External Magnetic Field Gradient Research Articles

Chemically-Driven Autonomous Janus Electromagnets as Magnetotactic Swimmers.

An electromagnet is a particular device that takes advantage of electrical currents to produce concentrated magnetic fields. The most well-known example is a conventional solenoid, having the form of an elongated coil and creating a strong magnetic field through its center when it is connected to a current source. Spontaneous redox reactions located at opposite ends of an anisotropic Janus swimmer can effectively mimic a standard power source, due to their ability to wirelessly generate a local electric current. Herein, we propose the coupling of thermodynamically spontaneous redox reactions occurring at the extremities of a hybrid Mg/Pt Janus swimmer with a solenoidal geometry to generate significant magnetic fields. These chemically driven electromagnets spontaneously transform the redox-induced electric current into a magnetic field with a strength in the range of μT upon contact with an acidic medium. Such on-board magnetization allows them to perform compass-like rotational motion and magnetotactic displacement in the presence of external magnetic field gradients, without the need of using ferromagnetic materials for the swimmer design. The torque force experienced by the swimmer is proportional to the internal redox current, and by varying the composition of the solution, it is possible to fine-tune its angular velocity.

Chemically‐Driven Autonomous Janus Electromagnets as Magnetotactic Swimmers

AbstractAn electromagnet is a particular device that takes advantage of electrical currents to produce concentrated magnetic fields. The most well‐known example is a conventional solenoid, having the form of an elongated coil and creating a strong magnetic field through its center when it is connected to a current source. Spontaneous redox reactions located at opposite ends of an anisotropic Janus swimmer can effectively mimic a standard power source, due to their ability to wirelessly generate a local electric current. Herein, we propose the coupling of thermodynamically spontaneous redox reactions occurring at the extremities of a hybrid Mg/Pt Janus swimmer with a solenoidal geometry to generate significant magnetic fields. These chemically driven electromagnets spontaneously transform the redox‐induced electric current into a magnetic field with a strength in the range of μT upon contact with an acidic medium. Such on‐board magnetization allows them to perform compass‐like rotational motion and magnetotactic displacement in the presence of external magnetic field gradients, without the need of using ferromagnetic materials for the swimmer design. The torque force experienced by the swimmer is proportional to the internal redox current, and by varying the composition of the solution, it is possible to fine‐tune its angular velocity.

Control of fluid flow movement in porous medium with NMR-relaxometry method

The possibility of fixing velocities of fluid motion in model porous medium (glass beads) by measuring the transverse relaxation time T2 by spin echo method is shown. The magnetic field gradient arising due to the difference in the magnetic permeability of the fluid and the porous medium causes a decrease in the average time T2, wich makes it possible to fix the fluid motion in the absence of an external magnetic field gradient. The addition of magnetic nanoparticles to the fluid under study increases the dependence of T2 on fluid velocity and increases the sensitivity in determining the permeability of porous medium by NMR-relaxometry. Keywords: porous media, fluid flow, NMR-relaxometry, magnetic nanoparticles.

Контроль движения жидкости в пористой среде методом ЯМР-релаксометрии

The possibility of fixing velocities of fluid motion in model porous medium (glass beads) by measuring the transverse relaxation time T2 by spin echo method is shown. The magnetic field gradient arising due to the difference in the magnetic permeability of the fluid and the porous medium causes a decrease in the average time T2, with makes it possible to fix the fluid motion in the absence of an external magnetic field gradient. The addition of magnetic nanoparticles to the fluid under study increases the dependence of T2 on fluid velocity and increases the sensitivity in determining the permeability of porous medium by NMR-relaxometry. V.V.Maikov, S.V.Zhakov, I.V.Byzov, A.A.Mysik

Effects of major guidance parameters on aggregated magnetic particles during magnetic drug targeting

Utilization of the aggregation phenomenon in magnetic nanoparticles (MNPs) under a magnetic field has been considered as an efficient mechanism to overcome the lack of actuation force and low imaging resolution for succesuful magnetic drug targeting (MDT). In previous studies, it is assumed that during MDT the aggregation happens in the chain shapes and they are in an equilibrium state and further aggregations do not occur. However, in reality, aggregated magnetic particles are in a non-equilibrium state due to the effects of blood flow and the time-varying magnetic field. As a result, further aggregation can occur. If the repeated aggregation of MNPs in the non-equilibrium state is not considered, it can cause the sticking and clogging phenomena inside the blood vessel, which can significantly affect targeting performance of MDT and raise the safety concerns about the method. Therefore, major paramters of the aggregated magnetic particles should be clearly examined under non-equilibrium state during MDT. Duing MDT, magnetic particle chains with individually different volumes can experience different magnetic field, magnetic field gradient, and flow rate. Therefore, in this paper, we have analyzed four main paramters that can influence the MDT, including chain length, magnetic field, magnetic field gradient, and flow rate. Finally, we have developed a MDT simulator to observe the aggregation phenomenon of magnetic particles and their targeting performance during steering in a Y-channel vessel using an intutive user interface. The results show that aggregation volume and targeting performance can be controlled by modulating the external magnetic field and magnetic field gradient. The proposed aggregation guidance studies can provide insightful guidelines for determining a magnetic drug targeting scheme.

