Typical experiment vs. in-cell like conditions in magnetic hyperthermia: Effects of media viscosity and agglomeration

Magnetic nanoparticles (MNPs) can be used to transform electromagnetic energy into heat in hyperthermic treatment of cancer and other thermally activated therapies. The MNPs heating efficiency depends strongly on the combination of the MNPs' structural properties and environmental conditions. MNPs hyperthermic yield is usually studied in diluted suspensions, although, in the actual therapy, the particles end mostly aggregated and fixed into cellular structures. In this work, the heating efficiency of low size dispersion Fe3O4 MNPs, defined as the Specific Absorption Rate (SAR), was studied in two conditions: liquid suspension (ferrofluid FF, typical characterization state) and gel matrix (ferrogel FG, mimicking biological application environment). The samples were characterized by TEM, ZFC-FC and SAXS. Their magnetic response to radio-frequency fields was measured by induction in order to obtain SAR values from the magnetization cycles area. 3D maps of SAR versus field amplitude and frequency were elaborated in order to compare the response of fixed and suspended MNPs. Structural characterization shows FG's MNPs agglomerated in a crystal-like mesostructure with a well defined interparticle distance. SAR results show a clear difference of behaviour between liquid and gel matrices, with larger SAR values for the FG sample indicating a lower resonance frequency, inside the studied region, for fixed MNP. Additionally, the local maximum suggested in FG's SAR map indicates a behaviour outside linear response regimen as expected for the applied field amplitudes.