Crosslinker mobility weakens transient polymer networks

Transient networks composed of polymers connected by short-lived bonds are a common design theme for biological and synthetic materials. Transient bonds can provide mechanical rigidity, while still allowing for viscoelastic flows on timescales longer than the bond lifetime. In many biological polymer networks, such as the actin cytoskeleton, the short-lived bonds are formed by accessory proteins that diffuse away after unbinding. By contrast, bonds in synthetic networks, such as the pendant groups of telechelic polymers, can only rebind in the same location. Using a recently developed theoretical model of the fracturing of viscoelastic materials, we here investigate the effect of linker mobility on the bond dynamics of a network under stress. We find that although mean-field properties such as the average bond linker lifetime are barely affected by bond mobility, networks crosslinked by mobile bonds fracture more readily due to “leaking” of linkers from crack areas to less-stressed regions within the network. We propose a theoretical model to describe the redistribution of mobile linkers, which we validate by simulations. Our work offers insight into a potential tradeoff that cells face, between fracture strength versus the modularity and tight dynamic control offered by mobile linkers.