Fast membrane hemifusion via dewetting between lipid bilayers.

The behavior of lipid bilayers is important to understand the functionality of cells like the trafficking of ions. Standard procedures to explore the properties of lipid bilayers and hemifused states typically use supported membranes or vesicles. Both techniques have several shortcomings in terms of bio-relevance or accessibility for measurements. In this article, the formation of individual free standing hemifused states between model cell membranes is studied using an optimized microfluidic scheme which allows for simultaneous optical and electrophysiological measurements. In the first step, two model membranes are formed at a desired location within a microfluidic device using a variation of the droplet interface bilayer (DiB) technique. In the second step, the two model membranes are brought into contact forming a single hemifused state. For all tested lipids, the hemifused state between free standing membranes forms within hundreds of milliseconds, i.e. several orders of magnitude faster than those reported in literature. The formation of a hemifused state is observed as a two stage process, whereas the second stage can be explained as a dewetting process under no-slip boundary conditions. The formed hemifusion states have a long lifetime and a single fusion event can be observed when triggered by an applied electric field as demonstrated for monoolein.