Greener way to spin spider silk
For its weight, spider silk is one of nature's strongest materials, and its elasticity and energy-absorbing properties make it an attractive prospect for materials scientists. But, our current ways of making artificial silk use very high temperatures and toxic chemicals. Or at least they did. Now a team of real life spidermen at Cambridge University - this time wearing labcoats rather than spandex - have invented a new, greener, cleaner form of spider silk. Georgia Mills spoke to Darshil Shah and Yuchao Wu...
Darshil - There's a fibre.
Georgia - Here’s a fibre here. Oh my God! I can barely see it. Are you sure there's anything there?
Darshil - 6 micrometres in diameter. Typical human hair is 80 micrometres in diameter so it’s really, really fine. That is why we need to convert it into yarn so that they are useable in engineering applications.
Georgia - This miniscule thread that I'm trying to look at is the new greener way of mimicking spider silk. The new method which doesn’t require extreme heat or toxic chemicals uses a hydrogel which is 98 per cent water and 2 per cent silica and cellulose. Yuchao Wu, a co-lead and PhD student at the Department of Chemistry told me where they got the idea.
Yuchao - If you look at the way a spider produce spider silks, the content inside their gland contains lots of proteins. These proteins have amorphous domains and crystalline domain which are soft and hard. So this is what we’re trying to reproduce.
Georgia - So you looked at how they do it. There's hard stuff in there, there's soft stuff in there. it’s all mixed together and you thought, “Let’s do it the same way” and that’s how you came up with your recipe, I suppose.
Yuchao - Yeah. Just imagine you go to the restaurant and you order some spaghetti. The spaghetti are the soft polymers while the meatballs are the hard silicon spheres. So when they mix together and there are some interaction between these meatballs and the spaghetti, in that case, the extension of the material can be extended into very large extent, and that’s why this material can be pulled into a fibre which has a very high aspect ratio.
Georgia - This aspect ratio refers to the relationship between width and height i.e. these threads can get very, very long and thin. Now, I wanted to see how this liquid hydrogel was spun into a thread.
Can I have a look at your machine? Do we have to run through the rain to get there?
Darshil - Yes. There are some bits through the rain.
Georgia - Okay.
Darshil - So we are just about to run a sample of the hydrogel and show you how the fibre forms from a reservoir of the soupy material – the hydrogel which is 98 per cent water – and we can pull a fibre from it up to around 250 millimetres in length.
Georgia - So the machine itself, it’s two little crocodile clips stuck onto these sort of pillars reaching towards each other. I'm assuming that is between these that the fibre will form. So we’ve got a tiny little blob of it. It just looks a bit like clear glue and now, the magic happens.
Yuchao - Ready?
Georgia - Here we go… it’s stretched out about 7 centimetres there. It was getting very, very thin but the blobs of glue were kind of stretching out to form this long fibre. Is that how it’s done then?
Darshil - Yeah. So basically, it draws and pulls out material from the reservoir and eventually, because the aspect ratio becomes very large, water starts to evaporate, and you're left with an entirely fibrous material based on modified silica and modified cellulose.
Georgia - You’ve got a green way of doing it. But isn’t the most green way just to get spiders to do it? Why can't we just have a room full of spiders making silk for us?
Darshil - First of all, spiders are cannibalistic in nature. So, what we find is that if you have many of them in a very small space, they will start eating each other up or protecting their own territory. And also, milking silk from spiders is quite a difficult task.
Georgia - Finally, have you compared this in strength and resilience to the traditionally made spider web?
Darshil - Yes, we have. So we have compared it to many other technical fibres and we found that the damping capacity of our fibre which is the ability of the material to absorb energy exceeds that of natural silks. So the application of these supermolecular fibres would probably be in technical textiles, particularly where energy absorption is important such as in blast proof shrapnel resistant military clothing, silk cloth for sailboats, fabrics for parachutes and air balloons, protective gears and devices such as helmets for cyclists and skateboarders, and finally, as sensors because we can alter the chemistry by introducing tiny amounts of other materials, and we can use these fibres for sensing applications and help monitoring. This is an important field of engineering to ensure safety, reliability, and functionality of a structure.