Untangling the Influence of Particle-Intrinsic Parameters and Experimental Conditions in Magnetic Fluid Hyperthermia

DANIELA P. VALDÉS; ENIO LIMA JR.; ROBERTO D. ZYSLER; GERARDO F. GOYA; EMILIO DE BIASI

Londres

Conferencia; Conference on the Scientific and Clinical Applications of Magnetic Carriers; 2022

Conference on the Scientific and Clinical Applications of Magnetic Carriers

Optimization of the specific power absorption (SPA) of magnetic nanoparticles (MNPs) formagnetic fluid hyperthermia (MFH) applications is currently focused on designing MNPs withcertain properties and finding favourable experimental conditions for each system. However, therole of relevant parameters in the relaxation is still under discussion. Moreover, in vitro and invivo experiments generally lead to interacting MNP systems due to agglomeration in the cellularenvironment. In the particular case of linear aggregates, the impact of dipolar interactions on theSPA of the system is still an open discussion: there are reports of both beneficial [1] anddetrimental [2] effects on the SPA.Through a nonlinear model [3-5] for the magnetic relaxation of single-domain MNPs withuniaxial effective anisotropy, we simulated systems with different particle-intrinsic parameters(size, anisotropy) and experimental conditions (frequency, interactions). We determined fourregions (I-IV) of magnetic behaviour as a function of relative anisotropy (anisotropy field withrespect to the amplitude of the ac field), that dictate the SPA in MFH experiments through thearea enclosed by hysteresis loops (see Figure) [4].The boundaries between regions change with all of these parameters. We analyzed linear MNParrangements and found out that, for the low relative anisotropy range, dipolar interactionsincrease the SPA while they are detrimental for the range of high relative anisotropy. Thisresolves the seemingly contradictory results of interaction effects in this kind of aggregatesreported in the literature [1,2]. For low relative anisotropy regions, we also explained how theenhancement of the SPA by dipolar interactions (reflected by an increase in coercivity) is actuallycaused by the shift between the local and the applied magnetic field [5].We also provide a simple, analytical tool aimed at the design of MNPs and the choice of theexperimental conditions for optimal heating. Through the thermal interpretation of its validityrange, we conclude that systems with low-thermal-fluctuation influence are the best candidatesfor MFH due to their high SPA values.Figure. Normalized area a as a function of relative anisotropyfield hk (area curve) of a noninteracting MNP system with o hdiameter 60 nm and anisotropy axes parallel to the external field = 05 1for a frequency f = 100 kHz. Regions I to IV are indicated bycoloured zones. Inset: Loop corresponding to the maximum ofthe area curve.[1] B. Mehdaoui et al, Phys. Rev. B 87 174419 (2013)[2] L.C. Branquinho et al, Sci. Rep. 3 2887 (2013)[3] E. De Biasi et al, J. Magn. Magn. Mater. 320 312 (2008)[4] D.P. Valdés et al, Phys. Rev. Applied 15 044005 (2021)[5] D.P. Valdés et al, Phys. Rev. Applied 14 014023 (2020)