kHz Electric Field Research Articles

Stimulus effects of extremely low-frequency electric field exposure on calcium oscillations in a human cortical spheroid.

High-intensity, low-frequency (1 Hz to 100 kHz) electric and magnetic fields (EF and MF) cause electrical excitation of the nervous system via an induced EF (iEF) in living tissue. However, the biological properties and thresholds of stimulus effects on synchronized activity in a three-dimensional (3D) neuronal network remain uncertain. In this study, we evaluated changes in neuronal network activity during extremely low-frequency EF (ELF-EF) exposure by measuring intracellular calcium ([Ca2+]i) oscillations, which reflect neuronal network activity. For ELF-EF exposure experiments, we used a human cortical spheroid (hCS), a 3D-cultured neuronal network generated from human induced pluripotent stem cell (hiPSC)-derived cortical neurons. A 50 Hz sinusoidal ELF-EF exposure modulated [Ca2+]i oscillations with dependencies on exposure intensity and duration. Based on the experimental setup and results, the iEF distribution inside the hCS was estimated using high-resolution numerical dosimetry. The numerical estimation revealed threshold values ranging between 255-510 V/m (peak) and 131-261 V/m (average). This indicates that thresholds of neuronal excitation in the hCS were equivalent to those of a thin nerve fiber.

Alternating electric fields transform the intricate network of tumour vasculature into orderly parallel capillaries and enhance the anti-angiogenesis effect of bevacizumab.

The search for effective strategies to target tumour angiogenesis remains a critical goal of cancer research. We present a pioneering approach using alternating electric fields to inhibit tumour angiogenesis and enhance the therapeutic efficacy of bevacizumab. Chicken chorioallantoic membrane, cell viability and in vitro endothelial tube formation assays revealed that electric fields with a frequency of 1000 kHz and an electric intensity of 0.6 V/cm inhibited the growth of vascular endothelial cells and suppressed tumour-induced angiogenesis. In an animal U87MG glioma model, 1000 kHz electric fields inhibited tumour angiogenesis and suppressed tumour growth. As demonstrated by 3D vessel analysis, tumour vasculature in the control group was a stout, interwoven network. However, electric fields transformed it into slim, parallel capillaries that were strictly perpendicular to the electric field direction. This architectural transformation was accompanied by apoptosis of vascular endothelial cells and a notable reduction in tumour vessel number. Additionally, we found that the anti-angiogenesis and tumour-suppression effects of electric fields synergised with bevacizumab. The anti-angiogenic mechanisms of electric fields include disrupting spindle formation during endothelial cell division and downregulating environmental angiogenesis-related cytokines, such as interleukin-6, CXCL-1, 2, 3, 5 and 8, and matrix metalloproteinases. In summary, our findings demonstrate the potential of alternating electric fields (AEFs) as a therapeutic modality to impede angiogenesis and restrain cancer growth.

Liquid Piezoelectric Materials: Linear Electromechanical Effect in Fluid Ferroelectric Nematic Liquid Crystals

AbstractThe first demonstration of converse piezoelectricity in 3D fluids is presented by measuring a linear electromechanical effect in ferroelectric nematic liquid crystals. The observed piezoelectric coupling constant below 6 kHz electric field is larger than 1 nC/N, comparable to, or better than, values for the strongest solid piezoelectric materials. Symmetry considerations indicate that the alignment of the ferroelectric nematic liquid crystal in the experimental study is not optimized, so the observed signal is likely only a fraction of the theoretically achievable signal. Understanding the electromechanical response of ferroelectric nematics will enable mechanical energy harvesting and open up a new avenue for developing fluid actuators, micro positioners, and electrically tunable optical lenses.

