Numerical and experimental investigation of a flow focusing droplet-based microfluidic device

Abstract

Droplet-based microfluidic devices are widely used for drug delivery and cell transport. In most of these applications, flow characteristics and geometry strongly affect the droplet generation process. In this study, a flow focusing droplet generator was designed using numerical simulation. Among all the simulation methods, the 2D phase field method was used to predict the process in a newly designed microfluidic device before fabrication. To this end, the numerical method was verified according to previous research, including ten different cases, which demonstrated its applicability in this regard. The deviation of simulations from experiments was less than 5%. The device was then simulated over a wide range of flow rate ratios (φ) and fabricated based on these results. Following fabrication, experiments were conducted for different ratios. The experimental results were compared with the simulations qualitatively and quantitatively. The investigation revealed pre-estimation effectiveness, indicating that the deviation of simulations from experiments was at most 11%. A wide range of φ from 0.25 to 1.05 was applied to study the droplet generation characteristics during the tests. Furthermore, two fundamental modes were introduced, and the flow regime shift from squeezing to dripping was studied over a wide range of φ. Given the droplets’ shape, the transition procedure is divided into three stages: pre-transition, transition, and post-transition. This study’s results can be used to investigate the capabilities of a newly designed microdevice before fabrication and choose the best flow regime that simultaneously reduces shear stress on cells and increases droplet generation frequency and monodispersity. Finally, this passive design can transport cells inside droplets up to 280 samples per second.