Yu Chang Kim

Analysis of pressure-driven air bubble elimination in a microfluidic device

We report an analysis of pressure-driven bubble elimination for a gas-permeable microfluidic device. In this study, we described bubble elimination in a microfluidic device employing a gas permeation model and calculated the removal efficiency of bubbles. The correction factor for the simplified model was estimated with respect to the applied pressure. Based on the established model, the required time to remove a trapped bubble with a certain area was shown to be within an error of 11.58% by comparison with experimental results. Exploiting the model equation, we were able to completely remove the air bubbles appearing during the process of filling a microfluidic device with an aqueous solution.

Microvalve-Assisted Patterning Platform for Measuring Cellular Dynamics Based on 3D Cell Culture

A microfluidic platform to satisfy both 3D cell culture and cell‐based assay is required for credible assay results and improved assay concept in drug discovery. In this article, we demonstrate a microvalve‐assisted patterning (MAP) platform to provide a new method for investigating cellular dynamics by generating a linear concentration gradient of a drug as well as to realize 3D cell culture in a microenvironment. The MAP platform was fabricated by multilayer soft lithography and several microvalves made it possible to pattern a cell–matrix (scaffold) and to exchange media solutions without breaking cell–matrix structure in a microchannel. This approach provides not only exact fluids control, bubble removal, and stable solution exchange in a microchannel, but also reliable scaffold fabrication and 3D cell culture. In this study, hepatotoxicity tests with human hepatocellular liver carcinoma cells (HepG2) were also performed in real‐time monitoring where cell morphologies exposed to different drug concentrations were observed at a time. Compared to 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) assay, the MAP platform could be used to reduce drug amount and assay time for cell‐based assays as much as 10 and 3 times, respectively. Biotechnol. Bioeng. 2008;101: 1005–1013.

A power-free blood plasma extraction device based on planar crossflow filter microstructure

This paper presents a simple blood plasma extraction device without any external driving force for point-of-care diagnosis. On the basis of capillary phenomenon and size exclusion, blood plasma was extracted through a planar crossflow filter using a surfactant-added poly(dimethyl siloxane)(PDMS) and SU8-based microstructure. The wetting property of PDMS was modified by mixing PDMS with nonionic surfactant, Silwet L-77. As a demonstration of the feasibility of this device, the contact angles and capillary filling rates according to the concentration of surfactant in PDMS were compared and the extraction of plasma from whole blood was confirmed through the planar filter with various heights.

Compressive Cell Stimulation using PDMS Membrane Deflection in a Microfluidic Device

We report a new kind of microfluidic compressive stimulation device for mechanotransduction studies. Mechanical stress was applied with the deflection of the poly(dimethylsiloxane) membrane between the microchannels formed by multilayer soft lithography. The membrane functions as an on-off valve for closing a fluid channel and a loading membrane for applying compressive stress; the deflected membrane press cells either directly or hydrostatically. As a demonstration of the feasibility of this microfluidic device, the viability of mammary gland epithelial (MCF7) cells in response to the compressive stress was assessed by the change of fluorescence intensity with calcein AM.