One of the first things I’ve written about in sci.casual was about some research on how to make silk stronger, strong though it already is. Although I’m sure that this research goes back far, far, far in the past considering how long it’s been cultivated and traded for centuries, we never stop improving. After all, with what good we’ve got, there’s got to be something better, right? Why should this be the pinnacle of wireless telephones:
When with more research (well, and time), we can have this:
(I tried playing Fruit Ninja with the previous phone, and they’re never letting me into that farmer’s market again)
In this week’s Featured Article, where a group of researchers from Tsinghua University (Beijing, China) proposes that one can reinforce silk fibers just by adding a touch of carbon to silkworms’ diet. Something to think about if you’re the type to wear a silk scarf and/or chew on pencils, but it’s not just as simple as force-feeding silkworms carbon. This isn’t exactly fine cuisine we’re talking here (there’s one particular practice I’m thinking of, and I’m not bringing that up), the authors just propose spraying mulberry leaves with a solution containing carbon nanotubes or graphene and letting it go through a silkworm’s gut, where it either becomes part of the silk fiber (yay) or completely passes through into poop (boo and/or eww). Before we get further into the science, there are probably a couple of concerns that you’re thinking of that need to be addressed. One, isn’t carbon, you know, breakable? You would think that this is a problem, especially if you’re a writer or a scientist – mathematics people and engineers would know this much too often – that carbon (the atoms that make up carbon nanotubes and graphene) has a tendency of being ‘brittle’ (OK, really breakable). Tell that to your pencil during an exam and/or when you’re in the middle of deriving an elegant solution or a beautiful piece of prose. There’s only one thing to feel:
Here’s the thing: bulk graphite (like what you find in your pencil) is made up of layers of carbon, each single layer called graphene. Graphene (you did click the link above, didn’t you?) is rather flexible, but more layers of graphene means less flexibility. The walls of carbon nanotubes work the same way; more layers in the walls means it’s stronger, but too many and it won’t be very flexible – so, same idea. The authors of the paper wanted something both strong and flexible, and carbon nanotubes and graphene seemed to be the way to go. Turns out that they were right; adding these carbon materials to silkworms’ diet made for stronger silk. Testing shows that more force is required to actually break (‘fracture strength’, as the paper calls it) the silk fiber, and you could stretch it just a little more before it does break. I personally like this idea, since I’d like to have silk socks that don’t get worn at the ankles from rubbing up against the topline of my dressy leather shoes. Now I have to go buy some more before my doctoral defense…
Anyway, the authors propose that this is possible because the presence of the carbon materials prevents silk proteins from taking on certain shapes that would make it tougher, yet stiffer. Don’t go overboard on this one, it’s not like you’re going to get silk that becomes as stiff like a piece of wood or even paper or anything, but at least it may not have the flowiness (this can’t be a word, and if not, I am totally a trend-setter) that we fashionables often associate with silk. The carbon materials reinforce the thinner silk fibers, making them harder to tear and stretch out without making them stiffer. By the way, remember what I said about why graphene is flexible but graphite isn’t? Further testing shows that’s exactly what happens – in fibers that came from a mulberry-leaf diet with higher carbon content, the fibers were more easily breakable and less-stretchy.
Oh, and the other issue: isn’t eating carbon going to be bad for the silkworms? Why do they have to eat carbon – why not just spray carbon material directly onto the silk itself? Doing that would mean that the carbon material – most if not all of it – is on the silk fibers, rather than in them as the authors confirmed with further testing. If that’s so, then the fibers won’t be as flexible and strong, since the structures only help with the outside. Not to mention they could probably be sloughed off when exposed to water. (Look, we can’t all afford dry-cleaning all the time, OK?) However, the authors don’t know for sure yet what’s the upper safety limit (or if there is one) for silkworm ingestion of carbon because it’s not even clear how the carbon is incorporated into the silk proteins or passed through their digestive systems. So of course they don’t have the answers: they don’t exist yet (it’s a common misconception that we scientists have all the answers to all the things) because no one’s asked. Now that the authors have asked the question, it’s up to biologists, most likely entomologists, to take up the cause.
And because scientific solutions are a free service we provide here in sci.casual, there’s one thing that we would like to ask: just how conductive are these carbon-reinforced silk fibers? For one thing, carbon materials are rather good at conducting heat and electricity, and with all sorts of research going into powered wearables, imagine a smart scarf. Not just smart in the sense that it could look good with a pair of slip-ons or Oxfords (OK, it seems that sci.casual is leaning fashionista lately), but smart in the sense that it could have all sorts of tech on it, like sensors and printed circuitry. If I ever open up a place for sci.casual merch, it’s going to get really expensive with all these prototype materials…
Featured Article: Wang Q, Wang C, Zhang M, Jian M, Zhang Y. (2016) “Feeding Single-Walled Carbon Nanotubes or Graphene to Silkworm-Reinforced Silk Fibers.” Nano Letters 16(10), 6695-6700. doi: 10.1021/acsnanolett.6b03597
Featured Image Credit: Wikimedia Commons, Free Art License (author: katpatuka)