Application Of Electric Field Pulses Research Articles

Molecular dynamics investigation of soliton propagation in a two‐dimensional Yukawa liquid

AbstractWe investigate via molecular dynamics simulations the propagation of solitons in a two‐dimensional many‐body system characterized by Yukawa interaction potential. The solitons are created in an equilibrated system by the application of electric field pulses. Such pulses generate pairs of solitons, which are characterized by a positive and negative density peak, respectively, and which propagate into opposite directions. At small perturbation, the features propagate with the longitudinal sound speed, from which an increasing deviation is found at higher density perturbations. An external magnetic field is found to block the propagation of the solitons, which can, however, be released upon the termination of the magnetic field and can propagate further into directions that depend on the time of trapping and the magnetic field strength.

DC Stark addressing for quantum memory in Tm:YAG

We observed a linear DC Stark effect for 3 H 6 – 3 H 4 optical transition of Tm 3+ ions in Y 3 Al 5 O 12 . We observed that application of electric field pulse suppresses the two-pulse photon echo signal. If we then apply a second electric pulse of opposite polarity the echo signal is restored again, which indicates the linear nature of the observed effect. The effect is present despite the D 2 symmetry of the Tm 3+ sites that prohibits a linear Stark effect. Experimental data analysis shows that the observed electric field influence can be attributed to defects that break the local crystal field symmetry near Tm 3+ ions. Using this effect we demonstrate selective retrieval of light pulses in two-pulse photon echo.

Lateral electric-field-driven non-volatile four-state memory in multiferroic heterostructures

A non-volatile four-state memory is formed using an in-plane side-polarization configuration in a Co/(011) Pb(Mg1/3Nb2/3)O3-PbTiO3 (Co/PMN-PT) heterostructure. The resistivity vs. electric field behavior shows a change from volatile butterfly to looplike to non-volatile butterfly characteristics when the temperature decreases from 290 K to 83 K under an electric field of 10 kV/cm and then increases back to 290 K; this behavior is attributed to the strain-mediated magnetoelectric effect. In addition, the in-plane resistivity of Co film, which was measured using the four-probe technique, can be controlled both electrically and magnetically. Specifically, a non-volatile resistivity is gained by the application of electric field pulses. Additionally, a four-state memory is obtained by co-mediation of the magnetic field and electric field pulses, compared with the two different states achieved under the application of the electric field only, which indicates that our results are highly important for multi-state memory and spintronic devices applications.

Cell electrotransfection and viability dependence on electrotransfection and viability dependence on electoporation medium

Electroporation is a physical method that uses electric fields to increase membrane permeability. The method is widely used for intracellular drug and gene delivery. In this study we aimed to investigate the importance of the medium for efficiency of cell electrotransfection and viability following the application of electric field pulses. The experiments were performed using 2 different cell lines: Chinese hamster ovary (CHO) and Chinese hamster lung fibroblast (DC-3F) and 2 different electroporation media: SMEM (medium conductivity equal to 1.3 S/m) and laboratory-made low-conductivity (0.1 S/m) electroporation (EP) medium. Cells suspended in these media were supplemented with plasmid (10 µg/ml) encoding luciferase and then were treated with 1, 5, or 10 high-voltage (1200 V/cm, 100 µs, at 1 Hz) pulses. Transfection efficiency was determined by luciferase activity 24 h after cell treatment, while cell viability was determined by clonogenic assay. Results showed significant differences between cell lines and used electroporation media. CHO transfection was higher when electroporation was performed in low conductivity EP medium. Low transfection efficiency in SMEM medium resulted from low viability. In contrast, transfection efficiency of DC-3F cells was higher in SMEM. Possible mechanisms governing these differences are discussed.

