Induction heating of magnetic nanoparticles: role of thermo-physical properties of the coating moieties

Abstract

Superparamagnetic nanoparticles (MNPs) are utilized for magnetic fluid hyperthermia (MFH)-based cancer therapeutics, where the MNPs are surface functionalized to impart desired stability and biological properties. In this study, the MFH properties of palmitic (PA) and stearic (SA) acid-coated superparamagnetic Fe3O4 MNPs, with similar sizes (∼ 10 ± 0.8 nm, and ∼ 11 ± 0.7 nm, respectively), and saturation magnetizations (∼ 40.8 emu/g, and ∼ 41 emu/g, respectively), are systematically probed to understand the role of the thermo-physical properties of the coating moieties on the MFH efficiency. PA and SA-coated MNPs are prepared using a one-step microwave-assisted co-precipitation technique, and the presence of the surface coatings is confirmed using Fourier transform infrared spectroscopy and thermogravimetric analyses. Magneto-calorimetric studies show a high induction heating efficiency, surpassing the threshold of MFH for a biologically relevant field-frequency range. The maximum heating efficiencies are found to be ∼ 164.5 ± 5.4 W/gFe and ∼ 223.9 ± 6.4 W/gFe for the PA and SA-coated MNPs, respectively. This indicates ∼ 36.1 % higher specific absorption rate (SAR) for the SA-coated MNPs under similar experimental conditions, even though the magneto-structural properties are identical for the PA and SA-coated MNPs. Further, finite element modelling is utilized to investigate the thermal transport from the magnetic core to the surrounding medium, where the thermo-physical properties of the coating moieties are considered. Finite element simulations indicate ∼ 32.6 % higher SAR for the SA-coated MNPs, which is consistent with the experimental findings. The higher SAR for the SA-coated MNPs is attributed to the ∼ 1.7 times higher thermal diffusivity of SA. The proposed model is experimentally validated using a third system consisting of lauric acid-coated Fe3O4 MNPs with comparable magneto-structural properties. Further, significant temperature rise in a tissue-equivalent agar medium and good bio-compatibility, as indicated by the in vitro cyto-toxicity studies, make the prepared MNPs potential candidates for MFH applications. The obtained results provide deeper insight into the role of the thermo-physical properties of the coating moieties on the induction heating efficiency of superparamagnetic MNPs.