The US military has developed a pair of hand-held, gecko-inspired paddles that will one day allow troops to scale vertical walls.
The US Defense Advanced Research Projects Agency (DARPA) has demonstrated the first known human climbing of a glass wall using climbing devices inspired by geckos.
The ascent involved a 98 kg climber ascending and descending 25 feet of glass, while also carrying an additional 23 kg load in one trial, with no climbing equipment other than a pair of hand-held, gecko-inspired paddles.
The novel polymer microstructure technology used in those paddles was developed for DARPA's Z-Man programme by Draper Laboratory of Cambridge, Massachusetts.
DARPA created the Z-Man programme to help warfighters overcome the limitations of climbing instruments, such as ropes and ladders, and deliver maximum safety and flexibility for manoeuvre and rapid response to warfighters operating in tight urban environments.
The goal of the programme is to develop biologically inspired climbing aids to enable warfighters carrying a full combat load to scale vertical walls constructed from typical building materials.
"The gecko is one of the champion climbers in the Animal Kingdom, so it was natural for DARPA to look to it for inspiration in overcoming some of the manoeuvre challenges that US forces face in urban environments," said Dr Matt Goodman, the DARPA programme manager for Z-Man.
"The challenge to our performer team was to understand the biology and physics in play when geckos climb and then reverse-engineer those dynamics into an artificial system for use by humans," Goodman said.
A gecko is able to climb on glass by using physical bond interactions - specifically van der Waals intermolecular forces - between the spatulae and a surface to adhere reversibly, resulting in easy attachment and removal of the gecko's toes from the surface.
The van der Waals mechanism implied that it is the size and shape of the spatulae tips that affect adhesive performance, not specific surface chemistry.
This suggested that there were design principles and physical models derived from nature that might enable scientists to fabricate an adhesive inspired by gecko toes.
One of the initial challenges in developing a device to support human climbing was the issue of scaling: a typical Tokay gecko weighs 200 grams, while an average human male weighs 75 kg.
To enable dynamic climbing like a gecko at this larger scale required that the engineers create climbing paddles capable of balancing sufficient adhesive forces in both the shear (parallel to the vertical surface) and normal (perpendicular to the vertical surface) directions.
That feature is necessary for a climber to remain adhered on a surface without falling off while in the act of attaching and detaching the paddles with each movement.
The first human climbing demonstration occurred in February 2012 and tests of the technology are ongoing, DARPA said.
