Soft, but not sawft

It seems like quite a few materials researchers get great ideas from nature. Perhaps stopping to smell the roses can lead to better solar panels, and you can prevent your jeans from blowing out thanks to some squid. So naturally (don’t point out the pun, do not even) with all this ado about wearable technology, we can take more cues from nature to make it more comfortable. What’s the point of wearing something for hours on end that feels like wearing a diaper, of all things?

Wirthl et al. – they’re the authors of this week’s Featured Article, mind – wanted to explore ways to not just bond two different kinds of material together (say, circuits and bone), but to get them to bond well. The authors wanted these materials to get tough. The challenge is the fact that these are ‘soft machines’ and ‘soft electronics’ – these are essentially flexible tech than can wrap around the complicated curves of, say, bones, plants, upside your head, and so on. Here‘s a good read for you if you want to know more, or this one if you’re not a materials scientist. Imagine, if you will: a smart (and hopefully inexpensive) bandage that not only keeps you from bleeding out, but it’s also wirelessly connected to other devices on your body (like these) that tracks your other vitals at the same time.

623px-flickr_-_official_u-s-_navy_imagery_-_a_sailor_helps_a_simulated_patient
Flickr/Public Domain (Author: Mackenzie P. Adams/United States Navy, 2013)

So how do the authors keep these soft electronics from being so…well, sawft? They harness the power of hydrogels; in general, these are solids that easily absorb water to the point that it becomes mostly water, yet behave like solids. You’ve seen these around before (link goes to YouTube video, so mind the ad). Anyway, these don’t have to be as fragile as a jelly dessert – depending on the solid used, these can be highly resistant to tearing. The authors didn’t invent hydrogels or soft electronics or soft machines; according to them, they are are about as abundant in nature as there are cells. That’s pretty much all cells are – complicated biological machines suspended in Jell-O. However, they wanted to figure out how to bond these hydrogel soft machines to surfaces without making them get brittle, which can lead to breakage. Good for peanuts, not for electronics.

360px-golden_peanut_brittle_cracked_on_a_serving_dish
Flickr/CC-BY-20 Generic (Author: Janet Hudson, 2010)

Using a different kind of agent to bond the electronics, they got no brittle surfaces, and the electronics and surface are essentially one instead of a glue sandwich. It can also conduct current (which is good, otherwise all they’ve done was create rubber bands); sure, it doesn’t carry a lot of current and not very far either, but if your electronics are mostly low-power sensors and LEDs, it’s not like you need to get hooked up to a car battery (for the second week in a row, PLEASE DO NOT EVER TRY THAT ANYWHERE, NOT THE LEAST AT HOME). It can also stretch quite far without breaking: the impressive part of it is that they got a piece of hydrogel to stretch more than three times in area, putting it under more than 1000% strain, and it didn’t break! In addition, regardless of what it’s bonded with (bone, leather, PET from plastic bottles, and anything else they mention in p. 3), depending on the hydrogel, the bond won’t rupture until about 2000 joules per square meter is applied to it (if you need to compare it to something, 2000 joules is the amount of energy expended by two Fiat 500s falling from a height of one meter), so it’ll be fine even if it’s bonded to your legs and you’ve got restless leg syndrome for sure.

The authors suggest all sorts of uses for this tech, now that they’re able to strongly attach LEDs, batteries, even sensors and Bluetooth antennas to this highly flexible material. For one thing, you could sync it to a smartphone so it could work with all those sensors. So that’s it – creating the electronic equivalent of a cell that you could hook up to a phone. Or a computer. Personally, I’m looking forward to something like this. If I get seriously hurt and require all sorts of telemetry, I’d rather not look like I got hurt from fighting a server rack.

server-rack-441494_640
Public Domain (Author: tylermax56, 2014)

If you could build your own piece of wearable soft electronics, where would you put it, and what would it do? Comment below, or hit me up on Twitter @sci_jonny (or just click on the Twitter logo at the top of the part) with your response and #wearables. And of course, throw in a #scicomm as well so the scicomm community (is there a shorter, less-awkward way of saying that?) knows you’re in on the conversation now.

‘Later, casuals.

Featured Article: Wirthl D, Pichler R, Drack M, Kettlgruber G, Moser R, Gerstmayr R, Hartmann F, Bradt E, Kaltseis R, Siket CM, Schausberger SE, Hild S, Bauer S, Kaltenbrunner M. (2017) Instant tough bonding of hydrogels for soft machines and electronics. Science Advances 3(6):e170053. DOI: 10.1126/sciadv.1700053.

Featured Image: Public Domain (Author: xaviervandeputte0, 2015)

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