Electric Field In Response Research Articles

A bioabsorbable mechanoelectric fiber as electrical stimulation suture.

In surgical medicine, suturing is the standard treatment for large incisions, yet traditional sutures are limited in functionality. Electrical stimulation is a non-pharmacological therapy that promotes wound healing. In this context, we designed a passive and biodegradable mechanoelectric suture. The suture consists of multi-layer coaxial structure composed of (poly(lactic-co-glycolic acid), polycaprolactone) and magnesium to allow safe degradation. In addition to the excellent mechanical properties, the mechanoelectrical nature of the suture grants the generation of electric fields in response to movement and stretching. This is shown to speed up wound healing by 50% and reduce the risk of infection. This work presents an evolution of the conventional wound closure procedures, using a safe and degradable device ready to be translated into clinical practice.

Piezoelectrically and Topographically Engineered Scaffolds for Accelerating Bone Regeneration.

Bone regeneration remains a critical concern across diverse medical disciplines, because it is a complex process that requires a combinatorial approach involving the integration of mechanical, electrical, and biological stimuli to emulate the native cellular microenvironment. In this context, piezoelectric scaffolds have attracted considerable interest owing to their remarkable ability to generate electric fields in response to dynamic forces. Nonetheless, the application of such scaffolds in bone tissue engineering has been limited by the lack of a scaffold that can simultaneously provide both the intricate electromechanical environment and the biocompatibility of the native bone tissue. Here, we present a pioneering biomimetic scaffold that combines the unique properties of piezoelectric and topographical enhancement with the inherent osteogenic abilities of hydroxyapatite (HAp). Notably, the novelty of this work lies in the incorporation of HAp into polyvinylidene fluoride-co-trifluoro ethylene in a freestanding form, leveraging its natural osteogenic potential within a piezoelectric framework. Through comprehensive in vitro and in vivo investigations, we demonstrate the remarkable potential of these scaffolds to accelerate bone regeneration. Moreover, we demonstrate and propose three pivotal mechanisms─(i) electrical, (ii) topographical, and (iii) paracrine─that collectively contribute to the facilitated bone healing process. Our findings present a synergistically derived biomimetic scaffold design with wide-ranging prospects for bone regeneration as well as various regenerative medicine applications.

Influence of Tectonic and Geological Structure on GIC in Southern South Island, New Zealand

AbstractAs part of a 5‐year project to assess the risk posed by geomagnetically induced currents (GIC) to the New Zealand electrical transmission network, long‐period magnetotelluric (MT) measurements have been made at 62 sites in southern South Island of New Zealand, a region where there was an absence of previous MT data. The data are largely 3‐dimensional in character, but show distinct features that can be related to the known tectonic and geological structure. In this work we focus on how the measured MT impedance tensors, and a simple interpretation of conductivity structure, can be used to assess the influence of tectonic and geological structure on GIC. We use the impedance tensors to calculate the magnitudes and orientations of induced electric fields in response to various orientations of inducing magnetic field. The electric fields so calculated are then used in a simplified model of the transmission network to calculate GIC at grounded substations. Our results confirm that tectonic/geological structure in the lower South Island and the resulting electrical conductivity variations have important impacts on the GIC magnitude. In the south‐west, smaller induced electric fields, associated with the higher conductivity in that region, lead to much reduced GIC at a substation in that area. In contrast, higher electric fields occurring in a NW‐SE band across the center of the region, contribute to much larger GIC in Dunedin city. Our results thus help explain the observed GIC reported at transformers in the region.

A theoretical examination of localized nanoscale induction by single domain magnetic particles

Single domain magnetic nanoparticles are increasingly investigated as actuators of biological and chemical processes that respond to externally applied magnetic fields. Although their localized effects have often been attributed to nanoscale heating, recent experimental evidence suggests the need to consider alternative hypotheses. Here, using the stochastic Landau–Lifshitz–Gilbert equation and finite element modeling, we investigate and critically examine an alternative hypothesis that localized effects may instead involve the induced electric fields arising from the dynamical behavior of individual single domain magnetic particles. We model the magnetization dynamics and resulting induced electric fields for two relevant and distinct cases of magnetic nanoparticles in alternating magnetic fields: (1) magnetogenetic stimulation of channel proteins associated with ferritin and (2) catalytic enhancement of electrochemical hydrolysis. For the first case, while the local electric fields that ferritin generates are shown to be insufficient to perturb the transmembrane potential, fields on the surface of its mineral core on the order of 102–103 V/m may play a more plausible role in mass transport of iron ions that indirectly lead to stimulation. For the second case, our model indicates that the highest interfacial electric field strengths, on the order of 102 V/m, are expected during reversal events. Thus, nanoparticles well suited for hysteresis heating can also act as intermittent sources of localized induced electric fields in response to an alternating applied field. Finally, we compare the magnitude and timescale of these electric fields to technologically relevant phenomena, showing that they are generally weaker and faster.

