Publications by authors named "Hong Woo Park"

11 Publications

  • Page 1 of 1

Study of Abnormal Group Velocities in Flexural Metamaterials.

Sci Rep 2019 Sep 27;9(1):13973. Epub 2019 Sep 27.

School of Mechanical, Aerospace and Nuclear Engineering, Ulsan National Institute of Science and Technology, UNIST-gil 50, Eonyang-eup, Ulju-gun, Ulsan, 44919, Korea.

Generally, it has been known that the optical branch of a simple one-dimensional periodic structure has a negative group velocity at the first Brillouin zone due to the band-folding effect. However, the optical branch of the flexural wave in one-dimensional periodic structure doesn't always have negative group velocity. The problem is that the condition whether the group velocity of the flexural optical branch is negative, positive or positive-negative has not been studied yet. In consequence, who try to achieve negative group velocity has suffered from trial-error process without an analytic guideline. In this paper, the analytic investigation for this abnormal behavior is carried out. In particular, we discovered that the group velocity of the optical branch in flexural metamaterials is determined by a simple condition expressed in terms of a stiffness ratio and inertia ratio of the metamaterial. To derive the analytic condition, an extended mass-spring system is used to calculate the wave dispersion relationship in flexural metamaterials. For the validation, various numerical simulations are carried out, including a dispersion curve calculation and three-dimensional wave simulation. The results studied in this paper are expected to provide new guidelines in designing flexural metamaterials to have desired wave dispersion curves.
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http://dx.doi.org/10.1038/s41598-019-50146-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6765006PMC
September 2019

Tetrahydrofolate increases suspension growth of dihydrofolate reductase-deficient chinese hamster ovary DG44 cells in chemically defined media.

Biotechnol Prog 2016 11 16;32(6):1539-1546. Epub 2016 Sep 16.

Dept. of Chemical Engineering, Hanyang University, Seoul, 133-791, South Korea.

Adaptation of dihydrofolate reductase (DHFR)-deficient Chinese hamster ovary (CHO) DG44 cells to chemically defined suspension culture conditions is a time-consuming and labor-intensive process because nonadapted DHFR-deficient CHO DG44 cells normally show poor growth in chemically defined medium (CDM). We examined the effects of folate derivatives, ribonucleotides, and nucleobases on the growth of suspension-adapted DHFR-deficient CHO DG44 cells in CDM. Among the tested additives, tetrahydrofolate (THF) was identified as an effective component for increasing cell growth. THF supplementation in the range of 0.2-359 μM enhanced cell growth in in-house CDM. Addition of 3.6 μM THF to in-house CDM resulted in a more than 2.5-fold increase in maximum viable cell density. Moreover, supplementation of six different commercial CDMs with 3.6 μM THF yielded up to 2.9-fold enhancement of maximum viable cell density. An anchorage- and serum-dependent DHFR-deficient CHO DG44 cell line was adapted within two consecutive passages to suspension growth in in-house CDM supplemented with 3.6 μM THF. These data indicate that supplementation of chemically defined cell culture media with greater than 0.2 μM THF can help achieve a high density of suspension-adapted DHFR-deficient CHO DG44 cells and may facilitate rapid adaptation of nonadapted DHFR-deficient CHO DG44 cells to suspension culture. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1539-1546, 2016.
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http://dx.doi.org/10.1002/btpr.2351DOI Listing
November 2016

Photosynthesis rates, growth, and ginsenoside contents of 2-yr-old Panax ginseng grown at different light transmission rates in a greenhouse.

J Ginseng Res 2015 Oct 28;39(4):345-53. Epub 2015 Mar 28.

Department of Horticultural Biotechnology, Kyung Hee University, Yongin, Korea.

Background: Ginseng is a semishade perennial plant cultivated in sloping, sun-shaded areas in Korea. Recently, owing to air-environmental stress and various fungal diseases, greenhouse cultivation has been suggested as an alternative. However, the optimal light transmission rate (LTR) in the greenhouse has not been established.

Methods: The effect of LTR on photosynthesis rate, growth, and ginsenoside content of ginseng was examined by growing ginseng at the greenhouse under 6%, 9%, 13%, and 17% of LTR.

