Heating Properties Of Magnetic Nanoparticles Research Articles

Multimodal Locomotion and Active Targeted Thermal Control of Magnetic Agents for Biomedical Applications.

Magnetic microrobots can be miniaturized to a nanometric scale owing to their wireless actuation, thereby rendering them ideal for numerous biomedical applications. As a result, nowadays, there exist several mechano‐electromagnetic systems for their actuation. However, magnetic actuation is not sufficient for implementation in biomedical applications, and further functionalities such as imaging and heating are required. This study proposes a multimodal electromagnetic system comprised of three pairs of Helmholtz coils, a pair of Maxwell coils, and a high‐frequency solenoid to realize multimodal locomotion and heating control of magnetic microrobots. The system produces different configurations of magnetic fields that can generate magnetic forces and torques for the multimodal locomotion of magnetic microrobots, as well as generate magnetic traps that can control the locomotion of magnetic swarms. Furthermore, these magnetic fields are employed to control the magnetization of magnetic nanoparticles, affecting their magnetic relaxation mechanisms and diminishing their thermal properties. Thus, the system enables the control of the temperature increase of soft‐magnetic materials and selective heating of magnetic microrobots at different positions, while suppressing the heating properties of magnetic nanoparticles located at undesired areas.

A simulation approach for the finite-temperature magnetic properties, stochastic dynamics and heating properties of magnetic nanoparticles composed of FM core/AFM shell

Using the Monte Carlo simulation method based on the Metropolis algorithm, we present some results regarding the magnetic and heating properties of three-dimensional nanoparticles composed of a ferromagnetic core surrounded by an antiferromagnetic shell. We investigate the variation of the exchange bias effect and its dependence on the particle shell thickness, as well as on the temperature. In terms of the stochastic dynamics, we applied a time-dependent alternating magnetic field on the system, and calculated the dynamic-order parameters, response functions and the hysteresis loop area from the AC hysteresis curves from which we have also quantified the specific absorption rate (SAR) of the particle over a wide range of field frequencies. A number of interesting results have been found regarding the variation of the heating properties of the system as a function of the antiferromagnetic shell thickness and the period of the alternating field.

Targeted magnetic nanoparticle hyperthermia for the treatment of oral cancer.

Patients with oral squamous cell carcinoma currently experience a five-year survival rate of approximately 60% with conventional surgical, chemotherapy and radiotherapy treatments. Magnetic hyperthermia offers an alternative treatment method by utilising the heating properties of magnetic nanoparticles to produce thermal ablation of the tumour site when exposed to an alternating magnetic field. In this study, we investigate in vitro if targeted magnetic hyperthermia offers a potential treatment for oral squamous cell carcinoma. Magnetic iron oxide nanoparticles, with a biocompatible silica coating, were produced and conjugated with antibodies to target integrin αvβ6, a well-characterised oral squamous cell carcinoma biomarker. Utilising the heating properties of the magnetic nanoparticles, we exposed them to an alternating magnetic field to produce thermo ablation of tumour cells either negative for or overexpressing integrin αvβ6. The cell surface biomarker, αvβ6 integrin, was upregulated in tissue biopsies from oral squamous cell carcinoma patients compared to normal tissue. Functionalisation of the silica coating with anti-αvβ6 antibodies enabled direct targeting of the nanoparticles to αvβ6 overexpressing cells and applying thermal therapy significantly increased killing of the targeted tumour cells compared to control cells. Combining antibody-targeting magnetic nanoparticles with thermal ablation offers a promising therapy for the targeted treatment of oral squamous cell carcinoma.

Coercivity Determines Magnetic Particle Heating.

Diseased cell treatment by heating with magnetic nanoparticles is hindered by their required high concentrations. A clear relationship between heating efficiency and magnetic properties of nanoparticles has not been attained experimentally yet due to limited availability of magnetic nanoparticles with varying size and composition. Here, versatile flame aerosol technology is used for the synthesis of 21 types of ferro-/ferrimagnetic nanocrystals with varying composition, size, and morphology for hyperthermia and thermoablation therapy. Heating efficiency, magnetic hysteresis, and first-order reversal curves of these materials are compared. The maximum heating performance occurs near the transition from superparamagnetic to single domain state, regardless of particle composition. Most importantly, the ratio between saturation magnetization and coercivity can be linked to the heating properties of magnetic nanoparticles. Magnetic interaction is controlled by changes in the architecture of the nanoparticles and closely analyzed by first-order reversal curves. Silica-coated nonstoichiometric Gd-Zn ferrite exhibits the most promising therapeutic capability at relatively low particle concentrations, as shown in vitro with cancerous prostate cells.

