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Sang-Hyun Park

Publications and source records attributed to Sang-Hyun Park.

17 recordsLinked to original sources
PubMed2006

Pumpless, selective docking of yeast cells inside a microfluidic channel induced by receding meniscus.

We present a simple cell docking method induced by receding meniscus to capture non-adherent yeast cells onto microwells inside a microfluidic channel. Microwells were fabricated either by capillary moulding of UV curable polyurethane acrylate (PUA) onto glass substrate or direct replica moulding of poly(dimethyl siloxane) (PDMS). A cell suspension of the budding yeast, Saccharomyces cerevisiae, was introduced into the microfluidic channel by surface tension driven capillary flow and a receding meniscus was subsequently generated by evaporation. As the meniscus progressed, one to multiple yeast cells were spontaneously captured onto microwells by lateral capillary force created at the bottom of the meniscus. Using this cell-based platform, we observed the response of yeast cells upon stimulation by a mating pheromone (alpha-factor) by monitoring the expression of green fluorescent protein (GFP) with time. It was observed that alpha-factor triggered the expression of GFP at 60 min after stimulation and the fluorescence intensity was sustained for an additional 60 min without changes.

Cells, Immobilized↗
PubMed2006

Development of the two Korean adult tomographic computational phantoms for organ dosimetry.

Following the previously developed Korean tomographic phantom, KORMAN, two additional whole-body tomographic phantoms of Korean adult males were developed from magnetic resonance (MR) and computed tomography (CT) images, respectively. Two healthy male volunteers, whose body dimensions were fairly representative of the average Korean adult male, were recruited and scanned for phantom development. Contiguous whole body MR images were obtained from one subject exclusive of the arms, while whole-body CT images were acquired from the second individual. A total of 29 organs and tissues and 19 skeletal sites were segmented via image manipulation techniques such as gray-level thresholding, region growing, and manual drawing, in which each of segmented image slice was subsequently reviewed by an experienced radiologist for anatomical accuracy. The resulting phantoms, the MR-based KTMAN-1 (Korean Typical MAN-1) and the CT-based KTMAN-2 (Korean Typical MAN-2), consist of 300 X 150 X 344 voxels with a voxel resolution of 2 X 2 X 5 mm3 for both phantoms. Masses of segmented organs and tissues were calculated as the product of a nominal reference density, the prevoxel volume, and the cumulative number of voxels defining each organs or tissue. These organs masses were then compared with those of both the Asian and the ICRP reference adult male. Organ masses within both KTMAN-1 and KTMAN-2 showed differences within 40% of Asian and ICRP reference values, with the exception of the skin, gall bladder, and pancreas which displayed larger differences. The resulting three-dimensional binary file was ported to the Monte Carlo code MCNPX2.4 to calculate organ doses following external irradiation for illustrative purposes. Colon, lung, liver, and stomach absorbed doses, as well as the effective dose, for idealized photon irradiation geometries (anterior-posterior and right lateral) were determined, and then compared with data from two other tomographic phantoms (Asian and Caucasian), and stylized ORNL phantom. The armless KTMAN-1 can be applied to dosimetry for computed tomography or lateral x-ray examination, while the whole body KTMAN-2 can be used for radiation protection dosimetry.

Adult↗
PubMed2005

Surface ordering of a perfluorinated, self-assembled, dendrimer on a water subphase.

We have investigated the surface ordering of a synthetic, asymmetric, fan-shaped dendrimer containing a carboxyl core and perfluorinated tails which was obtained by the esterification of the intermediary. X-ray diffraction patterns and transmission electron microscopy (TEM) images show the molecules self-assemble into a hexagonal, cylindrical mesophase. Surface pressure-area isotherms and Brewster angle microscopy measurements show the molecule forms a stable monolayer at the air-water interface with a single phase transition. As a condensed monolayer, the perfluorinated tails are well-packed with hexagonal symmetry with (10) spacing of approximately 0.5 nm from molecular-scale atomic force microscopy (AFM) images. Such dense molecular-scale packing has not been observed in other dendritic molecules thus far. Compared to the case of conventional dendritic molecules with alkyl tails, these molecules occupy a much smaller molecular area due to the strong microphase separation between the carboxylic core and perfluorinated tails at the air-water interface. After monolayer collapse, the irregular islands with terrace morphology are observed in contrast with conventional alkyl-terminated self-assembled dendritic molecules where irregular islands do not appear. The interfacial and internal structure of every terrace shows planar columnar morphology from AFM and TEM imaging. From these results, we discuss the stability of perfluorinated, self-assembled dendrimers on water, as well as how to generate planar morphology on a hydrophilic surface.

Journal Article↗
PubMed2004

Bovine oocyte cytoplasm supports nuclear remodeling but not reprogramming of murine fibroblast cells.

