On the feasibility of improving heat production in magnetic fluid hyperthermia: the time of topology

Gerardo F. Goya

Departamento de Física de la Materia Condensada & Instituto de Nanociencia de Aragón, Universidad de Zaragoza, Zaragoza, Spain

The use of magnetic nanoparticles (MNPs) as nanosized sources of intracellular heat to fight cancer, a therapy known as Magnetic Fluid Hyperthermia (MFH), relies on the capacity of MNPs to heat cancer cells up to temperatures of 42-46ºC by a remote radiofrequency magnetic field. Although already applied in clinical protocols, there is still a lot of room in MFH to further improve the heating efficiency, a desirable goal in order to lower the administered doses of MNPs while keeping their therapeutic efficacy. It has become clear along the last years that under physiological conditions, the power absorption is hindered by different effects like agglomeration, changes in local viscosity and pH within the cell, attachment to membranes, etc. Quite a lot of effort has been applied to understand how each one of these impairments can be overcome and make the MNPs to heat regardless of their physicochemical environment. The formation of low-dimensionality arrangements of single-domain MNPs is being considered lately as a possible way to use magnetic dipolar interactions to increase the power absorption by Néel relaxation. It has been reported that linear structures such as elongated clusters or chains can raise the values of the specific power absorption of MNPs. These structures have been theoretically modeled and it is now apparent that new magnetic phenomena are in place and require unequivocal experimental data in order to understand the complex magnetism of these systems. Our recent work addressed the issue of how agglomeration of MNPs in vitro affects the heating efficiency, and how the induced formation of low dimensional structures can improve it. We have observed that systematic data from naturally agglomerated MNPs in gel and resin phantoms can be compared to well-characterized clusters formed within the cytoplasm of cultured cells.  We found clear evidence that MNPs clusters grown under DC applied fields have lower fractal dimension than the corresponding control cells, and the resulting heating rates increased both in synthetic phantoms and within cells. The experimental data and numerical modelling support the idea that magnetic dipolar interactions can be maneuvered to increase the effective heating efficiency of the MNPs within cells.