Direct Observation of the Interplay of Catechol Bindingand Polymer Hydrophobicity in a Mussel-Inspired Elastomeric Adhesive

摘要

Marine organisms such as mussels have mastered the challenges in underwater adhesion by incorporating post-translationally modified amino acids like l-3,4-dihydroxyphenylalanine (DOPA) in adhesive proteins. Here we designed a catechol containing elastomer adhesive to identify the role of catechol in interfacial adhesion in both dry and wet conditions. To decouple the adhesive contribution of catechol to the overall adhesion, the elastomer was designed to be cross-linked through [2 + 2] photo-cycloaddition of coumarin. The elastomer with catechol moieties displayed a higher adhesion strength than the catechol-protected elastomer. The contact interface was probed using interface-sensitive sum frequency generation spectroscopy to explore the question of whether catechol can displace water and bond with hydrophilic surfaces. The spectroscopy measurements reveal that the maximum binding energy of the catechol and protected-catechol elastomers to sapphire substrate is 7.0 ± 0.1 kJ/(mole of surface O–H), which is equivalent to 0.10 J/m². The higher dry and wet adhesion observedin the macroscopic adhesion measurements for the catechol containingelastomer originates from multiple hydrogen bonds of the catecholdihydroxy groups to the surface. In addition, our results show thatcatechol by itself does not remove the confined interstitial water.In these elastomers, it is the hydrophobic groups that help in partiallyremoving interstitial water. The observation of the synergy betweencatechol binding and hydrophobicity in enabling the mussel-inspiredsoft adhesive elastomer to stick underwater provides a framework fordesigning materials for applications in tissue adhesion and moist-skinwearable electronics.