Anisotropic magnetic nanoparticles for biomedicine: bridging frequency separated AC-field controlled domains of actuation

Abstract

Magnetic nanoparticles constitute potential nanomedicine tools based on the possibility to obtain different responses (translation, rotation, heating, etc.) triggered by safe remote stimulus. However, such richness can be detrimental if the different performances are not accurately differentiatedand controlled. An example of this is the reorientation of magnetic nanoparticles under the influence of AC fields, which can be exploited for either magneto-mechanical actuation (MMA) at low frequencies (tens of Hz); or heat release at large ones (0. 1 -1 MHz range). While it is clear that Brownian rotation is responsible for MMA, its heating role in the high-frequency regime is not clear. In this work we aim to shed light on this issue, which needs to be well understood for applications in magnetic

Understanding MNPs Behaviour in Response to AMF in Biological Milieus and the Effects at the Cellular Level: Implications for a Rational Design That Drives Magnetic Hyperthermia Therapy toward Clinical Implementation

“…have been revised in detail to determine the transition between heat dissipative mechanisms and magneto-mechanical actuation. As a result, in viscous media the mechanical rotation induced by AMFs is mainly relevant for large MNPs (15–50 nm) and low frequency AMFs (<10 kHz) [ 63 , 64 ], although it can be exploited to exert effective mechanical torque on biological components [ 65 ]. This transition with AMF frequency becomes even clearer in the case of large anisometric NPs [ 63 ] and some empirical studies reported that AMFs induce a torque [ 66 ] or a physical movement of the MNPs [ 67 ] that may produce mechanical damage of the lysosome and cell membrane [ 68 , 69 ].…”

“…Magnetic materials tend to minimize their magnetic poles by locating their magnetization along their longest axis, establishing the geometrical easy magnetization axis. The geometric anisotropy can be enhanced by creating anisometric nanostructures like nanocubes, nanorods and nanodiscs [ 63 , 96 , 97 , 98 ]. These nanostructures are of general interest as they are good mechano-transducers that may apply large torques on biological components although they must be prepared with reduced dimensions to preserve their superparamagnetic response [ 99 , 100 ].…”

How size, shape and assembly of magnetic nanoparticles give rise to different hyperthermia scenarios

“…While at low frequencies it was predicted that the disks absorbed energy and transformed it into particle rotational energy, at high frequencies the behaviour depended on the amplitude of the applied field: for large field amplitudes (greater than the switching field) the energy went into internal energy (heating), whereas for small field amplitudes the energy went into rotational motion. 14 On the other hand, it has been widely reported that the magnetization dynamics under an AC field are intimately associated with the influence of dipole interactions among MNPs, being able to either improve or worsen the hyperthermic response of MNPs. In this context, K. Simeonidis et al demonstrated that even if anisometric nano-spindles heat via Brownian relaxation (and such a contribution can be discarded as a heating mechanism in relevant media similar to that of tumours), the formation of their corresponding chains led to the heat dissipation by the Néel reversal mechanism (due to a progressive reorientation of the elongated structures during the AC treatment).…”

Removal of Uranyl Ion from Wastewater by Magnetic Adsorption Material of Polyaniline Combined with CuFe2O4

“…Magnetic composite nanomaterials have been widely used in environmental protection, catalysis, and biomedicines and have broad application prospects. [25][26][27][28]. A large number of studies have been carried out on the removal of heavy metals in wastewater by using magnetic nanoparticles as magnetic core in the composite adsorption materials.…”