Biomedical subjects

Nadine Aubry

Publications and source records attributed to Nadine Aubry.

11 recordsLinked to original sources

PubMed2006

Trapping heavy metals by using calcium hydroxyapatite and dielectrophoresis.

We propose a novel technique for the removal of heavy metal waste from contaminated water. Our method consists in using dielectrophoresis (DEP) to trap hydroxyapatite (HAP) particles of 1 microm size in water after they have adsorbed heavy metal (Pb, Zn, Cu, Co and Cr). Although HAP can adsorb heavy metals in water and as such offers great promise as a waste-cleaning tool , one of the current challenges is the efficient removal of the HAP particles once they have adsorbed the heavy metals. We show in this paper that DEP can be used to concentrate such particles in certain regions, thus rendering the rest of the solution volume nearly free of contaminated particles. We present here both experimental and numerical results for suspensions at low concentrations.

Durapatite↗

PubMed2006

Influence of particle-particle interactions and particles rotational motion in traveling wave dielectrophoresis.

Traveling wave dielectrophoresis provides an interesting method for the controlled movement of microsized particles in suspended mixtures, and as such is a promising tool in microfluidic technology. In this case, the electrostatic force acting on the particles has two components: one due to the spatially varying magnitude of the electric field and the other due to the spatially varying phase. The actual movement of the particle is determined by the combined effect of these two forces and corresponding torques, the viscous drag exerted by the fluid on the particle, and the electrostatic and hydrodynamic particle-particle interactions. This paper presents the first numerical simulations of the motion of particles subjected to all previous forces and torques. Our technique is based on a finite-element scheme in which the particles are moved using a direct simulation scheme respecting the fundamental equations of motion for both the fluid and the solid particles. The fluid-particle motion is resolved by the method of distributed Lagrange multipliers and the electrostatic forces are computed using the point-dipole approximation. Our simulations show that the particle behavior strongly depends on the mismatch of the dielectric properties between the particles and the fluid, and that the particle-particle interaction force as well as particles rotation speeds play crucial roles in the various regimes.

Electrophoresis↗

PubMed2005

Dielectrophoresis induced clustering regimes of viable yeast cells.

We experimentally study the transient clustering behavior of viable yeast cells in a dilute suspension suddenly subjected to a nonuniform alternating current (AC) electric field of a microelectrode device. The frequency of the applied electric field is varied to identify two distinct regimes of positive dielectrophoresis. In both regimes, the yeast cells eventually cluster at electrodes' edges, but their transient behavior as well as their final arrangement is quite different. Specifically, when the frequency is much smaller than the cross-over frequency, the nearby yeast cells quickly rearrange in well-defined chains which then move toward the electrodes' edges and remain aligned as elongated chains at their final location. However, when the frequency is close to the cross-over frequency, cells move individually toward the regions of collection and simply agglomerate along the electrodes' edges. Our analysis shows that in the first regime both the dielectrophoretic (DEP) force and the mutual DEP force, which arises due to the electrostatic particle-particle interactions, are important. In the second regime, on the other hand, the DEP force dominates.

Electricity↗

PubMed2004

Electroosmotic mixing in microchannels.

Mixing is an essential, yet challenging, process step for many Lab on a Chip (LOC) applications. This paper presents a method of mixing for microfluidic devices that relies upon electroosmotic flow. In physical tests and in computer simulations, we periodically vary the electric field with time to mix two aqueous solutions. Good mixing is shown to occur when the electroosmotic flow at the two inlets pulse out of phase, the Strouhal number is on the order of 1, and the pulse volumes are on the order of the intersection volume.

Complex Mixtures↗

PubMed2004

Parameters influencing pulsed flow mixing in microchannels.

The rapid mixing of reagents is a crucial step for on-chip chemical and biological analysis. It has been recently suggested that microfluidic mixing can be greatly enhanced by simply using time pulsing of the incoming flow rates of the two fluids to be mixed (Glasgow, I.; Aubry, N. Lab Chip 2003, 3, 114-120). This paper elaborates on the latter technique, showing through computational fluid dynamics how the mixing efficiency strongly depends on certain dimensionless parameters of the system, while remaining nearly insensitive to others. In particular, it is demonstrated that higher Strouhal numbers (ratio of flow characteristic time scale to the pulsing time period) and pulse volume ratios (ratio of the volume of fluid pulsed to the volume of inlet/outlet intersection) lead to better mixing. This paper also presents a physical device capable of mixing two reagents using pulsing, which shows improved mixing with greater values of the Strouhal number.

Computer Simulation↗

PubMed2004

Aging increases stiffness of cardiac myocytes measured by atomic force microscopy nanoindentation.

It is well established that the aging heart exhibits left ventricular (LV) diastolic dysfunction and changes in mechanical properties, which are thought to be due to alterations in the extracellular matrix. We tested the hypothesis that the mechanical properties of cardiac myocytes significantly change with aging, which could contribute to the global changes in LV diastolic dysfunction. We used atomic force microscopy (AFM), which determines cellular mechanical property changes at nanoscale resolution in myocytes, from young (4 mo) and old (30 mo) male Fischer 344 x Brown Norway F1 hybrid rats. A measure of stiffness, i.e., apparent elastic modulus, was determined by analyzing the relationship between AFM indentation force and depth with the classical infinitesimal strain theory and by modeling the AFM probe as a blunted conical indenter. This is the first study to demonstrate a significant increase (P < 0.01) in the apparent elastic modulus of single, aging cardiac myocytes (from 35.1 +/- 0.7, n = 53, to 42.5 +/- 1.0 kPa, n = 58), supporting the novel concept that the mechanism mediating LV diastolic dysfunction in aging hearts resides, in part, at the level of the myocyte.

