This is an update on our developing understanding in a gecko's
ability to stick to surfaces better than expected. It may result in
better engineering of adhesive, but it certainly is teaching us how
and what to fine tune. It also reminds us that even nature cannot
produce a perfect solution.
Otherwise a nice bit of ongoing research.
Gecko feet hold
clues to creating bandages that stick when wet
Published: Thursday,
August 9, 2012 - 16:05 in Physics & Chemistry
Scientists already
know that the tiny hairs on geckos' toe pads enable them to cling,
like Velcro, to vertical surfaces. Now, University of Akron
researchers are unfolding clues to the reptiles' gripping power in
wet conditions in order to create a synthetic adhesive that sticks
when moist or on wet surfaces. Place a single water droplet on the
sole of a gecko toe, and the pad repels the water. The anti-wetting
property helps explain how geckos maneuver in rainy tropical
conditions. However, saturate that same toe pad in water or
drench the surface on which it climbs, and adhesion slips away, the
researchers say.
As researcher Alyssa
Stark, a doctoral candidate in UA's Integrated Bioscience Program and
research team leader explains, geckos don't fall from trees during
downpours in the tropics. What, then, makes them stick? The team
hopes to make that discovery in order to create synthetic materials
that hold their grip in wet environments, such as inside the body,
for surgical procedures.
Findings by Stark,
Timothy Sullivan, who received his bachelor's degree in biology in
May, and Peter Niewiarowski, UA professor of biology and integrated
bioscience, are published in the August 9, 2012 issue of The
Journal of Experimental Biology.
"We're gathering
many clues about how geckos interact with wet surfaces and this gives
us ideas of how to design adhesives that work under water," says
Ali Dhinojwala, UA department of polymer science chair and Morton
professor of polymer science. "Nature gives us a certain set of
rules that point us in the right direction. They help us understand
limitations and how to manipulate materials."
Stark and her research
team members tested gecko toe hair adhesion in a series of scenarios:
dry toe pads on dry, misted and wet surfaces and soaked toe pads on
dry, misted and wet glass. The soaked toe pads demonstrated low to no
adhesion proportionately with the wetness of the surface on which
they were applied and pulled. Likewise, dry toe pads lost their
adhesive grip increasingly with the amount of water applied to the
surface upon which they were pulled. For the experiments, geckos were
pulled on a glass surface by way of a small, gentle harness placed
around their midsections.
"There were
anecdotes before the study that geckos can't stick to wet glass. We
now know it is a bit more complicated than that. What we expect to
learn is going to be relevant to synthetics and their capabilities to
work not only on dry surfaces, but also wet and maybe, submerged
ones," Niewiarowski says. "This implies a more versatile
adhesive capability."
Gecko-inspired dry
adhesive
After close study of
the tiny hairs at the bottom of gecko feet that enable them to cling
to surfaces, Dhinojwala and his colleagues have already developed a
dry synthetic adhesive, composed of carbon nanotubes, that
outperforms nature's variety. Now, with these new findings,
Dhinojwala and his colleagues are one step closer to unfolding the
secrets behind gecko toe adhesion in wetness.
The researchers plan
to further study the lizards in their natural habitats and in
laboratory conditions that simulate them. They'll investigate
grasping and release mechanisms, habits of the geckos in wet
environments and other factors that enable the lizards to adhere to
surfaces in wetness, such as to trees during rainfalls.
"Our goal is to
go back and look at what they're doing in nature and at what kind of
surfaces they are walking or running on," says Stark, noting
that UA researchers have already studied such behavior of geckos in
Tahiti.
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