Biologically-Inspired Active Droplets: from Reaction Crucibles to Robots(?)

Living cells need to organize chemical reactions. In school, we learned how lipid bilayers create and maintain compartments with distinct compositions. Most attempts to mimic biological compartmentalization have re-capitulated this strategy, with impressive results. However, since thermodynamics favors the formation of symmetric compositions across the bilayer, efficient encapsulation requires precise control of kinetic pathways, often using microfluidic devices.

In the last decade, we have come to appreciate that cells alternatively use the spontaneous phase separation of macromolecules to compartmentalize chemical reactions. This approach to encapsulation, based on thermodynamics, is robust and easy to implement. Here, I will introduce a very simple and flexible model system for creating droplets of protein that readily partition enzymes, and allow for easy exchange of substrate and product with their surroundings. I will quantify their ability to localize chemical reactions, and demonstrate their ability to sense and respond to external chemical gradients - a type of rudimentary chemotaxis.