Accelerated Ostwald ripening by chemical activity

Biomolecular condensates are ubiquitous in living cells, promoting enzyme-substrate colocalization and enabling membrane-free compartmentalization. One passive mechanism of condensate coarsening is Ostwald ripening, in which large droplets grow at the expense of small ones due to Laplace-pressure differences. In this regime, Lifshitz-Slyozov theory predicts that the average droplet volume increases linearly with time. However, cells routinely utilize energy-consuming processes to regulate condensate dynamics. We were therefore motivated to devise a theory pinpointing if and how active chemical reactions, interconverting molecules between phase-separating and inert forms, might drive faster condensate coarsening. We find that mass conservation limits droplet volume growth to being linear in time regardless of activity, resembling the passive case. However, if reactions are restricted to occur only outside droplets, the rate of Ostwald ripening can be increased by an arbitrarily large factor. We posit that the ability to induce rapid biocondensate coarsening can be advantageous in synthetic-biological contexts, e.g., as a regulator of metabolic channeling.