Production of uniform drops of viscous liquids using a coaxial airstream

The effect of coaxial airstream velocity on the size of polymer solution droplets (300–1000 μm in diameter) extruded from a tapered needle have been measured and shown to be consistent with a force balance that equates the drag force to surface tension. However, droplet diameter was also dependent on polymer solution viscosity at higher air velocities (> 22 m/s), indicating that viscous dissipation forces must also be considered in the force balance. These results are relevant to the design of devices used to microencapsulate live mammalian cells which are based on similar extrusion techniques.