Characterization of interactive force acting on colloidal particles near an electrode in presence of a high-frequency (>10 kHz) AC electric field using particle diffusometry

Colloidal particles like polystyrene beads and metallic micro and nanoparticles are known to assemble in crystal-like structures near an electrode surface under both DC and AC electric fields. Various studies have shown that this self-assembly is governed by a balance between an attractive electrohydrodynamic (EHD) force and an induced dipole-dipole repulsion (Trau et al., 1997). The EHD force originates from electrolyte flow caused by interaction between the electric field and the polarized double layers of both the particles and the electrode surface. The particles are found to either aggregate or repel from each other on application of electric field depending on the mobility of the ions in the electrolyte (Woehl et al., 2014). The particle motion in the electrode plane is studied well under various conditions however, not as many references are available in the literature that discuss the effects of the AC electric field on their out-of-plane motion, especially at high frequencies (>10 kHz). Haughey and Earnshaw (1998), and Fagan et al. (2005) have studied the particle motion perpendicular to the electrode plane and their average height from the electrode mostly in presence of DC or low frequency AC (<1 kHz) electric field. However, these studies do not provide enough insight towards the effects of high frequency (>10 kHz) electric field on the particles’ motion perpendicular to the electrode plane.

Non-contact thin-film sheet conductance measurement based on the attenuation of low frequency electric potentials

Conductivity is a fundamental property of materials; in particular the precise quantification of electrical sheet resistance is essential for the development of electronic thin-film devices. Conventionally, resistive probes are used to perform the corresponding measurements. However, non-invasive methods are more desirable as they minimize the required sample preparation, as well as geometrical influences. Existing non-contact conductivity measurements mostly rely on the transmission of electromagnetic waves through conductive thin-films. Hence, they only characterize translucent samples at high frequencies. We present an alternative technique based on the attenuation of low frequency 10 kHz electric fields. The approach is used to quantify the field-effect induced conductivity variation of a flexible indium-gallium-zinc-oxide semiconductor film. A custom-built high-impedance electrometer is used to capacitively measure the attenuation of an alternating electric field passing through the film. The obtained data is discussed and related to the absolute conductivity with the aid of two bespoke models describing the impedance mismatch between the sample and its surroundings. The sheet conductivity is modulated and measured from 660 nS to 116 µS while conventional DC current/voltage measurements serve as a reference. Both methods show a high degree of correlation to the reference measurements. Unlike techniques based on light, the low frequency signal used here resembles quasi-static characteristics, and enables the direct measurement of DC parameters.

A Correlation Between Electric Fields That Target the Cell Membrane Potential and Dividing HeLa Cancer Cell Growth Inhibition.

Clinical studies show that low intensity (single V/cm), intermediate-frequency (100kHz-300kHz) electric fields inhibit the growth of cancer cells, while the mechanism is not yet understood. We examine the hypothesis that electric fields modify the cell membrane potential of dividing cancer cells in a way that correlates with cells growth inhibition. A Schwan based mathematical model calculates the changes in HeLa cells membrane potential due to single V/cm electric fields and frequencies from 0.1 to 1MHz. An experimental study examines the effect of these electric fields on the inhibition of HeLa cells growth in an incubator. The theoretical calculation shows that the effects of these electric fields on cell membrane potential decrease with an increase in frequency. The HeLa cells experiments verified the inhibitory effect of these fields on cell growth. The inhibitory effect is decreasing with an increase in frequency, in a way that is similar to the frequency dependent effect of these fields on the cell membrane potential. The superposition of the theoretical results and the experimental results suggest a correlation between the effect of these fields on the cell membrane potential and inhibition of cancer cell growth. It should be emphasized that correlations do not prove causality, however, they suggest an area for future research. These findings have value for the understanding of the mechanisms of cancer cells growth inhibition with electric fields and suggest an interesting area of research on the interaction between electromagnetic fields and cancer cells.

