Semi Jeong

A hybrid actuated microrobot using an electromagnetic field and flagellated bacteria for tumor‐targeting therapy

In this paper, we propose a new concept for a hybrid actuated microrobot for tumor‐targeting therapy. For drug delivery in tumor therapy, various electromagnetic actuated microrobot systems have been studied. In addition, bacteria‐based microrobot (so‐called bacteriobot), which use tumor targeting and the therapeutic function of the bacteria, has also been proposed for solid tumor therapy. Compared with bacteriobot, electromagnetic actuated microrobot has larger driving force and locomotive controllability due to their position recognition and magnetic field control. However, because electromagnetic actuated microrobot does not have self‐tumor targeting, they need to be controlled by an external magnetic field. In contrast, the bacteriobot uses tumor targeting and the bacterias own motility, and can exhibit self‐targeting performance at solid tumors. However, because the propulsion forces of the bacteria are too small, it is very difficult for bacteriobot to track a tumor in a vessel with a large bloodstream. Therefore, we propose a hybrid actuated microrobot combined with electromagnetic actuation in large blood vessels with a macro range and bacterial actuation in small vessels with a micro range. In addition, the proposed microrobot consists of biodegradable and biocompatible microbeads in which the drugs and magnetic particles can be encapsulated; the bacteria can be attached to the surface of the microbeads and propel the microrobot. We carried out macro‐manipulation of the hybrid actuated microrobot along a desired path through electromagnetic field control and the micro‐manipulation of the hybrid actuated microrobot toward a chemical attractant through the chemotaxis of the bacteria. For the validation of the hybrid actuation of the microrobot, we fabricated a hydrogel microfluidic channel that can generate a chemical gradient. Finally, we evaluated the motility performance of the hybrid actuated microrobot in the hydrogel microfluidic channel. We expect that the hybrid actuated microrobot will be utilized for tumor targeting and therapy in future. Biotechnol. Bioeng. 2015;112: 1623–1631.

3-D Locomotive and Drilling Microrobot Using Novel Stationary EMA System

For 3-D locomotion and drilling of a microrobot, we proposed an electromagnetic actuation (EMA) system consisting of three pairs of stationary Helmholtz coils, a pair of stationary Maxwell coils, and a pair of rotating Maxwell coils in the previous research . However, this system could have limited medical applications because of the pair of rotational Maxwell coils. In this paper, we propose a new EMA system with three pairs of stationary Helmholtz coils, a pair of stationary Maxwell coils, and a new locomotive mechanism for the same 3-D locomotion and drilling of the microrobot as achieved by the previously proposed EMA system. For the performance evaluation of the proposed EMA system, we perform a 3-D locomotion and drilling test in a blood vessel phantom. In addition, the two EMA systems are compared to show that the newly proposed EMA system has 440% wider working space and 49% less power consumption than the previous EMA system.

Active Locomotive Intestinal Capsule Endoscope (ALICE) System: A Prospective Feasibility Study

Owing to the limitations of the conventional flexible endoscopes used in gastrointestinal diagnostic procedures, which cause discomfort and pain in patients, a wireless capsule endoscope has been developed and commercialized. Despite the many advantages of the wireless capsule endoscope, its restricted mobility has limited its use to diagnosis of the esophagus and small intestine only. Therefore, to extend the diagnostic range of the wireless capsule endoscope into the stomach and colon, additional mobility, such as 3-D locomotion, and steering of the capsule endoscope, is necessary. Previously, several researchers reported on the development of mobility mechanisms for the capsule endoscope, but they were unable to achieve adequate degrees of freedom or sufficiently diverse capsule motions. Therefore, we proposed a novel electromagnetic actuation system that can realize 3-D locomotion and steering within the digestive organs. The proposed active locomotion intestinal capsule endoscope (ALICE) consists of five pairs of solenoid components and a capsule endoscope with a permanent magnet. With the magnetic field generated by the solenoid components, the capsule endoscope can perform various movements necessary to the diagnosis of the gastrointestinal tract, such as propulsion in any direction, steering, and helical motion. From the results of a basic locomotion test, ALICE showed a propulsion angle error of less than 4° and a propulsion force of 70 mN. To further validate the feasibility of ALICE as a diagnostic tool, we executed ex vivo testing using small intestine extracted from a cow. Through the basic mobility test and the ex vivo test, we verified ALICEs usefulness as a medical capsule endoscopic system.

