For
years, biologists have been amazed by the power of gecko feet, which let these
5-ounce lizards produce an adhesive force roughly equivalent to carrying nine
pounds up a wall without slipping. Now, a team of polymer scientists and a
biologist at the University
of Massachusetts Amherst
have discovered exactly how the gecko does it, leading them to invent
“Geckskin,” a device that can hold 700 lbs on a smooth wall.
Doctoral
candidate Michael Bartlett in Alfred Crosby’s polymer science and engineering
laboratory at UMass Amherst is the lead author of their article describing the
discovery in an online issue of Advanced Materials. The group includes
biologist Duncan Irschick, a functional morphologist who has studied the
gecko’s climbing and clinging abilities for over 20 years. Geckos are equally
at home on vertical, slanted, even backward-tilting surfaces.
“Amazingly,
gecko feet can be applied and disengaged with ease, and with no sticky residue
remaining on the surface,” Irschick says. These properties, high-capacity,
reversibility, and dry adhesion offer a tantalizing possibility for synthetic
materials that can easily attach and detach heavy everyday objects such as
televisions or computers to walls, as well as medical and industrial applications,
among others, he and Crosby say.
This
combination of properties at these scales has never been achieved before, the
authors point out. Crosby says, “Our Geckskin
device is about 16 in square, about the size of an index card, and can hold a maximum
force of about 700 lbs while adhering to a smooth surface such as glass.”
Beyond
its impressive sticking ability, the device can be released with negligible
effort and reused many times with no loss of effectiveness. For example, it can
be used to stick a 42-in television to a wall, released with a gentle tug and
restuck to another surface as many times as needed, leaving no residue.
Previous
efforts to synthesize the tremendous adhesive power of gecko feet and pads were
based on the qualities of microscopic hairs on their toes called setae, but
efforts to translate them to larger scales were unsuccessful, in part because
the complexity of the entire gecko foot was not taken into account. As Irschick
explains, a gecko’s foot has several interacting elements, including tendons,
bones and skin, that work together to produce easily reversible adhesion.
Now
he, Bartlett, Crosby, and the rest of the UMass Amherst team have unlocked the
simple yet elegant secret of how it’s done, to create a device that can handle
excessively large weights. Geckskin and its supporting theory demonstrate that
setae are not required for gecko-like performance, Crosby
points out. “It’s a concept that has not been considered in other design
strategies and one that may open up new research avenues in gecko-like adhesion
in the future.”
The
key innovation by Bartlett and colleagues was to create an integrated adhesive
with a soft pad woven into a stiff fabric, which allows the pad to
“drape” over a surface to maximize contact. Further, as in natural
gecko feet, the skin is woven into a synthetic “tendon,” yielding a
design that plays a key role in maintaining stiffness and rotational freedom,
the researchers explain.
Importantly,
the Geckskin’s adhesive pad uses simple everyday materials such as
polydimethylsiloxane (PDMS), which holds promise for developing an inexpensive,
strong and durable dry adhesive.
The
UMass Amherst researchers are continuing to improve their Geckskin design by
drawing on lessons from the evolution of gecko feet, which show remarkable
variation in anatomy. “Our design for Geckskin shows the true integrative
power of evolution for inspiring synthetic design that can ultimately aid
humans in many ways,” says Irschick.
