Arbitrary steering of multiple particles independently in an electro-osmotically driven microfluidic system

Abstract

Abstract-We demonstrate how to use feedback control of microflows to steer multiple particles independently in planar microfluidic systems driven by electro-osmotic actuation. This technique enables the handling of biological materials, such as cells, bacteria, DNA, and drug packets, in a hand-held format using simple and easy-to-fabricate actuators. The feedback loop consists of a vision system which identifies the positions of the particles in real-time, a control algorithm that computes the actuator (electrode) inputs based on information received from the vision system, and a set of electrodes (actuators) that create the required flow through electro-osmotic forces to steer all the particles along their desired trajectories and correct for particle position errors and thermal noise. Here, we focus on the development of control algorithms to achieve the steering of particles: vision system implementation, fabrication of devices, and experimental validation is addressed in other publications. In particular, steering of a single (yeast cell) particle has been demonstrated experimentally in our prior research and we have recently demonstrated experimental steering of three particles independently. In this paper, we develop the control algorithms for steering multiple particles independently and we validate our control techniques using simulations with realistic sources of initial position errors and thermal noise. In this study, we assume perfect measurement and actuation.

Using Feedback Control of Microflows to Independently Steer Multiple Particles

“…It is also possible to use this scheme to hold a particle in place: whenever the particle deviates from its desired position, the electrodes create a correcting flow to bring it back to its target location. Surprisingly, it is also possible to steer multiple particles independently using this feedback control approach [16]. A multielectrode device is able to actuate multiple fluid flow or electric field modes.…”

“…The development of a control algorithm that can combine modes in this manner is our key theoretical contribution: this algorithm is described in detail in [16] and is summarized here in Section V-C. The algorithm requires some knowledge of the particle and system properties (charged particles exhibit electrophoresis and react differently than neutral particles) but this knowledge does not have to be precise: the reason is that feedback, the continual comparison between the desired and actual particle positions, serves to correct for errors and makes the system robust to experimental uncertainties [17], [18].…”

“…It is possible to design a control algorithm for single particle steering without reference to a model but, even in that case, a model provides valuable insight. Details of our model are covered in [16] and are summarized next.…”

“…We also assume that the voltage is varied smoothly and slowly. The result is that the fluid flow simplifies to a uniform velocity profile in the vertical direction, and its velocity field at any time and place is given by a coefficient times the electric field, i.e., [16] where is the electroosmotic mobility. If the particles are neutral and sufficiently small they flow along with the fluid.…”

“…The net particle mobility coefficient is measured before we begin our steering experiments (see Section IV-D). Particles also exhibit Brownian motion, which is treated by an appropriate noise term in the model [16].…”