Fundamentals of droplet generation in microfluidic devices

Microfluidic droplets are generated from simple oil-in-water or water-in-oil droplets to complex higher-ordered multi-compartment containing droplets and microcapsules. This chapter intends to explore the fundamental principles and novel advancements in droplet generation, emphasize its crucial preparation approaches and practical applications, and offer fresh perspectives for the future development of droplet microfluidics. Passive droplet generation in microfluidics involves geometric manipulation of channels and fluids to achieve droplet formation without external forces. On the contrary, active droplet generation involves applying external forces, including electrical, magnetic, acoustic, and thermal forces, via tunning the interfacial tension, channel wettability, fluid density, and viscosity to achieve droplet formation. Owing to miniaturization, precise control, and high-throughput capacity, droplet-based microfluidics' have found applications in various industries, including cell culture, biochemical analysis, and material synthesis. The ongoing progress in droplet microfluidics technology will offer further insights for forthcoming advancements.