Asahi Tomitaka

Effects of particle dipole interaction on the ac magnetically induced heating characteristics of ferrite nanoparticles for hyperthermia

Magnetic particle dipole interaction was revealed as a crucial physical parameter to be considered in optimizing the ac magnetically induced heating characteristics of magnetic nanoparticles. The ac heating temperature of soft MFe2O4 (M=Mg,Ni) nanoparticles was remarkably increased from 17.6 to 94.7 °C (MgFe2O4) and from 13.1 to 103.1 °C (NiFe2O4) by increasing the particle dipole interaction energy at fixed ac magnetic field of 140 Oe and frequency of 110 kHz. The increase in “magnetic hysteresis loss” that resulted from the particle dipole interaction was the main physical reason for the significant improvement of ac heating characteristics.

Physical limits of pure superparamagnetic Fe3O4 nanoparticles for a local hyperthermia agent in nanomedicine

Magnetic and AC magnetically induced heating characteristics of Fe3O4 nanoparticles (IONs) with different mean diameters, d, systematically controlled from 4.2 to 22.5 nm were investigated to explore the physical relationship between magnetic phase and specific loss power (SLP) for hyperthermia agent applications. It was experimentally confirmed that the IONs had three magnetic phases and correspondingly different SLP characteristics depending on the particle sizes. Furthermore, it was demonstrated that pure superparamagnetic phase IONs (d < 9.8 nm) showed insufficient SLPs critically limiting for hyperthermia applications due to smaller AC hysteresis loss power (Neel relaxation loss power) originated from lower out-of-phase magnetic susceptibility.

Lactoferrin conjugated iron oxide nanoparticles for targeting brain glioma cells in magnetic particle imaging.

Magnetic Particle Imaging (MPI) is a new real-time imaging modality, which promises high tracer mass sensitivity and spatial resolution directly generated from iron oxide nanoparticles. In this study, monodisperse iron oxide nanoparticles with median core diameters ranging from 14 to 26 nm were synthesized and their surface was conjugated with lactoferrin to convert them into brain glioma targeting agents. The conjugation was confirmed with the increase of the hydrodynamic diameters, change of zeta potential, and Bradford assay. Magnetic particle spectrometry (MPS), performed to evaluate the MPI performance of these nanoparticles, showed no change in signal after lactoferrin conjugation to nanoparticles for all core diameters, suggesting that the MPI signal is dominated by Néel relaxation and thus independent of hydrodynamic size difference or presence of coating molecules before and after conjugations. For this range of core sizes (14-26 nm), both MPS signal intensity and spatial resolution improved with increasing core diameter of nanoparticles. The lactoferrin conjugated iron oxide nanoparticles (Lf-IONPs) showed specific cellular internalization into C6 cells with a 5-fold increase in MPS signal compared to IONPs without lactoferrin, both after 24 h incubation. These results suggest that Lf-IONPs can be used as tracers for targeted brain glioma imaging using MPI.

Evaluation of magnetic and thermal properties of ferrite nanoparticles for biomedical applications

Magnetic nanoparticles can potentially be used in drug delivery systems and for hyperthermia therapy. The applicability of Fe₃O₄, CoFe₂O₄, MgFe₂O₄, and NiFe₂O₄ nanoparticles for the same was studied by evaluating their magnetization, thermal efficiency, and biocompatibility. Fe₃O₄ and CoFe₂O₄ nanoparticles exhibited large magnetization. Fe₃O₄ and NiFe₂O₄ nanoparticles exhibited large induction heating. MgFe₂O₄ nanoparticles exhibited low magnetization compared to the other nanoparticles. NiFe₂O₄ nanoparticles were found to be cytotoxic, whereas the other nanoparticles were not cytotoxic. This study indicates that Fe₃O₄ nanoparticles could be the most suitable ones for hyperthermia therapy.

Self-Heating Property of Magnetite Nanoparticles Dispersed in Solution

The magnetic characterization of polyethyleneimine (PEI)-coated magnetite (Fe3O4) nanoparticles having diameters of 20-30 nm that were dispersed in a solution was performed, and their self-heating property was investigated. The hydrodynamic diameter of PEI-coated Fe3O4 nanoparticles was approximately 155 nm on an average. To investigate the self-heating property, the increase in the temperature of a sample heated by an applied ac magnetic field was measured, and the specific loss power (SLP) was calculated. The effect of magnetic relaxation loss was estimated by determining the dependence of the SLP on the frequency of an applied magnetic field. For the magnetic characterization of the nanoparticles, dc and ac magnetization curves of the sample were measured and compared with each other to elucidate the heating mechanism. Uncoated Fe3O4 nanoparticles having diameters of 20-30 nm exhibited ferromagnetic characteristics in dry condition. However, the PEI-coated Fe3O4 nanoparticles dispersed in a solution did not exhibit hysteresis of the dc magnetization curve because the particles could easily rotate with the changing magnetic field. The magnetization curve measured under an ac magnetic field had a large area compared to the dc magnetization curve. The results indicate that Brownian relaxation is dominant during magnetization reversal.

