Modeling and Control of Micro-Fluidic Systems: Control of Droplets by Electrowetting Actuation and Steering of Cells by Flow Control Tweezers

Professor Benjamin Shapiro, Aerospace / Bio-Engineering University of Maryland at College Park

My group is interested in developing control theory for micro-electro- mechanical-systems (MEMS), and applying it to demonstrate novel MEMS capabilities. Specifically, we focus on micro-fluidic systems. Here I show how control methods can improve existing performance in the UCLA lab-on-a-chip electrowetting system and can create entirely new capabilities in our ‘micro fluidic tweezers’ cell steering devices.

In the Electro-Wetting-On-Dielectric (EWOD) system developed at UCLA by CJ Kim, a grid of electrodes is used to locally change surface tension forces on liquid droplets. By choosing the electrode firing sequence it is possible to move, split, join, and mix liquids in the droplets. We present an experimentally validated 2-phase fluid flow model of the liquid dynamics, and then show the development of control algorithms validated on this model. Control ideas and real time image algorithms are presented for controlling material points on the liquid/gas boundaries, for precision splitting of droplets, and for steering of particles inside the droplets.

For the second example, we show how feedback flow control can enable particle steering in cheap, handheld micro-fluidic systems using real time vision feedback and routine electro-osmotic actuation. Here we create temporally and spatially varying flow fields that carry all the particles along their desired trajectories. We have demonstrated flow steering of many particles at once both in simulations and in experiments. (Flow control steering for a single yeast cell is shown above.) This system is being further developed to enable sample preparation (remove all but the interesting objects from the sample) and for cell loading for a ‘cell clinics’ olfactory and bio-chemical sensing system at the University of Maryland.

I will close the talk by outlining the underlying challenges that must be addressed for control of micro-scale systems based on other projects in our lab (e.g. shape control of vesicles with laser tweezers and modeling/control of conducting plastic actuators).