Shellfish-inspired waterproof adhesive to repair ships

Inspired by natural adhesives secreted by shellfish, MIT engineers have created a new stronger waterproof glue that can be used to repair ships and even heal wounds and surgical incisions.
Researchers at the Massachusetts Institute of Technology (MIT) engineered bacteria to produce a hybrid material that incorporates naturally sticky mussel proteins as well as a bacterial protein found in biofilms - slimy layers formed by bacteria growing on a surface.
When combined, these proteins form even stronger underwater adhesives than those secreted by mussels.
"The ultimate goal for us is to set up a platform where we can start building materials that combine multiple different functional domains together and to see if that gives us better materials performance," said Timothy Lu, an associate professor of biological engineering and electrical engineering and computer science (EECS).

The sticky substance that helps mussels attach to underwater surfaces is made of several proteins known as mussel foot proteins.
"A lot of underwater organisms need to be able to stick to things, so they make all sorts of different types of adhesives that you might be able to borrow from," Lu said.

The team wanted to engineer bacteria to produce two different foot proteins, combined with bacterial proteins called curli fibres - fibrous proteins that can clump together and assemble themselves into much larger and more complex meshes.
Lu's team engineered bacteria so they would produce proteins consisting of curli fibres bonded to either mussel foot protein 3 or mussel foot protein 5.

After purifying these proteins from the bacteria, the researchers let them incubate and form dense, fibrous meshes. The resulting material has a regular yet flexible structure that binds strongly to both dry and wet surfaces.
"The result is a powerful wet adhesive with independently functioning adsorptive and cohesive moieties," said Herbert Waite, a professor of chemistry and biochemistry at the University of California at Santa Barbara who was not part of the research team.
The researchers tested the adhesives using atomic force microscopy, a technique that probes the surface of a sample with a tiny tip.
They found that the adhesives bound strongly to tips made of three different materials - silica, gold, and polystyrene.

Adhesives assembled from equal amounts of mussel foot protein 3 and mussel foot protein 5 formed stronger adhesives than those with a different ratio, or only one of the two proteins on their own.
These adhesives were also stronger than naturally occurring mussel adhesives, and they are the strongest biologically inspired, protein-based underwater adhesives reported to date, the researchers said.
The research was published in the journal Nature Nanotechnology.