Earticle

Conventional point-of-care (POC) devices need to be more convenient because blood sampling and sample analysis are implemented in separate devices. Therefore, we have developed a one-step microfluidic POC device which can carry out blood sampling and sample analysis simultaneously on a device. The one-step microfluidic device has three components, a microneedle (an inner diameter: 80 μm) and a micropump for blood sampling and a microchannel for immuoassay. The micropump is a cylinder (dimameter: 9 mm, height: 15 mm) on a flexible thin film (1 mm tick) made of elastic polymer polydimethylsiloxane. The microchannel is fabricated with UV-curable polymer, Norland Optical Adhesive (NOA63), by contact printing method. Then, the surface of the channel was coated with PDMS nanolayer and modified to be hydrophilic by treating oxygen plasma. Finally, the microneedle and the micropump were assembled by bonding after oxygen plasma treatment and the microneedle was bonded to the side of the micropump. We observed the one-step microfluidic device could pump 300 ㎕ distilled water and blood mimicking solution as well. Then, the pumped sample solution was spontaneously flowed into the hydrophilic microchannel sequentially. Therefore, the one step microfluidic device can be used as a POC device for quick and convenient diagnosis on site.

Recently there has been considerable interest in trying to translate microtiter plate based assays into microfluidic platforms. Due to their small scale, microfluidic platforms have many practical advantages such as highly efficient reaction, sensitive detection and massive parallelism. Compared with microtiter plate based assays, the microfluidic platforms can continuously perform more complicated operation. Current method to mimic the microtiter plate based assay in microfluidic platforms categorized into droplet array. We present a programmable multiple droplet array systems that include droplet generation, array, storage, fusion, and elimination process. By integrating pneumatic microvalves with microfluidic system, we can achieve to precisely manipulate individual droplets for delivering, merging and mixing of distinct droplets. This method readily allow us to achieve in-situ monitoring and screening of several types of chemical and biochemical reactions. Thus, we expect that the proposed platform will be a powerful tool to study fundamental biological and chemical reactions, high throughput screening (HTS), or combinatorial synthesis or analysis.

A microfluidic device is a miniaturized analytical system in which pretreatment, reaction, separation, detection and analysis are integrated. The advantages are consumption of a small volume of reagent, short time for analysis, higher accuracy, easier automation and scale-up, etc. Room temperature ionic liquids (RTILs) are organic salts which do not crystallize at room temperature. RTILs are gaining increasing notoriety and investigation as green solvents, because of thier non-volatile character, thermal stability, versatility, and so forth. Formation a micro-plug of RTILs in a microfluidic device is useful for high-throughput application, such as chemical processing, DNA analysis, polymerization, etc. In this study, size-distribution of RTIL micro-plug in PDMS (polydimethyl siloxane)-based microfluidic device was investigated.1) The effect of flow rates of PBS (phosphate buffered saline) and RTILs on the size of micro-plug was determined. The interfacial tension proportionally increased in relation on the length of the alkyl chain of the RTILs. Consequently, capillary number was calculated for the estimation of the size of the micro-plug.2)

Vesosomes are widely used in the field of medicine, science, and engineering as model cells. However current techniques to create vesosomes are not up to date requiring long time (up to one day) and need expertise. Vesosomes are also difficult to control diameter, resulting in broad ranges of size distribution. Therefore, we demonstrate an automated platform of multiple materials-encapsulated vesosomes using microfluidic devices integrated with two phase T-junction systems. Water soluble fluorescently labeled liposomes are encapsulated into vesosomes. The entire system is integrated with specially designed microfluidic device, enabling full automation of vesosome formation with multiple encapsulants. The principles of automated vesosome formation employed a T-junction microfluidic device with two phase system, resulting in the monolayer of lipid along the interface. Emulsions with the lipid monolayer from the T-junction is introduced to another interface of a lipid monolayer. Specially designed microfluidic system enables this entire process automatable. To demonstrate that the vesicles generated from the device are vesosomes with multiple encapsulants, we show microscopic images from fluorescent microscope and confocal laser scanning microscope along with size distribution. Our work with vesosomes with multiple encapsulants will provide simple and efficient methods and apply to various fields of research including model cell/membrane studies.

The chemotaxis of C.elegans has been conventionally studied by analyzing their movements toward attractant gradient on agar plates. Since the gradient was generated by diffusion of the attractant through porous agar, its concentration profile is ever changing. Thus, it needs to build consistent chemical gradient to perform accurate chemotaxis. Herein, we describe a PDMS (polydimethyl siloxane) microfluidic device which consists of a gradient-generating portion [1] and array of posts. Posts help worms swimming in water by enhancing their motility via mechanosensational reflex upon their bumping to the posts. Using this device, we were able to observe C. elegans swimming up the attractant gradient or down the repellent gradient. Moreover the device with linear gradient provides a sensitive platform to investigate chemo-response.

