Science News, writing

Future!Tech: Slug-based Band-Aids

Your Random Science News Story From the Month of July

Throwback Thursday to that time a ragtag bunch of postgraduates ran into a slug on a failed trip to the Edinburgh Botanical Gardens and one tried poking it with a stick:

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Or that time I came home to my lodge in Marsfield and found a slug in my shower. I did not poke it with a stick, but used one to return it to that fresh (outside) Australian air:


Today’s random news story is not technically about slugs, however. It’s about one specific species of slug’s mucus – and how researchers are trying to make safer and more reliable biological tissue adhesives based on said mucus.

The report’s stuck behind a paywall, here. Thanks a lot, Science

Arion subfuscus, Credit: H. Krisp, CC BY 3.0

What happened?

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (HJAPSEAS) and Wyss Institute for Biologically Inspired Engineering (not WIBIE) have designed a new type of biocompatible adhesive.

They took inspiration from the Dusky Arion slug (scientific name: Arion subfuscus), which secretes a kind of gel1 when threatened capable of gluing itself in place. (Why might a slug want to do that, you ask? If a predator’s trying to take its lunch to go, it won’t be able to pry the slug off of whatever surface it’s stuck to.) Like a mucus, it’s highly deformable, but this gel is much stiffer than the snot you’re picturing – more akin to gelatin or agar. Those stiff gels, however, are usually brittle, so the Dusky Arion’s natural glue has the best of both worlds – producing a very tough2 adhesive.

But I did say “inspiration” – the researchers didn’t actually use the mucus to make their futuristic proto-bandages. They created a hydrogel – that is, a water-based gel3 – that uses a physics trick the mucus does: being full of positively-charged molecules (proteins in the mucus, polymers in the hydrogel). The polymers protrude from the hydrogel’s surface and adhere to tissues; in other words, they make the hydrogel sticky. The super-tough hydrogel matrix is made by mixing two polymers – alginate (a seaweed extract) and polyacrylamide, which you’ll find in soft contact lenses – and throwing in some calcium ions to increase how much the matrix can become deformed before breaking.

They tested their product on pig tissues – including skin, cartilage, heart, artery, and liver – as well inside living rats for 2 weeks. (You can watch them play around with hearts here and here.)

What’d they find?

The polymers in the hydrogel take advantage of three physical/chemical mechanisms in their stickiness.

  • First, because they’re positively charged, they’re attracted to negatively charged particles – say, the electrons on the surface we’re trying to get something to stick to.
  • Second, they form covalent bonds with nearby atoms on the surface we’re trying to get something to stick to (which then require energy to break).
  • And third, since they stick out of the hydrogel, there’s an interpenetration effect with the surface we’re trying to get something to stick to.

But that’s not the only part of the hydrogel that’s important – the actual matrix the polymer molecules exist in serves a necessary function, too. It dissipates energy by making use of “sacrificial” ionic bonds. Specifically, the calcium ions start out bonded to the polymer molecules in the hydrogel, and it’s those bonds that break first when the whole bandage is put under stress. Tests showed the matrix was capable of absorbing over three times the energy that other medical-grade adhesives could before breaking.

And when the hydrogel matrix failed, the outer adhesive layer was still bonded to the tissue. Compare that to the Band-Aid that flops off pathetically when you get your body sufficiently wet.

Unlike other commercial adhesives tested, the adhesive didn’t accidentally stick to or damage any surrounding tissues. And it remained sticky in the presence of blood.

So what?

Many adhesives used today come with one or more downsides; they’re cytotoxic – i.e. deadly to cells, don’t stick well to biological tissues (because they’re wet), or become inflexible after drying. The tested hydrogel has none of these, which makes it a possible candidate as an alternative to stitches and staples in wound repair, in addition to more advanced applications like attaching medical equipment to organs, or – as Imperial College London’s Adam Celiz suggests – “sticky robots“.

This adhesive, of course, hasn’t been tested on dead humans, let alone living ones, so you’ll have to wait to slap a slug-inspired sticker on that injury you totally got from rescuing a bus full of orphans from a rampaging herd of wildebeest as opposed to falling off your skateboard while trying to impress a disaffected teen with a sick ollie.

And, no. No one has come forward with their pitch for next-gen sticky hands. Not yet, anyway.

1. The gel is actually about 95% water – really dilute considering how effective it is as a glue.
2. “Toughness” is an actual term in materials science that means the ability to absorb energy and plastically deform without fracturing.
3. The “hydro” bit of the name refers to the Greek word for water. (See also: hydrate, hydroelectric, etc.)

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