Ever get frustrated at not being able to get out those last drops of shampoo from the bottle? Relief may be at hand.

Key points: Chemicals that make shampoo soapy also make it stick to plastic

Chemicals that make shampoo soapy also make it stick to plastic Scientists have been inspired by nature to create a surface coating to counter this

Scientists have taken a leaf out of nature to design a bio-inspired surface that ensures sticky liquids like shampoo and detergent slide cleanly out of their bottles.

"We've been working in the field of bio-inspired surfaces for some 10 years," said lead researcher Professor Bharat Bhushan from Ohio State University.

One of the most inspiring slippery surfaces in nature is the lotus leaf, which is famous for its ability to repel water.

"The way the lotus-inspired surface works is that you need a certain roughness to create air pockets," Professor Bhushan said.

Whether a liquid — like water or shampoo — slides along a surface depends on surface energy and surface tension: the surface must have a lower energy than the surface tension of the liquid sliding down it.

Water has a high surface tension, but the challenge with shampoo and detergent is that they are specifically designed to lower the surface tension of any liquid they are added to. This is what makes them so sticky, and so hard to extract from a bottle.

Sorry, this video has expired How the new surface makes shampoo and detergent slide off like water off a duck's back (Credit: Philip S Brown and Joe Camoriano/Ohio State University)

To get around this, the scientists used modelling to adapt the lotus leaf's air pocket system to design an incredibly slippery surface that even very low surface-tension liquids, like shampoo, will slide along.

To attach this slippery surface to polypropylene plastic shampoo bottles they mixed silica nanoparticles in a solvent, then sprayed that mix onto the surface of the polypropylene.

As the solvent softened and dissolved the surface of the plastic the tiny silicate particles became embedded and created the air pockets that make the surface so incredibly slippery.

When they tested it with shampoo, the drops of the liquid appeared to slide right off the surface.

However they did notice that over time, the surface did become less repellent, suggesting more work is needed to make the effect last as long as the shampoo bottle is in use.

The study is published today in Philosophical Transactions of the Royal Society A.