Wonseo Lee

Dual-body magnetic helical robot for drilling and cargo delivery in human blood vessels

We propose a novel dual-body magnetic helical robot (DMHR) manipulated by a magnetic navigation system. The proposed DMHR can generate helical motions to navigate in human blood vessels and to drill blood clots by an external rotating magnetic field. It can also generate release motions which are relative rotational motions between dual-bodies to release the carrying cargos to a target region by controlling the magnitude of an external magnetic field. Constraint equations were derived to selectively manipulate helical and release motions by controlling external magnetic fields. The DMHR was prototyped and various experiments were conducted to demonstrate its motions and verify its manipulation methods.

Control of a three-dimensional magnetic force generated from a magnetic navigation system to precisely manipulate the locomotion of a magnetic microrobot

We propose a method to generate a three-dimensional (3D) magnetic force to manipulate a magnetic microrobot in various environments by using a magnetic navigation system. The proposed method is based on the control of the magnetic force with respect to the change in the magnetization direction of the microrobot and an external magnetic flux gradient. We derived the nonlinear constraint equations which can determine the required direction of the uniform magnetic fields and magnetic gradients to generate the 3D magnetic force of a microrobot. The solutions of the equations were calculated using a geometrical analysis of the equations without any singular point. The proposed methodology was verified on 3D planar environments considering gravitational force, and we also conducted an experiment in a 3D water-filled tubular environment to verify the possibility of the clinical application in human blood vessels.

Selective Motion Control of a Crawling Magnetic Robot System for Wireless Self-Expandable Stent Delivery in Narrowed Tubular Environments

A novel crawling magnetic robot system manipulated by a magnetic navigation system is proposed for wireless self-expandable stent delivery in narrowed tubular environments. The crawling magnetic robot is composed of a crawling module to generate crawling motion for navigation in a tubular environment, and a magnetic pulley module to generate drilling motion to unclog the blocked region and uncovering motion of a stent cover for the self-expandable stent deployment. The magnetic navigation system composed of three orthogonal pairs of electromagnetic coils can generate three dimensional external magnetic field by controlling the applied current. We also proposed selective motion control methods and design processes with fabrication. Finally, we prototyped the proposed crawling magnetic robot and conducted several experiments to show the validity of the proposed crawling magnetic robot and its manipulation methods.

Effective Locomotion and Precise Unclogging Motion of an Untethered Flexible-Legged Magnetic Robot for Vascular Diseases

We propose an untethered flexible-legged magnetic robot (FLMR) manipulated by an external rotating magnetic field (ERMF) to generate effective locomotion and precise unclogging motion to treat vascular diseases. The proposed FLMR is composed of a front body with a drill tip, a cylindrical permanent magnet, a rear body, and flexible legs. The flexible legs are obliquely attached to the bodies like blades of a propeller, so that the FLMR can generate propulsive force in a fluidic environment for locomotion and unclogging motions. To provide manipulation guidelines for locomotion and unclogging motions, we developed a dynamic model of propulsive force, axial force, and friction force, and we established a control method of propulsive force according to the rotating frequency of the ERMF and the diameter of the tube, based on the proposed dynamic model. Finally, we prototyped the FLMR and conducted several experiments to verify its navigation performances and the control method of the propulsive force. Also, we conducted an in vitro experiment with a pseudo blood clot to demonstrate the validity of the locomotion and unclogging motions of the FLMR.

A Spiral Microrobot Performing Navigating Linear and Drilling Motions by Magnetic Gradient and Rotating Uniform Magnetic Field for Applications in Unclogging Blocked Human Blood Vessels

This research proposes a navigating and drilling spiral microrobot actuated by a magnetic gradient and rotating uniform magnetic field to unclog blocked human blood vessels. The proposed spiral microrobot consists of a cylindrical body that contains a cylindrical magnet and spiral drilling blades on the shaft. The cylindrical magnet can rotate freely inside the magnet slot of the body and align in any direction by applying an external uniform magnetic field. The spiral microrobot is prototyped by 3-D printing technology with ultraviolet curable acrylic plastic, then demonstrated by various experiments. These experiments show that the proposed microrobot successfully performs navigating and drilling motions, thus validating the effectiveness of the proposed spiral microrobot.

