Sitti develops gecko feet-inspired adhesive

Sitti and his team have developed an adhesive that mimics gecko feet.
 (credit: Metin Sitti) Sitti and his team have developed an adhesive that mimics gecko feet. (credit: Metin Sitti)

Geckos are the closet thing to a real life Spiderman — they can climb up walls and run across ceilings with extreme agility and quickness.

Carnegie Mellon’s Metin Sitti, head of Carnegie Mellon’s NanoRobotics Laboratory and professor of mechanical engineering, with courtesy appointments in biomedical engineering, electrical and computer engineering, and the Robotics Institute, has been working with his research teams on developing adhesive material that mimics the stickiness of geckos’ feet for the past decade.

Besides having adhesive feet, geckos also have the amazing ability to clear their feet of dust by walking on a clean surface. Similarly, Sitti and his team showed in their recent publication on Feb. 19 in the Interface Journal of the British Royal Society how their previously developed adhesive material can be cleaned using a similar technique, allowing their tape to be reusable.

Over 12 years ago, when Sitti was completing his postdoctoral research at the University of California, Berkley, he was approached by the Defense Advanced Research Projects Agency (DARPA) to work on developing climbing robots. In 2000, Keller Autumn, a professor of biology at Lewis & Clark College, published in Nature his research explaining how gecko feet were a smart adhesive that were controlled mechanically and not chemically. Sitti’s specialty is small robots, but when he came to Carnegie Mellon, his project translated into developing an adhesive that mimics gecko feet.

Sitti described the project as “mimicking nature in mechanics” by “replicating nature using synthetic materials.”

He explained that between 2006 and 2009, he and his team had a number of publications explaining their success in developing a tape-like adhesive “that could stick to surfaces with no chemical additives, purely based on mechanical design similar to gecko feet.” In 2009, Sitti commercialized their product through a Carnegie Mellon spinoff company called nanoGriptech to incorporate their adhesive technology into a wide variety of applications.

Similar to how geckos have patches of hair on their feet and folds that contribute to their stickiness, the adhesive that Sitti and his team created was mechanically designed to have fibers with mushroom-tipped structures at the end that act as suction cups. The small-scale physics between the suction cups and the surface allows the adhesive to stick to the surface very well with no chemicals involved. Currently, the adhesive can support up to one kilogram per centimeter squared.

Tape, one of the most commonly used adhesives, can only be used once because it is prone to getting dirty. Similarly, gecko feet and the adhesive the research team developed can also get dirty. Sitti shared that they recently “took upon the challenge of making their product reusable so it would be comparable to Velcro.”

Sitti said that their adhesive could be dipped in water, which would remove all dirt particles. But what if one does not have water at hand?

When gecko’s feet get dirty, and they find a lessened ability to stick to surfaces, they climb onto a clean surface and shed particles. Sitti explained that “biologists theorized that geckos have patches of hairs, but more importantly, gaps in between the hairs that dirt particles roll in between.” In addition, “fiber hair thickness was important because particles smaller than the fibers would be harder to get rid of.”
Based on these guidelines, Sitti and his team slightly modified their mechanical design and showed that their adhesive could be cleaned in a similar way.

Sitti explained that geckos use a load-drag-unload cleaning technique where “they first load their feet onto a surface, drag their feet slightly backward generating friction, and then release their feet to make their next step.”

The adhesive was exposed to silica beads and, using this technique, could be cleaned and returned to full functionality.

He believes that one of the great things about the project is that this mechanical model has actually helped scientists confirm their theory of how geckos clean their feet by examining the technique close up on the adhesive.

“This has been a very international project,” Sitti said. He and his team have collaborated with Hendrik Hoefscher and Michael Rohrig of Karlsruhe Institute of Technology in Germany. Members of the Carnegie Mellon team include Uyiosa Abusomwan, Ph.D. candidate in mechanical engineering, and Yigit Menguc, a former Ph.D. student with Sitti and current postdoctoral fellow at Harvard University.

Sitti was proud to announce that Abusomwan was awarded first place last week at the Adhesion Society’s Annual Conference in San Diego for best poster. The poster highlighted the gecko adhesive’s ability to clean and be reused. Sitti humbly believes that the credit for the success of their work should go to his students.

The adhesive has many widespread uses, from gloves to medical applications involving anything with temporary adhesion. Sitti shared his vision to use it to hang things up on walls. With the adhesive’s now reusable feature, an indecisive person could move a picture around their house and try multiple locations.

His team is now exploring uses of the adhesive in robotic manipulation, where it can be used to pick and place complex and fragile parts. For example, on an assembly line for televisions, parts must be carefully picked up and placed. Since no chemicals are involved, the adhesive would not leave any residue on the product. The gecko adhesive could potentially be attached to a balloon, which would adjust shape, providing softness when picking up fragile objects.