  Emulsions are a central component of many modern formulations in food,
pharmaceuticals, agrichemicals and personal care products. The droplets in
these formulations are limited to being spherical as a consequence of the
interfacial tension between the dispersed phase and continuous phase. The
ability to control emulsion droplet morphology and stabilise non-spherical
droplets would enable the modification of emulsion properties such as
stability, substrate binding, delivery rate and rheology. One way of
controlling droplet microstructure is to apply an elastic film around the
droplet to prevent it from relaxing into a sphere. We have previously shown
that BslA, an interfacial protein produced by the bacterial genus Bacillus,
forms an elastic film when exposed to an oil- or air-water interface. Here, we
highlight BslA's ability to stabilise anisotropic emulsion droplets. First, we
show that BslA is capable of arresting dynamic emulsification processes leading
to emulsions with variable morphologies depending on the conditions and
emulsification technique applied. We then show that frozen emulsion droplets
can be manipulated to induce partial coalescence. The structure of the
partially coalesced droplets is retained after melting, but only when there is
sufficient free BslA in the continuous phase. That the fidelity of replication
can be tuned by adjusting the amount of free BslA in solution suggests that
freezing BslA-stabilised droplets disrupts the BslA film. Finally, we utilise
BslA's ability to preserve emulsion droplet structural integrity throughout the
melting process to design emulsion droplets with a chosen shape and size.
