(116r) Capsule Formation and Separation in a Microfluidic Device

Microfluidic devices can be used for many applications, including the formation of calcium-alginate capsules through a suspension polymerization in an oil solution from aqueous droplets of calcium chloride and sodium alginate. Calcium-alginate capsules have many potential uses, such as immunoisolation of cells. The high surface tension between the droplet of calcium chloride and sodium alginate necessitates the use of a surfactant and an elastomeric device with a judiciously chosen geometry. After creating the capsules, it is necessary to separate them out of the oil solution and into an aqueous solution. A common method of separation is centrifugation, which can damage both the capsules and the cells inside. The use of a microfluidic device with channel walls of disparate hydrophobicity has been shown to stabilize co-laminar flow of an oil phase and an aqueous phase. The disparity of hydrophobicity is accomplished by defining one side of the microfluidic device with a hydrogel. Due to the difference in surface energy within the channel, the aqueous stream is stabilized near hydrogel and the oil stream is stabilized near optical adhesive. The surface energy difference has shown promising results in separating the calcium-alginate capsules from the oil phase and into the aqueous phase.