A Suitable Magnetic Field Source Composed of an HTS Coil and HTS Bulks for Magnetic Drug Delivery System

To realize Magnetic Drug Delivery System (MDDS), it is necessary to reduce the frictional force on the inner surface of the blood vessel and increase the magnetic force in the longitudinal direction of the blood vessel acting on magnetic drugs deep inside the body. In other words, where the magnetic drugs are concentrated, the magnetic flux density gradient in the longitudinal direction of the blood vessel must be large and the magnetic flux density gradient perpendicular to the blood vessel surface must be small. However, creating such a magnetic field distribution with a single magnetic field source is difficult. Therefore, we investigated a magnetic field source configuration method that can increase the magnetic flux density gradient in the longitudinal direction of the blood vessel and decrease the magnetic flux density gradient perpendicular to the blood vessel surface by configuring the magnetic field source with an HTS coil and zero-field-cooled HTS bulks and using the antimagnetic effect of the HTS bulks. We examined the effect of the number of cylindrical HTS bulks on the magnetic force acting on the magnetic drugs. The shielding current field of the HTS bulk had the effect of reducing the magnetic flux density gradient perpendicular to the blood vessel surface and the relative position of the area where the magnetic drugs are concentrated and the shielding current region within the HTS bulk greatly affected the magnetic flux density gradient perpendicular to the blood vessel surface. Based on these results, we examined the effect of the distance between two cylindrical HTS bulks placed inside an HTS coil on the magnetic force acting on the magnetic drugs. The magnetic force in the longitudinal direction of the blood vessel was able to be increased by placing the HTS bulks so that the boundary of the HTS bulk (shielding current region) is near the area directly below the area where the magnetic drugs are concentrated. The distance between the square-column HTS bulks that maximized the magnetic force was longer than that of the cylindrical HTS bulks.