Junha Park

Rapid three-dimensional passive rotation micromixer using the breakup process

Stretching and folding, diffusion, and breakup are three basic processes that occur while mixing fluids. Although stretching and folding the interface of two fluids by rotation enables the mixing at microscale level in both low and high Reynolds number flows, rotation is not as effective at a low Reynolds number as at a high Reynolds number. Therefore, developing a rapid micromixer for microfluidic systems that can be used at a low Reynolds number is a challenging task, because it can demonstrate the full potential of microfluidic systems in commercial markets. Here, to enhance the mixing efficiency of a micromixer based on passive rotation, we present a breakup method. The breakup method not only generates interface actively but also enhances the diffusion process at the interface. With our novel design, over 70% mixing can be achieved only after passing through a 4 mm long microchannel. In this work, the mixer was easily fabricated with polydimethylsiloxane by soft lithography and a self-aligned bonding method with methanol. We analyzed the flow in the micromixer using the computational fluid dynamics method. Also, we conducted quantitative analyses using a confocal scanning microscope and image processing.

Intravascular micro active catheter for minimal invasive surgery

The authors have developed an intravascular micro active catheter system for microsurgery in human vascular systems, such as cerebrovascular and coronary arteries. Also this system can be applied to laparoscopical treatment. It consists of the micro active bending catheter and some functional catheters. The former is a tube-like catheter which has an outer-diameter of 3.0 mm, an inner-diameter of 2.0 mm and a length of 1000 mm. Its inner hole is a pathway for the functional catheters, such as conventional guide wire, balloon catheter, conventional suction tube, micro ultrasound probe catheter, fiber optics (angioscope), angioplatic devices and drug injection lines. This active bending catheter is actuated with three SMA (shape-memory-alloy) zigzag type springs-SMA wires are connected with plastic and brass connection links. This actuator can be bent to any direction with the PWM controlled electric current. The authors also developed a micro drug infusion catheter and a micro ultrasound probe catheter fitted to the inner hole of active bending catheter. All of these systems were evaluated with the human mock circulation system. They can be introduced through 90/spl deg/, 120/spl deg/, 180/spl deg/ crooked branches to the brachiocephalic artery, common carotid artery, subelavian artery and so on in the mock circulation system. Also, the authors tested this endoscope system in vivo by performing laparoscopical surgery on a pig. They could easily induce the catheter to the point they wanted in the pig ovary.

Development of endovascular microtools

Endovascular microtools refers to catheter-like systems with microdevices that are put into arteries and veins. An intravascular micro active catheter system is the most advanced type of endovascular microtool. It consists of an active bending catheter and some functional catheters, such as intravascular micro ultrasound and micro drug infusion catheters. These systems are widely under development and commercialization. In this paper, we present a brief overview of the intravascular micro active catheter, followed by an explanation of the microsystems that have been developed at Seoul National University. This system consists of an active bending catheter, a micro drug infusion catheter and an ultrasound scanning catheter. All these systems show the proper functions for in vivo and in vitro tests.

Active sealing for soft polymer microchips: method and practical applications

This paper presents a new sealing method for soft polymer (elastomer) microchips. A robust and reversible sealing method, which allows various materials to be bonded and sealed tightly with each other even in aqueous solutions, is developed. A poly (dimethylsiloxane) microchip system, which can actively generate bonding and sealing forces by itself, is invented. By inducing negative pressure into additional closed areas, an instant sucking disc is made. This disc is used to tighten up the conformal contact of soft polymers. Other functionalities of active sealing such as making reusable microchips, patterning cells and performing cellular assays in a single dish have also been examined and will be discussed hereunder. This technique gives a robust and universal solution for microchip sealing issues by sealing soft polymers with diverse materials under various conditions. Active sealing will simplify numerous assays in lab-on-a-chip industry and will open a new era for cellular microchip assays.

Combined microchannel-type erythrocyte deformability test with optical tweezers

A combined microchannel-type erythrocyte deformability test with optical tweezers has been developed especially for more sensitive detection of cancerous diseases. To demonstrate the performance and sensitivity of the microchannel-type method, we measured the transit velocity of individual erythrocytes passing through a specific confinement region and calculated the modified elongation index defined by the ratio of the width of the microchannel to the elongated length of the squeezed erythrocytes. To know exactly the effect of optical tweezers on erythrocytes, we investigated several morphologies of optically deformed erythrocytes and measured the shape recovery time of erythrocytes in a static aqueous solution under various powers (~ 24 mW) of 1064-nm laser by a dual-trap optical tweezers. Finally we combined these two methods by considering the key parameters of erythrocyte deformability. The results show that the ambiguity of the overlapped experimental data from microchannel-type erythrocyte deformability test was conspicuously reduced, and that the subtle change (≈ 100-200 ms) in shape recovery time which is one of mechanical properties of erythrocyte membrane surface was remarkably amplified to readily discriminate the difference (≈ 2-3 s) between normal and cancerous blood. This suggests the combined method is more sensitive enough to pinpoint the minor quantitative differences between individual erythrocytes, especially in the field of cancer and cardiovascular diseases.

