Abstract
Coarsening, the growth of larger structures at the expense of smaller ones, is a fundamental process in multiphase systems. The cell cytoplasm is an example of an out-of-equilibrium multiphase system in which molecular phase-separated condensates nucleate and grow within an active fluid composed of biopolymers and energy-consuming enzymes. Here we uncover the mechanisms that govern the growth of condensates in a self-stirring active fluid. We study the coarsening of synthetic DNA-based condensates embedded within a three-dimensional reconstituted cytoskeleton composed of microtubules and molecular motors. By combining experiments and modelling, we explain the absence of self-similarity in active coarsening and the origin of the continuously varying coarsening exponents for condensates within either active or passive fluids. The coarsening dynamics are set by the statistics of binary collisions among droplets, which depend on their size-dependent motility, irrespective of their active or passive origins. We find that the scaling exponent of the collision kernel is a unifying control parameter for the coarsening and the size distribution of motile condensates. Our results expand our understanding of phase separation in far-from-equilibrium systems, with potential implications in materials science and biology.