Dynamic morphologies of microscale droplet interface bilayers

Abstract

Droplet interface bilayers (DIBs) are a powerful platform for studying the dynamics of synthetic cellular membranes; however, very little has been done to exploit the unique dynamical features of DIBs. Here, we generate microscale droplet interface bilayers (μDIBs) by bringing together femtoliter-volume water droplets in a microfluidic oil channel, and characterize morphological changes of the μDIBs as the droplets shrink due to evaporation. By varying the initial conditions of the system, we identify three distinct classes of dynamic morphology. (1) Buckling and fission: when forming μDIBs using the lipid-out method (lipids in oil phase), lipids in the shrinking monolayers continually pair together and slide into the bilayer to conserve their mass. As the bilayer continues to grow, it becomes confined, buckles, and eventually fissions one or more vesicles. (2) Uniform shrinking: when using the lipid-in method (lipids in water phase) to form μDIBs, lipids uniformly transfer from the monolayers and bilayer into vesicles contained inside the water droplets. (3) Stretching and unzipping: finally, when the droplets are pinned to the wall(s) of the microfluidic channel, the droplets become stretched during evaporation, culminating in the unzipping of the bilayer and droplet separation. These findings offer a better understanding of the dynamics of coupled lipid interfaces.

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].…”

Synthetic Biology in Aqueous Compartments at the Micro- and Nanoscale

“…Figure 3 displays some of the clusters that could be formed from multiple DIBs, including a 3-droplet cluster configuration, a 5-droplet cluster, or a 10-droplet chain. [15] For the 3-droplet cluster, the system still evaporated into the shape of a single sphere, but now the interior was partitioned into three equivalent compartments by three bilayers. Similarly, the 5-droplet cluster evaporated into a sphere with five compartments.…”

Dynamic Morphologies and Stability of Droplet Interface Bilayers

“…A number of membrane proteins have also been successfully reconstituted across DIBs, including the viral potassium channel Kcv, the light-driven proton pump bacteriorhodopsin, and the mechanosensitive channel of large conductance (MscL) [17][18][19][20]. Given these advantages, the potential applications of DIBs are wide-ranging, from droplet arrays for ion channel screening [19,20] and chemical microreactors [21,22] to responsive materials [9,23,24] and mimics of electrical circuits and logic gates [25].The stability of DIBs, however, remains a major issue [3,26,27], especially for DIBs below several hundreds of microns [26]. Furthermore, when DIBs become unstable, their morphological evolution is extremely rich [27].…”

“…Given these advantages, the potential applications of DIBs are wide-ranging, from droplet arrays for ion channel screening [19,20] and chemical microreactors [21,22] to responsive materials [9,23,24] and mimics of electrical circuits and logic gates [25].The stability of DIBs, however, remains a major issue [3,26,27], especially for DIBs below several hundreds of microns [26]. Furthermore, when DIBs become unstable, their morphological evolution is extremely rich [27]. As the droplets shrink due to evaporation, the lipid bilayer can (i) zip and increase in size, (ii) unzip until the droplets eventually detach, or (iii) the system can shrink almost uniformly.…”

“…Second, our theory predicts a size limit of stable DIBs. For the typical materials used in references [26,27], DIBs smaller than O(100 µm) can become unstable. Third, we elucidate a mechanistic understanding for both the dynamic morphology diagram and DIB stability, arising out of a competition between four characteristic timescales: lipid desorptions for the (i) mono-and (ii) bi-layers, (iii) droplet evaporation, and (iv) lipid exchange between the mono-and bi-layers.We begin by describing our model for lipid kinetics.…”