The gecko’s unique feet, which can scale smooth, vertical surfaces without surface tension, attracted the Defense Advanced Research Projects Agency’s (DARPA) Z-Man program, which seeks to give U.S. soldiers “maximum flexibility for maneuvering and responding to circumstances.”
A “novel polymer microstructure technology” was developed for DARPA by the Draper Laboratory of Cambridge, Mass., and built into paddles that allowed a 218-lb man, carrying a 50-lb pack, to go up and then down a 25-ft sheer glass wall, “with no climbing equipment other than a pair of hand-held, gecko-inspired paddles.”
In a paper published in the Journal of the Royal Society, the Draper scientists describe their advance as a “wedge-shaped gecko-like synthetic adhesive that exhibits several gecko-like properties simultaneously.” These include:
“Individual wedges independently detach and reattach during sliding, resulting in high levels of shear and normal adhesion during drag,” the paper notes. They keep the stickiness too, retaining 67% of the initial adhesion and 76% of initial shear after 30,000 “attachment/detachment cycles” without cleaning.
The gecko-like pads were molded from a silicone, polydimethylsiloxane, using an epoxy (SU-8 photoresist) mold in a lithography process.
After the molds were created, silicone-based elastomers were cast under vacuum, spun to a desired backing layer thickness, heat cured and pulled out of the mold by hand.
Not exactly automated, and not a production tool by any stretch. The researchers noted that the molds typically lasted for only 10 “cast-and-peel” cycles before “cracking”, “delaminating” or “clogging” due to residual polymers left in the cavities. Time for some P-20 tool steel and a mold-release agent, perhaps?