Showing papers by "Ali Beskok published in 2012"

Microfluidic impedance spectroscopy as a tool for quantitative biology and biotechnology

Abstract: A microfluidic device that is able to perform dielectric spectroscopy is developed. The device consists of a measurement chamber that is 250 μm thick and 750 μm in radius. Around 1000 cells fit inside the chamber assuming average quantities for cell radius and volume fraction. This number is about 1000 folds lower than the capacity of conventional fixtures. A T-cell leukemia cell line Jurkat is tested using the microfluidic device. Measurements of deionized water and salt solutions are utilized to determine parasitic effects and geometric capacitance of the device. Physical models, including Maxwell-Wagner mixture and double shell models, are used to derive quantities for sub-cellular units. Clausius-Mossotti factor of Jurkat cells is extracted from the impedance spectrum. Effects of cellular heterogeneity are discussed and parameterized. Jurkat cells are also tested with a time domain reflectometry system for verification of the microfluidic device. Results indicate good agreement of values obtained with both techniques. The device can be used as a unique cell diagnostic tool to yield information on sub-cellular units.

Surface–gas interaction effects on nanoscale gas flows

Abstract: Molecular dynamics (MD) method is used to simulate shear driven argon gas flows in the early transition and free molecular flow regimes to investigate surface effects as a function of the surface–gas potential strength ratio (ewf/eff). Results show a bulk flow region and a near wall region that extends three molecular diameters away from the surfaces. Within the near wall region the velocity, density, and shear stress distributions exhibit deviations from the kinetic theory predictions. Increased ewf/eff results in increased gas density, leading toward monolayer adsorption on surfaces. The near wall velocity profile shows reduced gas slip, and eventually velocity stick with increased ewf/eff. Using MD predicted shear stress values and kinetic theory, tangential momentum accommodation coefficients (TMAC) are calculated as a function of ewf/eff, and TMAC values are shown to be independent of the Knudsen number. Presence of this near wall region breaks down the dynamic similarity between rarefied and nanoscale gas flows.

Micro-PIV Measurements of Induced-Charge Electroosmosis Around a Metal Rod

Abstract: A cylindrical gold-coated stainless steel rod was positioned at the center of a straight microchannel connecting two fluid reservoirs on either end. The microchannel was filled with 1 mM KCl containing 0.5 μm diameter carboxylate-modified spherical particles. Induced-charge electro-osmotic (ICEO) flow occurred around the metallic rod under a sinusoidal AC electric field applied using two platinum electrodes. The ICEO flows around the metallic rod were measured using micro particle image velocimetry (micro-PIV) technique as functions of the AC electric field strength and frequency. The present study provides experimental data about ICEO flow in the weakly nonlinear limit of thin double layers, in which, the charging dynamics of the double layer cannot be presented analytically. The measured ICEO flow pattern qualitatively agrees with the theoretical results obtained by Squires and Bazant (J Fluid Mech 509:217–252, 2004). Flow around the rod is quadrupolar, driving liquid towards the rod along the electric field and forcing it away from the rod in the direction perpendicular to the imposed electric field. The measured ICEO flow velocity is proportional to the square of the electric field strength, and depends on the applied AC frequency.

Decorin Expression, Straw-like Structure, and Differentiation of Human Costal Cartilage

Abstract: Costal cartilage is much understudied compared with the load-bearing cartilages Abnormally grown costal cartilages are associated with the inherited chest wall deformities pectus excavatum and pectus carinatum resulting in sunken and pigeon chests, respectively A lack of understanding of the ultrastructural and molecular biology of costal cartilage is a major confounder in predicting causes and outcomes of these disorders This study analyzed the structure of marginal human costal cartilage (ribs 6–10) through scanning electron and atomic force microscopes and identified the presence of straw-like structures running longitudinally We also demonstrated that chondrocytes tend to occur singly or as doublets and that centrally located cells produce high levels of aggrecan compared with more peripherally located cells measured using immunohistochemistry Gene expression from mRNA extracted from cartilage showed high levels of decorin expression, likely associated with the large, complex tubular structures r

A Polymer-Based Microfluidic Resistive Sensor for Detecting Distributed Loads

Abstract: This paper reports on a polymer-based microfluidic resistive sensor for detecting distributed loads. The sensor is comprised of a polymer rectangular microstructure with an embedded electrolyte-filled microchannel and an array of electrodes aligned along the microchannel length. Electrolyte solution in the microchannel serves as impedance transduction. Distributed loads acting on the polymer microstructure give rise to different deflection along the microstructure length, which is recorded as the resistance change in electrolyte solution. This sensor can detect distributed loads by monitoring the resistance change at each pair of electrodes. A sensor with an in-plane dimension of ∼20mm×10mm and five pairs of electrodes is fabricated using a CNC machine. 1M KCl solution is used as the electrolyte. Using a custom built electronic circuit on breadboard and a custom LabVIEW program, the static and dynamic performance of the sensor is characterized, demonstrating the feasibility of employing this sensor to detect distributed loads.Copyright © 2012 by ASME