Metal coordination bonds are employed in protein based biological materials such as the mussel byssus as reversible sacrificial bonds to achieve autonomic and intrinsic self-healing behavior. In the present study, histidine residues capable of forming coordination bonds were recombinantly engineered into the consensus sequence of resilin, an insect protein that forms a rubbery and resilient biopolymeric network. The purified recombinant resilin mutant, AnG_2His16, was photo cross-linked to form thin films that exhibited a 30-fold increase in modulus compared with wild-type resilin sequences. Addition of Zn2+ ions to the mutant resilin films, led to a further increase in stiffness, which, according to Raman spectroscopic studies, arises from His-metal coordination cross-links. These findings show the potential for tuning mechanics and self-healing behavior in biopolymers using bio-engineered metal-binding sites.
The paper was originally published in Polymer Journal 69 (2015) Vol 255 - 263