Modeling F-actin Disassembly by Severing and its Effect on Stress Relaxation*

Actin filaments (F-actin), ubiquitous proteins biopolymers in cells, form networks that are crucial to cell mechanics. These biopolymers not only polymerize and depolymerize from their ends but also can be severed by actin severing proteins such as Cofilin. In this work, we develop a model for the dynamics of actin filament polymerization, depolymerization, and severing. This enables us to predict stress relaxation behavior of such complex, nonequilibrium networks. We identify various regimes with distinct length-dependent relaxation behavior, including both a regime with length-independent relaxation rate, as well as a regime with a relaxation rate that increases with filament length.