Eui-Sung Yoon

An implantable neural probe with monolithically integrated dielectric waveguide and recording electrodes for optogenetics applications

OBJECTIVE Optogenetics promises exciting neuroscience research by offering optical stimulation of neurons with unprecedented temporal resolution, cell-type specificity and the ability to excite as well as to silence neurons. This work provides the technical solution to deliver light to local neurons and record neural potentials, facilitating local circuit analysis and bridging the gap between optogenetics and neurophysiology research. APPROACH We have designed and obtained the first in vivo validation of a neural probe with monolithically integrated electrodes and waveguide. High spatial precision enables optical excitation of targeted neurons with minimal power and recording of single-units in dense cortical and subcortical regions. MAIN RESULTS The total coupling and transmission loss through the dielectric waveguide at 473 nm was 10.5 ± 1.9 dB, corresponding to an average output intensity of 9400 mW mm(-2) when coupled to a 7 mW optical fiber. Spontaneous field potentials and spiking activities of multiple Channelrhodopsin-2 expressing neurons were recorded in the hippocampus CA1 region of an anesthetized rat. Blue light stimulation at intensity of 51 mW mm(-2) induced robust spiking activities in the physiologically identified local populations. SIGNIFICANCE This minimally invasive, complete monolithic integration provides unmatched spatial precision and scalability for future optogenetics studies at deep brain regions with high neuronal density.

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.

Active locomotion of a paddling-based capsule endoscope in an in vitro and in vivo experiment (with videos)

BACKGROUND Capsule endoscopy that could actively move and approach a specific site might be more valuable for the diagnosis or treatment of GI diseases. OBJECTIVE We tested the performance of active locomotion of a novel wired capsule endoscope with a paddling-based locomotion mechanism, using 3 models: a silicone tube, an extracted porcine colon, and a living pig. DESIGN In vitro, ex vivo, and in vivo experiments in a pig model. SETTING Study in an animal laboratory. INTERVENTIONS For the in vitro test, the locomotive capsule was controlled to actively move from one side of a silicone tube to the other by a controller-operated automatic traveling program. The velocity was calculated by following a video recording. We performed ex vivo tests by using an extracted porcine colon in the same manner we performed the in vitro test. In in vivo experiments, the capsule was inserted into the rectum of a living pig under anesthesia, and was controlled to move automatically forward. After 8 consecutive trials, the velocity was calculated. MAIN OUTCOME MEASUREMENTS Elapsed time, velocity, and mucosal damage. RESULTS The locomotive capsule showed stable and active movement inside the lumen both in vitro and ex vivo. The velocity was 60 cm/min in the silicone tube, and 36.8 and 37.5 cm/min in the extracted porcine colon. In the in vivo experiments, the capsule stably moved forward inside the colon of a living pig without any serious complications. The mean velocity was 17 cm/min over 40 cm length. We noted pinpoint erythematous mucosal injuries in the colon. LIMITATION Porcine model experiments, wired capsule endoscope. CONCLUSIONS The novel paddling-based locomotive capsule endoscope performed fast and stable movement in a living pig colon with consistent velocity. Further investigation is necessary for practical use in humans.

Tribological behavior of sliding diamond-like carbon films under various environments

Abstract Tribological behaviors of amorphous diamond-like carbon (DLC) films were experimentally evaluated under various environments using a steel ball-on-disk wear-rig at dry sliding surfaces. The DLC films were prepared on Si wafer by r.f. PACVD method using benzene (C 6 H 6 ). Every test was performed under the normal load 4.9 N and sliding velocity of 0.05 m/s, and the coefficients of friction of DLC films were measured with the contact cycle. When the test was performed under a vacuum, the coefficient of friction of DLC films showed a significant fluctuation with the contact cycles, remarkably accompanied with roll-shaped polymeric wear debris. Another test using thermally-baked DLC films showed that the friction was lower and more stable. Under a humidity controlled air, friction of DLC films was also stable. Tests with dry O 2 and N 2 gas were extended to find any other environmental factors which could affect the tribological behavior of DLC films. It was found that tribological behavior of DLC films was dependent on the formation of friction layers which were mainly affected by the environment. In the final discussion of this work, effects of environment on the tribological behavior of DLC films were combined and discussed in terms of tribo-chemistry of DLC films.

Quantitative evaluation of cardiomyocyte contractility in a 3D microenvironment

Three-dimensional cultures in a microfabricated environment provide in vivo-like conditions for cells, and have been used in a variety of applications in basic and clinical studies. In this study, the contractility of cardiomyocytes in a 3D environment using complex 3D hybrid biopolymer microcantilevers was quantified and compared with that observed in a 2D environment. By measuring the deflections of the microcantilevers with different surfaces and carrying out finite element modeling (FEM) of the focal pressures of the microcantilevers, it was found that the contractile force of high-density cardiomyocytes on 3D grooved surfaces was 65-85% higher than that of cardiomyocytes on flat surfaces. These results were supported by immunostaining, which showed alignment of the cytoskeleton and elongation of the nuclei, as well as by quantitative RT-PCR, which revealed that cells on the grooved surface had experienced sustained stimuli and tighter cell-to-cell interactions.

