Mussels inspire new underwater glue

Now moving on to another sticky subject: glue, which, we’re told by the makers, only works on clean dry surfaces. That’s because getting the chemistry right for glues to work in the presence of water is very difficult. But one solution to finding good glues that will work in the wet is to look at how animals that make glues and live in water have solved the problem. The result, for a team of US scientists, is not just any glue, this stuff’s incredibly strong and even sets underwater. Sally Le Page reports...

Sally - Imagine this. You're on a warm sunny beach looking out to sea with the call of herring gulls piercing through the sound of kids clamouring over the barnacle encrusted rock pools. The waves crash, and you struggle to pull free a handful of silvery-blue mussels that are stuck firmly to the wet rock faces to cook for dinner. And perhaps you think to yourself, I should go back to the lab and invented a glue half as good as this that also works underwater. Or perhaps not, but Tufts university engineer, Fiorenzo Omenetto did begin to wonder.

Fiorenzo - If we think about adhesion, we look at some of the problems that exist in the real world, like barnacles that stick on the side of boats and are really, really hard to get off. Or muscles that are on rocks and that are very, very tightly bound to the rocks that they stick on in spite of waves and in spite of the people that go and want to get them to eat.

Sally - Indeed, barnacles and mussels manage to stick themselves tightly to submerged rocks and jetties, and even withstand being battered by waves. Mussels do it by secreting molecules that cross-link strongly with surfaces, anchoring themselves in place. Barnacles, on the other hand, produce a waterproof protein cement that provides a large surface area for maximum stickiness. Human-made synthetic glues also rely on similar forms of chemistry to do the same heavy lifting. They create molecular bonds between surfaces that make them hard to pull apart. But in many cases, water molecules can interfere with those bonds, making it much harder for glues to work underwater.

Fiorenzo - The water gets in the way and changes the way that the bonds occur. So it changes the way ultimately that the materials stick.

Sally - So how did the Tufts team solve the problem? One of Fiorenzo's research interests is silk that comes from silkworms. And when he looked closely at the barnacle cement, he spotted something surprisingly familiar.

Fiorenzo - These proteins assemble in a geometry that is very particular. And this particular geometry is very similar to the way that silk assembles.

Sally - But barnacle proteins are hard to extract, whereas we already know how to mass produce silk. So could you, he wondered, substitute silk proteins for barnacle proteins to produce a glue that still works underwater?

Fiorenzo - So mussels and barnacles have evolved strategies to create these bonds in wet environments. And so the thought was very simple. If we could get the chemical part that is used by the mussels, and we have silk that maybe provides the function that barnacles do, well let's mix the two and see what happens and see if we can get the advantages of both.

Sally - By combining silk proteins and the sticky molecules from mussels, they've created a new hybrid glue that is the strongest non-toxic underwater adhesive ever made. Underwater glues are incredibly useful, from the obvious cases, such as sticking pipes together to the less obvious, like sealing up wounds during surgeries without having to use stitches. And this mussel-silk hybrid doesn't have to use any strong solvents that, apart from sometimes being poisonous, also tend to smell terrible. So where can we get some? Well, don't hold your breath, except maybe if you're underwater, because if you are hoping to see a tube of this stuff in the shops, anytime soon, the bad news is that according to Fiorenzo, it's going to be a while.

Fiorenzo - It's not going to be within the next six months. It might be within the next six years. And anything in between is fair.