The mechanical aspects of intracellular structures during in vitro magnetic hyperthermia.

B. SANZ; R. CABREIRA-GOMES; J. DEPEYROT; T.E. TORRES; E. LIMA JR.; E. DE BIASI; R. ZYSLER; M.L. FANARRAGA; M.R. IBARRA; G. F. GOYA

Conferencia; 4th International Conference in Nanoscience, Nanotechnology and Nanobiotechnology; 2017

The dynamics of magnetic relaxation in single-domain magnetic nanoparticles (MNPs) dispersed in viscous fluids can be explained by classical theories from the Stoner-Wohlfarth model to the LandauLifshitz stochastic equations. However, the impact of different nano-assemblies like aggregates, clusters or chains of MNPs on the power absorption has only recently started to be assessed. In Magnetic Hyperthermia (MHT) the heat is generated by synthetic units (i.e., MNPs) at the intracellular space. This situation provokes two main questions: a) does the intracellular heat release mean a more efficient apoptotic mechanism than exogenous heating (EHT)? and b) is there any mechanical mechanism other tan heat dissipation at the nanoscale? We have partially addressed these questions by systematic comparison of MHT and EHT experiments with the same conditions and target temperatures. We used cultivated human neuroblastoma SH-SY5Y cells with MNPs and exposed to both EHT and MHT. The effect of both heating sources was studied following the cell viability at the same target temperatures. We found that MHT was able to induce a decrement in cell viability that is larger than the corresponding EHT for the same target temperatures. In terms of temperature efficiency, MHT requires an average temperature that is 6°C lower than that required with EHT to produce a similar cytotoxic effect. We have also increased the heating efficiency in vitro by design of MNPs with specific physical parameters such as magnetic anisotropy and magnetic moment. The output of these studies was the largest in vitro specific power absorption (SPA) values reported so far. Our results demonstrate the need of precise experimental data about the actual size, shape and structure of intracellular clusters to validate theoretical models about the role of dipolar interactions or cluster topology on power absorption.