Elasticity from entanglements in branched actin

Branched actin networks exert pushing forces in eukaryotic cells, and adapt their stiffness to their environment. To understand the microscopic underpinnings of their response, we show using high-sensitivity micromanipulation experiments, numerical simulations and theory that unlike usual crosslinked networks, branched actin is dominated by the proliferation of interfilament contacts under compression. The tree-like topology of the networks make them particularly prone to developing growth-induced entanglements, and is thus key to their active adaptive mechanics.