Hagan Bayley and colleagues at Oxford University describe in their review article the development of 'droplet interface bilayers'. As Hagan describes below, this system mimics cell membranes and enables scientists to study functional properties of membrane proteins. This approach may help in the study of neurological and cardiac disease.

1.  Please explain, for a non-specialist, the significance of your article.
The article describes a simple miniaturized system for forming lipid bilayers: the droplet interface bilayer (DIB). Lipid bilayers are the basis of biological membranes, which envelope all our cells providing a barrier for entry and exit. Biological membranes also contain proteins, such as transporters (for the uptake and secretion of molecules), receptors (for intracellular signaling) and ion channels (to provide electrical excitability). Therefore, it was clear from the start that DIBs could form a starting point for improved methods to explore the functional properties of membrane proteins. 

2.  What has motivated you to conduct this work?
At first it was purely curiosity. Could bilayers be formed by such simple means? After this was demonstrated by Matt Holden and the bilayers were shown to be extraordinarily robust, it was clear that DIBs had many potential applications. Notably, ion channels and pores can be incorporated into them and single-channel recordings carried out with greatly reduced volumes of reagents. Around a quarter of the proteins encoded in the human genome are membrane proteins, but they have proven difficult to handle and hence we know far less about their functional properties than we do for soluble proteins. DIBs in various formats provide a basis for the rapid screening of membrane proteins. For example, DIB chips or microfluidic systems have the potential to screen thousands of prospective ion channel blockers, which would be immensely valuable for discovering treatments for neurological or cardiac problems.

3.  Where do you see this work developing in the future?
DIBs are versatile, and I believe many other groups will adopt the approach. For example, asymmetric bilayers (bilayers in which each leaflet has a different lipid composition) are readily formed, and lipid composition has a profound effect on the activity of certain ion channels. The effects of lipid asymmetry are less well documented. Double bilayers are trickier to make, but there are important proteins complexes that span them, so they are worth pursuing. 

Mark Wallace, a co-author of the review, has made DIBs at the interface between a single droplet and a flat surface, providing a stable and convenient platform for state-of-the-art fluorescence measurements on membrane proteins, which can be combined with electrical recording. This is an enormously powerful approach for examining problems as different as the gating of ion channels to membrane-protein assembly.

With my own group, besides pushing rapid screening technologies, I am intrigued by DIB networks. While two droplets are needed to form a single DIB, large networks of droplets can be formed, each connected to its neighbors through lipid bilayers, which can contain proteins that allow the droplets to "communicate". I think it might be possible to build devices from these networks that are more sophisticated than the liposomes that have been used for drug delivery or the protocells examined by researchers interested in the origins of life; DIB devices would be in a sense prototissues. A chancy area, but academic scientists should take risks.  

4.  Are there any particular challenges facing future research in this area?
Right now, it is low-lying fruit. However, there are difficulties that may seem boring or trivial. But they are not- all of science is driven forward by technology, often solving seemingly minor problems. For example, with DIBs we need better means for introducing substances into droplets that have already been formed. There is also no general foolproof method for transferring membrane proteins into lipid bilayers- a crucial issue, but try getting a grant for that!