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GECKO TOES

Inspire scientists to dream of new bandages, cleaners, tape, and even harbor fantasies of spiderman come true

If you have ever traveled in the tropics you have probably indulged in a moment of fascination as you watched a gecko sneak across your ceiling. A welcome bug eating visitor, they can skitter across any surface; smooth, rough, wet or dry. Even Aristotle commented on their dexterity to "run up and down a tree in any way, even with the head down-wards" back around 350 BCE; " (as quoted in Sautun & Peattie, 2002). More recently, researchers have been employing biology, physics, chemistry, and nanoscience to try to solve the mystery; was it suction, friction, chemical bonding, water-based capillary adhesion or hydrophilic interactions with van der Waals dispersion forces (Ben-Ari, 2002). The question has finally been answered and the results are fascinatingly 'fuzzy' feet.

The pads of the Tokay gecko (Gecko gecko) used for the studies of Autumn and Peattie (2002) are covered with modified layers known as lamellae, each of these is then covered with similarly oriented tiny hairs known as setae. Each seta splits into as many as 1000 branches with spatula shaped tips, or spatulae, measuring a mere 200 nanometers wide. Although the energy from van der Waals interactions is weak, the billions of setae tips create such a vast surface area and are able to nestle so closely with their target surfaces, that the many weak interactions add up to a significant adhesive force. So strong that "scientists calculate that a gecko's-worth of setae, which would fit on a nickel, could lift about 250 pounds" (Ben-Ari, 2002). Another way to try and picture it: the combined charge is so powerful that, theoretically you could suspend a 90 pound weight from the gecko and they could still get across the ceiling (Robbins, 2001). Therefore in trying to duplicate this wonder scientists concentrate on "the smaller the hairs are, and the more of them you have, the greater the adhesion." (Ron Fearing, engineer at the University of California, Berkeley, as quoted in McDonagh, 2003).

Now one might consider that many of our adhesives could hold up a gecko; but what is even more fascinating in this story than the adhesion is the complimentary ability to detach. With these tiny hairs made from b-Keratin, a versatile substance used in many of nature's creations, from hair and nails, to scales and whale baleen. This life-friendly substance is not only able to create a structure that can stick to any surface, but can just as easily detach without leaving a mark. Autumn & Peattie (2002) found that it is all about the angle of the setae allowing for traction, and yet infinitely close to the angle in which the force in broken, allowing the gecko to simply change the angle of their foot to release.

For biomimics the real question is what do we do with this knowledge? The implications for manufacturing are already being researched. Even a non-scientist or business person can dream of the applications of a dry adhesive that can be used and reused like Velcro, but with out the need for an opposing side. An extremely versatile adhesive indeed, gecko technology can be used on any surface, even in a vacuum or underwater. Not only that, it is clean and reusable (McDonagh, 2003) because it would works without leaving a residue or picking up dirt (Ben-Ari, 2002), Certainly it could be used for the commonplace like, hanging up art like giant Post-its™ without harming the paint job, closures on packaging or clothes, even Band-aids™ that won't hurt when its time to take them off. It also has safety implications like safer tiers, or sutures. (Stroh, 2003). However the more adventurous minds quickly start to have Spiderman fantasies. Indeed Professor Andre Geim, Director of the Manchester Centre for Mesoscience and Nanotechnology has been able to make one graduate students' dream come true as he "hung out the window of a tall building" using their fittingly named Gecko tape (2003).

Like the pads of its inspiration this tape contains billions of tiny fibers less than a micrometer in diameter. The 1 cm2 prototype patch can bear 3kg, that is about 1/3 of the weight of a similar area of Gecko sole (McDonagh, 2003). In addition, the Gecko tape begins to lose its adhesive qualities after about five applications. Geim blames this shortcoming on polyimide's hydrophilicity (the plastic's tendency to attract water) as compared to the hydrophobic qualities of protein-based true gecko setae. (McDonagh, 2003). In other words, the hairs get soggy and can clump together where as the fibers of Gecko's keep water and dirt off. Scientists are still trying to live up to the abilities of those tiny little creatures and therefore currently the application of this new tape is being kept to smaller things on the market like a Gecko toy, but this is only the beginning. Bob Full from Berkeley University commented: "Geim's development is very exciting, as uses for the tape are nearly unlimited. In addition to a general adhesive, it can be used to move computer chips in a vacuum, pick up small fibers, and design novel bandages." (Manchester, 2003).

Perhaps these biomimics need to take the next step of biomimicry and look at the natural materials and processes that are able to create these fascinating surfaces with out the use of limiting petroleum based plastics. "Businesses should work like a living system…they should find a way to create conditions conductive to life, not toxic to life." (Benyus, 2002).