Controlling Magnetization Reversal and Hyperthermia Efficiency in Core-Shell Iron-Iron Oxide Magnetic Nanoparticles by Tuning the Interphase Coupling.

Magnetic particle hyperthermia, in which colloidal nanostructures are exposed to an alternating magnetic field, is a promising approach to cancer therapy. Unfortunately, the clinical efficacy of hyperthermia has not yet been optimized. Consequently, routes to improve magnetic particle hyperthermia, such as designing hybrid structures comprised of different phase materials, are actively pursued. Here, we demonstrate enhanced hyperthermia efficiency in relatively large spherical Fe/Fe-oxide core-shell nanoparticles through the manipulation of interactions between the core and shell phases. Experimental results on representative samples with diameters in the range 30-80 nm indicate a direct correlation of hysteresis losses to the observed heating with a maximum efficiency of around 0.9 kW/g. The absolute particle size, the core-shell ratio, and the interposition of a thin wüstite interlayer are shown to have powerful effects on the specific absorption rate. By comparing our measurements to micromagnetic calculations, we have unveiled the occurrence of topologically nontrivial magnetization reversal modes under which interparticle interactions become negligible, aggregates formation is minimized and the energy that is converted into heat is increased. This information has been overlooked until date and is in stark contrast to the existing knowledge on homogeneous particles.

Effect of low frequency magnetic fields on the growth of MNP-treated HT29 colon cancer cells.

Recent investigations have attempted to understand and exploit the impact of magnetic field-actuated internalized magnetic nanoparticles (MNPs) on the proliferation rate of cancer cells. Due to the complexity of the parameters governing magnetic field-exposure though, individual studies to date have raised contradictory results. In our approach we performed a comparative analysis of key parameters related to the cell exposure of cancer cells to magnetic field-actuated MNPs, and to the magnetic field, in order to better understand the factors affecting cellular responses to magnetic field-stimulated MNPs. We used magnetite MNPs with a hydrodynamic diameter of 100 nm and studied the proliferation rate of MNPs-treated versus untreated HT29 human colon cancer cells, exposed to either static or alternating low frequency magnetic fields with varying intensity (40-200 mT), frequency (0-8 Hz) and field gradient. All three parameters, field intensity, frequency, and field gradient affected the growth rate of cells, with or without internalized MNPs, as compared to control MNPs-untreated and magnetic field-untreated cells. We observed that the growth inhibitory effects induced by static and rotating magnetic fields were enhanced by pre-treating the cells with MNPs, while the growth promoting effects observed in alternating field-treated cells were weakened by MNPs. Compared to static, rotating magnetic fields of the same intensity induced a similar extend of cell growth inhibition, while alternating fields of varying intensity (70 or 100 mT) and frequency (0, 4 or 8 Hz) induced cell proliferation in a frequency-dependent manner. These results, highlighting the diverse effects of mode, intensity, and frequency of the magnetic field on cell growth, indicate that consistent and reproducible results can be achieved by controlling the complexity of the exposure of biological samples to MNPs and external magnetic fields, through monitoring crucial experimental parameters. We demonstrate that further research focusing on the accurate manipulation of the aforementioned magnetic field exposure parameters could lead to the development of successful non-invasive therapeutic anticancer approaches.

Arrangement at the nanoscale: Effect on magnetic particle hyperthermia.

In this work, we present the arrangement of Fe3O4 magnetic nanoparticles into 3D linear chains and its effect on magnetic particle hyperthermia efficiency. The alignment has been performed under a 40 mT magnetic field in an agarose gel matrix. Two different sizes of magnetite nanoparticles, 10 and 40 nm, have been examined, exhibiting room temperature superparamagnetic and ferromagnetic behavior, in terms of DC magnetic field, respectively. The chain formation is experimentally visualized by scanning electron microscopy images. A molecular Dynamics anisotropic diffusion model that outlines the role of intrinsic particle properties and inter-particle distances on dipolar interactions has been used to simulate the chain formation process. The anisotropic character of the aligned samples is also reflected to ferromagnetic resonance and static magnetometry measurements. Compared to the non-aligned samples, magnetically aligned ones present enhanced heating efficiency increasing specific loss power value by a factor of two. Dipolar interactions are responsible for the chain formation of controllable density and thickness inducing shape anisotropy, which in turn enhances magnetic particle hyperthermia efficiency.

A facile microwave synthetic route for ferrite nanoparticles with direct impact in magnetic particle hyperthermia.

The application of ferrite magnetic nanoparticles (MNPs) in medicine finds its rapidly developing emphasis on heating mediators for magnetic hyperthermia, the ever-promising "fourth leg" of cancer treatment. Usage of MNPs depends largely on the preparation processes to select optimal conditions and effective routes to finely tailor MNPs. Microwave heating, instead of conventional heating offers nanocrystals at significantly enhanced rate and yield. In this work, a facile mass-production microwave hydrothermal synthetic approach was used to synthesize stable ferromagnetic manganese and cobalt ferrite nanoparticles with sizes smaller than 14 nm from metal acetylacetonates in the presence of octadecylamine. Prolonging the reaction time from 15 to 60 min, led to ferrites with improved crystallinity while the sizes are slight increased. The high crystallinity magnetic nanoparticles showed exceptional magnetic heating parameters. In vitro application was performed using the human osteosarcoma cell line Saos-2 incubated with manganese ferrite nanoparticles. Hyperthermia applied in a two cycle process, while AC magnetic field remained on until the upper limit of 45 °C was achieved. The comparative results of the AC hyperthermia efficiency of ferrite nanoparticles in combination with the in vitro study coincide with the magnetic features and their tunability may be further exploited for AC magnetic hyperthermia driven applications.