Ho-Sup Jung

Direct differentiation of human embryonic stem cells into selective neurons on nanoscale ridge/groove pattern arrays

Human embryonic stem cells (hESCs) are pluripotent cells that have the potential to be used for tissue engineering and regenerative medicine. Repairing nerve injury by differentiating hESCs into a neuronal lineage is one important application of hESCs. Biochemical and biological agents are widely used to induce hESC differentiation. However, it would be better if we could induce differentiation of hESCs without such agents because these factors are expensive and it is difficult to control the optimal concentrations for efficient differentiation with reduced side effects. Moreover, the mechanism of differentiation induced by these factors is still not fully understood. In this study, we present evidence that nanoscale ridge/groove pattern arrays alone can effectively and rapidly induce the differentiation of hESCs into a neuronal lineage without the use any differentiation-inducing agents. Using UV-assisted capillary force lithography, we constructed nanoscale ridge/groove pattern arrays with a dimension and alignment that were finely controlled over a large area. Human embryonic stem cells seeded onto the 350-nm ridge/groove pattern arrays differentiated into neuronal lineage after five days, in the absence differentiation-inducing agents. This nanoscale technique could be used for a new neuronal differentiation protocol of hESCs and may also be useful for nanostructured scaffolding for nerve injury repair.

Anisotropic Adhesion Properties of Triangular‐Tip‐Shaped Micropillars

Directional dry adhesive microstructures consisting of high-density triangular-tip-shaped micropillars are described. The wide-tip structures allow for unique directional shear adhesion properties with respect to the peeling direction, along with relatively high normal adhesion.

AOT/isooctane reverse micelles with a microaqueous core act as protective shells for enhancing the thermal stability of Chromobacterium viscosum lipase

According to the different environmental systems for lipase reactions, changes in thermal stability were investigated by employing the Chromobacterium viscosum lipase and a two-step series-type deactivation model. The half-life (6.81 h) of the lipase entrapped in reverse micelles at 70 °C was 9.87- and 14.80-fold longer than that in glycerol pool or in aqueous buffer. The deactivation constants for the first and second step (k1 and k2) at all temperatures drastically decreased when the lipase was entrapped in reverse micelles. In particular, k1 (3.84 h(-1)) at 70 °C in reverse micelles was 1.57-fold lower than that in aqueous buffer (6.03 h(-1)). Based on the fluorescence spectrometry, the amount of excited forms of tryptophan and tyrosine increased markedly during the thermal-treatment in aqueous buffer, whereas no significant fluctuation was noted in the reversed micellar system. These results indicated that the encapsulation in reverse micelles could be favorable for preventing the enzyme from heat-induced denaturation.

Rapid detection of Mycoplasma pneumonia in a microfluidic device using immunoagglutination assay and static light scattering

We present real‐time, rapid detection of Mycoplasma pneumonia in PBS inside a Y‐channel PDMS microfluidic device via optical fiber monitoring of latex immunoagglutination. The latex immunoagglutination assay was performed with serially diluted M. pneumonia solutions using highly carboxylated polystyrene particles of 390 and 500 nm diameter conjugated with monoclonal anti‐M. pneumonia. Proximity optical fibers were located around the viewing cell of the device, which were used to measure the increase in 45° forward light scattering of the aggregated particles. The detection limit are slightly less than 50 pg mL−1 both for 390 and 500 nm microspheres and the detection time do not exceed 90 s.

Effect of C incorporation on relaxation of SiGe/Si

Thin fully strained Si1−xGex/Si1−x−yGexCy/Si1−xGex heterostructures (x=0.2), with controlled C incorporation sites, were grown on Si substrates using ultrahigh vacuum chemical vapor deposition. Following the growth, layers were relaxed using rapid thermal annealing at 1000 °C for 30 s, and high degrees of relaxation of 65% and 59% were achieved with and without interstitial C, respectively. We show that the difference in cross hatch density and step height between two samples, which correspond to different misfit dislocation pileup behaviors, suggests controllability of SiGe relaxation via variation in C incorporation sites in the SiGeC layer.

Amperometric Detection of Conformational Change of Proteins Using Immobilized-Liposome Sensor System

An immobilized liposome electrode (ILE)-based sensor was developed to quantify conformational changes of the proteins under various stress conditions. The ILE surface was characterized by using a tapping-mode atomic force microscopy (TM-AFM) to confirm surface immobilization of liposome. The uniform layer of liposome was formed on the electrode. The current deviations generated based on the status of the proteins under different stress were then measured. Bovine carbonic anhydrase (CAB) and lysozyme were tested with three different conditions: native, reduced and partially denatured. For both proteins, a linear dynamic range formed between denatured concentrations and output electric current signals was able to quantify conformational changes of the proteins. The pattern recognition (PARC) technique was integrated with ILE-based sensor to perform data analysis and provided an effective method to improve the prediction of protein structural changes. The ILE-based stress sensor showed potential of leveraging the amperometric technique to manifest activity of proteins based on various external conditions.

Gas-sensing array application for on-line monitoring in a heat-responsive bioprocess of Streptomyces griseus HUT 6037

The stress-responsive bioprocess concept has been developed into an environmentally friendly biosensor with low energy consumption and high recovery yield. To improve chitosanase production during Streptomyces griseus cultivation, heat-stress was applied to the bioprocess with monitoring using an on-line gas sensing system. When exposed to heat-stress with liposomes, the chitosanase productivity was 2.6 times greater than for conventional cultivation. The mixed gas components could be distinguished using a principal component analysis during chitosanase production. The online-monitoring system reflected basic changes in growth conditions and metabolite formation in cells. The array type gas-sensing system was capable of detecting bacterial infection faster than conventional sensor systems. The gas sensor system can play a key role in monitoring and controlling stress levels in a stress-responsive bioprocess.

Characterization of the physicochemical properties of phospholipid vesicles prepared in CO2/water systems at high pressure

Phospholipid vesicles were prepared by the nonsolvent method using high-pressure CO2/water systems. The membrane properties of vesicles prepared at different pressures and temperatures were mainly characterized based on analysis of the membrane fluidity and membrane polarity, using the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene and 6-dodecanoyl-N,N-dimethyl-2-naphthylamine, respectively. The CO2(liquid)/water(liquid) and the CO2(supercritical)/water(liquid) two-phase (heterogeneous) systems resulted in the formation of vesicles with high yield (ca. 85%-88%). The membrane fluidity and polarity of the vesicles were similar to those of liposomes prepared by the conventional method. It is suggested that high-pressure CO2 can be used to form an appropriate hydrophobic-hydrophilic interface where phospholipid molecules as a self-assembled membrane.

Effect of C Incorporation on the Growth Kinetics of Si 1-x- y Ge x C y Layers

In this article, SiGeC layers were grown on Si by ultra-high vacuum CVD (UHVCVD) and the growth kinetics of SiGeC layer were investigated by varying methylsilane flow rate and growth temperature. We investigated the incorporation behavior of C and observed the two-step growth kinetics due to strong C-H bonds and non-substitutional C incorporation