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Materials science

At a stretch

A polymer based on the elastic protein that enables fleas to perform their extraordinary jumping feats has been synthesized. The material, described by C. M. Elvin et al. in this issue (Nature 437, 999–1002; 2005), is, perhaps unsurprisingly, rubbery and highly resilient; indeed, some of its properties exceed those of a material used to make bouncy balls for the playground.

The elastic protein resilin, the source of the authors' inspiration, comes from the same family of biomacromolecules as spider silk and elastin (a protein that makes animal tissues flexible). It is, in fact, found in most insects, where it facilitates not just jumping, but also many actions requiring efficient energy storage and rapid repetitive movement — the chirping of cicadas and the flapping of dragonflies' wings being other examples.

Elvin et al. produced their polymer by first cloning part of a Drosophila fruitfly gene and expressing it in Escherichia coli bacteria. They thus produced large quantities of a peptide found in a precursor molecule to resilin that contains 17 repeats of an amino-acid sequence thought to be responsible for elasticity. A photochemical reaction established crosslinks in the peptide to produce a solid material.

The result, a thread about one millimetre across, glowed blue when bathed in ultraviolet light (see image), and was easily cast into a range of shapes. Its ability to recover from deformation (the property known as resilience) was as good as that of natural resilin taken from a wing tendon of a dragonfly. It was also similar to that reported for elastin, and far higher than that of several synthetic rubbery polymers. A strip of the crosslinked resilin could be stretched to more than three times its original length without breaking.

The authors attribute the mechanical properties of the polymer to the three-dimensional amorphous nature of the crosslinked protein matrix. They also believe that a clearer understanding of the part played by water as a solvent and plasticizer could lead to the development of a whole new range of rubbery materials. Meanwhile, they suggest, their jumping-flea polymer could be a leap forward for biomedical and other engineering fields.

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Daw, R. At a stretch. Nature 437, 961 (2005). https://doi.org/10.1038/437961a

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