Through COMSOL modeling and electrode design, positive dielectrophoretic (pDEP) cell trapping for media exchange has been demonstrated on live Chlamydomnas reinhardtii in regular growth medium in a PDMS-glass microfluidic MEMS device. Dielectrophoresis (DEP) is the force applied to dielectric particles in an alternating current (AC) non-uniform electric field. A DEP force toward the increasing electric field gradient is called positive (pDEP). There are several published DEP structures for various applications such as: simple interdigitated structures for particle sorting in flow, DEP tweezers for single cell manipulation, and spiral structures for general cell manipulation. pDEP trapping over large areas (area pDEP) has been demonstrated with the use of low conductivity suspending media, but for higher conductivity suspending media, such as growth media, the pDEP force is reduced, and less likely to trap and hold microalgae against the hydrodynamic forces during media exchange. Multiphysics software, COMSOL, was used to model repeating structures suited for trapping of cells over the bottom area of a microfluidic device, which is useful and necessary for media exchange of a cell culture in a simple microfluidic device. The theoretical model of dielectrophoretic (DEP) force on a homogenous sphere in a homogenous medium in an electric field is a function of the sphere radius and conductivity, medium permittivity, and the gradient of the electric field. By assuming the conductivities, permittivities, and the particle geometry remains constant, the gradient of the electric field is the determining factor for the strength of the pDEP force. Modeling the electric fields and the resulting electric field gradient of various interdigitated electrode configurations allowed for the optimization of an electrode structure’s area of higher electric field gradients. The completed microfluidic device consisted of a single channel and a wide growth chamber overlaid over patterned gold-chrome electrodes. The MEMS device was fabricated using soft lithography and photolithography on the etched chrome-gold glass slides. The pDEP trapping was successful in trapping C. reinhardtii for media exchange. Media exchange allows for nutrient replenishment and waste removal, allowing for control of the growth conditions.

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