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Science

In the Lab: Robots That Slink and Squirm

James Estrin/The New York Times

Manduca sexta and its silicone rubber analog.

Published: March 27, 2007

MEDFORD, Mass. — The robot lies dissected on the black slab of a lab table, its silicone rubber exterior spread and flattened like a trophy snakeskin. Hair-thin wires run in a zigzag line along the inner length of its pale artificial flesh.

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Barry Trimmer flicks a small switch and the wires contract, causing the silicone to bunch up; the skin crawls, so to speak.

So does mine.

“It’s very organic,” Dr. Trimmer says with a smile. Apparently, “organic” is a technical euphemism for “creepy.” But it is eerily lifelike, and that is the point.

Robots, once the stuff of science fiction, are everywhere. Robotic geologists are puttering around on Mars, little Roombas suck up dirt in the breakfast nook. But most robots are made up of hard components and don’t much resemble the creatures that walk, crawl and squirm all around us.

At Tufts University, a multidisciplinary team of researchers wants to take a softer approach. The Biomimetic Technologies for Soft-bodied Robots project is trying to make an ersatz caterpillar that will move around in pretty much the same way as the real thing. The researchers see the potential to use the squishable, relatively simple creations to find land mines, repair machinery in hard-to-reach spots and even diagnose and treat diseases.

The project, part of a wave of interest in life-imitating robotics, is a collaboration of seven Tufts faculty members from five departments in the schools of engineering and arts and sciences. Dr. Trimmer comes from the field of neurobiology, where he has been studying the tobacco hornworm, Manduca sexta, since 1990. He has long been fascinated by the way that a seemingly simple creature like the hornworm (which, confusingly enough, is not a worm but a caterpillar) can twist its body in almost any direction and climb among the tree branches.

He pulls a box from his backpack and takes out one of the caterpillars, and puts it on the back of my hand; the caterpillar, oddly hairless and the greenish-blue color of classic Crest toothpaste, has a slightly raspy feeling to the grippers at the ends of its many legs. It rears up and twists to face backward. “How do you make a machine move with that kind of versatility and dexterity?” Dr. Trimmer asks.

The problem with motion and conventional robots is that hard joints don’t just allow movement, and they restrict the range of motion. “Each joint adds exponential problems of control,” he says. The multiple-jointed arm of the space shuttle, for example, can take cameras, equipment and astronauts to an astonishing array of positions, but the process of planning every movement is enormously complex.

Yet, the Tufts researchers point out, a caterpillar needs no postgraduate training before it begins to slink across a leaf. Remove the hornworm’s primitive brain, and it still trudges forward. So Dr. Trimmer suggests that much of the secret of locomotion is inherent in the muscles and the body. The hornworm has just 70 muscles per segment, with just one nerve controlling each muscle, for the most part. The researchers suspect that the wonderfully flexible locomotion of the caterpillar might emerge naturally from relatively simple rules.

The researchers are seeking a similar elegance in their creations. The initial creatures are hollow tubes. The “muscles” are wire springs made from shape-memory alloy. Electrical current heats the springs, causing them to constrict; once the current stops, the elastic skin stretches the wire back into its resting shape. “It’s almost childish, the simplicity of the design,” Dr. Trimmer says.

The skin is a silicone rubber that goes by the brand name Dragon Skin, and its composition can be manipulated so that it can be leathery-tough or so supple and clammy that it gives a sense of what it must be like to shake hands with Gollum. Eventually, the researchers hope to build on the work of David Kaplan, a Tufts professor of biomedical engineering who has pioneered the creation of tough, flexible materials based on spider silk so that the creatures would be largely biodegradable.

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