Nuclear transfer (NT) is used to elucidate fundamental biological issues such as reversibility of cell differentiation and interactions between the cytoplasm and nucleus. To obtain an insight into interactions between the somatic cell nucleus and oocyte cytoplasm, nuclear remodeling and gene expression were compared in bovine oocytes that had received nuclei from bovine and mouse fibroblast cells. While the embryos that received nuclei from bovine fibroblast cells developed into blastocysts, those that received nuclei from mouse fibroblasts did not develop beyond the 8-cell stage. Similar nuclear remodeling procedures were observed in oocytes reconstructed with mouse and bovine fibroblast cells. Foreign centrosomes during NT were introduced into embryos reconstructed with both fibroblast cell types. A number of housekeeping mouse genes (hsp70, bax, and glt-1) were abnormally expressed in embryos that had received nuclei from mouse fibroblast cells. However, development-related genes, such as Oct-4 and E-cad, were not expressed. The results collectively suggest that the bovine oocyte cytoplasm supports nuclear remodeling, but not reprogramming of mouse fibroblast cells.

Animals↗
PubMed2004

Neuromuscular electrical stimulation enhances fracture healing: results of an animal model.

Neuromuscular electrical stimulation (NMES) could simulate physiological muscle functions known to be associated with the normal bone healing process. The object of the present study was to evaluate the effect of NMES on fracture healing, using an animal model. Thirty rabbits received unilateral, transverse, mid-tibial, 3-mm gapped osteotomies that were stabilized with double-bar external fixators. The femoral vein was ligated to induce venous stasis. From the fourth post-operative day, the study group was treated with 1 h daily of NMES for four weeks, while the control group was treated without NMES. For NMES, two surface electrodes were used: one above the patellar tendon and another around the lateral thigh. Callus area and mineral content at the osteotomy gap were measured, biweekly, using computerized tomographic examinations. Biomechanical properties of healing were evaluated with a torsion test, eight weeks after the index operation. Osteotomies treated with NMES exhibited 31% (p=0.01) higher mineral content and 27% (p=0.009) larger callus area than control osteotomies at eight weeks. The maximum torque, torsional stiffness, angular displacement at maximum torque, and energy required to failure of specimens in the study group were 62% (p=0.006), 29% (p=0.03), 34.6% (p=0.008), and 124% (p<0.0001) higher, respectively, than those in the control group at eight weeks. The results of the present study demonstrated that the use of NMES can enhance callus development and mineralization, with the consequent improvement in biomechanical properties of the healing bone.

Animals↗
PubMed2004

Fluorescence gel retardation assay to detect protein-protein interactions.

A gel mobility retardation assay can be used to detect a protein-protein interaction. The assay is based on the electrophoretic mobility of a protein-protein complex being less than that of either protein alone. Electrophoretic mobility is detected by the fluorescence of a green fluorescent protein variant that is fused to one of the protein partners. The assay is demonstrated by using the interaction of the S-protein and S-peptide fragments of ribonuclease A as a case study.

Animals↗
PubMed2004

Fluorescence polarization assay to quantify protein-protein interactions.

A fluorescence polarization assay can be used to evaluate the strength of a protein-protein interaction. A green fluorescent protein variant is fused to one of the protein partners. The formation of a complex is then deduced from an increase in fluorescence polarization, and the equilibrium dissociation constant of the complex is determined in a homogeneous aqueous environment. The assay is demonstrated by using the interaction of the S-protein and S-peptide fragments of ribonuclease A as a case study.

Animals↗
PubMed2003

Optimization of specificity in a cellular protein interaction network by negative selection.

Most proteins that participate in cellular signalling networks contain modular protein-interaction domains. Multiple versions of such domains are present within a given organism: the yeast proteome, for example, contains 27 different Src homology 3 (SH3) domains. This raises the potential problem of cross-reaction. It is generally thought that isolated domain-ligand pairs lack sufficient information to encode biologically unique interactions, and that specificity is instead encoded by the context in which the interaction pairs are presented. Here we show that an isolated peptide ligand from the yeast protein Pbs2 recognizes its biological partner, the SH3 domain from Sho1, with near-absolute specificity--no other SH3 domain present in the yeast genome cross-reacts with the Pbs2 peptide, in vivo or in vitro. Such high specificity, however, is not observed in a set of non-yeast SH3 domains, and Pbs2 motif variants that cross-react with other SH3 domains confer a fitness defect, indicating that the Pbs2 motif might have been optimized to minimize interaction with competing domains specifically found in yeast. System-wide negative selection is a subtle but powerful evolutionary mechanism to optimize specificity within an interaction network composed of overlapping recognition elements.

Amino Acid Motifs↗
PubMed2003

Rewiring MAP kinase pathways using alternative scaffold assembly mechanisms.