Partitioning and precipitation processes have been used successfully for the separation, purification and analysis of various biological materials. The properties of the coexisting phases are important determinants of the partitioning of proteins in both precipitation and aqueous two-phase systems (ATPS). In this investigation, the phase separation behavior of polyethyleneglycol (PEG) and PEGylated IgG with dextran based two-polymer systems have been studied. The studies focus on the phase behavior in the presence of mouse anti-human IgG that affect the PEGylated IgG. The volume ratio of two phases in microchannel was compared based upon the infused volumetric flow rate of each polymer solution. Developed technique will be used for the concurrent phase-separation and affinity separation of biomolecules.

Hybrid liposomes and Quantum Dots(QD) are widely used in medical fields of science as a novel fluorescent platform. Detection of disease related molecules and targeting of tumor cells can be done using functional group attached lipid. However, current techniques to create quantum dot(QD)- encapsulated liposome are not up to date requiring a long time and expertise. Moreover, liposomes created with conventional techniques are not evenly sized. Therefore, we demonstrate an automated platform of quantum dot(QD)-encapsulated liposome using microfluidic device and spinning device in order to collaborate multiple steps as a single process. In this paper, we illustrate the concept of automated formation method of quantum dot(QD)-encapsulated liposome. We have confirmed the properties of quantum dot(QD)- encapsulated liposome made by using microfluidic device and spinning device under fluorescent microscope, confocal laser scanning microscopy and particle analyzer. This automated formation method of quantum dot(QD)-encapsulated liposome will provide a more effective and efficient than formation method by using sonication or extruder instruments.

Purpose: The necessity for precise manipulation of bioparticles has greatly increased in the fields of bioscience, biomedical, and environmental monitoring. Dielectrophoresis (DEP) is considered to be an ideal technique to manipulate bioparticles. The objective of this study is to develop a DEP microfluidic device that can trap fluorescent beads, which mimic bioparticles, at the low voltage and frequency of the sinusoidal signal supplied to the microfluidic device. Methods: A DEP microfluidic device, which is composed of polydimethylsiloxane (PDMS) channels and interdigitated electrode networks, is fabricated to trap fluorescent beads. The geometry of the interdigitated electrodes is determined through computational simulation. To determine the optimum voltage and frequency of the sinusoidal signal supplied to the device, the experiments of trapping beads are conducted at various combinations of voltage and frequency. The performance of the DEP microfluidic device is evaluated by investigating the correlation between fluorescent intensities and bead concentrations. Results: The optimum ratio of the widths between the negative and positive electrodes was 1:4 ($20:80{\mu}m$) at a gap of $20{\mu}m$ between the two electrodes. The DEP electrode networks were fabricated based on this geometry and used for the bead trapping experiments. The optimum voltage and frequency of the supplied signal for trapping fluorescent beads were 15 V and 5 kHz, respectively. The fluorescent intensity of the trapped beads increased linearly as the bead concentration increased. The coefficient of determination ($R^2$) between the fluorescent intensity and the bead concentration was 0.989. Conclusions: It is concluded that the microfluidic device developed in this study is promising for trapping bioparticles, such as a cell or virus, if they are conjugated to beads, and their concentration is quantified.

Neural stem cells (NSCs) have the ability to self-renew and differentiate into multiple nervous system cell types. During embryonic development, the concentrations of soluble biological molecules have a critical role in controlling cell proliferation, migration, differentiation and apoptosis. In an effort to find optimal culture conditions for the generation of desired cell types in vitro, we used a microfluidic chip-generated growth factor gradient system. In the current study, NSCs in the microfluidic device remained healthy during the entire period of cell culture, and proliferated and differentiated in response to the concentration gradient of growth factors (epithermal growth factor and basic fibroblast growth factor). We also showed that overexpression of ASCL1 in NSCs increased neuronal differentiation depending on the concentration gradient of growth factors generated in the microfluidic gradient chip. The microfluidic system allowed us to study concentration-dependent effects of growth factors within a single device, while a traditional system requires multiple independent cultures using fixed growth factor concentrations. Our study suggests that the microfluidic gradient-generating chip is a powerful tool for determining the optimal culture conditions.

Purpose: The development of an efficient in vitro cell culture device to process various cells would represent a major milestone in biological science and engineering. However, the current conventional macro-scale in vitro cell culture platforms are limited in their capacity for detailed analysis and determination of cellular behavior in complex environments. This paper describes a microfluidic-based culture device that allows accurate control of parameters of physical cues such as pressure. Methods: A microfluidic device, as a model microbioreactor, was designed and fabricated to culture Saccharomyces cerevisiae and Chlamydomonas reinhardtii under various conditions of physical pressure stimulus. This device was compatible with live-cell imaging and allowed quantitative analysis of physical cue-induced behavior in yeast and microalgae. Results: A simple microfluidic-based in vitro cell culture device containing a cell culture channel and an air channel was developed to investigate physical pressure stress-induced behavior in yeasts and microalgae. The shapes of Saccharomyces cerevisiae and Chlamydomonas reinhardtii could be controlled under compressive stress. The lipid production by Chlamydomonas reinhardtii was significantly enhanced by compressive stress in the microfluidic device when compared to cells cultured without compressive stress. Conclusions: This microfluidic-based in vitro cell culture device can be used as a tool for quantitative analysis of cellular behavior under complex physical and chemical conditions.

