Modelling on the droplet formation and optimizing of the microfluidic cartridge used for the microfluidic impact printing

Microfluidic impact printing (MIP), which was proposed recently as a drop-on-demand microdroplet generation technology, shows a promising future in precision liquid handling. However, the working principle of the droplet formation and the performances of the generated droplets from the microfluidic chip are still unclear. In this article, we build a MIP system for multiplexed microdroplet dispensing, and develop a theoretical model to analyze the process of the droplet generation. As a result of the theoretical model which was validated against finite element simulations and experiments, the volume and the ejection velocity of the printed droplets can be predicted, demonstrating that the structure of the microfluidic cartridge plays the core role in the system. Based on the model, we have introduced a converging channel in the design of the cartridge to improve the performance of printing system. Owning to the asymmetric transfer characteristic of the converging channel, the aspirated volume of the air could be reduced by 40% during the membrane restoring, and the liquid in the cartridge reaches stability to the initial pre-printing state faster, that would enable the MIP system has a wider adjustable range of droplet volume and a higher printing frequency.