Heon-Ho Jeong

Pump-less static microfluidic device for analysis of chemotaxis of Pseudomonas aeruginosa using wetting and capillary action

Bacterial chemotaxis is a complex response to temporal changes of concentrations of chemoeffectors. Conventional methods, including microfluidic approaches, for the precise analysis of bacterial chemotaxis are limited in the accurate control of chemical gradients, low sensitivity, and longer analytical times although the advances in microfluidic technology provide a novel platform. Here, we present a diffusion-based microfluidic device to provide rapid diffusion of chemoeffectors using a liquid-liquid interface, which is a critical advance in the analysis of bacterial chemotaxis. The microfluidic method can rapidly analyze attractants and repellents, achieving a chemotaxis index corresponding to the concentrations and types of chemoeffectors. Moreover, we find that the dynamic switch in bacterial chemotaxis from attraction to repellence in response to specific chemoeffectors occurs in a concentration-dependent manner. Thus, our microfluidic method is promising and reliable for the analysis of bacterial chemotaxis.

Generation of uniform agarose microwells for cell patterning by micromolding in capillaries

AbstractWe described a simple and facile method to generate uniform agarose microwells on a polyelectrolyte (PEL) multilayer functionalized surface for efficient and reliable cell patterning. The PEL multilayers, composed of polyallylamine hydrochloride (PAH) and polystyrene sulfonate ammonium (PSS), provide an adhesive environment, which promotes cell proliferation in live cell-based assays. Agarose microwells, which are able to selectively isolate cells into individual compartments, are fabricated by micromolding the agarose solution in capillaries (MIMIC). Moreover, the fabricated agarose microwells are able to effectively form different shapes (e.g., circles, triangles, squares, and stars) and can isolate multiple cell types (e.g., HEK 293, NIH3T3, and HepG2). We also demonstrated how this technique can be used for the real-time monitoring of communication between primary neuronal cells in the agarose microwells.

The inhibitory effect of phloretin on the formation of Escherichia coli O157:H7 biofilm in a microfluidic system

A rapid and simple multiplex method to simultaneously investigate the effects of candidate drugs on the prevention of biofilm formation and to screen the biological activity of antimicrobial agents is urgently needed. Although several types of tools have been proposed for this purpose, conventional methods are still complicated and require long analytical times. This study presents a microfluidic approach to analyze the effect of phloretin on the formation of enterohemorrhagic E. coli O157:H7 biofilm in a single experiment. The microfluidic device is able to generate a continuous concentration gradient of phloretin in the main detection channel. Unlike conventional methods, this technique allows the analysis of the biofilm form of E. coli O157:H7 as an opportunistic pathogen and model organism; subsequently, mature biofilms were treated with phloretin to investigate the minimal biofilm eradication concentration (MBEC). In addition, inhibition assay of bacterial biofilm under concentration gradient is able to screen full concentration instead of point-to-point concentration assay. The results of MBEC determination clearly confirm that a low concentration of the antioxidant phloretin (30–35 μ/mL) significantly reduces biofilm formation, which suggests that phloretin acts as a biofilm inhibitor of E. coli O157:H7. The microfluidic approach for the evaluation of drug candidates could provide important information for the treatment of patients with chronic infection.

Optimization of microwell-based cell docking in microvalve integrated microfluidic device

This study presents a novel cell docking system based on microwells integratded with microvalves. Conventional cell docking device based on micro-well suffers from generation of dead volume and shear stress within micro-wells resulting in low efficiency of cell docking, limitation of nutrient, and low cell viability. Our approach to solve the problems adopts integration of microvalve controlled by pressure with microwells for provinding guided flow stream of cells and nutrients into microwell. We have optimized the efficiency of cell docking by varying several experimental parameters including flow rate, cell concentration, microvalve pressure, and size of microvalve. Under the optimized flow rate (1 µL/sec) and valve pressure (0.2 MPa), we obtain high efficiency of cell docking as 14.1 cells/microwell. In this study, we confirm that the perfusion culture of cells in microfluidic chip provides suitable environmental condition for cell culture at small scale and demonstrate the feasibility of universal cell culture platform.

Simple Analysis of Lipid Inhibition Activity on an Adipocyte Micro-Cell Pattern Chip

Polydimethyl-siloxane (PDMS) is often applied to fabricate cell chips. In this study, we fabricated an adipocyte microcell pattern chips using PDMS to analyze the inhibition activity of lipid droplets in mouse embryo fibroblast cells (3T3-L1) with anti-obesity agents. To form the PDMS based micropattern, we applied the micro-contact printing technique using PDMS micro-stamps that had been fabricated by conventional soft lithography. This PDMS micro-pattern enabled the selective growth of 3T3-L1 cells onto the specific region by preventing cell adhesion on the PDMS region. It then allowed growth of the 3T3-L1 cells in the chip for 10 days and confirmed that lipid droplets were formed in the 3T3-L1 cells. After treatment of orlistat and quercetin were treated in an adipocyte micro-cell pattern chip with 3T3-L1 cells for six days, we found that orlistat and quercetin exhibited fat inhibition capacities of 19.3% and 24.4% from 0.2 μM of lipid droplets in 3T3-L1 cells. In addition, we conducted a direct quantitative analysis of 3T3-L1 cell differentiation using Oil Red O staining. In conclusion, PDMS-based adipocyte micro-cell pattern chips may contribute to the development of novel bioactive compounds.

Morphological Control of Cells on 3-Dimensional Multi-Layer Nanotopographic Structures.

The extracellular matrix (ECM) environment is known to play an important role in the process of various cell regulatory mechanisms. We have investigated the ability of 3-dimensional ECM geometries to induce morphological changes in cells. Bi-layer polymeric structures with submicron scale stripe patterns were fabricated using a two-step nano-imprinting technique, and the orientation angle (θ(α)) of the upper layer was controlled by changing its alignment with respect to the orientation of the bottom layer. When cells were grown on the mono-layer stripe structure with a single orientation, they elongated along the direction of the stripe pattern. On bi-layer polymer structures, the cell morphologies gradually changed and became rounded, with an increase of θα up to 90 degrees, but the polarities of these cells were still aligned along the orientation of the upper layer. As a result, we show that the polarity and the roundness of cells can be independently regulated by adjusting the orientation of 3-dimensional hierarchical ECM topography.