In order to get the most of our a droplet microfluidic system, the microfluidic chip needs to be designed as a “droplet generator.” Droplets are typically generated by creating two liquid phases, one of which is an oil phase and the second of which is typically an aqueous phase. One of the phases is designated by the designer as the continuous phase while the other is the dispersed phase. Droplets are produced by incorporating channels and features in the microfluidic device that create the required hydrodynamic conditions for droplet formation, and the droplet formation process depends strongly on the interaction of flow rate, liquid physical properties and the geometry of the features on the chip.

The feature designs are typically classified as “co-flow”, “cross flow” and “flow focusing”. Co-flow is achieved using coaxial microchannels where the continuous phase flows in an outer concentric channel and the dispersed phase flows in the inner channel, both in the same direction. In the crossflow design the dispersed and continuous phases meet at an angle formed by fabricating intersecting microfluidic flow channels. The most common case is the T-junction, where dispersed and continuous phases converge in perpendicular channels. Other microfluidic channel designs for producing droplets via crossflow include the “K-junction” and the “V-junction”. Finally flow focusing designs incorporate a microfluidic contraction region through which coaxial immiscible streams flow and subsequently exit to a single microchannel resulting in the creation of uniform droplets. This method allows for making very small droplets as the formation process is closely related to the size of the narrow contraction.