Fine-Tuning of Material Properties via Catch Bonds

Semiflexible polymer networks are ubiquitous in biological systems, including a scaffolding structure within cells called the actin cytoskeleton. The polymers in these networks are often interconnected by transient bonds. For example, actin filaments in the cytoskeleton are physically connected via cross-linkers. The mechanical and kinetic properties of the cross-linkers significantly affect the rheological properties of the actin cytoskeleton. Here, we employed an agent-based model to elucidate how the force-dependent behaviors of the cross-linkers determine the material properties of passive networks without molecular motors and the force generation of active networks with molecular motors. The cross-linkers are assumed to behave as a slip bond whose dissociation rate is proportional to forces or as a catch-slip bond whose dissociation rate is inversely proportional to forces at low force level but proportional to forces at high force level. We found that catch-slip-bond cross-linkers can increase both stress and strain at a yield point by forming force-bearing elements that turn over continuously, which is impossible to achieve without the catch-slip bonds. In addition, we demonstrated that the catch-slip-bond cross-linkers help myosin motors generate greater internal contractile forces by reinforcing the force-bearing parts of the active network.