  For the past decade, droplet interface bilayers (DIBs) have had an increased
prevalence in biomolecular and biophysical literature. However, much of the
underlying physics of these platforms are poorly characterized. To further the
understanding of these structures, a study of lipid membrane tension on DIB
membranes is measured by analysing the equilibrium shape of asymmetric DIBs. To
this end, the morphology of DIBs is explored for the first time using confocal
laser scanning fluorescence microscopy (CLSM). The experimental results confirm
that, in accordance with theory, the bilayer interface of a volume asymmetric
DIB is curved toward the smaller droplet and a lipid asymmetric DIB is curved
toward the droplet with the higher monolayer surface tension. Moreover, the DIB
shape can be exploited to measure complex bilayer surface energies. In this
study, the bilayer surface energy of DIBs composed of lipid mixtures of
phosphatidylgylcerol (PG) and phosphatidylcholine (PC) are shown to increase
linearly with PG concentrations up to 25%. The assumption that DIB bilayer area
can be geometrically approximated as a spherical cap base is also tested, and
it is discovered that the bilayer curvature is negligible for most practical
symmetric or asymmetric DIB systems with respect to bilayer area.
