Dilute but Dense - Reversible Crosslinking Enables Water-Rich (Bio)polymer Condensates

Area of Science:

• Soft Matter Physics
• Polymer Science
• Materials Science

Background:

• Liquid-liquid phase separation (LLPS) is crucial for biomolecular condensates and functional soft materials.
• Traditional LLPS mechanisms involve solvent quality changes or associative coacervation.

Purpose of the Study:

• To demonstrate a novel, purely entropic mechanism for LLPS driven by reversible crosslinking.
• To explore the phase behavior and condensate properties resulting from this connectivity-driven mechanism.

Main Methods:

• Coarse-grained simulations of a minimal bead-spring polymer model in a good solvent.
• Analysis of phase behavior, including closed-loop coexistence and re-entrant percolation.
• Comparison with mean-field Semenov-Rubinstein theory.

Main Results:

• Transient, pairwise crosslinks alone can induce LLPS at very low polymer densities.
• Formation of highly swollen, water-rich condensates.
• Phase boundaries are robust to crosslinkable domain sequence, except for highly blocky sequences.

Conclusions:

• Reversible crosslinking provides an entropy-enabled mechanism for mesoscale organization.
• This mechanism offers pathways for designing programmable, membraneless materials.
• Findings are relevant for synthetic materials and biological contexts like RNA-protein interactions.