High Magnetic Field Gradient Research Articles

Levitation and position of T47D cells on a magnetic microsystem fabricated by ink jet printing

We present the levitation and residing at particular places of human breast cancer (T47D) cells on a magnetic microsystem quickly fabricated by printing. The microsystem consists of arrays of soft magnetic elements and is put adjacent to a bulk magnet. Under a magnetic field generated by the magnet, elements are magnetized, obtaining a significant magnetic field strength and a high magnetic field gradient in the micro-space above them. The field applies a magnetic force on the cells as they are dropped to the surfaces of the elements. As a result, levitation and a stable position for each cell are observed. The levitation and position of a cell can be predicted by a theory that takes into account the magnetic, buoyant, and gravitational forces on the cells. Our theoretical and experimental results agree well with one another, and the microsystem is capable of efficient cell manipulation.

Semi-circle magnetophoretic separation under rotated magnetic field for colorimetric biosensing of Salmonella.

Magnetic separation was often applied to isolate and concentrate foodborne bacteria using immunomagnetic nanobeads before downstream bacterial detection. However, nanobead-bacteria conjugates (magnetic bacteria) were coexisting with excessive unbound nanobeads, limiting these nanobeads on magnetic bacteria to further act as signal probes for bacterial detection. Here, a new microfluidic magnetophoretic biosensor was elaboratively developed using a rotated high gradient magnetic field and platinum modified immunomagnetic nanobeads for continuous-flow isolation of magnetic bacteria from free nanobeads, and combined with nanozyme signal amplification for colorimetric biosensing of Salmonella. First, the platinum modified immunomagnetic nanobeads were mixed with the bacterial sample to form the magnetic bacteria, and magnetically separated to eliminate non-magnetic background. Then, the mixture of free immunomagnetic nanobeads and magnetic bacteria was injected with sheath flow (PBS) at higher flowrate into the semi-circle magnetophoretic separation channel under rotated magnetic field, which was generated by two repulsive cylindric magnets and their in-between ring iron gear, leading to continuous-flow isolation of magnetic bacteria from free immunomagnetic nanobeads because they suffered from different magnetic forces and thus had different deviating positions at the outlet. Finally, the separated magnetic bacteria and unbound magnetic nanobeads were respectively collected and used to catalyze coreless substrate into blue product, which was further analyzed using the microplate reader to obtain bacterial amount. This biosensor could determinate Salmonella as low as 41CFU/mL in 40min.

Identification of Microorganisms that Bind Specifically to Target Materials of Interest Using a Magnetophoretic Microfluidic Platform.

Discovery of microorganisms and their relevant surface peptides that specifically bind to target materials of interest can be achieved through iterative biopanning-based screening of cellular libraries having high diversity. Recently, microfluidics-based biopanning methods have been developed and exploited to overcome the limitations of conventional methods where controlling the shear stress applied to remove cells that do not bind or only weakly bind to target surfaces is difficult and the overall experimental procedure is labor-intensive. Despite the advantages of such microfluidic methods and successful demonstration of their utility, these methods still require several rounds of iterative biopanning. In this work, a magnetophoretic microfluidic biopanning platform was developed to isolate microorganisms that bind to target materials of interest, which is gold in this case. To achieve this, gold-coated magnetic nanobeads, which only attached to microorganisms that exhibit high affinity to gold, were used. The platform was first utilized to screen a bacterial peptide display library, where only the cells with surface peptides that specifically bind to gold could be isolated by the high-gradient magnetic field generated within the microchannel, resulting in enrichment and isolation of many isolates with high affinity and high specificity toward gold even after only a single round of separation. The amino acid profile of the resulting isolates was analyzed to provide a better understanding of the distinctive attributes of peptides that contribute to their specific material-binding capabilities. Next, the microfluidic system was utilized to screen soil microbes, a rich source of extremely diverse microorganisms, successfully isolating many naturally occurring microorganisms that show strong and specific binding to gold. The results show that the developed microfluidic platform is a powerful screening tool for identifying microorganisms that specifically bind to a target material surface of interest, which can greatly accelerate the development of new peptide-driven biological materials and hybrid organic-inorganic materials.

