Geckos' van der Waals adhesion is replicatedRyan Clancy | February 06, 2023
Scientists have long been fascinated by the gecko’s amazing ability to climb walls and ceilings with remarkable ease, a seemingly impossible feat made possible thanks to its specialized toes that give it an incredibly strong grip. But until recently, replicating this much-admired adhesion power for human applications has remained elusive.
Now, after years of research, engineers are finally beginning to unlock the secrets of the gecko’s powerful adhesive capabilities, giving insight into a remarkable process that could pave the way for any number of new adhesive technologies, including in aerospace engineering.
Geckos have unique reptilian trait that permits them to scale any number of vertical and inverted surfaces. This unique property is due to the microscopic hairs on their feet, called setae, which allow them to grip and cling onto surfaces with extreme ease. The stickiness of a gecko’s toes is created by van der Waals forces, which is a non-electric and non-chemical attraction between non-polar molecules. Van der Waals are only prevalent as extremely small, microscopic distances – perfect for the millions of tiny hairs that outfit the toes of a gecko.
Harnessing gecko technology
Now, researchers from the Karlsruhe Institute of Technology (KIT) in Germany and Carnegie Mellon University in Pittsburgh are taking inspiration from this natural phenomenon and have created an original adhesive tape that is as reliable, self-cleaning and effective as a gecko’s toes.
This new type of adhesive tape is different than traditional tapes because it is not only able to adhere to surfaces with ease, but also repels dirt and dust particles. This allows for multiple uses of the same surface without any risk of losing adhesion over time - something that regular tapes cannot do. For example, food packaging or bandages could be closed and opened repeatedly without loss of the adhesive's grip.
The adhesive tape works thanks to two mechanisms: lateral friction contact and setae on the sole. The first mechanism works by dragging larger dirt particles off of a surface when moving across it, while the second deposits smaller particles in the skinfolds and among the setae on the sole.
To observe this phenomenon more closely, researchers created elastic micro hairs of varying sizes for their experiments. These micro hairs were then pressed onto a smooth plate covered with glass spheres 10-6 meters in size. They then shifted the tape laterally and lifted it off again. This process was repeated several times, while adhesive force was measured in parallel.
The results revealed that not only is this gecko-inspired adhesion self-cleaning and reliable, but it could potentially be used in many applications where traditional adhesives are no longer efficient. The next step for researchers will be to work on improving the load capacity of the adhesive and increasing its durability.
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The “gecko gripper”
The “gecko gripper” is a revolutionary mechanical attachment for robots, designed to enable them to grasp surfaces and objects using an adhesive inspired by the pads of a gecko’s feet. This groundbreaking technology has far-reaching applications, particularly in space exploration.
Developed by scientists at Stanford University, the “gecko gripper” is based on the unique properties of geckos' feet. The “gecko gripper” harnesses this extraordinary capability by mimicking the structure and function of these hairs with a special adhesive material. When applied to a robot's arm, it enables the robot to stick to surfaces just as effectively as a gecko would. The technology eliminates the need for difficult maneuvers involving constant reorientation and significant force to attach a robot arm to various surfaces, instead relying on adhesion alone.
The “gecko gripper” also has several advantages over traditional gripping technology, including greater flexibility and ease of use. By utilizing the adhesive material, robots can now move freely in any direction without having to worry about losing their grip on the surface they’re attached to.
Space applications for gecko-inspired adhesives
The mechanism of gecko-inspired adhesive is an appealing concept to researchers and engineers because it has the potential to allow robots, satellites and other spacecraft components to attach or affix themselves securely to nearly any surface. In theory, this means that these devices would be able to function in a variety of environments without relying on specific mating surfaces, mechanical interlocking mechanisms, magnets or suction cups. This could prove especially useful for space applications where reliable attachment is critical. One specific example of this technology in use is the "gecko gripper" that was tested in 2021 aboard the ISS.
Despite some progress over the years in developing gecko-inspired adhesives for low-Earth orbit (LEO), there are still many challenges associated with using them in extreme space environments. For example, one major challenge is the ability of these adhesives to endure exposure to atomic oxygen, a major component of the space environment. Atomic oxygen can break down many materials over time, making it difficult for adhesives to remain firmly attached in a steady state.
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In addition to the material challenges associated with gecko-inspired adhesives, there are also practical considerations that need to be addressed. For example, researchers must consider how these adhesive systems will interface with and attach to different surfaces in space. They need to understand the forces at play on those adhesives once they’re deployed and operating in the extreme conditions of outer space. Furthermore, data regarding the durability and longevity of these systems is limited; testing them in simulated or actual space environments is essential for determining their efficacy for space applications.
Overall, gecko-inspired adhesives offer a promising solution for secure attachment in space settings. However, there are still many challenges to be addressed before these systems can be successfully implemented. Research and development into the material properties of these adhesive systems as well as testing them in simulated or actual space environments will help to ensure their successful adoption in space applications.