Liquid-Liquid Phase Separation in an Elastic Network

Abstract

Living and engineered systems rely on the stable coexistence of two interspersed liquid phases. Yet, surface tension drives their complete separation. Here, we show that stable droplets of uniform and tunable size can be produced through arrested phase separation in an elastic matrix. Starting with a cross-linked, elastic polymer network swollen by a solvent mixture, we change the temperature or composition to drive demixing. Droplets nucleate and grow to a stable size that is tunable by the network cross-linking density, the cooling rate, and the composition of the solvent mixture. We discuss thermodynamic and mechanical constraints on the process. In particular, we show that the threshold for macroscopic phase separation is altered by the elasticity of the polymer network, and we highlight the role of correlations between nuclei positions in determining the droplet size and polydispersity. This phenomenon has potential applications ranging from colloid synthesis and structural color to phase separation in biological cells.

Drops and fibers — how biomolecular condensates and cytoskeletal filaments influence each other

“…(b) A dense cytoskeletal network can restrict the movement of embedded condensates and thereby hindering their fusion [27,75]. Furthermore, the growth of condensates can be controlled via elastic ripening, which is the growth of condensates in a soft environment on the expense of condensates in stiff networks [76][77][78].…”

“…When condensates grow, they can push the network outwards, which in turn applies a counterforce on the drops. This limits their growth and thereby narrows the size distribution of condensates [76]. Furthermore, the elastic energy can tune the nucleation and ripening of condensates.…”

ATP-Dependent Diffusion Entropy and Homogeneity in Living Cells

“…Cells have been shown to undergo an LLPS process that tends to segregate intracellular material into distinct areas, without the need for intracellular, membrane-bound organelles [ 14 , 15 , 16 ]. LLPS has been shown to influence cells’ physiology and pathophysiology.…”

“…According to the LLPS principle, liquid droplets consisting usually of a mixture of macromolecules, such as RNA and proteins, are created inside the liquid cytoplasm of living cells due to a phase separation process [ 15 ]. While creation of LLPS is controlled by a variety of parameters, including mixture composition, structure, and temperature [ 16 ], the LLPS-induced droplets may represent "active liquids" that are in a metastable state and consume ATP to control their fluidity [ 15 ].…”

Phase separation in swelling and deswelling hydrogels with a free boundary

“…The volume changes induced by this process lead to deformation of the boundary in contact with the surrounding bath as well as a host of patterns within a shrinking gel [17]. The polymer matrix can impede growth of the solvent-rich domains beyond a certain size, which is exploitable for applications: In [18], the authors use this arrested phase separation in a polymer gel to produce droplets of tunable size. The range of new potential applications that explore or exploit the relationship between forced mass transport and heterogeneous microstructures [19], for example in extreme mechanics, have led to a sharp rise in the interest in phase transitions of gels, as documented in the topical review by Dimitriyev et al [20].…”