Liquid-liquid phase separation modulates the elasticity of the entangled semi-flexible filament network

A filament network exhibits elasticity through inter-filament entanglements, but how the nucleation of liquid condensates within the network affects the elasticity of the network is still elusive. In this work, we combine helical bacterial flagella filaments and an intrinsic disordered protein that undergoes liquid-liquid phase separation. The helical bacterial flagella network exhibits elasticity by entanglement. Using oscillatory shear rheology, we investigate how the liquid-liquid phase separation of the protein affects the storage and loss moduli of the entangled network. We quantify the relationship between the change in inelasticity and the volume fraction of biomolecular condensate. The change in elasticity increases with volume fraction, but the sign of the change is strongly influenced by the filament-condensate interactions. Our observations provide evidence for the impact of biomolecular condensation on the mechanics of filamentous networks.