• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1758-1760
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• 2008

Under typical operating conditions, flows in microfluidic devices are laminar and molecular diffusion across the channels is slow, which makes an efficient mixing in microfluidic devices difficult to achieve. The mechanism to achieve effective mixing in laminar flows is that of repetitive stretching and folding. Essential is to generate spatially periodic flows with crossing cross sectional streamlines. A mapping method is employed to analyze mixing in micromixers, enabling us to investigate the progress of mixing both qualitatively and quantitatively. The progress of mixing is characterized by a measure of mixing, called the discrete intensity of segregation. The mapping method is applied to mixing in such micromixers as the staggered herringbone mixer, the barrier embedded micromixer, and the three-dimensional serpentine channel to demonstrate the capability of the numerical scheme to tackle general mixing problems in microfluidic devices.

• BMB Reports
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• v.44 no.11
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• pp.705-712
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• 2011

Advances in the fields of proteomics and genomics have necessitated the development of high-throughput screening methods (HTS) for the systematic transformation of large amounts of biological/chemical data into an organized database of knowledge. Microfluidic systems are ideally suited for high-throughput biochemical experimentation since they offer high analytical throughput, consume minute quantities of expensive biological reagents, exhibit superior sensitivity and functionality compared to traditional micro-array techniques and can be integrated within complex experimental work flows. A range of basic biochemical and molecular biological operations have been transferred to chip-based microfluidic formats over the last decade, including gene sequencing, emulsion PCR, immunoassays, electrophoresis, cell-based assays, expression cloning and macromolecule blotting. In this review, we highlight some of the recent advances in the application of microfluidics to biochemistry and molecular biology.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.5
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• pp.441-449
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• 2014

Thermoplastic fusion bonding is widely used to seal polymer microfluidic devices and optimal bonding protocol is required to obtain a successful bonding, strong bonding force without channel deformation. Besides, UV modification of the PMMA (poly-methyl methacrylate) is commonly used for chemical or biological application before the bonding process. However, study of thermal bonding for the UV modified PMMA was not reported yet. Unlike pristine PMMA, the optimal bonding parameters of the UV modified PMMA were $103^{\circ}C$, 71 kPa, and 35 minutes. A very low aspect ratio micro channel (AR=1:100, $20{\mu}m$ depth and $2000{\mu}m$ width) was successfully bonded (over 95%, n>100). Moreover, thermal bonding of multi stack PMMA chips was successfully demonstrated in this study. The results may applicable to fabricate a complex 3 dimensional microchannel networks.

• Journal of computational fluids engineering
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• v.14 no.4
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• pp.86-92
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• 2009

Nowadays, the development of microfluidic chip [i.e. biochip, micro-total analysis system ($\mu$-TAS) and LOC (lab-on-a-chip)] becomes more active, and the microchannels to deliver fluid by pressure or electroosmotic forces tend to be more complex like electronic circuits or networks. For a simple network of channels, we may calculate the pressure and the flow rate easily by using suitable formula. However, for complex network it is not handy to obtain such information with that simple way. For this reason, Graphic User Interface (GUI) program which can rapidly give required information should be necessary for microchip designers. In this paper, we present a GUI program developed in our laboratory and the simple theoretical formula used in the program. We applied our program to simple case and could get results compared well with other numerical results. Further, we applied our program to several complex cases and obtained reasonable results.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2658-2663
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• 2008

In the present study, we designed a microfluidic flatform that generates monodisperse droplets with diameters ranging from hundreds of nanometers to several micrometers. To generate fine droplets, T-junction and flow-focusing geometry are integrated into the microfluidic channel. Relatively large aqueous droplets are generated at the upstream T-junction and transported toward the flow-focusing geometry, where each droplet is broken up into the targeted size by the action of viscous stresses. Because the droplet prior to rupture blocks the straight channel that leads to the flow-focusing geometry, it moves very slowly by the pressure difference applied between the advancing and receding regions of the moving droplet. This configuration enables very low flow rate of inner fluid and higher flow rate ratio between inner and outer fluids at the flow-focusing region. It is shown that the present microfluidic device can generate droplets with diameters about 1 micrometer size and standard deviation less than 3%.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2688-2691
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• 2008

