Snail Slime

Posted: March 1, 2007

ANNA LEE STRACHAN: In case you haven't noticed, bugs have been running the world for almost half a billion years. They outnumber us 200 million to one and make up over 80% of known species. And yet, we spend over 31 billion dollars a year trying to figure out better ways to kill 'em.

What if one of these tiny "pests" had something amazing to tell us about physics, and if that's not enough, might inspire a new breed of robotics too? Take a look.

Spider-Man may have made one bug famous. But what about this guy? Yeah, they're slow. Ok, really slow, but snails do have some incredible superpowers.

RANDY EWOLDT: Spider-Man has nothing on these snails.

ANNA LEE STRACHAN: And MIT graduate student Randy Ewoldt is out to discover their secret.

RANDY EWOLDT EWOLDT: Check this out. It can even climb across razor blades.

ANNA LEE STRACHAN: So what's the key to their superpowers?

RANDY EWOLDT: Slime.

ANNA LEE STRACHAN: Slime?

RANDY EWOLDT: That's right. Slime has this very interesting property where it's a solid until you push on it hard enough, and instead of breaking like a typical solid material would, it actually flows.

ANNA LEE STRACHAN: Snail slime is what's called a "yield-stress fluid." That means it can behave like a solid glue or a slippery lubricant depending on how much pressure you put on it.

ANNA LEE STRACHAN: So how does the snail actually move in this stuff?

RANDY EWOLDT: That is a good question. So if you look underneath, you might be able to see waves traveling from the tail to the head. Underneath each of these waves it has liquefied the slim.

So we want to test it, and so you need to find a way to motivate the snails to crawl. The think that I like to use is beer.

ANNA LEE STRACHAN: (laughing) So you get the snails drunk, then what?

RANDY EWOLDT: (laughing) Put some beer down on the end, try to motivate them to crawl around a bit and as they're crawling around, I'll actually go in from behind and scrape up the slime with a razor blade like this and when I've collected enough I'll test it.

ANNA LEE STRACHAN: What Randy's found is that snail slime isn't your mild-mannered kind of matter. It's almost glue-like at rest, but as soon as it's touched it turns into a slippery fluid. Other things like mayonnaise, ketchup, and peanut butter have this property too, but so far, the closest thing Randy's found to snail slime is carbomer, a common thickening agent used in lotions and skin creams.

ANNA LEE STRACHAN: So what are you trying to find?

RANDY EWOLDT: We'd like to find an artificial slime to use for Robosnail.

NARRATION: That's right Spider-Man—you've met your match:Robosnail. And he's not made up in some comic book either—Randy and his lab partner Brian Chan are building him in their lab.

ANNA LEE STRACHAN: So is it actually moving like a real snail here?

BRIAN CHAN: Yeah. One section is always moving forward. And that is what a real snail does.

ANNA LEE STRACHAN: why would anyone want a robotic snail?

BRIAN CHAN: Well, one is to make robots that can explore the body. If we make really tiny robots, the fluids act like mud or slime, very viscous fluids. So a robot designed like this will be very good for that.

ANNA LEE STRACHAN: That means Robosnail's next quest might be inside you. Blood acts like snail slime on a small scale, so if Randy and Brian can perfect their work, Robosnail's successors could enable some high-tech medicine like remote-controlled chemo or targeted blood vessel repair—all inspired by nature's slowest little pest.

ANNA LEE STRACHAN: So what if there was some sort of chemical spill in here--would you guys end up with super snail powers?

RANDY EWOLDT/BRIAN CHAN: (laughing) Snailman? Snailmen! The power of slowness!

ANNA LEE STRACHAN: Not bad for a little guy who's gotten by half a billion years with a single foot.