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.