Seung Ki Lee

Fabrication of round channels using the surface tension of PDMS and its application to a 3D serpentine mixer

A novel fabrication technique was developed to fabricate round microchannels and applied to a micro mixer having a barrier structure using surface tension of PDMS. When the solidified PDMS layer (channel layer) contacts the liquid PDMS film (meniscus layer), a meniscus is formed around the sidewall in the microchannel due to surface tension. The external load pressure and contact area of the channel layer were adjusted to form various cross-sectional shapes such as a U shape, ellipse, semi-circle and circle. Since the width of the channel also determines the depth formed by the difference in capillary height, a multi-depth channel can be fabricated using a one-step process. It was applied to a dual-depth serpentine mixer, eliminating the aligned bonding of conventional soft lithography. The 3D-structure mixer enhanced mixing performance in the range of Re > 10 compared with a 2D-structure. It could fully mix phenolphthalein and sodium hydroxide when the Reynolds number was 80. The suggested fabrication method could be very useful in various microfluidic devices that need round corners and multi-depth channels.

Analysis of mechanical characteristics of the ionic polymer metal composite (IPMC) actuator using cast ion-exchange film

IPMC (Ionic Polymer Metal Composite) is a promising candidate actuator for bio-related applications mainly due to its biocompatibility, soft properties and operation in wet condition. The widely used and commercialized ion-exchange polymer film has limitation in thicknesses, but more various film thicknesses are required for extensive applications. Especially for the enhanced force as an actuator, acquisition of thick film is essential. Various ion-exchange polymer films with thickness of 0.4-1.2 mm have been prepared by casting of liquid ion-exchange polymer. As well, IPMC actuators using cast ion-exchange polymer films have been fabricated and the basic mechanical characteristics such as stiffness, displacement and force were measured and analyzed. These results can be used for the optimized design of actuators for different applications.

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.

An integrated bio cell processor for single embryo cell manipulation

In this paper, we present a novel integrated bio cell processor to handle individual embryo cells. Its functions are composed of transporting, isolation, orientation, and immobilization of cells. These functions are essential for biomanipulation of single cells, and have been typically carried out by a proficient operator. The purpose of this study is the automation of these functions for effective cell manipulation using a MEMS based bio cell processor. This device is realized with relatively simple design and fabrication process. To transport cells, microfluidic channel is employed. The isolation of a cell is performed by actuation of polypyrrole (PPy) valves. The orientation control of cells is accomplished by dielectrophoresis (DEP). By the suction from the micro-hole, the target embryo cell is immobilized. Experimental results show that this device can substitute the essential but very tiresome and repeatable embryo cell manipulation and contribute significantly to the improvement of speed and success rate of operation by facilitating the cell manipulation. The cell viability test for the device is studied through the distribution of mitochondria in mouse (B6CBA) embryo cells and cultivation of cells for 86 h after cell was manipulated by DEP.

Fabrication of ionic-polymer-metal-composite (IPMC) micropump using a commercial Nafion

This paper describes the fabrication and characteristics of an ionic polymer-metal composite (IPMC) membrane-shaped micro-actuator and its application to the fabrication of a micro-pump. After fabricating two 8mm×8mm IPMC membrane-shaped actuators using a Nafion film, their displacements were measured. The fabricated IPMC membrane-shaped micro-actuators showed displacement of 14~27μ at the applied voltage ranging from 4VP-P to 10VP-P at 0.5Hz. Displacement of the IPMC actuator fabricated with a commercially available Nafion is large enough to make the IPMC actuator a membrane-shaped micro-actuator for fabricating an IPMC micro-pump. IPMC micro-pump was fabricated by assembling IPMC membrane-shaped micro-actuator and PDMS(polydimethylsiloxane) micro-channel together. PDMS micro-channel was designed to have nozzle/diffuser structures which make the fluids flow from inlet to outlet when the IPMC membrane-shaped micro-actuator is deflected up and down by the applied voltages. The measured flow rate of the fabricated IPMC micro-pump was about 9.9μℓ/min at 0.5Hz when the input voltage and duty ratio were 8V P-P and 50%, respectively. The test results illustrate that the fabricated IPMC micro-pump is suitable for pumping fluid through micro-channel on a PDMS substrate. Mechanical performances of beam-shaped and bridge-shaped conductive polymer actuator in aqueous solution and in solid electrolyte have been measured and analyzed. The optimum thickness of polypyrrole for the best bending performance is about 17-19 μm which has been polymerized at the current density of 5.4 μA/mm2 for 120 minutes. For the application of conductive polymer actuator to a micropump, silicon bulk micromachining process has been combined.

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.

Biomedical applications of electroactive polymers and shape-memory alloys

Among many kinds of polymer materials, electronic conductive material, that is polypyrrole, shows potential possibility for bio-relate actuator materials. However, it may be an impediment for practical use in polypyrrole actuator that polypyrrole usually requires electrolyte solution for actuation. Our first research theme is focused on this problem solving. We have investigated many kinds of solid polymer electrolyes for the substitution of electrolyte solution. Our goals are to find the stable solid electrolyte in the air, to establish the reliable fabrication process of it and to apply it for micropump application. Besides actuators, the reduction and oxidation property of polypyrrole can be exploited for active drug delivery systems by the control of structural deformation of it. We have investigated this kind of new and bio-related possibility of polypyrrole. Shape memory alloy has another possibility in the biomedical field. Due to its inherent excellent advantages as actuator materials, it can be used for micro active intravascular catheter. We have developed thin tube type bending actuator using shape memory alloy and characterized its performance by in-vivo test.

Tadpole robot (TadRob) using ionic polymer metal composite (IPMC) actuator

We have developed the wireless tadpole robot that has simple geometry, driven by low voltage and the undulatory fin-motion using IPMC(Ionic Polymer Metal Composite) actuator. Behavior of TadRob is tested under various frequencies(1~8Hz) to find the correlation between actuator frequency and velocity of the robot. In addition, the robot velocity according to undulation motion and oscillation motion of the fin is compared to find the proper fin-motion to increase the efficiency of the robot. Also, steering capability is tested under variation of duty ratio. Based on experimental results, we can confirm that the velocity of TadRob can be controlled by changing frequency of input voltage and the steering angle can be increased with increasing the duty ratio.

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.

A disposable MEMS-based micro-biopsy catheter for the minimally invasive tissue sampling

This paper presents a novel minimally invasive MEMS (micro-electromechanical system)-based micro-biopsy catheter for the diagnosis of gastrointestinal tissue samples. Conventional macro-scale biopsy tools such as biopsy forceps often cause a significant discomfort, infectious risk, and injury to the patients. In this study, a disposable micro-scale biopsy tool is proposed for the first time and MEMS technology is implemented for the fabrication process. Micro-biopsy catheter successfully extracts tissue samples from the small intestines of the anesthetized rabbit and pig. The proposed micro biopsy catheter is found to be useful in minimally invasive diagnosis.