Molecular catch-bonds as a route to mechanical memory in active gels

Active gels like the cytoskeleton are non-equilibrium polymeric systems which display many fascinating behaviors.  These include contractility, dissipative self-organization, and, the focus of our talk, mechanical memory.  The ability for the gel to store a memory of its stress history through its orientation and chemical concentration fields should, in a cellular context, endow the gel with greater ability to produce contractile force in a tailored and useful manner.   We hypothesize that molecular catch-bonds, which are unbinding reactions with rates that decrease as the tension applied to the bound molecule increases, should constitute a mechanochemical feedback that allows for enhanced mechanical memory in active gels.  To explore this possibility, we developed hydrodynamical simulations of an active gel which, in a novel theoretical treatment, includes molecular catch-bonds.  The simulations account for non-equilibrium stresses, reaction-advection-diffusion dynamics of molecular motors with catch-bond kinetics, and viscoelasticity that locally depends on the underlying filament orientations. We will describe applications of this numerical approach to characterize the conditions and relevant timescales associated with catch-bond induced mechanical memory in active gels.