Inkjet printing is the most widespread technological application of microfluidics. It is characterized by its high drop productivity, small volumes, and extreme reproducibility. This review gives a synopsis of the fluid dynamics of inkjet printing and discusses the main challenges for present and future research. These lie both on the printhead side—namely, the detailed flow inside the printhead, entrained bubbles, the meniscus dynamics, wetting phenomena at the nozzle plate, and jet formation—and on the receiving substrate side—namely, droplet impact, merging, wetting of the substrate, droplet evaporation, and drying. In most cases the droplets are multicomponent, displaying rich physicochemical hydrodynamic phenomena. The challenges on the printhead side and on the receiving substrate side are interwoven, as optimizing the process and the materials with respect to either side alone is not enough: As the same ink (or other jetted liquid) is used and as droplet frequency and size matter on both sides, the process must be optimized as a whole.

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