Effect of Nanoclustering and Dipolar Interactions in Heat Generation for Magnetic Hyperthermia

Abstract

Biomedical magnetic colloids commonly used in magnetic hyperthermia experiments often display a bidisperse structure, i.e., are composed of stable nanoclusters coexisting with well-dispersed nanoparticles. However, the influence of nanoclusters in the optimization of colloids for heat dissipation is usually excluded. In this work, bidisperse colloids are used to analyze the effect of nanoclustering and long-range magnetic dipolar interaction on the magnetic hyperthermia efficiency. Two kinds of colloids, composed of magnetite cores with mean sizes of around 10 and 18 nm, coated with oleic acid and dispersed in hexane, and coated with meso-2,3-dimercaptosuccinic acid and dispersed in water, were analyzed. Small-angle X-ray scattering was applied to thoroughly characterize nanoparticle structuring. We proved that the magnetic hyperthermia performances of nanoclusters and single nanoparticles are distinctive. Nanoclustering acts to reduce the specific heating efficiency whereas a peak against concentration appears for the well-dispersed component. Our experiments show that the heating efficiency of a magnetic colloid can increase or decrease when dipolar interactions increase and that the colloid concentration, i.e., dipolar interaction, can be used to improve magnetic hyperthermia. We have proven that the power dissipated by an ensemble of dispersed magnetic nanoparticles becomes a nonextensive property as a direct consequence of the long-range nature of dipolar interactions. This knowledge is a key point in selecting the correct dose that has to be injected to achieve the desired outcome in intracellular magnetic hyperthermia therapy.

Structural and magnetic properties of multi-core nanoparticles analysed using a generalised numerical inversion method

“…Whilst this model offers an adequate description for single -core nanoparticle systems under consideration of polydispersity, recent work has suggested that so called multi -core particles252627 may be more suited to magnetic hyperthermia. Refs 5, 6, 7, 8, 9, 10 each observe an increase in magnetic heating for multi-core particles compared to single-cores under the same conditions. Multi-core particles consist of several magnetic cores per particle and consequently, long range dipolar interactions within one multi-core particle can be present.…”

“…Of the many proposed uses of iron oxide nanoparticles the most promising examples are cancer treatment by magnetic hyperthermia567891011, magnetic resonance1213 and particle imaging1415, magnetic biosensing1617 as well as magnetic drug targeting111213. The required magnetic response of the nanoparticles is typically determined by the application, and is in turn intrinsically dependent on the structural properties of the particle system.…”

Magnetic hyperthermia performance of magnetite nanoparticle assemblies under different driving fields

“…For those particles in clusters, they are in close contact and are highly interactive. 1 The random and competing interparticle interactions among MNP clusters alter the magnetic dynamic properties by affecting the energy barrier, thence changing the relaxation time and giving rise to a collective magnetic behavior. 2 For this reason, an understanding of the MNP aggregation effect on hyperthermia performance is crucial.…”

Una guía para el estudio de nanopartículas magnéticas de óxidos de hierro conaplicaciones biomédicas. Parte I

“…Los procesos de generación de calor en las NPM a partir de campos electromagnéticos son bien conocidos, tanto teórica [11], [13], [14] como experimentalmente [15], [16], [17], pero la concordancia entre las observaciones experimentales y las predicciones teóricas no son muy buenas [15], [18], [19]. Esto se debe principalmente a que las NPM están en un entorno altamente interactuante, es decir, una partícula está sometida a interacciones de carácter repulsivo, como la electrostática y la estérica, e interacciones de carácter atractivo, como la la de London-van der Waals.…”

“…Si bien, el modelado teórico predice comportamientos del SAR en función de las interacciones dipolares, moduladas por la concentración de NPM en la suspensión, que han sido recientemente confirmados experimentalmente [18], [25], obtener a partir de estos modelos el valor numérico del SAR aún es materia pendiente, una forma de resolver este problema es considerando una energía de activación magnética (o energía de barrera) efectiva, determinada a partir de medidas magnéticas bajo campos estáticos (midiendo la coercitividad en función de la temperatura) o bajo campos dinámicos (midiendo la susceptibilidad magnética en función de la temperatura) [23].…”