Washington, Sept 11 : In a pursuit to create a synthetic, gecko-like adhesive, researchers at the University of California, Berkeley have achieved a major breakthrough- the first adhesive that cleans itself after each use without the need for water or chemicals- much like the remarkable hairs found on the gecko lizard's toes.
In 2005, it was revealed that gecko lizard keeps its feet sticky but clean by shedding dirt particles with every step.
"It brings us closer to being able to build truly all-terrain robots, which will in the future be able to scamper up walls and across ceilings in everyday environments rather than only on clean glass. We can envision robots being able to go anywhere they are needed, perhaps in the search for survivors after a disaster," said Ron Fearing, UC Berkeley professor of electrical engineering and computer sciences and head of the research team developing the new material.
Since a long time, scientists have been trying to develop a man-made version of the toe hairs that make the lizard's acrobatic feats possible.
This year, the same researchers have developed another gecko-inspired adhesive using polymer microfibers that could easily attach to and detach from clean surfaces. But, according to the researchers replicating the gecko's ability to walk through dirty surfaces yet keep its feet clean enough to climb walls has been tricky.
"It goes completely against our everyday experience with sticky tapes, which are 'magnets' for dirt and can't be reused. With our gecko adhesive, we have been able to create the first material that is adhesive and yet cleans itself a little bit with every contact," said Fearing.
For the study, the researchers designed the adhesive with microfibers made from stiff polymers. By using microspheres that were 3 to 10 micrometers in diameter to simulate contaminants, they were able to show that the microfibers pushed the microsphere particles toward the fiber tips when the adhesive was not in contact with a surface.
The scientists observed that when the fibers were pressed against a smooth surface, the contaminants made greater contact with the surface than with the fibers. Since adhesion strength is proportional to contact area, the microsphere particles preferentially adhered to the glass rather than to the synthetic gecko fibers.
With each simulated step, designed to provide a force similar to a gecko's step, more and more microspheres were deposited onto the surface. After 30 simulated steps, the adhesive shed about 60 percent of the smaller-sized contaminants onto the glass surface.
"This new material likes to adhere to surfaces, but it does not like to collect dirt particles. We were able to recover one-third of the shear adhesion strength of clean samples after multiple steps," said Jongho Lee, UC Berkeley graduate student in mechanical engineering and lead author of the new study.
However, the larger contaminants were harder to shake off because they contact a larger number of fibers, and then adhere better to the fibers than to the glass.
The researchers said that to resolve this challenge, they will need to understand more features of the gecko toe, such as whether the size of the gaps between bundles of toe hairs helps remove dirt.
The development of the adhesive is reported online in Langmuir, a peer-reviewed journal of the American Chemical Society.