Kinetic Control over Droplet Ripening in Fuel-Driven Active Emulsions

Active droplets are made of phase-separated molecules that are activated and deactivated by a metabolic reaction cycle. Such droplets play a crucial role in biology as a class of membrane-less organelles. Moreover, theoretical studies show that active droplets can evolve to the same size or spontaneously self-divide when energy is abundant. All of these exciting properties, i.e., emergence, decay, collective behavior, and self-division, are pivotal to the functioning of life. However, these theoretical predictions lack experimental systems to test them quantitively. Here, we describe the synthesis of synthetic active droplets driven by a metabolic chemical cycle and we find a surprising new behavior, i.e., the dynamics of droplet-growth is regulated by the kinetics of the fuel-driven reaction cycle. Consequently, these droplets ripen orders of magnitude faster compared to Ostwald ripening. Combining experiments and theory, we elucidate the underlying mechanism, which could help better understand how cells regulate the growth of membrane-less organelles.