How scaffold proteins control information flow in signaling pathways is poorly understood: Do they simply tether components, or do they precisely orient and activate them? We found that the yeast mitogen-activated protein (MAP) kinase scaffold Ste5 is tolerant to major stereochemical perturbations; heterologous protein interactions could functionally replace native kinase recruitment interactions, indicating that simple tethering is largely sufficient for scaffold-mediated signaling. Moreover, by engineering a scaffold that tethers a unique kinase set, we could create a synthetic MAP kinase pathway with non-natural input-output properties. These findings demonstrate that scaffolds are highly flexible organizing factors that can facilitate pathway evolution and engineering.

Adaptor Proteins, Signal Transducing↗
PubMed2003

166Ho-coated balloon for vascular brachytherapy.

A simple procedure was developed for coating the surface of a conventional percutaneous transluminal coronary angioplasty balloon angioplasty catheter with 166Ho. The absorbed dose delivered by the surface-coated catheter is twice that of a similar catheter filled with a solution containing the same activity of 166Ho. Leakage tests show that <0.6% of the coated activity is removable from the surface of the catheter. The coated catheter removes the risk of release of the 166Ho into the body as a result of rupture of the balloon, and also reduces the radiation exposure to staff.

Angioplasty, Balloon, Coronary↗
PubMed2003

Interaction between active motion and exogenous transforming growth factor Beta during tibial fracture repair.

OBJECTIVE: Evaluate the effects of axial motion and transforming growth factor beta (TGF-beta) on callus formation and fracture healing.DESIGN Prospective experimental design with a 39-day postfracture recovery. SETTING: Unrestricted cage activity with weight bearing as tolerated. ANIMALS: Twenty-two skeletally mature, female New Zealand White rabbits. INTERVENTIONS: Displaced, closed tibial fractures were reduced and stabilized in external fixators on the fourth day following fracture. Half of the fixators were locked for the duration of healing. The other fixators were locked for one week, then unlocked for the remaining four weeks. Half of the fractures in each fixator group received two injections of recombinant human TGF-beta1 (rhTGF-beta1). One injection was administered at the time of reduction, and the second was given 48 hours later. MAIN OUTCOME MEASUREMENTS: Interfragmentary axial motion was measured during floor activity. Biomechanical properties were measured during a torsion test to failure. Callus area and the distribution of tissues within the callus were determined by computer-aided histomorphometry. RESULTS: The administration of TGF-beta1 did not alter callus size, mechanical properties, or the distribution of tissues in the callus of fractures that were stabilized in locked external fixators. Recoverable axial motion fixation increased callus size, quantity of mineralized bone bridging the fracture, and maximum torque relative to locked fixation. The injection of TGF-beta1 negated the beneficial effects of axial motion by promoting the formation of a peripheral callus bridged by fibrous tissue rather than mineralized trabecular bone. CONCLUSIONS: Injection of rhTGF-beta1 during the first postfracture week does not provide a biologic boost that improves fracture healing. Injection of TGF-beta1 may be detrimental to healing under conditions when fracture motion is present. The results suggest that there is a tendency for exposure to TGF-beta1 to inhibit the normal development of peripheral callus in response to axial interfragmentary motion.

Animals↗
PubMed2003

Effect of intermittent pneumatic soft-tissue compression on fracture-healing in an animal model.

BACKGROUND: The fracture-healing process is closely related to blood supply. Intermittent pneumatic compression of the surrounding soft tissue may alter blood flow and, therefore, modify the healing process. The object of the present study was to evaluate the effect of intermittent pneumatic compression on fracture-healing in an animal model. METHODS: Unilateral, transverse, mid-tibial osteotomies with a 3-mm gap were performed in thirty rabbits. The osteotomy site was stabilized with a double-bar external fixator. The femoral vein was ligated to induce venous stasis. Beginning on the fourth postoperative day, fifteen rabbits were treated with intermittent pneumatic compression with use of four rubber balloons, two around the distal part of the calf and two around the midpart of the calf, for one hour daily for four weeks (the study group) and fifteen rabbits were not treated with intermittent pneumatic compression (the control group). Peripheral computerized tomographic examination was performed biweekly to measure callus area and mineral content at the fracture gap. At eight weeks, the rabbits were killed, and the biomechanical properties of the healing fractures were evaluated with a torsional test. RESULTS: An increase in callus area and mineral content at the osteotomy gap was observed in the study group, compared with the values in the control group, starting four weeks after the index procedure. At six weeks, the rabbits treated with intermittent pneumatic compression exhibited, on the average, a 32.2% larger callus area (p = 0.035) and a 49.7% higher mineral content (p = 0.01) at the osteotomy site compared with the values in the control group. The torsional stiffness, maximum torque, angular displacement at maximum torque, and energy required to failure of specimens in the study group were an average of 27.0% (p = 0.05), 61.5% (p = 0.0001), 35.4% (p = 0.0003), and 110.8% (p = 0.0001) higher, respectively, than those in the control group at eight weeks. CONCLUSIONS: Intermittent pneumatic compression enhanced callus mineralization and development and it improved the biomechanical properties of a healing osteotomy site in the rabbit tibia.

