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Stronger Than Steel: Synthetic Spider Silk [video] (bloomberg.com)
51 points by pseudolus 54 days ago | hide | past | web | favorite | 24 comments

There are two main objectives when designing conventional structures: strength and serviceability. We want to make sure structures have sufficient strength under very rare and severe loading to prevent collapse. But we also want to make sure they don't move too much under normal loading. It sounds like using silk would be a challenge to satisfy both objectives in many applications. In order to actually mobilize the tensile strength, it would require huge strains that would be incompatible with conventional materials. Or everything would need to be pretensioned up to some high stress. Likewise, for serviceability it would require either lots of strand under low stress or pretensioned strand.

That's not to say these are insurmountable problems, just something Ive never thought about before.

The "obvious" solution to using spider silk is to create a weave of it, like a textile, and then use the spider-silk in the form of a composite.

Imagine spider silk replacing fiberglass threads for example, or carbon-fiber threads. Its not fiberglass or carbon-fibler per-se that makes the material strong, its the composite. The mixture of plastic (which provides compressive strength) with fiber (which provides tensile strength).

There are a ton of composite fibers in the marketplace. I'm not a materials engineer, so I don't know exactly what people are looking for in their fibers (aside from high tensile strength). Probably low-weight, high strength... and probably low-compressive strength (or at least, people ignore the figure).

"Elasticity" in spider-silk sounds interesting, but I'm not sure if thats good or bad for a composite.


The composite for structures is going to be Reinforced concrete: Steel Rebar provides tensile strength, while Concrete provides compressive strength.

Where spider-silk (or fiberglass / carbon fiber composites) shine, are low-weight applications. Bicycles, bullet-proof armor, and flywheels. The question is if spider-silk is actually any better than carbon fiber (or Kevlar)

That's the thing: we have a LOT of manufactured fibers. Maybe spider-silk has a niche that can be used. But its competing against Carbon Fiber, Fiberglass, and Kevlar.


It seems like Spider-silk has less tensile strength than Carbon Fiber / Kevlar. However, due to its flexibility, spider-silk can absorb significantly more energy before breaking (aka "Toughness").

So spider-silk might be superior for stopping bullets in a composite weave, but it would be awful as a load-bearing structure (unless that load-bearing structure were expected to be "catching" objects a lot). Hmmm... maybe a Tennis Racket would be the ideal use of Spider Silk...

Because I'm a structural engineer, I like to think about the future of structures, not bicycles. Many good ideas came about by taking something from one obvious application and transferring it to another. I also don't think we will be using reinforced concrete in the year 2070 the same way or as extensively as we are now - the carbon footprint is too large. Maybe these new materials can spawn completely new types of structural systems that were never possible with conventional strengths and stiffness. Low weight is ultimately a goal of structural engineering as well, but not to the same extreme as sporting goods. Obviously cost comes into play, but many things that were once prohibitively expensive are now used on structures, including carbon fiber.

Elasticity (or in the case of conventional materials, ductility) is a trait that has applications in seismic design, so I disagree with your last claim. The trick is combining the good parts of that material with the good traits of other materials into a composite that achieves stability under gravity and predictable deformability under seismic loads.

The problem with these silk biotech companies will be scale up and competing with existing cheap and abundant fibers.

Silkworm silk already has issues with water and such clothing has to be professionally cleaned. Many silks have the property of supercontraction and will shrink by 50% upon exposure to water.

Furthermore, these silk companies claim they can produce stuff as strong as natural spider silk, but that’s a very tall hurdle to jump. They stole VC interest by claiming that the fiber properties are engineerable, but very little academic research has been done in that space.

So you have to wonder what is the market for expensive fibers that don’t perform well in the context of clothing that gets wet.

Already you see companies like Bolt Threads pivoting towards cosmetics, because why not? The technical challenge is much lower and the profit per gram should be much higher.

Is this strong enough for a space elevator?

Spider Silk has a tensile strength of 1.3GPa, at a density of 1.3g/cm^3 [0]. This translates to 1300 kg/m3, or a specific strength around 1,000,000.

So short answer is probably “maybe?”, based on the equations here [1], however there are other mitigating considerations, everything from how would you mass produce it, to the fact it can constrict up to 50% when wet. Hopefully those are just engineering problems.

[0] https://en.m.wikipedia.org/wiki/Spider_silk#Density [1] https://en.m.wikipedia.org/wiki/Space_elevator

All the synthetic silk products I’ve ever seen are very susceptible to UV damage. Modern synthetic winch lines are synthetic silks, and while they are very strong, they need to be kept covered to ensure UV stability.

That’s very informative! What do you figure are potentially new applications for this that aren’t possible without it?

Safety. It’s light, and doesn’t store a lot of elastic energy, so when it does fail it doesn’t whip. That is a feature for winch lines and webbing bits for climbing.

Usually with these new fibers, the applications are lightness, since for applications without weight sensitivity steel is pretty awesome.

I read somewhere that spider silk has about 4% of the strength needed for a minimal space elevator.

Nothing is...

Whats the point of using such a good invention for making shoes?

What is the right kind of application for using spider silk?

Showing that their material has a breadth of applications, and can be worked into different shapes and contexts?

To be clear, they used their invention to make a shoe.

Shoes get literally kicked around a lot. It’s a good form factor for demonstrating durable, flexible strength. Just show it kicking something that would shred a lesser material.

The silk is also hard for bacteria to break down. So maybe as a shoe it would be less smelly than other fabrics over time?

It's probably extremely expensive, so you need to use it in very high value products.

I have no idea what we should make with it, but we currently make clothes out of it:


Leather was a pretty great invention too.

Maybe a really fast slingshot?

It's just a concept shoe made from spider silk. There can be many more application.

It's biodegradable (I guess) so probably we can use it to replace plastics.

Instead of plastic or metal or wood, we might end up using proteins.

I can really take stronger biodegradable grocery bags. The corn plastic based ones are an exercise in softness.

They were pretty adamant about how it didn’t biodegrade - “you can have a spiders web that doesn’t break down for hundreds of years”

I think another problem is high heat applications, how well does spider silk stand up to fire?

So, did they tried weaving a 1-cm diameter rope, and testing it against a similar diameter steel rope?

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