Results: The light-saturated net photosynthesis rate (A sat) and stomatal conductance (g s) of ginseng increased until the LTR reached 17% in the early stage of growth, whereas they dropped sharply owing to excessive leaf chlorosis at 17% LTR during the hottest summer period in August. Overall, 6-17% of LTR had no effect on the aerial part of plant length or diameter, whereas 17% and 13% of LRT induced the largest leaf area and the highest root weight, respectively. The total ginsenoside content of the ginseng leaves increased as the LTR increased, and the overall content of protopanaxatriol line ginsenosides was higher than that of protopanaxadiol line ginsenosides. The ginsenoside content of the ginseng roots also increased as the LTR increased, and the total ginsenoside content of ginseng grown at 17% LTR increased by 49.7% and 68.3% more than the ginseng grown at 6% LTR in August and final harvest, respectively.

Conclusion: These results indicate that 13-17% of LTR should be recommended for greenhouse cultivation of ginseng.
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http://dx.doi.org/10.1016/j.jgr.2015.03.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4593790PMC
October 2015

High zinc ion supplementation of more than 30 μM can increase monoclonal antibody production in recombinant Chinese hamster ovary DG44 cell culture.

Appl Microbiol Biotechnol 2016 Mar 29;100(5):2163-70. Epub 2015 Oct 29.

Department of Chemical Engineering, Hanyang University, Seoul, 133-791, South Korea.

Effects of high ZnSO4·7H2O supplementation on cell growth and monoclonal antibody (mAb) production in chemically defined suspension cultures of recombinant Chinese hamster ovary (rCHO) DG44 cells were examined. The supplementation of ZnSO4·7H2O up to 120 μM gradually increased specific mAb production rate of rCHO DG44 cells in the early growth phase (0-4 days of culture). The ZnSO4·7H2O concentration for enhancing mAb production without any cytotoxic effects on cell growth was 30-60 μM. In addition of 60 μM ZnSO4·7H2O to in-house protein-free medium and in-house chemically defined medium, mAb production was increased 2.0-fold and 6.5-fold, respectively. Moreover, addition of ZnSO4·7H2O to three kinds of commercial chemically defined media yielded a greater than 1.2-fold enhancement of mAb production. These data indicate that simple supplementation of a relatively high zinc ion concentration to cell culture media without significant changes of rCHO DG44 cell culture process can be useful for achieving high production of mAb.
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http://dx.doi.org/10.1007/s00253-015-7096-xDOI Listing
March 2016

Arginine as an eluent overcomes the hindrance of monoclonal antibody quantification by dextran sulfate in protein A affinity chromatography.

Biotechnol Prog 2015 Nov-Dec;31(6):1536-41. Epub 2015 Sep 12.

Dept. of Chemical Engineering, Hanyang University, Seoul, 133-791, Korea.

Analytical chromatography using protein A affinity columns was employed for the fast and simple quantitative analysis of monoclonal antibodies (mAb) from suspension cultures of recombinant Chinese hamster ovary (rCHO) cells. Reliable results could not be obtained from analysis of rCHO cell culture supernatants containing dextran sulfate using elution buffers such as phosphate, glycine, or MgCl2 . These problems increased as the number of analysis and the concentration of dextran sulfate in samples increased. Arginine was identified as an alternative eluent to overcome the hindrance by dextran sulfate. When the samples contain dextran sulfate up to 100 mg/L, the elution buffer containing 0.6-1.0 M arginine at pH 3.0-3.8 is useful for the effective analysis. Reproducible results in the mAb quantification could be obtained by this developed arginine elution buffer from rCHO cell culture supernatants containing dextran sulfate.
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http://dx.doi.org/10.1002/btpr.2164DOI Listing
October 2016

The Mechanism Underlying the Antibacterial Activity of Shikonin against Methicillin-Resistant Staphylococcus aureus.

Evid Based Complement Alternat Med 2015 21;2015:520578. Epub 2015 Jul 21.

Department of Herbal Crop Research, National Institute of Horticultural and Herbal Science, Rural Development Administration (RDA), Eumsung, Chungbuk 369-873, Republic of Korea.

