Nature-inspired smart glue stays sticky under water

Scientists are developing a 'smart glue' - using mussel proteins - that can bond securely underwater and may be turned on and off with electricity.
"This work is novel in the sense that there is no smart adhesive out there that can perform underwater," said Bruce Lee, assistant professor at Michigan Technological University in the US3.
"The chemistry that we can potentially incorporate into the adhesive, causing it to reversibly bond and de-bond, is quite new," he said.
Such a 'smart glue' could bind underwater sensors and devices to the hulls of ships and submarines and help unmanned vehicles dock along rocky coastlines or in remote locations.

There also are possible medical applications for an adhesive that can bind and un-bind at will.
It could lead to new kinds of bandages that will stay attached when someone sweats or gets wet, and make it less painful to remove a dressing.

The smart glue may even be used one day to attach prosthetic limbs and biometric sensors or seal surgical wounds.
"Biomimetic approaches (synthetic methods that imitate natural processes) have been used previously to develop materials for wet adhesion," said Laura Kienker, manager of Office of Naval Research (ONR).
"The unique aspect of Lee's research is that it aims to develop a biomimetic wet adhesive that can rapidly and repeatedly bond to, and separate from, a variety of surfaces in response to applied electrical current," said Kienker.

Like barnacles, mussels attach to rocks, docks and ship hulls - a natural occurrence called biofouling.
Mussels secrete a combination of natural liquid superglues and stretchy fibres, called byssal threads, that works equally well in saltwater and freshwater; can stick to both hard and soft surfaces; and is strong enough to withstand the roughest sea conditions.
The secret behind mussels' adhesive success is an amino acid called dihydroxyphenylalanine (DOPA).
DOPA also enables mussel secretions to be both cohesive and adhesive - meaning they can adhere to themselves and other surfaces.
Researchers blended DOPA with polymers like polyester and rubber to create synthetic glue that holds together when wet.

Laboratory tests demonstrated this material can attach to a variety of surfaces, including metal, plastic and even flesh and bone.
"One very valuable quality of this synthetic glue is its versatility," said Lee.
"We can change the chemistry to make it as rigid or flexible as we need-while still maintaining its overall strength and durability," he said.
Researchers are now trying to figure out how to use electrical currents to create a chemical "on-off" switch that temporarily changes DOPA molecules to make the synthetic adhesive sticky or non-sticky at will.