The world's new strongest natural material: Limpet teeth

February 19, 2015

The world's new strongest natural material: Limpet teeth

Step aside, spider silk: the strongest material in the world can be found inside the mouths of rock-dwelling marine gastropods.

Image by Tango 22, CC BY-SA 3.0
If you've ever been to the ocean, you've seen limpets: conical shells that seem glued to rocks and piers, almost impossible to pry loose. This is because they have a strong, muscular foot that can adhere to irregularities in the rock's surface. Combined with an adhesive mucus, this keeps the limpet from being washed away, and keeps moisture sealed inside its shell during low tide.

While clinging to the rock, the limpet uses a sort of "tongue" called a radula to feed. This is a long, chitinous ribbon, embedded with rows tiny sharp "teeth" that allow the limpet to scrape algae from the rock. And, according to new research, these teeth are the strongest natural material on Earth.

"Nature is a wonderful source of inspiration for structures that have excellent mechanical properties. All the things we observe around us, such as trees, the shells of sea creatures and the limpet teeth studied in this work, have evolved to be effective at what they do," said study leader Professor Asa Barber of the University of Portsmouth's School of Engineering.

"Until now we thought that spider silk was the strongest biological material because of its super-strength and potential applications in everything from bullet-proof vests to computer electronics; but now we have discovered that limpet teeth exhibit a strength that is potentially higher."

A scanning electron microscope image of limpet teeth. Each tooth is less than a millimetre in length.University of Portsmouth
The team used atomic force microscopy to examine the teeth, a method used to dissect materials all the way down to the atomic level. The sample used was microscopic -- 100 times thinner than a human hair. The technique for breaking down a sample of this size has only just been discovered.

Inside the teeth, the team discovered a mineral called goethite, which falls at about 5.0 to 5.5 on theMohs Scale of hardness. This mineral develops inside the limpet as it grows. The tooth is also curved, which contributes to its strength.

Optical image of the radula showing the rows of teeth.Interface
"Limpets need high-strength teeth to rasp over rock surfaces and remove algae for feeding when the tide is in. We discovered that the fibres of goethite are just the right size to make up a resilient composite structure," Professor Barber said.

"This discovery means that the fibrous structures found in limpet teeth could be mimicked and used in high-performance engineering applications such as Formula 1 racing cars, the hulls of boats and aircraft structures."

The other major discovery was that limpet teeth maintain the same strength no matter what size they are.
"Generally a big structure has lots of flaws and can break more easily than a smaller structure, which has fewer flaws and is stronger. The problem is that most structures have to be fairly big so they're weaker than we would like. Limpet teeth break this rule as their strength is the same no matter what the size," Professor Barber said.

Image by Tango 22, CC BY-SA 3.0
If you've ever been to the ocean, you've seen limpets: conical shells that seem glued to rocks and piers, almost impossible to pry loose. This is because they have a strong, muscular foot that can adhere to irregularities in the rock's surface. Combined with an adhesive mucus, this keeps the limpet from being washed away, and keeps moisture sealed inside its shell during low tide.

While clinging to the rock, the limpet uses a sort of "tongue" called a radula to feed. This is a long, chitinous ribbon, embedded with rows tiny sharp "teeth" that allow the limpet to scrape algae from the rock. And, according to new research, these teeth are the strongest natural material on Earth.

"Nature is a wonderful source of inspiration for structures that have excellent mechanical properties. All the things we observe around us, such as trees, the shells of sea creatures and the limpet teeth studied in this work, have evolved to be effective at what they do," said study leader Professor Asa Barber of the University of Portsmouth's School of Engineering.

"Until now we thought that spider silk was the strongest biological material because of its super-strength and potential applications in everything from bullet-proof vests to computer electronics; but now we have discovered that limpet teeth exhibit a strength that is potentially higher."

A scanning electron microscope image of limpet teeth. Each tooth is less than a millimetre in length.University of Portsmouth
The team used atomic force microscopy to examine the teeth, a method used to dissect materials all the way down to the atomic level. The sample used was microscopic -- 100 times thinner than a human hair. The technique for breaking down a sample of this size has only just been discovered.

Inside the teeth, the team discovered a mineral called goethite, which falls at about 5.0 to 5.5 on theMohs Scale of hardness. This mineral develops inside the limpet as it grows. The tooth is also curved, which contributes to its strength.

Optical image of the radula showing the rows of teeth.Interface
"Limpets need high-strength teeth to rasp over rock surfaces and remove algae for feeding when the tide is in. We discovered that the fibres of goethite are just the right size to make up a resilient composite structure," Professor Barber said.

"This discovery means that the fibrous structures found in limpet teeth could be mimicked and used in high-performance engineering applications such as Formula 1 racing cars, the hulls of boats and aircraft structures."

The other major discovery was that limpet teeth maintain the same strength no matter what size they are.
"Generally a big structure has lots of flaws and can break more easily than a smaller structure, which has fewer flaws and is stronger. The problem is that most structures have to be fairly big so they're weaker than we would like. Limpet teeth break this rule as their strength is the same no matter what the size," Professor Barber said.

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