Temporal interference stimulation targets deep brain regions by modulating neural oscillations

BackgroundTemporal interference (TI) stimulation of the brain generates amplitude-modulated electric fields oscillating in the kHz range with the goal of non-invasive targeted deep brain stimulation. Yet, the current intensities required in human (sensitivity) to modulate deep brain activity and if superficial brain region are spared (selectivity) at these intensities remains unclear. ObjectiveWe developed an experimentally constrained theory for TI sensitivity to kHz electric field given the attenuation by membrane low-pass filtering property, and for TI selectivity to deep structures given the distribution of modulated and unmodulated electric fields in brain. MethodsThe electric field threshold to modulate carbachol-induced gamma oscillations in rat hippocampal slices was determined for unmodulated 0.05–2 kHz sine waveforms, and 5 Hz amplitude-modulated waveforms with 0.1–2 kHz carrier frequencies. The neuronal effects are replicated with a computational network model to explore the underlying mechanisms, and then coupled to a validated current-flow model of the human head. ResultsAmplitude-modulated electric fields are stronger in deep brain regions, while unmodulated electric fields are maximal at the cortical regions. Both experiment and model confirmed the hypothesis that spatial selectivity of temporal interference stimulation depends on the phasic modulation of neural oscillations only in deep brain regions. Adaptation mechanism (e.g. GABAb) enhanced sensitivity to amplitude modulated waveform in contrast to unmodulated kHz and produced selectivity in modulating gamma oscillation (i.e. Higher gamma modulation in amplitude modulated vs unmodulated kHz stimulation). Selection of carrier frequency strongly affected sensitivity to amplitude modulation stimulation. Amplitude modulated stimulation with 100 Hz carrier frequency required ∼5 V/m (corresponding to ∼13 mA at the scalp surface), whereas, 1 kHz carrier frequency ∼60 V/m (∼160 mA) and 2 kHz carrier frequency ∼80 V/m (∼220 mA) to significantly modulate gamma oscillation. Sensitivity is increased (scalp current required decreased) for theoretical neuronal membranes with faster time constants. ConclusionThe TI sensitivity (current required at the scalp) depends on the neuronal membrane time-constant (e.g. axons) approaching the kHz carrier frequency. TI selectivity is governed by network adaption (e.g. GABAb) that is faster than the amplitude-modulation frequency. Thus, we show neuronal and network oscillations time-constants determine the scalp current required and the selectivity achievable with TI in humans.

Dielectric properties of healthy and diabetic alloxan-induced lenses in rabbits

The dielectric properties of the eye lens were studied for healthy and alloxane-induced diabetic rabbits in the frequency range from 500 Hz to 100 kHz electric field and temperatures from 25 to 50 °C. In the full temperature range, the average relative permittivity and dielectric loss values for a healthy lens are lower than those recorded for diabetic tissue. Dielectric relaxation of polar amino acids on the alpha-crystallin surface with a characteristic frequency of 7 kHz in the range of 25–50 °C for healthy and diabetic samples is accompanied by the activation energy of proton conductivity with an average values of 33 and 39 kJ mol−1, respectively. The permittivity decrement, which characterizes the size of the dielectric dispersion with a central relaxation time of 0.023 ms for a diabetic sample, is more than twice as high as for a healthy sample. Measurements on the rabbit eye lens were carried out at ambient temperature above and below the physiological range, since these conditions provide an appropriate pattern of dielectric behavior for the diagnosis of clinical dysfunction of the human lens.

Magnetoelectric coupling in multiferroic Z-type hexaferrite revealed by electric-field-modulated magnetic resonance studies

Temperature dependence of ferromagnetic resonance (FMR) frequency fFMR was revealed in Z-type hexaferrite (BaxSr1−x)3Co2Fe24O41 using microwave spectroscopy in zero external magnetic field. A linear decrease in fFMR toward magnetic phase transition temperature Tc2 = 500 K was observed, implicating magnetic anisotropy decrease. Ferromagnetic resonance studies performed near 9 GHz with the magnetic field up to 10 kOe also confirmed FMR anomaly near 500 K, where the magnetic structure changes from conical to collinear. FMR spectra are tunable by external dc and ac (100 kHz) electric fields which allowed us to determine the value of magnetoelectric coefficient αE = 390 ps/m at 170 K. αE is at about 0.5 kOe one order of magnitude lower than the reported value at 10 K, because in our case the electric field was applied along c-axis, while the previously reported value was obtained with the field in hexagonal plane. Nevertheless, our αE is still one or even four orders of magnitude higher than in other “high-temperature” multiferroics.

