Droplet-based fabrication of alginate hydrogel microparticles in presence of surfactants

Alginate-based hydrogels are frequently employed in biomedical fields, where their size and uniformity are important for applications such as encapsulating pharmaceuticals or biological agents. In this paper, we study alginate droplet formation in a flow-focusing microfluidic device with a rectangular orifice of 30 x 100 microns in the presence of different types of surfactants in the continuous phase. This study looks at how surfactant type and concentration affect the generation of alginate microdroplets using droplet-based microfluidics, as well as how they affect the created alginate gel beads. To make alginate hydrogels, we used an external ionic cross-linking approach. Alginate hydrogels are formed by on-chip emulsifying a sodium alginate solution in an oil phase and collecting the emulsions in a bath containing calcium ions. Off- chip introduction of the cross-linking agents will reduce clogging issues that are common in droplet microfluidics. The diameter of microdroplets varies depending on the surfactant added to the continuous phase, either Span 80 or Tween 80, and the flow rate ratio between the dispersed and continuous phases. The conditions under which microdroplets form (the flow rate of the continuous phase and the surfactant supplied to it) determine the degree of gelation, shape, size, and monodipersity of hydrogels. Tween 80 emulsification results in the most homogeneous, totally gelled, tail-shaped hydrogels, whereas Span 80 emulsification results in smaller hydrogels with a more irregular size distribution. Using Span 80 resulted in partial gelation, necessitating a change in the collection bath (such as adding ethyl acetate to the oil phase).