Droplet networks rearrange in response to electrical ruptures

The mechanics of membrane transport is important to understand for everything from drug delivery to biologically inspired batteries. In the lab, researchers often study this transport mechanics using small, lipid-coated aqueous droplets immersed in oil. But those networks are often static or change slowly on the time scale of the transport itself, limiting their adaptability and their usefulness for studying more dynamic transport networks.

In Biomicrofluidics, researchers report an early step toward studying droplet networks as they change by creating a network and selectively rupturing particular membranes within it using electrical pulses. They measured how the network reassembled after the ruptures and verified predictions for that reconfiguration based on the mechanical properties of the droplets’ surfaces.

In each rupture test, the researchers carefully measured out seven droplets — each about 800 micrometers across — of a solution containing dissolved salts and a small amount of an iron oxide (also called magnetite). After allowing time for a single layer of phospholipids to encase each droplet, the team collected all seven into a hexagonal grid using a permanent magnet. They then attached electrodes to two spots in the network and pulsed small voltages to rupture several of the intranetwork interfaces.

In tests of four different rupture patterns, the network coalesced into the same shape predicted by their model. In one case, there were two equally likely post-rupture shapes, and the observed collapse to one or the other was stochastic. In another case, mechanical forces favored coalescence into a three-dimensional arrangement. The authors say that the selective reconfiguration of such networks could enhance their utility as a biophysics testbed and may even lead to new methods for folding 3-D droplet structures.

Source: “Reconfiguring droplet interface bilayer networks through sacrificial membranes,” by Elio J. Challita, Michelle M. Makhoul-Mansour, and Eric C. Freeman, Biomicrofluidics (2018). The article can be accessed at https://doi.org/10.1063/1.5023386 .