United States

Magnetorheological fluid (MRF) is a magnetic particle reinforced fluidic material, which is mechanical properties, such as stiffness and damping, can be controlled with the application of a magnetic field.&lt;sup&gt;1&lt;/sup&gt; Smart sensor and actuator can be fabricated for adaptive vibration control systems where mechanical properties can be controlled by the application of a magnetic field. Manufacturability of MR fluid systems using the additive manufacturing (AM) process has gained great attention to enable the geometrical design of the MR fluid in an elastic component.&lt;sup&gt;2&lt;/sup&gt; In this research, MR fluid was prepared by carbonyl irons which are 6 – 10 μm in diameter with silicon oil (40% volume fraction). Thermoplastic polyurethane (TPU) with shore hardness 60A was used as an elastomeric system. A 3D printer is used to produce cylindrical TPU elastomer with grid structure using 50 % infill (Figure 1a). The MR fluid was added into the TPU elastomer, followed by adding a sealing layer with 3D printing. An external magnetic field (0 and 7 kG) was applied along the sample longitudinal axis at the time of uniaxial dynamic testing with 10% pre-strain. The TPU-MRF samples were characterized via force-displacement tests conducted at 1 Hz under strain amplitudes of 2%. The MR effect on the dynamic stiffness is defined as the ratio of the dynamic stiffness under the maximum magnetic field to the dynamic stiffness in the absence of a magnetic field. Mechanical testing results with the magnetic fields show that the MR effect on the dynamic stiffness is 1.65. (Figure 2a). The area of the force-displacement curve at 7 kG is about 6.5 times larger than the result with 0 kG, indicating a significantly large change in damping property. Frequency was varied from 1 to 10 Hz and the force-displacement curve didn’t show significant changes, indicating that the performance of the TPU-MRF system doesn’t diminish with increased frequency. (Figure 2b)

![](https://assets.underline.io/uploads/markdown_image/1/image/19adad7fc103540f67a0f0d92653914f.jpg)

Figure 1 (a) Schematic diagram of a TPU-MRF sample fabrication (b) Image of TPU grid structure, TPU sample with and without MR fluid.

![](https://assets.underline.io/uploads/markdown_image/1/image/38dc14fab1586b1c5bfaea4cfc340707.jpg)

Figure 2 (a) Force-displacement curve of TPU-MRF with 0 and 7 kG. (2% strain) (b) Force-displacement curves of TPU-MRF with a different frequency of vibration at 7 kG. (3% strain)

2022 Joint MMM-INTERMAG

Encapsulations of Magnetorheological Fluids using 3D Printed Elastomeric Rectangular Cellular Structures

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

MMM 2022 is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a tutorial, and several special sessions. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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For tickets to the event, please register at the following link: https://magnetism.org/registration

Please register for the MMM 2022 conference to join the event.

MMM 2022

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

Magnetorheological fluid (MRF) is a magnetic particle reinforced fluidic material, which is mechanical properties, such as stiffness and damping, can be controlled with the application of a magnetic field.1 Smart sensor and actuator can be fabricated for adaptive vibration control systems where mechanical properties can be controlled by the application of a magnetic field. Manufacturability of MR fluid systems using the additive manufacturing (AM) process has gained great attention to enable the geometrical design of the MR fluid in an elastic component.2 In this research, MR fluid was prepared by carbonyl irons which are 6 – 10 μm in diameter with silicon oil (40% volume fraction). Thermoplastic polyurethane (TPU) with shore hardness 60A was used as an elastomeric system. A 3D printer is used to produce cylindrical TPU elastomer with grid structure using 50 % infill (Figure 1a). The MR fluid was added into the TPU elastomer, followed by adding a sealing layer with 3D printing. An external magnetic field (0 and 7 kG) was applied along the sample longitudinal axis at the time of uniaxial dynamic testing with 10% pre-strain. The TPU-MRF samples were characterized via force-displacement tests conducted at 1 Hz under strain amplitudes of 2%. The MR effect on the dynamic stiffness is defined as the ratio of the dynamic stiffness under the maximum magnetic field to the dynamic stiffness in the absence of a magnetic field. Mechanical testing results with the magnetic fields show that the MR effect on the dynamic stiffness is 1.65. (Figure 2a). The area of the force-displacement curve at 7 kG is about 6.5 times larger than the result with 0 kG, indicating a significantly large change in damping property. Frequency was varied from 1 to 10 Hz and the force-displacement curve didn’t show significant changes, indicating that the performance of the TPU-MRF system doesn’t diminish with increased frequency. (Figure 2b)

