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January 2012 Issue

Using Biomimetics to Improve Anti-Fouling Technology
By Stefanie Wuttke

Any natural and artifical surface exposed to seawater suffers from the same problem. Bacteria immediately begin to form a thin biofilm, which serves as a suitable settlement place for other macroscopic fouling organisms such as algae, barnacles, bryozoa and mussels, offering them access to a sufficient food supply, protection and conspecifics for reproduction.

Not only the merchant ship sector but also navies and the fishing industry have to endure fouling-related problems. The increased surface roughness and additional biomass from fouling cause lower velocities with the same energy input, resulting in longer transit times or having to increase power input to maintain the same speed.

Anti-fouling paints have been used to eliminate the incrustation of fouling matter, but their use contaminates the seawater and seabed, especially in harbors, affecting many kinds of sea life. A widely distributed compound used in these paints, tributyltin, was banned by the International Maritime Organization in 2008 due to its toxicity. I expect the use of toxins, most likely copper-based coatings, will be banned in the near future, as experts rework biocide regulations in Europe.

Research into biomimetics, which learns from nature and searches for the underlying functional principles, offers great potential to invent an environmentally friendly anti-fouling coating. A variety of organisms living in marine environment have natural defenses against fouling. Some algae shed cell layers to get rid of adherent organisms. Crabs groom their legs and carapaces with their shears and molt when too heavily fouled. Most corals produce biological toxins, which are continously released into the water to prevent fouling organisms from settling.

Another example especially worth mentioning is the shark. Its skin, which is mostly free from fouling organisms, made it an interesting research candidate for a workgroup at the University of Applied Sciences, led by professor Antonia B. Kesel. Shark skin is composed of tiny scales, each of them featuring a structured surface with longitudinal narrow ridges. The distance between the peaks of the ridges is about 100 micrometers, depending on the shark species.

The base of each scale is fixed flexibly in the underlying connective tissue, allowing for a relative motion against each other. Kesel and her team found the combination of the scale's flexibility together with its surface texture leads to a reduction of settlement by larvae and spores.

But how is this transferable to ship hulls? Kesel's team found that silicone offered promising material characteristics, and so silicone surfaces with linear ridges like lenticular foil were cast with polydimethylsiloxane. The silicone molding was exposed in the North Sea offshore Germany for four months, during which barnacles, bryozoans and hydrozoans settled on the panels. The silicone surface showed a 67 percent decrease in biofouling compared to a nonfunctional surface.

Silicone surfaces provide other positive effects, too. The low surface energy does not allow fouling organisms to generate high adhesive forces, resulting in a self-cleaning ability. The silicone is not "used up" when preventing fouling, and in contrast to self-polishing anti-foulings, there is no leaching of oil in the water.

Moldings are difficult to attach to ship hulls, so a paint similar to shark skin was developed. Comparative tests showed the anti-fouling effect of shark skin does not depend on the linear structure but on the dimension of the microstructure. Glass granulates that had a diameter similar to the width of the narrow ridges on shark skin were added to the polymer. The resulting distribution of the granulates is similar to the peaks of the ridges. Since spring 2009, the product, Haifischhaut, has been sold by VOSSCHEMIE (Uetersen, Germany) as anti-fouling paint for sailing yachts and sport crafts.

In 2008, another anti-fouling project was also started at the Biomimetics-Innovation-Centre in Germany by Kesel's workgroup, including Antje Clasen and Katrin Mühlenbruch. Because purely physical anti-fouling mechanisms are rare, the team's research involved organisms that use those principles. The team found some interesting features in drifting seeds. Any fouling to seeds dispersed by sea currents would be disadvantageous, as it would make the seed less buoyant.

The team collected 52 species of sea- and marsh-related plants, such as palm trees, and exposed them to the North Sea. Twenty-four percent did not show any macrofouling. From these, only a minority revealed geometrically recordable surface structures. Test panels were produced with similar structures, some of which showed sufficient anti-fouling properties and better fouling release abilities. The researchers are now conducting ecotoxology tests in order to estimate possible toxin release of drifting seeds.

Nature has some promising solutions for technical problems. The shark skin-inspired anti-fouling coating is just one in a multitude of possibilities. Many studies focus on the thrust-producing elements of fish fins, which are quieter and more efficient than man-made propulsion systems. AUVs could benefit from this with a wider range of operation and applications.

Multifarious diatom structures could be used for optimized lightweight constructions in anchorages of offshore wind parks, which endure high wind and water loads. Acting forces could be evenly distributed without causing material fatigue, resulting in longer lifetime and reduced repair costs.

Biomimetic research is on the rise: There is a high request for biomimetic research at exhibitions; programs offering degrees in biomimetics have many applicants; and biomimetic research institutes have been built in Germany. With growing environmental awareness, new biomimetic research possibilities become more important, bringing with them endless possibilities.
Stefanie Wuttke is a research associate at the University of Applied Sciences' Biomimetics-Innovation-Centre in Bremen, Germany. She completed her bachelor's degree in biomimetics and now works on potential new nontoxic anti-fouling coatings.


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Sea Technology is read worldwide in more than 110 countries by management, engineers, scientists and technical personnel working in industry, government and educational research institutions. Readers are involved with oceanographic research, fisheries management, offshore oil and gas exploration and production, undersea defense including antisubmarine warfare, ocean mining and commercial diving.