High Gradient Magnetic Separation of Pure Gd2O3 Particles from Pure La2O3 Particles

Rare earth oxides such as La2O3 and Gd2O3 are abundant in waste optical glass. The separation of rare earth oxides is beneficial to the recycling of rare earth resources. In this study, the rare earth oxide Gd2O3 particles were separated from La2O3 particles using high gradient magnetic separation, and the influence of different fluid media (i.e., water, anhydrous ethanol, and their mixture) on the separation results was investigated. By using the measured zeta potential of oxide particles in water/ethanol of different pH and water with different dispersants (Na2SiO3 9H2O, citric acid, Na2CO3, and sodium hexametaphosphate), the DLVO (Derjaguin–Landau–Verwey–Overbeek) potential calculations and their analysis applied to high gradient magnetic separation results were also performed. The results showed that using anhydrous ethanol or adding a dispersant in water as a fluid medium can promote the separation of magnetic Gd2O3 particles under a high-gradient magnetic field. Among the different conditions, anhydrous ethanol can improve the grade of Gd2O3 to 95% from 70% with water. Furthermore, ethanol can be reused after filtration, making it an environmentally friendly fluid medium. Among the four dispersants, sodium hexametaphosphate, Na2SiO3, and Na2CO3 can also increase the separation rate of La2O3 and Gd2O3 to about 95%. The effect of citric acid on the separation performance is slightly worse, and the recovery rate of Gd2O3 is 80%. This study provides a new reference for selecting a fluid medium for magnetic separation.

Tailoring homogeneous immiscible alloy via magneto-Archimedes levitation

Processing of immiscible alloys with a homogeneous distribution of fine minor segregated phases is a great challenge. Al-10wt.%Bi immiscible alloys were solidified under the homogeneous and gradient high magnetic fields (HHMF and GHMF). X-ray computed tomography technique was applied to study the spatial features of the minor Bi-rich particles (MBPs). The results show that the MBPs displayed as centripetal and centrifugal distributions along the radial directions of the ingots solidified under the GHMF. The segregation of the minor Bi-rich droplets (MBDs) was dominated by both radial Marangoni migration and the vertical Stokes sedimentation under the HHMF. In the case of the GHMF, both the radial Marangoni migration and vertical Stokes sedimentation of the MBDs can be effectively stopped by the gradient forces. This work provides a novel path to design the novel alloys with homogeneous microstructures by utilizing the magneto-Archimedes levitation.

Electrodeposited magnetic nanoporous membrane for high-yield and high-throughput immunocapture of extracellular vesicles and lipoproteins.

Superparamagnetic nanobeads offer several advantages over microbeads for immunocapture of nanocarriers (extracellular vesicles, lipoproteins, and viruses) in a bioassay: high-yield capture, reduction in incubation time, and higher capture capacity. However, nanobeads are difficult to "pull-down" because their superparamagnetic feature requires high nanoscale magnetic field gradients. Here, an electrodeposited track-etched membrane is shown to produce a unique superparamagnetic nano-edge ring with multiple edges around nanopores. With a uniform external magnetic field, the induced monopole and dipole of this nano edge junction combine to produce a 10× higher nanobead trapping force. A dense nanobead suspension can be filtered through the magnetic nanoporous membrane (MNM) at high throughput with a 99% bead capture rate. The yield of specific nanocarriers in heterogeneous media by nanobeads/MNM exceeds 80%. Reproducibility, low loss, and concentration-independent capture rates are also demonstrated. This MNM material hence expands the application of nanobead immunocapture to physiological samples.

Research on the Gradient-Field Superconducting Magnet for Magnetoplasmadynamic Thruster Performance Improvement

Magnetoplasmadynamic thrusters (MPDTs) are characterized by their high specific impulse, high thrust, and long operational life. Hence, they are promising candidates as space electric thrusters for deep space exploration, such as for future interstellar voyages. To improve the performance of MPDTs, this article investigates the potential to enhance their plume performance using a high-gradient magnetic field based on superconductor technology. We introduce a high-intensity superconducting magnetic field constraint method based on a 100-kW MPDT, which involves making the solenoid and gradient-field superconducting magnets more compact. The central magnetic field can reach 1 T and the magnetic field homogeneity is optimized from 1.69% to 0.83%. In addition, the MHD method is used to simulate and verify the concentration-constrained acceleration of plasma by the gradient-field superconducting magnets. Experimental results show that with increases in magnetic field strength, the axial plasma plume becomes more concentrated. The plume distribution of the 100-kW gradient-superconducting MPDT is more uniform than that of a solenoid plume at the same discharge current due to better magnetic field homogeneity.

