Liquid-liquid phase separation within fibrillar networks

Liquid-liquid phase separation of protein condensates within the cell has recently been observed in a multitude of biological mechanisms. Ranging from dynamic biomolecular condensates such as stress granules and P-bodies to fibril-forming liquid protein aggregates, these liquid phase droplets are relevant to a variety of cellular mechanisms relating to health as well as to pathology. Within the cell, phase separation occurs within a complex viscoelastic medium which mediates the growth of such droplets. However, the physical principles underlying the droplets' formation, dynamics, and interaction with the viscoelastic medium are only now being developed. Here, we introduce a synthetic analog to biomolecular condensates within the cell. In this system, we demonstrate the formation of mesh-scale condensates constrained by a fibrillar network. We show that the competition between condensate capillarity and network elasticity dictates the relevant droplet mechanics. In particular, we demonstrate that droplet deformation due to confinement by the network may be a universal phenomenon in the precipitation of condensed liquid phases within fibrillar networks. Such results are of relevance to the formation of biomolecular condensates within the complex cellular interior.