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Double the benefits with 3D-printed shark skin

Barnacles and other marine organisms that attach themselves to boat hulls, a phenomenon known as biofouling, cause major problems globally, with increased costs for maintenance and fuel. By studying marine organisms’ own natural protection against these growths, RISE researchers are hoping to develop environmentally friendly alternatives for combating biofouling. One possible method is 3D-printed shark skin.

Barnacles are the main culprit in Swedish waters, causing increased fuel consumption, carbon dioxide emissions and serious damage to marine structures. It does not take an enormous amount of growth to cause major issues; a supertanker with a covering of around 10% will consume approximately 40 tonnes pf extra diesel every day. This makes the issue important both from an environmental and financial perspective.

Ships’ hulls are not the only structures negatively affected; oil rigs, desalination plants, jetties, aquaculture equipment and cooling plants are just a few examples of other impacted facilities.

An environmentally friendly alternative

While modern boat hull paints are admittedly effective against biofouling, they are also toxic and therefore exact a high toll on marine life. Generally speaking, these paints are based on the principle of continuously emitting a toxic substance into the surrounding sea water. When, for example, a barnacle larvae approaches the boat’s hull, it will either register the presence of the toxin and swim away, or absorb a fatal dose.

As said, this technique is effective; however, as well as poisoning the fouling organisms it is also toxic to all other marine life. In order to function, the paint must also slowly but surely dissolve and, as all boat owners know only too well, this means expending considerable effort on annual maintenance.

“What we are attempting to do is to phase out toxic hull paints and replace them with environmentally friendly antifouling techniques,” says Mattias Berglin, who is managing the project on behalf of RISE.

Recreating nature’s own protection

In principle, almost everything in the oceans suffers from biofouling; over time, everything from blue whales and oil rigs to leisure craft will pick up unwelcome stowaways. The project 3D-printed biomimetic microstructures for the control of marine biofouling is collaboration between RISE, the University of Gothenburg and Chalmers University of Technology to study how micro-structured surfaces can be made as inhospitable as possible for marine organisms.

“Somewhat like a hedgehog on land, except that we will be studying creatures such as mussels and crabs. These should be idle hosts for marine organisms but if one examines their shells or carapaces, they have a certain microstructure that seems to be designed to make it difficult for organisms such as barnacles to attach themselves,” explains Mattias Berglin.

Although the microstructures of mussels and crabs are useful, there is one creature in the ocean whose skin provides another advantage – the shark.

“we are testing various structures, but shark skin is of particular interest because it also reduces friction. The skin has a surface that has been used in other contexts to reduce friction, resulting in reduced fuel consumption. If we are able to combine the antifouling and low-friction properties, we will double the benefits.”

3D printing creates new opportunities

This is not the first time that attempts have been made to recreate shark skin; however, there is now a crucial difference – the 3D printer.

“With earlier techniques it was not possible to create such complex patterns. The usual methods led to regular microstructures, with all peaks being equal in size and height. Shark skin, however, is not regular. A 3D printer can make every structure individual, something that other methods can’t achieve,” says Mattias Berglin.

Using this technique it proved possible to achieve a structure more like natural shark skin, something that had a clear impact on biofouling. Although the drag resistance of the new surface has not yet been tested, it is highly likely that, given its close resemblance to nature, the product will also reduce friction.

At the press of a button

The first step of the project was to print the same type of regular surfaces that are already in use in order to demonstrate the ease with which a 3D printer could achieve this.

“We did this to show that we could achieve the same results as previously, but at the press of a button without leaving our desks. Among other things, manufacturing the same product using conventional techniques requires access to a cleanroom.”

So, how large is it possible to print out? RISE already has a patent for an antifouling surface on a role and this is also likely to be the technique used here. This offers a number of benefits over paints; it lasts longer, contains no solvents, can be stored for long periods and eliminates spillage and fire hazards.

An environmental necessity

In the final analysis, the solution for preventing marine biofouling is likely to be an environmentally friendly combination of methods. Even if none of the gentler approaches have so far proved as effective as toxic paints, alternatives to these must be developed.

Even if the shark skin structure does prove effective in terms of reducing friction, it is not optimised for boat hulls. Tests are underway to improve this microstructure using large wind tunnels in a collaboration between Chalmers and the Fluid Mechanics Group at the University of Melbourne, Australia.

“We also want to try to understand the behaviour of marine organisms; what genes are turned on and off when they search for surfaces on which to establish themselves. This study is being conducted in collaboration with the University of Gothenburg. If we can understand this then perhaps we can ‘talk’ to the larva in a new language, molecular biology, and convince it to choose a different surface to attache itself to,” concludes Mattias Berglin.