SPIDER silk is already , and now it can be made even more resilient with an injection of metal. By infiltrating the protein structure of the silk, the metal makes each strand 10 times as hard to snap.
The same technique might beef up other biomaterials for a host of applications such as making artificial tendons from collagen.
The inspiration comes from the many creatures that have tissues in jaws, stingers and claws strengthened and stiffened by metals. For instance, the mandibles of leaf-cutter ants and locusts are peppered with zinc, and some marine worms have copper in the protein matrix that makes up their jaws.
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Does that mean biopolymers such as spider silk and collagen could have their tensile strength improved by introducing metals into their organic matrix? That was the question for a team led by Seung-Mo Lee and Mato Knez at the in Halle, Germany.
To find out, the team fired beams of ionised metal compounds at lengths of silk from the orb-weaving spider using a technology called (ALD). As well as coating each silk fibre in a fine metal oxide, some metal ions penetrated the fibre.They tried zinc, aluminium and titanium compounds, all of which improved the mechanical properties of the silk. “With all three metals, the fibres can hold three to four times as much weight,” says Knez. The fibres also become stretchier, so that their toughness – the energy needed to break a strand – rises even more. “The work needed to break the fibre rises tenfold with titanium, ninefold with aluminium and fivefold with zinc,” he says. The results are published in the journal Science ().
The team believe that the metals are reacting with the spider silk’s protein structure, forming strong covalently bonded cross-links between the amino acid polymers within the silk. Normally, these polymers are only linked by weaker hydrogen bonds.
Spider silk is not a practical engineering material, but materials scientists are trying to produce artificial fibres that mimic its properties. If they succeed, the result could be super-tough textiles.
Knez thinks the technique has more immediate potential for toughening other biomaterials such as collagen. “Mechanically improving collagen using our technique might open several new possible applications, like artificial tendons.”
David Williams, a bioengineer at the University of Liverpool, UK, says that it will be crucial to make sure that these new materials are not poisonous. If the metals are covalently bound to the protein structure, they may remain safely locked up, he says. “But this would have to be stringently evaluated before any clinical applications.”
