Geckos may have the ability to stick to walls, but it seems that not much sticks to them.
The skin of the box-patterned gecko (Lucasium sp.) is able to prevent the adhesion of everything from household liquids to dirt and bacteria, according to new research. The skin also exhibited self-cleaning properties.
This discovery may have important implications for the design of medical implants, self-cleaning hospital surfaces and even water filters.
"Gecko skin is very thin -- only a few microns deep -- and they live in a hostile environment where bacteria can flourish, so we wondered what other protective measures the skin might confer," says Dr Greg Watson from the University of the Sunshine Coast, one of the leaders of the international team who undertook the research.
They found that the skin of the gecko consists of dome-shaped scales that are made up of super-tiny spinules -- or hairs -- ranging in size from several hundred nanometres to several microns in length.
When the researchers tested the skin's response to a range of contaminants such as pollen and dust, they found that they just didn't stick.
"The skin's topography provides a super-hydrophobic, anti-wetting layer that allows droplets as small as those found in fog to roll and even jump off the peaks and through the valleys in the skin, taking dirt, pollen and other contaminants with them," Watson explains.
Their study is published in Acta Biomaterialia.
Box-patterned geckos are found in the semi-arid Mingela Ranges in Western Queensland.
"The geckos are small, which means they have a high surface area to volume ratio, that is they have a lot of skin relative to their body mass," Watson says.
Watson and team also found that gecko skin shares many of the same structural properties as cicada wings, which are known to repel water and contaminants.
When the researchers placed Porphyromonas gingivalis, the bacteria that causes gingivtus and periodontal disease, on the gecko skin they found that most were killed within less than a day, without any application of chemicals.
Watson says that while they are not certain of what killed the bacteria, it is possible that they were impaled on the skin's spiny surface.
"However when human stem cells (from tooth pulp) were applied to the skin surface, they grew happily."
He says that stem cells are much larger than bacteria, which may explain why they were able to withstand the impact of the spines.
Watson says that the development of water-repelling, self-cleaning, anti-bacterial and biocompatible coatings in terrestrial and aquatic environments is of great interest worldwide.
"The gecko skin's anti-bacterial action may represent a new line of enquiry into such interactions where selective bacterial activity is required," he says.
"It may help deal with the growing problem of antibiotic resistance by providing an alternative way of minimising exposure to bacterial contamination in medical and dental implants, contact lenses, syringes and catheters and on hospital and other surfaces.
"It also has potential applications in marine structures and in membranes in water filters, which will allow water to be cleaned physically, rather than by using chemicals."