Numerical investigation of electrohydrodynamic effect for size-tunable droplet formation in a flow-focusing microfluidic device

Droplet-based microfluidics has received much attention in biofabrication due to its compatibility with 3D printers that use cell-laden bioinks. In order to tailor the printing resolution, droplet generation under a DC electric field in a flow-focusing device is explored numerically. The major purpose of simulations is to investigate how geometry affects droplet production and electric field intensity. The effects of the orifice's length, injection angle, and shape are discussed regarding the electric capillary number Ca-e. Based on the retardation effect, the necking stage of droplet formation changes to expansion, and the frequency of droplet formation declines when the capillary number rises. For a particular value of the applied electric potential, orifice elongation reduces the induced electric field within the orifice. By adjusting the angle of side flow, smaller droplets can be formed, and the linear decrease in droplet size is provided across a wider range. The electric field in the orifice was amplified by 64% by creating a wedge-shaped orifice. In other words, when the notch angle was sharpened, the electric force increased, and the droplet diameter reduced. Since the frequency of droplet production varied only slightly between different notch angles, it could be preferable to generate smaller droplets without significantly altering the frequency of droplet formation.

Automated summary

Droplet-based microfluidics has been widely studied in biofabrication for its compatibility with 3D printers. Numerical simulations were conducted to investigate the effects of geometry on droplet generation and electric field intensity. The results showed that the necking stage of droplet formation changed to expansion with increasing capillary number, and orifice elongation reduced the induced electric field. Smaller droplets could be formed by adjusting the angle of side flow, and wedged-shaped orifice amplified the electric field. The frequency of droplet formation varied slightly with different notch angles.