![](https://assets.underline.io/uploads/markdown_image/1/image/19adad7fc103540f67a0f0d92653914f.jpg)

Figure 1 (a) Schematic diagram of a TPU-MRF sample fabrication (b) Image of TPU grid structure, TPU sample with and without MR fluid.

![](https://assets.underline.io/uploads/markdown_image/1/image/38dc14fab1586b1c5bfaea4cfc340707.jpg)

Figure 2 (a) Force-displacement curve of TPU-MRF with 0 and 7 kG. (2% strain) (b) Force-displacement curves of TPU-MRF with a different frequency of vibration at 7 kG. (3% strain)

technical paper

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

Magnetic nanowires can be engineered using composition and shape, and by modulating both of these along their axes (10nm-100um) or their diameters (10-200nm). This talk will discuss applications of both single nanowires and arrays of vertically aligned nanowires in biomedical fields, such as nano-barcodes [1], and biolabels for cells and exosomes [2,3], nano-heaters for hyperthermia therapy and organ preservation [4], and biocomposites [5]. For most of these applications, the reversal mechanism of magnetization can play a critical role. For example, magnetic coercivity and remanence has been used for contact-free readout of nano-barcode signatures, and the motion of domain walls can limit heating. Magnetic reversal typically occurs by uniform precession and coherent rotation or by domain walls that are transverse or vortices. Here, a novel approach to decoding specific reversal signatures will be described via a fast modification of the first order reversal curve (FORC) technique, called the projection method. In addition to decoding, the method elucidates the mechanisms of reversal which is of interest to the fundamental understanding of nanomagnets and can lead to improved future devices, such as decoding using ferromagnetic resonance (FMR) [6]. By understanding the nanomagnetics, these nanowires have been used individually to isolate biospecies, such as cancer cells [2] and tumor-derived exosomes (TEXs) [3] for fundamental studies in medicine. As nanoscale objects, nanowires have also been suspended in cryopreservation agents to provide the rapid, uniform nanowarming needed to restore preserved tissues and organs [4]. The mechanical properties are also found to change in response to magnetic fields which can impact their applications [7]. Finally, by aligning nanowires vertically in bio-friendly polymers, applications such as internal band-aids can be coded or functionalized for personalized health care. This talk will focus on the measurement methods for each of the biomedical applications mentioned, and will relate these measurements back to the fundamental magnetization engineering of the cylindrical nanowires.

![](https://assets.underline.io/uploads/markdown_image/1/image/a968033564d55218858a02f4df8459f7.jpg)

By controlling the reversal behavior of magnetic nanowires, efficient nanowarming can be achieved. One future application is the uniform and rapid warming of cryopreserved tissues and organs, which will ethically extend the viability between donors and recipients.



