Optimized Inductive Heating of a Superparamagnetic Zn _x Mn _1–x Fe ₂ O ₄ Hydrophilic Magneto-viscoelastic Fluid for Hyperthermia Application

This article presents the synthesis and comprehensive investigation of the static and dynamic magnetization properties of large-scale PEG-400-coated superparamagnetic Zn_xMn_1-xFe₂O₄ (0 ≤ <i>×</i> ≤ 0.8) nanoparticles, highlighting their potential use as magnetic carriers in magnetic fluid hyperthermia (MFH). The Rietveld analysis of the X-ray diffraction spectra confirmed that the surface-functionalized core nanoparticles exhibit a single-phase spinel structure at the nanoscale, ranging from 15.4 to 11.2 nm. The use of PEG-400 as a hydrophilic shell over Mn-Zn ferrite enhances colloidal stability, as evidenced by the elevated zeta potential (ζ) values ranging from -40 to -26 mV. This enhancement reflects an increase in electrostatic repulsion among Zn_xMn_1-xFe₂O₄ nanoparticles, making them well-suited for formulating viscoelastic and water-based magnetic fluids for hyperthermia applications. The AC inductive heating efficiency for magnetic hyperthermia was systematically investigated as a function of particle concentration, applied alternating magnetic field (AMF), and radiofrequency. To optimize hyperthermic performance, AMF strengths of 9.5 kA/m, 18.3 kA/m, and 25.4 kA/m were applied at corresponding constant frequencies of 586.4 kHz, 154.8 kHz, and 103 kHz, using nanoparticle concentrations of 3 and 6 mg/mL. The optimal heating performance, with maximum specific absorption rate and intrinsic loss power (ILP) values of 273.4 W/g and 5.271 nHm²/kg, respectively, was achieved at 18.3 kA/m and 154.8 kHz for a 3 mg/mL concentration, which was comparable to clinically approved magnetic hyperthermia fluids (ILP range: 0.15-3.1 nHm²/kg). At the highest tested frequency (586.4 kHz), the system deviated from linear response theory, further enhancing heating efficiency due to nonlinear Brownian and Neel relaxation processes. The Zn_xMn_1-xFe₂O₄ MNPs exhibit good biocompatibility (95-70% cell viability) with tested concentrations of 50, 100, 250, 500, and 1000 μM over HeLa cell lines.