Sukho Park

Detection of microorganisms using terahertz metamaterials

Microorganisms such as fungi and bacteria cause many human diseases and therefore rapid and accurate identification of these substances is essential for effective treatment and prevention of further infections. In particular, contemporary microbial detection technique is limited by the low detection speed which usually extends over a couple of days. Here we demonstrate that metamaterials operating in the terahertz frequency range shows promising potential for use in fabricating the highly sensitive and selective microbial sensors that are capable of high-speed on-site detection of microorganisms in both ambient and aqueous environments. We were able to detect extremely small amounts of the microorganisms, because their sizes are on the same scale as the micro-gaps of the terahertz metamaterials. The resonant frequency shift of the metamaterials was investigated in terms of the number density and the dielectric constants of the microorganisms, which was successfully interpreted by the change in the effective dielectric constant of a gap area.

New paradigm for tumor theranostic methodology using bacteria-based microrobot.

We propose a bacteria-based microrobot (bacteriobot) based on a new fusion paradigm for theranostic activities against solid tumors. We develop a bacteriobot using the strong attachment of bacteria to Cy5.5-coated polystyrene microbeads due to the high-affinity interaction between biotin and streptavidin. The chemotactic responses of the bacteria and the bacteriobots to the concentration gradients of lysates or spheroids of solid tumors can be detected as the migration of the bacteria and/or the bacteriobots out of the central region toward the side regions in a chemotactic microfluidic chamber. The bacteriobots showed higher migration velocity toward tumor cell lysates or spheroids than toward normal cells. In addition, when only the bacteriobots were injected to the CT-26 tumor mouse model, Cy5.5 signal was detected from the tumor site of the mouse model. In-vitro and in-vivo tests verified that the bacteriobots had chemotactic motility and tumor targeting ability. The new microrobot paradigm in which bacteria act as microactuators and microsensors to deliver microstructures to tumors can be considered a new theranostic methodology for targeting and treating solid tumors.

Paddling based Microrobot for Capsule Endoscopes

Recently, the capsule endoscope can be widely used for the diagnosis of digestive organs. It is passively moved by the peristaltic waves of gastro-intestinal tract and thus has some limitations for doctor to get the image of the organ and to diagnose more thoroughly. As a solution of these problems, therefore, a locomotive mechanism of capsule endoscopes has being developed. Our proposed capsule-type microrobot has synchronized multiple legs that are actuated by a linear actuator and two mobile cylinders inside of the capsule. By the novel kinematic relation between the legs and the mobile cylinders, the microrobot can easily move forward in the gastro-intestine. For the feasibility test of the proposed locomotive mechanism, a series of experiments were carried out including in-vitro and in-vivo tests. Based on the experimental results, we conclude that the proposed locomotive mechanism is not only easy to be used for micro capsule endoscopes but also effective to move inside of intestinal tract.

An earthworm-like locomotive mechanism for capsule endoscopes

A wireless capsule endoscope, M2A, has been developed to replace the conventional endoscope. However, the commercialized capsule endoscope moves passively by peristaltic waves and gravity, which has some limitations for doctors to diagnose more thoroughly and actively. In order to solve this problem, a locomotive mechanism is proposed for a wireless capsule endoscope. Based on the tests of various actuators, a piezoactuator is selected as a microactuator for the capsule endoscope. Piezoactuators are known to have limited displacement with high voltage supply. In order to overcome the limitation of common piezoactuator, the impact based piezoactuator is developed to realize long stroke up to 11 mm. Moreover, clampers mimicked the claw of insects are employed. A prototype of the earthworm-like locomotive mechanism integrated with an impact based piezoactuator and engraved clampers is developed. It has 15 mm in diameter and 30 mm under retraction stage and 41 mm under elongation stage in total length. Hollow space is allocated to comprise essential endoscope components such as a camera, communication module, battery, and biosensors. For the feasibility test of proposed locomotive mechanism, a series of experiments was carried out including in-vitro tests. Based on results of the experiments, we conclude that the proposed locomotive mechanism is effective to be used for microcapsule endoscopes.

