(464i) Calcium-Alginate Capsule Formation and Passive Separation in Microfluidic Device

Microfluidic devices can be used for many applications, including the formation of well-controlled emulsions. In this study, the capability to continuously create mono-disperse droplets in a microfluidic device is used to form calcium-alginate capsules through chemical crosslinking from aqueous droplets of calcium chloride and sodium alginate suspended in an oil solution. Calcium-alginate capsules have many potential uses, such as immunoisolation of cells, microencapsulation of active drug ingredients, and encapsulation of bitter agents in food or beverage products. Capsule formation is accomplished through fusion of a sodium alginate droplet and a calcium chloride droplet. The high surface tension between the droplet of calcium chloride and sodium alginate necessitates the use of the surfactant sodium dodecyl sulfate (SDS) and a device with a judiciously designed 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 their contents. The use of a microfluidic device with channel walls of disparate hydrophobicity is used 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 the hydrogel poly (ethyl glycol) (PEG), which adheres to the glass surface of the device through the use of 3-(trichlorosilyl)-propyl methacrylate (TPM). Due to the difference in surface energy within the channel, the aqueous stream is stabilized near PEG and the oil stream is stabilized near a hydrophobic resin. The hydrophilic capsules travel to the interface of the oil and aqueous phase and are carried out of the device in the aqueous phase. The technique of continuous passive separation using co-laminar flow has shown promising results in separating the calcium-alginate capsules from the oil phase and into the aqueous phase. This unique method of passive separation can be used for other hydrophilic droplets and particles. The method is extended to the encapsulation of cells, molecules and particles of interest within the calcium alginate, and the entire process can be carried out under cell-friendly conditions.