Biomimetic subcellular structures from phase separation of an aqueous two-phase system

Hierarchical subcellular structures synergically regulate essential cellular activities through dynamic assembly. Despite extensive efforts, scientists and engineers have yet to reproduce a similar level of dynamics thoroughly. To understand and eventually demonstrate the dynamic structures and interactions, aqueous two-phase systems (ATPSs), emerge as a promising in-vitro model due to their all-water and biocompatible environment. Here, we design a smart ATPS consisting of poly (N-isopropyl acrylamide) (PNIPAM) and dextran. By regulating concentrations and ambient temperature, biomimetic subcellular structures such as phase-separated droplets and viscoelastic networks are generated through liquid-liquid phase separation and liquid-to-solid phase separation. The reversible changes of PNIPAM configurations from hydrophilic coils to hydrophobic globules enable the resulting ATPS to exhibit the reversible transition between liquid droplets and viscoelastic networks. Understanding the mechanism will enable precise control of the biomimetic subcellular structures, with potential implications on the regulation of the phase separation of biomolecular condensates.