I am choosing to continue collecting information and writing a review related to the theme from my previous
c_1 assignment:

“How can animals create such strong reversible adhesion to a diversity of surfaces? How can engineers recreate the same adhesion strength, fiber durability, reusability, and adaptability to different surfaces?”

I chose to continue with this subject because I find it interesting and would like to know more than from what I learned reading abstracts and skimming papers for the previous assignment. For this assignment though, because we are asked to focus on a specific robotic behavior, I will focus on gecko inspired adhesion enabling robots the climb a variety of surfaces at extreme angles.

Versatile Climbing (especially upside-down)

Robots can climb walls and even climb on the ceiling, but no robot can hold onto surfaces the way geckos do. Many climbing robots can use some kind of suction, but suction is slow, inefficient, and challenging to remove and recreate when walking. Additionally, a robot that can cling to cement won't necessarily be able to cling to a tree's bark, polished glass, or another textured surface. It takes a significant amount of suction to hold up heavy objects, and yet a gecko can support all of its weight with only one toe. This is because of setae, millions tiny hairs on every toe that each split into hundred of even tinier tips. These satae cover each gecko toe with an extremely powerful adhesive substance. Unlike robots, which often struggle in foreign environments, geckos can climb up, sideways, fast, slow, upside down, and through almost any terrain imaginable. Versatility in climbing upside-down and on different surfaces is a capability which robots still lack.

Uses for Versatile Climbing

Robots with adhesives for versatile climbing could be used by private companies or governments to inspect or test bridges, power plants, pipelines, oil tanks, offshore platforms, or ships. They could also be used for cleaning, especially for tall buildings, or the ceilings of restaurants. Lastly these robots could be used by the government and police force to climb swiftly and sneakily for stealthy security missions.

Capabilities of Existing Technology

There are many existing climbing robots, and some gecko inspired robots have already begun taking shape. Unfortunately most of these robots are still incapable of the flexibility, speed, and versatility of actual gecko adhesion. Quoting from source [1]:

Not much systematic information about the adhesion performance of artificial structured surfaces has been extracted up to now… However, one thing is clear: inspite of the great efforts, most of them still fall short of nature’s performance, mostly because of lower adhesion strength, fiber collapse after detachment, or limited adaptability and applicability to real (rough) surfaces.

This source goes on to discuss that over simplification causes models to be less effective, but that it is necessary because 3D micro and nanofabrication methods are underdeveloped and inaccessible for many. Additionally, article [1] shares that all of the current fabrication processes are currently suitable for mass production.
Article [3] extends off of article [1], breaking apart different fabrication processes of nanomolding based synthetic gecko foot-hair fabrication. Article [3] concludes by saying that while still not a realized possibility, robots with high quality attachment and detachment maneuverability may one day be possible.
Finally, article [7] tested different loading conditions and surfaces, and found that their model struggled with irreversible fiber collapses. All three articles indicate that while there is a lot of potential in this field, there is also a lot of work to be done.

Potential Biological Solutions or Bioinspired Approaches

Geckos create incredibly strong attachment forces by peeling and un-peeling their toes. Study [5] found that a single gecko seta can create enormous force when projecting toward a surface, but forces less than 0.3uN when being pulled along a surface. For this reason geckos are able to peel and un-peel their toes quickly, controlling what sticks and what doesn't. Similarly, article [4] found that geckos can attach by rolling down and gripping their toes inward and detach by rolling toes upward and backward. From [4]:

…both the adhesion and friction forces of geckos can be changed over three orders of magnitude, allowing for the swift attachment and detachment during gecko motion.

In source [2], they hung geckos upside down, each by a singular toe to study how the peeling mechanics of gecko toes work by measuring the detachment angles of isolated setal arrays. This study found that angles change the shear force, and frictional adhesion is a function of that shear force. All three of these studies agree that gecko setae create a unique kind of dry adhesive, allowing for more speed, efficiency, and power than in current robots.

