PARIS (AFP) - Inspired by the gecko, scientists have developed a tank-like robot that can scale vertical walls and crawl over ledges without using suction cups, glue or other liquid bonds to adhere to the surface. The 240-gramme (6.9-ounce) beast has tracks that are covered with dry microfibres modelled on the toe hairs of the gecko, which can famously zip up windows and along walls almost without effort. The lizard does the trick thanks to millions of ultra-fine hairs called setae, which interact with the climbing surface to create a molecular attraction known as the van der Waals force. Described on Tuesday in the British research journal Smart Materials and Structure, the robots tracks are studded with mushroom-shaped caps of polymer microfibres just 0.017 millimetres (0.00067 inches) wide and 0.01mm (0.0004 inches) high. By comparison, the human hair is around 0.1 mm (0.004 inches) thick. While van der Waals forces are considered to be relatively weak, the thin, flexible overhang provided by the mushroom cap ensures that the area of contact between the robot and the surface is maximised, said researcher Jeff Krahn of the Simon Fraser University at Burnaby, in Canadas British Columbia province.