In 2015, it was found that the strongest known biologically occurring material, was possessed by limpets, a marine mollusk that has a shallow conical shell, often found attached to rocks.
These small aquatic-snail-like mollusks use a tongue bristling with tiny microscopic teeth to scrape food off rocks and into their mouths. These teeth contain a hard yet flexible composite, found to be far stronger than spider silk and comparable to man-made substances, including carbon fiber and Kevlar.
Scientists have now ‘successfully mimicked’ limpet tooth formation in a laboratory and used it to create a new composite biomaterial. The study, published in the journal Nature Communications, suggests that the material could be upscaled into something super strong – that could rival the strength and flexibility of synthetics, but be disposed of without generating harmful waste products.
Strength like none other
“Fully synthetic composites like Kevlar are widely used, but the manufacturing processes can be toxic, the materials difficult and expensive to recycle. Here we have a material which potentially is much more sustainable in terms of how it’s sourced and made, and at the end of its life can be biodegraded,” lead author Robin Rumney, from the University’s School of Pharmacy and Biomedical Sciences, said in a statement.
What gives the limpet tooth this insurmountable strength?
It lies in a unique structure containing an amalgamation of flexible tightly packed fibers of a scaffold material called chitin, interspersed with fine crystals of an iron-containing mineral called goethite. Those fibers are laced through each other in much the same way as carbon fibers can be used to strengthen plastic.
To grow them outside of their natural environment, researchers developed methods where they deposited chitin and iron oxide, just as in the limpet tooth, on serum-coated glass.
After two weeks, they self-organized into structures that resembled the limpet organ, known as the radula, which makes the teeth. While this powerful regeneration has also been observed in sponges, they lack the ‘complex’ arrangement of tissues and organs found in limpets and other mollusks.
“I spent six months setting up this process. I went through every kind of permutation I could think of for what the cells might need and how they’d grow. It’s very different to growing bacteria or cancer cells which commonly grow in a lab environment, so we had to work out from scratch what would work,” said Rumney.
‘Replacing the use of plastics with a biological substitute’
After successfully replicating the limpet tooth formation, the team was then able to produce samples of biomaterial half a centimeter wide by mineralizing a sheet of chitin, a waste by-product of the fishing industry found in the exoskeletons of crustaceans, crabs, and shrimps.
Next, Rumney and the team want to explore the possibility that these minidiscs can be scaled up and mass manufactured.
“Our next step is to find other ways of getting the iron formation occurring, so we’re studying the secretions of the limpet cells to better understand that. If it works well, then we already have the gene readouts of the organ so we can lift the genes of interest out, and hopefully put them into bacteria or yeast to grow them at scale,” he said.
“We have a plastics crisis in the oceans right now, and I think it’s a nice symmetry that we can learn from a sea creature how to better protect them by replacing the use of plastics with a biological substitute,” he continued.
Senior author of the paper, Professor Darek Gorecki from the School of Pharmacy and Biomedical Science at the University of Portsmouth, said: “I started this as a curiosity project with a challenge to see if we grow cells from limpet’s radula using principles applied in my lab for culturing mammalian cells.
“It wasn’t just blue-sky research, where real-world applications are not immediately apparent, it was almost a pie-in-the-sky project. When it works, this is where science is at its best,” he added.