Alginate gelation in microfluidic channels

In this work we present the findings from a study which aims to produce monodisperse alginate gel droplets within a microfluidic system. To produce alginate drops two aqueous streams, one acidic and one containing alginate and calcium carbonate, merge immediately prior to entering a channel where a continuous flow of sunflower oil breaks the flow of the aqueous phase to form microdroplets. Flow diagrams, which show the relation between the flow rates of the fluids and the flow patterns within the channels, have been produced for different concentrations of alginate, acid and calcium carbonate. It has been found that the production of monodisperse get drops is governed by two independent factors: the time required for the formation of an alginate structured solution, which depends on the concentrations of the reagents, and the drop formation time, which depends on the flow rates of the fluids. If the drop formation time is shorter than the structuring time regular drop formation is observed, otherwise an alginate structured solution obstructs the channels. The mechanism of drop formation has also been studied and compared with break-up models reported in the literature. (C) 2007 Elsevier Ltd. All rights reserved.