Kyunghwan Kim

A Cytoprotective and Degradable Metal–Polyphenol Nanoshell for Single‐Cell Encapsulation

Single-cell encapsulation promises the cytoprotection of the encased cells against lethal stressors, reminiscent of the sporulation process in nature. However, the development of a cytocompatible method for chemically mimicking the germination process (i.e., shell degradation on-demand) has been elusive, despite the shell degradation being pivotal for the practical use of functional cells as well as for single cell-based biology. We report that an artificial shell, composed of tannic acid (TA) and Fe(III) , on individual Saccharomyces cerevisiae controllably degrades on-demand, while protecting the yeast from multiple external aggressors, including UV-C irradiation, lytic enzymes, and silver nanoparticles. Cell division is suppressed by the TA-Fe(III) shell, but restored fully upon shell degradation. The formation of a TA-Fe(III) shell would provide a versatile tool for achieving the chemical version of sporulation and germination.

Evaluation of Silver-coated Magnesium Bipolar Plate for Lightweight PEM Fuel Cell Stack

A magnesium bipolar plate whose surface was protected by a thinly deposited silver layer was investigated as an alternative to the existing graphite bipolar plate of polymer electrolyte membrane(PEM) fuel cells. A thin silver layer was deposited on a magnesium alloy substrate by physical vapor deposition at 180℃. A number of tests were conducted on the fabricated magnesium-based bipolar plates to determine their suitability for use in PEM fuel cell stacks. A test on corrosion resistance under the same pH conditions as those in a PEM operation demonstrated that the silver layer protected the magnesium alloy substrate, while an unprotected substrate suffered from severe corrosion. The contact resistance of the fabricated bipolar plate was less than 20 mΩ-cm2, which was superior to conventional bipolar plates. A single-cell was constructed using the fabricated bipolar plates and its power output was measured. Owing to the enhanced conductivity caused by low contact resistance, a slight increase was observed ...

Design, Fabrication, and Performance Evaluation of MEMS Solid Propellant Thruster Array

This paper presents the internal ballistic design, fabrication procedure, and performance evaluation of a Micro Electro Mechanical Systems (MEMS) solid propellant thruster array chip. The internal ballistic design was carried out to predict the performance of the thruster. Only the photosensitive glass wafer was used as the bare material for the thruster. We developed the micro igniter with improved structural stability by using a glass membrane with a thickness of tens of microns. The solid propellant was loaded into the propellant chamber without resort to a special technique due to the high structural stability of the glass membrane. An MEMS Solid Propellant Thruster (MSPT) array was fabricated through anisotropic etching of photosensitive glass. Ignition and combustion tests of the fully assembly MEMS thruster were performed successfully. Nomenclature P = pressure t = time R = gas constant T =

Performance assessment of Magnesium Bipolar Plates for Light Weight PEM Fuel Cell

In present paper, we used magnesium alloy having a lower density and higher electrical conductivity for bipolar plate to reduce the weight of PEM fuel cell. The silver was coated to prevent corrosion and form passivation film on the metal surface with sputtering. In acid proof evaluation for setting optimal coating conditions, the homogeneity of coating thickness was improved by coating with the thickness of 3 which not indicated any micro cracks and the temperature . The performance test and evaluation based on the clamping pressure and channel depth to determine the configuration of bipolar plate for assembling single cell was implemented. And then we assembled single cell with this bipolar plate and implemented the performance test to ensure and compare the current-voltage performance followed as several factors such as coating or non-coating, the change of clamping pressure, the change of channel depth, etc. As these results, the maximum power density of single cell with the coated bipolar plate was 192 and it was confirmed that the power density per unit mass was better than existing metal bipolar plate.