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The power released by magnetic nanoparticles (MNPs) submitted to an alternating driving field in the typical frequency range used in therapeutic treatments based on magnetic hyperthermia is studied using a rate-equation approach in which MNPs are modelled as double-well systems with randomly distributed easy axes.&lt;br/&gt;Taking into account the temperature dependency of MNP magnetization and anisotropy, a detailed picture of their hysteretic properties and of the resulting heating efficiency. The temperature variation in a host medium is then studied by solving a simple, radial Fourier equation with two typical boundary conditions. The time evolution of the temperature increment of the medium turns out to be strongly affected by the non-monotonic temperature dependence of the power released by NPs (see Figure 1a); the direct consequences on the heating efficiency make the determination of the specific loss power (SLP) and the resulting maximum temperature from the initial slope of the heating curve misleading.  An alternative, sounder method to measure the average power released by magnetic nanoparticles and the SLP is proposed [1].&lt;br/&gt;Another way of optimizing the performance of MNPs as heat generators consists in applying non-harmonic driving-field waveforms, with notable advantages with respect to the effects of harmonic magnetizing fields of same frequency and amplitude [2]. This improvement is related to the presence of fast, quasi-adiabatic transformations where the occupancy numbers in the two potential wells are virtually frozen, resulting in largely off-equilibrium magnetization states and in hysteresis loops with a greater area. In particular, changes of the inclination of the trapezoidal waveform’s lateral sides are also shown to induce controlled changes in the specific loss power generated by the activated nanoparticles (Figure 1b). Specific issues typical of the therapeutic practice of hyperthermia, such as the need for fine tuning of the optimal treatment temperature in real time, the possibility of combining sequential treatments at different temperatures, the ability to substantially reduce the heating transient in a hyperthermia treatment are properly addressed and overcome by making use of versatile non-harmonic driving fields of trapezoidal shape [3]. In the light of our results, features, methods, advantages and dangers of MNP-assisted precision nanomedicine are assessed in a more accurate way, and the efficiency of magnetic hyperthermia treatments is improved.

**References:**

[1] G. Barrera, P. Allia, P. Tiberto, Nanoscale, 2020,12, 6360.&lt;br/&gt;[2] P. Allia, G. Barrera, P. Tiberto, Phys. Rev. Applied, 2019, 12, 034041.&lt;br/&gt;[3] G. Barrera, P. Allia, P. Tiberto, Nanoscale Advances, 2020, 2, 4652.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/aceca2e127ef31688d27f6c19470c419.jpg)
(a) Left: Time evolution of the temperature increment. Right: released power by NPs as a fuction of temperature. (b) Temperature increment as a function of time for selected inclination of the trapezoidal waveform lateral sides.



INTERMAG 2021

 Heating efficiency of magnetic nanoparticles for magnetic hyperthermia: effects of temperature and driving-field waveform

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The great event is jointly organized by the Association for Computational Linguistics (ACL) and Asian Federation of Natural Language Processing (AFNLP).

The power released by magnetic nanoparticles (MNPs) submitted to an alternating driving field in the typical frequency range used in therapeutic treatments based on magnetic hyperthermia is studied using a rate-equation approach in which MNPs are modelled as double-well systems with randomly distributed easy axes. Taking into account the temperature dependency of MNP magnetization and anisotropy, a detailed picture of their hysteretic properties and of the resulting heating efficiency. The temperature variation in a host medium is then studied by solving a simple, radial Fourier equation with two typical boundary conditions. The time evolution of the temperature increment of the medium turns out to be strongly affected by the non-monotonic temperature dependence of the power released by NPs (see Figure 1a); the direct consequences on the heating efficiency make the determination of the specific loss power (SLP) and the resulting maximum temperature from the initial slope of the heating curve misleading. An alternative, sounder method to measure the average power released by magnetic nanoparticles and the SLP is proposed [1]. Another way of optimizing the performance of MNPs as heat generators consists in applying non-harmonic driving-field waveforms, with notable advantages with respect to the effects of harmonic magnetizing fields of same frequency and amplitude [2]. This improvement is related to the presence of fast, quasi-adiabatic transformations where the occupancy numbers in the two potential wells are virtually frozen, resulting in largely off-equilibrium magnetization states and in hysteresis loops with a greater area. In particular, changes of the inclination of the trapezoidal waveform’s lateral sides are also shown to induce controlled changes in the specific loss power generated by the activated nanoparticles (Figure 1b). Specific issues typical of the therapeutic practice of hyperthermia, such as the need for fine tuning of the optimal treatment temperature in real time, the possibility of combining sequential treatments at different temperatures, the ability to substantially reduce the heating transient in a hyperthermia treatment are properly addressed and overcome by making use of versatile non-harmonic driving fields of trapezoidal shape [3]. In the light of our results, features, methods, advantages and dangers of MNP-assisted precision nanomedicine are assessed in a more accurate way, and the efficiency of magnetic hyperthermia treatments is improved.

**References:**

[1] G. Barrera, P. Allia, P. Tiberto, Nanoscale, 2020,12, 6360. [2] P. Allia, G. Barrera, P. Tiberto, Phys. Rev. Applied, 2019, 12, 034041. [3] G. Barrera, P. Allia, P. Tiberto, Nanoscale Advances, 2020, 2, 4652.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/aceca2e127ef31688d27f6c19470c419.jpg)
(a) Left: Time evolution of the temperature increment. Right: released power by NPs as a fuction of temperature. (b) Temperature increment as a function of time for selected inclination of the trapezoidal waveform lateral sides.