Electromagnetic Navigation System Using Simple Coil Structure (4 Coils) for 3-D Locomotive Microrobot

Researches on the biomedical wireless microrobot are being actively carried out. In particular, compared with conventional catheter intervention, the wireless locomotive microrobot using an electromagnetic navigation system (ENS) can have many advantages in ischemic heart disease therapy. The ENSs generally use a uniform magnetic field and gradient magnetic field for the actuation of microrobots. However, because most ENSs require many coils, they have severe limitations, including a complex structure, large energy consumption, increased power supply, and large system volume. This paper proposes a new ENS for a 3-D locomotive microrobot using only four electromagnetic coils. The proposed ENS has a very simple structure, which consists of two circular coils and two saddle coils. The alignment and propulsion of the microrobot are determined by the generated magnetic field and gradient magnetic field from the four coils. This paper proposes a control algorithm and a gravity compensation for a 3-D locomotive microrobot and validates the performance of the microrobot using the proposed ENS. Finally, through a locomotion test of a blood vessel phantom, it was demonstrated that the microrobot can move to a target position in the phantom and deliver a drug to the target lesion.

Positioning of microrobot in a pulsating flow using EMA system

The purpose of this paper is the positioning control of the microrobot in a pulsating flow using electromagnetic actuation (EMA) System. Several types of EMA systems which are 2-dimensional and 3-dimensional locomotion control of microrobot were proposed and studied. Generally, these conventional researches of EMA systems showed the results of locomotion of microrobot in a fluid without flow. However, in the case of test of microrobot in a blood vessel, it is required that the experiments of locomotion should be performed in a pulsating flow like bloodstream. For that reason, we carried out basic locomotion research of the microrobot in the pulsating flow. For this experiment, we used simple 1-dimensional EMA system which consists of a pair of Helmholtz and Maxwell coils, and we set up a vascular simulator which can generate pulsating flow in the vessel phantom. The magnetized microrobot was inserted in the vascular simulator. The electromagnetic force which affects the motion of the microrobot was controlled by regulating input current to EMA system. The input current regulation was performed by considering the magnitude of flow rate and drag force of fluid to the microrobot. To measure the pressure variance of a pulsating flow in the vascular phantom, the pressure transducer was placed in front of the region of interest (ROI) and the control input which compensates the drag force to microrobot was generated by using the transducer signal. In addition, the position of microrobot was acquired through the CMOS camera and the feedback control loop was also implemented for accurate positioning control. The performance of the positioning control was evaluated by in-vitro experiments using vascular simulator. In addition, the feasibility of the position control of the microrobot was also evaluated by in-vivo animal experiments.

Position stabilization of microrobot using pressure signal in pulsating flow of blood vessel

The target of this paper is the pressure sensor based positioning control of the microrobot in a pulsating flow of blood vessel using an electromagnetic actuation (EMA) system. For treatment of these coronary arterial diseases, various type microrobots with a wireless locomotive actuating power using EMA were proposed. However, because the intravascular blood flows have pulsate fluctuating and high pressurized waves, it is estimated that the stable positioning control of the microrobot in the blood vessel was very difficult. In detail, the pulsating blood flow generates the pulse type drag force on the microrobot and the drag force makes the microrobots oscillating motion in the blood vessel. For the accurate positioning control of the microrobot, the pulse type drag force on the microrobot should be compensated. Therefore, for the compensation of the drag force on the microrobot, the pressure transducer in the blood vessel was introduced and the pressure signal of the blood flow was used. Through the pressure sensor based compensation of the drag force, the stabilization of the position of the microrobot could be tested and evaluated.

Electromagnetic actuation system for locomotive intravascular therapeutic microrobot

In this paper, we proposed an intravascular therapeutic microrobot using an electromagnetic actuation (EMA) system with bi-plane X-ray imaging device. The proposed EMA system consists of Helmholtz-Maxwell coils, uniform-gradient saddle coils. The Helmholtz-Maxwell coils are located along y-axis, and uniform-gradient saddle coils are located perpendicular to y-axis. In order to align the microrobot along a desired angle in 2D (dimensional) plane, it is necessary to control of the currents on Helmholtz coil and uniform saddle coil. For a forward and backward direction movement of the microrobot, we precisely control the currents of Maxwell coil and gradient saddle coil. Because the saddle coils can be rotated around the y-axis, the effective actuation plane of the microrobot can be also rotated, and the microrobot can move in 3D space. In addition, for the position recognition of the microrobot in a blood vessel, we adopted a bi-plane X-ray fluoroscopy. If the saddle coils are rotated around the y-axis, an open area is changed. Therefore, the saddle coils and bi-plane X-ray fluoroscopy must be rotated simultaneously. To confirm the feasibility of 3D locomotion of the microrobot, we executed a locomotion test of the microrobot in the blood vessel phantom, where the blood vessel phantom was fabricated by the rendering data from computed tomography (CT) images of the iliac artery and 3D printer.