Piezoelectric and Magnetoelectric Scaffolds for Tissue Regeneration and Biomedicine: A Review.

Electric fields are ubiquitous throughout the body, playing important role in a multitude of biological processes including osteo-regeneration, cell signaling, nerve regeneration, cardiac function, and DNA replication. An increased understanding of the role of electric fields in the body has led to the development of devices for biomedical applications that incorporate electromagnetic fields as an intrinsically novel functionality (e.g., bioactuators, biosensors, cardiac/neural electrodes, and tissues scaffolds). However, in the majority of the aforementioned devices, an implanted power supply is necessary for operation, and therefore requires highly invasive procedures. Thus, the ability to apply electric fields in a minimally invasive manner to remote areas of the body remains a critical and unmet need. Here, we report on the potential of magnetoelectric (ME)-based composites to overcome this challenge. ME materials are capable of producing localized electric fields in response to an applied magnetic field, which the body is permeable to. Yet, the use of ME materials for biomedical applications is just beginning to be explored. Here, we present on the potential of ME materials to be utilized in biomedical applications. This will be presented alongside current state-of-the-art for in vitro and in vivo electrical stimulation of cells and tissues. We will discuss key findings in the field, while also identifying challenges, such as the synthesis and characterization of biocompatible ME materials, challenges in experimental design, and opportunities for future research that would lead to the increased development of ME biomaterials and their applications.

Fabrication of piezoelectric porous BaTiO3 scaffold to repair large segmental bone defect in sheep.

Porous titanium scaffolds can provide sufficient mechanical support and bone growth space for large segmental bone defect repair. However, they fail to restore the physiological environment of bone tissue. Barium titanate (BaTiO3) is considered a smart material that can produce an electric field in response to dynamic force. Low-intensity pulsed ultrasound stimulation (LIPUS), as a kind of micromechanical wave, can not only promote bone repair but also induce BaTiO3 to generate an electric field. In our studies, BaTiO3 was coated on porous Ti6Al4V and LIPUS was externally applied to observe the influence of the piezoelectric effect on the repair of large bone defects in vitro and in vivo. The results show that the piezoelectric effect can effectively promote the osteogenic differentiation of bone marrow stromal cells (BMSCs) in vitro as well as bone formation and growth into implants in vivo. This study provides an optional alternative to the conventional porous Ti6Al4V scaffold with enhanced osteogenesis and osseointegration for the repair of large bone defects.

Determining absolute Seebeck coefficients from relative thermopower measurements of thin films and nanostructures

Measurements of thermoelectric effects such as the Seebeck effect, the generation of electric field in response to an applied thermal gradient, are important for a range of thin films and nanostructures used in nanoscale devices subject to heating. In many cases, a clear understanding of the fundamental physics of these devices requires knowledge of the intrinsic thermoelectric properties of the material, rather than the so-called “relative” quantity that comes directly from measurements and always includes contributions from the voltage leads. However, for a thin film or nanostructure, determining the absolute Seebeck coefficient, αabs, is challenging. Here, we first overview the challenges for measuring αabs and then present an approach for determining αabs for thin films from relative measurements made with a micromachined thermal isolation platform at temperatures between 77 and 350K. This relies on a relatively simple theoretical description based on the Mott relation for a thin film sample as a function of thickness. We demonstrate this technique for a range of metal thin films, which show that αabs almost never matches expectations from tabulated bulk values, and that for some metals (most notably gold) even the sign of αabs can be reversed. We also comment on the role of phonon and magnon drag for some metal films.