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I. Introduction Metasurfaces can be seen as two-dimensional metamaterial, which has been attracting attention for researchers these years [1]-[3]. In the early years, metasurfaces was considered as special frequency selective surfaces, the structure may be split-ring resonator, complementary split-ring resonator [4] or isotropic elements [5]. However, most researchers regard the metasurfaces as a novel periodic structure, that is different from frequency selective surfaces [2]. And metasurfaces can be using in many different and important applications such as reflection surface [2]–[4], perfect absorber [6]–[7] and holographic imaging. Polarization conversion surfaces are commonly used electromagnetic surfaces, which can be designed into reflective surfaces or transmissive surfaces [3], [4]. A traditional method to design polarization conversion surfaces is using birefringent materials, which can change the polarization state of incident wave and wavefront phase in each cardinal planes. Recently, research discovered that birefringent materials can be realized by anisotropic frequency selective surfaces. For all types of polarization conversion surfaces, the type which can converts linear polarization (LP) wave into circular polarization (CP) wave, is the most popular one. This type of metasurfaces converts an incident LP wave into a CP transmitted or reflected wave. In recent years, linear-to-circular polarization converter has great application prospect in satellite [5]-[6] and communication systems [7]. In this paper, a novel linear-to-circular polarization converter based on meander-line metasurfaces is presented. The proposed metasurfaces is a two-dimensional periodic structure which consists of two metallic layers separated by dielectric substrate. The structure of each unit is meander-line which is printed on the top and bottom metallic layers. By controlling different phase for vertical and horizontal electric field components of incident wave, the phase difference is 90° between two components, after passing through the metasurfaces. The metasurfaces converts the LP wave to CP wave with the bandwidth of 10.5~11.5 GHz. The simulation results show the metasurfaces is valuable for polarization conversion application. II. Metasurfaces Structure Design and Analysis A. Metasurfaces Structure The geometry of the metasurfaces is presented in Fig. 1. The structure is composed of two metallic layers and one dielectric substrate. The structure of two metallic layers is shown in Fig. 1(b). And the size of the metasurfaces unit is 6.2*6.2 mm2. Two metallic layers are printed on Rogers RT5880 substrate with the relative permittivity of εr =2.2 and the thickness of h=0.762 mm. The structure of the top metallic layer is meander-line which have different resonance characteristics to vertical and horizontal electric field components. And the bottom metallic layer is exactly the same as top layer. The geometric parameters of the metasurfaces are a=6.2 mm, p=0.9 mm and g=0.65 mm. B. Analysis of Metasurfaces To the vertical electric field, the meander-line can be equivalent to a shunt inductance. But, to the horizontal electric field, the meander-line will be equivalent to a shunt capacitance. Therefore, the incident wave with the 45° linear polarized, it can be divided into vertical and horizontal electric field components. Next, by controlling the phase difference between two components to 90°, the structure will convert LP wave to CP wave. The bandwidth of the metasurfaces can be increased by cascading several metasurfaces screen, and the additional dielectric layer can improve the oblique incidence stability. Equivalent circuit model (ECM) can be used to analyse the physical principle of the metasurfaces. Fig. 2(b) shows the ECM of the metasurfaces for vertical electric field. And Fig. 2(c) shows the ECM of the metasurfaces for horizontal E-field. Thus, adjusting the phase difference between two electric field components (|φ1-φ2|) is 90°, and a linear polarized wave can be converted into circular polarized wave. III. Simulation Results and Discussions The proposed metasurfaces can realize LP to CP conversion. For different electric field components, the metasurfaces has different functions. Fig. 3 and Fig. 4 show the simulated transmission coefficient of the metasurfaces with vertical and horizontal electric field. And TABLE I shows the amplitude and phase of transmission coefficient at 10.5 GHz and 11.5 GHz. Under two polarization waves and oblique incidence angles from 0° to 30°, the phase difference of vertical component and horizontal component is approximately 90°, and the transmissivity is over 50%. The polarization conversion bandwidth covers 10.5~11.5 GHz. The simulation results show that the proposed metasurfaces can convert linear polarization wave to circular polarization wave, and has good angular stability. IV. Conclusion A novel linear-to-circular polarization converter based on meander-line metasurfaces with angular stability is presented. The linear-to-circular polarization conversion bandwidth of the metasurfaces is 10.5~11.5 GHz for the transmissivity is over 50%. By controlling different phase for vertical and horizontal electric field components of incident wave, the phase difference between two electric field components can be adjusted to 90° after passing through the metasurfaces. The simulation results show the metasurfaces is valuable for linear-to-circular polarization conversion application.

**References:**

[1] J. Zhu and G. V. Eleftheriades, IEEE Antennas Wireless Propag. Lett., Vol. 8, pp. 295–298 (2009) [2] C. L. Holloway, E. F. Kuester and J. A. Gordon, IEEE Antennas Propag. Mag., Vol. 54, no. 2, pp. 10–35 (2012) [3] M. Euler, V. Fusco and R. Dickie, IEEE Trans. Antennas Propag., Vol. 59, no. 8, pp. 3103–3106 (2011) [4] B. A. Munk, Frequency Selective Surfaces: Theory and Design. Hoboken, NJ, USA: Wiley, 2005. [5] N. Yogesh, T. Fu, F. Lan and Z. Ouyang, IEEE Photon. J., Vol. 7, no. 3 (2015) [6] H. L. Zhu, S. W. Cheung and K. L. Chung, IEEE Trans. Antennas Propag., Vol. 61, no. 9, pp. 4615–4623 (2013) [7] M. Euler, V. Fusco and R. Cahill, IET Microw., Antennas Propag., Vol. 4, no. 11, pp. 1764–1772 (2010)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/54a372f181515a2c10a19b2098af8982.jpg)
Fig. 1. Geometry of the metasurfaces

![](https://assets.underline.io/uploads/markdown_image/1/image/fc59776639339ff41728641086a181f9.jpg)
Table 1. Amplitude and Phase for Two Electric Field Components

 Linear-to-Circular Polarization Converter Based on Meander-Line Metasurfaces

In recent years wireless systems have experienced a rapid and wide expansion. Although these services provide an expressive amount of electromagnetic energy in the environment, a large amount of this energy is actually wasted. Despite the low electromagnetic power density available ambient, it is permanent and can be harvested, by using a rectenna, in order to supply small electrical devices, such as Wireless Sensor Networks (WSNs) used in the Internet of Things (IoT) devices. The RF-based energy harvesting technology is especially suitable to power WSNs because if a compact rectenna is used it can be completely integrated in the distributed hosting sensors structure, reducing its cost, maintenance and environmental impact. The contribution of this work is to present a compact rectenna, which employs a patch antenna with a Metamaterial Unit Cell (MUC) as grounding plane, called Metamaterial Antenna (MA). The proposed rectenna is composed of a square patch antenna with a MUC operating as grounding plane and a double voltage rectifier circuit. Both were built by using a double-sided copper fiberglass substrate, FR-4, with thickness t=1.5mm and characterized relative electric permittivity εr=4.15 and tangent of losses δ=0.026. The initial antenna geometry was defined by using transmission line theory. The MUC geometry, composed of a Complementary Split Ring Resonator (CSRR) [1]-[2], was designed and optimized by using Computer Simulation Software (CST®) in order to obtain the value εr&lt;0 in 2.45GHz. Then, the antenna geometry was optimized together the obtained MUC geometry in order to find values of S11&lt;-10 dB in the range from 2.4 to 2.5GHz. The final topology of the optimized MA is shown in Fig. 1(a) and 1(b). A Conventional Antenna (CA), Fig. 1(c), with a perfect conductor grounding plane, also was designed and optimized by using the same goal of the MA, in order to process comparisons. The obtained results for CA and MA are 6.69dBi and 3.01dBi (simulated directivity) and -24.93dB and –20.58dB (measured S11 parameter), respectively. The rectifier circuit is composed of an open stub for impedance matching, a schottky diode HSMS-2852 and two 100uF capacitors. It was projected and optimized by using Advanced Design Software (ADS®) in order to obtain values of S11&lt;-10 dB in 2.45GHz for input power Pin= -20dBm. In order to experimentally evaluate the proposed rectenna performance it was positioned at a variable distance d from an internet router and a 10 kW resistive load was fed. The values of the measured voltage on the load (VL) are presented in Fig. 2. As can be observed the energy harvested by CA and MA rectennas is enough to supply low consumption loads, such as WSNs. As expected, CA is able to harvest more energy than MA, once it is more directive and larger (3.19 times bigger). However, since MA is more compact it can be more easily incorporated in the WSN structure. In the full paper, rectenna association results will be presented.

