Electrohydrodynamics of yeast cells in microchannels subjected to travelling electric fields

Abstract

While travelling wave dielectrophoresis (twDEP) offers a promising method for the control of micro-sized particles suspended in liquids, particularly when the motion of particles along the length of the channel is sought without having to pump the liquid itself, it leads to a variety of complex dynamical regimes which need to be clearly understood for the design of efficient microfluidic devices targeting particular functions. In this paper, we describe the various dynamical regimes in terms of the forces acting on the particles, i.e. the conventional dielectrophoretic and twDEP force and torque, the viscous drag exerted by the fluid on the particle and the electrostatic and hydrodynamic particle–particle interactions. We also explore the variation of the dynamical regimes in three different configurations typical of microfluidic channels whose electrodes are embedded in the bottom wall. The first two configurations have different, i.e. aligned and staggered, electrode geometries, and the third configuration consists of aligned electrodes but energized at different potentials. For these purposes, we use our direct numerical simulation code based on the distributed Lagrange multiplier method for solving the equations of motion for both the fluid and the individual particles, and the point dipole model to compute the electrostatic forces. The model particles are chosen so as to have mechanical and electrical properties of yeast cells suspended in an aqueous solution. It is found that the motion of the particles not only depends significantly on the Clausius–Mossotti factor, which is a function of the electric properties of the fluid and the particles, but also on the specific configuration considered. Particularly, the spinning of particles plays a crucial role in the particle translations and interactions, but the direction of such spinning motion depends on the particular device configuration used.