Active Plastisity*

Active nematics - systems made of biological filaments and motors - show a wide verity of interesting behaviors. These system transition form a passive gel to flowing states when supplied with ATP. To capture this change in rheological properties we propose a minimal model of the stress organization in these system where the activity is captured by self-extending force dipoles that are part of a cross linked network. This network can reorganize itself through buckling of extending filaments and cross linking events that alter the topology of the network. Mean field calculations and simulations of this network reveal that these force dipoles build up stress with time, coupled with an average dissociation time of these force dipoles this give a typical yield stress similar to a yielded plastic solid.