**References:**

[1] Y. Lee, Y. Hao, Characterization of microstrip patch antennas on metamaterial substrates loaded with complementary split-ring resonators, Microwave and Optical Technology Letters, vol. 50, no. 8, pp. 2131-2135, Aug. 2008. [2] P. D. Tung, P. H. Lam, N. T. Q. Hoa, A miniaturization of microstrip antenna using negative permitivity metamaterial based on csrr-loaded ground for wlan applications, Journal of Science and Technology, vol. 54 (6), pp.689-697, 2016.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/06e870b121ce4a323eef3a72c9a461aa.jpg)
Figure 1. Antennas Geometry: (a) MA, (b) MUC grounding plane and (c) CA.

![](https://assets.underline.io/uploads/markdown_image/1/image/cf2c1cf9b4f4b95ba3541d894bef05a6.jpg)
Figure. 2. Output voltage for CA and MA rectennas.

 Design of a Rectenna with Metamaterial Grounding Plane

1. INTRODUCTION A variety of smart materials have been focused on a broad range of engineering applications. Among several kinds of smart materials, magnetorheological (MR) fluids inducing a reversible change in rheological behavior under an external magnetic field are suspensions of soft-magnetic particles randomly dispersed in a non-magnetic liquid medium [1]. MR fluids enable rapid switching and proper control between a liquid-like and a solid-like structure by controlling the magnetic field strength. Soft-magnetic carbonyl iron (CI) microspheres have been extensively studied as a major material in MR fluids due to their appropriate particle size and magnetic properties but possess a serious sedimentation problem due to their high particle density [2]. On the other hand, spinel ferrites can be a good alternative to CI particles because of their low density [3]. In particular, spinel zinc ferrite of super-paramagnetic behavior with high magnetic susceptibility, saturation magnetization, low coercivity, and low remanent magnetization is seen as a promising candidate for the use as a dispersed particle in MR fluids [4]. In this work, ZnFe2O4 particles were coated with polyindole (PIn), a conducting polymer with high thermal stability, redox activity, and stable degradation rate [5]. By combining an inorganic with a conductive polymer, the density was lowered, showing better sedimentation improvement. Furthermore, these particles can be also responsive under an applied electric field strength in addition to magnetic fields. 2. EXPERIMENT ZnFe2O4 nanoparticles were synthesized by a solvothermal method, and the PIn was followed to be coated as a shell onto the core ZnFe2O4 nanoparticles during oxidation polymerization. A proper amount of ferric chloride hexahydrate and zinc chloride were mixed in ethylene glycol solvent by magnetic stirring. Sodium acetate and polyethylene glycol 400 were slowly poured into the solution. The vigorously stirred mixture was placed in an autoclave and heated at 200 °C for 12 h. After that, the product was washed several times and dried to obtain particles. In the next step, ZnFe2O4 was coated by a polymerization process of indole monomer using ammonium persulfate as an initiator. The final particles were collected using an external magnet. For rheological analysis, a smart fluid responding to both magnetic and electric fields was prepared by dispersing the synthesized ZnFe2O4/PIn particles in silicone oil (100cSt, 5 vol%) under sufficient sonication. Morphology and chemical elements of the ZnFe2O4/PIn were examined by the field emission transmission electron microscope in combination with an energy-dispersive X-ray spectroscopy, respectively. Rheological properties of the MR fluid were measured using a rotational rheometer via either a parallel-plate geometry under the magnetic field or a concentric cylinder geometry under the electric field. 3. RESULT AND DISCUSSION Figure 1 shows the FE-TEM image and line scan profiles of core/shell structured ZnFe2O4/Pin particles. The main elements of ZnFe2O4 were found abundantly in the center of the particle, and C was confirmed as the main element on the outside of the particle. This result definitively demonstrates that the particles consist of ZnFe2O4 as the core material and PIn composed of C and N as the shell material. In addition, as the detection amount of the core elements increased gradually toward the center of the line drawn along the particle diameter for line scan, it was clearly revealed that the ZnFe2O4 core had a spherical morphology. Figure 2 shows the shear stress as a function of shear rate for ZnFe2O4/PIn based on MR fluid under various magnetic field strengths up to 239 kA/m. Without the magnetic field strength, shear stress of MR fluids increased in proportion to shear rate showing a Newtonian fluid-like behaviour, but as the magnetic field was applied, shear stress was relatively maintained within a certain shear rate range and displayed non-Newtonian fluid-like behaviour. When the magnetic field strength was increased, the interaction between magnetic particles was formed more strongly compared to the hydrodynamic force, resulting in a strong chain-like structure of the particles leading to an increase in yield stress. The solid lines in Figure 2 were fitted by Herschel-Bulkley model expressed as τ=τ0+KÝn to explain the rheological behaviour of non-Newtonian fluids [6]. In the given model, τ0 is the yield stress of materials, K is the consistency factor and n is the flow behaviour index. The n of pseudo-plastic materials is generally known to be between 0 and 1. [7]. The chain-like structure of ZnFe2O4/PIn particles formed by the magnetic field is destroyed as the shear rate increases, resulting in a shear thinning behaviour. In addition to steady shear test, dynamic test was also performed to examine dynamic moduli under a magnetic field strength. Rheological properties of this smart fluid under an applied electric field strength were further tested to confirm the dual characteristics of the synthesized ZnFe2O4/PIn particles.

**References:**

[1] J. S. Oh and S. B. Choi, J. King Saud Univ. Sci., 29, 390 (2017). [2] B. Sim, H. S. Chae and H. J. Choi, Express Polym. Lett., 9, 736 (2015). [3] G. Wang, Y. Ma and Y. Tong, J. Intell. Mater. Syst. Struct., 28, 2331 (2017). [4] Y. Xu, D. Sun and H. Hao, RSC Adv., 6, 98994 (2016). [5] I. H. Park, S. H. Kwon and H. J. Choi, J. Magn., 24, 155 (2019). [6] G. Mullineux, Appl. Math. Model., 32, 2538 (2008). [7] C. H. Jeon and B. R. Hodges, Nat. Hazards Earth Syst. Sci., 18, 303 (2018).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/2c3c113e26171b2b321fc07d45e846b8.jpg)
Fig. 1 FE-TEM image of ZnFe2O4/PIn particle

![](https://assets.underline.io/uploads/markdown_image/1/image/43de2fa4ee266f281b0fd900148b2608.jpg)
Fig. 2 Shear stress curve of ZnFe2O4/PIn particle based MR fluid under various magnetic field strengths

 Fabrication of Polyindole Coated Zinc Ferrite Particles and Their Dual Rheological response under Magnetic and Electric Fields