How medium osmolarity influences dielectrophoretically assisted on-chip electrofusion

Cells submitted to an electric field gradient experience dielectrophoresis. Such a force is useful for pairing cells prior to electrofusion. The latter event is induced by the application of electric field pulses leading to membrane fusion while cells are in physical contact. Nevertheless, the efficiency of dielectrophoretic pairing and electrofusion of cells are highly dependent on medium properties (osmolarity and conductivity). In this paper, we examine the effect of medium osmolarity on volume, viability and electrical properties of cells. Then we characterize in real time the impact of electropermeabilization of cells on their dielectrophoretic response. To do so, a microfluidic device, inducing particular field topologies is used. These real time observations are correlated to numerical analysis of the Clausius–Mossotti factor. Taking into account the identified changes, an electrofusion protocol adequate to the optimal medium (100mOsm, 0.03S/m) is defined. Up to 75% simultaneous binuclear rapid electrofusions were achieved and monitored with average membrane fusion duration lower than 12s.

Study of the transmembrane potential distribution of cell pairs in a microfluidic device using polymer obstacles to initiate electrofusion

In this paper, we investigate the different parameters that affect the distribution of the transmembrane potential of cells brought into contact before electrofusion in a miniaturized fluidic device. In particular, we discuss the deviation of the effective transmembrane voltage compared to the one predicted by Schwan’s law. The application of electric field pulses to biological cells induces a transmembrane potential which leads to cell permeabilization. Electrofusion occurs when several cells are brought into contact while they are electropermeabilized. Nevertheless, we show that in this case, the mutual presence of cells interferes on Schwan’s equation. Consequently, the transmembrane voltage at the cell contacting point is drastically reduced, which is not favorable for an electrofusion in smooth conditions, as the applied voltage needs to be increased to compensate this phenomenon. We show that the introduction of polymer obstacles reverses this trend, as the high electric field region is focused on the fusion zone. To confirm the theory we developed, quantitative biological experiments are presented in which murine melanoma cells were paired and fused in both conditions (with and without obstacles).

Differential Cellular Effects of Electroporation and Electrochemotherapy in Monolayers of Human Microvascular Endothelial Cells

In vivo electroporation of tumours shows disruption of blood flow and creates a vascular effect with an initial rapid and transient vasoconstriction phase and a much longer lasting phase with changed microvascular endothelium. These changes are not well understood but are presumed to involve the cytoskeleton. The paper presents for the first time differential in vitro effects describing cytoskeleton changes and monolayer integrity changes by both electroporation and electrochemotherapy of monolayers of human microvascular endothelial cells (HMEC-1). After the application of electric field pulses, the morphology of cells, and both the F-actin and Beta-tubulin cytoskeleton proteins were affected. During both electroporation and electrochemotherapy, the initial phase of cellular damage was noticed at 10 min as swollen cells and honeycomb-like actin bundles. The electroporation-induced cellular effects, observed from electric pulses >150 V, were voltage-dependent and within 24 hrs partly recoverable. The electrochemotherapy-induced cellular effects developed at 2 hrs in spindle-like cells, and more densely packed F-actin and Beta-tubulin were observed, which were dependent on the amount of bleomycin and the voltages applied (>50 V). In addition, for electrochemotherapy with electric pulses >150 V cellular changes were not recoverable within 24 hrs. The effects on monolayer integrity were reflected in the enhanced monolayer permeability, with the electrochemotherapy showing an earlier onset and synergy. We conclude that electrochemotherapy as compared to electroporation leads within 24 hrs to a quicker and more pronounced monolayer integrity damage and endothelial cell death, which together provide further insight into the cellular changes of the vascular disruption of electrochemotherapy.

The Actin Cytoskeleton Has an Active Role in the Electrotransfer of Plasmid DNA in Mammalian Cells

Electrotransfer of molecules is a well established technique which finds extensive use for gene transfer and holds great promise for anticancer treatment. Despite its widespread application, the mechanisms governing the entry of DNA into the cell and its intracellular trafficking are not yet known. The aim of this study is to unravel the role of the actin cytoskeleton during gene electrotransfer in cells. We performed single-cell level approaches to observe the organization of the actin cytoskeleton in Chinese hamster ovary (CHO) cells. In addition, we performed experiments at the multiple-cell level to evaluate the efficiency of DNA transfer after alteration of the actin cytoskeleton using the drug latrunculin B. Actin patches colocalizing with the DNA at the plasma membrane were observed with additional characteristics similar to those of the DNA aggregates in terms of time, number, and size. The disruption of the microfilaments reduces the DNA accumulation at the plasma membrane and the gene expression. This is the first direct experimental evidence of the participation of the actin cytoskeleton in DNA electrotransfer.

