Marine organisms that fasten to the bottoms of ships have always been a scourge to seafaring. By monitoring how the larvae of acorn barnacles go about finding suitable spots to attach themselves, researchers at Linköping University in Sweden have managed to design surfaces that prevent growths – without using poisonous chemicals.
Acorn barnacles, which are animals, are among the most notorious stowaways at sea. A vessel with its hull covered by their hard calcium shells moves more slowly and uses more fuel.
The most common method to prevent surface fouling is to apply toxic hull paint. The most effective substance has been tributhyl tin (TBT), which is now totally banned. But until now no really good alternatives to toxic paint have been found.
“Our strategy, instead, is to design surfaces that the barnacle glue doesn’t stick to. The idea is for the larvae to swim off and find another place to fasten themselves for the rest of their lives,” says Tobias Ekblad, a doctoral candidate in molecular physics and an associate in the EU project AMBIO.
To study how a larva walks around on its ‘feet’ – actually the front parts of a couple of antennae – and leaves micrometer-size footprints, the scientists make use of so-called surface plasmon resonance. This measurement method, based on electromagnetic wave movements in the interface between the surface and sea water, can detect the minimal optical changes that occur when the thin (10 millionths of a millimeter) footprints are made. In this way they can see in real time how the prints occur and monitor their movements back and forth across the surface.
The findings presented in Tobias Ekblad’s thesis show that what determines whether the larvae like a surface or not is chemistry. Ekblad has developed a method to cover a material with a thin layer of water-filled gel, a hydrogel, that has been tested with different chemical components. For example, layers containing the polymer polyethylene glycol (PEG) have been shown to yield excellent results.
The researchers have also studied the effect of how blood coagulates on various surfaces, a problem that is encountered when prostheses are operated into the body. As in the barnacle growth project, they have found that the usable materials are those that dramatically decrease the binding of proteins to the surface.