Stable Membraneless Complex Coacervate Microdroplets

Complex coacervation is the phenomenon of liquid-liquid phase separation driven by electrostatic association of oppositely charged multivalent macromolecules in aqueous media, creating coacervate microdroplets enriched with charged moieties. These membraneless microdroplets possess numerous attributes desired in lipid-free protocell models and colloidal bioreactors, including spontaneous self-assembly leading to compartmentalization, stability across a wide range of physiochemical conditions (temperature, pH, and ionic strength), and crowded environments that mimic the interior of cells. Moreover, the self-assembly processes that drive coacervation result in highly selective sequestration of (bio)molecules into the crowded coacervate environments. Concomitantly, the membraneless coacervate-water interface facilitates rapid transport of small molecules, resulting in significant acceleration of bioreactions in coacervate microdroplets. However, the membraneless coacervate-water interface that facilitates many of the bio(techno)logical functions of the coacervate microdroplets also facilitates their coalescence, resulting in their rapid coarsening. In this presentation, we will demonstrate our progress on stabilization of complex coacervate microdroplets composed of oppositely charged homopolyelectrolytes by addition of anionic comb polyelectrolytes. We will also demonstrate tunability of microdroplet size and show that the droplets remain stable in solution for several months and can withstand high ionic strength environments. Furthermore, we will demonstrate strong partitioning of proteins into these droplets accompanied by an up to 10-fold increase in enzyme-mediated bioreaction rates. Due to the low cost of the constituent polymers, these results will be argued to pave the way for the use of stabilized coacervate dispersions as economical, large-scale bioreactors.