Droplet Shape Analysis and Permeability Studies in Droplet Lipid Bilayers

Abstract

We apply optical manipulation to prepare lipid bilayers between pairs of water droplets immersed in an oil matrix. These droplet pairs have a well-defined geometry allowing use of droplet shape analysis to perform quantitative studies of the dynamics during the bilayer formation and to determine time-dependent values for the droplet volumes, bilayer radius, bilayer contact angle, and droplet centerline approach velocity. During bilayer formation, the contact angle rises steadily to an equilibrium value determined by the bilayer adhesion energy. When there is a salt concentration imbalance between the droplets, there is a measurable change in droplet volume. We present an analytical expression for this volume change and use this expression to calculate the bilayer permeability to water.

Interdroplet bilayer arrays in millifluidic droplet traps from 3D-printed moulds

“…6, the low-salt droplet decreases in volume over time, whereas the high-salt droplets increase in volume, indicative of osmotic water transfer from the low-salt to the high-salt droplets. 38,39 From Fig. 6 we estimate that the high-salt droplet increased in volume by 2 μL in a one-hour period.…”

“…5) between the low-salt and the two high-salt droplets, the osmotic permeability of the bilayer calculated according to Dixit et al is 23 μm s −1 , in good agreement with the literature. 38 It should also be noted that the interdroplet bilayer array was stable despite the imposed osmotic gradient and that the dye molecules used to colour the droplets (500 μM Direct Red 23 and 250 μM erioglaucine as the red and the blue dye, respectively) were not able to traverse the lipid bilayer.…”

The interactions of squalene, alkanes and other mineral oils with model membranes; effects on membrane heterogeneity and function

“…Any model system must, however, provide a true representation of the membrane environment under consideration. A variety of oils have been used during the generation of DIBs including different alkanes [3,4,12,13], mineral oil [14], squalene [3] and soybean oil [15] and whilst the propensity of some of this oil to remain within the bilayer has been demonstrated previously, the extent and consequences of these interactions has not been fully elucidated and appear to be dependent upon the specific oil used within the protocol. In one case, for example, it was calculated that 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) DIBs would contain 9.2% hexadecane (used in many DIB preparation protocols [3,12]) or 38% decane by volume [16].…”

Air-stable droplet interface bilayers on oil-infused surfaces

“…When amphiphilic phospholipids are introduced into an oil reservoir containing water droplets, droplet interface bilayers (DIBs) can form between adjacent water droplets (24,25). Recently, DIBs have emerged as an ideal model membrane system due to attractive features such as durability (26,27), tunable size and curvature (28)(29)(30), deformability (31), facile electrical characterization of ion channels (32)(33)(34)(35), the option to introduce asymmetry into the system (36), and droplet interchangeability (26,32). In the absence of any stabilizing agents, water droplets colliding in an immiscible fluid will exhibit coalescence when their interaction time exceeds the time required to drain the film of fluid trapped between the droplets (37,38).…”