Micro-scale aerosol jet printing of superparamagnetic Fe3O4 nanoparticle patterns

The opportunity to create different patterns of magnetic nanoparticles on surfaces is highly desirable across many technological and biomedical applications. In this paper, this ability is demonstrated for the first time using a computer-controlled aerosol jet printing (AJP) technology. AJP is an emerging digitally driven, non-contact and mask-less printing process which has distinguishing advantages over other patterning technologies as it offers high-resolution and versatile direct-write deposition of a wide range of materials onto a variety of substrates. This research demonstrates the ability of AJP to reliably print large-area, fine-feature patterns of superparamagnetic iron oxide nanoparticles (SPIONs) onto both rigid material (glass) and soft and flexible materials (polydimethylsiloxane (PDMS) films and poly-L-lactic acid (PLLA) nanofilms). Investigation identified and controlled influential process variables which permitted feature sizes in the region of 20 μm to be realised. This method could be employed for a wide range of applications that require a flexible and responsive process that permits high yield and rapid patterning of magnetic material over large areas. As a first proof of concept, we present patterned magnetic nanofilms with enhanced manipulability under external magnetic field gradient control and which are capable of performing complex movements such as rotation and bending, with applicability to soft robotics and biomedical engineering applications.

Bioengineering 3D Neural Networks Using Magnetic Manipulations

AbstractControlling nerve cells to form pre‐designed 3D neural networks that recapitulate the intricate neural interconnectivity in the brain is essential for developing neuronal interfaces and new regeneration approaches. Here, nerve cells within 3D biomaterials are dynamically localized using nano‐based magnetic manipulations. Nerve cells are transformed into magnetic units and their organizational layout is manipulated using external magnetic field gradients. Iron oxide nanoparticles are incorporated into both Pheochromocytoma cell‐line 12 (PC12) cells and primary mice cortical neurons and the magnetized cells are subjected to multiple magnetic fields using pre‐designed magnetic arrays. Their movement is controlled inside multi‐layered 3D collagen scaffolds, which simulate the innate properties of in‐vivo tissue structures. Via these magnetic manipulations, functional 3D microarchitectures of neural networks are created. In light of the clustered and layered structure of the mammalian central nervous system, this strategy paves the way to creating customized 3D tissue architectures for bioengineering applications, enabling a broad range of advanced implementations and providing efficient models for investigating cellular and tissue behavior.

Rationally Designed Magnetic Nanoparticles for Cochlear Drug Delivery: Synthesis, Characterization, and In Vitro Biocompatibility in a Murine Model.

Magnetic nanoparticles (MNPs) for cochlear drug delivery can be precisely engineered for biocompatibility in the cochlea. MNPs are promising drug delivery vehicles that can enhance the penetration of both small and macromolecular therapeutics into the cochlea. However, concerns exist regarding the application of oxidative, metal-based nanomaterials to delicate sensory tissues of the inner ear. Translational development of MNPs for cochlear drug deliver requires specifically tuned nanoparticles that are not cytotoxic to inner ear tissues. We describe the synthesis and characterization of precisely tuned MNP vehicles, and their in vitro biocompatibility in murine organ of Corti organotypic cultures. MNPs were synthesized via 2-phase ligand transfer process with precise control of nanoparticle size. Core and hydrodynamic sizes of nanoparticles were characterized using electron microscopy and dynamic light scattering, respectively. In vitro biocompatibility was assayed via mouse organ of Corti organotypic cultures with and without an external magnetic field gradient. Imaging was performed using immunohistochemical labeling and confocal microscopy. Outer hair cell, inner hair cell, and spiral ganglion neurites were individually quantified. Monocore PEG-MNPs of 45 and 148 nm (mean hydrodynamic diameter) were synthesized. Organ of Corti cultures demonstrated preserved outer hair cell, inner hair cell, and neurite counts across 2 MNP sizes and doses, and irrespective of external magnetic field gradient. MNPs can be custom-synthesized with precise coating, size, and charge properties specific for cochlear drug delivery while also demonstrating biocompatibility in vitro.

