It’s stronger than steel and nylon, and more extensible than Kevlar. So what is this super-tough material? Spider silk; and learning how to spin it is one of the materials industries’ Holy Grails. John Gosline has been fascinated by spider silks and their remarkable toughness for most of his scientific career.
He explains that if we’re to learn how to manufacture spider silk, we have to understand the relationship between the components and the spun fibre’s mechanical properties; which is why he is focusing on major ampullate silk, one of the many silks that spiders spin.
According to Gosline, spiders use major ampullate silk for draglines and to build the frame and radial structures in webs, all of which have to deform and absorb enormous amounts of energy without fracturing. Comparing the amino acid sequences of major ampullate silk proteins from Araneus diadematus and Nephila clavipes, Gosline realised that the sequences differed on one count; Araneus silk is relatively rich in the amino acid proline, while proline levels in Nephila silk are very low.
Curious to know how the presence of proline affects the silks, Gosline and his student, Ken Savage, set about comparing the silks’ mechanical properties to find out how the amino acid affects spider silk toughness.
However, obtaining consistent spider silk samples is a problem. Gosline explains that spiders adjust the way they manufacture their silks depending on their circumstances, so he and Savage left the spiders roaming free so that the strands of dragline silk that they dropped were as uniform as possible. Having established a reliable silk supply, Savage set about testing the silks’ mechanical properties. Gently stretching the dry silk while measuring the force on it, the team quickly realised that the silks behaved almost identically; the presence of proline had little or no effect on dry silk. However, when Savage began investigating the hydrated silk it was a completely different story.
For a start, the wet Araneus silk shrank and swelled much more than the proline deficient Nephila silk. Savage also tested the silk’s stiffness, and found that the Nephila silk was almost ten times stiffer than the Araneus silk. Finally, knowing that regions of the silk proteins stack to form microscopic crystals in a fibre, Savage measured the fibre’s birefringence to see how the two silks compared and if the organisation of the proteins in the silk fibre changed when they were damp. The proteins in the Nephila silk were always more organised than the proteins in the Araneus silk, regardless of whether they were wet or dry. And as Savage stretched the silks, the degree of organisation in the hydrated Nephila silk increased much more than the Araneus silk.
Gosline realised that the different mechanical properties could be accounted for by the silk proteins’ amino acid composition. According to Gosline, proline amino acids are famed for breaking up the organised three-dimensional structures that protein chains fold into, so protein structures with high proline content would be poorly organised in comparison to proteins with little or no proline. Araneus silk contains 16% proline, found mostly in linker regions between the protein’s crystalline structures, which would make the linkers flexible and randomly arranged. Gosline realised that if this was the case, the hydrated silk might behave like an elastic band. Nephila silk, on the other hand, has a very low proline content in the linker regions, allowing the linkers to form a relatively well organised crystalline structure and behave more like a stiff spring. Gosline and Savage decided to investigate both silks’ stretchiness to see if they were more rubber-like or spring-like.
Stretching samples of the hydrated silks, Savage gently raised and lowered the temperature from 30 to 10°C while carefully measuring the minute forces required to maintain the extension. For Nephila silk the force remained essentially constant as the temperature changed, a clear indication of spring-like elasticity. However, for the proline-rich Araneus silk the force varied in direct proportion to the temperature, behaving like a rubber-band. So proline-rich spider silks extend like floppy rubber bands, while spider silks with low proline levels behave more like rigid springs.
Having found that proline amino acids have a dramatic effect on the mechanical behaviour of hydrated spider silks, Gosline and Savage are keen to find out why the behaviour of the dry silks is almost indistinguishable and what the functional significance is of the different proline contents.
John Gosline | EurekAlert!
What the world's tiniest 'monster truck' reveals
23.08.2017 | American Chemical Society
Treating arthritis with algae
23.08.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
23.08.2017 | Life Sciences
23.08.2017 | Life Sciences
23.08.2017 | Physics and Astronomy