In vivo non-thermal irreversible electroporation impact on rat liver galvanic apparent internal resistance

Non-thermal irreversible electroporation (NTIRE) is a biophysical phenomenon which involves application of electric field pulses to cells or tissues, causing certain rearrangements in the membrane structure leading to cell death. The treated tissue ac impedance changes induced by electroporation were shown to be the indicators for NTIRE efficiency. In a previous study we characterized in vitro tissue galvanic apparent internal resistance (GAIR) changes due to NTIRE. Here we describe an in vivo study in which we monitored the GAIR changes of a rat liver treated by NTIRE. Electrical pulses were delivered through the same Zn/Cu electrodes by which GAIR was measured. GAIR was measured before and for 3 h after the treatment at 15 min intervals. The results were compared to the established ac bioimpedance measurement method. A decrease of 33% was measured immediately after the NTIRE treatment and a 40% decrease was measured after 3 h in GAIR values; in the same time 40% and 47% decrease respectively were measured by ac bioimpedance analyses. The temperature increase due to the NTIRE was only 0.5 °C. The results open the way for an inexpensive, self-powered in vivo real-time NTIRE effectiveness measurement.

Mechanism of the effect of the electric field of a surface acoustic wave on the low-temperature photoluminescence kinetics in type-II GaAs/AlAs superlattices

Kinetics of the low-temperature photoluminescence (PL) of type-II GaAs/AlAs superlattices under the effect of the electric field of a surface acoustic wave is studied experimentally. It is found that application of electric-field pulses results in speeding up the PL kinetics of free and localized excitons and phonon replicas irrespective of the pulse duration. Analysis of the experimental data demonstrates that acceleration of the PL kinetics is related to the transport of excitons towards nonradiative recombination centers; this transport is promoted by the interaction of excitons with hot free charge carriers ejected from localized states.

Nonlinear current–voltage relationship of the plasma membrane of single CHO cells

The application of electric field pulses to Chinese Hamster Ovary (CHO) cells causes membrane electroporation (MEP). If a voltage or current ramp is applied to the cellular membrane of a single CHO cell, the membrane conductance increases nonlinearly with field strength reaching saturation. In particular, the kinetics of the induced conductance changes represents the data basis for the interpretation in terms of underlying structural changes. The current/voltage characteristic is found to be continuous, but displays occasionally a sharp increase in the conductance. The step-like increases are interpreted to reflect the formation of one (or more) larger pore(s). The analysis of current clamp data yields pores of radius ( r p) in the range of 2.5 ≤ r p/nm ≤ 20; the pores of the voltage clamp data are in the range of 2.5 ≤ r p/nm ≤ 55. The larger pores occur predominantly during hyperpolarising and less frequently during depolarising conditions, respectively. The different kinetics of pore formation in the hyperpolarising condition, where the inward field increases, and the depolarising condition, where the inward field first decreases and then increases in the opposite direction, suggests structural asymmetry with respect to the direction of the electric membrane field. At the required higher voltage, the effect of the resting potential is negligibly small.

Changes of the solution pH due to exposure by high-voltage electric pulses

The change of the pH of a NaCl solution (139–149 mM NaCl) buffered with 5–15 mM sodium phosphates (pH 7.4) during electromanipulation was studied. It has been determined that an increase in the pH value of electroporation solution of a whole chamber volume, caused by the application of electric field pulses, commonly used in cell electromanipulation procedures, can exceed 1–2 pH units. Several materials for the cathode were tested. In all cases a stainless steel anode was utilized. The aluminum cathode gave a two-fold greater ΔpH in comparison with platinum, copper or stainless steel cathodes. In addition, a substantial release of aluminum (up to 1 mg/l) from the cathode was observed. It has also been found that the shift in pH depended on the medium conductivity: ΔpH of the solution, in which sucrose was substituted for NaCl, was about 5 times less. On the basis of the results obtained here, to avoid the plausible undesirable consequences of the cathodic electrolysis processes, in particular under the conditions of strong electric treatment, it could be recommended that chambers with aluminum electrodes not be utilized and one should use strongly buffered solutions of low conductivity and alternating current (sine or square wave) bipolar electric pulses.

