An accessible droplet-on-demand device that combines 3D printing fabrication and commercially available nozzles

Droplet on Demand (DOD) devices are an important tool for generating single droplets of controlled size in various fluid studies. DOD designs have grown to be simpler and more accessible in terms of fabrication and cost by using SLA (resin) 3D printing techniques (Ionkin and Harris, Rev. Sci. Inst. 89, 116103 (2018)). The greatest limit to 3D printed DOD devices is in fabricating the nozzle with a sufficiently small orifice to produce smaller droplets. This challenge is further exacerbated when trying to use more common filament 3D printers. We show here a simple and effective modification to the DOD design that replaces the fabricated nozzle with two alternative nozzles readily available on the market: brass 3D printing nozzles and Luer Lock blunt-tip syringe needles. Both alternatives are available in a range of orifice sizes extending below the range of previously fabricated nozzles, thus allowing for droplet sizes smaller than those reported from work with recent DOD devices. We further show that the range of droplet sizes from a single nozzle/tip is larger than previously achieved allowing for more efficient experimentation.