Droplet Shape Control Using Microfluidics and Designer Biosurfactants

Many uses of emulsion droplets require precise control over droplet size and shape. Here we report a ‘shape-memorable’ micro-droplet formulation stabilized by a polyethylene glycol (PEG)-modified protein-surfactant, the droplets are stable against coalescence for months and can maintain non-spherical shapes for hours, depending on the surface coverage of PEGylated protein. Monodisperse droplets with aspect ratios ranging from 1.0 to 3.4 were controllably synthesized with a flow-focusing microfluidic device. Mechanical properties of the interfacial protein network were explored to elucidate the mechanism behind the droplet shape conservation phenomenon. Characterization of the protein film revealed that the presence of a PEG layer at interfaces alters the mechanical responses of the protein film, resulting in interfacial networks with improved strength. Taking advantage of the prolonged stabilization of non-spherical droplets, we demonstrate the possibility of functionalization of the droplet interface with accessible biotin moieties. The stabilization of micro-droplet shape with surface-active proteins that also serve as an anchor for integrating functional moieties, provides a tailorable interface for diverse applications.