The MAESFLO Device: A Complete Microfluidic Control System

Abstract

AbstractIn spite of considerable efforts, flow control in micro-channels remains a challenge owing to the very small ratio of channel/supply-system volumes, as well as the induction of spurious flows by extremely small pressure or geometry changes. We present here a robust and complete system for flow control in complex microchannel network that both monitors and controls all the flow relevant parameters, that is to say flow rate and pressure. Based on a dynamic control of reservoir pressures at the end of each channel and external thermal flow-sensors, all the parameters are measured with a precision down to 25 μBar and 2nL/min. Thanks to adaptative feed back control loop, the MAESFLO can control either the flow rate or the pressure with high stability over long period whatever the microsystem characteristics. Compared to classic pumps, a significant increase of stability has been reached as no mechanical parts are involved. Indeed the flow rate is pulse free and is stable down to 0.1% of the full scale. Besides, pressure control enables to achieve short response time (less than hundreds of millisec). The MAESFLO is thus a unique system to control flow in complex network architecture and can be considered as an alternative to integrated micro-valves using only external equipments. Indeed, the MAESFLO can stop the flow to nearly zero in one or several branches of a complex microfluidic network while keeping other flows constant. Sequential manipulation of liquids in a definite part of a micro-device is thus possible without expensive and time consuming fabrication processes. It can be particularly useful when dealing with washing steps in the case of biological assay for example. Controlling flow with short response time along with high precision is also a key issue in microfluidic. By combining pressure actuation with flowrate monitoring, short response time are achievable keeping a high precision flow rate. It can be particularly useful for droplet generation and size control, droplet on demand generation, long time living cell perfusion and drug injection… In this work we will present the benefit to control and monitor both pressure and flow rate with the MAESFLO. A lot of information can be extracted from these simple parameters, as hydraulic resistance, monophasic and biphasic apparent viscosity, the volume and the position of a trapped air bubble and many more. The proof of concept of stop flow control will also be shown with experimental results stressing the advantages of the “virtual micro-valve”.