Chapter 2: Building Blocks
41 - Resilience (Part One)
That’s not the case with hedgehogs. You wouldn’t want to actually bounce a hedgehog, Julian Vincent says. But the point is that you could. They fall out of trees all the time without getting hurt. The reason is something to which Vincent has given a lot of attention. Director of the Centre for Biomimetic and Natural Technologies at the University of Bath in southwest England, Vincent is one of the more persuasive thinkers and doers in the rapidly changing world of materials science. In the case of the hedgehog, what he and a former student, Paul Owers, found was that the sharp hollow spines protecting it from attack are also exceptionally good shock absorbers. So much so that the late James Gordon—Vincent’s mentor and a major figure in this field—once designed a puncture-proof car tire by ringing a wheel with a bristling fringe of hedgehog spines.
The hedgehog’s secret is that the cores of its hollow spines are filled with a natural honeycomb. That core prevents the tubes from collapsing like crimped drinking straws when they’re bent by an attacking predator, or by the ground moving toward it at unusual speed.
“Every organism is a bag of solutions to problems posed by the need to survive,” Vincent says. And he believes we can learn from that. It’s a common engineering trick to stiffen hollow tubes with foam; it’s often used in the suspension struts for race cars, for example. If we can learn to make an internal honeycomb as nature does, he says, we’ll have support structures of all kinds that are at once lighter, cheaper, and stronger.
At ease in his cluttered office, Vincent is a thoughtful, good-natured man with an ample reserve of wonder for his favorite subject. One of the things he finds most extraordinary is the surprisingly few components from which natural materials are made. “For their ceramics,” he notes, “most organisms use one of two calcium salts.” Or occasionally silica. He goes on to list the rest: “Organic fibers in animals are largely collagen, a protein. In plants they are mostly cellulose, a sugar polymer.” Chitin, a strong fiber related to cellulose, turns up in arthropods—insects, spiders, crabs, prawns—and some plants and fungi. And then there are the keratins, another protein family, which figure in various guises as nails, horns, hair, and feathers, not to mention hedgehog spines.
Summing up, he counts them down: Broadly speaking, nature probably has no more than two main types of ceramics, two fibrous sugar polymers, four fibrous proteins, and some globular structural proteins. Beyond those lie a lesser assortment of fillers and lubricants, and the fatty molecules called lipids that are used in cell membranes.
Compare that, he says, with the surfeit of artificial materials we’ve come up with: ten main types of ceramics, fifteen plastics, ten fibers. Many of those require toxic ingredients and vast amounts of energy during production, then can’t be disposed of without poisoning other systems. Given the subtlety, economy, and infinite variety of nature’s designs, he says, and how simple and clean her methods are, we still have a lot to learn.
In looking to nature for lessons, Vincent likes dandelions, whose flowering stems are only 7 percent solids and yet grow nearly a foot tall and withstand all kinds of weather. A good example, he suggests, for lightweight buildings and aerospace design. Or consider how a spider handles one of the toughest problems in engineering—attaching one kind of material to another at a right angle. When a spider glues the main support for its web to a leaf, it does so with one hundred tiny threads that it generates “by dropping its bottom on the ground twice for about half a second.” In that brief moment it achieves a near-perfect adhesive joint, of a quality equal to what you might find at the terminus of a well-designed bridge.
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