For years, my friend Peri and her erstwhile husband had their very own imaginary friend. Known simply as "Snail," he was rarely seen, but often heard from, in the form of cryptic notes, emails, and the occasional postcard sent from France (or London, or Italy, or wherever her itinerant artist spouse was traveling at the moment). Snail went on to found his own imaginary artzine, Gastropod Cineaste (with a heavy emphasis on French New Wave films). Yes, Snail had a touch of intellectual snobbery; Jen-Luc Piquant simply adored him, dubbing him "mon petit escargot," despite the whole mucus thing.
Mucus, you say? Mais oui! That's how a snail gets around, after all, even those that dwell in the realm of imagination. Snails store a crystalline form of their mucus and then mix it with liquid to produce the long sticky trails of slime they leave in their wake. It's all about equal and opposite reaction: the snails push backward to create a pressure gradient that propels them forward. Mucus might be a bit gross to homo sapiens, but for snails, it's a miracle substance, enabling the creatures to crawl over all kinds of uneven terrain: sand, mud, ground scattered with leaves or twigs. And if they encounter a wall or ceiling, no problem! Thanks to the sticky stuff, they can maneuver those non-horizontal surfaces just fine.
Smart scientists know we can learn a lot from Mother Nature, and a bunch of folks at MIT are looking to how snails do the locomotion for insight into building robotic snails. Anette "Peko" Hosoi and a few of her students introduced Robosnail Version 1.0 back in 2003: a six-inch long machine, just one inch wide, that could "glide" over a thin film of silicon oil -- their version of mucus, called Carbopol, which is simply a gel-like, water-based polymer solution. There's lots of fascinating information -- like the fact that snails have three different modes of locomotion, including a bizarre kind of "gallop" --contained in MIT's 2003 press release on the subject.
If Robosnail dates back to 2003, why am I even bringing it up? Well, the latest iteration was just described in talks by Hosoi and her collaborators at the recent (November 19-21) meeting of the APS Division of Fluid Dynamics in Tampa Bay, Florida. It's a fluids-related project because it could provide insights into how blood flows through a vein. Like blood flow, snail movement is essentially a fluid flow contained by a flexible boundary. Anyway, Robosnail Version 2.0 is even more impressive than its predecessor: it can climb walls and move upside, thanks in large part to its light weight (less than 31 grams) and a slick layer of another mucus-like substance called Laponite. One promising application is the use of Robosnails to aid in oil exploration by maneuvering through harsh, hard-to-reach environments. Surgeons might also find them useful to crawl to hard-to-reach areas of the body. These are pretty far afield in terms of development but Robosnails 1 and 2 are the first exploratory tools to that end.
There are some drawbacks to the snail's otherwise ingenious approach to locomotion, namely, it's not exactly energy-efficient (or fast). Slugs, for example, also move along trails of excreted slime. Marine scientist Mark Denny of Stanford University, who studies slugs, says they expend 70% of their energy making those mucus trails. That's about 10 times more the energy expenditure of animals that move by running, swimming, or flying. Mile for mile, it might not be the best choice for locomotion, unless there's no better alternative means of movement.
Speaking of the lowly slug, there's also a swarm of slugbots in the works. I kid you not. Ian Kelly of the University of the West of England, has been working on this project since, oh, about 2000. His little battery-powered robot is designed to patrol fields looking for slugs and scooping them up, using their decaying bodies to recharge its batteries -- a concept that seems like he ripped it straight out of The Matrix. British farmers purportedly spend some 20 million pounds a year trying to prevent invading armies of slugs from devouring their tender crops. (I grew up in the Pacific Northwest, and a sprinkling of salt does the trick. But slugbots are just so much cooler!) Kelly estimates that as many as 200 slugs could be found for every square meter of a wheat field, providing a bounteous source of energy for his slugbot.
These are the kinds of fascinating scientific tidbits you can pick up by hanging around fluid dynamics meetings, or least browsing their online abstracts and epitomes. I'm sad to have missed the DFD meeting, which also featured the following nifty papers:
* Scientists at Tokyo University (Seiji Ichikawa and Osamu Mochizuki) are trying to mimic the swimming motion of a jellyfish by building a micro-robot out of an unspecified "soft material." My knowledge of the locomotion of jellyfish is a bit imprecise -- mostly they seem to just float about, waiting for the perfect opportunity to sting someone -- but they can produce thrust, and thereby some momentum, by creating a "vortex ring." Basically, they can expand and contract their mushy little bodies and expel air into the water behind them, creating a little whirlpool that gives them a shot of propulsive power. Jellybots -- can't wait to see the prototypes!
* A collaboration among scientists at Philips Research and Eindhoven University of Technology are also drawing on biological phenomena, this time to aid in in the design of better micro-actuators. Many micro-organisms, like paramecium, have small hairs or flexible rods (called cilia) attached to the surface, a natural covering that can beat, like tiny wings, to induce fluid flow. (Fluids, for the non-scientifically inclined, technically include air and those nasty gels currently being targeted by the TSA, not just liquids.) The Philips/Eindhoven team have built "artificial cilia": very tiny actuators made out of polymers that qualify as "smart materials" -- that is, they change shape or size in response to an applied electrical or magnetic field. The expansion/contraction of the artificial cilia mimics those found in nature, and can induce some fairly significant velocities of fluid flow. The hope is that this will be a new means of micro-fluidic actuation to control flow in tiny biosensors.
* MIT is just a hothouse of innovation, isn't it? Also on hand at the DFD meeting were Manu Prakash and Neil Gershenfeld. Gershenfeld runs MIT's Center for Bits and Atoms, and is perhaps best known for his fervent espousal of the coming revolution in personal "fab labs." He and Prakash, however, are working on an entirely different project involving bubbles. Bubbles can be problematic for fluid dynamicists because they're so difficult to control, and can seriously affect the smooth flow of a fluid. For P&G, the formation of bubbles offers a unique opportunity for microfluidic "bubble logic". Presence or absence of a bubble would represent a "bit," so bubbles could carry both information and some sort of material "payload" at the same time. The men have experimented already with creating microfluidic bubble logic gates and memory, with an eye towards applying this approach to large-scale integrated biochemical processors.
* Einstein apparently once observed the motion of tea leaves, noting that they tend to centrally accumulate at the base of a stirred teacup. Monash University researchers led by James Friend find this to be a useful analogy for their new method for microfluidic blood plasma separation in miniaturized blood diagnostic kits. Their technique also uses an electric shock of sorts to generate a form of thrust inside a microfludic chamber. They noted that the colloidal particles they deliberately suspended in the liquid swirl about and deposit at a "stagnation point" at the center of the chamber's bottom, just like Einstein's tea leaves. Can microfluidic-colloidal-particle fortune tellers be far behind?
Each one of these could probably be a blog post in and of itself, but there's just no time to do the topics justice. Because this coming week, it's all about sound. We're in Hawaii now, for the fall meeting of the Acoustical Society of America. I have a fantastic ocean view from my hotel room balcony, which conveniently looks out onto Waikiki Beach. (I slept with the sliding glass doors open to let in the sound of waves breaking on the beach, which explains my Fourier-transform-enhanced dreams.) I'll be posting occasionally about any acoustics talks of particular interest (or befuddlement, on the off chance my readers can be of assistance). And maybe there'll be time to tour a volcano, take a few hula lessons, or take in some quality rays before I return to the chilly Northeast.