Younghak Cho

Microfabricated Microbial Fuel Cell Arrays Reveal Electrochemically Active Microbes

Microbial fuel cells (MFCs) are remarkable “green energy” devices that exploit microbes to generate electricity from organic compounds. MFC devices currently being used and studied do not generate sufficient power to support widespread and cost-effective applications. Hence, research has focused on strategies to enhance the power output of the MFC devices, including exploring more electrochemically active microbes to expand the few already known electricigen families. However, most of the MFC devices are not compatible with high throughput screening for finding microbes with higher electricity generation capabilities. Here, we describe the development of a microfabricated MFC array, a compact and user-friendly platform for the identification and characterization of electrochemically active microbes. The MFC array consists of 24 integrated anode and cathode chambers, which function as 24 independent miniature MFCs and support direct and parallel comparisons of microbial electrochemical activities. The electricity generation profiles of spatially distinct MFC chambers on the array loaded with Shewanella oneidensis MR-1 differed by less than 8%. A screen of environmental microbes using the array identified an isolate that was related to Shewanella putrefaciens IR-1 and Shewanella sp. MR-7, and displayed 2.3-fold higher power output than the S. oneidensis MR-1 reference strain. Therefore, the utility of the MFC array was demonstrated.

Whole-Cell Impedance Analysis for Highly and Poorly Metastatic Cancer Cells

A micro electrical impedance spectroscopy (muEIS) system has been developed and implemented to analyze highly and poorly metastatic head and neck cancer (HNC) cell lines with single-cell resolution. The microsystem has arrays of 16 impedance analysis sites, each of which is capable of capturing a single cell and analyzing its whole-cell electrical impedance spectrum. This muEIS system was used to obtain the electrical impedance spectra of the poorly metastatic HNC cell line 686 LN and the highly metastatic HNC cell line 686 LN-M4e over a frequency range of 40 Hz - 10 MHz. The 686 LN cells had higher impedance phase compared to that of 686 LN-M4e cells at frequencies between 50 kHz and 2 MHz. This result demonstrates that the metastatic state of HNC cells can be distinguished using the developed muEIS system. This system is expected to serve as a powerful tool for future detection and quantification of cancer cells from various tumor stages.

Research trends in biomimetic medical materials for tissue engineering: 3D bioprinting, surface modification, nano/ micro-technology and clinical aspects in tissue engineering of cartilage and bone

This review discusses about biomimetic medical materials for tissue engineering of bone and cartilage, after previous scientific commentary of the invitation-based, Korea-China joint symposium on biomimetic medical materials, which was held in Seoul, Korea, from October 22 to 26, 2015. The contents of this review were evolved from the presentations of that symposium. Four topics of biomimetic medical materials were discussed from different research groups here: 1) 3D bioprinting medical materials, 2) nano/micro-technology, 3) surface modification of biomaterials for their interactions with cells and 4) clinical aspects of biomaterials for cartilage focusing on cells, scaffolds and cytokines.

Analysis of the variable length nonzero window method for exponentiation

Abstract The variable length nonzero window method is a way of computing exponentiation and modular exponentiation. This method has been analyzed, but there is a substantial difference between the analysis and experimental results. The difference results from some logical errors in the analysis. We analyze the variable length nonzero window method by modeling it as a Markov chain. We consider all details and our analysis predicts the behavior of the variable length nonzero window method exactly.

Acoustophoretic force-based compressibility measurement of cancer cells having different metastatic potential

Mechanical properties of cells such as compressibility are regarded to be different as cancer cells progress into metastatic state. Traditional methods for measuring mechanical properties of single cells such as AFM and micropipette aspiration require labor-intensive procedures and can cause damage to cells due to direct contact, thus unsuitable for high-throughput measurement. Acoustophoretic force exerted on particles under acoustic-standing-waves depends on the particle and medium’s vibro-acoustic properties. Thus, cells with different mechanical properties show different mobility under acoustic resonant field, which can be analyzed to decipher the mechanical properties of cells. Here we present a high-throughput, single-cell-resolution, cell compressibility measurement approach based on acoustic-standing-wave-induced force, and the finding that head and neck cancer cells having different metastatic capacities show noticeable differences in compressibility. The acoustophoresis chip has a straight flow ...

Lateral-flow particle filtration and separation with multilayer microfluidic channels

Separating particles from a suspension and sorting particles into different size ranges are important to many chemical, biological, and bioengineering applications. In this article, a novel lateral-flow particle separation device is presented for continuous particle fractionation from suspensions. This device is based on three-dimensional multilayer poly(dimethylsiloxane) microchannels, which can be fabricated by high-yield and low-cost molding and transfer-bonding techniques. By varying the dimensions of the microchannels in each layer, particles in a suspension can be fractionated into specific layers based on their sizes. Particle separation is successfully achieved in sorting polystyrene microbeads of 1, 10, and 45μm in diameter into different layers. The yield and selectivity of particle separation can be controlled by device geometries such as channel width and length. This novel continuous-flow particle filtration and separation device is expected to find applications in micrototal analysis systems...

Flow instability of semicrystalline polymer melt during micro-injection molding

This work investigates the flow instability of thermoplastic polymer melt that occurs on the flow front when it enters micro-cavities. On the flow front, it was observed that small balls are formed and coalesce with each other, creating many micro-weld lines. The experimental results in this work showed occurrence of this phenomenon for polypropylene and polyamide but not for high density poly(ethylene), poly(methylmethacrylate) or acrylonitrile butadiene styrene. It was found that onset of this instability is related to the spherulite size. The effects of temperature and geometry have been scrutinized. As a conclusion, the ratio of spherulite size and channel width has been proposed as a dimensionless number related to this instability.

Acoustic standing wave based microsystem for low-concentration oil detection and separation

Detection and quantification of extremely small amount of oil on site and at low cost has broad applications in environmental monitoring, both in oil spills as well as in routine marine/costal ecosystem monitoring. For example, dispersed oil, generated through the use of chemical dispersants in oil spills to break up oil slick into small droplets so that they can be rapidly diluted in 3D space are the greatest concern and poses the most challenges in detection. Fluorometry is the current standard method, however is bulky and expensive, limiting its wide deployment in the field. Here we demonstrate for the first time the development of an acoustic standing wave based microfluidic platform capable of processing large amount of liquid samples from which dispersed oil can be concentrated and separated to a detectable level by acoustophoretic force. The microfluidic platform consists of a recirculation channel structure into which dispersed oil droplets can be continuously separated from the main sample flow s...

A microfabricated microbial fuel cell array for high throughput screening (HTS) of electricity generating microbes from environment

This paper presents the development of a microfabricated microbial fuel cell (MFC) array for screening microbes capable of direct electricity generation. The compact and user-friendly platform enables direct characterization and comparison of electrochemically active microbes in parallel. The MFC array consists of 24 independent miniature MFCs on a single 5×7.5 cm chip format, capable of 24 parallel analyses. A parallel screening of environmental microbes using the MFC array identified an isolate displaying 233% higher power than the S. oneidensis MR-1 reference strain. This result was validated using a conventional MFC.