Sewan Park

Fabricaton of Poly(dimethylsiloxane) Microlens for Laser-Induced Fluorescence Detection

In laser-induced fluorescence (LIF) detection, the focusing of the excitation laser beam into a focal point of the channel in a microfluidic chip is important to obtain the largest excitation intensity, and consequently to obtain the emitted fluorescence light collected to the photodetector with a high efficiency. In this paper, we present a poly(dimethylsiloxane) (PDMS) microfluidic chip consisting of an integrated PDMS microlens. The PDMS microlens was fabricated by the photoresist reflow and replica molding method. This fabrication technique is simple and has a good property in terms of the microlens and a high-dimensional accuracy. We showed that fluorescence intensities using the microlens were found to be approximately four times higher than those without the microlens. The microlens integrated on the microfluidic channel was verified to improve fluorescence intensity, and consequently signal to noise ratio.

Substrates and dimension dependence of MEMS inductors

In this work, the effects of metal dimension and substrates on the characteristics of MEMS inductors have been studied. The suspended spiral inductors were fabricated by MEMS technologies with microelectroplating and thick film photolithography. The inductors were suspended by 20 µm over the substrate to reduce the substrate coupling loss and designed a 10 µm thick metal layer to reduce the ohmic loss. We also characterized the properties of inductors according to the substrates, the size of gap between the inductor metal lines and the width of the inductor metal lines. The measured quality factor of inductors fabricated on a silicon substrate was over 20 at 2 GHz. The inductors were also fabricated and measured on various substrates such as high resistive silicon, glass and quartz wafers. The quality factor of the inductor fabricated on the glass substrate was almost 30 at 4 GHz and that of the inductor fabricated on the quartz wafer was over 40 at the same frequency region. Substrate resistance and the dimension of metal are factors important to the inductor performance.

Potential of Poly-(N-Isopropylacrylamide) hydrogel as a clamper of the microrobot in gastrointestinal tract

We successfully demonstrate that a thermally actuated reversible hydrogel, the poly N-isopropylacrylamide (PNIPAAm), based clampers holds the intestines of a pig during the inchworm motion of microrobot. Although there are no direct relationship between hydro affinity and friction force, we found the significant friction force difference according to the surface condition change of PNIPAAm hydrogel. On the small intestine of a pig, a clamping mechanism was realized based on simple switching hydrophobic/hydrophilic surface conditions of PNIPAAm due to heating/cooling. In order to estimate response time of the clamper, the characteristic transition time of PNIPAAm film from hydrophilic to hydrophobic condition was investigated. Water contact angle (WCA) was monitored to normalize the transition time characteristics of PNIPAAm film in the course of time. From these results, we calculated the minimum heating time of the various thickness of PNIPAAm film to the clamping after its change to the hydrophobic condition. The minimum heating time was 15 seconds until 1 mm thickness of PNIPAAm film had enough friction force

Recent Progress of Moving-Actuator type Mechanical Circulatory Support Systems: AnyHeart and T-PLS

The mechanical circulatory support system using moving-actuator mechanisms were developed by Seoul National University and Korea University. AnyHeart is a fully implanted pulsatile bi-ventricular assist device, and T-PLS is a pulsatile flow versatile extracorporeal life support system. Through lots of in-vitro and in-vivo experiments, the developed mechanical systems are faced to produce on commercial scale. This paper describes the recent progress of two mechanical circulatory support systems, AnyHeart and T-PLS.

Differential floating mass type vibration transducer for MEI system

A new of vibration transducer, a DFMT (differential floating mass type) is introduced for use in an MEI (middle ear implant) system. The DFMT transducer is not influenced by external noise magnetic flux and has a very high vibration efficiency because its two magnets, which are glued back to back with the same poles facing, are located in the coil.

Realistic computational modeling for hybrid biopolymer microcantilevers

Three dimensional cultures in a microfabricated environment provide in vivo-like conditions to cells, and have used in a variety of applications in basic and clinical studies. Also, the analysis of the contractility of cardiomyocytes is important for understanding the mechanism of heart failure as well as the molecular alterations in diseased heart cells. This paper presents a realistic computational model, which considers the three dimensional fluid-structural interactions (FSI), to quantify the contractile force of cardiomyocytes on hybrid biopolymer microcantilevers. Prior to this study, only static modeling of the microscale cellular force has been reported. This study modeled the dynamics of cardiomyocytes on microcantilevers in a medium using the FSI. This realistic model was compared with static FEM analysis and the experimental results. Using harmonic response analysis in FSI modeling, the motion of a hybrid biopolymer microcantilever in the medium was identified as a second-order system and the influence of the dynamics of cardiomyocytes could be evaluated quantitatively

Cardiomyocytes Self-Powered Polymer Microrobot

We established a novel method to fabricate a micro-machine that can actuate for long-term in physiological condition. Backbone of micro machine is built with bio-compatible material of PDMS by using specially designed 3D molding aligner. The high generative force of hybrid actuator is realized based on selective cell culture on groove surface that leads higher concentration of cells. Those key techniques enable the developed micro-machines to work for two weeks in medium condition. For performance demonstration of micro-machine, we construct a tripod micro-machine and observe sustained and synchronous locomotion in medium condition for almost two weeks-period.

Fabricaton of PDMS microlens for LIF detection

This paper presents PDMS microlens using photoresist reflow and molding method. This fabrication technique is simple and has good property in terms of the microlens. The microlens integrated on the microfluidic channel was verified to improve the fluorescent intensity, and consequently S/N ratio.

A study on inteference between 3D MEMS inductor and VCO

We have inquired further into the interference effect between active circuit and spiral inductors. Through the VCOs integrated with MEMS inductors, we investigated the phase noise characteristics according to inductors position in circuits. These experimental results were further studied by electromagnetic theory and simulation. We have concluded that the magnetic field induced by inductor have small magnitudes, thus they do not affect the MOSFET operation and the vertical component of the inductor electric field affects the transistor operation and output by theoretical approach. We have simulated roughly these effects of electric field induced by inductor using CLESICO, mixed-mode simulator. These simulation results show that the currents induced by noise voltage source are small but cannot be bypassed.

Integrated CE chip - concentration and high-resolution cyclic CE technology

Single column transient isotachophoresis (TITP) system and cyclic CE chip is integrated on PDMS (polydimethylsiloxane) chip. ITP part can concentrate low concentrated sample by over the 500-folded times. In addition, as additional coating of EOF modifier, the velocity and resolution is improved. The focusing of sample and separation is processed in a single column. The TITP chip has the disadvantage of low resolution, because it has the limited channel length with a limited voltage for a general CE chip. So, the focused sample was separated in the cyclic CE. The focused high concentration sample became the plug of the cyclic CE. Cyclic CE, which is the one of the channel network structures, has advantages in downsizing and a low operation voltage. However, there are some problems such as sample loss when the injected plug encounters the junctions in the middle of the channel. This paper will show the optimum design that these problem was considered. By a dyestuff experiment, the procedure of focusing step and separation are observed and studied. All these procedure is operated by just E-field. The chloride ion is used as the leading electrolyte, and the volume of injection is about 20 /spl mu/L. Under our LIF conditions, the sample concentrated over the 500-folded times and cyclic CE chip showed < 2 % degradation per junction. This means the high resolution CE analysis has 100,000 plate numbers after a three and one quarter cycle in just 3.5 /spl times/ 6 cm chip.