Abstract

The adhesive secretions of marine animals such as P. californica and M. edulis combine covalent and non-covalent interactions to afford strong underwater adhesion. Characteristic of the proteins found in the adhesive plaque of mussels and sandcastle worms is a high proportion of cationic, anionic and catecholic residues (hydroxylated tyrosine, DOPA ). DOPA is involved in a versatile combination of functions: covalent crosslinking, complexation to mineral substrates, and bonding to hydrophobic (fouled) surfaces. The anionic and cationic residues are often said to be involved in a secondary interaction that aids cohesion, namely complex coacervation. This is an attractive phase separation of mixtures of polyanions and polycation that results in a highly polyelectrolyte-rich phase in equilibrium with almost pure solvent. Complex coacervates have very low surface tensions, which makes them highly desirable as non-water soluble adhesive agents. Additionally, they are mechanically very well-suited to adhesion due to their high storage and loss moduli that provide, respectively, bonding strength and dissipation of strain. In this study, we aim at reproducing the working mechanism of mussels and sandcastle worms by developing a new class of underwater adhesives based on complex coacervates reinforced with physical interactions.