Abstract
We present a detailed study of permalloy (Ni80Fe20) nanostructures with variable shape (disk, cylinder and sphere) for magnetic hyperthermia application, exploiting hysteresis losses for heat release. The study is performed modifying nanostructure aspect ratio and size (up to some hundreds of nanometres), to find the optimal conditions for the maximization of specific heating capabilities. The parameters are also tuned to guarantee negligible magnetic remanence and fulfilment of biophysical limits on applied field amplitude and frequency product, to avoid aggregation phenomena and intolerable resistive heating, respectively. The attention is first focused on disk-shaped nanostructures, with a comparison between micromagnetic simulations and experimental results, obtained on nanodisks still attached on the lithography substrate (2D array form) as well as dispersed in ethanol solution (free-standing). This analysis enables us to investigate the role of magnetostatic interactions between nanodisks and to individuate an optimal concentration for the maximization of heating capabilities. Finally, we study magnetization reversal process and hysteresis properties of nanocylinders (diameter between 150 nm and 600 nm, thickness from 30 nm up to 150 nm) and nanospheres (size between 100 nm and 300 nm), to give instructions on the best combination of geometrical parameters for the design of novel hyperthermia mediators.
Highlights
Magnetic hyperthermia is a promising tumour therapy that exploits magnetic nanostructures, typically superparamagnetic iron oxide nanoparticles (SPIONs), and alternating magnetic fields, to increase the temperature of diseased tissues[1,2,3,4,5]
Magnetic nanostructures are injected into the tumour and excited by an ac magnetic field, with a given frequency that ranges from 50 kHz to 1.2 MHz
Coated SPIONs are considered promising candidates for hyperthermia applications, because of good biocompatibility and weak tendency to agglomeration[16,17]. Their heating efficiency is limited, since thermal energy comes from size-dependent Néel and Brownian relaxation, with negligible hysteresis loss contribution
Summary
Magnetic hyperthermia is a promising tumour therapy that exploits magnetic nanostructures, typically superparamagnetic iron oxide nanoparticles (SPIONs), and alternating magnetic fields, to increase the temperature of diseased tissues[1,2,3,4,5]. Coated SPIONs are considered promising candidates for hyperthermia applications, because of good biocompatibility and weak tendency to agglomeration[16,17] Their heating efficiency is limited, since thermal energy comes from size-dependent Néel and Brownian relaxation, with negligible hysteresis loss contribution. A possible way is to use materials with high saturation magnetization and/or high uniaxial magneto-crystalline anisotropy, like cobalt or cobalt-zinc ferrites[19,22,23,24,25,26] Another strategy consists in modifying nanostructure geometry, introducing shape anisotropies; promising results were obtained with magnetite nanorods[27], maghemite, magnetite or cobalt ferrite nanocubes[28,29,30] and octahedral magnetite nanoparticles[31]
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