Progress in the design of nanoscale
magnets for localized hyperthermia
cancer therapy has been largely driven by trial-and-error approaches,
for instance, by changing of the stoichiometry composition, size,
and shape of the magnetic entities. So far, widely different and often
conflicting heat dissipation results have been reported, particularly
as a function of the nanoparticle concentration. Thus, achieving hyperthermia-efficient
magnetic ferrofluids remains an outstanding challenge. Here we demonstrate
that diverging heat-dissipation patterns found in the literature can
be actually described by a single picture accounting for both the
intrinsic magnetic features of the particles (anisotropy, magnetization)
and experimental conditions (concentration, magnetic field). Importantly,
this general magnetic-hyperthermia scenario also predicts a novel
non-monotonic concentration dependence with optimum heating features,
which we experimentally confirmed in iron oxide nanoparticle ferrofluids
by fine-tuning the particle size. Overall, our approach implies a magnetic hyperthermia trilemma that may constitute a simple
strategy for development of magnetic nanomaterials for optimal hyperthermia
efficiency.
Iron oxide nanoparticles have found an increasing number of biomedical applications as sensing or trapping platforms and therapeutic and/or diagnostic agents. Most of these applications are based on their magnetic properties, which may vary depending on the nanoparticle aggregation state and/or concentration. In this work, we assess the effect of the inter- and intra-aggregate magnetic dipolar interactions on the heat dissipation power and AC hysteresis loops upon increasing the nanoparticle concentration and the hydrodynamic aggregate size. We observe different effects produced by inter- (long distance) and intra-aggregate (short distance) interactions, resulting in magnetizing and demagnetizing effects, respectively. Consequently, the heat dissipation power under alternating magnetic fields strongly reflects such different interacting phenomena. The intra-aggregate interaction results were successfully modeled by numerical simulations. A better understanding of magnetic dipolar interactions is mandatory for achieving a reliable magnetic hyperthermia response when nanoparticles are located into biological matrices.
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