Shikonin (SKN), a highly liposoluble naphthoquinone pigment isolated from the roots of Lithospermum erythrorhizon, is known to exert antibacterial, wound-healing, anti-inflammatory, antithrombotic, and antitumor effects. The aim of this study was to examine SKN antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). The SKN was analyzed in combination with membrane-permeabilizing agents Tris and Triton X-100, ATPase inhibitors sodium azide and N,N'-dicyclohexylcarbodiimide, and S. aureus-derived peptidoglycan; the effects on MRSA viability were evaluated by the broth microdilution method, time-kill test, and transmission electron microscopy. Addition of membrane-permeabilizing agents or ATPase inhibitors together with a low dose of SKN potentiated SKN anti-MRSA activity, as evidenced by the reduction of MRSA cell density by 75% compared to that observed when SKN was used alone; in contrast, addition of peptidoglycan blocked the antibacterial activity of SKN. The results indicate that the anti-MRSA effect of SKN is associated with its affinity to peptidoglycan, the permeability of the cytoplasmic membrane, and the activity of ATP-binding cassette (ABC) transporters. This study revealed the potential of SKN as an effective natural antibiotic and of its possible use to substantially reduce the use of existing antibiotic may also be important for understanding the mechanism underlying the antibacterial activity of natural compounds.
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http://dx.doi.org/10.1155/2015/520578DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4523682PMC
August 2015

Control of specific growth rate to enhance the production of a novel disintegrin, saxatilin, in recombinant Pichia pastoris.

J Biosci Bioeng 2010 Sep 27;110(3):314-9. Epub 2010 Apr 27.

Department of Integrated Biotechnology, Sogang University, Seoul 121-742, Republic of Korea.

The methylotrophic yeast Pichia pastoris is one of the best hosts for the production of foreign proteins because of the presence of a strong alcohol oxidase 1 (AOX1) promoter that can be induced by methanol. Feeding the yeast, methanol induces protein production and provides an energy source for the host cells. However, excessive levels of methanol inhibit the growth of host cells, and insufficient methanol levels lead to poor growth and protein production. We have used various methanol feeding strategies to enhance the production of saxatilin. Saxatilin is a novel snake venom-derived disintegrin that inhibits tumor angiogenesis and metastasis and has been shown to suppress ovarian cancer cell invasion. A two-step increase feeding strategy to control the specific growth rate led to the best results in terms of specific protein production rates and final saxatilin amounts within the limited fermentation time.
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http://dx.doi.org/10.1016/j.jbiosc.2010.03.013DOI Listing
September 2010

Adaptation of Chinese hamster ovary cells to low culture temperature: cell growth and recombinant protein production.

J Biotechnol 2006 Apr 25;122(4):463-72. Epub 2005 Oct 25.

Department of Biological Sciences, Korea Advanced Institute of Science and Technology, 371-1 Kusong-Dong, Yusong-Gu, Daejon 305-701, Republic of Korea.

Recombinant Chinese hamster ovary (rCHO) cells producing erythropoietin (EPO) and rCHO cells producing follicle-stimulating hormone (FSH) showed a significant increase in specific productivity (q) when grown at 32 degrees C compared to 37 degrees C. However, low culture temperature suppressed cell growth, and therefore, did not increase volumetric productivity as much as q. In an attempt to increase the volumetric productivity through improvement of hypothermic growth, EPO producing rCHO (CHO-EPO) cells and FSH producing rCHO (CHO-FSH) cells were adapted at 32 degrees C in a repeated batch mode using spinner flasks. Cell growth of both CHO-EPO and CHO-FSH gradually improved during adaptation at 32 degrees C. Specific growth rates of CHO-EPO and CHO-FSH cells at 32 degrees C, through adaptation, were increased by 73% and 20%, respectively. During adaptation at 32 degrees C, mRNA levels of cold-inducible RNA-binding protein (CIRP) of both rCHO cell lines did not change significantly, suggesting that CIRP expression may not be the only cause for growth suppression at low culture temperature. Unlike cell growth, the recombinant protein production of both rCHO cell lines was not increased during adaptation due to decreased specific productivities. The specific EPO productivity and specific FSH productivity were decreased by 49% and 22%, respectively. Southern blot analyses showed that the decreased specific productivities were not due to the loss of foreign gene copies. Taken together, improvement of hypothermic cell growth by adaptation does not appear to be applicable for enhanced recombinant protein production, since specific productivity decreases during adaptation to the low culture temperature.
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http://dx.doi.org/10.1016/j.jbiotec.2005.09.010DOI Listing
April 2006

