Abstract-In this paper, we show how to combine microfluidics and feedback control to independently steer multiple particles with micrometer accuracy in two spatial dimensions. The particles are steered by creating a fluid flow that carries all the particles from where they are to where they should be at each time step. Our control loop comprises sensing, computation, and actuation to steer particles along user-input trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. Our method achieves inexpensive steering of particles by using conventional electroosmotic actuation in microfluidic channels. This type of particle steering does not require optical traps and can noninvasively steer neutral or charged particles and objects that cannot be captured by laser tweezers. (Laser tweezers cannot steer reflective particles, or particles where the index of refraction is lower than (or for more sophisticated optical vortex holographic tweezers does not differ substantially from) that of the surrounding medium.) We show proof-of-concept PDMS devices, having four and eight electrodes, with control algorithms that can steer one and three particles, respectively. In particular, we demonstrate experimentally that it is possible to use electroosmotic flow to accurately steer and trap multiple particles at once.[1541]

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.

This paper describes results and challenges in feedback control of microfluidic systems. Results are provided for two representative examples: control of liquid droplets by electrically actuated surface tension forces and steering of many particles at once by micro flow control.

We show how it is possible to combine micro-fluidics and feedback control (sense, compare, and apply corrective actuation) to steer many particles at once. The particles are steered by creating a spatially complex and time-varying fluid flow that carries all particles along their desired trajectories. We demonstrated experimental results for steering of a single yeast cell and realistic simulation results for the steering of many particles at once. INTRODUCTIONWe show how it is possible to combine micro-fluidic devices and feedback control methods to enable new behavior in MEMS systems, In particular, we demonstrate steering of individual particles, without the need for lasers and optical traps, by using flow control, vision sensing, and common electroosmotic actuation. Since cameras are already available in miniaturized format (for example in cell phones), this will allow us to replicate the capability of laser tweezers in a hand held format. This technology also allows us to steer particles and objects that cannot be captured by laser tweezers such as particle with the wrong dielectric properties and objects that are too big to fit inside optical traps.