Instructing Liquid-Liquid Phase Separation Inside Membranous Protocells

The bottom-up fabrication of compartmentalized cell-like entities represents a promising avenue for reconstituting hierarchical organization within cells and emulating life-like behaviors. Integrating the creation of semipermeable membranes and membraneless artificial organelles has recently garnered significant attention, aiming to achieve cytomimetic properties. We briefly describe the concept of liquid-liquid phase separation and review approaches for the fabrication of cell-sized membranous protocells (e. g., giant unilamellar vesicles, polymersomes and proteinosomes). Three strategies are emphasized for the construction of advanced cell-like structures consisting of liquid-like subcompartments enclosed by a membrane: (i) adsorption and assembly of organic or inorganic species onto the surface of preformed coacervate microdroplets; (ii) interfacial assembly of a lipid or polymer bilayer on the surface of an aqueous pool containing preformed microdroplets; and (ii) triggering phase separation within a preformed semipermeable membrane with chemical or physical stimuli. This review underscores the significance of the hierarchical organization of these synthetic cellular structures in mimicking cytomimetic functions, including transmembrane signaling, protocell communication, prototissue formation, and their compelling biomedical applications.