1. INTRODUCTION While magnetorheological (MR) fluids consisting of soft-magnetic particles in non-magnetizable carrier fluid draw a huge attention with their active tune-ability under a magnetic field strength, electro/magnetorheolocial (E/MR) fluids prepared with conducting polymer and magnetic particle composite particles dispersed in a non-conducting carrier fluid exhibit a dual response under both magnetic and electric fields. The smart dual electro/magneto-responsive characteristics of fine tuning and the quick response make them appropriate candidates in wide engineering areas such as clutches, optical finishing systems, medical therapies, actuators, haptic master, micro-fluidic control which have been already adopted separately for either ER fluids or MR fluids [1]. Meanwhile, soft-magnetic carbonyl iron (CI) particles have been widely used in MR fluids, but possess several disadvantages such as their high density and low dispersion stability. Therefore, spinel ferrites with low density and sufficient magnetic behavior are also introduced as a new family of MR materials [2]. In this work, ZnFe2O4, a magnetic particle constituting the core, was synthesized in a spherical shape using the solvothermal method, and poly(diphenylamine) (PDPA), which has low density and suitable electrical conductivity, was coated through radical polymerization. ZnFe2O4/PDPA based MR fluid showed appropriate MR property due to the spinel structure of ZnFe2O4. Furthermore, it showed improved sedimentation stability because of the advantage of low density of particle [3]. 2. EXPERIMENT First of all, ZnFe2O4 was synthesized using the surfactant-assistant solvothermal method. 1.35g iron chloride hexahydrate (FeCl3.6H2O) (5mmol) and 0.34g Zinc chloride (ZnCl2) (2.5mmol) were added to 50ml of ethylene glycol, and agitation was performed using a magnetic bar. After stirring, sodium acetate of 3.6g (40mmol) as a weak base and polyethylene glycol 400 (1g) as a surfactant were slowly added to the prepared solution. After vigorously stirring the solution for about 1 h, it was transferred to a Teflon-lined stainless-steel autoclave, and the reacted at 200 for 12 h. After making the reactor to room temperature, black solid particles were obtained using magnets after several washing with ethanol and DI-water. Then, 0.75g ZnFe2O4 was added to a mixture of methanol and water 40ml/10ml, and then reaction was proceeded at 40 and 1ml of N-[(3-trimethoxysilyl)-propyl] aniline was added as a grafting agent, followed by stirring for 18 h. Modified ZnFe2O4 and diphenylamine (3mmol) were mixed with ethanol. Subsequently, HCl 1M 40ml was added and stirred at 5 for 30 min. Ammonium persulfate (4mmol) dissolved in 1M 10ml HCl was added to the solution, the reaction was carried out for 5 h, and the particles were obtained using a magnet and dried for 12h. 3. RESULT AND DISCUSSION TEM image of Fig. 1 for ZnFe2O4/PDPA particle synthesized shows that the size of synthesized material is about 300nm with its morphology of a core-shell structure. The thickness of the shell is about 14 nm, and by coating the polymer on the magnetic particle, the density of the particle is reduced, and the dispersion stability of its MR fluid can be improved. Figure 2 shows flow curve of MR fluid made by dispersing the synthesized core-shell particles in 100 cs silicone oil at 5 vol%. From the controlled shear rate test mode, the shear rate from 0.01s-1 to 200s-1 was applied, depending on the strength of the magnetic field up to 205kA/mm. In the absence of a magnetic field, the fluid behaves like a Newtonian fluid in which the shear stress increases lineary as the shear rate increases. This is because MR fluid behaves like a simple particle suspension following an Einstein equation behavior. On the other hand, when an external magnetic field is applied, the shear stress rises sharply and shows a certain specific yield. This behavior is due to the fact that the attractive force between magnetic particles becomes strong when a magnetic field is applied, and the particles form a chain-like structure in the fluid. As the strength of the magnetic field increases, the attractive force between particles also increases, so the shear stress value increases gradually [4]. To fit the curves representing non-Newtonian fluid properties of MR fluid, a solid line was drawn using the Herschel-Bulkley equation, which is expressed as τ=τ0+KÝn. Here, τ means shear stress and τ0 is the yield stress exhibited by the chain-like structure when a magnetic field is applied. The K value of the consisteny index refers to the viscosity of the fluid and n is the power law index [5]. As the solid lines fit well with the graph, it can be seen that Herschel-Bulkley equation interprets the behavior of MR fluid well over a wide shear rate range. In this work, we synthesized a core-shell structured magnetic particles and conducting polymer and confirmed MR properties such as yield stress and shear thinning under external magnetic field along with ER characteristics under an applied electric field.

**References:**

[1] M. T. Ramesan, Adv. Polym. Technol., 302, 21362 (2013) [2] G. S. Wang, Y. Y Ma, Yu Tong and J. Intell. Mater. Syst. Struct., 28, 2331 (2017) [3] J. H. Lee, H. J. Choi, Colloid Polym. Sci., 296, 1857 (2018) [4] Y. Z. Dong, H. J. Choi, IEEE Trans. Magn., 54, 4601004 (2018) [5] M. Zubieta, S. Eceolaza and M. J. Elejabarrieta, Smart Mater. Struct., 18, 095019 (2009)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/05763e8056ec6cf88c5358ef8935fc89.jpg)
Fig 1. TEM image of core shell structure coated with PDPA on ZnFe2O4

![](https://assets.underline.io/uploads/markdown_image/1/image/754b14d10e8ee19da44d563737667334.jpg)
Fig 2. Flow curve of ZnFe2O4 coated with PDPA under the external magnetic field of ZnFe2O4 coated with PDPA

 Fabrication and shear response of conducting polymer coated zinc ferrite particles under magnetic/electric field

