posted on 2020-12-02, 18:44authored byAdriele
A. de Almeida, Emilio De Biasi, Marcelo Vasquez Mansilla, Daniela P. Valdés, Horacio E. Troiani, Guillermina Urretavizcaya, Teobaldo E. Torres, Luis M. Rodríguez, Daniel E. Fregenal, Guillermo C. Bernardi, Elin L. Winkler, Gerardo F. Goya, Roberto D. Zysler, Enio Lima
In
specific power absorption models for magnetic fluid hyperthermia
(MFH) experiments, the magnetic relaxation time of nanoparticles (NPs)
is known to be a fundamental descriptor of the heating mechanisms.
The relaxation time is mainly determined by the interplay between
the magnetic properties of NPs and the rheological properties of NPs’
environment. Although the role of magnetism in MFH has been extensively
studied, the thermal properties of the NP medium and their changes
during MFH experiments have been underrated so far. Herein, we show
that ZnxFe3–xO4 NPs dispersed through different media with phase
transition in the temperature range of experiment as clarified butter
oil (CBO) and paraffin. These systems show nonlinear behavior of the
heating rate within the temperature range of MFH experiments. For
CBO, a fast increase at ∼306 K is associated with changes in
the viscosity (η(T)) and specific heat (cp(T)) of the
medium at its melting temperature. This increment in the heating rate
takes place around 318 K for paraffin. The magnetic and morphological
characterization of NPs together with the observed agglomeration of
NPs above 306 and 318 K for CBO and paraffin, respectively, indicate
that the fast increase in MFH curves could not be associated with
the change in the magnetic relaxation mechanism, with Néel
relaxation being dominant. In fact, successive experimental runs performed
up to temperatures below and above the CBO and paraffin melting points
resulted in different MFH curves due to agglomeration of NPs driven
by magnetic field inhomogeneity during the experiments. Our results
highlight the relevance of the thermodynamic properties of the system
NP-medium for an accurate measurement of the heating efficiency for
in vitro and in vivo environments, where the thermal properties are
largely variable within the temperature window of MFH experiments.