National Geographic : 2008 Apr
this age-old conundrum, with a gecko-inspired climber that he christened Stickybot. In reality, gecko feet aren't sticky-they're dry and smooth to the touch-and owe their re markable adhesion to some two billion spatula tipped filaments per square centimeter on their toe pads, each filament only a hundred nano meters thick. These filaments are so small, in fact, that they interact at the molecular level with the surface on which the gecko walks, tapping into the low-level van der Waals forces generated by molecules' fleeting positive and negative charges, which pull any two adjacent objects together. To make the toe pads for Sticky bot, Cutkosky and doctoral student Sangbae Kim, the robot's lead designer, produced a urethane fabric with tiny bristles that end in 30-micrometer points. Though not as flexible or adherent as the gecko itself, they hold the 500-gram robot on a vertical surface. But adhesion, Cutkosky found, is only part of the gecko's game. In order to move swiftly-and geckos can scamper up a vertical surface at one meter per second-its feet must also unstick effortlessly and instantly. To understand how the lizard does this, Cutkosky sought the aid of biologists Bob Full, an expert in animal locomotion, and Kellar Autumn, probably the world's foremost authority on gecko adhesion. Through painstaking anatomical studies, force tests on individual gecko hairlets, and slow motion analysis of lizards running on vertical treadmills, Full and Autumn discovered that gecko adhesion is highly directional: Its toes stick only when dragged downward, and they release when the direction of pull is reversed. With this in mind, Cutkosky endowed his robot with seven-segmented toes that drag and release just like the lizard's, and a gecko-like stride that snugs it to the wall. He also craft ed Stickybot's legs and feet with a process he calls shape deposition manufacturing (SDM), which combines a range of metals, polymers, and fabrics to create the same smooth gradation from stiff to flexible that is present in the lizard's limbs and absent in most man-made materials. SDM also allows him to embed actuators, sensors, and other specialized structures that An electron micrograph reveals sharkskin's secret to speed: tooth-like scales called dermal denticles. Water "races through the microgrooves without tumbling," says shark researcher George Burgess, reducing friction. "It's like a fast-moving river current versus the gurgling turbulence of a shallow stream." The scales also discourage barnacles and algae from glomming on-an inspiration for synthetic coatings that may soon be applied to Navy ship hulls to reduce such biofouling.