Open Droplets: Programming Chemical Flow in Microfluidics

J-C. Baret
University of Bordeaux,

Keywords: fluidics, microfluidics


Droplet-based microfluidics is the key technology for the miniaturization and automation of assays in microcompartments. It relies on the use of emulsion droplets as microreactors each encapsulating a biological system of interest (genes, cells, drugs,...) which can be analyzed at a ultra-high throughput. However, emulsions are metastable dispersions in which molecular transport is a major mechanism driving the system towards its state of minimal energy. In practice, such a molecular transport leads to the breakdown of the compartmentalization principle. Determining the underlying mechanisms of molecular transport between droplets is therefore essential. It is however in general challenging due to the complexity of a typical emulsion system. Here we introduce the concept of ?minimal emulsions?, which are controlled emulsions produced using microfluidic tools, simplifying an emulsion down to its minimal set of relevant parameters. We use these minimal emulsions to unravel the fundamentals of transport of small organic molecules in water-in-fluorinated-oil emulsions, a system of great interest for biotechnological applications. Our results are of practical relevance to guarantee a sustainable compartmentalization of compounds in droplet microreactors and to design new strategies for the dynamic control of droplet compositions. They also lead to new means to actively control the transport of molecules from the interior of the droplets to its exterior, which is a key elementary for the build up of a new generation of cell-like microcompartments, opening the door to chemical programming in soft matter systems. Ref: P. Gruner, B. Riechers, B. Semin, J. Lim, A. Johnston, K. Short & J.-C. Baret, Nature Communication, 7, 10392 (2016)