Penetration of an artificial arterial thromboembolism in a live animal using an intravascular therapeutic microrobot system

The biomedical applications of wireless robots are an active area of study. In addition to moving to a target lesion, wireless locomotive robots can deliver a therapeutic drug for a specific disease. Thus, they hold great potential as therapeutic devices in blood vessel diseases, such as thrombi and occlusions, and in other diseases, such as cancer and inflammation. During a percutaneous coronary intervention (PCI), surgeons wear a heavy shielding cloth. However, they cannot escape severe radiation exposure owing to unstable shielding. They may also suffer from joint pains because of the weight of the shielding cloth. In addition, the catheters in PCIs are controlled by the surgeons hand. Thus, they lack steering ability. A new intravascular therapeutic system is needed to address these problems in conventional PCIs. We developed an intravascular therapeutic microrobot system (ITMS) using an electromagnetic actuation (EMA) system with bi-plane X-ray devices that can remotely control a robot in blood vessels. Using this proposed ITMS, we demonstrated the locomotion of the robot in abdominal and iliac arteries of a live pig by the master-slave method. After producing an arterial thromboembolism in a live pig in a partial iliac artery, the robot moved to the target lesion and penetrated by specific motions (twisting and hammering) of the robot using the proposed ITMS. The results reveal that the proposed ITMS can realize stable locomotion (alignment and propulsion) of a robot in abdominal and iliac arteries of a live pig. This can be considered the first preclinical trial of the treatment of an artificial arterial thromboembolism by penetration of a blood clot.

Position-based compensation of electromagnetic fields interference for electromagnetic locomotive microrobot

Recently, the locomotion of a microrobot wirelessly actuated by electromagnetic actuation systems has been studied in many ways. Because of the inherent characteristics of an electromagnetic field, however, the magnetic field of each coil in the electromagnetic actuation system induces magnetic field interferences, which can distort the desired electromagnetic field, preventing the microrobot from following the desired path. In this article, we used two pairs of Helmholtz coils and two pairs of Maxwell coils in a two-dimensional electromagnetic actuation system. Generally, the two pairs of Helmholtz coils generate the torque for the rotation of the microrobot and the two pairs of Maxwell coils generate the propulsion force of the microrobot. Both pairs of Helmholtz and Maxwell coils have to work to simultaneously align and propel the microrobot in a desired direction. In this situation, however, the electromagnetic fields produced by the Helmholtz coils can interfere with those produced by the Maxwell coils. This interference is closely dependent on the position of the microrobot in the region of interest inside the electromagnetic coils system. This means that the alignment direction and propulsion force of the microrobot can be distorted according to the position of the microrobot. Therefore, we propose a compensation algorithm for the electromagnetic field interference using the position information of the microrobot to correct the magnetic field interferences. First, the interference of an electromagnetic field obeying the Biot–Savart law is analyzed by numerical analysis. Second, a position-based compensation algorithm for the locomotion of a microrobot is proposed. Various locomotion tests of a microrobot verified that the proposed compensation algorithm could reduce the normalized average tracking error from 5.25% to 1.92%.

Electromagnetic actuation methods for intravascular locomotive microrobot

Heart diseases such as angina pectoris and myocardial infarction have been becoming the leading causes of death all over the world in recent years. The pharmacotherapy and the surgical operations have been executed for treating heart problems. The percutaneous coronary intervention (PCI) with catheter is frequently used for the treatment of coronary artery diseases, but the treatment of chronic total occlusion (CTO) is very difficult and challenging operation, since there is no efficient alternative therapy until now. For this reason, the microrobot to improve the intravascular treatment is one of the growing research areas. In this paper, various electromagnetic actuation (EMA) systems to supply driving power for the microrobot were proposed. The performance of the locomotion of microrobot in the 2D and 3D space were validated with in-vitro experiments and also the in-vivo tests were performed for demonstrating the movement of microrobot in the living rabbit.