Dispensing uniform droplets of phosphate buffer saline using electrohydrodynamic jetting

Abstract

Generating a stable cone jet regime in electrohydrodynamic (EHD) jetting for water or water-based solutions is difficult due to the high surface tension of the liquid. To overcome this challenge and produce uniform droplets of ∼O(100) μm, alternative EHD jetting regimes need to be investigated. This study presents EHD jetting characteristics using phosphate buffered saline (PBS). Three blunt-tip steel needles with internal diameters (IDs) of 100, 260, and 400 μm were used as electrodes. A high-speed camera was used to capture electrospray phenomena. The effect of flow rate and voltage on electrospray regimes, droplet size, generation frequencies, and velocities are presented. Regime maps are generated for PBS 1X, PBS 10X, and DI water, highlighting differences in spray characteristics due to electrical conductivity. The focus is on the Spindle regime, revealing unique observations not previously reported. The study demonstrates that a droplet generation frequency of 4314 Hz can be achieved in the Spindle regime, which is 308% of frequency in Microdripping, and the mean droplet size is ∼67% of size in the Microdripping regime. Based on these findings, recommendations are made for generating uniform droplets of PBS, including suggestions regarding the choice of the regime, nozzle dimensions, and electrode spacing.