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Abstract :
[en] Numerous living creatures have developed adhesion strategies to stick to inorganic or organic surfaces in wet environments. A classic example of permanent bioadhesion is exemplified by mussels, which secrete adhesive proteins containing a high concentration of 3,4-dihydroxyphenylalanine (DOPA) 1, 2. The catechol species of DOPA are thought to be responsible for the strong adhesion to inorganic surfaces, whereas the oxidized o-quinone species trigger the cross-linking of the glue, ensuring cohesion. The unoxidized form of DOPA is known to adhere to a large variety of inorganic surfaces, although the adhesion mechanism is not yet fully understood.3, 4 A clear understanding is however essential for the design of synthetic adhesive polymers required in many surface science applications.
Here we investigate at the single-molecule level the interaction forces between AFM tips coated with bio-inspired polymers and a variety of inorganic and organic surfaces. We prepared polymers bearing several amounts of DOPA units and covalently attached them to AFM tips following our previously published strategy.5, 6 They were homo-or co-polymers and were cross-linked or not. These original bio-inspired tips were used to perform single-molecule force spectroscopy on a range of model, as well as industrial such as stainless and galvanized steel, substrates. The specific interaction forces measured in water were compared with the ones exerted by the same polymers without DOPA. It was found that, depending on the nature of the substrate, the presence of DOPA strongly, or only slightly, increases the interaction forces with the surface. We also investigated the influence of the oxidation state of the catechol species on the intensity of the interaction forces. Again, this influence is strongly related to the nature of the substrate. Finally, we studied the effect of polymer cross-linking on the adhesive interactions.
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