Jeonghoon Lee

Integration of microfluidic chip with biomimetic hydrogel for 3D controlling and monitoring of cell alignment and migration

A biomimetic hydrogel was integrated into microfluidic chips to monitor glioma cell alignment and migration. The extracellular matrix-based biomimetic hydrogel was remodeled by matrix metalloprotease (MMP) secreted by glioma cells and the hydrogel could thus be used to assess cellular behavior. Both static and dynamic cell growth conditions (flow rate of 0.1 mL/h) were used. Cell culture medium with and without vascular endothelial growth factor (VEGF), insensitive VEGF and tissue inhibitor of metalloproteinases (TIMP) were employed to monitor cell behavior. A concentration gradient formed in the hydrogel resulted in differences in cell behavior. Glioma cell viability in the microchannel was 75-85%. Cells in the VEGF-loaded microchannels spread extensively, degrading the MMP-sensitive hydrogel, and achieved cell sizes almost fivefold larger than seen in the control medium. Our integrated system can be used as a model for the study of cellular behavior in a controlled microenvironment generated by fluidic conditions in a biomimetic matrix.

A Study of Black Carbon Measurement in Metropolitan Area and Suburban Area of the Korean Peninsula Performed during Pre KORea-US Air Quality Study (KORUS-AQ) Campaign

Abstract Black carbon(BC) aerosols were monitored at the KIST site(37.603°N, 127.046°E) and Cheonan-KOREATECH site(36.766°N, 127.281°E) during the pre KORea-US Air Quality Study(KORUS-AQ) campaign using a couple of Muliti Angle Absorption Photometers(MAAP). BC mass concentrations were presented as 2.14μg/m± 3 1.06 and 0.94±0.60 μg/m 3 at KIST site(Seoul) and KOREATECH site(Cheonan), respectively. BC mass concentrations measured at KIST and KOREATECH sites from 22:00 on May 22 to 12:00 on May 23, 2015 showed 80% and 72% higher than average BC mass concentrations measured during campaign period, respectively. It indicates both sites could be influenced by a remote source. Similar patterns of BC concentrations between two sites from 20:00 to 24:00 on June 6, 2015 implies that the BC could be transported into both sites and then be stagnant inside the Korean Peninsula. Diurnal variation of BC in weekdays and weekends were also presented for the KIST and KOREATECH sites. Morning rush hour peak was observed at KIST site located in metropolitan area though no distinct morning rush hour peak was not observed at KOREATECH site located in a suburban area. This study revealed transport pathways of BC near the Korean Peninsula using back-trajectory analysis of BC measured both in a metropolitan area and in a suburban area.

Monitoring of black carbon concentration at an inland rural area including fixed sources in Korea.

We monitored black carbon (BC) concentration for 6months to understand the characteristics of atmospheric aerosols of an inland rural area in Korea. A multi-angle absorption photometer was used to continuously monitor the BC concentration, which was compared with elemental carbon (EC) concentration measured by an OC/EC Analyzer. For the atmospheric aerosols less than 10μm, size distributions were measured using both an optical particle counter and a scanning mobility particle sizer. The diurnal variations for BC concentration show that the average BC concentration was 1.43μgm(-3) and exhibited peaks in the morning rush hours. However, the BC concentration measured at night from 20:00 to 08:00 was higher than that measured during the day. The reason why the BC concentration at night was higher would be partly due to the regional characteristics influenced by the combination of local fixed sources and traffic condition. It is suggested that the traffic and transporting of pollutants from the west influenced the increase in the BC concentration at inland rural area including fixed sources.

Comparison of light absorption properties for various absorbing particles

We experimentally determined optical properties of various absorbing particles such as nigrosins, black-dyed polystyrene latex, and diesel black carbon (BC). The absorption coefficient (Qabs) was measured to determine the absorption cross section (σabs) for given particle sizes. Our experimental system consists of a differential mobility analyzer (DMA), a condensation particle counter (CPC), a multi-angle absorption photometer (MAAP), an elemental carbon/organic carbon (EC/OC) analyzer, an aerosol sampler, a dilution device, and a diesel engine. We diluted the exhaust from the diesel engine in order to provide similarity to aerosol particles of accumulation mode in the atmosphere. We measured the size distribution of diesel BC using the DMA and the CPC. The mode diameter was changed as the diesel BC was grown. We measured the number concentration (N) and the absorption coefficient for black carbon using the CPC and the MAAP, respectively. Then, we obtained absorption cross sections for various particle sizes. Preliminary result showed that the absorption cross section for diesel BC having a 200-nm diameter was measured to be 1.06u2009×u200910−14xa0m2/particle. For diesel BC, mass concentrations measured by the MAAP were in good agreement with those measured by the OC/EC analyzer.