High-gradient magnetic fields and starch metabolism: results from a space experiment

Directing plant growth in weightlessness requires understanding the processes that establish plant orientation and how to manipulate them. Both gravi- and phototropism determine directional growth and previous experiments showed that high gradient magnetic fields (HGMF) can induce curvature in roots and shoots. Experiments with Brassica rapa verified that that gravitropism-like induction of curvature is possible in space and that the HGMF-responsive organelles are amyloplasts. We assessed the effect of space and HGMF based on 16 genes and compared their transcription with static growth and clinorotation. Amyloplasts size in root tips increased under weightlessness but decreased under clinorotation but not in response to magnetic fields. Amyloplast size changes were correlated with reduced amylase transcription in space samples and enhanced transcription after clinorotation. Mechanostimulation and weightlessness have opposite effects on the size of amyloplasts. The data show that plants perceive weightlessness, and that their metabolism adjusts to microgravity and mechanostimulation. Thus, clinorotation as surrogate for space research may lead to incorrect interpretations.

A Permanent Magnet Ferromagnetic Wear Debris Sensor Based on Axisymmetric High-Gradient Magnetic Field.

The detection of wear debris in lubricating oil is effective for determining current equipment operating conditions for fault diagnosis. In this paper, a permanent magnet ferromagnetic wear debris sensor is proposed that is composed of a compact structure and a detection coil that generates an induced voltage when wear debris passes through a magnetic field. A three-dimensional model of the sensor is established, the internal axisymmetric high-gradient magnetic field of the sensor is analyzed, and a mathematical model of the sensor signal is proposed. The effects of the air gap structure of the sensor and the relative permeability, velocity, and volume of the wear debris on the sensor performance are analyzed. The correctness of the theoretical results is proven by single particle experiments, and the sensor is calibrated to achieve quantitative analysis of the wear debris.

Single NV centers array preparation and static magnetic field detection.

To solve the problem of static magnetic field detection accuracy and consistency, we prepared an array of single NV centers for static magnetic field vector and gradient detection using the femtosecond laser direct writing method. The prepared single NV centers are characterized by fewer impurity defects and good stress uniformity, with an average spatial positioning error of only 0.2 µm. This array of single NV centers can achieve high accuracy magnetic field vector and gradient measurement with GBZ≈-0.047 µT/µm in the Z-axis. This result provides a new idea for large-range, high-precision magnetic field vector and gradient measurements.

A New Drive System for Microagent Control in Targeted Therapy Based on Rotating Gradient Magnetic Fields

Using magnetically powered microagents as precise delivery carriers is a promising technology for targeted therapy. It is a significant challenge to converge microagents to the desired position without sufficient support of real‐time imaging feedback. Herein, a new drive solution is proposed, which generates a rotating gradient‐based magnetic field by sequentially energizing each coil of the electromagnetic coil system. With this method, a high magnetic field gradient concentrated onto a specific target site is generated, which will attract microagent swarms to automatically converge to the target site from different directions. Based on the established model of rotating gradient magnetic field actuation, the relationship between the current inputs of coils and the location of the aggregation center is characterized, so that the target site can be adjusted in the entire workspace by changing the coil current inputs. The method drives microagents to rotate while moving forward, thereby reducing the viscous resistance and friction on microagents. It does not rely on specific trajectory planning and real‐time visual guidance to navigate microagents, and can drive magnetic microagents with different characteristics such as size, shape, and materials. This research provides a basis for using microagent delivery in clinical applications and precision‐targeted therapy.

