Structure‐Property Relationships Governing Membrane‐Penetrating Behaviour of Complex Coacervates

Abstract Complex coacervates are phase‐separated liquid droplets composed of oppositely charged multivalent molecules. The unique material properties of the complex coacervate interior favours the sequestration of biomolecules and facilitates reactions. Recently, it is shown that coacervates can be used for direct cytosolic delivery of sequestered biomolecules in living cells. Here, it is studied that the physical properties required for complex coacervates composed of oligo‐arginine and RNA to cross phospholipid bilayers and enter liposomes penetration depends on two main parameters: the difference in ζ ‐potential between the complex coacervates and the liposomes, and the partitioning coefficient ( K p ) of lipids into the complex coacervates. Following these guidelines, a range of complex coacervates is found that is able to penetrate the membrane of living cells, thus paving the way for further development of coacervates as delivery vehicles of therapeutic agents.