Animals↗

PubMed2004

Dielectrophoresis of nanoparticles.

A numerical scheme based on the distributed Lagrange multiplier method (DLM) is used to study the motion of nano-sized particles of dielectric suspensions subjected to uniform and nonuniform electric fields. Particles are subjected to both electrostatic and hydrodynamic forces, as well as Brownian motion. The results of the simulations presented in this paper show that uniform electric fields the evolution of the particle structures depends on the ratio of electrostatic particle-particle interactions and Brownian forces. When this ratio is of the order of 100 or greater, particles form stable chains and columns, whereas when it is of the order of 10 or smaller the particle distribution is random. For the nonuniform electric field cases considered in this paper, the relative magnitude of Brownian forces is in the range such that it does not influence the eventual collection of particles by dielectrophoresis and the particular locations where the particles are collected. However, Brownian motion is observed to influence the transient particle trajectories. The deviation of the particle trajectories compared to those determined by the electrostatic and hydrodynamic forces alone is characterized by the ratio of Brownian and dielectrophoretic forces.

Diffusion↗

PubMed2003

Electro-hydrodynamic micro-fluidic mixer.

Fluid mixing in microchannels is needed for many applications ranging from bio-arrays to micro-reactors, but is typically difficult to achieve. A simple geometry micro-mixer is proposed based on the electro-hydrodynamic (EHD) force present when the fluids to be mixed have different electrical properties and are subjected to an electric field. The electrodes are arranged so that the electric field is perpendicular to the interface between the two fluids, creating a transversal secondary flow. The technique is demonstrated experimentally using the flow of two liquids with identical viscosity and density, but different electrical properties. The volume flow rate and average velocity are 0.26 microl s(-1) and 4.2 mm s(-1), respectively, corresponding to a Reynolds number Re= 0.0174. The effect of a continuous (DC) electric field and two alternating (AC)- sinusoidal and square - electric fields is explored. At the appropriate parameter values, very good mixing takes place in less than 0.1 s, over a very short distance (within a fraction of the width 250 microm of the electrodes).

Journal Article↗

PubMed2003

Enhancement of microfluidic mixing using time pulsing.

Many microfluidic applications require the mixing of reagents, but efficient mixing in these laminar (i.e., low Reynolds number) systems is typically difficult. Instead of using complex geometries and/or relatively long channels, we demonstrate the merits of flow rate time dependency through periodic forcing. We illustrate the technique by studying mixing in a simple "T" channel intersection by means of computational fluid dynamics (CFD) as well as physically mixing two aqueous reagents. The "T" geometry selected consists of two inlet channel segments merging at 90 degrees to each other, the outlet segment being an extension of one of the inlet segments. All channel segments are 200 microm wide by 120 microm deep, a practical scale for mass-produced disposable devices. The flow rate and average velocity after the confluence of the two reagents are 48 nl s(-1) and 2 mm s(-1) respectively, which, for aqueous solutions at room temperature, corresponds to a Reynolds number of 0.3. We use a mass diffusion constant of 10(-10) m(2) s(-1), typical of many BioMEMS applications, and vary the flow rates of the reagents such that the average flow rate remains unchanged but the instantaneous flow rate is sinusoidal (with a DC bias) with respect to time. We analyze the effect of pulsing the flow rate in one inlet only as well as in the two inlets, and demonstrate that the best results occur when both inlets are pulsed out of phase. In this case, the interface is shown to stretch, retain one fold, and sweep through the confluence zone, leading to good mixing within 2 mm downstream of the confluence, i.e. about 1 s of contact. From a practical viewpoint, the case where the inlets are 180 degrees out of phase is of particular interest as the outflow is constant.

Computer Simulation↗

PubMed2003

Breaking of space-time symmetries in modulated traveling waves.

In this paper, we investigate the structure of traveling waves whose amplitude is spatially and/or temporally modulated. In particular, in the case of short wavelength modulations, we completely describe the breaking of symmetry induced by such modulations and their dynamical consequences.

Journal Article↗

PubMed1995

The dynamics of spatiotemporal modulations.

The modulational instability of traveling waves is often thought to be a crucial point in the mechanism of transition to space-time disorder and turbulence. The aim of this paper is to study the effect of spatiotemporal modulations on some dynamics u(0)(x,t), which may occur as an instability process when a control parameter varies, for instance. We analyze the properties of the modulated dynamics of the form g(1)(x)g(2)(t)u(0)(x,t) compared to those of the reference dynamics u(0)(x,t), using operator theory. We show that, if the reference dynamics is invariant under some space-time symmetry in the sense of Ref. [J. Nonlinear Sci. 2, 183 (1992)], the modulation has the effect of either deforming this symmetry or breaking it, depending on whether the corresponding operator remains unitary or not. We also demonstrate that the smallest Euclidean space containing the modulated dynamics has a dimension smaller than or equal to the smallest Euclidean space containing u(0)(x,t). The previous results are then applied to the case of modulated uniformly traveling waves. While the spatiotemporal translation invariance of the wave never persists in the presence of a modulation, the existence of a spatiotemporal symmetry depends on the resonance of the Fourier sidebands due to the modulation. In case of nonresonance, a spatiotemporal symmetry exists and is explicitly determined. In this situation, the modulated wave and the carrier wave have the same spectrum (up to a normalization factor), the same entropy, and the spatial (resp., temporal) two-point correlation is deformed only by the spatial (resp., temporal) modulation. (c) 1995 American Institute of Physics.

Journal Article↗