Optimizing detachment control using the magnetic configuration of divertors

As tokamak research moves to reactor conditions, the control of a stable, optimally-detached divertor plasma has become increasingly relevant. Simple predictions of such detachment control have been performed previously using the detachment location sensitivity (DLS) model (Lipschultz et al 2016 Nucl. Fusion 56 056007). In this study the DLS model is extended and combined with SOLPS-ITER simulations of isolated divertor grids to study the effects of alternate divertor magnetic field properties on detachment control. The DLS model predicts that divertors can achieve easier access to detachment through a long connection length, a high total flux expansion, and a high average magnetic field in the divertor compared with that at the x-point. SOLPS-ITER simulations suggest an even stronger impact of total flux expansion and connection length on detachment access than the DLS model predicts. In terms of detachment evolution, both simulation and modelling show a high gradient in the total magnetic field and low are able to more easily keep a detachment front at a desired poloidal location. Regions with no stable detachment front locations can arise for high magnetic field gradients directed towards the target. Significant differences have been found between impurity scan simulations and the DLS model. These differences may be attributed to sources and sinks of power and electron pressure, and should be explored further in future work.

Investigation of scale inhibition effect and mechanism of S-HGMF in the clean recirculating cooling water system

The formation of scales in a recirculating water system is a common problem in industrial water treatment; it seriously affects the production in various industries and pollutes the environment. Although conventional scale inhibition methods are effective, they are expensive and harm the environment. Herein, an advanced method is proposed to solve the scaling issue in recirculating cooling water systems using the superconducting high-gradient magnetic field (S-HGMF) treatment. The scale inhibition performance could be improved by changing the magnetic flux density, operation time, and flow rate. The results showed that S-HGMF could increase the number of hydrogen bonds in the recirculating cooling water, enhance molecular interaction, increase the thickness of the ion hydration shell, reduce the nucleation rate, stabilize the water quality, improve the solubility of scale-forming ions, and inhibit scale formation. The scale inhibition performance reached 8.10%. Interestingly, S-HGMF had a memory effect in that it could maintain the scale inhibition effect for some period after treatment completion. Moreover, S-HGMF changed the crystal structure of the scale and promoted the transformation of the scale to a metastable phase. Ultimately, calcite was transformed to aragonite to reduce the precipitation of hard scale (calcite), achieving the purpose of scale inhibition. As a physical method, the application of S-HGMF to inhibit scaling has great potential for industrial applications.

Rare Earth Magnets and Limescale: Analysis of Magnetic Water Treatment Using a Dynamic Scale Rig

Treatment of limescale build-up in process- and municipal pipes by magnetic water treatment has been a topic of research for decades. However, there is no realistic mechanistic hypothesis as to why such treatments would be effective. Therefore, a test regime was established to explore scale inhibition by means of magnetic forces in a robust and reproducible manner. In this study, two magnetic devices were developed using Neodymium-based rare earth magnets for the application of static magnetic fields. One device, based on a Halbach array, is designed to test high-intensity (965 mT) magnetic fields. The other is based on a Halbach trap arrangement, designed to test high magnetic field gradients (490 mT, 82.5 T/m). The precipitation reactions of calcium carbonate, calcium sulfate, and calcium phosphate were monitored in real-time to determine the effectiveness of these devices for inhibiting scale. No magnetic treatment effects were observed.

Constitutional supercooling and corresponding microstructure transition triggered by high magnetic field gradient during directional solidification of Al-Fe eutectic alloy

Directional solidification experiments of eutectic AlFe alloys were carried out under different high magnetic field gradients. High magnetic field gradient changed the microstructure selection during solidification process, induced the solidification microstructure to undergo eutectic instability, cellular transition, single-phase instability, and dendrite transition, which is similar to the planar-cellular-dendritic crystal growth pattern transition usually induced by an increasing growth velocity without magnetic field. The single phase was proved to be formed through an independent nucleation mechanism during single-phase instability. The effect of high magnetic field gradient on solidification was analyzed. Through the coupling effect of magnetic force and Lorentz force on solute migration and diffusion during solidification, high magnetic field gradient triggered a constitutional supercooling at the front of solid-liquid interface, which led to the growth pattern transition. A solidification model of eutectic alloy under high magnetic field gradient was proposed, and the microstructure selection map of AlFe alloy under gradient magnetic field was qualitatively drawn for the first time. This work proved that an alloy material with a microstructure usually obtained at high growth velocity can be obtained at a low growth velocity by applying a high magnetic field gradient, and suggested a new potential method for the future controlling of alloy structures and properties.