During the last decade, iron borate FeBO3 based crystals have been attracting an increased interest of scientific community, mainly for the following reasons: (i) these materials can be applied in modern technical devices, e.g. serving as sensitive instruments for measuring magnetic field, pressure, etc., or as monochromators for use with synchrotron radiation [1]; (ii) mixed iron gallium borate FexGa1-xBO3 crystals are quite suitable objects for studying properties of trigonal weak ferromagnets with zero orbital moment [2, 3]. We have recently shown that with decreasing iron contents the magnetic state of FexGa1-xBO3 crystals shows a gradual passage from easy-plane weak ferromagnet to diluted paramagnet, passing through magnetic clusters at intermediate iron contents [2]. Thus, by isomorphously substituting paramagnetic Fe3+ ions in iron borate, FeBO3, by diamagnetic Ga3+ ions one can synthetize a series of isostructural single crystals allowing not only fine-tuning their magnetic characteristics, thus creating new materials with sought-for properties, but also studying the nature of magnetic state, magnetocrystalline anisotropy, etc. [2, 3]. Such crystals can be synthesized using well-known flux growth technique [4]. However, obtaining high quality FexGa1-xBO3 crystals in wide range of substitutions, 0≤x≤1, has required many trials in order to find out optimal regimes for crystallization at different concentrations and a considerable improvement of the standard synthesis technique [1]. In this work, we have focused on microscopic characterization of certain magnetic properties of FexGa1-xBO3 borates by considering in detail intracrystalline interactions in these materials. The density of the magnetic energy for FexGa1-xBO3 crystals can be expressed as follows [5]: E=1/2 Em2+D (lxmy-lymx)+ 1/2 alz2+d (3lx2-ly2) lylz+e (lx4-14lx2ly2+ly4) (lx2-ly2) (1) where m and l are reduced ferromagnetic and antiferromagnetic vectors, D and E are the Dzyaloshinskii-Moriya and exchange constants, is the uniaxial anisotropy constant, and d and e are the basal anisotropy constants. Different mechanisms responsible for the magnetic properties have different dependences on the concentration of paramagnetic ions and temperature; therefore, experimental studies of the latter dependences and a subsequent modelling based on eq. (1) could, on the one hand, single out dominating mechanisms of the magnetic transitions observed and, on the other hand, get better insight in the nature of intracrystalline interactions in trigonal weak ferromagnets. Since the Dzyaloshinskii-Moriya and exchange constants characterize pair interactions between paramagnetic ions, we have assumed that the corresponding microscopic constants for a pair of Fe3+ ions in mixed crystals remain the same as those in unmixed crystal. Thus, we can express both constants for mixed iron-gallium borates through the macroscopic D and E constants for unmixed iron borate and obtain an analytical expression of the macroscopic constants for mixed crystals. We have put forward a computer code modelling the diamagnetically diluted crystal lattice by the Monte-Carlo technique [6] and implementing a summation, first, over the nearest-neighbouring Fe3+ for a reference Fe3+ ion and, next, over all sites occupied by Fe3+ ions. As a result, we have shown that the dependences of both D and E constants on x (at 0 K) follow a parabolic law. In calculating the magnetocrystalline anisotropy for FexGa1-xBO3 crystals one should take into account only crystal field and dipole-dipole contributions. Indeed, the 3d5 electronic configuration of Fe3+ has zero orbital moment; therefore, the exchange energy in a good approximation is isotropic [7]. Recently we have calculated the dipole-dipole interaction energy in the model of “extended dipoles” [8], having non-negligible dipole size. Unlike the point dipoles, the extended dipoles bring a non-zero dipole-dipole contribution to the basal magnetocrystalline anisotropy, and earlier we have evaluated it for unmixed iron borate [3]. In the model of extended dipoles, a calculation of the Ampérian current, i.e., a circular current loop of a radius R, results in two possible sizes of the magnetic dipole represented by a Fe3+ ion: R1 = 0.2189 and R2 = 0.0797 Å [3]. In this work, we have applied the model of extending dipoles to evaluating the dipole-dipole contributions to the magnetocrystalline anisotropy constants of mixed iron-gallium borates. To this purpose, we have put forward a computer code implementing the lattice-sum method [3] and modelling the diamagnetically diluted crystal lattice using the Monte Carlo technique in the same way as in calculating D and E constants, vide supra [6]. Resultantly, the dependences on x of the dipole-dipole contribution to the magnetocrystalline constants for FexGa1-xBO3 crystals have been obtained, see Figures 1 and 2. The dipole-dipole contributions to the basal anisotropy constants have been calculated at 0 K for different x using both possible effective dipole sizes, R1 and R2, determined for Fe3+ ions. This work was partially supported by the V.I. Vernadsky Crimean Federal University Development Program for 2015-2024 Grant no. VG04/2019; and by the RFBR projects Grants No. 19-32-90054 and 18-42-910008.

**References:**

1. E.S. Smirnova, N.I. Snegirev, I.S. Lyubutin et al., Acta Cryst., Vol. B76, p. 1100 (2020) 2. K. Seleznyova, M. Strugatsky, S. Yagupov et al., J. Appl. Phys., Vol. 125, p. 223905 (2019) 3. M. Strugatsky, K. Seleznyova, S. Yagupov et al., J. Magn. Magn. Mater., Vol. 442, p. 417 (2017) 4. S. Yagupov, M. Strugatsky, K. Seleznyova et al., Appl. Phys. A, Vol. 121, p. 179 (2015) 5. E.A. Turov and N.G. Guseinov, Soviet Physics JETP, Vol. 11, p. 955 (1960) 6. L. Devroye, Non-Uniform Random Variate Generation, Springer, 843 pp. (1986) 7. J. Kanamori, in: Magnetism, eds., G.T. Rado, H. Suhl, Acad. Press, Vol 1, pp. 127 (1963) 8. K. Seleznyova, M. Strugatsky and J. Kliava, Eur. J. Phys., Vol. 37, p. 025203 (2016)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/c80785883160de382473c88ba885d8ea.jpg)
Fig.1 Dipole-dipole contribution to a vs. x in FexGa1-xBO3 crystals at 0 K.

![](https://assets.underline.io/uploads/markdown_image/1/image/530198f9d062fa644639968bd67c1f2b.jpg)
Fig.2 Dipole-dipole contributions to d (left) and e (right) vs. x in FexGa1-xBO3 crystals, calculated for two possible effective dipole sizes: R1 (dashed curves) and R2 (dash-dotted curves) at 0 K.

 Modelling of the Intracrystalline Interactions in Trigonal Weak Ferromagnets with Zero Orbital Moment

