Coaxial air flow device for the production of millimeter-sized spherical hydrogel particles

We describe a method to produce millimeter-sized hydrogel particles, by dispersing aqueous droplets in an oil using a nozzle and subsequently solidifying them. We show that we can vary the size of the particles using an air flow along the nozzle. The resulting particle size can be well predicted by a simple model where a drag force generated by the air flow, adds to the weight pulling the droplet from the nozzle. Particles produced using this method have diameters ranging from 0.7 to 2.3 mm. Production rates up to 0.5 ml/min per nozzle have been achieved, which compares favorably to standard microfluidic techniques. Finally, we show that the method can be used to produce both physical and chemical gel particles and is thus highly universal.