Structural Phase Separation of Membranes and Fibers.

Lipid membranes interact with protein filaments on a superstructural level such that they may colocalize or spatially segregate in a living cell, whereas higher-order organization of membranes and fibers is less well explored in artificial systems. Herein, we report on the structural separation of a dispersed, membranous phase and a continuous, fibrous phase in a synthetic system. Systematic characterization of its thermodynamics and kinetics uncovers a physical principle governing phase separation: Interlamellar repulsion, favoring expansion of the membranous phase, is balanced by fibrous network elasticity, preferring the opposite. A direct consequence of this principle is the spatial addressability of the phase separation, preferably localized to soft regions of the fibrous network. Guided by this principle, we design a fibrous network with different spatial heterogeneity to modulate the phase separation, realizing a "memory" effect, patterned separation, and gradient separation. The current spatially addressable phase separation is in great contrast to the conventional ones, in which nucleation is difficult to predict or control. The fact that the membranous and fibrous phases compete for space has implications for the intracellular interactions between endoplasmic reticulum membranes and cytoskeletal filaments.