1,721,235 research outputs found
Specific loss power of magnetic nanoparticles: A machine learning approach
Full text linkA machine learning approach has been applied to the prediction of magnetic hysteresis properties (coercive field, magnetic remanence, and hysteresis loop area) of magnetic nanoparticles for hyperthermia applications. Trained on a dataset compiled from numerical simulations, a neural network and a random forest were used to predict power losses of nanoparticles as a function of their intrinsic properties (saturation, anisotropy, and size) and mutual magnetic interactions, as well as of application conditions (temperature, frequency, and applied field magnitude), for values of the parameters not represented in the database. The predictive ability of the studied machine learning approaches can provide a valuable tool toward the application of magnetic hyperthermia as a precision medicine therapy tailored to the patient's needs. (C) 2022 Author(s)
Temperature-dependent heating efficiency of magnetic nanoparticles for applications in precision nanomedicine
Full text linkThe power released by magnetic nanoparticles submitted to an alternating driving field is temperature dependent owing to the variation of the fundamental magnetic properties. Therefore, the heating efficiency of magnetic nanoparticles for applications in precision nanomedicine (such as magnetic hyperthermia or heat-assisted drug delivery) can be significantly affected by the local instantaneous temperature of the host medium. A rate equation approach is used to determine the hysteretic properties and the power released by magnetite nanoparticles, and the heat transport equation is solved in a simple geometry with boundary conditions appropriate to both in-lab experiments and in vivo applications. Size plays a fundamental role in determining the heating efficiency of magnetic nanoparticles; above a critical size, nanoparticles remain inactive, although they can undergo secondary activation. The experimental conditions for optimal thermal efficiency are expressed by a thermal activity diagram for nanoparticles. In the light of the model's results, features, methods, advantages and dangers of magnetic-particle assisted precision nanomedicine ought to be reconsidered. In vivo antitumor applications should take into account the hazards arising from the heat generated by magnetic nanoparticles that diffuse into the neighboring healthy tissue
Magnetic nanoparticle hyperthermia enhanced by a rotating field
Full text linkThe heating efficiency of magnetite nanoparticles for therapeutic hyperthermia is shown to be substantially enhanced by applying a uniformly rotating magnetic field in place of a field directed along an axis, when all other factors are held constant. Optimization of the heating efficiency is actively pursued in order to keep the volume fraction of nanoparticles as low as possible, reducing the adverse effects emerging from nanoparticle accumulation in organs. The effect of a rotating magnetic field is calculated by solving rate equations for the magnetic moments of magnetite nanoparticles with predominant N & eacute;el relaxation and pictured as double-well systems. The model results in a simple expression for the power density generated by nanoparticles with random easy-axis directions. A thermal model of a tissue simulant is used to show that applying a rotating instead of a linear field permits us to more than halve the dose of nanoparticles needed to attain the target temperature in the tissue
Fine tuning and optimization of magnetic hyperthermia treatments using versatile trapezoidal driving-field waveforms
Full text linkApplying trapezoidal driving-field waveforms to activate magnetic nanoparticles optimizes their performance as heat generators in magnetic hyperthermia, with notable advantages with respect to the effects of harmonic magnetic fields of the same frequency and amplitude. A rate equation approach is used to determine the hysteretic properties and the power released by monodisperse and polydisperse magnetite nanoparticles with randomly oriented easy axes subjected to a radio-frequency trapezoidal driving field. The heating ability of the activated nanoparticles is investigated by means of a simple model in which the heat equation is solved in radial geometry with boundary conditions simulating in vivo applications. Changes of the inclination of the trapezoidal waveform's lateral sides are shown to induce controlled changes in the specific loss power generated by the activated nanoparticles. 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, and the ability to substantially reduce the heating transient in a hyperthermia treatment are suitably addressed and overcome by making use of versatile driving fields of a trapezoidal shape
Multifunctional effects in magnetic nanoparticles for precision medicine: combining magnetic particle thermometry and hyperthermia
Full text linkAn effective combination of magnetic hyperthermia and thermometry is shown to be implementable by using magnetic nanoparticles which behave either as a heat sources or as temperature sensors when excited at two different frequencies. Noninteracting magnetite nanoparticles are modeled as double-well systems and their magnetization is obtained by solving rate equations. Two temperature sensitive properties derived from the cyclic magnetization and exhibiting a linear dependence on temperature are studied and compared for monodisperse and polydisperse nanoparticles. The multifunctional effects enabling the combination of magnetic hyperthermia and thermometry are shown to depend on the interplay among nanoparticle size, intrinsic magnetic properties and driving-field frequency. Magnetic hyperthermia and thermometry can be effectively combined by properly tailoring the magnetic properties of nanoparticles and the driving-field frequencies
Magnetic nanoparticles in square-wave fields for breakthrough performance in hyperthermia and magnetic particle imaging
