Abstract
The heating performance of magnetic nanoparticles (MNPs) under an alternating magnetic field (AMF) is dependent on several factors. Optimizing these factors improves the heating efficiency for cancer therapy and meanwhile lowers the MNP treatment dosage. AMF is one of the most easily controllable variables to enhance the efficiency of heat generation. This paper investigated the optimal magnetic field strength and frequency for an assembly of magnetite nanoparticles. For hyperthermia treatment in clinical applications, monodispersed NPs are forming nanoclusters in target regions where a strong magnetically interactive environment is anticipated, which leads to a completely different situation than MNPs in ferrofluids. Herein, the energy barrier model is revisited and Néel relaxation time is tailored for high MNP packing densities. AMF strength and frequency are customized for different magnetite NPs to achieve the highest power generation and the best hyperthermia performance.
Highlights
Magnetic hyperthermia treatment using magnetic nanoparticles (MNPs) is often considered as an alternative therapy for cancer treatment, currently in clinical trials
For a single nanoparticle immobilized in tumor tissues, the energy barrier is its anisotropy energy competing with thermal fluctuation kBT
If this particle sits in a nanocluster which lots of neighbors are in close contact with, dipolar interaction energy plays an important role in altering energy barrier and relaxation time
Summary
Magnetic hyperthermia treatment using magnetic nanoparticles (MNPs) is often considered as an alternative therapy for cancer treatment, currently in clinical trials. There are single nanoparticles coexisting with nanoclusters in tumor tissues 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. For hyperthermia treatments in clinical applications, the magnetic field strength is limited by physiological considerations because the induced eddy current in non-magnetic tissues will cause necrosis or carbonization of healthy tissues.[3] Brezovich[4] has experimentally determined a safety threshold for AMF with field strength H and frequency f as follows: H · f < 5 × 109 Am−1s−1. Technical consideration limits the field frequencies f to a narrow range,[3] namely, from 100 kHz to 300 kHz, which, as a result, sets the upper limits of field strength H under different scenarios
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