Jeong Ho An

Effect of the structure of chain extenders on the dynamic mechanical behaviour of polyurethane

The dynamic mechanical behaviors of polyurethanes with different types of non-linear chain extenders are compared with those of corresponding linear chain extender. The Tg of the soft segment matrix showed much variation depending on the type of the chain extenders. The use of non-linear chain extender results in at least 30°C shift toward the higher temperature compared with the sample with 1,4-butanediol. The softening temperature of the hard segment domains is dependent on the detailed structure of the chain extender. Cyclic chain extender and some chain extenders with pendent groups showed a quite significant increase in the softening temperature and well-developed rubbery plateau regions. In tan δ peaks, the peak representing the soft segment matrix becomes much sharper and larger when non-linear chain extenders are employed.

An ultra-sensitive biophysical risk assessment of light effect on skin cells

The aim of this study was to analyze photo-dynamic and photo-pathology changes of different color light radiations on human adult skin cells. We used a real-time biophysical and biomechanics monitoring system for light-induced cellular changes in an in vitro model to find mechanisms of the initial and continuous degenerative process. Cells were exposed to intermittent, mild and intense (1-180 min) light with On/Off cycles, using blue, green, red and white light. Cellular ultra-structural changes, damages, and ECM impair function were evaluated by up/down-regulation of biophysical, biomechanical and biochemical properties. All cells exposed to different color light radiation showed significant changes in a time-dependent manner. Particularly, cell growth, stiffness, roughness, cytoskeletal integrity and ECM proteins of the human dermal fibroblasts-adult (HDF-a) cells showed highest alteration, followed by human epidermal keratinocytes-adult (HEK-a) cells and human epidermal melanocytes-adult (HEM-a) cells. Such changes might impede the normal cellular functions. Overall, the obtained results identify a new insight that may contribute to premature aging, and causes it to look aged in younger people. Moreover, these results advance our understanding of the different color light-induced degenerative process and help the development of new therapeutic strategies.

Development of simple and sensitive hydrogel based colorimetric sensor array for the real-time quantification of gaseous ammonia

A real-time colorimetric sensor array (CSA) offers the advantages of diversity and accuracy for the quantification of multiple analytes; however, traditional sensors require a complex fabrication process. Therefore, to take full advantage of this sensing platform, we have developed a simple CSA system composed of a polymer, a reducing agent, and different pH indicators. Distinctive color response patterns were classified by extracting the hidden information, (i.e., red, green, and blue (RGB) values) from the indicators. This triple-channel sensing platform is further applied for statistical analysis, to quantify different concentrations of ammonia and other analytes. The sensor array showed a limit of detection of 0.3ppm, which is well below the diagnostic criteria for ammonia concentration in the breath of healthy individuals and of patients with end-stage renal disease. As this sensor would be able to quantify gaseous ammonia in the breath, it is relevant to the point-of-care diagnosis of patients with renal diseases.

A novel CMOS image sensor system for quantitative loop-mediated isothermal amplification assays to detect food-borne pathogens

Loop-mediated isothermal amplification (LAMP) is considered as one of the alternatives to the conventional PCR and it is an inexpensive portable diagnostic system with minimal power consumption. The present work describes the application of LAMP in real-time photon detection and quantitative analysis of nucleic acids integrated with a disposable complementary-metal-oxide semiconductor (CMOS) image sensor. This novel system works as an amplification-coupled detection platform, relying on a CMOS image sensor, with the aid of a computerized circuitry controller for the temperature and light sources. The CMOS image sensor captures the light which is passing through the sensor surface and converts into digital units using an analog-to-digital converter (ADC). This new system monitors the real-time photon variation, caused by the color changes during amplification. Escherichia coli O157 was used as a proof-of-concept target for quantitative analysis, and compared with the results for Staphylococcus aureus and Salmonella enterica to confirm the efficiency of the system. The system detected various DNA concentrations of E. coli O157 in a short time (45min), with a detection limit of 10fg/μL. The low-cost, simple, and compact design, with low power consumption, represents a significant advance in the development of a portable, sensitive, user-friendly, real-time, and quantitative analytic tools for point-of-care diagnosis.

Influence of microstructure on the dynamic mechanical behavior of polymeric composites containing structured latexes

Abstract The dynamic mechanical behavior and mechanical behavior of polymeric composites containing three different kinds of dispersed phase are discussed. The first system has a structure of island-in-island type of morphology which is formed by phase separation inside of the crosslinked latex particles. The second system has a dispersed phase with a core-shell type of morphology which is prepared by heterocoagulation of large amphoteric latex and small anionic latex. The last one makes use of hollow particles containing a central void of 0.4 μm. The surface of the hollow particle has been modified to provide chemical bonds with a matrix phase composed of epoxy resins. The effect of morphology, the characteristics of the shell and the extent of interfacial bonding on the dynamic mechanical behavior or fracture behavior are discussed.