Papers by Yoon-kyoung Cho
Cells, Jun 9, 2020
The shape of epithelial tissue supports physiological functions of organs such as intestinal vill... more The shape of epithelial tissue supports physiological functions of organs such as intestinal villi and corneal epithelium. Despite the mounting evidence showing the importance of geometry in tissue microenvironments, the current understanding on how it affects biophysical behaviors of cells is still elusive. Here, we cultured cells on various protruded convex structure such as triangle, square, and circle shape fabricated using two-photon laser lithography and quantitatively analyzed individual cells. Morphological data indicates that epithelial cells can sense the sharpness of the corner by showing the characteristic cell alignments, which was caused by actin contractility. Cell area was mainly influenced by surface convexity, and Rho-activation increased cell area on circle shape. Moreover, we found that intermediate filaments, vimentin, and cytokeratin 8/18, play important roles in growth and adaptation of epithelial cells by enhancing expression level on convex structure depending on the shape. In addition, microtubule building blocks, α-tubulin, was also responded on geometric structure, which indicates that intermediate filaments and microtubule can cooperatively secure mechanical stability of epithelial cells on convex surface. Altogether, the current study will expand our understanding of mechanical adaptations of cells on out-of-plane geometry.
Raw data for Wang et al., "Boosted molecular mobility during common chemical reactions," Science (2020) 369, 537-541
This repository contains NMR raw data (main text figures, SI figures, SI tables) for Wang et al.,... more This repository contains NMR raw data (main text figures, SI figures, SI tables) for Wang et al., "Boosted molecular mobility during common chemical reactions", <em>Science </em><strong>2020,</strong> <em>537-541</em>. The files can be opened using Mestrenova software (Bruker).
Fitness of cell colonies to navigate obstacles
Bulletin of the American Physical Society, Mar 2, 2020
Permeation of Solvent through Adsorbed Polymer Brushes
APS, Mar 1, 1997
We are investigating the drainage of a theta-solvent(trans-decalin at 24 ^circC) between solid su... more We are investigating the drainage of a theta-solvent(trans-decalin at 24 ^circC) between solid surfaces bearing polystyrene(PS) brushes. PS brush was formed by selective adsorption of PVP(polyvinylpyridine) block of PS-PVP diblock copolymer onto mica. A newly modified surface forces apparatus (SFA) which allows applying small amplitude of oscillatory displacement both to the shear and the normal direction simultaneously has been used.
Tribology International, Dec 1, 1997
Knowledge of the bulk viscosity provides little guidance to predict accurately the interfacial sh... more Knowledge of the bulk viscosity provides little guidance to predict accurately the interfacial shear strength and effective viscosity of a fluid in a lubricated contact. To quantify these differences between bulk and thin-film viscosity, an instrument was developed to measure the shear of parallel single crystal solids separated by molecularly-thin lubricant films. The effective shear viscosity is enhanced compared to the bulk, relaxation times are prolonged, and nonlinear responses set in at lower shear rates. These effects are more prominent, the thinner the liquid film. Studies with lubricant additives cast doubt on the usefulness of the concept of a friction coefficient for lubricated sliding.
Spectroscopie Studies of Confined Molecules Under Shear
MRS Proceedings, 1996
ABSTRACTWe introduce two new techniques with the sensitivity to measure spectroscopie properties ... more ABSTRACTWe introduce two new techniques with the sensitivity to measure spectroscopie properties of confined molecules under shear. One concerns rheo-optics of fluids in micron-sized gaps. The experimental approach consists in applying periodic shear motion to fluid films confined between parallel plates separated by controllable film thickness from 0.1 to 100 micrometers. A key aspect is the concurrent ability to perform spectroscopie experiments (infrared or dielectric spectroscopy, or x-ray or neutron spectroscopy) of these fluids during flow.The second technique consists in flow field experiments of polymer adsorption and orientation. The experimental approach is to produce one-directional shear, at rates up to 104 sec−1, past adsorbed polymer layers of thickness less than 0.01 micrometers. The selective augmentation of vibrational modes oriented preferentially along the chain backbone is then used to probe chain orientation in the direction of flow in a laminar flow field.
