Anette Hosoi, in an e-mail that may be unlike any an MIT professor has ever received from a student, this summer got a query from one of her grad students while he was vacationing in California.
His question: “Do you know how to get banana slugs onto an airline?”
Hosoi was familiar with the creatures, which are bright yellow and which, in slug terms, can be pretty huge — close to a foot long.
Her response, she says, was, “I’m not going to go there.” The student ultimately decided his plan wouldn’t work. But if it had, the animals would have joined a small menagerie of slugs and snails in Hosoi’s lab — and might well have helped accelerate one of its projects.
How so? Hosoi’s interests include properties of the slime that snails and slugs trail behind them. But to study slime you need ample quantities, so relying solely on small snails and slugs is a problem.
“Banana slugs produce lots of mucus,” she notes, “but unfortunately, they don’t seem to live in the East.”
Hosoi’s work with snails, slugs and the stuff they slide on reflects her interest in thin films. These are fluids that can be as little as a few millionths of a meter deep, a scale at which their behavior may be much different than at deeper depths.
At such scales, very liquid fluids can appear to acquire honey-like qualities even if their make-up hasn’t changed at all. But some fluids, including snail-produced mucus, exhibit other qualities, too. One example: under low shear rates — that is, when one surface is moving slowly with respect to another — the mucus not only stops being slithery but can actually serve as a traction-conferring substance, like sand on snow.
Hosoi and her group investigated this phenomenon by building “Robosnail,” a 10-inch long device that uses a large, undulating pad to propel itself forward. “I don’t think anyone else has studied how to use these viscous forces for propulsion,” she says.
That’s just one of the findings that Hosoi hopes will flow from her studies. She also wants to understand how it is that creatures like snails can crawl perpendicularly and upside down. It’s work with implications not only for new modes of locomotion but also for effective development of the minuscule instruments, known as “labs-on-a-chip,” whose operation depends on moving tiny amounts of fluid through microscopic conduits.
An Amazing Tube
For Hosoi, an assistant professor of mechanical engineering at MIT, slug-and-snail studies are a new focus in a scientific career with deep roots.
She grew up in Corvallis, Oregon, and from early in life she loved math and science. In high school, Hosoi won her region’s Westinghouse Science Contest competition. She went to Princeton for her bachelor’s degree, majoring in physics, and after that enrolled in the University of Chicago’s physics Ph.D. program.
There, her focus was on how tiny particles fall out of liquids and turn into sediment. But a chance event caused her to change course.
A thin-films expert from another university came to Chicago to give a talk and brought a show-and-tell item: a clear plastic tube that looks like a stubby neon light bulb, but with a crank at one end and a clear, syrupy liquid inside. Hosoi was fascinated by the fact that when you turned the crank, the liquid didn’t back up uniformly on the tube’s uphill side. Instead, it formed an exaggerated sawtooth pattern.
“This researcher said to me, ‘If you can figure it out, you can keep the cylinder,’” she says. With a colleague, Hosoi worked out the complex math involved. Their paper, published in the journal Physics of Fluids, has stirred considerable interest in the thin-films world, and Hosoi now has the tube on display in her office.
Chip-Based Blood Tests
Hosoi and her co-workers are currently probing why snails and slugs can navigate pretty much any surface they choose. One key to the creatures’ success, says Hosoi: “When they’re climbing and they want to stop for a while, they basically cement themselves to the surface.” She and her group, though, want to analyze not just what lets the mucus turn temporarily solid but many other aspects of snail locomotion, too.
Their work could help yield advances from “go-anywhere” crawling robots to brand new kinds of transport devices. It could also boost technologies like the lab-on-a-chip.
In such labs, some in development at MIT, you could put a tiny blood sample through a series of almost infinitesimal tubes, where it would be exposed to agents that would reveal key things about the sample: its cholesterol levels, say, or signs of infection.
The device would let you get a diagnosis on the spot in a doctor’s office — but only if its makers can make sure the blood is actually working its way through the chip-mounted network of conduits. Understanding viscosity effects at very small scales is critical to this aim.
Hosoi, though, is interested in making sense of unexplained phenomena as well as setting the stage for useful innovations. “I’ve always wanted to understand how things work,” she notes.
And while she’s quick to say that at the time, her childhood encounters with banana slugs didn’t inspire her to study them — “I thought they were pretty disgusting” — she is delighted it has happened.
“One of the best things about science is that it sometimes sends you off into uncharted territory,” she notes, “and you find yourself investigating issues that few if any other scientists have ever explored.”