A microfluidic droplet generator based on a piezoelectric actuator.

Droplet based microfluidic systems have been shown to be most valuable in biology and chemistry research. However droplet modulation and manipulation requires still further improvement in order to make this technology feasible particularly for biological applications. On demand generation of droplets and droplet synchronization, which is crucial for coalescence, remain largely unanswered. The present study describes a simple and robust droplet generator based on a piezoelectric actuator which is integrated into a microfluidic device. The droplet generator is able to independently control the droplet size, rate of formation and distance between droplets. Moreover, the droplet uniformity is especially high, deviating from the mean value by less than 0.3%. The cross flow and T-junction configurations are tested and show no significant differences, yet the inlet to main channel ratio is found to be important. As this ratio increases, droplets tend to be generated in bursts instead of individually. The physical mechanisms involved are discussed, providing insight into optimized design of such systems.