Design and experimental research of abrasive particle detection sensor based on coil magnetic field

This paper develops a dual-coil sensor integrated with high-permeability materials based on inductive sensor technology to detect wear particles in oil. This method is mainly used for online detection and fault analysis of pollutants in hydraulic and lubricating oil systems. The sensor innovatively embeds permalloy into the sensing unit of the sensor to generate high gradient magnetic field in the sensing area, consequently improving the detection sensitivity of the sensor. The detection unit consists of two pieces of permalloy and two plane coils. The permalloys have a rectangular groove at the center, which is placed in line with the inner hole of the coil, thereby forming the detection area. Particles in the microchannel can be detected as they flow through the detection area. The article theoretically analyzes the working principle of the sensor and establishes a verification experiment system. The experimental results show that after adding permalloy to the sensing unit, the signal-to-noise ratio (SNR) of iron particles is increased by more than 40%, and the SNR of copper particles is increased by more than 30%. As the particle size increases, the SNR decreases. Using this design, the range of the lower limit detection for ferromagnetic metal particles increased to 10–15 μm, while that of non-ferromagnetic metal particles increased to 60 μm. Compared with traditional inductive sensors, the addition of permalloy greatly improves the sensor's performance, which significantly boosts the sensitivity of the dual-coil type sensor.

Monte Carlo evaluation of high-gradient magnetically focused planar proton minibeams in a passive nozzle

Objective. To investigate the potential of using a single quadrupole magnet with a high magnetic field gradient to create planar minibeams suitable for clinical applications of proton minibeam radiation therapy. Approach. We performed Monte Carlo simulations involving single quadrupole Halbach cylinders in a passively scattered nozzle in clinical use for proton therapy. Pencil beams produced by the nozzle of 10–15 mm initial diameters and particle range of ∼10–20 cm in water were focused by magnets with field gradients of 225–350 T m−1 and cylinder lengths of 80–110 mm to produce very narrow elongated (planar) beamlets. The corresponding dose distributions were scored in a water phantom. Composite minibeam dose distributions composed from three beamlets were created by laterally shifting copies of the single beamlet distribution to either side of a central beamlet. Modulated beamlets (with 18–30 mm nominal central SOBP) and corresponding composite dose distributions were created in a similar manner. Collimated minibeams were also compared with beams focused using one magnet/particle range combination. Main results. The focusing magnets produced planar beamlets with minimum lateral FWHM of ∼1.1–1.6 mm. Dose distributions composed from three unmodulated beamlets showed a high degree of proximal spatial fractionation and a homogeneous target dose. Maximal peak-to-valley dose ratios (PVDR) for the unmodulated beams ranged from 32 to 324, and composite modulated beam showed maximal PVDR ranging from 32 to 102 and SOBPs with good target dose coverage. Significance. Advantages of the high-gradient magnets include the ability to focus beams with phase space parameters that reflect beams in operation today, and post-waist particle divergence allowing larger beamlet separations and thus larger PVDR. Our results suggest that high gradient quadrupole magnets could be useful to focus beams of moderate emittance in clinical proton therapy.

Clinical validity of non-contrast-enhanced VI-RADS: prospective study using 3-T MRI with high-gradient magnetic field