Generation of micron-sized droplet streams by high frequency electric fields

Generation and transfer of micron-sized droplets are of significant interest for several applications such as electronics cooling, lab-on-chip, microscale printing, etc. We report generation of microscale droplet streams when a larger droplet is exposed to high frequency (>10 kHz) electric fields using dielectric covered coplanar electrodes. Generation of these droplet streams is found to be a function of the actuation frequency and voltage. Our experiments rule out electrospray as the relevant mechanism. Experiments further reveal that the droplet streams are formed due to (1) Evaporation of the larger droplet due to Joule heating; and (2) Enhanced localized condensation on nucleation sites originating from the leakage currents at high electric fields. The condensed droplets are dragged along with the convection current of the larger droplet, leading to the observation of streams. A computational model is used to solve for the convection velocities which is compared with the experimental high-speed videos. The stream velocity is found to increase with the applied field, which is attributed to the smaller size of the condensed droplet at higher electric fields. Capability to generate microscale droplets and transfer them to other substrates is desired in current microfluidic platforms for various applications. This study reports a viable technique and presents critical information for its design.

Abstract 3209: Numerical modeling of intracellular mechanisms in tumor-treating fields

Abstract Tumor Treating Fields (TTFields) are 100-500 kHz electric fields with intensities of about 1-4 V/cm. They are known to exert an antimitotic effect on cancer cells, most likely by exerting forces on highly polar tubulin dimers, thereby disrupting spindle formation. Calculations show that TTFields-tubulin interaction energy is negligible compared to the thermal energy in the cell (1). Therefore, this interaction is unlikely to disrupt cellular function. Conductivity of polymerized tubulin, microtubules (MTs), was measured to be 20 S/m, which is 400 times higher than that of the ambient cytosol (0.05 S/m) (2). Thus when TTFields penetrate the cytosol, they may induce electric currents along MTs that are strong enough to disrupt key cellular functions. In particular, if the power (energy per unit time) deposited by these currents is on par with that the power consumed by the molecular motor kinesin, then TTFields may disrupt the forces needed for cell division, thereby disrupting mitosis. To test this hypothesis, we performed numerical simulations evaluating the magnitude of the electric current along MTs exposed to TTFields at 200 kHz. Based on studies of MTs and their microenvironment, we model the MT as a layered cylindrical structure (1): Innermost is the lumen (15 nm in thickness), surrounded by 13 strands of alpha-beta tubulin dimers linked in a helix (4.5 nm). C-termini extend out from the helix with a thickness of 3.5 nm. MTs carry net negative charge; thus they are surrounded by a counter-ion layer (2 nm), and an outer nonconductive Bjerrum layer (3 nm). We built a finite element model in COMSOL Multiphysics (tm) incorporating these layers and examined the current density induced in each layer by TTFields for MTs varying in length from 1-10 µm within an ambient 200 kHz AC electric field of 1-4 V/cm. Our model shows that MTs act as electrical "shunts" that conduct electric current within them. The highest current flows through the counter-ion layer surrounding the C-termini. The current density in this layer exceeds the level likely to disrupt the motor protein kinesin "walk" along the C-termini. The current density is highest when both the field and the MTs are aligned with the cell axis, in accord with in vitro experiments (3). Our model is consistent with the hypothesis that when cells are exposed to TTFields, MTs act as cables carrying high-density electric currents strong enough to disrupt the function of molecular motors, ultimately disrupting mitosis.

Effect of crystalline phase on the dielectric and energy storage properties of poly(vinylidene fluoride)

The crystal structure shows great influence on dielectric and energy storage performance of poly(vinylidene fluoride) (PVDF) films. In this paper, a γ-phase PVDF film was fabricated by crystallization of PVDF from a DMF solution through a solution-casting method and a quenching treatment. The influences of crystalline phases on the dielectric and energy storage properties of the films were studied. It has been found that, compared with common α- and β-phase, the obtained γ-phase PVDF film presents much higher relative permittivity of about 9.8 in a 1 kHz electric field. The ferroelectric hysteresis loop investigation indicates that the γ-phase PVDF film exhibits much slimmer polarization–electric field hysteresis loops than α- and β-phase PVDF films and a high energy efficiency more than 72 % is obtained. This γ-phase PVDF film also shows low leakage current at high working voltage, which is more desirable and promising for high performance pulse discharge capacitor application.

