Liquid DNA coacervates form porous capsular hydrogels via viscoelastic phase separation on microdroplet interface

Liquid-liquid phase separation (LLPS) droplets of biopolymers are known as functional microdroplets in living cells and have recently been used to construct protocells and artificial cells. The formation of DNA coacervates (also referred to as DNA droplets) from branched DNA nanostructures and the control of their physical properties via DNA nanostructure design were demonstrated previously. For the construction of artificial cells or protocells, however, even though physical effects such as surface tension, wetting, and viscoelasticity are more important in a tiny (micrometer-sized), confined environment than in a bulk solution environment, they have not been explored yet. This study shows that a tiny, confined environment using a water-in-oil (W/O) microdroplet interface modulates the phase separation dynamics of DNA coacervates, leading to micrometer-sized porous capsular structures. The porous structures were produced via two types of viscoelastic phase separation (VPS) processes in DNA coacervates: (i) simple VPS and (ii) cluster-cluster aggregation after VPS. Finally, it was shown that environmental chemical stimulation can manipulate porous capsular DNA hydrogels extracted from W/O microdroplets. These results provide an approach for designing and fabricating artificial cells or protocells with complex structures and physicochemical properties.