Angew. Chem. Int. Ed. (2014)

Marine mussels stick to underwater surfaces and hence must have mechanisms by which they can overcome the repulsive forces usually prevalent between adhesive materials and hydrated surfaces. Mimicking this 'wet adhesion' with synthetic adhesives remains challenging, however, because methods to analyse the interaction between mussel proteins and the hydrated layers of solid surfaces by, for example, atom force microscopy or surface force apparatus experiments, apply disruptive forces to the repulsive layers and mask the mechanisms involved. Now, Songi Han and colleagues use force-free conditions to analyse the diffusion dynamics of surface water between various mussel foot proteins and polystyrene surfaces that are suspended in bulk water. In the approach, which combines Overhauser dynamic nuclear polarization and electron spin resonance spectroscopy, the interfacial interactions are observed. The researchers find that the most hydrophobic protein, which has a weaker hydrated layer surrounding it than the hydrophilic proteins, can more easily disrupt the surface-bound water barrier. Once these repulsive forces have been overcome, it is likely that other mussel foot proteins, rich in 3,4-dihydroxyphenylalanine (DOPA), can approach the surface and complete the adhesion process.