The complications of high tibial osteotomy: CLOSING- VERSUS OPENING-WEDGE METHODS

We compared the incidence and severity of complications during and after closing- and opening-wedge high tibial osteotomy used for the treatment of varus arthritis of the knee, and identified the risk factors associated with the development of complications. In total, 104 patients underwent laterally based closing-wedge and 90 medial opening-wedge high tibial osteotomy between January 1993 and December 2006. The characteristics of each group were similar. All the patients were followed up for more than 12 months. We assessed the outcome using the Hospital for Special Surgery knee score, and recorded the complications. Age, gender, obesity (body mass index > 27.5 kg/m(2)), the type of osteotomy (closing versus opening) and the pre-operative mechanical axis were subjected to risk-factor analysis. The mean Hospital for Special Surgery score in the closing and opening groups improved from 73.4 (54 to 86) to 91.8 (81 to 100) and from 73.8 (56 to 88) to 93 (84 to 100), respectively. The incidence of complications overall and of major complications in both groups was not significantly different (p = 0.20 overall complication, p = 0.29 major complication). Logistic regression analysis adjusting for obesity and the pre-operative mechanical axis showed that obesity remained a significant independent risk factor (odds ratio = 3.23) of a major complication after high tibial osteotomy. Our results suggest that the opening-wedge high tibial osteotomy can be an alternative treatment option for young patients with medial compartment osteoarthritis and varus deformity.

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.

Development of Biomedical Microrobot for Intravascular Therapy

Recently, coronary artery disease such as angina pectoris and myocardial infarction has become the major causes of death. As a method of medical treatment for the disease, the pharmacological approaches and the surgical operations are executed. Especially, percutaneous coronary intervention (PCI) using catheters are the mostly preferred treatment for coronary artery diseases. The PCI technologies are advanced and the various useful devices are developed and utilized. However, some clinical operations such as the treatment of chronic total occlusion (CTO) remain a limitation of PCI and a major challenge. As robot-assisted coronary interventions, this paper proposes the microrobot for the therapy of CTO. The microrobot consists of the functions of position recognition, locomotion and treatment in the blood vessels. The functions of the microrobot can be validated through in-vitro & in-vivo experiments. The innovative technologies and surgical concept using the microrobot are currently being developed.

Friction enhancement via micro-patterned wet elastomer adhesives on small intestinal surfaces

A micro-pillar-based silicone rubber adhesive coated with a thin silicone oil layer is investigated in this paper for developing friction-based clamping mechanisms for robotic endoscopic microcapsules. These adhesives are shown to enhance the frictional force between the capsule and the intestinal wall by a factor of about seven over a non-patterned flat elastomer material. In this study, tests performed on fresh samples of pig small intestine are used to optimize the diameter of the micro-pillars to maximize the frictional forces. In addition, the effects of other factors such as the oil viscosity and applied normal forces are investigated. It is demonstrated that the proposed micro-pillar pattern based elastomer adhesive exhibits a maximal frictional force when the pillar diameter is 140 microm and coated silicon oil has a very high viscosity (10,000 cSt). It is also found that the frictional force of the micro-patterned adhesive increases nonlinearly in proportion to the applied normal force. These adhesives would be used as a robust attachment material for developing robotic capsule endoscopes inside intestines with clamping capability.

A new endoscopic microcapsule robot using beetle inspired microfibrillar adhesives

The diagnosis of gastrointestinal diseases within the small intestine has been greatly advanced with the introduction of the endoscopic microcapsule in recent years. In an effort to increase its reliability and expand its functionality, a mechanism for stopping and locomoting the capsule within the digestive tract is proposed in this paper. This mechanism, actuated by shape memory alloy wires, utilizes a synthetic microfibrillar adhesive similar to the attachment mechanisms employed by beetles. This fibrillar attachment mechanism is a combination of molecular adhesion caused by van der Waals forces and liquid adhesion caused by capillary forces. The molecular adhesion is enhanced by the presence of microfibers, and the liquid adhesion arises from a secretion from the beetles footpad. A synthetic version of the beetles footpad was fabricated from PDMS using a silicon mold. Another version was created from SU-8 using photolithography. Testing revealed decent adhesion with glass and prepared pig intestine in vitro both with a silicone oil to simulate the secretion and without it. A prototype robot with simple polymer adhesive pads for stopping successfully attached and detached inside a flexible vinyl tube. An inch worm locomotion mechanism is proposed and is in the preliminary stages of fabrication and testing