RESUMEN
Sample deposition based on micro-droplet ejection has broad application prospects in the field of biomedicine. Ejection of RPMI-1640 medium (with and without cells) is investigated experimentally using a home-build electrohydrodynamic (EHD) ejection system, consisting of a liquid supplier and a nozzle, a high voltage source, a droplet collector, and a high speed photography module. High electric voltage is applied between the nozzle and the droplet collector. The liquid surface is electrically charged and the ejection takes place when electric force overcomes the surface tension. The ejection process is studied by using high speed photography and image processing. At low voltage, a stable ejection state is established with ejection frequency ranging from a few to a few tens of Hertz. At high voltage, another stable ejection state is reached with ejection frequency as high as 1300 Hz. At the transition voltage range, the ejection exhibits a periodic behaviour. During each cycle, the meniscus rapidly oscillates with gradually increased amplitude, and with several non-uniform droplets ejected at the final stage of the cycle. Human peripheral blood mononuclear cells, after ejection, shows survival rates higher than 79%, manifesting EHD ejection as a promising technique for cell printing.