In silico simulation and in vitro validation of a continuous microfluidic device for separation of magnetic nanoparticles

Magnetic separation is introduced to separate paramagnetic or superparamagnetic particles and beads from a suspension by implementing an external magnetic field gradient. The strength of this magnetic field declines with rising distance. Batch containers commonly separate nanoparticles from a fluid by imposing an external magnetic field gradient using a permanent magnet. In this system, magnetic particles aggregate the container's wall or bottom, therefore creating a continuous process without any aggregation is desired. In this paper, COMSOL Multiphysics ver. 5.6 (FEM) has been utilized to simulate a continuous microfluidic device with two geometrical designs, linear design (LD) and curved design (CD). The variables are the velocity of the primary fluid and buffer and the channel's width. The optimal designs of both microfluidic devices have been achieved by changing the variables in a specific range without aggregating them to the device's wall. The optimal structures for both designs were built and tested in the laboratory. The optimal velocity was 0.1 mm/s, the optimal channel width was 200 µm for LD, and it was 0.1 mm/s and 400 µm for CD, respectively. The separation percentage in the simulation was 63 %, the spectrophotometry result was 64.08 for LD, and CD showed better results in simulation (85 %) and laboratory experiment (80.24 %). So, this method can be used to optimize nanoparticle separation in microfluidic.

Spin-Photon Coupling for Atomic Qubit Devices in Silicon

Electrically addressing spin systems is predicted to be a key component in developing scalable semiconductor-based quantum processing architectures, to enable fast spin qubit manipulation and long-distance entanglement via microwave photons. However, single spins have no electric dipole, and therefore a spin-orbit mechanism must be integrated in the qubit design. Here, we propose to couple microwave photons to atomically precise donor spin qubit devices in silicon using the hyperfine interaction intrinsic to donor systems and an electrically-induced spin-orbit coupling. We characterise a one-electron system bound to a tunnel-coupled donor pair (1P-1P) using the tight-binding method, and then estimate the spin-photon coupling achievable under realistic assumptions. We address the recent experiments on double quantum dots (DQDs) in silicon and indicate the differences between DQD and 1P-1P systems. Our analysis shows that it is possible to achieve strong spin-photon coupling in 1P-1P systems in realistic device conditions without the need for an external magnetic field gradient.

Dispersive electrostatic waves on a cold magnetized electron gas half-space

Dispersive electrostatic waves on the plane interface between a vacuum and a cold magnetized homogeneous electron gas are predicted for the case where an applied static magnetic field is parallel to the surface and the direction of propagation of the wave, known as Faraday configuration, and also static magnetic field is weakly non-uniform in a direction which is perpendicular to the surface. An expression for dispersion relation of these surface waves is presented based on the Wentzel–Kramers–Brillouin approximation. The dispersion relation shows the importance of the influence of the external static magnetic field gradient on the surface wave behavior.

The use of iron oxide nanoparticles in hyperthermia of Ehrlich tumor: Thesis abstract

Nanotechnology offers important new tools expected to have a great impact on many areas in medical technology. It provides extraordinary opportunities to improve materials and medical devices and they contain several chemical, physical, engineering and biological sciences. Magnetic hyperthermia is a relatively new method used for cancer therapy. Magnetic nanoparticles are an attractive option because they can be remotely targeted by application of external magnetic field gradients or other active and passive targeting methods. Given that tumor cells are more sensitive to a temperature increase than healthy ones, this property can be used in vivo to increase the temperature of tumor tissue (40–43° C) and to destroy the pathological cells by hyperthermia. It was found that, magnetic fluid based on superparamagnetic Fe3O4 nanoparticles coated by biocompatible layer is suitable for hyperthermia because the particles have a high magnetic moment, strong magnetic specific loss power (SLP) and non-toxicity. The paper presents results of research on preparing the magnetic fluid based on Fe3O4 nanoparticles by co-precipitation method and its potential hyperthermia application. The magnetic fluid was used as a mediator for heating by Neel relaxation when exposed to ultrasound and / or microwave energy. The magnetic fluid hyperthermia (MFH) results caused a significant anti-tumor effect on cancer cells. Ultrastructural changes were evaluated by (TEM). These results indicate that intratumoral injection of monodisperse MNPs can attenuate the tumor cells after exposure to ultrasound energy followed by microwave energy.

