Associative Phase Separation-induced Precision Assembly (APSPA) in Aqueous Droplets

The emergence of remarkably organized functional structures from solutions in nature has fascinated both cell biologists and materials scientists. To introduce heterogeneity into an otherwise homogeneous solution, new and immiscible solution phases are required. One way to induce the appearance of such phases is through a liquid-liquid phase separation (LLPS) process, where the formation of a coacervate phase is triggered by a change in the solution composition, temperature, or pH. The resulting coacervate droplets can be used for compartmentalization. Thus, LLPS has aroused immense interest among scientists interested in understanding the origin of life, as well as biologists interested in understanding the intracellular transfer of molecules and information. LLPS can be classified into segregative LLPS and associative LLPS, with the driving force for phase separation arising from repulsive and attractive interactions, respectively. As a common segregative LLPS system, the aqueous two-phase system has been extensively used to fabricate controlled droplets, particles, and capsules, as well as jets and fibers, with biocompatible and dynamic properties. However, despite its prevalence in cell biology, for instance, in intracellular liquid organelles, associative LLPS has scarcely been investigated for the fabrication of materials with unique properties in such systems. For instance, although such molecular arrangements as the RNA sequence are known to affect the phase separation process, these sequence-specific molecules have not been systematically applied in assembly using associative LLPS systems. The inclusion of molecular arrangements as a parameter will provide more precise control over the assembly and properties of the resultant structures. A comprehensive understanding of associative LLPS will enable the engineering and design of coacervates and coacervate-templated materials with more sophisticated morphologies and functions. The aims of the proposed project are to (1) investigate the physics behind the assembly across the aqueous-aqueous interfaces of associative phase separation systems, (2) elucidate the role of sequence-specific molecular interactions in determining the phase separation dynamics and resultant droplet morphology, and (3) devise an associative phase separation-induced precision assembly (APSPA) platform for formulating novel and dynamic hierarchical materials. In the short term, the project will provide a fundamental understanding of the effect of macromolecular interactions between different molecules on associative LLPS and the APSPA of hierarchical structures with sequence-specific properties. In the long term, it will lay a foundation for understanding the emergence of functional hierarchical structures in solutions and for fabricating nature- and cell-inspired assembly, promising more coherent integration at the synthetic and natural interface.