Lock-In Thermography as an Analytical Tool for Magnetic Nanoparticles: Measuring Heating Power and Magnetic Fields

Magnetic nanoparticles and their ability to convert electromagnetic energy into heat are of explicit interest for various applications. However, precise quantification of their heating efficiency is not always upfront, and several parameters render comparative studies challenging. This paper describes the theory behind lock-in thermography, a new technique for quantifying the heating properties of magnetic nanoparticles. This technique allows the investigation of some of the potential sources of variability: key factors such as magnetic field inhomogeneity and its effects on the heating power are explored in detail. The presented results, obtained from various nanoparticle batches of different origins, highlight the importance of pursuing a standardized and systematic approach when quantifying the heating efficiency of magnetic nanoparticles.

Susceptibility losses in heating of magnetic core/shell nanoparticles for hyperthermia: a Monte Carlo study of shape and size effects.

Optimizing the heating properties of magnetic nanoparticles is of great importance for hyperthermia applications. Recent experimental results show that core/shell nanoparticles could give an increased specific absorption rate (SAR) compared to the magnetic oxide nanoparticles currently used. We have developed a modified phenomenological model based on the linear Néel-Brown relaxation model to calculate the SAR due to susceptibility losses in complex nanoparticles with ferromagnetic (FM) core/ferrimagnetic (FiM) shell morphology. We use the Monte Carlo (MC) simulation technique with the implementation of the Metropolis algorithm to investigate the effect of size and shape on the magnetisation behaviour of complex ferromagnetic/ferrimagnetic nanoparticles covered by a surfactant layer. The findings of our simulations are used as an input in our modified model for the calculation of the SAR. Our calculations show that for all the sizes and shapes the complex FM/FiM nanoparticles give higher SAR values than the pure ferrimagnetic ones due to their higher core saturation magnetisation. For all sizes the nanoparticles with the truncated cuboctahedral shape give the highest SAR values and the cubic ones the lowest ones. The decrease in the surfactant thickness results in an increase of the SAR values. Our results have the same characteristics as the available experimental data from Fe/Fe3O4 nanoparticles, confirming that the complex nanoparticles with core/shell morphology can optimise the heating properties for hyperthermia.

Simple models for dynamic hysteresis loop calculations of magnetic single-domain nanoparticles: Application to magnetic hyperthermia optimization

To optimize the heating properties of magnetic nanoparticles (MNPs) in magnetic hyperthermia applications, it is necessary to calculate the area of their hysteresis loops in an alternating magnetic field. The separation between “relaxation losses” and “hysteresis losses” presented in several articles is artificial and criticized here. The three types of theories suitable for describing hysteresis loops of MNPs are presented and compared to numerical simulations: equilibrium functions, Stoner–Wohlfarth model based theories (SWMBTs), and a linear response theory (LRT) using the Néel–Brown relaxation time. The configuration where the easy axis of the MNPs is aligned with respect to the magnetic field and the configuration of a random orientation of the easy axis are both studied. Suitable formulas to calculate the hysteresis areas of major cycles are deduced from SWMBTs and from numerical simulations; the domain of validity of the analytical formula is explicitly studied. In the case of minor cycles, the hysteresis area calculations are based on the LRT. A perfect agreement between the LRT and numerical simulations of hysteresis loops is obtained. The domain of validity of the LRT is explicitly studied. Formulas are proposed to calculate the hysteresis area at low field that are valid for any anisotropy of the MNP. The magnetic field dependence of the area is studied using numerical simulations: it follows power laws with a large range of exponents. Then analytical expressions derived from the LRT and SWMBTs are used in their domains of validity for a theoretical study of magnetic hyperthermia. It is shown that LRT is only pertinent for MNPs with strong anisotropy and that SWMBTs should be used for weakly anisotropic MNPs. The optimum volume of MNPs for magnetic hyperthermia is derived as a function of material and experimental parameters. Formulas are proposed to allow to the calculation of the optimum volume for any anisotropy. The maximum achievable specific absorption rate (SAR) is calculated as a function of the MNP anisotropy. It is shown that an optimum anisotropy increases the SAR and reduces the detrimental effects of the size distribution of the MNPs. The optimum anisotropy is simple to calculate; it depends only on the magnetic field used in the hyperthermia experiments and the MNP magnetization. The theoretical optimum parameters are compared to those of several magnetic materials. A brief review of experimental results as well as a method to analyze them is proposed. This study helps in the determination of suitable and unsuitable materials for magnetic hyperthermia and provides accurate formulas to analyze experimental data. It is also aimed at providing a better understanding of magnetic hyperthermia to researchers working on this subject.