A 3D Monte Carlo (MC) simulation approach is developed and employed to study the effect of the oscillation mode on the squeeze-film air damping in the free-molecule regime. By tracking individual gas molecule's motion and its interaction with the resonator, the MC approach is by far the most accurate modeling approach for the modeling of squeeze-film damping in the free-molecule regime. The accuracy of this approach is demonstrated on several cases in which either analytical solutions or experimental measurements are available. It has been found that unlike the case when resonators oscillate in an unbounded domain, squeeze film damping is very sensitive to the mode shape, which implies that some of the existing modeling approaches based on rigid-resonator assumption may not be accurate when applied to model resonators oscillating at their deformed shape. ©2010 IEEE.

Knudsen force acting on a heated microbeam adjacent to a cold substrate in a rarefied gas is a mechanical force created by unbalanced thermal gradients. The measured force has its direction pointing towards the side with a lower thermal gradient and its magnitude vanishes in both continuum and free-molecule limits. In our previous study, negative Knudsen forces were discovered at the high Knudsen regime before diminishing in the free-molecule limit. Such a phenomenon was however not observed in the experiment. In this paper, the existence of such a negative Knudsen force is further confirmed using both numerical simulation and theoretical analysis. The asymptotic order of the Knudsen force near the collisionless limit is analyzed and the analytical expression of its leading term is provided, from which approaches for the enhancement of negative Knudsen forces are proposed. Copyright © 2012 by ASME.

Electroendocytosis (EED) is a pulsed-electric-field (PEF) induced endocytosis, facilitating cells uptake molecules through nanometer-sized EED vesicles. We herein investigate the effect of a chemical inhibitor, Cytochalasin D (CD) on the actin-filaments (F-Actin) behavior of single-cell EED. The CD concentration (C CD) can control the depolymerization of F-actin. A multi-chamber micro cell chip was fabricated to study the EED under different conditions. Large-scale single-cell data demonstrated EED highly depends on both electric field and C CD. © 2012 IEEE.

Both theoretical analysis and nonlinear 2D numerical simulations are used to study the concentration difference and Peclet number effect on the measurement error of electroosmotic mobility in microchannels. We propose a compact analytical model for this error as a function of normalized concentration difference and Peclet number in micro electroosmotic flow. The analytical predictions of the errors are consistent with the numerical simulations. © 2012 IEEE.

A theoretical and experimental study of electroporation (EP) of red blood cells (RBCs) was presented in this paper. With additional strain energy, an energy-based model of an electropore induced on a RBC's membrane at different electric fields was proposed to predict the critical EP electric field strength. In addition, EP experiments with red blood cells at single-cell level was carried out on a micro EP chip. The measured critical EP electric field strengths are in agreement with the numerical predictions. ©2010 IEEE.

Experimental study of electroporation of bone marrow mesenchymal stem cells (MSCs) at the single-cell level was carried out on a micro EP chip by using single electric rectangular pulse. The threshold values of the electrode potential and pulse width for gas bubble generation on the micro electrodes due to electrolysis of water were revealed as 4.5 volt and 100 μs, respectively. Quantitative EP study was performed with various electric field strengths for various pulse widths, ranging from 20μs to 15ms. Over 1,000 single-cell EP results were used to construct an EP "phase diagram", which delineates the boundaries for (1) effective EP of MSCs and (2) electric cell lysis of MSCs. Finally, the micro EP chip showed successful transfection of the pEGFP-C1 plasmid into the MSCs by properly choosing the electric parameters from the EP "phase diagram". © 2011 IEEE.