Bioapplications of magnetic nanowires: barcodes, heaters, biocomposites

Magnetic fluid hyperthermia is a promising cancer therapy in which magnetic nanoparticles (MNPs) act as heat sources activated by an external AC magnetic field. The MNPs, located near or inside the tumor, absorb energy from the magnetic field and then heat up the cancerous tissues [1]. However, during a hyperthermia treatment, it is crucial to control the temperature of different tissues: the desired therapeutic effect is not achieved with too low temperature. On the contrary, an excessive temperature increment can produce undesired damage [2]. Nevertheless, the current conventional thermometry in magnetic hyperthermia presents some important technical problems. For example, the widely used optical fiber thermometers only provide the temperature in a discrete. Moreover, surgery is required to locate these probes in the correct place. In this scope, we propose here a non-invasive method to measure the temperature of a MNP sample. The approach is based on the thermal dependence of the high order harmonic phases of the MNP dynamic magnetization. The method is non-invasive and it does not need any additional probe or sensor attached to the MNPs. In addition, this method has the potential to be used to map the spatial distribution of the temperature [3]. In the present work, a previously tested lab-made AC magnetometer [4] was used to study the variation with temperature of high order harmonics (3rd , 5th and 7th) from iron oxide MNPs. These MNP samples are identical to those used in a previous work [5]. External AC magnetic fields typical from magnetic hyperthermia were chosen (40-550 kHz). The actual temperature of the sample (30-50 °C) was measured by optical fiber thermometry. I was observed that the high order harmonic phases vary with temperature in an almost linear manner (see figure 1a). Therefore, we propose here the measurement of the harmonic phases as a non-invasive method to obtain the sample temperature. In this scope, the temperature would be obtained via previous calibration of the harmonic phase with temperature. In order to prove this concept an in-vitro experiment has carried out with water dispersed iron oxide MNPs. As it can be observed in figure 2, there is an error less than 0,5 °C.

![](https://assets.underline.io/uploads/markdown_image/1/image/e8e239b2390362d06b2ac387e5d3f1bd.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/03c17ce20f966d21290570234dd22127.jpg)

Harmonic Phases of the Nanoparticle Magnetization: an Intrinsic Temperature Probe

Magnetic hyperthermia (MH) is a nanotechnology-driven therapy that seizes the heat release of magnetic nanoparticles when exposed to an alternating magnetic field. It has already been and is currently trialed in clinical settings as adjuvant of chemotherapy and radiotherapy to successfully treat several types of tumors [1, 2]. In silico testing (computer simulations) allows us to mimic several clinical situations and to evaluate the treatment safety in terms of dosimetry and temperature rise, including possible hot spots due to eddy currents, in a cheap and fast way. MH has taken advantages of this virtual testing in its way towards personalized therapy. The versatility of the simulations to evaluate many clinical setups allows us to study the actual risks of the current exclusion criteria [1, 3]. Nowadays, bearing any kind of metallic object, orthopedic implants for example, constitutes a contraindication for the treatment. This is based on the knowledge obtained from MRI related studies, but there is an important lack in the literature about the quantification of these risks in the context of clinical MH. In this work, we use computer simulations to study the actual risks of potential MH patients carrying different orthopedic prosthesis, as well as the influence of the presence of this metallic object in the effective magnetic field reaching the nanoparticles site. We have considered different treatment setups varying tumor locations, implant types and materials to evaluate the temperature increase and the dosimetric values in the major tissue groups. These safety parameters have been included in a multi-criteria decision analysis to asses a risk index for each tissue group in every clinical situation analyzed [4]. Acknowledgements We acknowledge COST Action MyWave (CA 17115), NoCanTher project (grant agreement No 685795), Regional Government of Madrid under contract PEJD-2017-PRE/IND-3663, Spanish Ministry of Economy and Competitiveness through the grants MAT2017-85617-R, Ramón y Cajal RYC2018-025253-I, the “Severo Ochoa” Program for Centers of Excellence in R&D (SEV-2016-0686) and the support of NVIDIA Corporation through the GPU Grant Program with the donation of the Quadro P6000 GPU used in this work.