Polarization behavior of polystyrene particles under direct current and low‐frequency (<1 kHz) electric fields in dielectrophoretic systems

Electrophoresis 2016, 37, 635–644. DOI: 10.1002/elps.201500338 The relative polarization behavior of micron and sub-micron polystyrene particles was investigated under direct current (DC) and low frequency (<1 kHz) alternating current (AC) electric fields. Relative polarization of particles with respect to the suspending medium is expressed in terms of the Clausius-Mossotti factor, a parameter of crucial importance in dielectrophoretic-based operations. Experiments and mathematical modeling were performed with insulator-based dielectrophoresis (iDEP) devices with cylindrical posts made from polydimethylsiloxane. The results illustrated that particle polarizability and dielectrophoretic response depend greatly on particle size. Small particles (diameter < 500 nm) tend to exhibit positive DEP at the higher frequencies (200–1000 Hz) as illustrated by particles clustering at the constriction between the insulating posts (left image). Large particles (diameter > 500 nm) exhibit negative DEP at lower frequencies (20–200 Hz) as illustrated by particle depletion at the constrictions between the posts (right image). These differences in relative polarization responses can be exploited for the design of iDEP-based separations and analysis of particle mixtures.

Polarization behavior of polystyrene particles under direct current and low-frequency (

The relative polarization behavior of micron and submicron polystyrene particles was investigated under direct current and very low frequency (<1 kHz) alternating current electric fields. Relative polarization of particles with respect to the suspending medium is expressed in terms of the Clausius-Mossotti factor, a parameter of crucial importance in dielectrophoretic-based operations. Particle relative polarization was studied by employing insulator-based dielectrophoretic (iDEP) devices. The effects of particle size, medium conductivity, and frequency (10-1000 Hz) of the applied electric potential on particle response were assessed through experiments and mathematical modeling with COMSOL Multiphysics(®). Particles of different sizes (100-1000 nm diameters) were introduced into iDEP devices fabricated from polydimethylsiloxane (PDMS) and their dielectrophoretic responses under direct and alternating current electric fields were recorded and analyzed in the form of images and videos. The results illustrated that particle polarizability and dielectrophoretic response depend greatly on particle size and the frequency of the electric field. Small particles tend to exhibit positive DEP at higher frequencies (200-1000 Hz), while large particles exhibit negative DEP at lower frequencies (20-200 Hz). These differences in relative polarization can be used for the design of iDEP-based separations and analysis of particle mixtures.

The Axial Double Probe and Fields Signal Processing for the MMS Mission

The Axial Double Probe (ADP) instrument measures the DC to ∼100 kHz electric field along the spin axis of the Magnetospheric Multiscale (MMS) spacecraft (Burch et al., Space Sci. Rev., 2014, this issue), completing the vector electric field when combined with the spin plane double probes (SDP) (Torbert et al., Space Sci. Rev., 2014, this issue, Lindqvist et al., Space Sci. Rev., 2014, this issue). Two cylindrical sensors are separated by over 30 m tip-to-tip, the longest baseline on an axial DC electric field ever attempted in space. The ADP on each of the spacecraft consists of two identical, 12.67 m graphite coilable booms with second, smaller 2.25 m booms mounted on their ends. A significant effort was carried out to assure that the potential field of the MMS spacecraft acts equally on the two sensors and that photo- and secondary electron currents do not vary over the spacecraft spin. The ADP on MMS is expected to measure DC electric field with a precision of ∼1 mV/m, a resolution of ∼25 μV/m, and a range of ∼±1 V/m in most of the plasma environments MMS will encounter. The Digital Signal Processing (DSP) units on the MMS spacecraft are designed to perform analog conditioning, analog-to-digital (A/D) conversion, and digital processing on the ADP, SDP, and search coil magnetometer (SCM) (Le Contel et al., Space Sci. Rev., 2014, this issue) signals. The DSP units include digital filters, spectral processing, a high-speed burst memory, a solitary structure detector, and data compression. The DSP uses precision analog processing with, in most cases, >100 dB in dynamic range, better that −80 dB common mode rejection in electric field (E) signal processing, and better that −80 dB cross talk between the E and SCM (B) signals. The A/D conversion is at 16 bits with ∼1/4 LSB accuracy and ∼1 LSB noise. The digital signal processing is powerful and highly flexible allowing for maximum scientific return under a limited telemetry volume. The ADP and DSP are described in this article.