Value of Quality Sources

To help me decide what to focus on, I began by searching "bioinspir*" and "robo*" is Scopus. When I eventually settled on the topic of adhesion, I searched for "bioinspir*" and "adhes*" and came up with a variety of adhesion methods based off of several different types of animals, and some which were not bioinspired at all. Some of the papers which had great titles turned out to not be about robotics (especially when I did not enter "robo*") as a term. Additionally, so many of the sources that I found were unsighted and had disreputable authors, that I eventually began listing papers by "most cited," and then searching through the papers that those articles referenced either as sources or future works.

Open Problems

The biggest problems in this field seem to be issues with fabrication. It seems as if the concepts behind gecko toes and the use of Van Der Waals forces for dry adhesion are generally understood. Alternatively, we do not currently have the technology to reproduce the gecko's micro and nano setae with the scale and properties necessary to recreate their adhesive properties. Even if this fabrication were possible, recreating it on a large scale would be an entirely new challenge.

Precursors to the papers used in this assignment

Robotics Paper

For paper [3], one of the most important sources was [5], which is highly cited papers on gecko adhesion with a total of 566 citations on Scopus. The other course, [8], I have seen cited in many of the papers I have looked through, including some of the other papers in this assignment. It has been cited 382 times on Scopus.

Biological Paper

For paper [4] the two most important precursors are actually both also used in the assignment. The qualifications for source [2] are shown as a part of my c-1. [5] is again one of the most important sources.

Successors to the papers used in this assignment

Robotics Paper

Looking at source [3], one of the most important successor papers is source [6]. Source [6] has been sited 123 times on Scopus. More information on its quality as a paper can be found as part of my c-1. The study in [6] extends past the dry adhesives in [3], making them more effective by coating them in a wet adhesive found in mussels.

Biological Paper

One of the most cited successors to source [4] is source [8], which has been cited 40 times on Scopus. This paper used more advanced technology to create self-sleaning gecko inspired reversible adhesives, and used [4] as a background in gecko toe adhesion in attachment and detachment.


Bibliographic data and annotation information is available by clicking on the title of each paper.
1. Del Campo, A., & Arzt, E. (2007). Design parameters and current fabrication approaches for developing bioinspired dry adhesives. Macromolecular Bioscience, 7(2), 118-127.
2. Autumn, K., Dittmore, A., Santos, D., Spenko, M., & Cutkosky, M. (2006). Frictional adhesion: A new angle on gecko attachment. Journal of Experimental Biology, 209(18), 3569-3579.
3. Sitti M (2003). Synthetic gecko foot-hair micro/nano-structures as dry adhesives. Journal of adhesion science and technology [0169-4243] Sitti yr:2003 vol:17 iss:8 pg:1055 -1073.
4. Tian, Yu et al., Adhesion and friction in gecko toe attachment and detachment (2006). Proceedings of the National Academy of Sciences of the United States of America [0027-8424] Tian yr:2006 vol:103:51 pg:19320 -19325.
5. Autumn K, Liang YA, Hsieh ST, Zesch W, Chan WP, Kenny TW, Fearing R, Full RJ (2000). Adhesive force of a single gecko foot-hair. Nature [0028-0836] Autumn yr:2000 vol:405 iss:6787 pg:681 -685.
6. Lee, H., Lee, B. P., & Messersmith, P. B. (2007). A reversible wet/dry adhesive inspired by mussels and geckos. Nature, 448(7151), 338-341.
7. Sameoto, D., Li, Y., & Menon, C. (2008). Multi-scale compliant foot designs and fabrication for use with a spider-inspired climbing robot. Journal of Bionic Engineering, 5(3), 189-196.
8. K. Autumn, M. Sitti, Y.A. Liang, A.M. Peattie, W.R. Hansen, S. Sponberg, T. Kenny, R. Fearing, J.N. Israelachvili, and R.J. Full (2008), Evidence for van der Waals adhesion in gecko setae, Proceedings National Academy of Sciences, vol. 99, no. 19, pp. 12252-12256.
9. Sethi, S., Ge, L., Ci, L., Ajayan, P. M., & Dhinojwala, A. (2008). Gecko-inspired carbon nanotube-based self-cleaning adhesives. Nano Letters, 8(3), 822-825