Despite waves and strong currents, creatures like mussels and barnacles stay cemented on rocks in the splash zone as well as on the pillars of piers and bottoms of boats thanks to their naturally endowed super stickiness. Now, researchers trying to better understand wet adhesion have turned to a molecule produced by bacteria. They discovered an effective combo of substances that can help “prime” underwater surfaces for an adherence that rivals that of mussels: The amino acid lysine acts as a primer for an adhesive chemical compound called catechol. The findings were published in Science this week.
In the hunt for synthetic adhesives suitable for high pH solutions, a team of researchers from the University of California, Santa Barbara (UCSB), examined a microbial substance with high binding capabilities called cyclic trichrysobactin (CTC). "We specifically looked at the synergy between the role of the amino acid lysine and catechol," UCSB’s Alison Butler says in a statement. "Both are present in mussel foot proteins and in CTC." A mussel sticking to Teflon is pictured to the right.
The team created half a dozen different compounds with varying amounts of lysine and catechol. Then to tease out the contributions of the two, they tested these compounds for their adhesion to a mica surface submerged in a saline solution. Lysine, they discovered, was key. It helps remove salt ions from the surface to allow the glue to get to the underlying surface, according to UCSB’s Greg Maier.
By replacing the salt ions on the rock’s surface, CTC increased the adhesion force by a factor of 30. "There's a one-two punch," Butler adds. "The lysine clears and primes the surface and the catechol comes down and hydrogen bonds to the mica surface."
They created a synthetic version of CTC that offers similar adherence strengths and works in saline solutions with pH levels between 3.3 to 7.5. "There's real need in a lot of environments, including medicine, to be able to have glues that would work in an aqueous environment," Butler says. Current synthetic materials don’t adhere well in solutions with higher pH values. "So now we have the basis of what we might try to develop from here."
Wet adhesion of the catechol-amine compound to a mica surface. Lysine (pink) is depicted as penetrating through the hydration layer, evicting potassium ions (gold balls) and preparing the mica surface for catechol hydrogen bonding (highlighted by the green aura). Illustration by Peter Allen, UCSB
Images: Jonathan Wilker (top, middle), Peter Allen, UCSB (bottom)