Lipids in Action: Gravity Defying Geckos
Have you ever wondered how geckos are capable of climbing perfectly smooth surfaces? In the past, many hypotheses were formed about their ability to defy gravity. Some of the more common beliefs were that geckos had tiny suction cups on their feet, they were able to secrete a sticky substance from their toes, or that they had tiny hooks that were able to grab on to small indentations on surfaces they were climbing. These hypotheses have long since been laid to rest.
Taking a closer look at the toe pads of a gecko, scientists observed that they are covered in millions of tiny hair-like structures called setae. Taking an even closer look, scientists discovered that these setae are made of a protein called keratin. At the end of the setae are even smaller structures made of keratin called spatulae. A study published earlier in 2022 showed that the spatulae of these setae were made of β-keratin mostly in a “flat” and untwisted structure. It is hypothesized that these flat β-keratin structures are necessary to produce extremely thin and flat surfaces for consistently reliable contact with other flat surfaces (Holler, et al.; 2022).
Taking an even closer look at the β-keratin structures of gecko toe pads, scientists have observed these structures to be covered in lipids. Lipids are known to be able to alter adhesion properties and surface hydrophobicity which could also play a key role in adhesion to smooth surfaces. The same group previously mentioned for identifying the structure of the β-keratin spatulae also wanted to have a better understanding of the lipids on these structures. So, they used near-edge X-ray absorption fine structure imaging to get to the bottom of it.
What they found was that the spatulae were covered in a thin film of lipids ordered in densely packed layers. The total thickness of these lipid layers was observed to be about one nanometer! They hypothesized that these lipids serve at least two purposes: 1) they protect the protein structures and keep them from drying out and 2) the lipids render surfaces hydrophobic and increase the hydrophobic-hydrophobic interactions of the spatulae with the smooth surfaces being climbed (Rasmussen, et al.; 2022).
It would still be interesting to know exactly what lipids are on the surface of gecko toes so, maybe one of you reading this will take a look!
Just to compare – since gecko’s are small creatures, only less than 5% of their total surface area needs to be covered in these setae structures. If a human wanted to have the same climbing abilities as a gecko, it is estimated that about 40% of our body’s surface area would have to be covered in setae. Since this would make our hands and feet way too big for our body, it doesn’t look like we’ll be doing this any time soon.
Check out the article published on phys.org for more information!