Estimation of emission properties for silica particles using thermal radiation spectroscopy

This paper shows that spectrally resolved thermal radiation from silica aggregate particles can be used to extract an emissivity and a temperature in the visible regime. Emissivity of silica aggregate particles at temperatures above 2000u2009K is measured by the analysis of emission radiation spectra from the particles. Temperature is estimated from the relation between the emission intensity and the wavenumber. Relative emissivities at temperatures from 2150 to 2919u2009K are presented. Proper knowledge of optical properties for silica aggregate particles will help further the understanding of thermophysics at high temperature.

Development of Image-based Fluorescence Photobleaching Technique for Measuring Macromolecule Diffusion in Biological Porous Medium

Fluorescence recovery after photobleaching (FRAP) has been widely used for the measurement of molecular diffusion in living cells and tissues. We developed an image-based FRAP (iFRAP) technique using a modified real-time microscope and a 488 nm Ar-ion laser. A fractional intensity curve was obtained from the time-lapse images of fluorescence recovery in the bleached spot to determine the diffusion coefficient of fluorescently labeled macromolecules in porous medium. We validated iFRAP through experiments with agar gels (0.5% and 1.5% w/v) containing FITC-Dextrans (10, 70 and 500 kDa MW). Further validation was performed by a Monte Carlo approach, where we simulated the three-dimensional random walk of macromolecules in agar gel model. Diffusion coefficients were deduced from the mean square displacement curves and showed good agreements with those measured by iFRAP.

Measurement of Black Carbon Concentration in Rural Area

We measured black carbon concentration in rural area to understand the characteristic of atmospheric aerosol by comparing the black carbon concentration and meteorological factors such as PM10 concentration, relative humidity, temperature and wind velocity. A MAAP (Multi Angle Absorption Photometer) which is one of filter based equipments was used to measure black carbon concentration. Black carbon concentration was measured to be high from April to May and low from June to September. Black carbon concentration was proportional to PM10 concentration. Black carbon concentration was correlated to relative humidity. Black carbon concentration was inversely proportional to wind velocity and temperature. Finally, we suggest that the volume fraction of black carbon in the atmosphere can be estimated from the size, number concentration and absorption coefficient measured using the MAAP. Corresponding Author, jlee@koreatech.ac.kr 2014 The Korean Society of Mechanical Engineers C

Toward reducing uncertainty in Fluorescence Recovery After Photobleaching

We investigate the uncertainty associated with the Fluorescence Recovery After Photobleaching, FRAP, which is widely used in the determination of diffusion coefficient for bio molecules. The uncertainty of our FRAP technique stems from the measurement of the spot size and the half time. The uncertainties of the FRAP is evaluated by considering the uncertainty propagation through the measurements of both spot size and the half time. Finally, we suggest an approach to estimate the effective diffusion coefficient by considering slip conditions between the fluorescent beads and the fluid. The diffusion coefficients measured by the FRAP is close to those obtained from the Stokes-Einstein relation together with the slip correction factor rather than that obtained solely by the Stokes-Einstein equation.

Liquid-phase sample preparation method for real-time monitoring of airborne asbestos fibers by dual-mode high-throughput microscopy

Asbestos that had been used widely as a construction material is a first-level carcinogen recognized by the World Health Organization. It can be accumulated in body by inhalation causing virulent respiratory diseases including lung cancer. In our previous study, we developed a high-throughput microscopy (HTM) system that can minimize human intervention accompanied by the conventional phase contrast microscopy (PCM) through automated counting of fibrous materials and thus significantly reduce analysis time and labor. Also, we attempted selective detection of chrysotile using DksA protein extracted from Escherichia coli through a recombinant protein production technique, and developed a dual-mode HTM (DM-HTM) by upgrading the HTM device. We demonstrated that fluorescently-labeled chrysotile asbestos fibers can be identified and enumerated automatically among other types of asbestos fibers or non-asbestos particles in a high-throughput manner through a newly modified HTM system for both reflection and fluorescence imaging. However there is a limitation to apply DM-HTM to airborne sample with current air collecting method due to the difficulty of applying the protein to dried asbestos sample. Here, we developed a technique for preparing liquid-phase asbestos sample using an impinger normally used to collect odor molecules in the air. It would be possible to improve the feasibility of the dual-mode HTM by integrating a sample preparation unit for making collected asbestos sample dispersed in a solution. The new technique developed for highly sensitive and automated asbestos detection can be a potential alternative to the conventional manual counting method, and it may be applied on site as a fast and reliable environmental monitoring tool.

Study of Aerosol Light Absorption Measurement Operated in a Vehicle Using an Interferometer

We propose a method operated in a vehicle to measure light absorption of particles in atmosphere. The advantage of this method is that it is insensitive to light scattering and hence can be used for the direct measurement of the light absorption coefficient without suffering from light scattering. With this method atmospheric light absorption can be measured at a time constant of 10 s. Further, our method allows for the real-time measurement of light absorption near a highway. The light absorption coefficients were high near a race track, an airport and the main gate where vehicles emitted carbonaceous particles.