Journal of Polymer Science Part B, Dec 1, 1997
We study the drainage of a near-theta solvent through densely grafted polymer layers and compare ... more We study the drainage of a near-theta solvent through densely grafted polymer layers and compare to recent notions that these layers display little permeability to solvent flow at surface separations less than a ''hydrodynamic thickness.'' The solvent is trans-decalin (a near-theta solvent at the experimental temperature of 24ЊC). The polymer is polystyrene (PS) end-attached to two opposed mica surfaces via the selective adsorption of the polyvinylpyridine (PVP) block of a PS-PVP diblock copolymer. The experimental probe was a surface forces apparatus modified to apply smallamplitude oscillatory displacements in the normal direction. Out-of-phase responses reflected viscous flow of solvent alone-the PS chains did not appear to contribute to dissipation over the oscillation frequencies studied. The value of the hydrodynamic thickness ( R H ) was less than the coil thickness ( L o ) measured independently from the onset of surface-surface interactions in the force-distance profile, implying significant penetration of the velocity field into the polymer layer. As the surface-surface separation was reduced from 3 L o to 0.3 L o , the apparent hydrodynamic thickness ( R* H ) decreased monotonically to values R* H Ӷ R H . Physically, this indicates that the ''slip plane'' moved progressively closer to the solid surfaces with decreasing surface-surface separation. This was accompanied by augmentation of the effective viscosity by a factor of up to approximately 5, indicating somewhat diminished permeability of solvent through the overlapping polymer layers. Similar results hold for the flow through surface-anchored polymers in a good solvent. It is interesting to note the strong stretching of densely end-grafted polymers in a theta solvent.
Cell migration in microengineered tumor environments
Lab on a Chip, 2017
Recent advances in microengineered cell migration platforms are discussed critically with focus o... more Recent advances in microengineered cell migration platforms are discussed critically with focus on how cell migration is influenced by engineered tumor microenvironments, the medical relevance being to understand how tumor microenvironments may promote or suppress the progression of cancer.
Boosted molecular mobility during common chemical reactions
Science, Jul 31, 2020
Reactions give solvents a kick During a chemical reaction, the reorganization of solvent molecule... more Reactions give solvents a kick During a chemical reaction, the reorganization of solvent molecules not directly in contact with reactants and products is normally viewed as a simple diffusion response. Wang et al. studied molecular diffusion in six common reactions—including the copper-catalyzed click reaction and the Diels-Alder reaction—with pulsed-field gradient nuclear magnetic resonance. They observed a boost in mobility relative to Brownian diffusion that was stronger for the catalyzed reactions that were studied. The mobilities for the click reaction were verified with a microfluidic gradient method. They argue that energy release produces transient translational motion of reacting centers that mechanically perturbs solvent molecules. Science , this issue p. 537
Proceedings of the National Academy of Sciences of the United States of America, Nov 1, 2018
Proceedings of the National Academy of Sciences of the United States of America, Dec 18, 2017
Günther et al. report that their control experiment using randomized magnetic field gradient sequ... more Günther et al. report that their control experiment using randomized magnetic field gradient sequences disagreed with findings we had reported using linear gradients. However, we show that measurements in our laboratory are consistent using both methods.
Adaptive architecture and mechanoresponse of epithelial cells on a torus
Biomaterials, 2021
Curvature is a geometric feature widely observed in the epithelia and critical to the performance... more Curvature is a geometric feature widely observed in the epithelia and critical to the performance of fundamental biological functions. Understanding curvature-related biophysical phenomena remains challenging partly owing to the difficulty of quantitatively tuning and measuring curvatures of interfacing individual cells. In this study, we prepared confluent wild-type Madin-Darby canine kidney cells on a torus structure presenting positive, zero, and negative Gaussian curvatures with a tubule diameter of 2-7 cells and quantified the mechanobiological characteristics of individual cells. Cells on the torus surface exhibited topological sensing ability both as an individual cell and collective cell organization. Both cell bodies and nuclei, adapted on the torus, exhibited local Gaussian curvature-dependent preferential orientation. The cells on the torus demonstrated significant adjustment in the nuclear area and exhibited asymmetric nuclear position depending on the local Gaussian curvature. Moreover, cells on top of the torus, where local Gaussian curvature is near zero, exhibited more sensitive morphological adaptations than the nuclei depending on the Gaussian curvature gradient. Furthermore, the spatial heterogeneity of intermediate filament proteins related to mechanoresponsive expression of the cell body and nucleus, vimentin, keratin and lamin A, revealed local Gaussian curvature as a key factor of cellular adaptation on curved surfaces.
