Development of cell-mimetic sponge droplets stable to coalescence

The advent of synthetic cells has allowed the precise reconstruction of cellular functionalities by offering well-defined systems for compartmentalization of biomolecules and biochemical reactions. Coacervates are liquid-liquid phase separated microdroplets that have emerged as an attractive synthetic cell model owing to their robustness of formation and molecularly crowded nature. Sponge droplets are coacervates composed of a bicontinuous network of surfactant bilayers interspersed by aqueous channels, and are engineerable in a facile manner. However, a significant limitation to the use of these sponge droplets as synthetic cell mimics, is their inherent tendency to coalesce, a process wherein smaller droplets rapidly fuse in solution to form a single separate phase, and therefore the identities of the individual microcontainers is lost. Here, we describe for the first time, a strategy for developing sponge droplets that are stable to coalescence. Programming the surface of sponge droplets with a peripheral protein layer endows them with a resistance to fusion. Our data shows that despite the peripheral protein layer; these stable sponge droplets retain their sponge-like nanostructure and ability to sequester molecules in a programmable fashion. Remarkably, perturbing the protein layer eliminates their stability, and the droplets become susceptible to coalescence, over again. Our results delineate a novel approach for the construction of fusion-resistant sponge droplets using an interfacial protein coating, which allows robust generation of distinct cell-mimetic microcompartments that combine the utilities of lipid membrane-based self-assembled systems and coacervate droplets.