When it comes to adhesives — materials applied between two surfaces to hold them together — water’s presence is detrimental. This disruption is primarily caused by the polar nature of water molecules. As water comes into contact with adhesives, it creates a thin layer that coats the sticky surface. Therefore, adhesives often lose their binding ability under wet conditions. Because water is highly abundant in biological systems, maintaining stickiness in the face of water would immediately benefit research in tissue repair, drug delivery, and biomedical devices.

But of course, nature has already figured out the solution to this problem. In the ocean, mussels have perfected their own adhesive recipe to firmly attach to wet rocks. They mediate attachment through their byssus, or foot, which secretes proteins with high adhesive power. The repetitive pattern of two amino acids, lysine (K) and DOPA (Y), in these proteins have been shown to play a crucial role in binding. Prior studies have centered on DOPA, and questions remain regarding the impact of lysine.

Researchers at the University of California, Berkeley have studied the combination of both amino acids, K and Y. They measured the detaching force of several mussel protein analogs by sticking them to a rock mimic made of titanium dioxide. Results showed that the analog composed of three KY amino acid pairs was the strongest, and that further pair addition did not increase strength.

With these results, the researchers also created a knock-off copy of the most abundant mussel foot protein (mfp-5). They did this by using three KY pairs separated by non-amino acid linkers, then they measured the detaching force again. Results indicated that this material was "stickier" than three KY repeats without the linker addition.

With the development of a full-length model of mfp-5, researchers think this work could serve as a solid foundation for further wet adhesive design and preparation.