A highly sensitive hybridized soft piezophotocatalyst driven by gentle mechanical disturbances in water

Promoting semiconductor photocatalytic power is expected to address global energetic and environmental challenges. Piezophotocatalysis is an effective strategy to achieve superior catalytic performance, however, realistic applications of previous piezophotocatalysts have been hampered by the ultrasonication conditions that they require. We propose a new material design to achieve superior piezophotocatalysis by combining semiconductors with a self-powered energy cushion that is driven by gentle mechanical disturbances such as water flows. The energy cushion consists of a porous composite graphene-piezoelectric polymeric film which combines piezoelectric and dielectric power generation and stores the electricity in situ. This energy cushion results in a large and prolonged electric field in response to gentle mechanical disturbances. The electric field, in turn, enhances photocatalytic performances of TiO2, BiOI, or CdS by 300%, 21%, and 400%, respectively. In addition, this new material does not consume additional energy when promoting the catalytic performance of semiconductors. We expect the concept of combining these semiconductors with such an energy cushion to lead photocatalysis a step closer to realistic future applications.

Mapping the Brain\u2019s electric fields with Magnetoelectric nanoparticles

BackgroundNeurodegenerative diseases are devastating diagnoses. Examining local electric fields in response to neural activity in real time could shed light on understanding the origins of these diseases. To date, there has not been found a way to directly map these fields without interfering with the electric circuitry of the brain. This theoretical study is focused on a nanotechnology concept to overcome the challenge of brain electric field mapping in real time. The paper shows that coupling the magnetoelectric effect of multiferroic nanoparticles, known as magnetoelectric nanoparticles (MENs), with the ultra-fast and high-sensitivity imaging capability of the recently emerged magnetic particle imaging (MPI) can enable wirelessly conducted electric-field mapping with specifications to meet the requirements for monitoring neural activity in real time.MethodsThe MPI signal is numerically simulated on a realistic human brain template obtained from BrainWeb, while brain segmentation was performed with BrainSuite software. The finite element mesh is generated with Computer Geometry Algorithm Library. The effect of MENs is modeled through local point magnetization changes according to the magnetoelectric effect.ResultsIt is shown that, unlike traditional magnetic nanoparticles, MENs, when coupled with MPI, provide information containing electric field’s spatial and temporal patterns due to local neural activity with signal sensitivities adequate for detection of minute changes at the sub-cellular level corresponding to early stage disease processes.ConclusionsLike no other nanoparticles known to date, MENs coupled with MPI can be used for mapping electric field activity of the brain at the sub-neuronal level in real time. The potential applications span from prevention and treatment of neurodegenerative diseases to paving the way to fundamental understanding and reverse engineering the brain.

Ferroelectric polymer nanostructure with enhanced flexoelectric response for force-induced memory

Through utilizing individual nanodots, as smallest memory units, to convert stress into readable electronic information, we report force-induced high-density data storage in the periodic nanostructure of ferroelectric polymer fabricated by nanoimprinting lithography. The nanostructure is ideal for the stress concentration and increasing the non-uniformity of strains, thus leading to strain gradients inversely proportional to the feature size. A force as low as 400 nN is applied to generate the internal electric field in response to strain gradients and switch polarization state of each memory unit. It can achieve storage density theoretically up to TB/inch2 with the up-to-date nanofabrication technology to miniaturize the unit size.

Equatorial plasma bubble generation/inhibition during 2015 St. Patrick's Day storm

AbstractAll‐sky camera observations carried out over Taiwan showed intense equatorial plasma bubbles (EPBs) in 630.0 nm airglow images on consecutive nights of 13–16 March 2015 but were absent in the following night of 17 March when St. Patrick's Day magnetic storm occurred. Rate of total electron content (TEC) index by using Global Positioning System (GPS) network data also confirmed the absence of irregularities on the night 17 March. The results, however, revealed strong irregularities over Indian sector on the same night. Flux tube integrated Rayleigh‐Taylor instability growth rates computed using the prior (forecast) state of Thermosphere‐Ionosphere Electrodynamics General Circulation Model output after assimilating the GPS‐TEC measurements also agree with the observations, showing smaller values over Taiwan and larger values over India on the night of 17 March. The ionospheric response to the storm over Taiwan that resulted in the apparent inhibition of EPB is investigated in this study by using the data assimilation output. Results indicate that on the night of the magnetic storm, prereversal enhancement of zonal electric field over Taiwan was weaker when compared to that over India. Further analysis suggests that the absence of enhancement in the zonal electric field could be due to westward penetration electric field in response to rapid northward turning of interplanetary magnetic field that occurred during the dusk period over Taiwan.