Hyperthermia Using Antibody-Conjugated Magnetic Nanoparticles and Its Enhanced Effect with Cryptotanshinone

Heat dissipation by magnetic nanoparticles (MNPs) under an alternating magnetic field can be used to selectively treat cancer tissues. Antibodies conjugated to MNPs can enhance the therapeutic effects of hyperthermia by altering antibody-antigen interactions. Fe3O4 nanoparticles (primary diameter, 20–30 nm) coated with polyethylenimine (PEI) were prepared and conjugated with CH11, an anti-Fas monoclonal antibody. HeLa cell growth was then evaluated as a function of antibody and MNP/antibody complex doses. HeLa cell growth decreased with increased doses of the antibody and complexes. However, MNPs alone did not affect cell growth; thus, only the antibody affected cell growth. In hyperthermia experiments conducted using an alternating magnetic field frequency of 210 kHz, cell viability varied with the intensity of the applied alternating magnetic field, because the temperature increase of the culture medium with added complexes was dependent on magnetic field intensity. The HeLa cell death rate with added complexes was significantly greater as compared with that with MNPs alone. Cryptotanshinone, an anti-apoptotic factor blocker, was also added to cell cultures, which provided an additional anti-cancer cell effect. Thus, an anti-cancer cell effect using a combination of magnetic hyperthermia, an anti-Fas antibody and cryptotanshinone was established.

Magnetization and self-heating temperature of NiFe2O4 nanoparticles measured by applying ac magnetic field

Magnetic and self-heating properties of various size NiFe2O4 (7.7-242.0 nm) were evaluated. The self heating temperature of each sample measured by applying ac magnetic field was affected by its magnetic property. The particle size dependence was also explained by the magnetic properties of the samples. At the lower frequency, the self heating was contributed by hysteresis loss. The ac magnetization process was also evaluated and the result could clarify the origin of self-heating. The 7.7 nm particle was heated by relaxation losses by the applied field at higher frequency. The energy efficiency of a magnetic field to generate self heating was analyzed. It was found that the particle of 130.7 nm exhibited the highest temperature rise and heat generation efficiency for the applied field of low amplitude and frequency.

Self-Heating Temperature and AC Hysteresis of Magnetic Iron Oxide Nanoparticles and Their Dependence on Secondary Particle Size

Magnetic nanoparticles are expected to be used as hyperthermia agents. The mechanism of self-heating of the magnetic nanoparticles under an ac magnetic field is different according to their size. In this study, the temperature rise for the ac/dc hysteresis loops of magnetic nanoparticles were evaluated to clarify the contribution of the Néel and Brownian relaxations to heat dissipation. The samples were dextran-coated magnetic iron oxide nanoparticles of different hydrodynamic diameters (40, 54, and 86 nm), but the same primary diameter of 10 nm. From these diameters, the peak frequencies for the Brownian and Néel relaxations were calculated. The Néel relaxation time, determined by the primary particle size, is much shorter than the Brownian relaxation time for these samples. Although the Néel relaxation is dominant, the self-heating temperature rise of the 86 nm sample was higher than that of the 40 and 54 nm samples. These results suggest that the effect of the magnetic interaction between the nanoparticles depends on the hydrodynamic diameter.

Effects of Mn concentration on the ac magnetically induced heating characteristics of superparamagnetic MnxZn1−xFe2O4 nanoparticles for hyperthermia

The effects of Mn2+ cation concentration on the ac magnetically induced heating characteristics and the magnetic properties of superparamagnetic MnxZn1−xFe2O4 nanoparticles (SPNPs) were investigated to explore the biotechnical feasibility as a hyperthermia agent. Among the MnxZn1−xFe2O4 SPNPs, the Mn0.5Zn0.5Fe2O4 SPNP showed the highest ac magnetically induced heating temperature (ΔTac,mag), the highest specific absorption rate (SAR), and the highest biocompatibility. The higher out of phase susceptibility (χm″) value and the higher chemical stability systematically controlled by the replacement of Zn2+ cations by the Mn2+ cations on the A-site (tetrahedral site) are the primary physical reason for the promising biotechnical properties of Mn0.5Zn0.5Fe2O4 SPNP.

Recent trends on hydrogel based drug delivery systems for infectious diseases

Since centuries, the rapid spread and cure of infectious diseases have been a major concern to the progress and survival of humans. These diseases are a global burden and the prominent cause for worldwide deaths and disabilities. Nanomedicine has emerged as the most excellent tool to eradicate and halt their spread. Various nanoformulations (NFs) using advanced nanotechnology are in demand. Recently, hydrogel and nanogel based drug delivery devices have posed new prospects to simulate the natural intelligence of various biological systems. Owing to their unique porous interpenetrating network design, hydrophobic drug incorporation and stimulus sensitivity hydrogels owe excellent potential as targeted drug delivery systems. The present review is an attempt to highlight the recent trends of hydrogel based drug delivery systems for the delivery of therapeutic agents and diagnostics for major infectious diseases including acquired immune deficiency syndrome (AIDS), malaria, tuberculosis, influenza and ebola. Future prospects and challenges are also described.