Full text linkDriving immobilized, single-domain magnetic nanoparticles at high frequency by square wave fields instead of sinusoidal waveforms leads to qualitative and quantitative improvements in their performance both as point-like heat sources for magnetic hyperthermia and as sensing elements in frequency-resolved techniques such as magnetic particle imaging and magnetic particle spectroscopy. The time evolution and the frequency spectrum of the cyclic magnetization of magnetite nanoparticles with random easy axes are obtained by means of a rate-equation method able to describe time-dependent effects for the particle sizes and frequencies of interest in most applications to biomedicine. In the presence of a high-frequency square-wave field, the rate equations are shown to admit an analytical solution and the periodic magnetization can be therefore described with accuracy, allowing one to single out effects which take place on different timescales. Magnetic hysteresis effects arising from the specific features of the square-wave driving field results in a breakthrough improvement of both the magnetic power released as heat to an environment in magnetic hyperthermia treatments and the magnitude of the third harmonic of the frequency spectrum of the magnetization, which plays a central role in magnetic particle imaging
From spectral analysis to hysteresis loops: A breakthrough in the optimization of magnetic nanomaterials for bioapplications
Full text linkAn innovative method is proposed to determine the most important magnetic properties of bioapplication-oriented magnetic nanomaterials exploiting the connection between hysteresis loop and frequency spectrum of magnetization. Owing to conceptual and practical simplicity, the method may result in a substantial advance in the optimization of magnetic nanomaterials for use in precision medicine. The techniques of frequency analysis of the magnetization currently applied to nanomaterials both in vitro and in vivo usually give a limited, qualitative picture of the effects of the active biological environment, and have to be complemented by direct measurement of the hysteresis loop. We show that the very same techniques can be used to convey all the information needed by present-day biomedical applications without the necessity of doing conventional magnetic measurements in the same experimental conditions. The spectral harmonics obtained analysing the response of a magnetic tracer in frequency, as in magnetic particle spectroscopy/imaging, are demonstrated to lead to a precise reconstruction of the hysteresis loop, whose most important parameters (loop's area, magnetic remanence and coercive field) are directly obtained through transformation formulas based on simple manipulation of the harmonics amplitudes and phases. The validity of the method is experimentally verified on various magnetic nanomaterials for bioapplications submitted to ac magnetic fields of different amplitude, frequency and waveform. In all cases, the experimental data taken in the frequency domain exactly reproduce the magnetic properties obtained from conventional magnetic measurements
Magnetization Dynamics of Superparamagnetic Nanoparticles for Magnetic Particle Spectroscopy and Imaging
Full text linkAn exact theory is developed with the aim of assessing the properties of the harmonics spectrum of the dynamic magnetization originating from superparamagnetic nanoparticles submitted to a high-frequency driving field. The magnetization is assumed to be always close to equilibrium at the frequencies of interest, so that it can still be described by the anhysteretic Langevin function. The theory, valid for an extended range of values of physical properties and sizes of particles, is aimed at interpreting typical results of mag-netic particle spectroscopy and imaging. The analytical framework is exploited to get a deeper knowledge of the spectral properties of nanoparticle magnetization and to assess the persistence of the superpara-magnetic behavior at the operating frequencies. The spectral properties of the time-dependent Langevin function are analyzed in detail and compared with experimental results on polydisperse, immobilized nanoparticles. The system function usually exploited in magnetic particle imaging is calculated with precision as a function of both particle size and driving field's amplitude
Dipolar interactions among magnetite nanoparticles for magnetic hyperthermia: a rate-equation approach
Full text linkRate equations are used to study the dynamic magnetic properties of interacting magnetite nanoparticles viewed as double well systems (DWS) subjected to a driving field in the radio-frequency range. Dipole-dipole interaction among particles is modeled by inserting an ad-hoc term in the energy barrier to simulate the dependence of the interaction on both the interparticle distance and degree of dipole collinearity. The effective magnetic power released by an assembly of interacting nanoparticles dispersed in a diamagnetic host is shown to be a complex function of nanoparticle diameter, mean particle interdistance and frequency. Dipolar interaction markedly modifies the way a host material is heated by an assembly of embedded nanoparticles in magnetic hyperthermia treatments. Nanoparticle fraction and strength of the interaction can dramatically influence the amplitude and shape of the heating curves of the host material; the heating ability of interacting nanoparticles is shown to be either improved or reduced by their concentration in the host material. A frequency-dependent cut-off length of dipolar interactions is determined and explained. Particle polydispersity entailing a distribution of particle sizes brings about non-trivial effects on the heating curves depending on the strength of dipolar interaction
Heating ability modulation by clustering of magnetic particles for precision therapy and diagnosis
Full text linkMagnetic and thermal properties of clustered magnetite nanoparticles submitted to a high-frequency magnetic field is studied by means of rate equations. A simple model of large particle clusters (containing more than one hundred individual particles) is introduced. Dipolar interactions among clustered particles markedly modify shape and area of the hysteresis loops in a way critically dependent on particle size and cluster dimensions, thereby modulating the power released as heat to a host medium. For monodisperse and polydisperse systems, particle clustering can lead to either a significant enhancement or a definite reduction of the released power; in particular cases the same particles can produce opposite effects in dependence of the dimensions of the clusters. Modulation by clustering of the heating ability of magnetic nanoparticles has impact on applications requiring optimization and accurate control of temperature in the host medium, such as magnetic hyperthermia for precision therapy or fluid flow management, and advanced diagnostics involving magnetic tracers
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