Jaesool Shim

Microporous Cell-laden Hydrogels for Engineered Tissue Constructs

In this article, we describe an approach to generate microporous cell‐laden hydrogels for fabricating biomimetic tissue engineered constructs. Micropores at different length scales were fabricated in cell‐laden hydrogels by micromolding fluidic channels and leaching sucrose crystals. Microengineered channels were created within cell‐laden hydrogel precursors containing agarose solution mixed with sucrose crystals. The rapid cooling of the agarose solution was used to gel the solution and form micropores in place of the sucrose crystals. The sucrose leaching process generated homogeneously distributed micropores within the gels, while enabling the direct immobilization of cells within the gels. We also characterized the physical, mechanical, and biological properties (i.e., microporosity, diffusivity, and cell viability) of cell‐laden agarose gels as a function of engineered porosity. The microporosity was controlled from 0% to 40% and the diffusivity of molecules in the porous agarose gels increased as compared to controls. Furthermore, the viability of human hepatic carcinoma cells that were cultured in microporous agarose gels corresponded to the diffusion profile generated away from the microchannels. Based on their enhanced diffusive properties, microporous cell‐laden hydrogels containing a microengineered fluidic channel can be a useful tool for generating tissue structures for regenerative medicine and drug discovery applications. Biotechnol. Bioeng. 2010; 106: 138–148.

Effects of ampholyte concentration on protein behavior in on-chip isoelectric focusing.

The effects of mobility corrections on carrier ampholytes are studied at various ampholyte concentrations to understand protein behavior during IEF. IEF simulations are conducted in the presence of 25 biprotic carrier ampholytes within a pH range of 6–9 after applying the Onsager–Debye–Hückel correction to the carrier ampholytes. Two model proteins with ten charge states but without ionic strength corrections are allowed to focus under an electric field of 300 V/cm in a 1 cm long channel. The IEF simulation results show that higher ionic strengths (50 – 100 mM) cause significant changes in the transient movement as well as the final focused profiles of both ampholytes and proteins. The time required for a single, well‐defined peak to form increases with ionic strength when Onsager corrections are applied to the carrier ampholytes. For a particular ampholyte concentration, the space‐averaged conductivity does not change during the final focusing stage, but the magnitude of space averaged conductivity is different for different ampholyte concentration. The simulation results also reveal that at steady‐state ionic strength profiles remain flat throughout the channel except at the locations of proteins where a significant change in ampholyte concentration is obtained.

Finite-Volume Methods for Isotachophoretic Separation in Microchannels

Numerical simulation results are obtained for isotachophoresis (ITP) in two-dimensional (2-D) straight microchannels. This 2-D ITP model is formulated based on finite-volume schemes using five ionic components: one leader, one terminator, two samples, and a counter-ion electrolyte. Distinct mobilities and diffusion coefficients are assigned to all ionic components, and an electric field is maintained along the channel to carry out the electrophoretic separation in the microchannel. The computer model is developed to solve the mass and charge conservation equations and to satisfy electroneutrality condition in the system. Three different finite-volume schemes, power-law, hybrid, and upwind, are tested to obtain the best numerical solution of this nonlinear electrophoretic problem. The normalized standard deviation technique is introduced to evaluate the performance of these three schemes. Numerical results show that the power-law scheme performs better; grid Peclet numbers up to 23 are acceptable for this nonlinear isotachophoresis. The effects of the applied electric potential, ionic mobilities and initial distribution of samples on the separation behavior are also presented.

A Compact Vertical Scanner for Atomic Force Microscopes

A compact vertical scanner for an atomic force microscope (AFM) is developed. The vertical scanner is designed to have no interference with the optical microscope for viewing the cantilever. The theoretical stiffness and resonance of the scanner are derived and verified via finite element analysis. An optimal design process that maximizes the resonance frequency is performed. To evaluate the scanner’s performance, experiments are performed to evaluate the travel range, resonance frequency, and feedback noise level. In addition, an AFM image using the proposed vertical scanner is generated.

In vitro anticancer potential of BaCO3 nanoparticles synthesized via green route

Green synthesis of nanoparticles is a growing research area because of their potential applications in nanomedicine. Barium carbonate nanoparticles (BaCO3 NPs) were synthesized using an aqueous extract of Mangifera indica seed as a reducing agent. These particles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Transmission electron microscopy (TEM), selected area electron diffraction (SAED), Energy-dispersive-X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. HR-TEM images are confirmed that green synthesized BaCO3 NPs have spherical, triangular and uneven shapes. EDX analysis confirmed the presence of Ba, C and O. The peaks at 2θ of 19.45, 23.90, 24.29, 27.72, 33.71, 34.08, 34.60, 41.98, 42.95, 44.18, 44.85, and 46.78 corresponding to (110), (111), (021), (002), (200), (112), (130), (221), (041), (202), (132) and (113) showed that BaCO3 NPs average size was ~18.3 nm. SAED pattern confirmed that BaCO3 NPs are crystalline nature. BaCO3 NPs significantly inhibited cervical carcinoma cells, as evidenced by cytotoxicity assay. Immunofluorescence and fluorescence assays showed that BaCO3 NPs increased the expression and activity of caspase-3, an autocatalytic enzyme that promotes apoptosis. According to the results, green synthesis route has great potential for easy, rapid, inexpensive, eco-friendly and efficient development of novel multifunctional nanoparticles for the treatment of cancer.

