Before we dive into this week’s post, take out a sheet of paper and a writing utensil or open up a word processor. Now that you’ve done that, write or type the following (and no, it doesn’t have to be in italics):
Think about what you just did, the fine control required for your hands copy the quote above (your penmanship notwithstanding – I have atrocious handwriting). You don’t think about the muscles involved when you’re writing or typing, but these tiny muscles are complicated and require more than just simple pushing and pulling. For one thing, they may even twist or bend around a bone as they push or pull. Need proof that this whole muscle thing is complicated? Alright, wise person, try this: rewrite (don’t type) the quote above, but you can’t move your fingers. That’s right, you can only use your biceps and triceps. I’ll wait.
Apart from looking foolish, especially if you were doing this in public, your penmanship probably isn’t worth writing (hah!) home about. Also, ha ha, made you write. Also also, that just goes to show how fine control of your body’s muscles work, which leads us to this week’s Featured Article: artificial muscles that are not only flexible and controllable, but cheap too. You may have seen news articles recently about artificial muscles that can lift 1000 times its own weight; this was the study that news agencies have been covering. Now I‘m covering it.
The authors describe how they can make these artificial muscles by borrowing a few concepts from origami – no, they’re not going to be making paper cranes, they’re building muscles by folding sheets of what is essentially strong plastic wrapped up in a fluid-filled PVC pouch. The ‘muscle’ ‘contracts’ by sucking the fluid out of the pouch, causing the plastic to get shorter. If you’re drinking out of a plastic bottle (especially one that’s rather thin), see what happens to the bottle when you suck up too much air from it and you’ll get the idea. Also:
If one wants the muscles to contract in a different way, the authors suggest that you just fold it however you like; make it a spring instead of something that looks like gym mats if you want to. This method of folding can even make the muscle more or less tense if you want it to contract slower or faster. Imagine this kind of tech in MMA…
So how well did these muscles perform? Apart from the whole 1000 times its own weight thing (it was a 2.6g ‘muscle’ that could lift a 3 kg object), the artificial muscles could stay under six times greater stress than human muscle, mostly because it can contract by over 90%. Picture this, if you will – the heart is a muscle. It’s not one you can control, but it’s muscle nonetheless (and in some places, it’s quite thick). If you can imagine that the heart is the size of your fist, imagine if it can contract to one-tenth of its size. That is how much this muscle can contract. This amount of contraction probably explains its strength, but it’s also quite powerful. The authors measured its power density (how much power it generates for its weight) is six times that of human muscles – that means it can get to work quickly. Imagine the kind of CrossFit chin-ups you can do with these things!
Li et al. also discuss energy efficiency, especially mechanical efficiency, which is a concern since a lot of energy tends to get wasted as heat anyway. Depending on what pump is used to contract the muscles, the muscles can get up to 59% efficiency – most of the energy spent to move the muscle actually moves the muscle. That’s like working out without breaking a sweat. Not bad for a muscle built using origami using materials that, according to the authors, cost “less than $1.” I’m guessing each piece of material that they use is less than a dollar, not counting the measuring equipment, but it’s something to think about for hobbyists with 3-D printers.
The authors mention several uses for this kind of tech, like exoskeletons, deep-sea robotics (what with all the stress placed on robot arms at those depths), and so on. You could check out the article for yourself, or you could let your imagination fly and comment below – what could you use these artificial muscles for? While you let your imagination fly, I’m going to go into hiding because my imagination had been tempered by far too much ’80s science fiction…
*translated from gamer speak: ‘cyborg is underpowered, buff please’
Featured Article: Li S, Vogt DM, Rus D, Wood RJ (2017). Fluid-driven origami-inspired artificial muscles. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1713450114.
Featured Image: Public Domain (Author: Petra, 2015)