Animals↗
PubMed2002

Effect of repeated irrigation and debridement on fracture healing in an animal model.

The initial management of open fractures often requires repeated irrigation and debridement of the open wound and stabilization of the fracture. However, washing out the fracture hematoma could delay the early healing process of stable fractures. Because delayed union and non-union are serious complications, the effect of repeated irrigation and debridement on the fracture healing process was investigated. Twenty-four rabbits received unilateral, transverse. mid-tibial open osteotomies with a 3 mm gap. The osteotomy site was thoroughly irrigated and stabilized with double-bar external fixators. The osteotomy sites in the study groups underwent repeat irrigation and debridement on either the third day (Group II), the fourth day (Group III), or consecutively on the first and second days (Group IV) after the index procedure. The bone healing was assessed with weekly radiographs and peripheral quantitative computerized tomographs. In Group I (control), all osteotomies healed radiographically before the tenth week. In Group II, five out of six osteotomies healed radiographically before the tenth week. In Group III, only two of five osteotomies healed before the tenth week. In Group IV, none of the osteotomies had healed by week fifteen. All of the non-healed osteotomies exhibited atrophic non-unions at fifteen weeks. Compared to the control group at the tenth week, the average bone mineral content at the osteotomy site and the area of high mineral density callus (> or = 890 mg/cm3) were significantly lower in Groups III (63%, p = 0.002 and 95%, p = 0.05, respectively) and IV (99%, p < 0.001 and 100%, p = 0.05, respectively). The results of this study suggest that repeated irrigation and debridement, associated with persistent rigid immobilization, may contribute to the development of delayed unions or atrophic non-unions.

Animals↗
PubMed2002

Genetic screen to dissect protein-protein interactions: ribonuclease inhibitor-ribonuclease A as a model system.

Protein-protein interactions are critical for the function of biological systems. Here, we describe a means to dissect a protein-protein interaction. Our method is based on the in vivo interaction between a target protein and the peptide epitopes derived from its partner. This interaction is detected by using hybrid proteins in which the target protein and peptide epitopes are fused to the DNA-binding domain of the lambda repressor protein. An interaction prevents the transcription of a reporter gene. The efficacy of this approach is demonstrated with the ribonuclease inhibitor protein and ribonuclease A, which form a complex with an equilibrium dissociation constant in the femtomolar range. Our method can enable the identification of residues important in a designated protein-protein interaction and the development of antagonists for that interaction.

Enzyme Inhibitors↗
PubMed2001

A Rationally Designed NH(4)(+) Receptor Based on Cation-pi Interaction and Hydrogen Bonding We gratefully acknowledge the Korean Ministry of Science and Technology (Creative Research Initiative Program) for support of this work, and the Korean Ministry of Education (Brain Korea 21 program) for graduate studentships to J.H. and W.S.J. M.K. is grateful to POSTECH for an Undergraduate Research Fellowship. We also thank Professor P. K. Bharadwaj for helpful discussions.

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Journal Article↗
PubMedDate not supplied

Image analysis of bioparticles accumulation and diamagnetic alignment in high-gradient magnetic field.

Magnetic properties of biological particles are measured in high-gradient magnetic separation (HGMS) analysis, revealing the concentrating process of nucleoprotein particles, ferritin, red blood cells, and eggs. A magnetic force acting on micrometer and submicrometer biological particles having diamagnetic or paramagnetic susceptibility with respect to the solution causes their movement and accumulation in gradient magnetic fields dependent on the values of the magnetic moments. The methods developed enable us to obtain the magnetic moments values of single particles and their assembly directly from magnetic separation and image analyses without assuming the detection of sizes. Our precision methods for the measurement of the capture traveling (magnetic diffusion) time and the accumulation (magnetic sedimentation) radius in HGMS show that it is really possible to determine the weak dia- or paramagnetic shifts of magnetic susceptibility up to 0.7x10(-10) (SI units). HGMS analysis of the concentrating process of nucleoprotein granules (microcells, DNA granules, or nucleosome core particles) with polarization microscopy reveals phase transitions for DNA in granules, and separation accumulation of particles enables the determination of the diamagnetic susceptibility and anisotropy properties. Magnetic concentration effects always occur in living systems because micrometer-located gradient magnetic fields inside an organism are strong enough to cause drifts of cellular complexes and organelles of micrometer and submicrometer sizes. We report the appearance of superparamagnetic contamination inside developing shrimp eggs. In the developing shrimps eggs, ferritin aggregates are observed under weak gradient magnetic fields and diaparaferromagnetic changes are detected. A significant interruption of egg development is revealed in such fields.

Animals↗