An exciting new biological discovery was published yesterday (18 February 2015) based on research by scientists, Asa H. Barber , Dun Lu and Nicola M. Pugno. They have revealed the natural biological material that ranks the highest on record for tensile strength is none other than…..Limpet Teeth!
Okay, so be honest. Did you know that limpets had teeth? I must admit that I did not. My experience of limpets is limited to marvelling at the way that their little conical shells clung to rock faces, forevermore, being pounded by the sea. They seemed impossible to remove. As I child I wondered what they did in there and how they ate, but I had mostly put those questions aside…until now! This is an opportunity to learn more about limpets and these lessons could even teach our greatest engineers a thing or two.
Beneath the pointy shell, limpets have a strong muscular foot, which attaches to the rough surface of the rock. They also emit a sticky mucous, like a glue which seals them tight in their chosen position. This barrier keeps moisture locked inside and prevents them from being washed away by the sea. It also stops meddling…should I say, curious kids from prying them off!
They feed using a long tongue, known as a radula. This consists of a long chitinous ribbon, covered with tiny sharp teeth. The teeth scrape against the rock, removing algae..delicious!
Prof Steven Hawkins, of the University of Southampton described Limpets as “….the bulldozers of the seashore. The reason limpet teeth are so hard is that when they’re feeding, they actually excavate rock. In fact, if you look at their faecal pellets they actually look like little concrete blocks – because by the time it’s gone through their gut it’s hardened.”
Atomic Force Microscopy
A limpet’s tooth is around 1mm long and is made up of a mix of protein and fine tightly packed mineral non fibres – called goethite. The teeth were ground down and the tensile strength was measured using new technology – atomic force microscopy. Barber, Lu and Pugnon were able to analyse a minute sample of a limpet’s tooth, down to it’s atomic level. Each sample was 100 times thinner than a human hair!
They found that the goethite fibres were laced through a protein base, while the tooth itself was curved – providing perfect conditions for a high reading in the Mohs scale of hardness. The final score was an average of 5 Gpa. This trumped the previous high score holder, spider’s silk which has a Gpa of 4 (around the same as steel).
“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.” – Barber
This rating is about the same as the pressure required to create a diamond from carbon under the Earth’s crust. Interestingly, Professor Barber likened the strength to a string of spaghetti holding up 3,000 half-kilogram bags of sugar!
Many of our great engineering feats have been inspired by nature. Each organism has evolved to be perfect at fulfilling its purpose and we can learn from them.
“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.” Barber
One particular aspect that could benefit industry is the fact that the strength of a limpet’s tooth comes from its size. They are so incredibly thin that they avoid holes and flaws that are common in larger structures.
“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.
This is truly a fascinating discovery that could change mechanical technology in the future. We can learn so much from organisms, including marine animals, that we may simply overlook. It is another lesson in taking care of every aspect of our planet.