A 3D printed size-tunable flow-focusing droplet microdevice to produce cell-laden hydrogel microspheres

Flow-focusing droplet generators have been extensively employed for the generation of monodisperse droplets. However, the droplet device is usually designed with an application-specific performance that includes prescribed droplet size and generation frequency. To achieve an ideal device, cost- and time-inefficient iterations for the chip design and fabrication are usually needed. In this study, we take an advantage of 3D printing technology to rapidly prototype the droplet device that enables the facile control of the droplet size as well as the droplet generation frequency. Our device was designed with a screw-and-nut combination and the gap height (h_g) between the dispersed phase outlet and the orifice could be easily and finely controlled by rotating the head of the threaded screw. The h_g values can be precisely adjusted from 0 to 2000 μm supported by 20 designated control teeth on the screw head, which enable us to produce droplets in different sizes or in the same size with different generation frequencies. The proposed 3D printed device was employed to synthesize a variety of Ca-alginate microspheres containing A549 cells. The facile assembly of the screw-and-nut components allows us to prepare the droplet generator in a simple yet effective manner, and the size controllability of the droplets resulted in the production of various sizes of A549 cell-encapsulated microspheres, which can be used for drug screening.