Magnetic Material for Electrical Vehicle Recent trends of magnetic mate- rial research about electrical motor drive system for electrical vehicle are shown in this lecture for magnetic material and electrical researcher and engineers. Motor drive system consists of electrical motor and power elec- tronics circuit, and magnetic material are used and an important role in both equipment. The purpose of the electrical motor is to make an electromag- netic torque to drive a vehicle based on Maxwell stress equations. The power electronics circuit such as inverter or DC-DC converter is an electrical power source in controlling the variable voltage and/or variable frequency based on a switching operation of power semiconductors [1]. Soft magnetic mate- rial is used in the stator core and the rotor core in the electrical motor, and permanent magnet is used in the field part of the motor. The electromagnetic torque is almost proportional to square of magnetic flux density. So higher magnetic flux density is required to obtain higher electromagnetic torque. Soft magnetic material is much useful to obtain a higher magnetic flux density in smaller electrical current, which is supplied by the power elec- tronics circuit. Magnetic Material for Motor Most of the electrical motor uses an electrical steel with a few % silicon due to high performance of magnetic characteristics with low price. Mechanical stress in manufacturing the motor core, magnetic non-linearity, and magnetic anisotropy, magnetic hysteresis, magnetic flux distribution base on grain shape and orientation, magnetic vector property of magnetic field and magnetic flux density, higher harmonics components derived from the slot shape of the stator core as well as the power electronics circuit base on the switching operation are main properties of the electrical steel to be discussed and researched. Mutual interaction between the power electronics circuit and the magnetic material or motor are often observed [2, 3]. To reduce the motor core loss, low iron loss magnetic materials such as amorphous and nano-crystal material are reported to be applied to the motor core [4, 5]. The details are shown in the presentation. Hard magnetic material is used in the field of the motor due to no electrical current supply and no slip ring. So most of electrical vehicle are driven by permanent magnetic synchronous motor, because the higher efficiency and the downsizing of the electrical motor can be realized. Due to almost the same electrical conductivity of the NdFeB permanent magnet as the stainless steel, the temperature of the permanent magnet increases and the demagnetization phenomena occur. To avoid it, rare earth problem generates such as Dy or so. Weakening field control scheme is used in the PM motor for the high speed rotation. So higher coercive force is required for the permanent magnet. Magnetic Material for Power Electronics In the electrical vehicle, variable speed operation is required to move from a starting point to a stopping point. So variable speed control is required for electrical motor. Variable voltage and variable frequency are required for the power source of the electrical PM motor, due to the electromotive force theory and the synchronous condition of the mechanical rotational speed and the magnetic rotation speed. The power electronics technology is possible to be realized by the switching operation of the power semiconductors. So the higher frequency operation can be realized by the high performance power semiconductor such as IGBT or GaN-FET or SiC-FET devices because it realizes the downsizing of the power electronics circuits. However, the bottle neck technology for the realization is a soft magnetic material in high frequency and high power operation. Nowadays, the hindrance for the reali- zation of power electronics technology might be said to be a high frequency magnetic material in a point of view of the downsizing, high efficiency and the low cost [6-8]. Ferrite is mainly used in the high frequency magnetic material up to 100 MHz or so. However, it has the low saturation magneti- zation such as 0.4 or 0.5 T, the thermal runaway phenomena of self-heating in high temperature, and the weakening of mechanical vibration which often occurs in automobile car. Metal material such as iron or steel is possible to solve the problems. Iron powder has good performance as the high satu- ration magnetization, no thermal runaway phenomena and no problem for the mechanical vibration. However, magnetic permeability is relative small due to the demagnetization in a small particle. So, as far as high frequency transformer which is quite useful for electrical circuit insulation, leakage magnetic flux may increase and then the low loss transformer might be diffi- cult. Thin plate shape of the steel or iron has no demagnetization phenomena, and then high magnetic permeability can be realized. Micro-meter order steel is trial manufactured by sputtering method, rolling or so [9]. The details will be shown in the presentation at that time.

**References:**

(1) Editor and author: Keisuke Fujisaki, “Magnetic Material for Motor Drive System - Fusion Technology of Electromagnetic Fields-”, Material Engineering, Springer-Nature, 2020. (2) N. Denis, M. Inoue, K. Fujisaki, H. Itabashi, T. Yano, “Iron Loss Reduction of Permanent Magnet Synchronous Motor by Use of Stator Core Made of Nanocrystalline Magnetic Material,” IEEE Transactions on Magnetics, Volume: 53, Issue: 11, 8110006, 2017. (3) S. Okamoto, N. Denis, M. Ieki, K. Fujisaki, “Core Loss Reduction of an Interior Permanent Magnet Synchronous Motor Using Amorphous Stator Core,” IEEE Transactions on Industry Applications, vol.52, no.3, pp.2261-2268, May/June 2016. (4) K. Fujisaki, S. Liu “Magnetic Hysteresis Curve Influenced by Power-Semiconductor Characteristics in PWM Inverter,” Journal of Applied Physics, Vol. 115, 17A321, 2014. (5) A. Yao, K. Tsukada, and K. Fujisaki, “Investigating Iron Loss Properties in an Amorphous Ring Excited by Inverters based on Silicon and Gallium Nitride,” IEEJ Journal of Industry Applications, Vol. 7, No. 4, p. 321-328, 2018. (6) J. W. Kolar, Future Challenges for Research and Teaching in Power Electronics, Presentation held at the 14th Int. Conf. Optimization of Electrical and Electronic Equipment (OPTIM 2014), Brasov, Romania, May 22-24, 2014. (7) Tim Heidel, “ARPA-E Initiatives in High Efficiency Power Conversion,” APEC Plenary Session Ft. Worth, TX, March 14, 2014. (8) J.S. Glaser, et. al. “A 900 W, 300V to 50 V dc-dc power converter with 30 MHz switching frequency,” In Proc. Twenty-Fourth Annual IEEE Applied Power Electronics Conf. and Exposition APEC 2009, pp. 1121-1128, 2009. (9) J. Tanase, E. Tsuchida, K. Fujisaki, “Magnetic characteristics of 1µm-thick pure iron sheets for power electronics circuits with GaN devices," IEEE Intermag2020, CW-02, 2020.

**Images:**

 Magnetics of Motor Drive System for Electrical Vehicle



Rare earth elements (REE) are crucial for many applications including clean energy, transportation, high-tech devices, medicine, advanced manufacturing and military. The most important usage of REE by value is the NdFeB permanent magnet. Rare earths recycling was always presented as a negligible amount (&lt;1%) and the low price of REO was blamed for that. On the other hand, China has been recycling REE from magnetic scrap for over a decade and the amounts are growing. What are the main drivers of REE recycling in China vs the main prohibitors of REE recycling outside of China? What are the advancements in REE recycling from permanent magnets outside of China? What are the main feeds that are recycled and how can one drive an increase of REE recycling in the future?

**References:**



**Images:**





 Rare Earth Magnet Recycling: The Missing Link in a Circular Economy

Magnetism plays an instrumental role in biomedical applications and healthcare, both from the perspectives of devices and techniques. In particular, Magnetic Resonance Imaging (MRI, [1]) addresses the magnetization induced on the patients’ constituent matter when subject to a magnetic field, and exploits the time-varying signal resulting from the contribution of the ubiquitous hydrogen nuclei spins for high quality spatial reconstructions. At present, MRI is the only available medical imaging technique known to deliver high resolution images of deep biological tissues in vivo and without harmful ionizing radiation. However, MRI does not come without its own limitations. In particular, it is much more efficient at detecting soft tissues and fluids than hard, solid samples. This is due to the weak, short-lived signals emitted by the latter, by cause of dipolar magnetic interactions between neighboring spins in the sample, which constitute a noisy environment that decoheres the quantum nature of the MR signal. The environment’s contribution averages out for soft tissues, but not so for solids, where nuclei are approximately fixed with respect to each other in the laboratory reference frame. This explains the scarcity of useful (with diagnostic value) MR images of dental tissues [2-4], the hardest in the human body. Furthermore, the MRI scanners employed so far use static magnetic field strengths ranging from 4 to 12 T, which makes them large and expensive. At around 1 M$ per Tesla [5], this precludes their penetration in dental clinics. In this symposium, devoted to evaluating the transition of biomagnetic research from laboratory to clinical environments, we present a new, inexpensive approach to MRI of combined hard and soft biological tissues, with a view on dental applications [6]. We will show 3D reconstructions of human teeth (Figures 1 and 2), as well as a rabbit head and a cow femur, all obtained at a field strength of only 260 mT. These images are, to the best of our knowledge, the first featuring soft and hard tissues simultaneously at sub-Tesla fields, and have been acquired in a home-made special-purpose MRI scanner designed with the goal of demonstrating dental imaging at low field settings. We also present two recently patented sequences for efficient encoding of spatial information and image reconstruction: VIEWS (Volumetric Image Encoding Without k-Space) and MASSIF (Magic Angle Spinning of Spatially Inhomogeneous Fields). These are key players in the roadmap we envision to shorten scan times from several hours, as in our first prototype, to a few minutes, as desired for clinical applications.

