Quantitative modeling of forces in electromagnetic tweezers

Bijamov, A.; Shubitidze, Fridon; Oliver, Piercen M.; Vezenov, Dmitri V.

doi:10.1063/1.3510481

Cited by 22 publications

(20 citation statements)

References 27 publications

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“…To investigate the applied force in the area of interest, we calculated the field gradient in proximity of the magnetic tip from the measured field distribution for different tip lengths (17 mm and 10 mm) and radii (1 mm and 2 mm). Our experiments are in good agreement with Bijamov simulation results 18 and revealed a significant dependence of the gradient field on the radius of curvature of the tip of the core. This increased field gradient leads to a threefold increase in force by decreasing the tip radius from 2 mm to 1 mm.…”

Section: Magnetic Core Profilesupporting

confidence: 88%

Magnetic tweezers optimized to exert high forces over extended distances from the magnet in multicellular systems

Selvaggi

Pasakarnis²,

Brunner³

et al. 2018

Review of Scientific Instruments

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Magnetic tweezers are mainly divided into two classes depending on the ability of applying torque or forces to the magnetic probe. We focused on the second category and designed a device composed by a single electromagnet equipped with a core having a special asymmetric profile to exert forces as large as 230 pN-2.8 μm Dynabeads at distances in excess of 100 μm from the magnetic tip. Compared to existing solutions our magnetic tweezers overcome important limitations, opening new experimental paths for the study of a wide range of materials in a variety of biophysical research settings. We discuss the benefits and drawbacks of different magnet core characteristics, which led us to design the current core profile. To demonstrate the usefulness of our magnetic tweezers, we determined the microrheological properties inside embryos of Drosophila melanogaster during the syncytial stage. Measurements in different locations along the dorsal-ventral axis of the embryos showed little variation, with a slight increase in cytoplasm viscosity at the periphery of the embryos. The mean cytoplasm viscosity we obtain by active force exertion inside the embryos is comparable to that determined passively using high-speed video microrheology.

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Section: Magnetic Core Profilesupporting

confidence: 88%

Magnetic tweezers optimized to exert high forces over extended distances from the magnet in multicellular systems

Selvaggi

Pasakarnis²,

Brunner³

et al. 2018

Review of Scientific Instruments

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“…Indeed, we find that we achieve comparable, and in some cases, higher magnetic field gradients than are predicted for an electromagnet consisting of a mumetal core encased by a solonoidal wire coil under conditions of near-magnetic field saturation of the core. 22 Finally, we have shown through this work that magnetic saturation of yokes can be developed with a relatively small magnet array. The ability to develop very high forces using relatively small cube magnets (each <1 in.…”

Section: Discussionmentioning

confidence: 97%

Design and optimization of arrays of neodymium iron boron-based magnets for magnetic tweezers applications

Zacchia

Valentine

2015

Review of Scientific Instruments

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We present the design methodology for arrays of neodymium iron boron (NdFeB)-based magnets for use in magnetic tweezers devices. Using finite element analysis (FEA), we optimized the geometry of the NdFeB magnet as well as the geometry of iron yokes designed to focus the magnetic fields toward the sample plane. Together, the magnets and yokes form a magnetic array which is the basis of the magnetic tweezers device. By systematically varying 15 distinct shape parameters, we determined those features that maximize the magnitude of the magnetic field gradient as well as the length scale over which the magnetic force operates. Additionally, we demonstrated that magnetic saturation of the yoke material leads to intrinsic limitations in any geometric design. Using this approach, we generated a compact and light-weight magnetic tweezers device that produces a high field gradient at the image plane in order to apply large forces to magnetic beads. We then fabricated the optimized yoke and validated the FEA by experimentally mapping the magnetic field of the device. The optimization data and iterative FEA approach outlined here will enable the streamlined design and construction of specialized instrumentation for force-sensitive microscopy.

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“…MAS is a robust and accurate numerical technique for evaluating electromagnetic wave propagation and scattering problems [61, 62]. In this method, boundaries between materials of differing electrical parameters are defined and discretized into pairs of points along a surface.…”

Section: Methodsmentioning

confidence: 99%

Mitigation of eddy current heating during magnetic nanoparticle hyperthermia therapy

Stigliano

Shubitidze

Petryk

et al. 2016

International Journal of Hyperthermia

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Magnetic nanoparticle hyperthermia therapy is a promising technology for cancer treatment. The technique involves delivering magnetic nanoparticles (MNPs) into tumors, then activating the MNPs using an alternating magnetic field (AMF). The AMF generating system produces not only a magnetic field, but also an electric field. The electric field penetrates normal tissue and induces eddy currents, which result in unwanted heating of normal tissues. The magnitude of the eddy current depends, in part, on the AMF source and the size of the tissue exposed to the field. The majority of in vivo MNP hyperthermia therapy studies have been performed in small animals, which, due to the spatial distribution of the AMF relative to the size of the animals, do not reveal the potential toxicity of eddy current heating in larger tissues. This limitation has posed a nontrivial challenge for researchers who have attempted to scale up from a small animal model to clinically relevant volumes of tissue. For example, the efficacy limiting nature of eddy current heating has been observed in a recent clinical trial, where patient discomfort was reported. Until now, much of the literature regarding increasing the efficacy of MNP hyperthermia therapy has focused on increasing MNP specific absorption rate or increasing the concentration of MNPs in the tumor; i.e. - improving efficacy at what is thought to be the maximum safe field strength and frequency. There has been a relative dearth of studies focused on decreasing the maximum temperature resulting from eddy current heating, to increase therapeutic ratio. This paper presents two simple and clinically applicable techniques for decreasing maximum temperature induced by eddy currents. Computational and experimental results are presented to understand the underlying physics of eddy currents induced in conducting, biological tissues and to leverage these insights for the mitigation of eddy current heating during MNP hyperthermia therapy. Phantom studies show that these techniques, termed the displacement and motion techniques, reduce maximum temperature due to eddy currents by 74% and 19% in simulation, and by 77% and 33% experimentally. Further study is required to optimize these methods for particular scenarios; however, these results suggest larger volumes of tissue could be treated, and/or higher field strengths and frequencies could be used to attain increased MNP heating, when these eddy current mitigation techniques are employed.

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Quantitative modeling of forces in electromagnetic tweezers

Cited by 22 publications

References 27 publications

Magnetic tweezers optimized to exert high forces over extended distances from the magnet in multicellular systems

Magnetic tweezers optimized to exert high forces over extended distances from the magnet in multicellular systems

Design and optimization of arrays of neodymium iron boron-based magnets for magnetic tweezers applications

Mitigation of eddy current heating during magnetic nanoparticle hyperthermia therapy

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