Biomedical subjects

Byungkyu Kim

Publications and source records attributed to Byungkyu Kim.

8 recordsLinked to original sources

PubMed2006

Guided three-dimensional growth of functional cardiomyocytes on polyethylene glycol nanostructures.

We introduce well-defined nanopillar arrays of a poly(ethylene glycol) (PEG) hydrogel as a cell culture platform to guide a 3D construct of primary rat cardiomyocytes in vitro for potential tissue engineering applications. Ultraviolet (UV)-assisted capillary lithography was used to fabricate highly uniform approximately 150 nm PEG pillars with approximately 400 nm height. It was found that cell adhesion was significantly enhanced on PEG nanopillars (132 +/- 29 cells/mm2) compared to that on the bare PEG control (39 +/- 17 cells/mm2) (p < 0.05) but substantially reduced compared to that on the glass control (502 +/- 45 cells/mm2) (p < 0.01). Furthermore, in colonizing cardiomyocytes, the nanopillars stimulated self-assembled aggregates among the contacting cells with 3D growth, which is a unique feature for nanopatterned PEG hydrogels as a cell culture substrate. The 3D-grown cardiomyocytes retained their conductive and contractile properties, as evidenced by the observation of beating cardiomyocytes with robust action potential generation.

Animals↗

PubMed2006

Mechanical analysis of chorion softening in prehatching stages of zebrafish embryos.

During early development, the chorion envelope of the zebrafish embryo undergoes a thinning process called "chorion softening," which has so far only been characterized chemically. In this study, a micromechanical force sensing system was used to characterize and quantitate mechanical modifications of the zebrafish embryo chorion during early development. Quantitative relationships between applied forces and chorion structural deformations were established at various embryonic stages. The measured penetration force into the chorion at the blastula stage was 1.3-fold greater than those at the prehatching stage. Furthermore, chorion elastic modulus values were determined by using a biomembrane elastic model. The elastic modulus of the chorion at the blastula stage was 1.66-fold greater than that at the prehatching stage, thus indicating that the chorion envelope become mechanically "softened" at the prehatching stage. The experimental results quantitatively describe "chorion softening," which is most likely due to proteolytic activities at the prehatching stage. Gradual chorion softening during embryonic development was also artificially achieved by treating blastula chorion with pronase, a proteolytic enzyme. The forces required to penetrate the pronase-treated chorion were similar to those at the prehatching stage. This similarity suggests that "chorion softening" may be induced by the release of protease from the embryos, and the chemical nature of the process involves proteolytic fragmentation of the ZP2 protein.

Animals↗

PubMed2005

Design and fabrication of a largely deformable sensorized polymer actuator.

Polypyrrole (PPy), with its biomimetic properties such as high power density, large strain, and biocompatibility, is an excellent candidate for a biomimetic microactuator in microrobotics and bioengineering. A polyvinylidene fluorid (PVDF) sensor is also biocompatible, flexible, and chemically stable. Therefore, a PPy actuator is integrated with a PVDF sensor to realize a sensorized polymer actuator. A novel sensorized polymer actuator can accurately measure its bending motion precisely with real time. Experimental results demonstrate the feasibility of the sensorized polymer actuator. The polymer actuator can be actuated while it senses signals induced from the bending motion. In addition, the position of the sensorized polymer actuator can be controlled and adjusted precisely with feedback signals from its embedded sensor at the time of operation. If this system becomes more robust and reliable, its applications are promising and can be realized in cell handling, microrobotics, and microsurgery with the integration of standard microfabrication techniques.

Biocompatible Materials↗

PubMed2005

Real-time measurement of the contractile forces of self-organized cardiomyocytes on hybrid biopolymer microcantilevers.

We present a microfabricated hybrid biopolymer microcantilever, in which the contractile force of self-organized cardiomyocytes can be measured and studied, as a prototype for the development of cell-driven actuators. The microcantilever is made of a flexible, transparent, biocompatible poly(dimethylsiloxane) substrate, using a simple microfabrication technique. Seeding and culturing cardiomyocytes on the specific cantilever allows us to perform highly sensitive, quantitative, and noninvasive measurement of the contractile force of the self-organized cells in real time. The motions of the microcantilever showed good agreement with an analytical solution based on Stoney's equation and finite element modeling (FEM) of the hybrid system. Immunostaining of the cells on the hybrid system showed continuous high-order coalignment of actin filaments and parallel sarcomeric organization in the direction of the longitudinal axis of the microcantilever without structural constraints, such as microgrooves or lines, and proved our FEM and the synchronous contraction of cardiomyocytes. The presented device should facilitate measurement of the contractile force of self-organized cardiomyocytes on a specific area, which may help the understanding of heart failure and the design of optimal hybrid biopolymer actuators, as well as assist development of a microscale cell-driven motor system.