Shear of confined perfluorinated molecules: Effect of side branching
Wear, Dec 1, 1996
To understand the dependence of nanorheology on molecular architecture for perfluorinated molecul... more To understand the dependence of nanorheology on molecular architecture for perfluorinated molecules, studies were performed using two lubricants commonly used in the magnetic storage industry. Experiments mimicked a single asperity by confining liquids to molecular spacings between atomically smooth mica and applying oscillatory shear forces. The force-distance profiles were compared. Large differences were obtained for the linear shear response. The
WORLD SCIENTIFIC eBooks, Apr 1, 2000
The thin-film dielectric response of organic films confined within a surface forces apparatus ͑SF... more The thin-film dielectric response of organic films confined within a surface forces apparatus ͑SFA͒ and also between parallel sheets of atomically smooth mica is reported for the first time. Analysis is presented to infer dielectric properties of the organic film from the measured capacitance of the total system: sample, and mica sheets intervening between sample and electrodes. Measurements concerned the frequency dependence of normal-mode dielectric relaxation of cis-polyisoprene having dipoles aligned in the same direction along the chain backbone. We find that in thin-film geometries the peak frequency, f peak , of normal mode dielectric loss (⑀Љ) is moderately lower than for bulk samples and that, more important, the expected terminal tail, observed in the bulk sample ͑⑀Љϰ f for f Ͻ f peak ͒, is not observed even at the lowest frequency examined. Thus the slow normal mode distribution is much broader and the terminal relaxation time is much longer for chains in the thin layers. These dielectric features are attributed to spatial constraints on global chain motion in the thin layers and also to adsorption of chains on mica surfaces when the layer thickness is comparable to the unperturbed chain dimension. Independent measurements of shear relaxation, performed using a SFA modified for measurement of dynamical mechanical shear rheology, found a tremendously retarded viscoelastic response relative to bulk samples. There is the possibility that the broad distribution of the dielectric response of individual polymer chains may correspond to the observed retarded viscoelastic relaxation. However, we cannot rule out the other possibility that the dielectrically detected relaxation of individual chains is still faster than the terminal viscoelastic relaxation and that the latter thus corresponds to the collective motion of many confined chains.
Nanotribology responses and their connection to molecular conformations
American Chemical Society, Polymer Preprints, Division of Polymer Chemistry, Aug 1, 1998
Biomaterials Science, 2019
We demonstrate a method to prepare giant unilamellar vesicles (GUVs) with biologically-active pro... more We demonstrate a method to prepare giant unilamellar vesicles (GUVs) with biologically-active protein activity, by mixing erythrocyte (red blood cell) membrane extract with phospholipids and growing their mixture in a porous hydrogel matrix. This presents a pathway to retain protein biological activity without prior isolation and purification of the protein, though only the activity of the membrane protein GLUT1 is investigated to date. Using the cascade enzymatic reaction glucose oxidase and horseradish peroxidase to assay glucose concentration specifically within the GUV interior, we show that glucose is internalized by GLUT1 whereas adding cytochalasin B, a GLUT1 inhibitor, blocks glucose transport. The method presented here operates at biological ionic strength and is both simple and potentially generalizable. † Electronic supplementary information (ESI) available. See
Langmuir, Nov 9, 2001
We report the first use of a surface forces apparatus to study the hybridization of DNA. We study... more We report the first use of a surface forces apparatus to study the hybridization of DNA. We study the regime of very high ionic strength (≈1 M) at which commercial DNA chip operations are performed. Using a thiol end-attached single-stranded oligonucleotide, we find that exposure to the complementary strand resulted in larger thickness. In addition, the resistance to small-amplitude shear deformations when opposed to a nonadsorbing surface (mica) increased significantly after hybridization. The thickness at onset of significant shear resistance was, for single-stranded DNA, considerably less than that of hybridized DNA. This could provide a new method to detect DNA hybridization efficiency.
The interface between an electrode and a liquid plays a critical role in the overall performance ... more The interface between an electrode and a liquid plays a critical role in the overall performance of electrochemical biosensors. Surface morphology and roughness affect key parameters, such as the active area, diffusion profiles, and apparent electron transfer kinetics, whereas porosity may hinder the diffusion of fouling proteins. However, there is no simple and rapid method compatible with photolithographic electrodes to generate both nanostructured and porous surfaces. Herein, we demonstrate the interplay between the preferential etching of chloride and surfactant-assisted anisotropic gold reduction to create homogeneous, nanostructured, and nanoporous substrates on photolithographic gold electrodes within a minute and without using templates. We coined this process, SEEDING, that is, Surfactant-based Electrochemical Etch-Deposit Interplay for Nanostructure/Nanopore Growth. SEEDING on electrodes enhanced the sensitivity and anti-biofouling capabilities, enabling direct analysis of...
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Papers by Yoon-kyoung Cho