Even the strongest glues collapse when soaked. Just watch a plaster slide off a finger or toe whilst in the shower. However, with support from the Office of Naval Research (ONR), one researcher has developed a nature-inspired adhesive that stays sticky when wet.
Dr. Bruce Lee, an assistant professor of biomedical engineering at Michigan Technological University, is using a protein produced by mussels to create a reversible synthetic glue that not only can bond securely underwater – but also may be turned on and off with electricity.
Mussels attach to rocks, docks and ship hulls. They 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, for short. A chemical relative of dopamine—the neurotransmitter that helps control the human brain’s pleasure and reward centers – DOPA is a critical ingredient in fastening the superglues and byssal threads to a location. It also enables mussel secretions to be both cohesive and adhesive—meaning they can adhere to themselves and other surfaces.
Lee and his research team blended DOPA with polymers such as 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.”
Lee and his team 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. So far, they’ve been able to accomplish this by tweaking the glue’s pH balance, but are still working to achieve this capability using electrical stimulation.
“This work is novel in the sense that there is no smart adhesive out there that can perform underwater,” said Lee. “The chemistry that we can potentially incorporate into the adhesive, causing it to reversibly bond and de-bond, is quite new.”
Lee envisions multiple uses for such a “smart glue”, including binding underwater sensors and devices to the hulls of ships and submarines.