Early stage shape change of human erythrocytes after application of electric field pulses

Click to increase image sizeClick to decrease image sizeErythrocyte Membrane Erythrocyte Shape Electric Field Pulse Aminophospholipid Distribution Flip-FLOP Process

Early stage shape change of human erythrocytes after application of electric field pulses.

Erythrocytes which receive electric field pulses are subject to poration, fusion and shape changes due to electrodynamic forces, aminophospholipid perturbation and influences on the normal flip-flop process. The shape change characteristics of cells suspended in different media were analysed after application of rectangular electric field pulses from t=11-44 micros and from E=4-8 kV/cm. Albumin is shown to decelerate the echinocyte shape change within the first few seconds after pulse application. The addition of fluoride and vanadate accelerates the shape change due to their inhibiting influence on the aminophospholipid translocase. For both the duration of the field pulse and its field strength, there exist lower threshold values under which no early stage shape change is observable. The activation energy calculated from the dissipative influence of the electric field alone is smaller than expected, indicating the electrodynamic influence on the flip-flop process. Cell shapes were additionally analysed by contour tracing to focus on the echinocyte spicule distribution after pulse application. This image analysis revealed that, with an increase of both pulse duration and field strength, the shape change velocity and the shape change intensity increase.

Electrophysiological model of intact and processed plant tissues: cell disintegration criteria.

Frequency versus conductivity relationships of food cell system, based on impedance measurements as characterized by polarization effects of the Maxwell-Wagner type at intact membrane interfaces, are presented. The electrical properties of a biological membrane (represented as a resistor and capacitor) are responsible for the dependence of the total conductivity of the cell system on the alternating current frequency. Based on an equivalent circuit model of a single plant cell, the electrical conductivity spectrum of the cell system in intact plant tissue (potato, carrot, banana, and apple) was determined in a frequency range between 3 kHz and 50 MHz. The electrical properties of a cell system with different ratios of intact/ruptured cells could also be predicted on the basis of a description of a cell system consisting of elementary layers with regularly distributed intact and ruptured cells as well as of extracellular compartments. This simple determination of the degree of cell permeabilization (cell disintegration index, p(o)) is based upon electric conductivity changes in the cell sample. For accurate calculations of p(o), the sample conductivities before and after treatment, obtained at low- (f(l)) and high-frequency (f(h)) ranges of the so-called beta-dispersion, were used. In this study with plant cell systems, characteristic conductivities used were measured at frequencies f(l) = 3 kHz and f(h) = 12.5 MHz. The disintegration index was used to analyze the degree of cell disruption after different treatments (such as mechanical disruption, heating, freeze-thaw cycles, application of electric field pulses, and enzymatic treatment) of the plant tissues.

Calcium Waves Induced by Large Voltage Pulses in Fish Keratocytes

Intracellular calcium waves in fish keratocytes are induced by the application of electric field pulses with amplitudes between 55 and 120 V/cm and full width at half-maximum of 65–100 ms. Calcium concentrations were imaged using two-photon excited fluorescence microscopy (Denk et al., 1990. Science. 248:73–76; Williams et al., 1994. FASEB J. 8:804–813) and the ratiometric calcium indicator indo-1. The applied electric field pulses induced waves with fast calcium rise times and slow decays, which nucleated in the lamellipodium at the hyperpolarized side of the cells and, less frequently, at the depolarized side. The effectiveness of wave generation was determined by the change induced in the membrane potential, which is about half the field strength times the cell width in the direction of the field. Stimulation of waves began at voltage drops across the cell above 150 mV and saturated at voltage drops above 300 mV, where almost all cells exhibited a wave. Waves were not induced in low-calcium media and were blocked by the nonselective calcium channel blockers cobalt chloride and verapamil, but not by specific organic antagonists of voltage-sensitive calcium channel conductance. Thapsigargin stopped wave propagation in the cell body, indicating that calcium release from intracellular stores is necessary. Thus a voltage pulse stimulates Ca 2+ influx through calcium channels in the plasma membrane, and if the intracellular calcium concentration reaches a threshold, release from intracellular stores is induced, creating a propagating wave. These observations and the measured parameters (average velocity ∼66 μm/s and average rise time ∼68 ms) are consistent with a wave amplification model in which {formula not available us MathML} determines the effective diffusivity of the propagating molecules, D ≈ 300 μm 2/s (Meyer, 1991. Cell. 64:675–678).