Immunoliposomes (antibody-conjugated liposomes) are highly useful as both a drug carrier in drug delivery and as a reporting probe in immunodiagnostics. However, antibody conjugation is lengthy and cumbersome, because this includes several steps such as derivatization of the antibody, conjugation of the derivatized antibody to liposomes, and separation of the unbound antibodies from immunoliposomes. Recently, liposome preparation steps have simplified by using microfluidic devices (${\mu}FDs$) where liposomes are formed when a stream of lipids in solvent is hydrodynamically focused between two oblique buffer streams in a microchannel. Herein, we report a simple method for the production of immunoliposomes (rabbit IgG-conjugated liposomes) using microvalve-controlled ${\mu}FD$. The presence of antibody on the liposome was verified by observing the binding of immunoliposomes to rabbit IgG on the surface. The results suggest that immunoliposomes can be easily prepared through sequential mixing of antibody, conjugation reagents, preformed liposomes using microvalve-controlled ${\mu}FD$.

BRAF inhibitors (e.g., vemurafenib) are widely used to treat metastatic melanoma with the BRAF V600E mutation. The initial response is often dramatic, but treatment resistance leads to disease progression in the majority of cases. Although secondary mutations in the mitogen-activated protein kinase signaling pathway are known to be responsible for this phenomenon, the molecular mechanisms governing acquired resistance are not known in more than half of patients. Here we report a genome- and transcriptome-wide study investigating the molecular mechanisms of acquired resistance to BRAF inhibitors. A microfluidic chip with a concentration gradient of vemurafenib was utilized to rapidly obtain therapy-resistant clones from two melanoma cell lines with the BRAF V600E mutation (A375 and SK-MEL-28). Exome and transcriptome data were produced from 13 resistant clones and analyzed to identify secondary mutations and gene expression changes. Various mechanisms, including phenotype switching and metabolic reprogramming, have been determined to contribute to resistance development differently for each clone. The roles of microphthalmia-associated transcription factor, the master transcription factor in melanocyte differentiation/dedifferentiation, were highlighted in terms of phenotype switching. Our study provides an omics-based comprehensive overview of the molecular mechanisms governing acquired resistance to BRAF inhibitor therapy.

Microfluidic technologies hold high promise and emerge as a potential molecular tool to facilitate the progress of fundamental and applied biomedical researches by enabling miniaturization and upgrading current biological research tools. In this review, we summarize the state of the art of existing microfluidic technologies and its' application for characterizing biophysical properties of individual cells. Microfluidic devices offer significant advantages and ability to handle in integrating sample processes, minimizing sample and reagent volumes, and increased analysis speed. Therefore, we first present the basic concepts and summarize several achievements in new coupling between microfluidic devices and mass spectrometers. Secondly, we discuss the recent applications of microfluidic chips in various biological research field including cellular and molecular level. Finally, we present the current challenge of microfluidic technologies and future perspective in this study field.

This study aimed to compare the efficacies of conventional and non-conventional (modified hydrostatic microfluidic pumpless device, MHPD) systems on ovarian tissue culture and in vitro follicle growth using a mouse model. A total of 56 ovarian cortical tissues retrieved from seven wild-type mice were divided into three groups: 1) fresh control, 2) conventional culture system (control), and 3) non-conventional system with MHPD. Ovarian tissues were cultured for 96 hours and evaluated for follicle morphology, developmental stage, intact follicle density, and relative gene expression levels (proliferating cell nuclear antigen, insulin like growth factor 1, BAX, and Bcl-2). Our major data demonstrated that the mean percentage of primary follicle development was increased by the MHPD (P<0.05). In addition, this device could maintain and support follicle development better than the conventional culture systems. However, the overall outcomes were not significantly improved by our first-design prototype. Consequently, nextgeneration platforms should be developed as alternative medical tools for fertility preservation research.

