Stuck on you
If you’ve ever superglued your fingers together and struggled to break the bond, you are forgiven for thinking that the acrylic resin is the strongest glue known to man. In fact, the most super glue on earth was first described 150 years ago by Darwin and is none other than the adhesive cement secreted by barnacles that attach themselves to the bottoms of boats and ships.
Barnacles are tiny crustaceans that cling to rocks and ships permanently, and feed by filtering particles from the water by waving their microscopic feathery legs. Barnacle glue sticks to any surface under any conditions, including the hull of a ship moving through in sea water, which varies in composition, pH value, and salinity across the world. Despite this, barnacle glue continues to perform better than anything we’ve ever formulated — probably because until now no one has known exactly how it works.
Now, a study published in the journal Nature Communications by an international team of scientists led by Newcastle University and funded by the US Office of Naval Research, has described for the first time the mechanism barnacles use to adhere to a surface.
“We’ve known for a while there are two components to the bioadhesive but until now, it was thought they behaved a bit like some of the synthetic glues — mixing before hardening,” said Nicholas Aldred, a research associate in the School of Marine Science and Technology at Newcastle University.
“But that still left the question, how does the glue contact the surface in the first place if it is already covered with water? This is one of the key hurdles to developing glues for underwater applications.”
Using imaging techniques such as 2-photon microscopy, the researchers have observed how barnacle larvae release an oily droplet that clears the water from surfaces before they stick down using a phosphoprotein adhesive.
The team has also been able to observe the adhesion process and characterise the two components. “We now know that these two substances play very different roles — one clearing water from the surface and the other cementing the barnacle down,” he added.
Barnacles have two larval stages, not just one. The nauplius stage is common to most crustacea, wherein it swims around freely, feeding on plankton after it hatches out of the egg.
The second larval stage, known as the cyprid, is unique to barnacles. During this phase, the larva investigates surfaces, and finally selects one that provides suitable conditions for growth. Once it has decided to attach, the cyprid clears the water, then releases its glue and cements itself to the surface where it will live out the rest of its days.
As evolution, goes, the process is an elegant and clever way of dealing with the water barrier on a surface, and “it will change the way we think about developing bio-inspired adhesives that are safe and already optimised to work in conditions similar to those in the human body,” said Aldred.
The reasons for studying it were twofold: one, because developing such a strong glue has far reaching implications and applications. The findings could pave the way for the development of novel synthetic bioadhesives for use in medical implants and micro-electronics, says Aldred. Even now, the major constituent of Superglue, a chemical called cyanoacrylate, is used medically to repair lacerations and during in cartilage, skin and bone transplants.
Then, there’s the issue of biofouling — whereby marine life and barnacles along for the ride weigh down a ship’s hull so much, it costs the global shipping industry an estimated $7.5 billion a year in wasted fuel. The research will also be important in the production of new anti-fouling coatings and paints for ships.