Analysis of chemical and physical relaxation processes of polyelectrolytes by electric field pulse methods: A comparison of critical comments with facts

AbstractAccording to some statements in the literature, it is very hard or virtually impossible to get meaningful relaxation data for macromolecular systems by methods involving electric field pulses (electric field jump and Joule temperature jump), mainly because of perturbations resulting from field induced orientation effects. These statements have been presented until recently, in spite of the fact that the magic angle technique for suppression of such effects has been described in the literature quite some time ago. Apparently there is not sufficient knowledge on the existence/validity/practicability of this technique. More than 20 years experience with magic angle detection is summarized, including a recent detailed comparison of magic angle fluorescence T‐jump data with corresponding stopped flow data for the case of ethidium intercalation into DNA double helices. The results demonstrate that chemical relaxation induced by application of electric field pulses to macromolecular solutions can be measured without perturbations, provided that appropriate procedures are used. Moreover, techniques using electric field pulses proved to be the only practicable approach to analysis of many macromolecular reactions.It is not always necessary to suppress orientation effects; on the contrary, orientation effects can be very useful to follow reactions which cannot be detected by other procedures. A special case is demonstrated where reaction and orientation effects appear as a convolution product.

Relaxation of CDW polarization of various initial states

We have investigated the decay of the polarization induced by the application of electric field pulses of various lengths. Most experiments were carried out in K 0.3 MoO 3 around 60 K. In this case the characteristic time of the stretched exponential relaxation between two equilibrium states is a few ms. The pulse length was varied between 5 μs<Δt<10 ms, and the resulting weak relaxation was detected over 7 decades in time. Our results resemble to the «aging effect» found in the low temperature thermal relaxation experiments, but we argue that both phenomena can be well described in the framework of a simple linear response theory

Analysis of the photoelastic effect in ionic crystals

Cells submitted to an electric field gradient experience dielectrophoresis. Such a force is useful for pairing cells prior to electrofusion. The latter event is induced by the application of electric field pulses leading to membrane fusion while cells are in physical contact. Nevertheless, the efficiency of dielectrophoretic pairing and electrofusion of cells are highly dependent on medium properties (osmolarity and conductivity). In this paper, we examine the effect of medium osmolarity on volume, viability and electrical properties of cells. Then we characterize in real time the impact of electropermeabilization of cells on their dielectrophoretic response. To do so, a microfluidic device, inducing particular field topologies is used. These real time observations are correlated to numerical analysis of the Clausius–Mossotti factor. Taking into account the identified changes, an electrofusion protocol adequate to the optimal medium (100 mOsm, 0.03 S/m) is defined. Up to 75% simultaneous binuclear rapid electrofusions were achieved and monitored with average membrane fusion duration lower than 12 s.

Electrical Measurements on Photographic Emulsion Grains. I. Dark Conductivity

By exposing with light flashes delayed by short time intervals after the application of electric field pulses, it is possible to measure ionic conduction on large silver bromide grains from a photographic emulsion. Values of conductivity were obtained by an analysis of the transient decay of internal field pulses resulting from the application of known pulses of the external field. The internal field was measured by means of its effect in causing displacement of latent-image centers formed by the exposure flashes. The room-temperature ionic conductance of these grains was found to be the equivalent of about 9×10−6Ω−1 cm−1 with an activation energy of about 0.42 ev. This conductance is several powers of ten higher than that reported for large silver bromide crystals of high purity and is thought to be primarily the result of surface effects. The implications of this result in terms of modern theories of photographic latent-image formation are discussed.