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The foam that some frogs produce to make nests could be a good candidate for future pharmaceuticals and cosmetics because it can keep its shape for more than a week, isn鈥檛 likely to irritate human skin and can slowly release drugs for days.

Most synthetic and natural foams 鈥� like medical foams, beer foam, and the 鈥渟pit鈥� left on grass by insects called leafhoppers 鈥� collapse into a liquid within minutes or hours. But some frogs produce an incubator foam 鈥� protecting eggs and tadpoles from germs, dryness, and sun rays 鈥� so robust, it can withstand 10 days of harsh tropical conditions, says at the University of Strathclyde in Glasgow, UK.

To investigate the foam, Hoskisson and his colleagues collected about 200 whole foam nests from wild t煤ngara frogs (Engystomops pustulosus) and removed the eggs for safekeeping.

They ran protein analyses and various kinds of spectroscopy on the foam, confirming earlier findings that it has six differently sized proteins, which create what the researchers call 鈥渃lamshell-like鈥� structures. The structures include 鈥渨ater-loving and water-repellent鈥� sides allowing them to hold liquid inside the foam, says Hoskisson.

Force testing revealed that the foam could withstand remarkably high shear stress 鈥� 100 pascals, or about as strong as a 45 kilometre per hour wind 鈥� before breaking down. By comparison, stiffly peaked egg white foam can only withstand about half that force, he says.

To see if the foam could work in human medicine, the researchers incubated human skin cells with foam fluid and found no toxicity, says Hoskisson. Next, they loaded different kinds of dyes and an antibiotic, rifampicin, into the foam to measure time-release abilities. The foam released the compounds slowly, over periods of between two and seven days 鈥� in stark contrast to the hours or even minutes of extended drug release provided by current medical foams, he says.

This could be especially useful in burn cases, because the foam could administer antibiotics under the bandages. 鈥淭he way we envisage it is that you get one to three days鈥� worth of antibiotic release before you need to change the dressing, so you鈥檙e not ripping the dressing off every day but rather leaving wounds time to heal,鈥� says Hoskisson.

And because of its compatibility with human skin and its pleasant feel, the foam could also provide a good base for facial cosmetics, he says.

The researchers have also successfully produced the foam鈥檚 proteins in a laboratory using bacteria, without any frogs. 鈥淲e can actually just whisk the foam up,鈥� says Hoskisson.

As for the eggs that were removed in the experiment, the researchers hatched them all in a laboratory incubator and returned the tadpoles to the wild, where they subsequently thrived, says Hoskisson.

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