This study addresses a microfluidic method to uniformly form diacetylene (DA) liposomes and control their size. DA liposomes are biochemical sensor materials with a unique property such that when they are polymerized to polydiacetylene (PDA) they exhibit non-fluorescent blue to fluorescent red phase transition upon chemical or thermal stress. The liposome size and distribution are important because they significantly affect the phase transition. So far, DA Liposomes, have been prepared by mixing of bulk phases leading to heterogeneous, polydisperse distribution in size. Therefore, additional post-processes are required such as sonication or membrane extrusion to obtain an appropriate size of liposomes. Here, we report a novel strategy using a microfluidic chip and hydrodynamic focusing to form DA liposomes and control their size. Preliminary results obtained by scanning electron microscope (SEM) and dynamic light scattering (DLS) show that the microfluidic strategy generates more monodispersed liposomes than a bulk method.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2696-2699
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• 2008

Microfluidic chips have been frequently utilized to perform biochemical analysis, like cell culture, because they reduce the consumptions of analytes and reagents and automate multi-step analysis processes. It is often critical to monitor temperature in a microchannel for the analyses in order to control a reaction condition of bio or chemical molecules. We propose a novel method to monitor temperature of a microchannel flow by using polydiacetylene (PDA), a conjugated polymer, that has a unique property to transform its color from visible blue to fluorescent red by thermal stress. We inject PDA sensor droplets generated by hydrodynamic instability into a microchannel with a microheater incorporated on the channel bottom. Also, we change the channel temperature by providing the different electric power to the microheater. The results show that the florescence intensity of PDA sensor droplets linearly increases in response to the flow temperature increase within a certain range.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2374-2376
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• 2005

본 연구에서 제안한 microfluidic system은 열공압 방식으로 구동되고 indium tin oxide (ITO) 및 polydimethylsiloxane(PDMS)로 제작하여 공정이 간단하고 비용이 저렴하여 일회용으로 사용이 가능하며 투명한 장점을 갖는다. 또한 마이크로 펌프는 인-채널 구조의 마이크로 밸브와 동일한 공정으로 제작하였다. 제안된 마이크로 펌프는 인-채널 구조의 마이크로 밸브와 같은 기판 위에 쉽게 집적하여 제작할 수 있다. 마이크로 펌프의 pumping rate는 인가 펄스 전압의 주파수와 duty비를 변화시켜 최적화하였다. Duty 비가 1%이고 주파수가 2 Hz일 때 최대 pumping rate를 보였으며 이때 pumping rate는 26.18nl/min이였다. 마이크로 밸브는 ITO 히터에 전력을 인가함으로서 유량의 on/off 제어가 잘 됨을 확인할 수 있었고 유체를 closing하기 위해 필요한 전력은 100mW이다.

• Biotechnology and Bioprocess Engineering:BBE
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• v.8 no.4
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• pp.240-245
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• 2003

The use of microfabricated microfluidic devices offers significant advantages over current technologies including fast analysis time and small reagent requirements. In the context of proteomic research, the possibility of using affinity-based separations for prefractionation of samples using microfluidic devices has significant potential. We demonstrate the use of microscale devices to achieve affinity separations of proteins using a device fabricated from borosilicate glass wafers. Photolithography and wet etching are used to pattern individual glass wafers and the wafers are fusion bonded at 650$^{\circ}C$ to obtain enclosed channels. A polymer has been successfully polymerized in situ and used either as a frit for packing beads or, when derivatized with Cibacron Blue 3GA, as a separation matrix. Both of these technologies are based on in situ UV photopolymerization of glycidyl methacrylate (GMA) and trimethylolpropane trimethacrylate (TRIM) in channels.

• Macromolecular Research
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• v.17 no.3
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• pp.163-167
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• 2009

This study presents a microfluidic method for the production of monodisperse poly(ethylene glycol) (PEG) microspheres using continuous droplet formation and in situ photopolymerization in microfluidic devices. We investigated the flow patterns for the stable formation of droplets using capillary number and the flow rate of the hexade-cane phase. Under the stable region, the resulting microspheres showed narrow size distribution having a coefficient of variation (CV) of below 1.8%. The size of microspheres ($45{\sim}95{\mu}m$) could be easily controlled by changing the interfacial tension between the two immiscible phases and the flow rates of the dispersed or continuous phase.