Borrowing from nature

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Published: March 19, 2015 2:59:01 AM

News of the remarkable hardness of the teeth of Patella vulgata has restored the lost importance of the limpet

Patella vulgata, a common limpet which spends its lifespan of about 20 years rasping at rocks for sustenance, has acquired rockstar status in the material sciences. A paper in the journal Interface of the Royal Society has established that its teeth are made of the hardest known substance created by life. In their abstract, the authors Asa H Barber, Dun Lu and Nicola M Pugno write: “We show that the tensile strength of limpet teeth can reach values higher than spider silk, considered currently to be the strongest biological material, and only comparable to the strongest commercial carbon fibres.”

The marine gastropod has 1,920 teeth but so far it has been better known for being eaten, rather than eating. Shells of Patella vulgata discovered in the 19th century in the Altamira cave in Spain were interpreted as the remains of a meal from the Upper Paleolithic, from about 15,000 years ago. The shellfish are still used for food in the Iberian peninsula but generally Patella vulgata has fallen into gastronomic disrepute. Only its novelty value is globally appreciated—it is food that you can literally comb off the beach. From Victorian times in Britain, it has been regarded not as regular food but as emergency rations for hard times. But the prevalence of Patella vulgata in Mesolithic middens suggested that it used to be more mainstream, and fell off the dining table as populations became better-off and were able to afford a wider variety of food.

Indeed, limpets were revealed to be politically charged in 1762, when they triggered a “kelp riot” in the Orkneys—technically, though, it was a limpet riot. At the time, kelp was harvested from the coast of Scotland and burned to produce lucrative soda ash (sodium carbonate). This created jobs, but the over-harvesting of kelp also destroyed the habitat of shellfish like limpets, and the poor rebelled at the destruction of what was probably an important source of food for them. Fortunately, the Solvay process has been producing sodium carbonate cheaply from mineral feedstock since the 1860s, and this particular ecological flashpoint is permanently past.

Now, news of the remarkable hardness of their teeth has restored the lost importance of Patella vulgata. The teeth are so hard that the limpets actually masticate part of the rocks whose surfaces they scrape for food, and the wastes they eject are somewhat like concrete. Sounds like undergrad quiz trivia but, at some future date, this knowledge may assume commercial importance. In the realm of speculative technology, machines could become easier to maintain if parts exposed to high stress were generated by living tissue, which looks after itself. Besides, it could be cheaper and greener to create specialised materials by life processes rather than conventional industrial methods. On both counts, extant species with the required characteristics could provide models and, quite possibly, the required genetic material.

Living things have frequently inspired industrial design and architecture. The honeycomb is probably the commonest structure that industry has borrowed from nature. It finds use in high-strength, low-weight materials in applications ranging from prefab building parts to satellite and aerospace components that must not crumple under massive forces of acceleration. Honeycomb materials built out of carbon nanotubules are anticipated. In the 1970s, tall grasses in general and bamboos in particular attracted great interest for their resilience under the tremendous shear stresses unleashed by tropical storms. Usually, bamboos are the only plants left standing in the wake of severe weather events on our coasts. Architects attempted to mimic the structure of fibres in a bamboo stalk in the design of beams and girders, and even in that of whole skyscrapers.

Such biomimetic design has a long tradition, stretching from the 19th century to the present. The best-known example is Antoni Gaudi’s vast Sagrada Familia basilica in Barcelona, whose dome is supported by design borrowed from the structure of trees that combine to hold up forest canopies. The latest manifestation of biomimesis is the dreadful Gherkin in London, which is actually based on a sponge rather than a pickle.

The growth of genetic science ensures that we can get not only ideas from natural structures like teeth, but the structures themselves too. Patella vulgata is, therefore, suddenly a valuable property, and one wonders how many potential properties, whether structures, chemicals, processes or behaviours, are lost every time a species becomes extinct. Of course, it would be absurd to reduce the possibilities to commercial terms. The debate on conservation has been skewed by the tendency to put a value on species and a cost to their conservation, and do a displacement analysis. A gnus versus grasshoppers argument is as ludicrous as Goebbels’ guns versus butter argument. Life transcends commerce, and its valuation requires more imagination than a spreadsheet cell can hold.

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