Pneumatic Dispensing System
Dispensing mechanism using integrated backflow stopper
The dispensing mechanism is briefly illustrated below. First, negative pressure is applied to the flexible membrane, which flexes slightly upward (to glass part) and thus sucks the liquid through the inlet hole. Then positive pressure is applied to the membrane, which flexes downward to close the inlet hole with the bump structure. After the membrane covers the inlet, the applied positive pressure pushes the membrane further down, thus driving the liquid away from the chamber and dispensing the liquid through the outlet. During the dispensing process, the bump structure with the inlet hole functions as a flow-restrictor. Although established micropumps use passive check valves which close the inlet by diaphragm deflection, our backflow stopper is different in the sense that the flexible membrane itself closes the inlet during dispensing actuation without any valve. In addition, the design and fabrication of our system is simple because the bump structure stops the backflow.
A cartridge-type pneumatic dispensing system
A simple yet effective cartridge-type (i.e. an integrated liquid reservoir) pneumatic dispensing system is developed and characterized. The unique design was a backflow stopper inside the dispensing chip to function as a flow restrictor. A thin flexible membrane with computer-controlled pneumatic actuation is used to produce various droplet volumes. MEMS fabrication techniques are adopted to fabricate dispensing chips in order to earn target volume based on characterized design parameters. Systematic characterization verified the performance of our device. Current device configuration can dispense droplet volumes from 200 nL to 1000 nL by controlling the pressure applied to the flexible membrane.