Controllable stickiness: In the first image, the angled polymer fiber holds a one-kilogram weight in one direction. The second image shows how a 300-gram weight pulling in another direction causes the bonds to break.
Other researchers have been able to achieve sticking power far greater than a gecko’s using carbon nanotubes. While stiffer nanotube fibers can strongly hold on to a wall, they have a harder time hanging from a ceiling, says Sitti, adding that his adhesive was able to hold 500 grams from the ceiling. Another major advantage of the polymer fibers used by Sitti is that “they are easily scalable in manufacturing, and cost effective,” he says.
Sitti is now commercializing these angled polymer fibers for use in sporting equipment and skin adhesives through his startup, nanoGriptech.
“The design on the tip is interesting,” says Liming Dai, a professor of materials engineering at the University of Dayton, who used carbon nanotubes to achieve a force 10 times stronger than gecko feet. “The one thing with polymers is, you can easily make it in nanofabrications for the tip. Also, it’s cheap.”
“This is clearly innovative work,” says Jeffrey Karp, a bioengineer in the Harvard-MIT Division of Health Sciences, who created one-time-use, safe medical gecko tape. “It will be interesting to see if this process can be scaled for industrial applications, or if the adhesives perform better under wet conditions–a major limitation for many of the gecko-mimicking adhesives.”
Sitti says that his group plans to coat the mushroom-shaped tips with materials to make them work in water as well. This could be important for medical applications: it could ensure that drug patches, for example, don’t slide off when skin gets sweaty, says Sitti.
Other challenges remain. Currently, the tips only stick for a few hours before releasing their grip. Ali Dhinojwala, a professor at the University of Akron who also works on gecko-inspired adhesions, says that ideally, the adhesive will be self-cleaning so that it can be used again and again.