Coating Causes Mussels to Slip Right Off
Huge tankers often move at a snail's pace when they also have to haul thick layers of shells and barnacles on their hulls. This heavy load drives up fuel consumption, and mussel infestation also causes severe environmental problems: foreign species essentially hitch a ride to distant ecosystems and can sometimes have a very harmful impact on the ecosystems' fragile equilibrium. The vast majority of the "weapons" deployed against mussels kill numerous organisms indiscriminately with toxic chemicals and must be replaced often; they are also not as effective as desired. Newer coatings based on silicone or fluoropolymers only allow the infestation to be more easily removed.
Slippery layer inspired by pitcher plant
A group of researchers with Professor Nicolas Vogel from the Institute of Particle Technology and a member of the Engineering of Advanced Materials cluster of excellence at FAU (Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany), Professor Joanna Aizenberg from Harvard University and Ali Miserez from Nanyang Technological University (NTU), Singapore, have developed a new approach to mussel control. "We were inspired by the carnivorous pitcher plant. Whereas the plant surface is not slippery when dry, it binds rain water after a downpour and hence becomes extremely slippery. Insects cannot hold on to its slick lip and slide helplessly into the interior of the plant, where they are digested. We have transferred this effect to synthetic materials", Vogel explains.
The newly developed material similarly prevents the mussels from sticking efficiently. Due to their structure and surface chemistry, surfaces could be wetted with a liquid that forms a closed film on the surface, like on the pitcher plant. This prevents direct contact to the solid surface and acts as a repellent. In the laboratory, the scientists observed that the animals seemed irritated by being on the wetted surfaces. "Immediately after the foot of mussel came into contact with the surface, it snapped back into its protective shell. It almost seemed that the mussel had touched a hot stove", says Vogel, describing his observations. A possible explanation is provided by the liquid properties of the coating, which strongly alter the forces occurring between the surface and the foot of the mussel upon contact with the mussel.
The results obtained in the laboratory were confirmed by field tests at the port of Scituate near Boston, Massachusetts, where there was very little fouling after several months. In comparison, all the control surfaces had already been completely colonised by marine organisms. In follow-up trials, the scientists are investigating how to apply the developed materials over large areas on ships, thereby ending unwanted mussel infestation.