Magneto-transport phenomena of type-I multi-Weyl semimetals in co-planar setups

Having the chiral anomaly (CA) induced magneto-transport phenomena extensively studied in single Weyl semimetal as characterized by topological charge n = 1, we here address the transport properties in the context of multi-Weyl semimetals (m-WSMs) where n > 1. Using semiclassical Boltzmann transport formalism with the relaxation time approximation, we investigate several intriguing transport properties such as longitudinal magneto-conductivity (LMC), planar Hall conductivity (PHC), thermo-electric coefficients (TECs) and planar Nernst coefficient (PNC) for m-WSMs in the co-planar setups with external magnetic field, electric field and temperature gradient. Starting from the low-energy model, we show analytically that at zero temperature both LMC and PHC vary cubically with topological charge as n 3 while the finite temperature (T ≠ 0) correction is proportional to (n + n 2)T 2. Interestingly, we find that both the longitudinal and transverse TECs vary quadratically with topological charge as n 2 and the PNC is found to vary non-monotonically as a function of n. Our study hence clearly suggests that the inherent properties of m-WSMs indeed show up distinctly through the CA and the chiral magnetic effect induced transport coefficients in two different setups. Moreover, in order to obtain an experimentally realizable picture, we simultaneously verify our analytical findings through the numerical calculations using the lattice model of m-WSMs.

Superior cooling performance of a single channel hybrid magnetofluidic cooling device

Efficient transfer of heat is a major challenge in a plethora of industrial systems and devices. Lower device temperatures can improve energy efficiency and reduce premature device failure. We report the development of a single channel magnetofluidic cooling (MFC) device with high passive cooling performance. MFC is based on thermo-magnetofluidic (TMF) convection, i.e., spontaneous ferrofluid motion due to the gradients of external magnetic field and temperature. Our novel Cu-silicone hybrid design exhibited the highest heat load temperature drop of 183 °C, which is ~3 times higher cooling than previous reports in the literature. Experimental studies of TMF flow are challenging due to the opaque nature of the ferrofluid. Hence we developed a novel TMF setup and quantified the temperature and velocity profiles. We also developed a simulation model to describe the MFC process; the results are in good agreement with our experimental findings. The high cooling performance of our device was found to be due to high vorticity and mixing. Our MFC device is useful for transferring waste heat load from a variety of systems. It is a passive, green, self-regulating, noise, and vibration-free cooling technology.

Manipulating 1-dimensional skyrmion motion by the external magnetic field gradient

We have investigated an approximated analytic form of the one-dimensional motion of skyrmions accelerated by a gradient of the external magnetic field. We find excellent agreement between the analytical calculations and micromagnetic simulations when the skyrmion size is large. The skyrmion motion is related to not only the skyrmion size but also the skyrmion wall width. We also have performed the numerical calculation without approximation in comparison. The numerical calculation results are entirely in agreement with those of micromagnetic simulation for all the skyrmion size. These results introduce an efficient control of skyrmions to next-generation spintronic devices.

Trap stiffness modification of an optically trapped microsphere through directed motion of nanoparticles.

We report an enhancement in the corner frequency of an optically trapped non-magnetic microsphere in the plane perpendicular to the laser propagation direction on addition of ferrofluid to the suspension medium. We conjecture that a directed motion of the nanoparticles toward the trap in this plane is responsible for the augmentation. Changes in the corner frequency in the presence of external magnetic field gradients lend credence to this conjecture. Corner frequency augmentation is also observed when zinc oxide nanoparticles are used. Here, however, no further changes are seen in the presence of magnetic field gradients.

Levitation Force Characteristics of High-Temperature Superconducting Bulks in a High Magnetic Field

The levitation force of high temperature superconducting (HTS) bulks can be enhanced by raising the strength of the external magnetic field. As to the field of HTS magnetic levitation (maglev), many researchers have also obtained this conclusion by levitation experiments above a permanent magnet guideway (PMG). However, the experimental results have limitations because the magnetic field above the PMG is relatively low, around 0.4 T at the 15 mm working height. In order to obtain more comprehensive levitation force characteristics of HTS bulks, it is necessary to carry out more experiments in high magnetic field. In this paper, the effects of magnetization angle and external field gradient on the levitation force of an HTS YBCO bulk which was manufactured with a top-seeded multi-seeded melt-textured process were studied. We set up a levitation force measurement system based on a 5-T Cryogen-Free Magnet (CRY-CFM-5 T-300-H3, Cryogenic Limited). The HTS bulk was cooled by liquid nitrogen in zero-field-cooling condition, and the external magnetic field was enhanced from 0 to 3 T. The HTS bulk was rotated 30° each time and finally rotated to 90°. Experiments show that the levitation force decreases from θ = 0° to 90°, where θ is the angle between the upper surface of the HTS bulk and the horizontal plane. The conclusion that the levitation force increases with the increase of the external magnetic field gradient in high magnetic field was also further confirmed.

