Constant Pressure Microfluidic Pump System Based Droplet Sorting

Droplet microfluidic is an important branch of microfluidic technology, the manipulation of droplets has fundamental significance. Droplet separation is isolate target droplets from a large number of droplets, which can be used in droplet purification and enrichment. A stable fluid driving is the precondition of droplets generation and manipulation. There are various kinds of fluid driving, one commonly used is syringe pump, but it has many inherent shortcomings such as its distribution may be influenced by temperature variation, gel bubble and the screw speed, and it has bigger ripple, single injector has narrow flow range. Pneumatic driving pump has smaller ripple, faster response, but their cost is expensive and pressure control range is small.To combine these advantages of pneumatic pump, we developed a constant pressure microfluidic pump with two cylinders. Pressure control of these two cylinders is completely independent, this pump is suitable for droplet microfluidic research. It has many advantages such as wide pressure range(0.0-10.0 bar), high precision, stability (±1 mbar), fast response compared with other pumps. This system has two softwares for PC and Android tablet, they can communicate with the pump by WiFi, record experiment data in real time, show operation parameters with a friendly interface.Two kinds of sorting chip was designed by CAD software, used inverse piezoelectric effect of piezoelectric ceramic and dielectrophoresis force generated by non-uniform electric field respectively. Constant pressure microfluidic pump was used as the driving force of sorting. Firstly we studied the relationship of the droplet diameter, droplet generation speed and the ratio of oil phase pressure and water phase pressure where the pressure is 0-240 mbar. Found that for a fixed oil phase pressure, the bigger ratio of oil phase and water phase pressure leads to the smaller droplet and slower droplet formation, while for a fixed ratio the bigger oil phase pressure leads to the smaller droplet and faster droplet formation.Two sorting chips were used to separate droplets. Piezoelectric ceramic based chip can sort one droplet from 11 Hz droplets when add a single pulse to PZT and the pressure is 0?200 mbar. This chip can continuously sort 305 Hz droplets if add a continuous square wave to PZT and set oil phase pressure to 10000 mbar and water phase pressure to 1000 mbar. Dielectrophoresis sorting chip can pull all droplets to the target channel when applying appropriate voltage amplitude and frequency to the gold electrodes and the pressure is 0?450 mbar. Full separation needs higher voltage amplitude and lower frequency or inversely.Constant pressure microfluidic pump is suitable for microfluidic driving. Droplet sorting based on this pump is a basic research, lays the foundation for high speed micro droplet separation in the future.