Selective Navigating and Unclogging Motions of an Intravascular Helical Magnetic Millirobot Actuated by External Biaxial Rotating Magnetic Fields

Intravascular helical magnetic millirobots (IHMMs) capable of navigating in and unclogging human blood vessels have been widely investigated as a possible means for the treatment of occlusive vascular diseases. However, conventional IHMMs are based on a bodily helical motion whereby the overall structure of the IHMM rotates at the same time, making it impossible to separate the navigating and unclogging motions. Herein, we propose a novel IHMM composed of a helical body and a drilling rotary tip whose rotating axes are perpendicular to each other. We have also derived an external biaxial rotating magnetic field (EBRMF), composed of two orthogonally rotating magnetic fields, that is suitable for independent or simultaneous manipulation of the helical navigating and rotary-tip drilling (unclogging) motions of the proposed IHMM. This enables safe and precise use of the IHMM for treatment of occlusive vascular diseases, including the generation of fast rotary-tip drilling motion combined with relatively slow helical navigating motion toward a clogged point. This kind of motion reduces the risk of damaging the blood vessel walls. We conducted various experiments demonstrating the EBRMF and controlled motions of the IHMM to show the efficacy of the proposed structure and method.