Droplet position control in digital microfluidic systems

Research on so called digital microfluidic systems (DMS) capable of manipulating individual microdroplets on a cell-based structure has enormously increased in the past few years, mainly due to the demand of the technology-dependent biomedical applications. Significant research in this area has been related to the simulation and modeling of droplet motion, demonstration of different drop actuation techniques on laboratory-scale prototypes, and droplet routing and scheduling for more efficient assay procedures. This paper introduces the basics of the control analysis and design of a DMS, which is a relatively unexplored area in digital microfluidics. This paper starts with a discussion on a simplified dynamic model of droplet motion in a planar array of cells, and continues with more complicated dynamic models that are necessary to realize the structure of an appropriate closed-loop control system for the DMS. The control analysis and design includes both the transient and steady-state responses of the DMS under external driving forces. The proposed control analysis and design approach is implemented into SIMULINK models to demonstrate the performance of the DMS through simulation using the system parameters previously reported in the literature.