Inspired by the natural adhesives secreted by shellfish, which can cling to underwater rock ledges and ship hulls, a team of engineers at Massachusetts Institute of Technology, Cambridge, has designed new waterproof materials that could be used to help heal wounds and surgical incisions.

This image shows adhesion between the silica tip of an atomic force microscope and adhesive fibers made by fusing mussel foot proteins and curli amyloid fibers.(Credit: Yan Liang)

To create their new adhesives, the researchers engineered bacteria to produce a hybrid material that incorporates naturally sticky mussel proteins as well as a bacterial protein found in biofilms formed by bacteria. When combined, these proteins form even stronger underwater adhesives than those secreted by mussels, they say.

“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,” says Timothy Lu, an associate professor of biological engineering and electrical engineering and computer science.

The sticky substance that helps mussels attach to underwater surfaces is made of several proteins known as mussel foot proteins. Scientists have previously engineered E. coli bacteria to produce individual mussel foot proteins, but these materials do not capture the complexity of the natural adhesives, Lu says.

In their study, the researchers wanted to engineer bacteria to produce two different foot proteins, combined with bacterial proteins called curli fibers, which can clump together and assemble into larger, more complex meshes.

Lu’s team engineered bacteria so they would produce proteins consisting of curli fibers 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 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 say.

The team also plans to try to create “living glues” consisting of films of bacteria that could sense damage to a surface and then repair it by secreting an adhesive.

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