![](https://assets.underline.io/uploads/markdown_image/1/image/5b88302d4b166afa56c0e9833b44c1ec.jpg)

In Silico Safety Analysis of Magnetic Hyperthermia Treatments of Implant-Bearing Patients

Achieving homogeneous tumour heating is one of the most long-standing challenges in magnetic hyperthermia for cancer therapy. Clinical studies must meet strict safety regulations that require knowledge and control over the physical properties of the chosen magnetic nanoparticles [1]. Whereas it is well-established that the heat released by magnetic nanostructures is influenced by interparticle interactions, as of today there is no method to analyze heat exchange at single-particle level in interacting systems at nonzero temperature. This gap needs to be bridged so to harness nanoparticle magnetization dynamics for the sake of biomedical applications. Building on previous theoretical work [2], we present an equation to estimate the heat dissipation of individual, interacting particles at nonzero temperature that perform both field-induced and thermal switching. After validating this equation, we use the macrospin simulation tool Vinamax [3], to investigate a system of interacting particles with different anisotropies, as we showed in this contribution [4]. Our preliminary results indicate (see figure) that the generated heat becomes more homogeneously distributed at larger fields. We believe that this homogenization of the particle heating will help to achieve a more homogenized heating of tumors during hyperthermia treatments. The use of the proposed equation would simplify the selection process of optimum nanoparticle distributions leading to optimal tumour heating. Its simplicity and flexibility also allow it to be integrated into multi-scale, multi-physics simulations to accurately assess the magnetic hyperthermia therapy without impacting the overall computational time.

![](https://assets.underline.io/uploads/markdown_image/1/image/cd66b63a757f78697365ef1ca41b5bd1.jpg)

Figure: Heat generated in a system consisting of two interacting nanoparticles with different anisotropies. Both particles show switching behavior as soon as the excitation field amplitude overcomes their anisotropy barrier. The heat generation tends to become more uniform with increasing excitation fields.

Homogenization of Heating in Magnetic Hyperthermia Through Exploitation of Magnetisation Dynamics of Interacting Particles

Novel magnetic nanostructures (MNS) present a unique spin arrangement in the magnetic ground state, namely spin-vortex or synthetic antiferromagnetic state. MNS showed promising results in cell separation, as a contrast enhancing agents in MRI and in magneto-mechanically induced cell annihilation. The main advantages of magneto-mechanically induced cell annihilation are the usage of weaker magnetic fields with lower frequencies, as well as the need for a lower concentration of particles [1,2]. In this work, we developed one subset of biocompatible magnetic nanostructures that exhibit a spin-vortex state. First, micromagnetic simulations, using mumax3 of sub-micron iron discs, were performed for different interdot distance and aspect-ratio (thickness/diameter). By analysing the nucleation and annihilation fields, as well as the magnetic susceptibility, it was found that the (ideal) discs could be considered as isolated for interdot distances greater than twice the radius of the disc (2R) [3]. We also found that discs with an aspect ratio between 5 and 15 should sustain the vortex state in remanence [4]. Iron nano-discs in a vortex state, with a diameter of about 500 nm, were fabricated by electron beam evaporation on a Si substrate pre-patterned by interference lithography. Then, the magnetic vortex nano-discs were released from the substrate by chemical etching of a sacrificial layer. Subsequently, cell viability and uptake assays were performed in a human leukaemia monocyte cell line (THP-1) [5]. Several concentrations of nano-discs were studied by flow cytometry. As a result, the discs were internalized by the cells and found to be innocuous to them, in the absence of an external magnetic field.

Vortex nano-discs: from micromagnetic simulations to cancer cells internalization for magneto-mechanically induced damage applications.

