Seongtae Bae

Effects of particle dipole interaction on the ac magnetically induced heating characteristics of ferrite nanoparticles for hyperthermia

Magnetic particle dipole interaction was revealed as a crucial physical parameter to be considered in optimizing the ac magnetically induced heating characteristics of magnetic nanoparticles. The ac heating temperature of soft MFe2O4 (M=Mg,Ni) nanoparticles was remarkably increased from 17.6 to 94.7 °C (MgFe2O4) and from 13.1 to 103.1 °C (NiFe2O4) by increasing the particle dipole interaction energy at fixed ac magnetic field of 140 Oe and frequency of 110 kHz. The increase in “magnetic hysteresis loss” that resulted from the particle dipole interaction was the main physical reason for the significant improvement of ac heating characteristics.

Applications of NiFe2O4 nanoparticles for a hyperthermia agent in biomedicine

Self-heating temperature rising characteristics, cytotoxicity, and magnetic properties of NiFe2O4 nanoparticles have been investigated to confirm the effectiveness as an in vivo hyperthermia agent in biomedicine. NiFe2O4 nanoparticles showed both superparamagnetic and ferrimagnetic behaviors depending on particle sizes. The quantitative cytotoxicity test verified that both uncoated and chitosan-coated NiFe2O4 nanoparticles had noncytotoxicity. The solid state 35nm size NiFe2O4 nanoparticles first exhibited a maximum self-heating temperature of 44.2°C at H0f=5.1×108Am−1s−1. The physical nature of the self-heating was primarily thought to be due to the magnetic hysteresis loss, Neel rotations, and Brownian rotations of 35nm size NiFe2O4 nanoparticles.

AC Magnetic-Field-Induced Heating and Physical Properties of Ferrite Nanoparticles for a Hyperthermia Agent in Medicine

AC magnetic-field-induced heating, cytotoxicity, and bio-related physical properties of two kinds of spinel ferrite nanoparticles, soft (NiFe₂O₄) and hard (CoFe₂O₄), with different mean particle sizes were investigated in this paper to confirm the effectiveness for an in vivo magnetic nanoparticle hyperthermia agent in biomedicine. AC magnetically induced heating temperature of the nanoparticles measured both in a solid and an agar state at different applied magnetic fields and frequencies clarified that the maximum heating temperature of NiFe₂O₄ nanoparticles is much higher than that of CoFe₂O₄ nanoparticles. In addition, it was demonstrated that solid-state NiFe₂O₄ nanoparticles with 24.8 and 35 nm mean particle size exhibited a promisingly high heating temperature (21.5degC-45degC) for a hyperthermia agent in the physiologically tolerable range of the ac magnetic field with less than 50 kHz of applied frequency. According to the magnetic and physical analysis results, the superior ac magnetically induced heating performance of NiFe₂O₄ nanoparticles was primarily due to their higher magnetic susceptibility (permeability) that directly induces a larger magnetic minor hysteresis loop area at the low magnetic field. Cytotoxicity test results, quantitatively estimated by methylthiazol tetrazolium bromide test method, verified that uncoated NiFe₂O₄, chitosan-coated NiFe₂O₄, and CoFe₂O₄ showed a noncytotoxicity, which is clinically suitable for a hyperthermia agent application.

Physical limits of pure superparamagnetic Fe3O4 nanoparticles for a local hyperthermia agent in nanomedicine

Magnetic and AC magnetically induced heating characteristics of Fe3O4 nanoparticles (IONs) with different mean diameters, d, systematically controlled from 4.2 to 22.5 nm were investigated to explore the physical relationship between magnetic phase and specific loss power (SLP) for hyperthermia agent applications. It was experimentally confirmed that the IONs had three magnetic phases and correspondingly different SLP characteristics depending on the particle sizes. Furthermore, it was demonstrated that pure superparamagnetic phase IONs (d < 9.8 nm) showed insufficient SLPs critically limiting for hyperthermia applications due to smaller AC hysteresis loss power (Neel relaxation loss power) originated from lower out-of-phase magnetic susceptibility.

Dependence of Frequency and Magnetic Field on Self-Heating Characteristics of NiFe

Self-heating temperature-rising characteristics of nano-size controlled NiFe2O4 particles were analyzed as a function of applied frequency and magnetic field in order to investigate the physical principle of self-heating and to confirm the possibility for a real in vivo hyperthermia application. According to the magnetic properties of 35-nm size NiFe2O4 nanoparticles, it was confirmed that the physical mechanism of self-heating is mainly attributed to the hysteresis loss. In addition, it was found that the self-heating temperature was linearly increased by increasing frequency and was proportionally square to the applied magnetic field. The self-heating temperature was rapidly increased in an initial stage and then it reached to the maximum. The maximum self-heating temperature was controlled from 2.8degC to 72.6degC by changing the applied frequency and magnetic field. The corresponding product of the frequency and the strength of magnetic field H0f was between 1.9times108 Am-1s-1 and 13.4times10 8 Am-1s-1. These values are in the biological safety and tolerable range for hyperthermia considering deleterious physiological response of human body during hyperthermia treatment

