(464d) Understanding Marine Mussel Adhesion: Interfacial Energy from Microscopic to Macroscopic Length Scales

The marine mussel adheres to organic and inorganic surfaces under water through a combination of physical and chemical bonds, and translates these interactions into energy dissipation and high detachment forces through macroscopic geometry. This work explores protein-surface interactions and the behavior of a mussel-inspired single-component coacervate adhesive in a confined geometry. The mussel delivers its adhesive proteins to surfaces in a protein-rich liquid phase called a coacervate that readily spreads on and adheres to surfaces. The interaction energy often depends on the molecular-scale geometry between the adhesive proteins and the surface (determined by the primary and secondary structure of the protein). For example, the proximity of cationic residues to the aromatic residue 3,4-dihydroxyphenylalanine (Dopa)—nearly ubiquitous in marine adhesion—impacts the ability of Dopa to form long-lived bidentate hydrogen bonds with the surface. Geometry is also crucial on the macroscopic scale: the force of detachment and energy dissipation of the mussel holdfast (the byssus) results from its unique structure. Inspired by the success of mussel adhesion, a random copolymer incorporating Dopa was designed that forms a polymer-dense liquid phase in aqueous environments over a wide pH range without precipitating (a single-component coacervate). The cohesion of this material as a function of pH and Dopa content was investigated between molecularly smooth mica surfaces. An understanding of the adhesion mechanisms of marine mussels has motivated the development of this and many other adhesives for use in aqueous environments, and will continue to guide the development of adhesives for medical, dental, and marine applications.