Thermosensitive Implant for Magnetic Hyperthermia by Mixing Micro-Magnetic and Nano-Magnetic Particles

Recently, self-controlled heating mediators were widely investigated for magnetic hyperthermia. In our previous studies, we succeeded in developing a ferromagnetic implant with low Curie temperature (FILCT). Then, to improve the heating efficiency of FILCT, we coated it with gold. By utilizing the temperature-dependent permeability of FILCT, we proposed a wireless temperature measurement. However, the gold coating layer decreases the change in magnetic flux density caused by FILCT, thus decreasing the accuracy of the thermometry. Therefore, we attempted to use nano-magnetic particles with high heating efficiency instead of gold coating. In this paper, FILCT particles with an average diameter of 83.6 μm were mixed with a commercially available nano-ferrofluid named Resovist (maghemite particles with an average diameter of 3.6 nm) and a lab-made nano-ferrofluid (magnetite particles with an average diameter of 13.9 nm), respectively. The proposed mixture was evaluated compared to FILCT under a magnetic field (500 kHz and 4.73 kA/m). The results show that the heating efficiency of the mixture using Resovist was superior to that of FILCT (approximately 15 times). More importantly, the change in magnetic flux density caused by its permeability was enhanced compared to FILCT (1.2 times). The results also show that a similar tendency was obtained when using both types of nano-ferrofluid.