The use of color in wear debris analysis

A method and results of classification of metallic wear debris using their color features are presented. The color images of wear debris were used as initial data. The color features of the debris are specified by an HSI color model. Each particle is characterized by a set of statistical features derived from a distribution of HSI color model components. The initial feature set was optimized by principal component analysis. A multidimensional scaling procedure was used for definition of the classification plane. The selected features allow us to distinguish copper-based alloys, red and dark iron oxides and steel particles. A method was proposed of probabilistic decision of class assignment based on analysis of debris coordinates distribution in the classification plane. The obtained results have demonstrated the feasibility of using color features for automated wear particle analysis.

Self-formation of protective oxide films at dry sliding mild steel surfaces under a medium vacuum

The friction and wear at dry sliding steel surfaces under different vacuum conditions have been investigated to understand the mechanisms of wear of mild steel in vacuum. For the test, a ball-on-disk type of wear-rig has been built and implemented, allowing control of sliding speed, load and vacuum. A theoretical analysis of frictional heating at sliding surfaces and an experimental analysis of the influence of oxidation wear under different vacuum conditions are described. Results show that, at a low sliding velocity, a low load and under a medium vacuum, effective, protective oxide films can be formed on the sliding surface in a friction process with a self-regulating way, which results in both very low coefficient of friction (about 0.3) and mild wear. It is found that significant reduction in friction and wear is caused by formation of thin layer of Fe3O4 steel oxides on the surface which are promoted by a high surface temperature and a high plastic deformation at the local surface area, and they are formed of the compaction of wear debris while supporting the bearing load and preventing the direct intermetallic contact on the surface. Oxide films under a high vacuum and at a high sliding velocity are found that they are ineffective to protect the surface against severe wear. Results suggest that there is a critical regime with contact conditions for producing effective, protective oxide films of mild steel.

Evaluation of frictional characteristics for a pin-on-disk apparatus with different dynamic parameters

Frictional characteristics in response to changes of the dynamic parameters of a pin-on-disk apparatus were experimentally and theoretically investigated for dry sliding. The apparatus has been designed and built to allow control of sliding speed, load, stiffness and loading mechanism. Dynamic friction and normal force were measured for various conditions of the system parameters, e.g. different stiffness in the normal direction, loading mechanisms and test materials. For a normal load, mechanisms using a dead weight, a compression-type spring and a pneumatic cylinder were selectively applied. Stiffness in the loading direction was also varied using a spring with different stiffness. Steel, rosin and polytetrafluoroethylene were tested because they have different types of frictional behavior. Test results showed that frictional characteristics at various loading mechanisms were different even though the operating parameters were the same. They are also strongly dependent on both the sliding velocity and the run-out of the disk surface. Effects of the surface run-out on the friction behavior were further evaluated using a tapered steel disk. When the surface run-out was high, the coefficient of friction was computed differently with the data processing. A theoretical analysis for a simple model of a pin-on-disk apparatus showed that surface irregularities, such as surface roughness, waviness and run-out, result in dynamic normal forces which depend on both the dynamic parameters of the system and the sliding velocity.

Wear monitoring based on the analysis of lubricant contamination by optical ferroanalyzer

Abstract Lubricant contamination analysis is one of the common and prospective methods of machine condition monitoring. Wear debris formed in rubbing is a source of valuable information on the wear mechanism and severity, while total oil contamination gives information on oil lubricity. Development of new methods and means of reliable condition monitoring of friction units remains a challenging task for rating the condition of equipment, reducing losses for idle time or failures, and saving lubricants. Despite the fact that direct reading (DR) ferrograph was proposed more than 20 years ago its main principle—accumulation and estimation of deposited particles content—underlies the basis of creation of new effective built-in devices and criteria for condition monitoring. In the presented paper, the principle of operation of the optical ferroanalyzer (OF) jointly developed by V.A. Belyi Metal-Polymer Research Institute of Belarus National Academy of Sciences and Korea Institute of Science and Technology is presented. Optical ferroanalyzer in addition to ferrograph allows us to estimate total contamination of oil, increasing reliability of tribosystem condition monitoring. The results of bench tests of the analyzer are described and example of its application for condition monitoring of engine is shown.

The Effect of Topography on Water Wetting and Micro/Nano Tribological Characteristics of Polymeric Surfaces

The effect of surface topography on the water-wetting nature and micro/nano tribological characteristics of polymer surfaces was experimentally studied. A plasma-treated thin polymer film and ion-beam-treated PTFE (polytetrafluoroethylene) were used as flat specimens. Thin polymer films were deposited on Si-wafer (100) by the parallel-plate plasma technique. The ion-beam-roughening treatment was performed to change the PTFE surface topography using a hollow cathode ion gun under different argon-ion dose conditions in a vacuum chamber. Micro and nano tribological characteristics, water-wetting angles and roughness were measured with a micro-tribotester, SPM (scanning probe microscope), contact anglemeter and profilometer, respectively. The plasma-treated thin polymer film and ion-beam-treated PTFE surfaces were rendered increasingly hydrophobic as a function of the treatment time. The wetting characteristics were strongly dependent on the micro-roughness and the sharpness of the asperities. The tribological characteristics on the nano-scale showed different results from those on the micro-scale. It was noted that the contact-size ratio, especially the ratio of the tip or ball to the average surface roughness at a standard cut-off length, should be considered for evaluating the micro- and nano-scale tribological test results.