Geckos manage adhesive marvels thanks to vanishingly small hairlike setae that expand the surface area of their toes enough for van der Waals forces to cling to a surface. The last time he checked, Hawkes says, 384 scientific papers have discussed gecko-inspired adhesives, and labs have developed plenty of variations. Scaling up to human weights has been difficult. The DARPA Z-man project released pictures this summer of a person climbing with a gecko-style adhesive but did not release details of the structure.
Hawkes, study coauthor Mark R. Cutkosky and colleagues, who had worked on an initial stage of the Z-man project, developed a wall-climbing robot called Stickybot, which relied on gecko-inspired adhesives. But at the robot’s scale, the adhesives didn’t perform as well as they do for the dainty little lizards. “As an engineer, it bugs you,” Hawkes says. When he, Cutkosky and colleagues began working on a NASA project for a grabber to gently snag debris in space, the researchers took a new look at the scaling problem.
After working through a system of squishy pads and other alternatives, Hawkes turned to nitinol, which has the unusual property of growing stretchier as the force pulling it increases. That’s the opposite of rubber bands and various other elastics.
