Nowadays, magnetic hyperthermia constitutes a complementary approach to cancer treatment. The use of magnetic particles as heating mediators, proposed in the 1950s, provides a novel strategy for improving tumor treatment and, consequently, patient's quality of life. This review reports a broad overview about several aspects of magnetic hyperthermia addressing new perspectives and the progress on relevant features such as the ad hoc preparation of magnetic nanoparticles, physical modeling of magnetic heating, methods to determine the heat dissipation power of magnetic colloids including the development of experimental apparatus and the influence of biological matrices on the heating efficiency.

Fundamentals and advances in magnetic hyperthermia

The performance of magnetic nanoparticles is intimately entwined with their structure, mean size and magnetic anisotropy. Besides, ensembles offer a unique way of engineering the magnetic response by modifying the strength of the dipolar interactions between particles. Here we report on an experimental and theoretical analysis of magnetic hyperthermia, a rapidly developing technique in medical research and oncology. Experimentally, we demonstrate that single-domain cubic iron oxide particles resembling bacterial magnetosomes have superior magnetic heating efficiency compared to spherical particles of similar sizes. Monte Carlo simulations at the atomic level corroborate the larger anisotropy of the cubic particles in comparison with the spherical ones, thus evidencing the beneficial role of surface anisotropy in the improved heating power. Moreover we establish a quantitative link between the particle assembling, the interactions and the heating properties. This knowledge opens new perspectives for improved hyperthermia, an alternative to conventional cancer therapies.

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Learning from Nature to Improve the Heat Generation of Iron-Oxide Nanoparticles for Magnetic Hyperthermia Applications

Localized magnetic hyperthermia using magnetic nanoparticles (MNPs) under the application of small magnetic fields is a promising tool for treating small or deep-seated tumors. For this method to be applicable, the amount of MNPs used should be minimized. Hence, it is essential to enhance the power dissipation or heating efficiency of MNPs. Several factors influence the heating efficiency of MNPs, such as the amplitude and frequency of the applied magnetic field and the structural and magnetic properties of MNPs. We discuss some of the physics principles for effective heating of MNPs focusing on the role of surface anisotropy, interface exchange anisotropy and dipolar interactions. Basic magnetic properties of MNPs such as their superparamagnetic behavior, are briefly reviewed. The influence of temperature on anisotropy and magnetization of MNPs is discussed. Recent development in self-regulated hyperthermia is briefly discussed. Some physical and practical limitations of using MNPs in magnetic hyperthermia are also briefly discussed.

https://www.mdpi.com/2079-4991/5/1/63/pdf

Magnetic Properties of Magnetic Nanoparticles for Efficient Hyperthermia.

The reversal time, superparamagnetic relaxation time, of the magnetization of fine single domain ferromagnetic nanoparticles owing to thermal fluctuations plays a fundamental role in information storage, paleomagnetism, biotechnology, etc. Here a comprehensive tutorial-style review of the achievements of fifty years of development and generalizations of the seminal work of Brown [Phys. Rev. 130, 1677 (1963)] on thermal fluctuations of magnetic nanoparticles is presented. Analytical as well as numerical approaches to the estimation of the damping and temperature dependence of the reversal time based on Brown's Fokker-Planck equation for the evolution of the magnetic moment orientations on the surface of the unit sphere are critically discussed while the most promising directions for future research are emphasized.

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Thermal fluctuations of magnetic nanoparticles: Fifty years after Brown

Despite magnetic hyperthermia being considered one of the most promising techniques for cancer treatment, until now spherical magnetite (Fe3O4) or maghemite (γ-Fe2O3) nanoparticles, which are the most commonly employed and only FDA approved materials, yield the limited heating capacity. Therefore, there is an increasing need for new strategies to improve the heating efficiency or the specific absorption rate (SAR) of these nanosystems. Recently, a large improvement in SAR has been reported for nanocubes of Fe3O4 relative to their spherical counterpart, as a result of their enhanced surface anisotropy and chainlike particle formation. Considering the proven advantages of high aspect ratio one-dimensional (1D) Fe3O4 nanostructures over their spherical and cubic counterparts, such as larger surface area, multisegmented capabilities, enhanced blood circulation time, and prolonged retention in tumors, we propose a novel approach that utilizes this 1D nanostructure for enhanced hyperthermia. Here, we demonstrat...

Tunable High Aspect Ratio Iron Oxide Nanorods for Enhanced Hyperthermia

It is shown that the magnetic dynamics of an assembly of nanoparticles dispersed in a viscous liquid differs significantly from the behavior of the same assembly of nanoparticles immobilized in a solid matrix. For an assembly of magnetic nanoparticles in a liquid two characteristic mode for stationary magnetization oscillations are found that can be called the viscous and magnetic modes, respectively. In the viscous mode, which occurs for small amplitude of the alternating magnetic field H0 as compared to the particle anisotropy field Hk, the particle rotates in the liquid as a whole. In a stationary motion the unit magnetization vector and the director, describing the spatial orientation of the particle, move in unison, but the phase of oscillations of these vectors is shifted relative to that of the alternating magnetic field. Therefore, for the viscous mode the energy absorption is mainly due to viscous losses associated with the particle rotation in the liquid. In the opposite regime, H0 ≥ Hk, the dir...

Dynamics of magnetic nanoparticle in a viscous liquid: Application to magnetic nanoparticle hyperthermia

The hysteresis losses of a dense assembly of magnetite nanoparticles with an average diameter D = 25 nm are measured in the frequency range f = 10 – 200 kHz for magnetic field amplitudes up to H0 = 400 Oe. The low frequency hysteresis loops of the assembly are obtained by means of integration of the electro-motive force signal arising in a small pick-up coil wrapped around a sample which contains 1 – 5 mg of a magnetite powder. It is proved experimentally that the specific absorption rate diminishes approximately 4.5 times when the sample aspect ratio decreases from 11.4 to 1. Theoretical estimate shows that experimentally measured hysteresis loops can be approximately described only by taking into account appreciable contributions of magnetic nanoparticles of both very small, D 30 nm, diameters. Thus the wide particle size distribution has to be assumed.

B.Ya. Liubimov

Papers

Dynamics of magnetic nanoparticle in a viscous liquid: Application to magnetic nanoparticle hyperthermia

Hysteresis losses in a dense superparamagnetic nanoparticle assembly

The influence of a demagnetizing field on hysteresis losses in a dense assembly of superparamagnetic nanoparticles

Magnetic nanoparticle motion in external magnetic field

Correlation of electrical and magnetic properties of Co-rich amorphous ferromagnetic microwires after DC Joule heating treatment