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Ocular neuroprotection induced by localized heat shock proteins (HSPs) has been paid considerable attention as an efficacious treatment modality for glaucoma. However, the current clinical approaches to induce HSPs in the retinal ganglion cells (RGCs) are limited due to undesirable side effects. Here, we present that the induction of HSPs by local magnetic hyperthermia using engineered superparamagnetic Mn(0.5)Zn(0.5)Fe(2)O(4) nanoparticle agents (EMZF-SPNPAs) with a 5.5 nm mean particle size is promisingly feasible for a physiologically tolerable ocular neuroprotection modality. The sufficiently high specific absorption rate (SAR) (∼256.4 W/g in an agar solution) achieved at the biologically safe range of applied AC magnetic field and frequency as well as the superior biocompatibility of EMZF-SPNPA, which were confirmed from both in-vitro and in-vivo animal pilot studies, allowing it to be considered as a potential localized HSPs agent. Furthermore, the successful demonstration of a newly designed infusion technique, which diffuses the EMZF-SPNPAs through the vitreous body to the retina in a rat eye, more strongly verified the promises of this biotechnical approach to the ocular neuroprotection modality in glaucoma clinics.

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Magnetic nanoparticles can potentially be used in drug delivery systems and for hyperthermia therapy. The applicability of Fe₃O₄, CoFe₂O₄, MgFe₂O₄, and NiFe₂O₄ nanoparticles for the same was studied by evaluating their magnetization, thermal efficiency, and biocompatibility. Fe₃O₄ and CoFe₂O₄ nanoparticles exhibited large magnetization. Fe₃O₄ and NiFe₂O₄ nanoparticles exhibited large induction heating. MgFe₂O₄ nanoparticles exhibited low magnetization compared to the other nanoparticles. NiFe₂O₄ nanoparticles were found to be cytotoxic, whereas the other nanoparticles were not cytotoxic. This study indicates that Fe₃O₄ nanoparticles could be the most suitable ones for hyperthermia therapy.

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The effects of perpendicular anisotropy on the interlayer coupling in perpendicularly magnetized [Pd∕Co]∕Cu∕[Co∕Pd] spin valves have been explored. It was clearly confirmed that the perpendicular anisotropy of soft and hard [Co∕Pd] multilayers plays a crucial role in determining the physical characteristics of perpendicular interlayer coupling in the [Pd∕Co]∕Cu∕[Co∕Pd] spin valves. In addition, theoretical calculations demonstrated that the behavior of experimentally observed perpendicular interlayer coupling dominantly followed a Ruderman–Kittel–Kasuya–Yoshida oscillation modified by including a physical parameter directly relevant to the angle deviation of soft or hard [Co∕Pd] magnetizations from the perpendicular direction in the spin valves rather than a topologically induced interlayer coupling.

Nanoparticles for Hyperthermia

Magnetic and self-heating properties of various size NiFe2O4 (7.7-242.0 nm) were evaluated. The self heating temperature of each sample measured by applying ac magnetic field was affected by its magnetic property. The particle size dependence was also explained by the magnetic properties of the samples. At the lower frequency, the self heating was contributed by hysteresis loss. The ac magnetization process was also evaluated and the result could clarify the origin of self-heating. The 7.7 nm particle was heated by relaxation losses by the applied field at higher frequency. The energy efficiency of a magnetic field to generate self heating was analyzed. It was found that the particle of 130.7 nm exhibited the highest temperature rise and heat generation efficiency for the applied field of low amplitude and frequency.

Engineered superparamagnetic Mn0.5Zn0.5Fe2O4 nanoparticles as a heat shock protein induction agent for ocular neuroprotection in glaucoma

The exchange coupling characteristics for both Si/α-Fe2O3/NiFe and Si/NiFe/α-Fe2O3 bilayers have been investigated. These two bilayers showed completely different exchange coupling characteristics. The Si/α-Fe2O3 (50 nm)/NiFe(5 nm) bilayer had Hex=62.5 Oe, Hc=137.5 Oe, while the Si/NiFe(5 nm)/α-Fe2O3(50 nm) bilayer had Hex=4.5 Oe, Hc=9.5 Oe. The larger exchange bias field of α-Fe2O3/NiFe bilayer was mainly attributed to good crystallinity of α-Fe2O3 and the smooth interface between NiFe and α-Fe2O3. The interfacial exchange energy, Jex was also calculated for these two bilayers. The case of the rougher surface of bilayer (Si/NiFe/α-Fe2O3) exhibited smaller interfacial exchange energy. In order to verify the effect of α-Fe2O3 crystal structure on the exchange bias coupling characteristics, Ti (hcp), Zr (hcp), Ta (bcc), and Cu (fcc) were used as buffer layers for the Si/buffer layer/α-Fe2O3/NiFe structures. Ti and Zr buffer layers showed good exchange coupling performance, which was strongly related to good...