**References:**

[1] Haacke, E. Mark, et al. Magnetic resonance imaging: physical principles and sequence design. Vol. 82. New York:: Wiley-Liss, 1999. [2] Weiger, Markus, et al. "High-resolution ZTE imaging of human teeth." NMR in Biomedicine 25.10 (2012): 1144-1151. [3] Idiyatullin, Djaudat, et al. "Dental magnetic resonance imaging: making the invisible visible." Journal of endodontics 37.6 (2011): 745-752. [4] Mastrogiacomo, Simone, et al. "Magnetic Resonance Imaging of Hard Tissues and Hard Tissue Engineered Bio-substitutes." Molecular Imaging and Biology (2019): 1-17. [5] Sarracanie, Mathieu, et al. "Low-cost high-performance MRI." Scientific Reports 5 (2015): 15177. [6] Algarín, José Miguel, et al. "Simultaneous imaging of hard and soft biological tissues in a low-field dental MRI scanner." Scientific Reports 10 (2020): 21470.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/6feb2d6202cc6897130f3a2a8eb5112c.jpg)
(a) Picture of the scanned rabbit head. (b) Picture of a rabbit skull. (c) Top: Single slices for 90 us dead time with PETRA; middle: the same slices for 1 ms dead time; bottom: difference between the above images.

![](https://assets.underline.io/uploads/markdown_image/1/image/1e40f4cf67c994af04ff3b7c6402f824.jpg)
(a) 2 dimensional slices of four human teeth embedded in a piece of pork ham (PETRA). (b) Photograph of the sample.

 Hard Tissue Magnetic Resonance Imaging with Fast Control of Intense Magnetic Fields

The median survival of glioblastoma, the main primitive brain tumor, 15 months. The progress of imaging, surgery, robotic, chemoradiotherapy, as well as last generation molecular biology and targeted therapy did not provide any curative strategies. Innovative therapies are warranted to increase our therapeutical efficacy. Magnetic nano and micro particles are widely studied for biomedical applications such as contrast agents for MRI, regenerative medicine, cell sorting, tissue engineering, protein purification, hyperthermia or magnetofection. For cancer therapy, Magnetic Particles (MP) offer new perspectives for untreated diseases such as glioblastoma. Indeed, new pharmacotherapies struggle to prove their efficacy while therapies based on physical effect, such as Tumor Treating Fields demonstrate promising results. An approach based on mechanical destruction of cancerous cells by low-frequency vibration of magnetic particles, that we call Treatment by Magneto-Mechanical Effect of Particles (TMMEP) has been studied for several years. Kim et al. first showed that they were able to reduce glioma cancer cells viability from 90% by applying a 20 Hz alternating field on cells incubated with permalloy microdisks. Master et al. put superparamagnetic iron oxide nanoparticles (SPIONs) on breast cancer cells and applied a 100 kA/m alternating magnetic field at 50 Hz for a total of 30 min, with 10 min on / 5 min off patterns. They demonstrated a reduction in cell viability up to 75%. Interestingly, they showed that healthy cells were less affected by the treatment because of different cell mechanical properties. A comparative study of cylindrical particles with different length and diameter was conducted by Wong et al. They showed that MP with smaller diameter have a better efficacy with about 75% of cell viability after application of a biaxial pulsed magnetic field thanks to 4 coils. In vivo study on an orthotopic model of glioblastoma was conducted by Cheng et al. In a preliminary approach, they injected cancerous cells mixed with disks microparticles in brain mice and showed a better survival of mice submitted to a daily exposition of a 1 T rotating magnetic field at 20 Hz for 1 h. In this work, we used permalloy microdisks submitted to a Rotating Magnetic Field (RMF) and optimized in in vitro assay the particle concentration, magnetic field amplitude, and duration of exposure. We demonstrate here a strong lethal effect of TMMEP in vitro. We conducted in vivo assay on an orthotopic model of glioblastoma on mice but could not demonstrate efficacy of the treatment. We explain this failure by a strong difference in cell mechanical properties between in vitro and in vivo assay. To face this difficulty, we propose an in vitro 3D model by the use of spheroids put in a gel which can then be treated as a tumor and enable to mimic particle injection and RMF exposure. We also developed a 3D gel model mimicking peri-tumoral invasion of glioblastoma cells. Similarly, to the spheroid model, no effect was observed on the tumor proliferating cell in the core of the tumor. Moreover, migrating cells outside the core were strongly altered in their migration by the mechanical stimulation. Indeed, the data in the literature that supported our approach to TMMEP are essentially in vitro experimental results and no evaluation of TMMEP had yet been performed on an in vitro 3D model. Only a few articles showed in vivo efficacy, but the only survival benefit has been obtained with particles injected at the same time as the cells. The use of spheroids and organoids for the study of cancer and its treatments is now booming. Taking into account the importance of mechanical properties in tumor development, this model, placed in between 2D cell culture and animal experiments, mimics the architecture and heterogeneity of the tumor microenvironment. Closer to the in vivo tumor environment, this technique enables to better optimize and test in vitro treatments before moving to the preclinical phase, thus reducing the number of animals used in medical research. Preclinical models have been also extensively questioned, poorly mimicking the human disease. We demonstrated that results obtained in 2D culture are not relevant for the in vivo situation. Similarly, classical animal models are also poorly relevant, harboring a few invasive cells in the peritumoral area that is the main driver for tumor relapse. The model developed in this study will be crucial to modelize potential effect of magnetic vibration. The anti-invasive properties of magnetic vibration discovered using this innovative model could be explained by the specificity of the cell cytoskeleton in the migrating machinery, potentially highly sensitive to mechanical impact. A new preclinical strategy is emerging using new models to detect potential therapeutical effect of nano-magnetic vibrations. Similarly, a new design of the clinical trials should be implemented using highly cognitive trials, multimodal imaging including mechanical imaging and in situ molecular and cellular analysis of the tumor after local delivery of magnetic particles and mechanical actuation. These new translational paradigms also warrant a rigorous ethical analysis.

