Computer aided design of an EWOD microdevice

Digital microfluidics is foreseen as a convenient way to perform biological processes like DNA manipulation and cell analysis. A promising method for droplet displacement is electrowetting on dielectric (EWOD). It has been recently shown that many basic manipulations of microdrops can be achieved in EWOD microsystems. These manipulations are imposed by the different biological processes taking place on the biochip. The key manipulations are: microdrop dispense from a reservoir onto the microchip, droplet motion from one electrode to the next one, separation of a droplet into two daughter droplets, merging of two droplets into one unique droplet, and microdrop crossing from a covered EWOD to an open EWOD sector and vice versa. In order to optimize these manipulations and contribute to the developments of such microsystems, it is mandatory to closely understand the physical phenomena involved in electrowetting. To do so, we have used an approach based on a numerical method using surface energy minimization, justified by the fact that capillary forces are dominant in microdrops mechanical behavior. The results have led us to improve the morphological design of an EWOD microchip. We present here the computational approach, a comparison with the experimental results and the consequences for the realization of an EWOD microsystem. (c) 2005 Elsevier B.V. All rights reserved.