Early detection of disease biomarkers, toxins, and infectious microorganisms is a major goal in modern health care, environmental control, and food safety to help contain and reverse illness or prevent contaminants from entering the food chain. To achieve this, materials scientists develop biosensing platforms whose requirements may differ depending on the application. When biosensing is a tool for screening or point-of-use applications (e.g., at the patient's bedside, in the industrial plant, or harsh environments), it must be fast, low-cost, and easy to use and transport. Lateral flow immunoassays (LFI) meet these requirements. They are paper-based tests, whose best-known example is the home pregnancy test, developed to detect high levels of human chorionic gonadotropin in urine. Thanks to advances in immunology, the method has been extended with great success to a large variety of targets, the most recent the rapid diagnostic tests for SARS-CoV2 [1]. There are some limitations for LFIA expansion, mainly their sensitivity and detection limit, which are not sufficient for some applications. Magnetic nanoparticles and magnetic detectors can be an excellent way to overcome such constraints. LFI (Fig. 1) uses a strip of nitrocellulose along which a liquid sample (urine, saliva, blood, serum, or plasma) can flow by capillary action. The target molecule is selectively captured on the strip by an immunological reaction and tagged by a reporter particle or enzyme that makes it detectable. For this purpose, plasmonic or fluorescent nanoparticles, visible with the naked eye, provide the positive/negative response. Although this is good enough for pregnancy, diagnoses frequently demand quantifying biomarkers, cells, bacteria, viruses, genes, or toxins. Quantification of color reporters involves image analysis, reflectance, or fluorescence measurements. However, these methods are sensitive to ambient light, humidity, and staining of the paper strip, which cause difficulties in calibration and reproducibility, especially in samples with a complex matrix [2]. To improve upon this, ferrite magnetic nanoparticles are now being used as alternative LFI reporters [3]. Although their bio-functionalization can be more challenging than for plasmonic particles, their advantages are clear for many applications. First, iron oxide nanoparticles provide a brownish color that is detectable by the naked eye or on a smartphone camera image. Magnetism can be used for pre-concentration or isolation of the target analyte from the sample matrix, and the magnetic reporters can be relocated closer to the visible membrane surface to increase their visibility. Second, magnetic nanoparticles produce a magnetic perturbation that a magnetic sensor can detect without optical interference [2]. Additionally, magnetic sensors report particles not only from the paper's surface but from the entire cross-section of the strip [4]. Finally, the magnetic signal from the nanotags does not decrease significantly with time. We review the principles and design of magnetic LFI and detail the requirements for magnetic nanoparticles to be used as reporters. We address the current methods used to read their signals that do not sacrifice the simplicity and low cost of the paper-based method. As proof of how magnetic LFI can be a useful analytical tool for biomedicine and food safety applications, we give examples of pneumonia biomarker detection (Fig. 2) and toxin quantification in foods and beverages [2], [4]. We acknowledge support from the Spanish Ministry of Science and Innovation (EIN2020-112354), the Principality of Asturias (IDI/2018/000185), and the Instituto Universitario de Tecnología Industrial de Asturias (SV-20-GIJÓN-1-22).

![](https://assets.underline.io/uploads/markdown_image/1/image/55e5c243e8177961bca7912e0981d64c.jpg)

Magnetic sensor reading out of a lateral flow strip for pneumolysin detection. The calibration yields a limit of detection of 0.2 ng of protein per mL of sample. Inset: Scheme (left) and image (right) of a magnetic lateral flow immunoassay.

Magnetic Techniques for Rapid Diagnostic Testing for Health Care and Environmental Monitoring

Magnetic Particle Imaging (MPI) is an emerging biomedical imaging modality designed to image distributions of superparamagnetic iron oxide nanoparticles (SPIONs) with high sensitivity1. In MPI, the continuous excitation of the SPION is provided by a sinusoidal magnetic field with rf frequencies. The spatial encoding of the signal is produced by selective saturating the SPION with a superimposed magnetic field gradient. Scanning the field-free region across the imaging volume senses the local concentration of SPION that allows a tomographic reconstruction of the tracer distribution inside the volume. SPIONs may serve as tumor markers2, which would allow the MPI device to be used for in vivo screening of cancer once translated to clinic. Several MPI devices have been developed but to date no translation to human has been done. Our single-sided field-free line (FFL) design, with the hardware to one side of the imaging volume, potentially enables nonrestrictive imaging in larger subjects, promoting utilities such as screening for cancer3. In our device, a selection field gradient is generated by a pair of co-planar elongated coils and an excitation magnetic field is generated by a single elongated drive coil4. The spatial encoding is provided by dynamical shifting the position of the FFL from altering the relative current between the two selection coils. Pertinent to this unilateral geometry the magnetic field profiles generated by the coils are inhomogeneous thus presenting a challenge to imaging. By implementing an algorithm of selection field compensation by applying a bias current to the drive coil we demonstrate that imaging can be performed. Here, we show the results from imaging simulations by means of specifically tailored filtered backprojection image reconstruction technique. In addition, we present first experimental results from 1D imaging of SPION phantoms (Fig.1) using ony moderate encoding field gradients thus providing proof of concept of our scanner.

