A team of chemistry researchers based out of the University of Sydney Nano Institute, led by associate professor Chiara Neto, has devised antifouling surface coatings that do not contain any toxic components, using the surface structure of a carnivorous plant as inspiration.
The need for alternative antifoulants has been on the rise since the ban of tributyltin, a toxic antifouling agent that was commonly used in the past.
The carnivorous Nepenthes pitcher plant, the research team’s inspiration, traps a layer of water on the tiny structures around the rim of its opening, noted The University of Sydney. This creates a slippery layer that causes insects to aquaplane, at which point they slip into the “pitcher” and are digested.
By stopping the initial adhesion of the bacteria, the coating in turn inhibits the formation of a biofilm and the further growth of marine fouling organisms.
Lab tests demonstrated that these surfaces resisted much of the fouling caused by a common strain of marine bacteria. In comparison, layers of Teflon that went untreated by the coating were completely fouled. To ensure the coating’s ability to hold up under a variety of conditions, the research team also tested the coating in contact with the surface of the ocean.
For this, test surfaces were attached to swimming nets at Watsons Bay baths in Sydney Harbor for seven weeks. Even in this environment, the coating still resisted fouling.
The coatings are also transparent and moldable, which can be useful for underwater cameras and sensors, noted the University of Sydney.
The new coating uses ‘nanowrinkles’ inspired by the carnivorous Nepenthes pitcher plant. The plant traps a layer of water on the tiny structures around the rim of its opening. This creates a slippery layer causing insects to aquaplane on the surface, before they slip into the pitcher where they are digested.
Nanostructures utilise materials engineered at the scale of billionths of a metre — 100,000 times smaller than the width of a human hair. Associate Professor Neto’s group at Sydney Nano is developing nanoscale materials for future development in industry.
Biofouling can occur on any surface that is wet for a long period of time, for example aquaculture nets, marine sensors and cameras, and ship hulls. The slippery surface developed by the Neto group stops the initial adhesion of bacteria, inhibiting the formation of a biofilm from which larger marine fouling organisms can grow.
The interdisciplinary University of Sydney team included biofouling expert Professor Truis Smith-Palmer of St Francis Xavier University in Nova Scotia, Canada, who was on sabbatical visit to the Neto group for a year, partially funded by the Faculty of Science scheme for visiting women.
In the lab, the slippery surfaces resisted almost all fouling from a common species of marine bacteria, while control Teflon samples without the lubricating layer were completely fouled. Not satisfied with testing the surfaces under highly controlled lab conditions with only one type of bacteria the team also tested the surfaces in the ocean, with the help of marine biologist Professor Ross Coleman.
Test surfaces were attached to swimming nets at Watsons Bay baths in Sydney Harbour for a period of seven weeks. In the much harsher marine environment, the slippery surfaces were still very efficient at resisting fouling.
The antifouling coatings are mouldable and transparent, making their application ideal for underwater cameras and sensors.