Heat Generation in Magnetic Hyperthermia by Manganese Ferrite-Based Nanoparticles Arises from Néel Collective Magnetic Relaxation

Abstract

Collective magnetic relaxation of coupled nanoparticle’s magnetic moments and its influence in magnetic nanoparticle hyperthermia (MNH) therapy are studied by combining experimental data, numerical simulations, and theoretical approaches. Frequency-dependent MNH of Mn-ferrite nanoparticles with different particle sizes and different nanoparticle arrangements, controlled by medium pH and surface coating, revealed that the hyperthermia efficiency could increase or decrease depending on the nanoparticle’s organization within the aggregate. Effective relaxation times of ∼10–7 s were obtained for heat generation that are not explained by Brownian or single-particle Néel relaxation. In particular, we propose a theoretical approach that is a generalization of the Allia–Knobel phenomenological model that allows us to build magnetic regime diagrams and find the conditions for single-particle relaxation (superparamagnetic, interacting superparamagnetic, and single-particle blocked regimes) and collective magnetic relaxation. The regimes depend on dipolar strength, temperature, particle size, aggregate shape and length, magnetization, and magnetic anisotropy (together with axes arrangement). We demonstrate through a detailed nanoparticle characterization (including the temperature dependence of magnetization and anisotropy) that the collective relaxation is responsible for the heat generation of magnetic nanostructures. We believe that our findings and our approach to study the collective magnetic relaxation open new perspectives for designing more efficient magnetic nanocarriers for hyperthermia and explain superferromagnetism as a collective blocked regime.

Toward the Separation of Different Heating Mechanisms in Magnetic Particle Hyperthermia

“…Another approach to further optimize the heating efficiency may be achieved by tuning the MNP–medium parameters such as dosage (namely MNP concentration) and the viscosity of the medium based on a water/agarose solution. In clinical practice, the iron concentration typically varies between 0.5 and 8.0 mg mL –1 in in vitro studies. , At higher concentration, the shorter the interparticle distance between MNPs, the greater their dipolar interaction with a direct impact on eventual heat release. , Further, recent studies have shown that the heating efficiency changes as a function of the viscosity of the medium. − However, there have been only a few studies addressing the different heating mechanisms as a function of medium viscosity. , Finally, for a given set of particle size, magnetic anisotropy, dipolar interactions, and the medium, the external field amplitude and frequency should match the MNP features for the largest heat release in MPH. Using an optimized set of parameters, heat release can be tuned by adjusting the field amplitude or frequency.…”

Hybrid Nanoparticles of Citrate-Coated Manganese Ferrite and Gold Nanorods in Magneto-Optical Imaging and Thermal Therapy

“…Note that there is no contribution from the GNRs since the eddy’s current loss at this size is negligible. Further studies may help to evaluate if the GNRs are influencing the Néel collective relaxation of the aggregates of MnFe 2 O 4 NPs coupled to the GNRs [ 27 ]. Nevertheless, these hybrid NPs may be used similarly to Ci-MnFe 2 O 4 as a feasible heat generator for MH.…”

“…Ci-MnFe 2 O 4 NPs were synthesized via the coprecipitation route by Zufelato et al [ 27 ]. The core, crystal, hydrodynamic sizes, and polydispersity index (PDI) of these MNPs were 16.7, 14, 38 nm, and 0.32, respectively.…”

“…Manganese ferrites (MnFe 2 O 4 ) are interesting spinel ferrite NPs among the various mixed ferrites (Afe 2 O 4 ) with other transition metal ions (e.g., A = Mn, Ni, Cu, and Zn) due to their biocompatibility, saturation magnetization, and chemical stability [ 18 , 19 , 20 , 21 , 22 , 23 ]. Considering the advantages of MnFe 2 O 4 , these NPs are promising candidates to develop theranostic platforms, particularly in the field of personalized nanomedicine like magnetic resonance imaging (MRI) [ 24 , 25 ] and magnetic hyperthermia (MH) [ 26 , 27 , 28 ].…”

“…In the current study, we suggest a hybrid NP, for theranostic purpose, made of Ci-MnFe 2 O 4 and CTAB-GNRs through a simple combination in which CTAB-GNRs and Ci-MnFe 2 O 4 were synthesized using a gold-seed-mediated method [ 35 ] and a coprecipitation route [ 27 ], respectively. The interaction of these NPs was investigated using several characterizations, including a magnetic separation system (SEPMAG), UV-Visible spectroscopy, transmission electron microscopy (TEM), and attenuated total reflection (ATR).…”