- THE INSPIRATION FROM NATURE: THE BIOLOGY OF GECKO ADHESION
- Geckos have long fascinated the science world by their ability to climb up walls and survey ceilings upside down with ease. Their ability to adhere to a variety of surfaces, including both hydrophillic, hydrohobic materials, fascinated scientists. Most biology adhesive systems involve the attractive forces of thin films of water with another hydrophillic surface. The cohesive forces of water molecules is usually attributed to most biological adhesives but what is unique about the gecko system is that the adhesive process occurs between the gecko's foot and any surface. Most the early scientific studies performed on Geckos included work by Autumn & Peattie (2002) and Andre Geim (Wiki;, 2014). What was discovered in studies peformed by Hansen and Autum (2005) is that the attractive forces are due to the weakest of all intermolecular, that is , the Van Der Waals attractive forces. How can the gecko's use the weakest of all molecular forces to acheive the strongest known attraction to hydrophobic surfaces? The answer lies primarily in the structure of the gecko's foot "setae." (See figures below)
- The gecko's setae are able to flex and lay flat against any surface providing "intimate molecule contact" with any surface. Even in superdry, low humidity environments, gecko's feet are able to take advantage of the atom to atom contact providing by the weak attraction between the nucleus of on atom and the electrons of another. (Autum, 2002). In other words, it is shear NUMBERS of atomic interactions that prevail. See the embedded video clip explaining the role of VanDerWaals forces and Gecko adhesion. In a nutshell it is the very structure of the foot, not an secreting liquid adhesive, that is responsible for the adhesive properties of the gecko's foot.
- You Tube Video of Gecko's Foot and Van Der Waals Attraction:
- Most adhesives rely on liquid products that spread over a surface to initiate the adhesive process OR the rely on pressure or exposure to oxygen. Because of the irreversible sticky nature of traditional adhesives and the potential for the adhesive to not only stick to itself or attract dirt or other unwanted particles to its surface, this "gecko" technology solves all of the above. HOW? The secret is in the STRUCTURE not the secretions. In the pictures below, you will notice that the real gecko foot expands and contracts. In the relaxed form, the foot is not adhesive. When the gecko stretches its foot out, the setae spead out flat, increasing the molecular contact with the surface and engaging the intermolecular forces by contact. When the gecko pulls its foot off, the adhesion stops. The gecko's feet do not stick together, and neither does the surface of the artifical fibers created in the lab. SEE PICTURES BELOW.
- The "gecko tape" works just as shown in Figure 4 above. A flexible, artifical fiber composed of polyamide is constructed. This artificial, mostly hydrophobic material is able to spread out when pressure is added and the highly convoluted surface area flattens out and increased contact with the surface. The spread out version ,similar to Figure 5b, is the active form. Keratin, the natural component of Gecko "setae" is hydrophobic. What limits the use of the tape to only a few appliations is that because the polyamide is slightly hydrophillic, a thin layer of water forms between the surface of the tape and the surface below. The cohesive force of water is not as strong as the collective molecular VanDerWaals interaction. The picture below describes the process:
- Descripiton of the Process Involved in Development
- Many scientists contributed to the development of this product. The early players include A.K Geim who developed the first Gecko tape. (Nature, 2003). He developed the first polyamide fibers used in the tape. Since his initial product development in 2005, newer materials have been developed. The most notable development include the use of carbon nanofibers. The advantage of such material is not only its flexibility, but its complete hydrophobicity which will eliminate the accumulation of a hydration layer (and maintain the atom to atom contact with the surface). As long as the material is "smashed" onto the surface, until the fiber is flexed back, the material should maintain contact (just as a Gecko flexes and peels back its foot).
- Applications of the technology
- Major advantages: reusable, firm contact with surface, does not collect dirt (self-cleaning), won't stick to itself, no liquids involved, less use of flammable and/or glue "vapors." May be used in military or police force to scale walls in combat or hostage situations. Potential applications in space since most adhesives require oxygen for polymerization to occur and do not work in vacuums. (Highfield, 2008).
- Is this new technology a societal win?
- I believe this has tremendous potential in reducing the amount of landfill wastes simply by elimating all of the plastic "rolls" and old tape used in parades, packaging, parties, etc, and reducing the amount of organic solvents needed to create the adhesive material. Althought the first Gecko tapes use plastic-based fibers, the new versions which incorporate carbon nanofibers have the potential of not only being extremely effective, but also very durable and LONG-LASTING. The main drawback now is that produced carbon nanofibers is expensive but hopefully new research will lead to more cost-effective methods of mass-production.
- Bioinspiration or Biomimicry?
- I believe this is an example of bioinspiration since the materials currently used to produce the artificial "setae" are not reusable and are not controlled by muscles and are not derived from natural stock. (However, the term biomimetics was used often in my research on "gecko tape). Even the carbon nanofibers require much energy to produce and the main benefit now as far as being useful is the fact that the tapes are reusable. If the cost of carbon nanogfiber production is reduced, thsi could be a major benefit to society as far as waste (think of all of the tape, glue, sticky labels, ect, we use and throw away each Christmas, birthday, high school dance??
Primary Sources (Peer Review):
Autumn, K., and N. Gravish. "Gecko Adhesion: Evolutionary Nanotechnology." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 366.1870 (2008):
Autumn, K., et al., Proc. Natl. Acad. Sci. USA (2002) 99 (19).
Geim, A. K.; Dubonos, S. V.; Grigorieva, I. V. Novoselov, K.S. , Zhukov, A. A.; Shapoval, S. Y. (2003). “Microfibricated adhesive mimicking gecko foot-hair.” Nature Materials 2 (7): 461–463.
Hansen, W. & Autumn, K. 2005 Evidence for self-cleaning in gecko setae. Proc. Natl Acad. Sci.
USA 102, 385–389
"Andre Geim." Wikipedia. Wikimedia Foundation, 20 June 2014. Web. 18 June 2014. <http://en.wikipedia.org/wiki/Andre_Geim>.
Black, Richard. "." BBC News. BBC, 6 Jan. 2003. Web. 18 June 2014. <http://news.bbc.co.uk/2/hi/science/nature/2953852.stm>.
Highfield, Roger. "Gecko lizards inspire 'Spiderman gloves'". The Daily Telegraph. 23 January 2008. Retrieved 25 October 2010.
Mangels, John. "University of Akron's Research into Geckos' Natural Stickiness May Pay off in Companies and Products (video)." Cleveland.com. N.p., Sept. 2012.
Naik, Rajesh R., and Morley O. Stone. "Integrating Biomimetics." Materials Today 8.9 (2005): 18-26.
Smart Materials: "Gecko Adhesive Fit for Superman". PBS/NOVA, 2011. YouTube. Film. (https://www.youtube.com/watch?v=gzm7yD-JuyM)