A pneumatically controlled microfluidic rectifier enabling zero backflow under pulsatile flow regime

A pulsatile microfluidic pump transports discrete volume to specific target locations. However, backflow in the pulsatile microfluidic pump often decreases the pumping efficiency and causes unwanted sample mixing due to unsteady boundaries. Employing the concept of a transistor, we developed a pneumatically controlled microfluidic rectifier (PCMR) that prevents backflow in the pulsatile flow regime. This PCMR was interconnected with a microfluidic pulsatile pumping system to characterize the functions of PCMR under continuous pumping sequences (CPS) and discrete pumping sequences (DPS) with various gate pressures on the PCMR. In the passive mode (zero gate pressure), 1.07% backflow for a DPS and 0.12% for a CPS were achieved. However, by adjusting the gate pressure on PCMR actively, we were able to achieve zero backflow for both pumping sequences at the cost of pumping efficiency. Interestingly, when the flow passes through the PCMR under the controlled gate-pressure, a fluidic oscillation was observed due to the force balance between the fluidic pressure and the gate-pressure. This microfluidic system successfully demonstrated half-rectification from various pulsatile flow profiles. By incorporating multiple three-microvalve systems in parallel with frequency modulation, a fully rectified flow pattern can be realized to enable steady laminar flow from pulsatile micropumps.