Extremely Low Forces Induce Extreme Axon Growth.

Stretch-growth has been defined as a process that extends axons via the application of mechanical forces. In the present article, we used a protocol based on magnetic nanoparticles (NPs) for labeling the entire axon tract of hippocampal neurons, and an external magnetic field gradient to generate a dragging force. We found that the application of forces below 10 pN induces growth at a rate of 0.66 ± 0.02 µm h-1 pN-1 Calcium imaging confirmed the strong increase in elongation rate, in comparison with the condition of tip-growth. Enhanced growth in stretched axons was also accompanied by endoplasmic reticulum (ER) accumulation and, accordingly, it was blocked by an inhibition of translation. Stretch-growth was also found to stimulate axonal branching, glutamatergic synaptic transmission, and neuronal excitability. Moreover, stretched axons showed increased microtubule (MT) density and MT assembly was key to sustaining stretch-growth, suggesting a possible role of tensile forces in MT translocation/assembly. Additionally, our data showed that stretched axons do not respond to BDNF signaling, suggesting interference between the two pathways. As these extremely low mechanical forces are physiologically relevant, stretch-growth could be an important endogenous mechanism of axon growth, with a potential for designing novel strategies for axonal regrowth.SIGNIFICANCE STATEMENT Axon growth involves motion, and motion is driven by forces. The growth cone (GC) itself can generate very low intracellular forces by inducing a drastic cytoskeleton remodeling, in response to signaling molecules. Here, we investigated the key role of intracellular force as an endogenous regulator of axon outgrowth, which it has been neglected for decades because of the lack of methodologies to investigate the topic. Our results indicate a critical role of force in promoting axon growth by facilitating microtubule (MT) polymerization.

Isotope Shift of Nuclear Magnetic Resonances in 129Xe and 131Xe Caused by Spin-Exchange Pumping by Alkali Metal Atoms

The effect of isotope shifts of nuclear magnetic resonance (NMR) frequency in xenon isotopes 129Xe and 131Xe polarized by optically-oriented alkali metal atoms is not only of fundamental interest, but also of practical significance, since it is the main factor limiting the accuracy of a whole class of prospective navigation and metrological devices. Our study of the parametric dependences of the isotope shift has shown that this effect is largely due to incomplete averaging of an inhomogeneous local magnetic field by two xenon isotopes, and therefore, its value can be influenced by applying an external magnetic field gradient. A numerical model is derived that qualitatively describes the effect of the isotopic frequency shift, as well as its dependence on the cell temperature and the external magnetic field gradient. The model provides a good quantitative agreement with the experiment – e.g., at a temperature of 85°C, the isotope shift values predicted by the model coincide with experimental data with an accuracy of up to the experimental error, which, in turn, does not exceed 8% of the total change in the isotopic shift in the entire range of applied magnetic field gradients.

Electrostatically modulated magnetophoretic transport of functionalised iron-oxide nanoparticles through hydrated networks.

Factors that determine magnetophoretic transport of magnetic nanoparticles (MNPs) through hydrated polymer networks under the influence of an external magnetic field gradient were studied. Functionalised iron oxide cores (8.9 nm core diameter) were tracked in real-time as they moved through agarose gels under the influence of an inhomogeneous magnetic field. Terminal magnetophoretic velocities were observed in all cases, these were quantified and found to be highly reproducible and sensitive to the conditions. Increasing agarose content reduced magnetophoretic velocity, we attribute this to increasingly tortuous paths through the porous hydrated polymer network and propose a new factor to quantify the tortuosity. The impact of MNP surface functionalisation, charge, network fixed charge content, and ionic strength of the aqueous phase on velocity were studied to separate these effects. For MNPs functionalised with polyethylene glycol (PEG) increasing chain length reduced velocity but the tortuosity extracted, which is a function of the network, was unchanged; validating the approach. For charged citrate- and arginine-functionalised MNPs, magnetophoretic velocities were found to increase for particles with positive and decrease for particles with negative zeta potential. In both cases these effects could be moderated by reducing the number of agarose anionic residues and/or increasing the ionic strength of the aqueous phase; conditions under which tortuosity again becomes the critical factor. A model for MNP transport identifying the contributions from the tortuous pore network and from electrostatic effects associated with the pore constrictions is proposed.