrical properties in wt and ko fibers. Preliminary non-linear capacitive current measurements indicate that maximum charge moved (Qmax) is less in ko than wt fibers (wt Qmax = 43.6 ± 3.4 nC/μF, ko Qmax = 32.0 ± 3.5 nC/μF; p < .05). The temporally delayed, steeply voltage dependent component of intramembrane charge movement at intermediate depolarizations (Qγ) is less pronounced in ko than in wt fibers, consistent with a steeper voltage dependence of charge moved (wt k = 7.2 ± .5, ko k = 10.8 ± 1.2, p < .05). The midpoint voltage of charge moved was not different (wt Vhalf = -26.1 ± 2.8 mV, ko Vhalf = -28.5 ± 1.5 mV). Both the amplitude and the voltage dependence of Cav1 Ca2+ currents were similar in wt and ko fibers. In vivo maximal specific force (force normalized to muscle mass) was significantly decreased in ko compared with wt muscles (wt Po = 1.52 ± .09 g/mg, ko Po = 1.11 ± .09 g/mg; p < .05). These results are consistent with muscles lacking S100A1 having decreased charge moved during membrane depolarization, causing depressed SR Ca2+ release, and ultimately decreased force generation.

Characterization and applications of nanofiltration membranes: State of the art

There is a voluminous literature on the determination of structural and electrical properties of a nanofiltration (NF) membrane and its separation performance. Theories used to characterize a NF membrane usually include: the non-equilibrium thermodynamic model, the pore model, the TMS model, the electrostatic and steric-hindrance pore model, and the semi-emprical model. In the article, we briefly trace the origins or the general ideas of the above-mentioned theories. From there, recent researches on the evaluation of membrane structural and electrical properties are reviewed. We then turn to research on the separation performance of a NF membrane for single component solutions of inorganic electrolytes, neutral organic solutions, and mixture solution of inorganic electrolytes or that of electrolyte and neutral organic solute. Finally, we conclude with suggestions as to the role of models in the contributions to the application of the NF technology in product separation processes.

Numerical simulation of dielectric spectra of aqueous suspensions of non-spheroidal differently shaped biological cells

The effect of shape on the dielectric and conductometric spectra of aqueous suspensions of non-spheroidal biological cells has been investigated by means of numerical simulation methods. This work extends our previous investigation directed to biological cell systems where a superficial electric charge distribution is present on the outer interface of the cell membrane. This generalization results in a more composite dielectric spectra, where a low-frequency and a high-frequency contribution are expected. We consider different geometries, from ellipsoids, discoids, pear-shaped vesicles, cup-shaped vesicles to budded vesicles, which model a biological cell during different processes of biological relevance. The overview of the evolution of the dielectric spectra with the progressive change in the cell shape, maintaining constant the electrical properties of the different media involved and the fractional volume of the dispersed cells, offers a preliminary opportunity to separate contributions derived exclusively from the geometry to those due to the bulk and/or interface polarizations. These aspects are particularly relevant since dielectric spectroscopy of biological cell suspensions has proved its effectiveness in the characterization of the passive electrical properties of the cell membrane and also in controlled manipulations of biological systems.

A COMPARISON BETWEEN STEM CELLS FROM THE ADULT HUMAN BRAIN AND FROM BRAIN TUMORS

To directly compare stem cells from the normal adult human brain (adult human neural stem cells [AHNSC]), Grade II astrocytomas (AC II), and glioblastoma multiforme (GBM), with respect to proliferative and tumor-forming capacity and differentiation potential. Cells were isolated from tissue obtained during epilepsy surgery (AHNSCs) or tumor surgery (glioma stem cells [GSC]). They were cultured and investigated in vitro or after transplantation in immunodeficient mice. Under identical experimental conditions, the following were found: 1) GBM stem cells formed tumors after orthotopic transplantation; AHNSCs showed no sign of tumor formation; 2) GSCs showed a significantly higher growth rate and self-renewal capacity; 3) both the growth rate and telomerase expression were high in GSCs and correlated with malignancy grade (GBM higher than AC II); AHNSCs had low telomerase expression; 4) GSCs invaded normal neurospheres, not vice versa; 5) both AHNSCs and stem cells from AC II and GBM responded to differentiation cues with a dramatic decrease in the proliferation index (Ki-67); 6) GSCs differentiated faster than AHNSCs; 7) upon differentiation, AHNSCs produced normal glia and neurons; GSCs produced morphologically aberrant cells often expressing both glial and neuronal antigens; and 8) differentiation of AHNSCs resulted in 2 typical functional phenotypes: neurons (high electrical membrane resistance, ability to generate action potentials) and glial cells (low membrane resistance, no action potentials). In contrast, GSCs resulted in only 1 functional phenotype: cells with high electrical resistance and active membrane properties capable of generating action potentials. AHNSCs and stem cells from AC II and GBM differ with respect to proliferation, tumor-forming capacity, and rate and pattern of differentiation.

