Quick Answer
Geckos can climb walls due to specialized toe pads on their feet, which utilize intermolecular forces to adhere to surfaces. Their toes contain microscopic hair-like structures called setae, which branch into even smaller structures called spatulae. These spatulae make close contact with surfaces, allowing van der Waals forces to create adhesion. Geckos can control the adhesion by adjusting the angle of their setae.
Background on Gecko Feet
Geckos have unique feet that allow them to climb various smooth surfaces, even upside down. Their toe pads have evolved to take advantage of intermolecular attraction forces to stick and unstick from surfaces as they climb quickly.
Specifically, the bottom of a gecko’s toes contain lamellae, small ridges housing thousands of hair-like structures called setae. These setae are only 5-10 microns in length. At the tips of these tiny setae are even smaller structures called spatulae, which are only 0.2 microns. That means there can be over a million spatulae on just one toe!
Intermolecular Forces Create Adhesion
When a gecko presses its spatulae against a surface, the highly close contact allows weak intermolecular attractions called van der Waals forces to form between the spatulae and the surface. While these forces are weak individually, the cumulative effect of millions of spatulae bonds creates a robust overall adhesion that supports the gecko’s weight.
The van der Waals forces used by geckos represent the same type of temporary attractive forces that cause the water droplets to form on the outside of a glass. So, while gecko adhesion relies on “stickiness” just like tape or glue, it is a completely dry and reusable stickiness deriving from basic intermolecular physics.
Adjustable Angle of Setae Controls Adhesion
A key innovation that allows geckos to climb up walls and across ceilings rapidly is the ability to control the adhesion of their feet. Gecko toes can be adherent enough to support their body weight while climbing but then instantly released to take the next step.
This switchable stickiness arises from the gecko’s ability to change the angle of their setae relative to the surface. When the 6-10 million setae on a toe press closely parallel to the surface, the spatulae make full contact and maximize adhesion. However, when the gecko shifts the angle of the setae to 30 degrees or more, fewer spatulae can touch the surface and the bonds are easily broken as the foot lifts.
So, during the step cycle of climbing, geckos first press their toe pads straight onto the surface to initiate a firm bond, then peel their toes back to end contact and release. This lets them swiftly detach and reattach their feet as they climb.
Unique Gecko Skin Assists Climbing
In addition to the exceptional properties of gecko feet, the skin on their toes also contributes in key ways to successful climbing. Notably, the skin overlaying the setae and spatulae is highly permeable. This allows air to pass through during the attachment so the spatulae can get very close to surfaces without being impeded.
Furthermore, a gecko’s skin is weakly attached to the underlying bones and tendons. This allows the skin to bend and deform independently, maximizing contact across the millions of setae regardless of whether the surface has microscopic ridges or bumps.
So while the setae provide the adhesive force, the mechanical properties of the skin assist in utilizing that stickiness for climbing. This combination allows geckos to traverse irregular rocky surfaces in addition to smooth vertical walls.
Applications to Technology
The unique adhesion system of geckos offers an inspiring model for human-engineered products. Over the last two decades, researchers have studied and mimicked gecko feet to create bio-inspired adhesives.
While early prototypes could match some capabilities of gecko feet, more recent synthetics demonstrate better durability and strength. Their reusable stickiness works in wet and dry conditions, functions in extreme temperatures, and does not wear down easily over repeated use.
Already, gecko-like adhesives show promise for medical bandages, climbing gloves, robotics, and other applications where removable stickiness offers advantages. As researchers optimize features like shear strength, potential uses will likely expand greatly in the coming years.
So, ultimately, unlocking the secrets of gecko adhesion could provide diverse technological innovations that offer similar climbing abilities to these remarkable lizards.
Concluding Thoughts
In conclusion, geckos can climb up sheer walls because their feet utilize specialized structures and physical forces to support their body weight. Van der Waals interactions between millions of microscopic spatulae and surfaces keep geckos firmly stuck as they climb. Notably, geckos can also rapidly detach their feet by controlling the angle of these structures.
We are only beginning to grasp the nuances of gecko adhesion, including the vital role of the skin overlaying their feet. As researchers reveal more detailed insights, this knowledge can further the development of advanced synthetic adhesives. Already, scientists have created gecko-tape and gecko-like gloves that can match some of the climbing capabilities of these animals.
Ultimately, the goal is to mimic what geckos can do and uncover design and engineering principles that can power diverse new technologies. So these tiny lizards still have much to teach us about the wonders of the natural world and applications that can benefit humankind.
References
Hawkes, E. W., Eason, E. V., Christensen, D. L., & Cutkosky, M. R. (2015). Human climbing with efficiently scaled gecko-inspired dry adhesives. Journal of The Royal Society Interface, 12(102), 20140675. https://doi.org/10.1098/rsif.2014.0675
Song, Y., Dai, Z., Wang, Z., & Full, R. J. (2020). Role of multiple, adjustable toes in distributed control shown by sideways wall-running in geckos. Proceedings of the Royal Society B: Biological Sciences, 287(1922), 20200123. https://doi.org/10.1098/rspb.2020.0123
Wang, Z., Ji, A., Ren, L., & Xing, Q. (2015). Biomechanics of gecko locomotion: the patterns of reaction forces on inverted, vertical and horizontal substrates. Bioinspiration & Biomimetics, 10(1), 016019. https://doi.org/10.1088/1748-3190/10/1/016019