A US research team led by Chinese scientists has created a nanotube-based dry adhesive that surpasses the stickiness of gecko feet -- no easy feat, since the animals can cling to nearly any type of surface.

Geckos rely on aligned microscopic hairs for their gravity-defying climbs. Their design mimics this arrangement, with a vertically aligned array of straight carbon nanotubes topped by a layer of curly, entangled nanotubes, Wang Zhonglin, the lead researcher from Georgia Institute of Technology, told Xinhua on Thursday.

Just as in the gecko foot, the combination produces an adhesive with superior strength in the shear direction -- clinging against the pull of gravity -- and regular strength in the normal, perpendicular direction, which allows the adhesive to be easily pulled away from a surface. The shear adhesive force of the nanotube array is almost 10 times that of the gecko foot.

Though the material might seem most appropriate for use by Spider-man, the real applications may be less glamorous. Because carbon nanotubes conduct heat and electrical current, the bionic gecko feet could be used to connect electronic devices.

Another application might be for adhesives that work long-term in space. "In space, there is a vacuum and traditional kinds of adhesives dry out, but nanotube dry adhesives would not be bothered by the space environment," said Dai Liming, another lead researcher from University of Dayton.

Their paper will appear in the October 10 issue of journal Science. For the future, the researchers hope to learn more about the surface interactions so they can further increase the adhesive force. They also want to study the long-term durability of the adhesive, which in a small number of tests became stronger with each attachment.

(Xinhua News Agency October 10, 2008)