ID 112

Droplet Dynamics Under Electrostatic Actuation For Clinical Diagnostics

 

Abstract:

Several authors stand for the use of microdroplets, under electrostatic actuation, to transport biosamples to be analyzed in microfluidic devices for biomedical and clinical applications. The description of the dynamic behavior of these biofluid droplets is paramount to design effective devices. This paper addresses the numerical and experimental characterization of biofluid droplets dynamics, under electrostatic actuation, in the design and test of lab-on-chip devices for future clinical diagnostics. The temporal evolution of droplet diameter and contact angles provides important information to determine droplet motion and to establish preliminary sizes and positioning of the electrodes, which are then optimized using a numerical model. This experimental approach stresses the importance of the wetting properties of the dielectric materials that cover the electrodes and are in direct contact with the biofluid droplets. Hence, superhydrophobic properties assure the effective droplet spreading and receding and minimize surface energy dissipation. The numerical approach further shows that the distance between electrodes affects significantly the magnitude of the applied electrical force, thus influencing droplet spreading and motion. An experimental evaluation of the effect of mass diffusion in the evaporation of the sample droplets showed that the practical implementation of such devices requires a mild control of the ambient conditions (temperature and relative humidity), since droplet evaporation by mass diffusion is significant, even at high values of relative humidity. Hence, droplets diameters can decrease up to almost 40% with respect to their initial dimensions for relative humidity values as high as 70%, for ambient temperatures of 20±3ºC.