Crosslinker mobility governs fracture behavior of catch-bonded networks

TL;DR

This study uses computer simulations to show that catch bonds in actin networks enhance fracture resistance by stabilizing cracks, especially when the crosslinkers are mobile, leading to more ductile behavior under stress.

Contribution

It demonstrates how catch bond mobility influences fracture behavior in cytoskeletal networks, revealing a protective mechanism against mechanical failure.

Findings

Catch bonds accumulate in high stress regions, stabilizing cracks.

Mobile catch bonds lead to more ductile fracture behavior.

Networks with catch bonds are more resistant to high stress fracture.

Abstract

While most chemical bonds weaken under the action of mechanical force (called slip bond behavior), nature has developed bonds that do the opposite: their lifetime increases as force is applied. While such catch bonds have been studied quite extensively at the single molecule level and in adhesive contacts, recent work has shown that they are also abundantly present as crosslinkers in the actin cytoskeleton. However, their role and the mechanism by which they operate in these networks have remained unclear. Here, we present computer simulations that show how polymer networks crosslinked with either slip or catch bonds respond to mechanical stress. Our results reveal that catch bonding may be required to protect dynamic networks against fracture, in particular for mobile linkers that can diffuse freely after unbinding. While mobile slip bonds lead to networks that are very weak at high stresses, mobile catch bonds accumulate in high stress regions and thereby stabilize cracks, leading to a more ductile fracture behavior. This allows cells to combine structural adaptivity at low stresses with mechanical stability at high stresses.