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."
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).