Enhanced contrast ratio and viewing angle of polymer-stabilized liquid crystal via refractive index matching between liquid crystal and polymer network

Long standing electro-optic problems of a polymer-dispersed liquid crystal (PDLC) such as low contrast ratio and transmittances decrease in oblique viewing angle have been challenged with a mixture of dual frequency liquid crystal (DFLC) and reactive mesogen (RM). The DFLC and RM molecules were vertically aligned and then photo-polymerized using a UV light. At scattering state under 50 kHz electric field, DFLC was switched to planar state, giving greater extraordinary refractive index than the normal PDLC cell. Consequently, the scattering intensity and the contrast ratio were increased compared to the conventional PDLC cell. At transparent state under 1 kHz electric field, the extraordinary refractive index of DFLC was simultaneously matched with the refractive index of vertically aligned RM so that the light scattering in oblique viewing angles was minimized, giving rise to high transmittance in all viewing angles.

Frequency dependence of slab coupled optical sensor sensitivity

This paper presents the frequency-dependent sensitivity of slab-coupled optical fiber sensors (SCOSs). This dependence is caused by the frequency characteristics of the relative permittivity. We show experimentally the frequency dependence of SCOS sensitivity for frequencies in the range of 1 kHz to 1 MHz for SCOS fabricated with both potassium titanyl phosphate (KTP) and lithium niobate (LiNbO(3)). We conclude that x-cut KTP SCOSs are preferred for measuring fields above 300 kHz as they are 1.55× more sensitive than x-cut LiNbO(3) SCOSs to the higher frequency fields. However, since KTP SCOSs experience increasing permittivity for low frequencies, SCOSs made with LiNbO(3) may be used for low frequency sensing applications due to their flat sensitivity response. For a 10 kHz electric field, an x cut LiNbO(3) SCOS is approximately 3.43× more sensitive than an x-cut KTP SCOS.

The Effects of Electrical Stimuli on Calcium Change and Histamine Release in Rat Basophilic Leukemia Mast Cells

We apply electric fields at different frequencies of 0.1, 1, 10 and 100 kHz to the rat basophilic leukemia (RBL) mast cells in calcium-containing or calcium-free buffers. The stimuli cause changes of the intracellular calcium ion concentration [Ca2+]i as well as the histamine. The [Ca2+]i increases when the frequency of the external electric field increases from 100 Hz to 10 kHz, and then decreases when the frequency further increases from 10 kHz to 100 kHz, showing a peak at 100 kHz. A similar frequency dependence of the histamine release is also found. The [Ca2+]i and the histamine releases at 100 Hz are about the same as the values of the control group with no electrical stimulation. The ruthenium red (RR), an inhibitor to the TRPV (transient receptor potential (TRP) family V) channels across the cell membrane, is used in the experiment to check whether the electric field stimuli act on the TRPV channels. Under an electric field of 10 kHz, the [Ca2+]i in a calcium-concentration buffer is about 3.5 times as much as that of the control group with no electric stimulation, while the [Ca2+]i in a calcium-free buffer is only about 2.2 times. Similar behavior is also found for the histamine release. RR blockage effect on the [Ca2+]i decrease is statistically significant (∼75%) when mast cells in the buffer with calcium are stimulated with a 10 kHz electric field in comparison with the result without the RR treatment. This proves that TRPVs are the channels that calcium ions inflow through from the extracellular environment under electrical stimuli. Under this condition, the histamine is also released following a similar way. We suggest that, as far as an electric stimulation is concerned, an application of ac electric field of 10 kHz is better than other frequencies to open TRPV channels in mast cells, and this would cause a significant calcium influx resulting in a significant histamine release, which could be one of the mechanisms for electric therapy.