Sensitive and Simple Methodologies for Measuring of Red Blood Cell (RBC) Electrical Properties and Cell Aggregation.

The red blood cell membrane contains proteins and glycoproteins embedded in a fluid lipid bilayer that confers viscoelastic behaviour. Sialylated glycoproteins of the RBC membrane are responsible for a negatively charged surface, which creates a repulsive electric zeta potential (ζ) between the cells.The compact layer of charge or Stern consists of ions rigidly bonded to the cell and the double layer includes ions diffusely distributed around the cell. Measurement of RBC layer of charge and zeta potential can be use as a marker of RBC membrane injury. Study of membrane electrical properties and forces and bindings between cells, can provide a better comprehension of membrane injury presented in RBC unit storage, after RBC unit irradiation, cell senescence process and in addition, also to improve the sensitivity and specificity of the hemoagglutination reaction. The aim of this study was to measure the RBC double layer thickness of the charge (DLC) around the cell, zeta potential (ζ) and cell aggregation force, using optical tweezers.To measure DLC (d) and zeta potential (ζ) a special chamber was built consisting of 2 platinum electrodes separated by a channel. An external electrical field (E) was applied with a voltage power supply connected to the electrodes. The optical tweezers consisted of Nd:YAG laser beam focused through the 100x objective of a microscope equipped with a minicam, which registered the trapped cell image in real time. These images were recorded in VHS and captured in a computer where they could be analyzed using Image Pro Plus software. Optical tweezers utilizes the light momentum transfer to trap the silica beads with pico Newtons forces (10−12). Ten RBC units from healthy blood donors were collected in CPDA-1. Samples were diluted (1:1000μl) in AB plasma. Silica beads were added to a RBC solution (10μl). DLC thickness (d) was obtained measuring, in the special chamber, the force on the silica bead attached to a single RBC in response to an applied voltage (50–100V). Zeta potential (ζ) was obtained by measuring the RBC terminal velocity (Tv) after being released from the optical trap at a constant voltage applied supply (100V) Tv=(εE/η) ζ; ε= medium dielectric constant; η= viscosity). The DLC was calculated by the equation Fop= (Aεζ/d)E (Fop= optical force; A= RBC area). DLC median size (d) was 0,85 μm (min 0.4/max 1.3) and zeta potential was ζ=−12,5 mV (min- 9.3/max −15). These results were in accordance with the data in literature, where other methods to measure the same property were used.For measuring RBC aggregation, a silica bead attached to RBCs was trapped and the force needed to slide one RBC over the other, as a function of the velocities (2,5,7,12,18,32X10−7m/s) was determined. RBC O Rh(D) positive were diluted (1:1000μl) in plasma AB (control group) and in agglutination potentiator solutions, used in immunohematological tests (dextran 0.15%, low ionic strength solution-LISS, bromelain and papain enzymes). Aggregation was also analyzed using anti-D antibodies serum (5μl). The median aggregation force obtained of 20 RBC control samples was 1x10−3 (0.1–2.5) poise.cm. Samples analyzed with dextran 0.15%, LISS and bromelain lacking antibodies showed no agglutination. RBCs treated with papain enzyme presented high adherence preventing the capability of separating cells. The 20 samples analyzed with anti-D serum showed median aggregation force 2x10−3 (1.0–4.0) poise.cm. These results obtained from RBC with antibodies were statistically higher (p<0.001) when compared to control. The method revealed to be sensitive and results were in accord with serological tests used in transfusionroutine, where false positive results could be frequently found in RBC treated with papain, however rarely obtained with dextran and bromelain. In conclusion, the methodologies proposed are simple and may provide specific information on RBC interaction in addition to cell aggregation. Individual cell analyze methods are always more sensitive to small differences than those based on average values. This is the first time that the size of the double layer was measured using optical tweezers and the ability of the optical trap also allowed us to obtain the zeta potential and DLC thickness for the same RBC.

Modeling on electrokinetic phenomena of charged porous membrane

Studies on streaming potential (SP), an important electrokinetic phenomena, is chiefly within the scope of microfiltration (MF) and ultrafiltration (UF) membrane processes based on the Helmholtz-Smoluchowski (HS) equation. However, the HS equation has some limitations, which is an adequate cause of the less study of SP for nanofiltration (NF) membranes. In this paper, experiments of SP for two commercial NF membranes (NTR7250 and ESNA 1-K) have been carried in four electrolytes (KCl, MgCl 2, Na 2SO 4 and MgSO 4) solutions. We proposed a new modified HS equation to analyze the experimental data and predict the electrical properties of NF membranes. Results show that the modified HS equation is more applicable than the classical HS equation in the evaluation of surface electrical properties of NF membranes. The established strategy to evaluate the SP of two typical NF membranes in the paper has important significance for other membranes processes.