The typical structure of biopolymer coacervates are spherical droplets; however, they can have porous structures that occur via interactions with other intracellular structures, such as the nuclear membrane. For example, the viscoelastic phase separation (VPS) of chromatins partly tethered to the cell nuclear membrane is expected to be used to form a sponge-like chromatin structure . Like this, the interaction between biopolymer coacervates and a tiny, confined environment often plays essential roles in self-organized structure formations.