Duskside enhancement of equatorial zonal electric field response to convection electric fields during the St. Patrick's Day storm on 17 March 2015

AbstractThe equatorial zonal electric field responses to prompt penetration of eastward convection electric fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F layer to >550 km and development of intense equatorial plasma bubbles (EPBs) were observed. These EPBs were found to extend up to 27.13°N and 25.98°S magnetic dip latitudes indicating their altitude development to ~1670 km at apex. In contrast, at few degrees east in the premidnight sector (Thailand‐Indonesian longitudes), no significant height rise and/or EPB activity has been observed. The eastward electric field perturbations due to PPEF are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo (IDD) fields, whereas they were mostly counter balanced by the IDD fields in the premidnight sector. In situ observations from SWARM‐A and SWARM‐C and Communication/Navigation Outage Forecasting System satellites detected a large plasma density depletion near Indian equatorial region due to large electrodynamic uplift of F layer to higher than satellite altitudes. Further, this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator. This study brings out the significantly enhanced equatorial zonal electric field in response to PPEF that is uniquely confined to dusk sector. The responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field Bz.

Disturbance dynamo electric fields in response to geomagnetic storms occurring at different universal times

Perturbed electric fields in the Earth's ionosphere during storm activities may result from the penetration electric fields from high latitudes and/or from the dynamo mechanism driven by the neutral disturbances, depending on the storm phases. In general, the identification of the penetration electric fields is easier than that of the dynamo electric fields. At times, the latter becomes unperceivable or difficult to identify. This is an interesting problem that motivates a model study to investigate the possible reasons. Model runs made from the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model will be presented. Theoretical studies of ionospheric responses to geomagnetic storms with model simulations indicate that the intensities of disturbance dynamo electric fields are highly dependent on various parameters, for example, solar activities, seasonal effects and universal times, etc. When geomagnetic activities commence at 01 ~ 07 UT in summer solstices with low solar fluxes, the disturbance dynamo electric fields become very small. Compared with the general daily variations, they seem to be unperceivable. This phenomenon can be explained by the model results, which show that the positive charge accumulation at low latitudes will be weakened when the equatorward neutral disturbances penetrate the opposite hemisphere in the storm time. For other cases, the magnitudes of the dynamo electric fields are relatively larger under the same geomagnetic activities.

Electromechanical Characterization of Polyelectrolyte Gels by Indentation

We report an indentation method to quantify the electromechanical coupling in polyelectrolyte gels (PGs). PGs produce electric fields in response to mechanical stress and are therefore promising for mechanical sensor applications. The method exposes thin gel samples to well-defined pressure distributions through a spherical indentor, while the electrical response is measured with an array of platinum electrodes embedded in the support. A series of copolymer gels of acrylamide and acrylic acid were synthesized and equilibrated at a fixed pH, leading to samples with systematically varying spatial densities of both charged groups and cross-links. They were characterized by measuring the potential difference between the gel and the equilibrating solution (Donnan potential) as well as their electromechanical coupling through the indentation method. The electromechanical coupling was found to be proportional to the Donnan potential, while the latter is a universal function of the spatial density of ionizable groups in the gel, irrespective of the cross-link density.

Strain dependence of piezoelectric coefficients for pseudomorphically grown semiconductors

We address the issue of strain dependence of piezoelectric effect in semiconductor materials, which is manifested by the appearance of an electric field in response to crystal deformation. For III–V materials such as GaAs and InAs we find that strain considerably modifies the value of the piezoelectric coefficients. For the case of InAs pseudomorphically grown on GaAs substrate, our model predicts a sign reversal of the piezoelectric coefficients e14, e25 and e36 from negative to positive for strains of around 7%. This might explain several discrepancies between the theoretical and experimental observations made on nanostructures such as III–V quantum dots.

A hydrophobic element secures S4 voltage sensor in position in resting Shaker K+ channels

The S4 transmembrane alpha-helix in voltage-gated channels contains several regularly spaced basic amino acid residues that could be protonated and moved across the membrane electric field in response to membrane potential changes. The translocation of the charge-carrying S4 transduces membrane voltage to gating conformational changes of the channel, but how it is positioned and moved with respect to membrane lipid remains controversial. We found that hydrophilic and especially arginine and lysine substitution for L361 at the external end of S4 causes a large negative shift with shallowed slope of both activation and inactivation curves in Shaker K+ channels. Also, the macroscopic kinetics of activation and inactivation become much faster and barely voltage dependent, especially in the L361R mutant channel. These steady-state and kinetic data suggest that the replacement of one single hydrophobic residue, leucine, with arginine may profoundly destabilize the resting conformation of S4, which therefore takes a partially extruded position (partly activated position) at resting potentials (e.g. -120 mV). Consistently, the L361R point mutation gives rise to an extracellularly exposed R365C that is readily modified by external hydrophilic sulfhydryl-specific agents in the resting channel. Moreover, the extruded S4 in the L361R mutant channel could be retracted by strong hyperpolarizing potentials ( approximately -180 mV), from which the mutant channel is gated with slower kinetics but evidently stronger voltage dependence. We conclude that hydrophobic interaction involving a highly conserved residue at the top of S4 is crucial for properly securing the gating voltage sensor in the resting position and thus appropriate gating control of the voltage-gated channels.

