Droplet-based microfluidics has a variety of applications, such as material synthesis and single-cell analysis. In this paper, we propose a modular microfluidic system using projection micro-stereolithography three-dimensional (3D) printing technology for droplet generation. All modules are designed using a standard cubic structure with a specific leakage-free connection interface. Versatile droplets, including single droplets, alternating droplets, merged droplets, and Janus particles, have been successfully produced. The droplet size and the generation rate can be flexibly controlled by adjusting the flow rates. The influence of the flow rate fraction between the discrete phase and the continuous phase over the generation of the alternating and merged droplets is discussed. Furthermore, the 'UV curing' module can be employed to solidify the generated droplets to avoid coalescence and fix the status of the Janus particles. The proposed modular droplet generators are promising candidates for various chemical and biological applications, such as single-cell incubation, screening of protein crystallization conditions, synthesis of nanoparticles, and gene delivery. In addition, we envision that more functional modules, e.g., valve, microreactor, and detection modules, could be developed, and the 3D standardized modular microfluidics could be further applied to other complex systems, i.e., concentration gradient generators and clinical diagnostic systems.
Keywords: droplet generation; modular microfluidics; standardized microfluidics.