Sung Yang

Universal curves for the van der Waals interaction between single-walled carbon nanotubes.

We report very simple and accurate algebraic expressions for the van der Waals (VDW) potentials and the forces between two parallel and crossed carbon nanotubes. The Lennard-Jones potential for two carbon atoms and the method of the smeared-out approximation suggested by Girifalco were used. It is found that the interaction between parallel and crossed tubes is described by two universal curves for parallel and crossed configurations that do not depend on the van der Waals constants, the angle between tubes, and the surface density of atoms and their nature but only on the dimensionless distance. The explicit functions for equilibrium VDW distances, well depths, and maximal attractive forces have been given. These results may be used as a guide for the analysis of experimental data to investigate the interaction between nanotubes of various natures.

Topology optimization of the shear thinning non-Newtonian fluidic systems for minimizing wall shear stress

This paper suggests the topology optimization process to minimize wall shear stress by considering shear thinning non-Newtonian fluid effects in the systematic design of fluidic systems dealing with blood. Topology optimization was originally developed for mechanical design problems, and within the last decade the method has been extended to a range of fluidic applications. In this paper, the Carreau-Yasuda constitutive equation model is used for shear thinning non-Newtonian fluid modeling. The fundamental idea is that the material density of each element or grid point is a design variable, thus, the geometry is parameterized in a pixel-like pattern. Then, material interpolation functions for inverse permeability and dynamic viscosity are used to ensure convergence of the solution and resolve non-linearity. In order to define wall shear stress on implicit boundary between solid and fluid (i.e., blood) occurring in fluidic topology optimization, the relaxation method of wall shear stress is first proposed in this study. We then apply the proposed fluidic topology optimization to actual fluidic systems dealing with blood (e.g., a femoral bypass graft). These design examples validate the efficiency of the proposed approach and show that topology optimization can be used for the initial conceptual design of various fluidic systems.

On-chip Extraction of Intracellular Molecules in White Blood Cells from Whole Blood.

The extraction of virological markers in white blood cells (WBCs) from whole blood—without reagents, electricity, or instruments—is the most important first step for diagnostic testing of infectious diseases in resource-limited settings. Here we develop an integrated microfluidic chip that continuously separates WBCs from whole blood and mechanically ruptures them to extract intracellular proteins and nucleic acids for diagnostic purposes. The integrated chip is assembled with a device that separates WBCs by using differences in blood cell size and a mechanical cell lysis chip with ultra-sharp nanoblade arrays. We demonstrate the performance of the integrated device by quantitatively analyzing the levels of extracted intracellular proteins and genomic DNAs. Our results show that compared with a conventional method, the device yields 120% higher level of total protein amount and similar levels of gDNA (90.3%). To demonstrate its clinical application to human immunodeficiency virus (HIV) diagnostics, the developed chip was used to process blood samples containing HIV-infected cells. Based on PCR results, we demonstrate that the chip can extract HIV proviral DNAs from infected cells with a population as low as 102/μl. These findings suggest that the developed device has potential application in point-of-care testing for infectious diseases in developing countries.

Micro-Viscometer for Measuring Shear-Varying Blood Viscosity over a Wide-Ranging Shear Rate

In this study, a micro-viscometer is developed for measuring shear-varying blood viscosity over a wide-ranging shear rate. The micro-viscometer consists of 10 microfluidic channel arrays, each of which has a different micro-channel width. The proposed design enables the retrieval of 10 different shear rates from a single flow rate, thereby enabling the measurement of shear-varying blood viscosity with a fixed flow rate condition. For this purpose, an optimal design that guarantees accurate viscosity measurement is selected from a parametric study. The functionality of the micro-viscometer is verified by both numerical and experimental studies. The proposed micro-viscometer shows 6.8% (numerical) and 5.3% (experimental) in relative error when compared to the result from a standard rotational viscometer. Moreover, a reliability test is performed by repeated measurement (N = 7), and the result shows 2.69 ± 2.19% for the mean relative error. Accurate viscosity measurements are performed on blood samples with variations in the hematocrit (35%, 45%, and 55%), which significantly influences blood viscosity. Since the blood viscosity correlated with various physical parameters of the blood, the micro-viscometer is anticipated to be a significant advancement for realization of blood on a chip.

A microfluidic-based lid device for conventional cell culture dishes to automatically control oxygen level

Most conventional hypoxic cell culture systems undergo reoxygenation during experimental manipulations, resulting in undesirable effects including the reduction of cell viability. A lid device was developed herein for conventional cell culture dishes to resolve this limitation. The integration of multilayered microfluidic channels inside a thin membrane was designed to prevent the reoxygenation caused by reagent infusion and automatically control the oxygen level. The experimental data clearly show the reducibility of the dissolved oxygen in the infusing reagent and the controllability of the oxygen level inside the dish. The feasibility of the device for hypoxia studies was confirmed by HIF-1α experiments. Therefore, the device could be used as a compact and convenient hypoxic cell culture system to prevent reoxygenation-related issues.

Protein patterning utilizing region-specific control of wettability by surface modification under atmospheric pressure

Wettability control can be crucial in improving the uniformity of selective protein immobilization in high-density microarrays. In this study, we propose an atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD)-based method in conjunction with photolithography to implement region-specific control of wettability on Si substrate. The proposed PECVD method under atmospheric pressure condition would be a useful alternative of conventional reactive plasma-based treatments methods requiring vacuum condition for uniform protein patterning. Layers with dissimilar wettability and roughness prepared by AP-PECVD process using tetraethoxysilane (TEOS) or TEOS-O2 as precursors could realize uniform protein patterning in a micrometer-scale.