DNA Liquid Droplets Embedded in Cytoskeletal Networks

Actin is a model biomolecular gel. Above a critical overlap concentration c*, long, semi-flexible actin fibers entangle to produce a soft solid (shear modulus G' ~ 1 Pa). However, inside cells, actin networks exist in a complex environment that includes phase-separated liquid compartments called membraneless organelles. We investigate a model experimental system of biomolecular phase separation, DNA nanostars, in a network of entangled actin filaments. When nanostar droplets form, they are embedded in the three-dimensional actin network. Notably, droplets grow to sizes much larger than the mesh size of gel (actin mesh size: 300 nm, mean droplet diameter: 5 μm) and transiently entrain actin fibers inside the nanostar liquid. We also find that droplet-embedded actin networks stiffen substantially, G' ~ 100 Pa, 100 times higher than actin networks without droplets. These biomolecular materials composed of entangled polymer networks and phase-separated droplets may lead to an entirely new class of functional composites with tunable material properties.