It’s one of those scientific truisms — spider silk is maybe the strongest biological material, stronger than steel. But we just found something even stronger: the tiny teeth of a rock-scraping limpet.
When scientists talk of spider silk’s strength, they are talking about its “tensile strength.” Tensile strength is a measure of how much pulling force a substance can withstand before it deforms and breaks (per the substance’s cross-sectional area). For spider silk, that measurement is four and a half billion Newtons per square meter, or about half the pressure it takes to form a diamond from a less glamorous allotrope of carbon.
According to a new study published in Journal of the Royal Society Interface, the teeth that limpets use to scrape over rocks when feeding have a tensile strength of five billion Newtons per square meter (and maybe even more). But where does all that strength come from?
“Recent work has shown that the teeth of limpets approximate to an almost ideal model natural composite material,” write study authors Asa Barber, Dun Lu, and Nicola Pugno.
Limpet teeth aren’t made entirely of organic material, like spider silk is. Instead, the tiny rock rakes are composed of a protein matrix weaved through with mineral nanofibers (specifically, goethite). And because the limpet teeth are so small, only a few nanometres in diameter, there is almost no room for the flaws that inevitably creep into larger and more complicated structures.
“Limpet teeth therefore present a natural structure with the potential to optimize composite strength towards a theoretical maximum.”
A) The limpet’s tongue-like radula containing bands of teeth. B) The goethite fibers embedded in the teeth protein. C) The teeth under scanning electron microscope. D+E) Close-ups reveal how closely the goethite embedding resembles human-made composite materials.
To find out just how much stress the teeth could take, the team “sacrificial” a few limpets from the seawater of Southampton, UK and extracted samples of their teeth. The scientists then immersed those teeth in expoxy to give their equipment something to grab on to. Then the epoxy-teeth combination was pulled apart millimeter by millimeter until a tooth broke.
In short, the performance of limpet teeth is only comparable to our strongest commercial carbon fibers. These little snails show just how innovative and perfecting nature can be — the teeth are as close to the theoretical maximum strength of the materials that make them up. “Outstanding” is how the team described the results of their tests.
Outstanding microscopic snail teeth.