EDMONTON JOURNAL (Alberta) 08 November 13 Gecko feet inspire U of A researchers; New adhesive mimics tiny hairs that allow reptile to climb walls (Alexandra Zabjek)
When a gecko scampers across a ceiling, it might inspire a little fear in the person standing below.
But the seemingly gravitydefying abilities of the tiny creatures won't fail, a phenomenon that has prompted researchers such as University of Alberta Prof. Dan Sameoto to study their super stickiness to develop new adhesive materials.
The work has paid off as the mechanical engineering professor, along with graduate student Walid Bin Khaled, recently published a study showing how new adhesive materials can mimic the directional stickiness of a gecko's foot.
The feet are covered in millions of tiny hairs, each one being thousands of times smaller than a human hair.
"It's been described in the literature as the worst case of split ends imaginable," Sameoto said.
The number and size of the hairs allow something called van der Walls forces to create adhesive strength, allowing a gecko to connect to surfaces.
The first study on a gecko's adhesive abilities was published about 10 years ago but research in the field has exploded as scientists have tried to apply the same principles to produce other materials.
"The amount of detail a gecko has on its feet, it's really not feasible to directly mimic ... we're trying to find ways to produce the same kinds of functionality without going into as much fabrication difficulties as if you were trying to imitate the exact structures," Sameoto said.
In the paper published in the most recent issue of Bioinspiration and Biometrics, Sameoto and Bin Khaled show how they can mimic the ability of a gecko's foot to stick when it pulls in a certain direction but lift off when it puts pressure in a different direction. A gecko accomplishes this through angled fibres in its hairs.
They found that if they used fibres with an overhanging cap on the end, and inserted a specific "defect" in the same place in each cap, it created a controlled "flaw."
"It's similar on the microscale to how if you try to remove a piece of tape from the middle, it's very difficult. But if you had an edge already peeled off, it's quite easy to pull off ... that would be like having a thousand different pieces of tape, but they're all peeled up from the righthand side. If I tried to peel them from the left hand side, it would be quite difficult. But if I'm peeling from the opposite direction it's much easier.
"Through making these defects, we can produce an adhesion that's different depending on whether we put a shear load toward the defect or away from it," Sameoto said.
The findings could be used in robotics laboratories where tiny objects must be moved in a delicate manner and with simple motions. The researchers are also interested in the potential commercial products. The adhesive doesn't leave a residue, doesn't stick to human skin, but sticks well to most manmade surfaces. Sameoto said the material could potentially be used for wall hangings or window insulation.
"There's many ways we can adapt the materials to be the functional equivalent of Velcro but instead of needing fabrics, we need a hard, flat surface."
The next step for the researchers is to approach industrial partners to see how the new materials could be used in manufacturing.
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