Mechanical properties of branched actin networks

Gels of fibrous bio-polymers are ubiquitous within cells and their rigidity is crucial for their function. Our current understanding of their elastic response is usually understood as an interplay between the bending and stretching of their filaments. This point of view however fails when applied to the weakly coordinated branched actin networks found throughout the cell. Through experiments, simulations and theory, we show that their elasticity crucially involves reversible entanglements between their filaments. Additional entanglements may get locked in during network growth, setting the final properties of the network. These properties could be key to understanding how moving cells dynamically adapt their cytoskeleton to their environment.