Beyond Metaphor: Biomimicry and the Case of the Gecko

Beyond Metaphor: Biomimicry and the Case of the Gecko

Understanding the limits of nature is critical to understanding the strategies that living things employ and how we as designers can best emulate them.

For instance, I might say, “I can jump like a bunny,” but I really can't, now can I? My anatomy is quite different from a jackrabbit's, and it is inconceivable that I could cross my lawn in 20 seconds and two touches of the ground, even on Easter Sunday.

I might, however, want to study the biomechanics of animal motion, compare different mechanisms and distill some general principles of motion and physiology. Armed with these, I might then be ready to propose an innovative way to help humans jump higher or longer.

In other words, I would have gone beyond metaphor because I understood the principles at work and, hopefully, applied them in an appropriate venue. Designers of tomorrow's buildings will similarly have to go beyond metaphor in order to apply truly useful biomimetic innovation to the problems of our built world.

Bob Full, director of U.C. Berkeley's CIBER lab and professor in the Integrative Biology Department is cheerfully and unrelentingly skeptical of many of the proposals popularly espoused as biomimetic because of what he sees as a blithe disregard of scientific principles.

Dr. Full, along with professor Kellar Autumn of Lewis and Clark College, is part of the team that has patented the adhesive mechanism that the gecko uses to walk on ceilings (see the well-written “The Gecko's Foot” by Peter Forbes). Nearly 10 years into the R&D, an interdisciplinary team of biomechanics, engineers and physicists led by engineering professor Ron Fearing is still working to overcome the limits of manufacturing this phenomenon at the nanoscale.  

When the manufacturing problems are solved, however, this will be a revolution in fabrication of all kinds. Why? Think what you could do with a dry tape that could stick to anything, resist great forces, and then peel off easily when you wanted it to, to be used again somewhere else. No glues, no surface preparation, no interlocking parts, no receptor pads. What if you got rid of the notion of “tape” altogether, and made your parts selectively adhering or not? Component construction, cradle to cradle recycling, reduction of material and energy use all could be affected by this development.

It strikes me that the implications are enormous because the application is closer to universal than anything that has come before. Increased universality seems to happen when basic principles are understood.

Gecko foot - CC license by Flickr user belgianchocolateSo, what are the principles associated with gecko adhesion? First off, there is our previously mentioned notion of bottom-up, component linked construction. In the gecko's case, each foot has hundreds of fringes or lamellae; these fringes have bristles or setae (about 500,000 on each foot); these bristles have hundreds of split ends; these split ends all have spatula-shaped ends to them, like tiny toe pads. All this results in an enormous amount of contact surface that runs up through many magnitudes of scale. It is estimated that a single gecko might have a billion of these tiny points of contact. Again, bigger is not necessarily better in nature, but often, more is.

Secondly, although walking on ceilings seems magical, the gecko does have to operate within the bounds of space and physics. Indeed, it is the effects of physical forces, not living tissue or animal behavior, that are the key to the gecko's talent.

What Autumn discovered and presented in 2000 was that all this contact surface was operating at the 2 nanometer range, and was therefore subject to van der Waals forces, the static molecular attraction between objects that only occurs at this scale. The tiny split ends were essentially filling in all the microscopic pits and bumps of an object's surface and sticking to it by this molecular attraction. We can't walk on the ceiling because our feet can't get close enough.

Finally, the gecko has developed over millions of years of natural selection to take advantage of these forces (to surf for free). One of the key features of the gecko phenomenon is that the animal can place a foot on a surface, “load” it so it sticks, and then peel it off effortlessly when it wants to move on. As anyone who has seen these creatures knows this can happen in a split second. Full and his team have discovered that it is all about angle when it comes to effective sticking and the gecko has merely adapted to an efficient way of peeling back its toes when it wants to move on.  

Much remains to be discovered about the gecko's leg and tail mechanisms and, of course, about how to make all those tiny, compliant hairs that stick. While fascinated by and respectful of the gecko's ability, Full remains focused on human problems and on our ability to improve on nature's devices. He is fond of saying that “nature designs to the adequate,” and firmly believes in our ability to progress beyond what we observe in the natural world in order to solve our particular problems. In other words, of going beyond metaphor.

Tom McKeag teaches bio-inspired design to undergraduate design students at the California College of the Arts and to graduate architectural, science and engineering students at the University of California, Berkeley. He is the founder and president of BioDreamMachine, a nonprofit educational institute that brings bio-inspired design and science education to K12 schools. In 2006, McKeag helped establish the nation's first public elementary school course in biomimicry at the Dixie Elementary School in Marin County, Calif. In his spare time he works as a licensed landscape architect and community planner.

Geckos - CC license by jpockele, Nick Hobgood and belgianchocolate