Spiders Ingest Nanotubes, Then Weave Silk Reinforced with Carbon

MIT Technology Review ^ | 5-6-2015

[Citizen Zed]

Spiders sprayed with water containing carbon nanotubes and graphene flakes have produced the toughest fibers ever measured, say materials scientists.

Spider silk is one of the more extraordinary materials known to science. The protein fiber, spun by spiders to make webs, is stronger than almost anything that humans can make.

The dragline silk spiders use to make a web’s outer rim and spokes is amazing stuff. It matches high-grade alloy steel for tensile strength but is about a sixth as dense. It is also highly ductile, sometimes capable of stretching to five times its length.

This combination of strength and ductility makes spider silk extremely tough, matching the toughness of state-of-the-art carbon fibers such as Kevlar.

So it goes without saying that the ability to make spider silk even stronger and tougher would be a significant scientific coup. Which is why the work of Emiliano Lepore at the University of Trento in Italy and a few pals is something of a jaw-dropper.

These guys have found a way to incorporate carbon nanotubes and graphene into spider silk and increase its strength and toughness beyond anything that has been possible before. The resulting material has properties such as fracture strength, Young’s modulus, and toughness modulus higher than anything ever measured.

The team’s approach is relatively straightforward. They started with 15 Pholcidae spiders, collected from the Italian countryside, which they kept in controlled conditions in their lab. They collected samples of dragline silk produced by these spiders as a reference.

The team then used a neat trick to introduce carbon nanotubes and graphene flakes into the spider silk. They simply sprayed the spiders with water containing the nanotubes or flakes and then measured the mechanical properties of the silk that the spiders produced.

For each strand of silk, they fixed the fiber between two C-shaped cardboard holders and placed it in a device that can measure the load on a fiber with a resolution of 15 nano-newtons and any fiber displacement with a resolution of 0.1 nanometers.

The results make for impressive reading. “We measure a fracture strength up to 5.4 GPa, a Young’s modulus up to 47.8 GPa and a toughness modulus up to 2.1 GPa,” say Lepore and co. “This is the highest toughness modulus for a fibre, surpassing synthetic polymeric high performance fibres (e.g. Kelvar49) and even the current toughest knotted fibers,” they say.

In other words, giving spiders water that is infused with carbon nanotubes makes them weave silk stronger than any known fiber.

The work raises some interesting questions. For a start, exactly how the spiders incorporate carbon nanotubes and graphene flakes into their silk is not clear. The team use spectroscopic methods to show that the carbon-based materials are present in the fiber but are unable to show exactly how.

One possibility is that the silk becomes coated with these carbon-based materials after it is spun. Lepore and co cannot rule this out but say it is unlikely because the resulting structure would not have the strength they measured. “Such external coating on the fibre surface is not expected to significantly contribute to the observed mechanical strengthening,” they say.

Instead, the team say it is more likely that the spiders ingest the water along with the carbon-based materials and these are then incorporated into the fiber as it is spun. So the nanotubes and graphene end up in the central part of each fiber,e where they can have the biggest impact on its strength.

The team have even simulated the resulting molecular structure and say that the mechanical properties are in good agreement with the experimental results.

There are challenges ahead, of course. Nobody has discovered an efficient way to harvest spider silk, although not for lack of trying.  So an important future step will be the development of such a technique that can work on an industrial scale. That would open the way to widespread applications in everything from tissue repair to garment design.

This isn’t the first time that researchers have attempted to modify spider silk. Various groups have added metallic elements by placing the silk in the appropriate vapor. In this way they have significantly increased the strength and toughness of the silk, although never to the extent that Lepore and co have managed.

Which is why their work is impressive. The extraordinary properties of spider silk are the result of 400 million years of evolution. So such a significant improvement is clearly something special.

And the technique’s simplicity suggests that a similar approach could be used on other organisms. “This new reinforcing procedure could also be applied to other animals and plants, leading to a new class of bionic materials,” they say.

Ref: arxiv.org/abs/1504.06751 : Silk Reinforced With Graphene Or Carbon Nanotubes Spun By Spiders

[tacticalogic]

Steel is 30,000 psi.

Not an engineer, but I know what the head markings on steel bolts mean, and that appears to be some pretty sorry steel you've got there.

[Lurkina.n.Learnin]

Ain’t exactly 3d printing bud damned interesting anyway.

[GraceG]

I am worried carbon nanotubes may be the next asbestos... if they run through the spiders system and get crapped out the spinerets... where else are the accumulating?

[Faith65]

BKMK

[imardmd1]

It matches high-grade alloy steel for tensile strength . . .

I doubt it. I'd like to see somebody come up with numbers/stress diagrams to prove it. Sounds like BS to me.

[Lurkina.n.Learnin]

Can goats produce it?

BioSteel
http://en.wikipedia.org/wiki/BioSteel

[NicknamedBob]

"... if they run through the spiders system and get crapped out the spinerets... where else are the accumulating?"

In the soot around your candle and your kerosene lamp.

We've had this stuff forever, but didn't know it.

It's tricky to get it concentrated so that it can be spun as a fiber. That's what's remarkable about getting it into and through the spiders.

If they can mix it with the protein they're getting from transgenic goats, they can spin their own.

Then that's when we'll have some really light weight armor, and maybe some impressively strong escape lines for tall buildings and stuff.

[imardmd1]

Don't know where you got this, but ResearchGate Materials Data Book gives high carbon steel Young's modulus as roughly 1000 GPa and tensile strength as about 1000 MPa.

For your information, Young's modulus is not the yield strength. Engineering is a bit more complex than one mught suppose.

[Scrambler Bob]

From Wikipedia

Steel (ASTM-A36) 200GPa 29.0×10^6 psi

Need to check units, and not confuse with Yield Strength.

(Trying to remember from 50 years ago.)

[Darksheare]

ferrulefiber is one step closer to reality.

[Darksheare]

Johnny mnemonic and the monomolecular wire weapon.

[NicknamedBob]

Larry Niven had “Sinclair” monofilament. Exceedingly deadly. Like a Star Wars light-saber on a spool of thread.

[GeronL]

Should be tested on liberals

[bajabaja]

Three D Printing Ping List leader, null and void, might be interested. Live three dee printing.

[Fred Hayek]

OK, it’s been a while since I had strength of materials. Steel is 29,000,000 psi. I was off by some decimal points.

[Rodamala]

Tensile strength is not the same as Young's Modulus, which is a measure of elasticity. For reference, the Young's Modulus, E, for Steel is 200 GPa ≅ 29 x 10⁶ psi.

[Rodamala]

Sorry... didn't see that others had already pointed out your error... I don't like to "dog pile on the rabbit".

[Scrambler Bob]

I was off by some decimal points. —

Back in the day (before calculators) we had to track the decimals for slide rule calcs.

I think I still can. The new IT guys don’t know how a slide rule works.

I showed an IT tech once, when his system was down. Joked that my slide rule was backup for system down times.

[moose07]

Wouldn't trust it for a steel beam replacement ,but:

link

In fact, their mechanical properties can be considered above those of steel itself. Its absorbed energy at breaking point is almost two orders of magnitude higher, while its tensile strength [stress] is almost six times higher and the stresses at breaking point are equivalent. Additionally, although the Young’s modulus of steel is about three times higher than the spider-silk modulus, this last material has a much lower density. Its ratio of tensile strength to density is perhaps five times better than steel. Therefore, at equal mass, the spider silk behaves much better than steel. In conclusion, spider-silk fibers are nearly as strong as several of the current synthetic fibers and can outperform them in many applications in which total energy absorption is important.

[Nailbiter]

bflr