Initial transcriptome and proteome analyses of low culture temperature-induced expression in CHO cells producing erythropoietin.

Biotechnol Bioeng 2006 Feb;93(2):361-71

Department of Biological Sciences, Korea Advanced Institute of Science and Technology, 373-1 Kusong-Dong, Yusong-Gu, Daejon 305-701, Korea.

Low culture temperature is known to enhance the specific productivity of Chinese hamster ovary (CHO) cells expressing erythropoietin (EPO) (LGE10-9-27). Genomic and proteomic approaches were taken to better understand the intracellular responses of these CHO cells resulting from use of low culture temperature (33 degrees C). For transcriptome analysis, commercially available rat and mouse cDNA microarrays were used. The data obtained from the rat and mouse cDNA chips were only somewhat informative in understanding the gene expression profile of CHO cells because of their different sequence homologies with CHO transcriptomes. Overall, transcriptome analysis revealed that low culture temperature could lead to changes in gene expression in various cellular processes such as metabolism, transport, and signaling pathways. Proteome analysis was carried out using 2-D PAGE. Based on spot intensity, 60 high intensity protein spots, from a total of more than 800, were chosen for MS analysis. Forty of the 60 protein spots, which represent 26 different kinds of proteins, were identified by MALDI-TOF-MS and validated by MS/MS. Compared to the reference temperature (37 degrees C), the expression levels of seven proteins (PDI, vimentin, NDK B, ERp57, RIKEN cDNA, phosphoglycerate kinase, and heat shock cognate 71 kDa protein) were increased over twofold at 33 degrees C and those of two proteins (HSP90-beta and EF2) were decreased over twofold at 33 degrees C. Taken together, the results demonstrate the potential of combined analysis of transcriptome and proteome analyses as a tool for the systematic comprehension of cellular mechanisms in CHO cells.
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http://dx.doi.org/10.1002/bit.20717DOI Listing
February 2006

Tissue engineering of cartilage with chondrocytes cultured in a chemically-defined, serum-free medium.

Biotechnol Lett 2004 May;26(9):709-12

Department of Chemical Engineering, Hanyang University, Seoul 133-791, Korea.

Cell culture with serum-containing medium has potential problems associated with contamination of infectious agents. This study demonstrates for the first time the feasibility of regenerating cartilage tissues in vivo by implantation of chondrocytes cultured in vitro in a chemically-defined, serum-free medium. Chondrocytes cultured in the serum-free medium grew similarly to those in a serum-containing medium. Implantation of chondrocytes cultured in the serum-free medium and seeded on to polymer scaffolds resulted in the regeneration of cartilage tissues with histological aspects similar to those of cartilage tissues regenerated from chondrocytes cultured in serum-containing medium.
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http://dx.doi.org/10.1023/b:bile.0000024093.94151.d8DOI Listing
May 2004

Suspension culture of hematopoietic stem cells in stirred bioreactors.

Biotechnol Lett 2003 Jan;25(2):179-82

Department of Chemical Engineering, Hanyang University, Seoul, Korea.

Hematopoietic stem cells have applications in bone marrow transplantations for the treatment of hematopoietic disorders. When murine hematopoietic stem cells were cultured in 50 ml stirred bioreactors for 14 d, stem-cell-antigen-1 positive cells (hematopoietic primitive progenitor cells) and long-term culture-initiating cells (hematopoietic stem cells) grew by 5-fold and 4-fold, respectively. These results show the possibility of growing hematopoietic stem cells using a stirred bioreactor.
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http://dx.doi.org/10.1023/a:1021994026859DOI Listing
January 2003