ObjectivesTo develop a modified Vesical Imaging Reporting and Data System (VI-RADS) without dynamic contrast-enhanced imaging (DCEI), termed “non-contrast-enhanced VI-RADS (NCE-VI-RADS)”, and to assess the additive impact of denoising deep learning reconstruction (dDLR) on NCE-VI-RADS.MethodsFrom January 2019 through December 2020, 163 participants who underwent high-gradient 3-T MRI of the bladder were prospectively enrolled. In total, 108 participants with pathologically confirmed bladder cancer by transurethral resection were analyzed. Tumors were evaluated based on VI-RADS (scores 1–5) by two readers independently: an experienced radiologist (reader 1) and a senior radiology resident (reader 2). Conventional VI-RADS assessment included all three imaging types (T2-weighted imaging [T2WI], diffusion-weighted imaging [DWI], and dynamic contrast-enhanced imaging [DCEI]). Also evaluated were NCE-VI-RADS comprising only non-contrast-enhanced imaging types (T2WI and DWI), and “NCE-VI-RADS with dDLR” comprising T2WI processed with dDLR and DWI. All systems were assessed using receiver-operating characteristic curve analysis and simple and/or weighted κ statistics.ResultsMuscle invasion was identified in 23/108 participants (21%). Area under the curve (AUC) values for diagnosing muscle invasion were as follows: conventional VI-RADS, 0.94 and 0.91; NCE-VI-RADS, 0.93 and 0.91; and “NCE-VI-RADS with dDLR”, 0.96 and 0.93, for readers 1 and 2, respectively. Simple κ statistics indicated substantial agreement for NCE-VI-RADS and almost perfect agreement for conventional VI-RADS and “NCE-VI-RADS with dDLR” between the two readers.ConclusionNCE-VI-RADS achieved predictive accuracy for muscle invasion comparable to that of conventional VI-RADS. Additional use of dDLR improved the diagnostic accuracy of NCE-VI-RADS.Key Points• Non-contrast-enhanced Vesical Imaging Reporting and Data System (NCE-VI-RADS) was developed to avoid risk related to gadolinium-based contrast agent administration.• NCE-VI-RADS had predictive accuracy for muscle invasion comparable to that of conventional VI-RADS.• The additional use of denoising deep learning reconstruction (dDLR) might further improve the diagnostic accuracy of NCE-VI-RADS.

Continuous-Flow Magnetic Fractionation of Red Blood Cells Based on Hemoglobin Content and Oxygen Saturation—Clinical Blood Supply Implications and Sickle Cell Anemia Treatment

Approximately 36,000 units of red blood cells (RBCs) are used every day in the U.S. and there is a great challenge for hospitals to maintain a reliable supply, given the 42-day expiration period from the blood donation date. For many years, research has been conducted to develop ex vivo storage solutions that limit RBC lysis and maintain a high survival rate of the transfused cells. However, little attention is directed towards potential fractionation methods to remove unwanted cell debris or aged blood cells from stored RBC units prior to transfusion, which could not only expand the ex vivo shelf life of RBC units but also avoid adverse events in transfused patients. Such fractionation methods could also limit the number of transfusions required for treating certain pathologies, such as sickle cell disease (SCD). In this work, magnetic fractionation is studied as a potential technology to fractionate functional and healthy RBCs from aged or sickle cells. It has been reported that during ex vivo RBC storage, RBCs lose hemoglobin (Hb) and lipid content via formation of Hb-containing exosomes. Given the magnetic character of deoxygenated- or met-Hb, in this work, we propose the use of a quadrupole magnetic sorter (QMS) to fractionate RBCs based on their Hb content from both healthy stored blood and SCD blood. In our QMS, a cylindrical microchannel placed inside the center of the quadrupolar magnets is subjected to high magnetic fields and constant field gradients (286 T/m), which causes the deflection of the paramagnetic, Hb-enriched, and functional RBCs from their original path and their collection into a different outlet. Our results demonstrated that although we could obtain a significant difference in the magnetic mobility of the sorted fractions (corresponding to a difference in more than 1 pg of Hb per cell), there exists a tradeoff between throughput and purity. Therefore, this technology when optimized could be used to expand the ex vivo shelf life of RBC units and avoid adverse events in transfused individuals or SCD patients requiring blood exchange therapy.

Fabrication of surface ion traps with integrated current carrying wires enabling high magnetic field gradients

A major challenge for quantum computers is the scalable simultaneous execution of quantum gates. One approach to address this in trapped ion quantum computers is the implementation of quantum gates based on static magnetic field gradients and global microwave fields. In this paper, we present the fabrication of surface ion traps with integrated copper current carrying wires embedded inside the substrate below the ion trap electrodes, capable of generating high magnetic field gradients. The copper layer’s measured sheet resistance of 1.12 mΩ/sq at room temperature is sufficiently low to incorporate complex designs, without excessive power dissipation at high currents causing a thermal runaway. At a temperature of 40 K the sheet resistance drops to 20.9 μΩ/sq giving a lower limit for the residual resistance ratio of 100. Continuous currents of 13 A can be applied, resulting in a simulated magnetic field gradient of 144 T m−1 at the ion position, which is 125 μm from the trap surface for the particular anti-parallel wire pair in our design.