**References:**

Cécile Naud, François Berger, Hélène Joisten et al. Cancer treatment by magneto-mechanical effect of particles, a review. Nanoscale Adv., 2020, 2, 3632. Jain KK. A Critical Overview of Targeted Therapies for Glioblastoma. Front Oncol. 2018;8(October):1–19. Kim D-H, Rozhkova EA, Ulasov I V, Bader SD, Rajh T, Lesniak MS, et al. Biofunctionalized magnetic-vortex microdiscs for targeted cancer-cell destruction. Nat Mater. 2010;9(2):165–71. Master AM, Williams PN, Pothayee N, Zhang R, Vishwasrao HM, Golovin YI, et al. Remote Actuation of Magnetic Nanoparticles for Cancer Cell Selective Treatment Through Cytoskeletal Disruption. Sci Rep. 2015;1(919):1–13. Zhang E, Kircher MF, Koch XM, Eliasson L, Goldberg SN, Renstrom E. Dynamic Magnetic Fields Remote-Control Apoptosis via Nanoparticle Rotation. ACS Nano. 2014;8(4):3192–201. Leulmi S, Chauchet X, Morcrette M, Ortiz G, Joisten H, Sabon P, et al. Triggering the apoptosis of targeted human renal cancer cells by the vibration of anisotropic magnetic particles attached to the cell membrane. Nanoscale. 2015;7(38):15904–14. Wong DW, Gan WL, Liu N, Lew WS. Magneto-Actuated cell apoptosis by biaxial pulsed magnetic field. Sci Rep . 2017;7(1):1–8. Cheng Y, Muroski ME, Petit DCMC, Mansell R, Vemulkar T, Morshed RA, et al. Rotating magnetic field induced oscillation of magnetic particles for in vivo mechanical destruction of malignant glioma. J Control Release. 2015 Feb;223:75–84. Mansell R, Vemulkar T, Petit DCMC, Cheng Y, Murphy J, Lesniak MS, et al. Magnetic particles with perpendicular anisotropy for mechanical cancer cell destruction. Sci Rep. 2017;7(1):1–7. Fong ELS, Harrington DA, Farach-Carson MC, Yu H. Heralding a New Paradigm in 3D Tumor Modeling. Biomaterials. 2016;108:197–213.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/ba8b6c4eeab8d4b2dfb813ca3884c747.jpg)
Figure 1: Spheroid model for preclinical mechanical stimulation testing. 1) mechanical stimulation using Halbach cylinder 2) in situ local delivery of magnetic nanoparticles.

![](https://assets.underline.io/uploads/markdown_image/1/image/d0c76220555207e62848ace21d7b64c5.jpg)
Figure 2

 Nanoviber: magnetic nanovibrations for brain tumor therapy: the translational road also needs innovation

Transition metal elements play many essential roles in the normal functioning of the human brain. These elements are transported, stored, and used by a vast range of proteins and enzymes. In most examples they are bound as individual metal ions (such as cobalt in vitamin B12), but some mineralized forms (such as the iron oxide core in ferritin) are also present. Neurodegenerative disorders (an umbrella term encompassing many forms of dementia and movement disorders), exhibit complex pathological changes within the central nervous system and beyond. Among these changes, altered patterns of transition metal element storage and utilization are generally observed in neurodegenerative disorders, as reviewed by others (e.g. Mezzaroba 2019). Magnetism plays key roles both in distinguishing the post-mortem materials properties of transition metals in biology, and in the clinical detection of transition metals in brain tissues (Collingwood & Telling, 2016). To advance the field, it is necessary to be able to image and quantify these transition metal elements in the human brain with sensitivity and specificity. From an analytical perspective, these brain compartments are effectively dilute systems, and the abundance, distribution, and material properties of the respective metal elements in their local environments vary greatly between cell types, tissues, and brain regions, and this in turn has implications for detection. The earliest histochemistry studies of post-mortem tissue revealled the heterogeneity of elements throughout the brain architecture, for example with Perls staining for iron. The ways in which these metals are bound affects staining efficacy, and efforts have been made to quantify metal ion concentrations in brain tissue as a function of brain region and ageing (e.g. Hallgren & Sourander 1958). Imaging transition metals within the living human brain with sensitivity and specificity presents many challenges. Transcranial sonography has shown sensitivity to tissue iron concentration, and scope to apply Dual-Energy Computed Tomography to image the most abundant elements is being explored. The most widely recognised opportunity came with the advent of Magnetic Resonance Imaging (MRI), which created the opportunity for sensitive, if not specific, clinical imaging of iron in the human brain (Drayer 1986). Subsequent efforts to improve specificity have included i) Bartzokis’ approach with sequential MRI scans using two distinct (B0) magnetic fields, which enable measurement of the field-dependent transverse relaxation increase associated with ferritin-encapsulated iron oxide nanoparticles (e.g. Bartzokis 2000), and ii) Quantitative Susceptibility Mapping, a method utilizing phase images to determine magnetic susceptibility distributions within tissues to thereby infer chemical composition (e.g. Haacke 2015). Post-mortem analysis continues to play an important role in testing the relationships between the properties of transition metals in brain tissue, and the signals detected with clinically-applicable methods. Magnetometry methods enable the proportion of iron present as iron oxide to be distinguished and characterized, although historically this has been applied to bulk samples, so spatial distribution information has not been preserved. Opportunities for magnetic imaging continue to evolve, and recently we demonstrated the application of synchrotron X-ray Magnetic Circular Dichroism to image the magnetic properties of post-mortem tissue from Alzheimer’s disease patients at sub-micron spatial resolution (Everett 2018). Meanwhile, the relative distribution of transition metals can be measured with outstanding sensitivity and specificity using focused beam synchrotron X-ray fluorescence imaging, creating the opportunity to correlate these distributions with high resolution quantitative MRI (Finnegan 2019). These findings can in turn inform interpretation of clinical MRI data. In conclusion, current developments in both post-mortem and clinical imaging are supporting efforts to determine whether altered patterns of transition metals can be used as biomarkers, and to investigate the extent to which disease-associated changes in the regulation of transition metals may provide insight into the pathogenesis of neurodegenerative disorders.

**References:**

G. Bartzokis and T. Tishler, Cell Mol. Biol., Vol. 46, p.821 (2000) J. Collingwood and N. Telling, Iron Oxides: from Nature to Applications, Chap. 7, p143 (2016) B. Drayer, P. Burger, R. Darwin et. al., AJR Am. J. Roentgenol. Vol. 147, p.103 (1986) J. Everett, J. Collingwood, V. Tjendana-Tjhin et. al., Nanoscale, Vol. 10, p.11782 (2018) M. Finnegan, N. Visanji, I. Romero-Canelon et. al., J. Neurosci. Methods, Vol. 319, p.28 (2019) E. Haacke, S. Liu, S. Buch et. al., Magnetic Resonance Imaging, Vol. 33, p.1 (2015) B. Hallgren and P. Sourander, J. Neurochem. Vol. 3, p.41 (1958) L. Mezzaroba, D. Alfieri, A. Simão, and E. Reiche, Neurotoxicology, Vol. 74, p.230 (2019)

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Heating efficiency of magnetic nanoparticles for magnetic hyperthermia: effects of temperature and driving-field waveform

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