Dual-Stimulus Programmed Multiphase Separation and Organization in Coacervate Droplets

Stimuli-responsive (multiphase) coacervates deserve significant attention as cell-like entities that can adapt to their environment and undergo morphological reconfiguration. In this study, a tandem-triggered transition system is presented that enables the transformation of single-phase coacervates into multiphase structures through the sequential application of two external stimuli: pH and salt concentration. A polyanion containing acid-labile amide bond is incorporated into the membrane-less coacervates. Upon exposure to an acidic pH, hydrolysis of the amide bond induces charge reversal from polyanion to polycation, triggering the first transition from single-phase to nested multiphase coacervates. This transformation alters the spatial redistribution and viscosity of coacervate components and influences sequestration behavior toward various (macro) molecules. Subsequently, the introduction of hypertonic environment as secondary stimulus induces selective dissociation and structural reconfiguration of nested multiphase coacervates into vesicular-like multiphase coacervates, further altering the coacervate components' fluidity and partitioning properties. Notably, the diverse inherent properties of coacervates among this tandem-triggered transition enables the variation of spatial organization for enzymatic reactions. Overall, the findings demonstrate a strategy for the sequential control of coacervate structural reconfiguration through dual stimuli, providing a versatile platform for the development of programable and adaptive coacervate-based protocells.