 multivalent ions are known to allow for reversible cross - linking in soft biological materials , providing stiffness and extensibility via sacrificial bonds . 
 we present a simple model where stiff nanoscale elements carrying negative charges are coupled in shear by divalent mobile cations in aqueous media . 
 such a shear coupling through a soft glue has , indeed , been proposed to operate in biological nanocomposites . 
 while the coupling is elastic and brittle when the negative charges are periodically arranged , sufficient randomness in their distribution allows for large irreversible deformation . 
Supplementary Material