Biosensing Techniques↗

PubMed2005

An efficient cell separation system using 3D-asymmetric microelectrodes.

An efficient 3D-asymmetric microelectrode system for high-throughput was designed and fabricated to enhance sorting sensitivities to the dielectric properties-size, morphology, conductivity, and permittivity-of living cells. The principle of the present system is based on the use of the relative strengths of negative dielectrophoretic and drag forces, as in a conventional 3D-microelectrode system. Whereas the typical 3D-microelectrode system has a constant electric field magnitude due to the constant width of the microelectrodes and a fixed gap between face-to-face microelectrodes, the present 3D-asymmetric microelectrode system has electric fields of continuously varying magnitudes along the transverse direction of a channel owing to the changing widths of the electrodes in the half-circular shaped cross section of the microchannel. Thus, varying dielectric forces are generated, leading to increased sorting sensitivity through differentially induced forces to definitely distinct cell types. Numerical analysis verified the improved sensitivity of the present system for sorting living cells. The feasibility of using the newly fabricated system under experimental conditions was tested by demonstrating that a mixed population of mouse P19 embryonic carcinoma (EC) and red blood cells (RBCs) was effectively sorted to different wells depending on their respective relative physical properties.

Animals↗

PubMed2005

Investigating chorion softening of zebrafish embryos with a microrobotic force sensing system.

The zebrafish is a model organism for addressing questions of vertebrate embryo development. In this paper, the softening phenomenon of the chorion envelope of zebrafish embryos at different developmental stages was mechanically quantitated by using a microrobotic force sensing system. The microrobotic system integrates a piezoelectric cellular force sensor to measure the required forces for penetrating the chorion envelope. Magnitude of penetration forces was found to decrease as an embryo develops. The results mechanically quantitate "chorion softening" in zebrafish embryos due to protease activities subtly modifying the chorion structure, providing an understanding of zebrafish embryo development.

Animals↗

PubMed2004

Design and fabrication of an integrated cell processor for single embryo cell manipulation.

This paper presents an integrated cell processor for the automatic handling of individual embryo cells. The integrated processor can perform various functions such as cell transport, isolation, orientation, and immobilization. These functions are indispensable and frequently used for the manipulation of single cells, but can only be carried out by a skillful operator. The purpose of this study was the integration and automation of these functions for effective cell manipulation, using a MEMS approach. The isolation of a cell was performed using polypyrrole (PPy) valves in a microchannel into which cells were transported. The orientation of cells was controlled by electrorotation (ER), and the target cell was immobilized by suction from a microhole. All of these functions were seamlessly realized on a single chip. Excellent experimental results with mouse (B6CBA) embryo cells showed that this device could substitute for routine and cumbersome manual work. It is expected that the integrated chip will contribute significantly to faster and more reliable manipulation of cells.

Animals↗

PubMed2003

Analysis of plausible downstream target genes of Hoxc8 in F9 teratocarcinoma cells. Putative downstream target genes of Hoxc8.

Although Hox genes are known to mediate developmental decisions involved in pattern formation during embryogenesis, it is still not well understood what Hox regulates. In order to analyze Hoxc8 downstream target genes, a stable cell line overexpressing Hoxc8 was established using F9 murine teratocarcinoma cells, proteom samples were analyzed by 2-DE, and compared with controls. The protein spots having differences more than 4 fold in intensity were selected, analyzed by MALDI-TOF, and grouped in terms of putative function; cytoskeleton and motility (vimentin, gamma-actin, tropomyosin, and tubulin beta-5 chain); folding, modification and degradation of protein (GRP78, proteasome subunit alpha type 5, 26S proteasome regulatory subunit p27 protein, and PDIR); metabolism (ATP synthase beta subunit, Pgam1, and CAII); transcription/translation factors and general nucleic acid binding proteins (RbAp46, PCNA, eEF-1-beta, and nucleophosmin). Although it may not be significant, 50% of the genes were located on chromosomes 2 and 3, suggesting the possibility of a non-random distribution of Hox downstream genes. Almost 50% of the genes analyzed showed some relation with Hox protein directly or indirectly; i.e., tubulin beta 5, EF-1 beta and PCNA have been reported to contain putative Hox binding regulatory sites and genes like vimentin, pgam1 and nucleophosmin to be regulated by RA, a potent modulator of Hox expression. These results altogether imply that proteom analysis could be a possible tool for the analysis of the potent Hox realizator genes, which provides a new insight into the function of Hox on pattern formation during embryogenesis.

Animals↗