Endovascular micro tools

Endovascular micro tools mean the catheter-like systems with micro devices which are put into arteries and veins. An intravascular micro active catheter system is the most famous type of endovascular micro tools and it consists of active bending catheter and some functional catheters such as guide wire, balloon catheter, angioscope, drug delivery catheters, micro surgery tools and so on. These systems have been widely developed and commercialized. A brief overview of the intravascular micro active catheter is presented, followed by an explanation of the micro systems being developed at the Seoul National University. This system consists of an active bending catheter, micro drug infusion catheter and ultrasound-scanning catheter. All of these systems show the proper functions in in-vivo and in-vitro tests.

Non-linear I–V characteristics of polypyrrole micro-line synthesized using scanning probe microscope

AbstractWemeasuredtemperaturedependenceofvoltage–currentcharacteristicsofelectrochemicallypolymerizedpolypyrroleinmicronscaleusingscanningprobemicroscope.Themorphologyandthemagnitudeofroomtemperatureresistivity,q RT ¼ 0:016Xcm,aresimilartootherelectrochemicallysynthesizedpolypyrrole.I–Vcharacteristicsbecamenon-linearforT < 100Kandcanbefittedtofluctuation-inducedtunnelingconductionmodel. 2002ElsevierScienceB.V.Allrightsreserved. PACS:72.80.-r;72.80.Le;73.63.-b;73.63.NmKeywords:Polypyrrole;Micor-line;Electrochemicalsynthesis;Scanningprobemicroscope;Non-linearI-Vcharacteristics 1.IntroductionConjugatedpolymerhasinterestingphysicalproper-tiesincludingmetallicbehaviourandeventhesuper-conductivity [1] as well as applicability to electronicdevices such as LED [2] or field-effect transistor orconductivewireetc.Conductingpolymersuchaspoly-acetylene (PA), polypyrrole (PPy), polythiophen (PT)andpolyaniline(PANI)haslongbeeninvestigatedtoelucidate their intrinsictransport properties owing totheirlowdimensionality.Thelocalexcitationssuchassoliton [3], polaron and bipolaron are suggestedfor their conducting carriers. However the transportmechanisminconductingpolymerinnanoscaleisnotunderstoodwellyet.Recentlywehavereportedtrans-portmeasurementsofPAnanofibernetworkinmicronscale[4]andthatofPAsinglenanofiberin100nmscale[5].ContrarytothefibrillarstructureofPA,thegranularstructureofelectrochemicallypolymerizedconductingpolymermakesitdifficulttoapplythenanopatternedarrayofelectrodesfortheelectricalmeasurement.Inthecaseofusingtemplatesuchasanodicaluminumoxide(AAO) or zeolite, we can polymerize the conductingpolymer inside the template [6] and then separate itfromthetemplate.Othermethodstosynthesizealinearstructure of conducting polymer is using SPM localoxidation[7],e-beamirradiationtoPANI[8]orpoly-octylthiophene [9], self-assembled monolayer (SAM)pattern [10] and Langmuir–Bloddgett (LB) technique[11].STMlocaloxidationhassomedifficultiestomakealinearstructureinnarrowscaleduetotherandomnessofthegrowthdirection.UsingaSAMhaslimitationonthestamptogeneratetheSAMpatternanditisali-thography dependent technique. Here we present thetransport measurements of PPy line that is electro-chemicallypolymerizedbybiasingtothemetalcoatedSPMtipontopofthepatternedelectrodes.2.ExperimentalMicron and submicron electrodes for transportmeasurement were patterned using JEOL JBX5D-IIe-beamlithographysystem.300nmSiO

Techniques in the Development of Endovascular Microtools & Their Applications

Endovascular is an English word meaning “within the vessel” from Latin endo (within) and vascularis (vessel) and is synonymous with intravascular. Cardiovascular refers to the interaction between the heart and the system of blood vessels from Greek cardio (heart) and Latin vascularis (vessel). In this chapter the word endovascular is used to refer to the vascular system and endovascular microtool refers to a utensil that transports substances to tissues. An endovascular microtool is designed for use in surgical operations on vascular systems that remove byproducts of metabolism, maintain the body temperature, and control the oxygen and nutrient supply. Blood flows rapidly in the vascular system. The average human male has 5 to 6 liters of blood, and blood circulates through the body in 30 seconds [78].

Fabrications and Applications of Micro Hemocytometer for Early Detection of Cancer

There are a lot of clinical studies about the relations between the erythrocyte deformability and the local blood flow mediated diseases like cancer. [1,2] Normally they have used the hemorheological techniques for the erythrocyte deformability assessment, but these have the practical limitations.[3] This paper presents the advanced schemes of the blood cell deformability measurement using PDMS micro fluidic chips. Developed microchip and system can characterize the mechanical properties of cancerous erythrocyte, and can be used a practical pre-diagnostic apparatus for the early detection of cancer.

Development of Serial Dilution Chip for Cellular Based Analysis

Dilution of microfluids is very complex because of the flexibility of microfluids concerned with the channel size, surface characteristics and Reynolds number. With the simulation results of dilution in microchannel, we developed the novel serial dilution chips made of PDMS and glass plate. These chips can be applied to the cell toxicity test, bacteria counting test and Minimal Inhibitory Concentration test of antibiotics and so on.