Nature is capable of producing materials of incredible strength, with spider silk one of the most celebrated examples. In 2015, a group of scientists made a game-changing discovery in this area, demonstrating that the teeth of clingy molluscs called limpets actually have the strongest tensile strength of any biological material. Drawing inspiration from these flinty fangs, the team has produced a composite biomaterial with extreme strength, which could provide a more sustainable alternative to high-performance materials such as Kevlar.
Limpets are aquatic snails with hat-shaped shells that cling exceedingly well to rocks along shorelines. Part of this coastal lifestyle involves scraping their teeth over the rugged surfaces to collect algae for feeding, and herein lie the secrets to the creatures' unparalleled tensile strength.
In 2015, University of Portsmouth researchers used atomic force microscopy to study limpet tooth material and analyze it an atomic level. The work revealed limpet teeth have a tensile strength of 3 to 6.5 gigapascals (GPa). For context, spider dragline silk has a tensile strength of around 1.3 GPa, while steel sits at around 1.65 GPa. The scientists believe the reason for the limpet tooth's incredible tensile strength is a dense network of chitin fibers with fine crystals of iron-containing geothite spread throughout.
The team has now created a system that allows similar structures to be formed in the lab that begins with serum-coated glass and chitin and iron oxide deposited on top. In two weeks, these self-organize into the organ responsible for limpet teeth formation, called the radula. Using a combination of isolated radula cells, tissue samples, mineralized chitin and a technique called electrospinning, the scientists were then able to grow ribbons of biomimetic limpet teeth half a centimeter (0.2 in) wide.
"I spent six months setting up this process," said Dr Robin Rumney, lead author of the research. "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."
The new composite biomaterial with extreme strength could come to occupy an important place in the realm of synthetic materials. If the team can successfully scale up the process, it could offer a more sustainable alternative to materials like Kevlar and plastic, which are resource-intensive to produce and aren't so easily recycled.
“Fully synthetic composites like Kevlar are widely used, but the manufacturing processes can be toxic, the materials difficult and expensive to recycle," explained Rumney. “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.”
The researchers are now turning their attention to optimizing the process, and expanding it to produce the synthetic limpet teeth at the scale needed for mass manufacturing.
“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," said Rumney. "If it works really 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. Obviously 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."
The research was published in the journal Nature Communications.
Source: University of Portsmouth