Dispersion of protein bands in a horseshoe microchannel during IEF

Ampholyte‐based IEF is simulated for a 2‐D horseshoe microchannel. The IEF model takes into account ionic‐strength‐dependent mobility corrections for both proteins and ampholytes. The Debye–Huckel–Henry model is employed to correct the protein mobilities and the Onsager–Debye–Huckel model is used to obtain effective mobilities of ampholytes from their limiting mobility. IEF simulations are conducted in the presence of 25 ampholytes (ΔpK=3.0) within a pH range of 6–9 under an electric field of 300 V/cm and using four proteins (pIs=6.49, 7.1, 7.93 and 8.6) focused in a 1‐cm‐long microchannel. The numerical results show that the concentrations of proteins and ampholytes are different when mobility corrections are considered but that the focusing positions remain the same regardless of mobility corrections. Our results also demonstrate that, unlike linear electrophoresis in which the bands deform significantly as they traverse a bend, during the transient portion of IEF racecourse dispersion is mitigated by focusing and, at focused‐state, those bands that focus in the bend show no radial concentration dependence, i.e. they completely recover from racecourse dispersion, even within a tight turn.

Rapid detection of dysfunctional high-density lipoproteins using isoelectric focusing-based microfluidic device to diagnose senescence-related disease.

Recently, we reported elevated levels of advanced glycated end products (AGEs) in human high‐density lipoproteins (HDL), with fragmentation of apoA‐I in an elderly group, compared with a younger group. More dysfunctional HDL from human plasma was demonstrated in the elderly group, including reconstituted HDL containing glycated apoA‐I (gA‐I‐rHDL) with elevation of AGEs. Based on SDS‐PAGE analysis, HDL3 from the elderly group (E‐HDL3) exhibited increased multimerization with increased smear band intensity compared to HDL3 from the younger group (Y‐HDL3). According to isoelectric focusing gel analysis, gA‐I‐rHDL and E‐HDL3 showed electromobility to the basic region of pH with a broader band range. In a microfluidic channel, E‐HDL3 had faster mobility with a broader range and a higher isoelectric point (pI, approximately 8.1), whereas Y‐HDL3 showed a narrow band range with a lower pI (approximately 6.9). In conclusion, gA‐I‐rHDL and E‐HDL share several electrophoretic properties with multimerization and faster mobility in microfluidic channels, depending on the isoelectric point. These results can be applied to develop a rapid detection system for modified HDL to predict the extent of aging and aging‐related metabolic diseases, such as cardiovascular disease and diabetes.

Efficient algorithm for simulation of isoelectric focusing

IEF simulation is an effective tool to investigate the transport phenomena and separation performance as well as to design IEF microchip. However, multidimensional IEF simulations are computationally intensive as one has to solve a large number of mass conservation equations for ampholytes to simulate a realistic case. In this study, a parallel scheme for a 2D IEF simulation is developed to reduce the computational time. The calculation time for each equation is analyzed to identify which procedure is suitable for parallelization. As expected, simultaneous solution of mass conservation equations of ampholytes is identified as the computational hot spot, and the computational time can be significantly reduced by parallelizing the solution procedure for that. Moreover, to optimize the computing time, electric potential behavior during transient state is investigated. It is found that for a straight channel the transient variation of electric potential along the channel is negligible in a narrow pH range (5∼8) IEF. Thus the charge conservation equation is solved for the first time step only, and the electric potential obtain from that is used for subsequent calculations. IEF simulations are carried out using this algorithm for separation of cardiac troponin I from serum albumin in a pH range of 5–8 using 192 biprotic ampholytes. Significant reduction in simulation time is achieved using the parallel algorithm. We also study the effect of number of ampholytes to form the pH gradient and its effect in the focusing and separation behavior of cardiac troponin I and albumin. Our results show that, at the completion of separation phase, the pH profile is stepwise for lower number of ampholytes, but becomes smooth as the number of ampholytes increases. Numerical results also show that higher protein concentration can be obtained using higher number of ampholytes.

Dynamic effect of surface contact angle on liquid transfer in a low speed printing process

In this study, experiments on liquid transfer were performed to observe the change of the surface contact angle with respect to the process speed. The liquid transfer ratio from the experiments was compared with that from numerical simulation for low speed ranges. While the surface contact angle on the lower plate was almost constant in the experiment regardless of operating speed, the surface contact angle on the upper plate was found to be significantly changed during the process at the low speed ranges. This resulted in a reduction of the transfer ratio. By applying the time-dependent values of contact angle to the numerical simulation model, the transfer ratio showed better agreement with the experimental results. The dynamic effect of surface contact angle should be considered as an additional variable, especially for the analysis of liquid transfer in a low speed printing process.

Effect of Co2+ and Ni2+-doped zinc borate nano crystalline powders by co-precipitation method

A simple co-precipitation method has been used for the synthesis of Co(2+) and Ni(2+)-doped zinc borate nanopowders. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), UV/Vis absorption, Scanning electron microscope (SEM) with EDS and photoluminescence (PL) spectroscopies techniques has been employed for their characterization. Powder X-ray diffraction data reveals that the crystal structure belongs to monoclinic for both as-prepared samples. SEM images showed surface morphology of the prepared samples. Optical absorption spectra showed the characteristic bands of doped ions in octahedral site symmetry. From the optical absorption data crystal field and inter-electronic repulsion parameters are evaluated. The FT-IR spectra showed the characteristic vibrational bands related to ZnO, BO3 and BO4 molecules. Photoluminescence spectra exhibited the emission bands in ultraviolet and blue regions.