New Mechanism Discovered for Gecko Adhesion
by Meg Marquardt
Materials Research Society | Published: 08 May 2014
Adhesives are not universal; what works best for one surface, such as glass, may not be ideal for another, such as brick. This is especially true for adhesives with peel-and-stick properties that are meant to be reusable. In order to create a sticky surface that could be applied anywhere and removed just as quickly, researchers at the University of Massachusetts Amherst looked to one of nature's most adept climbers, the gecko. The resulting material, Geckskin, utilizes analogs of the skin and tendon structure of the gecko to create a whole new line of adhesive materials.
This study is not the first to mimic gecko adhesion properties. In previous research carried out by Alfred J. Crosby, a polymer scientist at UM-Amherst, and others groups, adhesive material was designed to copy the surface of geckos' feet. The gecko, who can even dart across ceilings, has tiny cilia-like hairs on the bottom of its feet. These hairs were thought to be behind the gecko's ability to cling to any surface, so researchers reproduced the effect with nano-fibers that covered the surface of the synthesized adhesives. But while the hairs worked great for some surfaces, it wasn't ideal for all, such as drywall, and especially at large size scales.
"So we went back to the gecko," says Crosby. Working with biologist Duncan Irschick, also at UM-Amherst, they began to investigate what was under the gecko's sticky skin. What they found was a scaffolding of tendon that connected directly to the skin. This is much different than human anatomy, says Crosby. Our tendons don't attach to the skin, and so we cannot minutely control the stiffness of our skin. Geckos, on the other hand, can maintain a stiff connection all the way from their bone to the surface they are attaching to.
With a new understanding of how the gecko's anatomy helped its ability to stick and release from surfaces, Ph.D. candidate Daniel King, lead author on the study published in Advanced Materials , went back to the drawing board, creating a simplified equation that might explain this phenomenon.
"It has two parts," says King. "We needed to understand what makes it stick and what makes it release." The main elements have to do with contact area and load bearing direction. The adhesive needed to be able to hold weight that would be pulled directly down by gravity. But it also needed to be able to be easily pulled away from the contact point.
The material they designed integrated both soft elastomers and stiff fibers of glass or carbon fiber - without any nano-fiber hairs. The combination creates an adhesive material that sticks to any surface that is perpendicular to the floor - such as a wall or door. But, just like the gecko, because the material has a high stiffness, when it is pulled directly away from the surface it's sticking to, it releases easily.
The study is a good start to designing new materials that can work on any variety of surfaces, Crosby points out. King wants to pursue the material farther, seeing what has to change in order to create adhesives that stick and remove as reliably on surfaces that are at angles to the floor.
Crosby also hopes the research can continue to be a two-way street. "We learned something new about geckos because of this," he says, information that could lead to a better understanding of the animal in its natural habitat. Future research, in continued collaboration with Irschick, will hopefully benefit both materials science and biology.
Read the abstract in Advanced Materials here.