Long‐Range Self‐Governing Motion of Polymer Gel on a Gradiently Charged Insulating Substrate

Herein, we report a special poly(vinyl alcohol)/dimethylsulfoxide (PVA/DMSO) gel electromechanical system with great self-governed capability. The system is operated in air by applying a noncontacted DC electric field. When the applied electric field exceeds a certain critical value, the gel exhibits fast and self-governing locomotion on the gradiently charged glass substrate. In contrast to field-controlled gel systems developed earlier, the crawling direction of the gel is independent of the direction of the applied electric field and can be actively controlled. The maximum crawling velocity can reach 3.22 mm s(-1), which is much larger than that of the actuators described earlier. Furthermore, some factors that influence the critical driving electric field and the average crawling speed of the gel were studied. The mechanism analysis indicates that, the self-governing linear motion of the gel is due to the spatially and temporally varying electrostatic interaction between the gel and the applied electric field in response to the gradient change of the charge density and the charge polarity on the substrate.

Composition and strain dependence of the piezoelectric coefficients inInxGa1−xAsalloys

We address the issue of the composition and strain dependence of the piezoelectric effect in semiconductor materials, which is manifested by the appearance of an electric field in response to shear crystal deformation. We propose a model based on expressing the direct and dipole contributions to the polarization in terms of microscopic quantities that can be calculated by density functional theory. We show that when applied to the study of ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ alloys, the model is able to explain and accurately predict the often-observed discrepancies between the experimentally deduced values of ${e}_{14}$ and those linearly interpolated between the values of $\mathrm{InAs}$ and $\mathrm{GaAs}$. The values of the piezoelectric coefficient predicted by our approach compare very well with values deduced from photocurrent measurements of quantum well samples grown on (111) $\mathrm{GaAs}$ substrates by molecular beam epitaxy.

Importance of Second-Order Piezoelectric Effects in Zinc-Blende Semiconductors

We show that the piezoelectric effect that describes the emergence of an electric field in response to a crystal deformation in III-V semiconductors such as GaAs and InAs has strong contributions from second-order effects that have been neglected so far. We calculate the second-order piezoelectric tensors using density-functional theory and obtain the piezoelectric field for [111]-oriented In(x)Ga(1-x)As quantum wells of realistic dimensions and concentration x. We find that the linear and the quadratic piezoelectric coefficients have the opposite effect on the field, and for large strains (large In concentration) the quadratic terms even dominate. Thus, the piezoelectric field turns out to be a rare example of a physical quantity for which the first-order and second-order contributions are of comparable magnitude.

Tryptophan scanning mutagenesis of the HERG K+ channel: the S4 domain is loosely packed and likely to be lipid exposed

Inherited mutations or drug-induced block of voltage-gated ion channels, including the human ether-à-go-go-related gene (HERG) K+ channel, are significant causes of malignant arrhythmias and sudden death. The fourth transmembrane domain (S4) of these channels contains multiple positive charges that move across the membrane electric field in response to changes in transmembrane voltage. In HERG K+ channels, the movement of the S4 domain across the transmembrane electric field is particularly slow. To examine the basis of the slow movement of the HERG S4 domain and specifically to probe the relationship between the S4 domain with the lipid bilayer and rest of the channel protein, we individually mutated each of the S4 amino acids in HERG (L524-L539) to tryptophan, and characterized the activation and deactivation properties of the mutant channels in Xenopus oocytes, using two-electrode voltage-clamp methods. Tryptophan has a large bulky hydrophobic sidechain and so should be tolerated at positions that interact with lipid, but not at positions involved in close protein-protein interactions. Significantly, we found that all S4 tryptophan mutants were functional. These data indicate that the S4 domain is loosely packed within the rest of the voltage sensor domain and is likely to be lipid exposed. Further, we identified residues K525, R528 and K538 as being the most important for slow activation of the channels.