Role of the Fraction of Blocked Nanoparticles on the Hyperthermia Efficiency of Mn-Based Ferrites at Clinically Relevant Conditions

Abstract

To investigate the role of magnetic anisotropy on magnetic hyperthermia heating efficiency at low field conditions, Mn, MnZn, and MnCo-ferrite nanoparticles were synthesized using the hydrothermal method. The coercive field temperature dependence method was used to determine the blocking temperature distribution of the particles by considering the temperature dependence of anisotropy and magnetization and the random anisotropy axis configuration. The data allowed one to estimate the room-temperature quasi-static superparamagnetic diameter, which was found to be lower than the theoretical value. Magnetic hyperthermia experiments of the magnetic nanocolloids at 522 kHz indicated that soft nanomagnets heat more efficiently at clinically relevant conditions. The heating performance was found to decrease at the higher fraction of blocked nanoparticles. For instance, samples with similar size distribution and mean diameter of 10 nm, at a field amplitude of only 120 Oe (9.6 kA m–1), showed a decrease of specific loss power of 56% for the Mn-ferrite and 93% for the MnCo-ferrite in comparison with the MnZn-ferrite nanoparticle. The fractions of blocked particles of the MnZn, Mn, and MnCo-ferrite were 5, 10, and 25%, respectively, at room temperature.

In vivo magnetic nanoparticle hyperthermia: a review on preclinical studies, low-field nano-heaters, noninvasive thermometry and computer simulations for treatment planning

“…Immobilizing the nanoparticles strongly affects the harmonic signals, indicating the importance of Brownian relaxation at this frequency range. This is consistent with the analysis of the hydrodynamic radii of multicore nanostructures that, in the range of 50-100 nm, predicts Brownian relaxation in the frequency range lower than 20 kHz, as experimentally found by AC susceptibility measurements [192] or estimated theoretically using linear response theory [148]. On the other hand, Bender et al clearly demonstrated that at typical magnetic hyperthermia frequencies (100-500 kHz) the magnetic response of multicore nanoparticles is governed by intrinsic magnetic relaxation, i.e., by N eel-like relaxation [163,192].…”

“…According to this criteria it is clear from Figure 1 that no preclinical study from the literature is satisfactory (as far as we know) which means, in principle, that the experimental conditions that have been studied would not be applicable for human use, since they are predicted to generate a lot of non-localized heat by eddy currents. This is very disappointing, and suggests that several studies had not focused enough on the priority for clinical translation, which is related to improving the heating efficiency of magnetic nanoparticles at low-field condition [147,148]. On the other hand, Dutz and Hergt suggest that this limit can increase by a factor of 10 [25,26]; even so, note that only a few investigations are within the expected safety range of the second clinical limit.…”

“…To address some of the current limitations of this thermal therapy modality, not only for GBM treatment but mainly for its widespread application as an elective treatment modality for cancer, the development of better nano-heaters with low toxicity formulations and high specific loss power (SLP) in low-field conditions (i.e., feasible combinations of AMF amplitude and frequency) [148], are eagerly needed in order to explore the real potential of the technique, which in principle might not need to be combined with ionizing radiation.…”

Single‐phase and binary phase nanogranular ferrites for magnetic hyperthermia application

“…Indeed, the dynamic hysteresis is strongly influenced by this term and shows optimum anisotropy values for hyperthermia. 11,49 The τ N of the ferrites varies in accordance with K eff , and the volume of the ferrite particles (V), as given in; 21 where τ 0 is the characteristic relaxation time approximately equal to 10 −9 s, k B and T are the Boltzmann constant and temperature, respectively (see Table 2). From the graphs (Figures 5 and 6), it is very clear that the heating rates of CFO_UR and CuF_20 show better efficiency compared to other ferrite samples.…”

Specific Loss Power of Co/Li/Zn-Mixed Ferrite Powders for Magnetic Hyperthermia

“…When exposed to an alternating magnetic field, magnetic particles, considered in a broad sense as passive sensors, are able to detect and transduce it in a controlled and localized release of heat; this ability has promoted the use of these materials for advanced therapeutic applications such as magnetic hyperthermia and heat-assisted drug release [13,[21][22][23]. The physical mechanism at the base of heat generation has been recently identified to be mainly the magnetic hysteresis losses [24].…”