For the measurement of biophysical properties related with cardiovascular diseases (CVD), various microfluidic devices were proposed. However, many devices were monitored by optical equipment. Ultrasound measurement to quantify the biophysical properties can provide new insights to understand the cardiovascular diseases. This study aims to check feasibility of microfluidic device for ultrasound image analysis based on 3D printer. To facilitate acoustic transmission, agarose solution is poured around 3D mold connected with holes of the acrylic box. By applying speckle image velocimetry(SIV) technique, flow information in the bifurcated channel was estimated. Considering that ultrasound signal amplitude is determined by red blood cell (RBC) aggregation, RBC aggregation in the bifurcated channel can be estimated through the analysis of ultrasound signal. As examples of microfluidic device which mimic the CVD model, velocity fields in microfluidic devices with stenosis and aneurysm were introduced.

미세 유체 제어 시스템 (마이크로 펌프, 마이크로 밸브, 마이크로 채널, 마이크로 믹서 등)의 집적은 화학 및 바이오 유체를 제어하는 Lab-on-a-chip 의 일부분으로서 사용되며 이러한 시스템의 집적은 Lab-on-a-chip 개발을 위해 필수적으로 요구된다. 본 논문에서는 이러한 microchip을 구현하기 위해서 초미세 유체 제어 소자인 마이크로 펌프와 마이크로 밸브를 같은 기판 위에 Polydimethylsiloxane (PDMS)와 indium tin oxade (ITO)를 사용하여 집적하였다. 그리고 밸브의 반복 작동 시 계속적인 유량의 감소를 줄이기 위해 PDMS 의 혼합비를 달리하여 PDMS membrane 의 기계적 특성을 강화시켰다.

액적기반의 미세유체 시스템은 마이크로 시험관으로서 화학, 생물학 연구에 적용하기 위해 개발되었다. 미세유체 시스템에서 피코부피(picoliter)의 매우 작은 액적은 소형화된 시스템 내에서 잘 정형화 되고 구획화된 반응기로 제공되어 진다. 매우 작은 액적에서의 반응은 자동화된 초고속 대용량 스크리닝 시스템을 통하여 저가이면서 고효율적으로 수행될 수 있다. 본 총설에서는 액적 기반의 미세유체시스템의 기능들인 액적 형성, 정교한 액적 제어, 다양한 응용분야에 대해 소개하고자 한다. 또한 화학적, 생물학적 새로운 응용분야에 관해 알아보고, 기존의 방법과 비교하여 액적기반의 미세유체 시스템이 갖는 장점에 관해 논의하고자 한다.

Droplet based microfluidic systems have been developed for the application of biological and chemical research field. A picoliter droplet in microfluidic device provides a compartmentalized and well-defined reactor in miniaturized system. The microfluidic system with small droplets can reduce reagent cost and enhance efficiency through automated high-throughput screening system. In this review, we summarize the functionality of droplet based microfluidic system including droplet generation, precise droplet control, and various applications. In addition, this article reviews current applications in chemistry and biology, and discuss advantages of droplet based microfluidics compared with conventional manner.

목적: 본 연구는 현장현시 건성안 진단 테스트 중에 현재 사용되고 있으나 부정확한 결과로 신뢰도가 떨어지는 쉬르머 용지를 대체 할 수 있는 차세대 건성안 진단 테스트 용지를 미세유체공학을 이용하여 개발하고자 하였다. 방법: 왁스로 패턴을 제조한 친수성 크로마토그래피 용지를 pH에 따른 색 변화가 나타나도록 안토시안으로 염색을 하였다. 인공 누액의 젖음 속도를 인공 누액과 32명의 참가자의 눈물을 이용하여 임상 측정하였다. 결과: 인공 누액을 이용하였을 경우 쉬르머 용지에서는 소량의 용액은(0.5 ml이하) 흡수거리가 도출되지 않았으나 새로 개발된 용지는 시간에 따른 인공 누액의 흡수거리가 확연히 나타났다. 임상실험에서도 새로 개발된 검사 용지는 TBUT (tear break-up time)결과와 부합하는 건성안 진단 결과를 보였다. 결론: 개발된 건성안 진단 용지는 간편하게 사용될 수 있을 뿐만 아니라 기존 쉬르머 용지와 같은 현장현시 건성안 진단 매체와 비교 했을 경우 건성안 판별의 정확성이 높았다.

Purpose: The aim of this study was to develop a dry eye test method using a paper based microfluidic device that improves inaccuracy caused by using one of current point-of-care dry eye tests such as Shirmer's. Methods: Wax printed hydrophilic chromatography papers were dyed with anthocyanin extracts to detect colorimetric display of liquid samples with varying pH. Fluid distribution rates were measured using artificial tears and human tears directly from 32 subjects. Results: With Shirmer's, fluid distribution rates with small amount of samples (less than $0.5{\mu}l$) were not displayed. However, with paper based microfluidic device, fluid imbibition distances over time were clearly showed. Also clinical results of dry eye from newly developed paper based microfluidic device showed correlation with the results from tear break up time tests. Conclusions: The newly developed paper based microfluidic devices were easy to use and exhibited more accurate clinical results than current dry eye point of care tests such as Shirmer's.