In vitro tests of electromagnetic interference of electromagnetic navigational bronchoscopy to implantable cardioverter defibrillators

To characterize the electromagnetic field emitted by the electromagnetic navigational bronchoscopy (ENB) superDimension(®) Bronchus system (SDBS) and to determine whether current implantable cardioverter defibrillator (ICD) systems are suitable for use in conjunction with SDBS. The electromagnetic emission of the SDBS location board were measured using a field strength meter connected to a low-frequency (5 Hz-100 kHz) electric and magnetic field analyser; the static magnetic field was measured using a three-axis Tesla meter. A human torso simulator was used in the in vitro experiment: a polyethylene plastic box (61 cm length × 43 cm depth × 16.5 cm height) was filled with a semisolid gel and a 0.45% saline solution to provide electric conductance similar to tissue. The ICDs were immersed 1 cm into the gel and connected with a dual-coil integrated bipolar pacing/sensing/shock lead. Tip and right ventricular coil of the lead were connected to an arrhythmia simulator using low-impedance cables. The system transmits electromagnetic waves of 2.5, 3.0, and 3.5 kHz frequency. The maximum magnetic fields measured were B = 53 and 12 µT at location board plane and at ICD plane, respectively. Corresponding figures for the electric field were E = 16.6 and 4.4 V/m. None of the tested ICDs recorded any noise signal during the period in which the location board was switched-on. Stored electrogram analysis confirmed the correct detection of simulated tachyarrhythmia and therapy delivery by every tested ICD. The results of this study demonstrated that tested ICDs are compatible with ENB performed with SDBS. They also suggest that these results may be extended to all ICDs manufactured in compliance with current EN regulations.

Osteoblastic differentiation and stress response of human mesenchymal stem cells exposed to alternating current electric fields.

BackgroundElectric fields are integral to many biological events, from maintaining cellular homeostasis to embryonic development to healing. The application of electric fields offers substantial therapeutic potential, while optimal dosing regimens and the underlying mechanisms responsible for the positive clinical impact are poorly understood.MethodsThe purpose of this study was to track the differentiation profile and stress response of human bone marrow derived mesenchymal stem cells (hMSCs) undergoing osteogenic differentiation during exposure to a 20 mV/cm, 60 kHz electric field. Morphological and biochemical changes were imaged using endogenous two-photon excited fluorescence (TPEF) and quantitatively assessed through eccentricity calculations and extraction of the redox ratio from NADH, FAD and lipofuscin contributions. Real time reverse transcriptase-polymerase chain reactions (RT-PCR) were used to track osteogenic differentiation markers, namely alkaline phosphatase (ALP) and collagen type 1 (col1), and stress response markers, such as heat shock protein 27 (hsp27) and heat shock protein 70 (hsp70). Comparisons of collagen deposition between the stimulated hMSCs and controls were examined through second harmonic generation (SHG) imaging.ResultsQuantitative differences in cell morphology, as described through an eccentricity ratio, were found on days 2 and days 5 (p < 0.05) in samples exposed to the electric field. A delayed but two fold increase in ALP and col1 transcript was detected by week 2 (p < 0.05) in differentiating hMSCs exposed to an electric field in comparison to the nonstimulated controls. Upregulation in stress marker, hsp27, and type 1 collagen deposition were correlated with this response. Increases in NADH, FAD, and lipofuscin were traced in the stimulation group during the first week of field exposure with differences statistically significant on day 10 (p < 0.05). Changes in hsp27 expression correlate well with changes in lipofuscin detected in the stimulation group, suggesting a connection with oxidative stress. Both differentiation factors and electrical stimulation improved hMSC differentiation potential to bone based on calcium deposition on day 28.ConclusionsElectrical stimulation is a useful tool to improve hMSC osteogenic differentiation, while heat shock proteins may reveal underlying mechanisms, and optical non-invasive imaging may be used to monitor the induced morphological and biochemical changes.