![](https://assets.underline.io/uploads/markdown_image/1/image/c300fc352d7ab15af437594d347da963.jpg)

Fig. 1: (a) Projection signal of SPION phantom (gradient of 0.42 T/m); (b) reconstructed image of a phantom using a single projection and knowledge of the phantom’s shape; (c) phantom of undiluted Synomag-D SPION (20 mm separation with 1.2 mm diameter).

Imaging of a superparamagnetic iron oxide nanoparticle distribution by a single-sided magnetic particle imaging scanner

Transcranial magnetic stimulation (TMS)1,2 is clinically used in patients with depression2,3, while the effects of TMS-like magnetic fields on extracranial tissues are almost unknown4. Here, we explored effects of TMS-like repetitive magnetic stimulation (RMS) on metabolic activity of human hepatocellular carcinoma (HCC) and colorectal cancer (CRC) cells. The HuH7 (HCC) and HCT116 (CRC) cell cultures were treated using a TMS device “Magstim Rapid2” with an AFC70 coil. Intermittent RMS (iRMS) modes (4 trains of 150 pulses with frequency f=1, 5, 10, 20 or 40 Hz and equal intertrain intervals) and burst RMS (600 pulses delivered in trains, f=40 Hz/ bursts, f=3 Hz). The coil power output /magnetic field strength was (100% or 50%, B=0.8 T or 0.4 T, respectively) in burst modes or 100% in iRMS. The activity of SDG, an enzyme essential for energy production, was measured by MTT colorimetric assay in 24 h post-RMS. The control groups included: (1) untreated cells, (2) 20 min room temperature control, and (3) strong metabolic suppression by 100% DMSO solution. The main results are shown in Figures 1 and 2. Dashed red lines are CI95% for mean absorbance in the untreated control group; Abs is MTT assay product absorbance, a.u. In HuH7 cells, the tested protocols of RMS either did not change or stimulated the metabolic activity. However, correlation analysis indicated that the modes with higher frequency, burst pattern, and shorter cycles are more probable as suppressors of the liver cancer cells’ metabolism. In HCT116 cells, an iRMS mode 1B100 (f=1 Hz) induced a statistically significant decrease of metabolic activity, while high-frequency iRMS and burst modes stimulated it. In CRC, correlation analysis revealed the opposite to HCC trend of reduction of the metabolic rate at lower frequencies, intermittent PRMS, and the increase of it at high frequencies and burst modes. Our pioneering findings demonstrate the tumour-specific and mode-specific effects of re-purposed TMS technology on hepatic and colorectal cancer cells. The potential of RMS as adjuvant anti-cancer treatment will be discussed. We thank Medilink Australia for providing the “Magstim”.

![](https://assets.underline.io/uploads/markdown_image/1/image/3328edd15f9c1f201697574351fdeb65.jpg)

Figure 1. Effect of RMS on HuH7 cells.

![](https://assets.underline.io/uploads/markdown_image/1/image/181596c78a02d0fe7e97c8ea95446c42.jpg)

Figure 2. Effect of RMS on HCT116 cells.

TMS-like Magnetic Fields Modulate Metabolic Activity of Hepatic and Colorectal Cancer Cells

