Hyun Chul Choi

Reductive determination of hydrogen peroxide with MWCNTs-Pd nanoparticles on a modified glassy carbon electrode

This paper introduces the use of multi walled carbon nanotubes (MWCNTs) with palladium (Pd) nanoparticles in the electrocatalytic reduction of hydrogen peroxide (H(2)O(2)). We have developed and characterized a biosensor for H(2)O(2) based on Nafion(®) coated MWCNTs-Pd nanoparticles on a glassy carbon electrode (GCE). The Nafion(®)/MWCNTs-Pd/GCE electrode was easily prepared in a rapid and simple procedure, and its application improves sensitive determination of H(2)O(2). Characterization of the MWCNTs-Pd nanoparticle film was performed with transmission electron microscopy (TEM), Raman, and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) and amperometry (at an applied potential of -0.2V) measurements were used to study and optimize performance of the resulting peroxide biosensor. The proposed H(2)O(2) biosensor exhibited a wide linear range from 1.0 μM to 10 mM and a low detection limit of 0.3 μM (S/N=3), with a fast response time within 10s. Therefore, this biosensor could be a good candidate for H(2)O(2) analysis.

Magnetic Navigation System With Gradient and Uniform Saddle Coils for the Wireless Manipulation of Micro-Robots in Human Blood Vessels

A magnetic navigation system (MNS) for the wireless manipulation of micro-robots in human blood vessels is a possible surgical tool for coronary artery disease. This paper proposes a novel MNS composed of one conventional pair of Maxwell and Helmholtz coils and one newly developed pair of gradient and uniform saddle coils. The proposed system was theoretically developed using the Biot-Savart law, and it was verified experimentally after constructing the proposed MNS. The proposed MNS is geometrically compact to allow a patient to lie down, and magnetically efficient compared with the conventional MNS which has two pairs of Maxwell and Helmholtz coils.

Two-dimensional actuation of a microrobot with a stationary two-pair coil?system

This paper proposes a new two-dimensional (2D) actuation method for a microrobot that uses a stationary two-pair coil system. The coil system actuates the microrobot by controlling the magnitude and direction of the external magnetic flux. The actuation of the microrobot consists of an alignment to the desired direction and a linear movement of the microrobot by non-contact electromagnetic actuation. Firstly, the actuation mechanism of the stationary coil system is theoretically derived and analyzed. Secondly, the tendency of the magnetic flux in the coil system are analyzed and compared by preliminary theoretical analysis. Through various locomotive experiments of the microrobot, the performance of the electromagnetic actuation by the proposed stationary two-pair coil system is evaluated. Using the proposed 2D actuation method, the microrobot is aligned to the desired direction by Helmholtz coils and is driven to the aligned direction by Maxwell coils. By the successive current control of the coil system, the microrobot can move along a desired path, such as a rectangular-shaped or a diamond-shaped path.

Preparation of reusable Ag-decorated graphene oxide catalysts for decarboxylative cycloaddition

In this study, we demonstrated a noble Ag-decorated graphene oxide catalyst (GOSH-Ag) for use in the decarboxylative cycloaddition reaction. The catalyst was easily prepared by depositing Ag nanoparticles on thiolated graphene oxide (GOSH) surfaces. Transmission electron microscopy (TEM) indicated that the nanoparticles were well-dispersed and of a small, approximately 3.7 nm average size. These characteristics resulted in a high surface area, which enhanced the catalytic activity of the supported catalyst. Moreover, it was found that the aggregation of Ag catalysts was inhibited by the strong adhesion between the GOSHs and the Ag nanoparticles during the chemical reactions, thereby permitting their reuse. Indeed, the supported catalyst could easily be separated and recovered from the reaction mixture and reused several times.

Preparation, characterization and catalytic properties of Pd-decorated carbon nanotubes possessing different linkers

To investigate the relationship between the linker length and the catalytic activities of metal-decorated CNTs, three samples were prepared with different linker molecules, viz.NaSH, HSCH2CH2SH, and C2H2N2S3. The structures of the prepared samples were characterized using transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The analysis of the TEM images and XRD patterns showed that the Pd nanoparticles strongly adhered to the outside of the CNTs, with average particle sizes of ∼3 nm, ∼5 nm, and ∼6 nm for samples A, B and C, respectively. The XPS spectra revealed that the Pd species on the Pd-decorated CNTs consisted of Pd0, Pd2+ and Pd4+. The oxidized Pd species were formed by the interaction of the electron-donor Pd0 atoms with the electrophilic neighboring protons (H+) during the sample preparation. The oxidized Pd species become more abundant with increasing linker length, causing a decrease of their catalytic activities in organic and electrocatalytic reactions. Nevertheless, all of the samples exhibited higher activity in organic and electrocatalytic reactions than that of the reference systems.

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.

Shape memory alloy–based biopsy device for active locomotive intestinal capsule endoscope

Recently, capsule endoscopes have been used for diagnosis in digestive organs. However, because a capsule endoscope does not have a locomotive function, its use has been limited to small tubular digestive organs, such as small intestine and esophagus. To address this problem, researchers have begun studying an active locomotive intestine capsule endoscope as a medical instrument for the whole gastrointestinal tract. We have developed a capsule endoscope with a small permanent magnet that is actuated by an electromagnetic actuation system, allowing active and flexible movement in the patient’s gut environment. In addition, researchers have noted the need for a biopsy function in capsule endoscope for the definitive diagnosis of digestive diseases. Therefore, this paper proposes a novel robotic biopsy device for active locomotive intestine capsule endoscope. The proposed biopsy device has a sharp blade connected with a shape memory alloy actuator. The biopsy device measuring 12mm in diameter and 3mm in length was integrated into our capsule endoscope prototype, where the device’s sharp blade was activated and exposed by the shape memory alloy actuator. Then the electromagnetic actuation system generated a specific motion of the capsule endoscope to extract the tissue sample from the intestines. The final biopsy sample tissue had a volume of about 6mm3, which is a sufficient amount for a histological analysis. Consequently, we proposed the working principle of the biopsy device and conducted an in-vitro biopsy test to verify the feasibility of the biopsy device integrated into the capsule endoscope prototype using the electro-magnetic actuation system.