Magnetic Navigation System Utilizing Resonant Effect to Enhance Magnetic Field Applied to Magnetic Robots

We propose a novel magnetic navigation system (MNS) with the resonant effect of an RLC circuit to generate large magnetic field in high frequency. The variable capacitors of the proposed MNS make it possible not only to change the resonant frequency of the RLC circuit, but also to maximize the output current without phase delay at variable resonant frequencies. The proposed MNS can compensate for the amplitude decrease and phase delay due to the inductance effect of a conventional MNS, while generating a uniform magnetic field with a wide range of rotating frequencies to effectively operate a helical robot in human blood vessels. For verification of the constructed MNS, we measured currents and magnetic fields at several resonant frequencies, and the experimental values corresponded well with the calculated values. We finally demonstrated that the proposed MNS substantially improves both moving and unclogging capabilities of a helical robot as compared to the conventional MNS.

Development of a magnetic catheter with rotating multi-magnets to achieve unclogging motions with enhanced steering capability

We developed a novel magnetic catheter structure that can selectively generate steering and unclogging motions. The proposed magnetic catheter is composed of a flexible tube and two modules with ring magnets that can axially rotate in a way that enables the catheter to independently steer and unclog blood clots by controlling external magnetic fields. We mathematically modeled the deflection of the catheter using the large deflection Euler-Bernoulli beam model and developed a design method to determine the optimal distance between magnets in order to maximize steering performance. Finally, we prototyped the proposed magnetic catheter and conducted several experiments to verify the theoretical model and assess its steering and unclogging capabilities.

Magnetic Helical Robot for Targeted Drug-Delivery in Tubular Environments

We propose a novel magnetic helical robot (HR) that can helically navigate, release a drug to a target area, and generate a mechanical drilling motion to unclog tubular structures of the human body. The proposed HR is composed of two rotating cylindrical magnets (RMs), four fixed cylindrical magnets (FMs), and a helical body. The RMs can be rotated in different directions under two orthogonal external rotating magnetic fields (ERMF). Utilizing these ERMFs, we can generate various motions. The ERMF along the axis of the RMs can generate the drug-release motion, while the ERMF orthogonal to the axis of the RMs can generate navigating and drilling motions. On the other hand, the magnetic torque and the attractive magnetic force between RMs and FMs tightly seal the nozzles in the drug chamber. We analyze these magnetic torque and force of the magnets for the navigating, drug-release, and drilling motion. Especially, the drug-release motion utilizes an eccentric rotational motion of the RMs due to the attractive and repulsive magnetic force between RMs and FMs. This motion squeezes and discharges the drug through a nozzle. We designed the mechanical structure of the proposed HR considering the magnetic properties to achieve the proposed functions. Finally, we prototyped the HR and conducted several experiments to verify the navigating, drug-delivery and drilling capabilities of the HR. We also confirmed that drug-enhanced drilling could unclog the clogged area more effectively than the simple drilling motion.

A Crawling Magnetic Robot Actuated and Steered via Oscillatory Rotating External Magnetic Fields in Tubular Environments

We propose a novel crawling magnetic robot and a driving method utilizing an oscillatory rotating external magnetic field. The crawling magnetic robot is composed of an actuating body with a permanent magnet, two steering bodies with permanent magnets, and flexible legs. The proposed crawling magnetic robot can increase actuating torque with long cylindrical magnet to crawl in tubular environments and navigate in pulsatile flow more than conventional spiral robots. The rotating external magnetic field synchronizes the driving plane of the crawling magnetic robot with the oscillating external magnetic field, while the oscillating external magnetic field generates actuating motion in order to stably generate the crawling motion at any posture. Finally, we prototyped the crawling magnetic robot, and verified the effectiveness of the proposed crawling magnetic robot and driving method in various tubular environments.

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.