Early in 2021, we presented the quintuple AISI 1010 steel core coil (QCC) [1], a novel device for transcranial magnetic stimulation (TMS) able to produce focal stimulation in areas as small as 1 mm2. With it, we introduced the oriented control of the electric field (E-field) based on the path of the highest current density. This technique induces groups of peripheral and central charges of the same sign, whose electric repulsion restricts the central charges to propagate vertically below the central coil. As a result, an oriented central path of the highest current density is obtained, which focally passes through the target at a certain cortical depth, increasing the E-field on it. Now, modifying the elliptical cross-section of the QCC, we created a new figure-of-flower coil (FFC), in which the central coil (gynoecium) and peripheral coils (petals) are formed by round-cross-section multilayer solenoids with independent AISI 1010 cores. This configuration allowed us to induce controlled gradients in the current densities based on the independent modulation of every coil. This dynamically changes the orientation of the directional vector of the central path of the highest current density and -therefore- of the E-field. The technique, named Space-varying E-field Vector Modulation (SEVM), simultaneously varies amplitude, frequency, and/or phase of the coil currents, in combinations that produce a final direction, translatable to stimulation coordinates. Using ANSYS Maxwell software, we performed finite element simulations of the FFC, varying the number of petals between 4 and 10 (Fig.1). Each coil is made of 50 turns, wire diameter = 1 mm, and AISI 1010 steel cores of similar diameter and saturation at 2 T. Coil currents of 5kA at 2.5kHz were used in simulations over a 4-layer homogeneous spherical rat head model of D = 30 mm, with similar electromagnetic properties to those used to investigate TMS in rats [1-2]. The results show dynamic variations in size and position of the stimulated area (Fig.2) (including rotating patterns) with a fixed FFC, eliminating the need for multiple coils for multiple TMS targets. SEVM, QCC, and FCC are efforts towards the next generation of TMS devices with improved controllability.

![](https://assets.underline.io/uploads/markdown_image/1/image/cca2f8b66026c8ab2eaf526588f6468f.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/c5a155a592f213dcea28784ac110d774.jpg)

Oriented Control of the Stimulation Target During Transcranial Magnetic Stimulation Using Space-varying E-field Vector Modulation with Multi-Core Figure-of-Flower Coil

Oriented Control of the Stimulation Target During Transcranial Magnetic Stimulation Using Space-varying E-field Vector Modulation with Multi-Core Figure-of-Flower Coil

Introduction: Transcranial magnetic stimulation (TMS) can be affected by anatomical features. Therefore, neuroanatomy could influence corticomotor excitability after intermittent theta burst stimulation (iTBS). The relationship between iTBS aftereffects and neuroanatomy was investigated via motor evoked potentials (MEPs) and finite element analysis modeling (FEM) of TMS of MRI-derived head models. Targets were the biceps brachii and first dorsal interosseus (FDI) due to their relevance in activities of daily living. Experimental Details: Ten nonimpaired individuals participated, completing sham-controlled iTBS sessions (one each targeting the biceps and FDI cortical hotspots). MEPs were acquired at an intensity of 120% of resting motor threshold (RMT) while iTBS was delivered at 80% of active motor threshold, both via 70 mm figure-of-eight coils targeting the primary motor cortex. MEPs were recorded with surface electromyography. Each participant underwent an MRI of the head, and models were generated from T1 & T2 weighted images. Fiber tract geometry was extracted from diffusion tensor images for the biceps and FDI corticospinal tracts. Neuroanatomical parameters established were fiber tract surface area (FTSA), tract fiber count (TFC), and brain scalp distance (BSD) at the point of stimulation. Cortical electric field strength (EFS) was obtained by FEM of TMS of the head models. A linear mixed effects model was used to assess effects of these parameters and RMT on MEPs recorded after iTBS. RMT was included as a metric of the muscle's measured responsiveness to TMS. Results: iTBS targeting the biceps was faciliatory (p = 0.013), and dependent on FTSA (p &lt; 0.001) and TFC (p &lt; 0.001). There was no effect of iTBS on the FDI (p = 0.223) but individual changes in corticomotor excitability due to stimulation type scaled with RMT (p &lt; 0.001), EFS (p = 0.001), BSD (p = 0.004), and FTSA (p = 0.011). Conclusion: There were unique relationships between neuroanatomical parameters and empirical iTBS response. MRI-based measures of target-specific neuroanatomy impact how the motor system responds to iTBS, making MRI-based modeling potentially useful in selection of motor targets when designing iTBS protocols.

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