Carnivorous plant inspires ultra-slippery shipping solution
Australian research potentially solves a costly underwater problem caused by the banning of a toxic chemical. Andrew Masterson reports.
A newly developed nano-scale coating inspired by the carnivorous pitcher plant could save the global aquaculture and shipping industries billions of dollars.
Researchers at the University of Sydney’s Nano Institute, in Australia, have invented a surface coating covered in wrinkles 100,000 times smaller than a human hair. In field tests the coating prevented the build-up of bacterial sludge on underwater surfaces – opening the way to an elegant and non-toxic solution to a costly problem known as bio-fouling.
The term describes the accumulation of microbial muck on submerged materials, such as the hulls of ships or equipment used in fish farming. The build-up occurs because waterborne bacteria wash up against the surfaces and promptly follow their hard-wired evolutionary imperative to establish colonies.
The thick, filmy result not only has the capacity to interfere with mechanical components, but also dramatically affects the physics of the host structure. Biofilm significantly increases drag, so that ships, in particular, have to expend extra energy keep moving. One estimate suggests that biofouling costs the Australian shipping industry a whopping $320 million a year.
For decades, the standard response of the global shipping industry to biofouling was to hinder it by coating hulls with paint containing tributyltin – a chemical that was very effective at killing algae and barnacles, but was also described by the US Environmental Protection Agency as the most toxic substance ever deliberately released into the environment.
In 2007, after 40 years, tributyltin was banned worldwide. The action was good for human and environmental health, but it left the shipping industry without an effective strategy to combat microbial colonisation of its vessels.
Now, a team led by the Nano Institute’s Chiara Neto seems to have solved the problem.
In a paper published in the journal ACS Applied Materials & Interfaces, Neto and his team reveal the creation of a family of polymer-formed and lubricant infused “nanostructured wrinkled surfaces” that when coated onto submerged surfaces prevent algae taking up residence.
The scientists report that the coatings stood up well to field testing for seven weeks in the waters of Sydney Harbour, although efficiency decreased slowly as the time progressed. The coating is clear, they add, making it suitable for use on underwater optical equipment, such as cameras and sensors.
The design of the nanowrinkles was inspired by the carnivorous pitcher plant (of the genus Nepenthes). To capture its prey, the plant traps water around tiny, uni-directional spikes embedded in the opening at the top of its characteristic tube.
The result is an ultra-slippery surface on which prey insects find it impossible to gain purchase, causing them inevitably to slide into the pitcher and the pool of digestive juices there waiting for them.
Seen under extreme magnification, Neto nanowrinkles adopt a similar, though less directional, pattern – and, to common marine bacteria, cause very much the same effect.