Ships to strap on shark suits
A new material for ship hulls that mimics shark skin may improve vessel speed and fuel efficiency.
The artificial skin, developed by Ralph Liedert, a biologist at the University of Applied Sciences in Bremen, Germany, wards off the build-up of barnacles by imitating the microscopic ridges and flexibility characteristic of a shark's hide.
Not only could the surface reduce the growth of marine organisms on ship bottoms, it could also help the industry phase out the toxic coating tributyltin, banned by the International Maritime Organization.
"There are no reliable nontoxic alternatives on the market yet," says Liedert, who invented the material while working on his PhD.
Liedert focused on barnacles, which produce a cement-like protein to glue themselves to both sea-faring fleets and fauna.
Barnacles make up the majority of this kind of biofouling, and are responsible for corrosion as well as weighing down ships, which decreases speed, manoeuvrability and fuel efficiency.
Like many ocean-dwelling creatures, sharks have a defence against barnacles.
Millions of microscopic teeth-like scales imbedded in a flexible layer of their skin create an uncomfortable and unstable surface for the barnacle and its gluey secretions.
Liedert imitated nature's success by combining the uncomfortable and unstable aspects of shark skin into a surface lined with microscopic ridges made from elastic silicone.
In field tests he conducted on immersed panels, Liedert found that wobbly, parallel ridges spaced between 2 micrometers and 2 millimeters apart inhibited barnacle growth up to 67%.
"It's like walking on a stony beach with bare feet," says Liedert. The barnacle larvae can't stick or if they try, they soon let go.
Liedert says the barnacle glue sits on top of the micro-peaks instead, oozing into the valleys.
In theory, even if tiny larvae can cling for a while, the combination of an unstable surface and the natural drag from a ship's motion should peel them off as they grow.
Although Liedert's nontoxic solution seems to works for barnacles, other marine organisms, including mussels, algae and bacterial films that increase the drag resistance of ships must be addressed.
At the US Office of Naval Research (ONR) in Arlington, Virginia, research to prevent biofouling is focused on biomimetics as well as chemistry and smart coatings.
"The ultimate solution is going to have to be a combination of things, maybe of topographies combined with some specific surface chemistry," says Dr Stephen McElvany, who manages environmental research projects at the ONR to develop nontoxic coatings for hulls.
But the success of a coating to prohibit one organism holds the promise for coatings that can stave off many, he says.
Liedert is currently collecting more conclusive evidence for his solution. In a few months, he'll begin to analyse data from small patches of artificial skin he's applied to moving ships.