In a bid to create an adhesive patch that can be repeatedly used without losing its grip and work underwater or in a moist environment, researchers from Sungkyunkwan University in South Korea inadvertently uncovered the trick behind one of the cephalopod's most impressive tricks.
The key to the success of their suction is not the shape of their cups or the material, but what is going on in the middle of the dimples. If you look closely, you’ll see that at the very center of the octopuses' suction cups is a little spherical protrusion. This is what makes them so good at clinging to surfaces, even underwater.
While testing this in the lab, the researchers used flat polymer sheets covered in dimples, each containing spheres of different sizes to see which ones were the stickiest. Publishing their results in Nature, they found through trial and error that the best-sized cups were around 50 micrometers in diameter, which as it turns out closely matches what is seen on real octopuses. They then put their artificial version under the microscope in order to fully understand exactly how the suction is generated.
When the cup first attaches to a surface, a little bit of water gets trapped in it, filling the void. But when pressure is applied, the water is forced to the back of the cup, behind the sphere. This has the effect of creating a vacuum chamber in the cup and thus allowing it to stick to even rough surfaces underwater.
The researchers hope this new discovery will help in the development of adhesive patches, which could be used in plasters or underwater tape. The fact that they need no glue makes them an ideal option for covering wounds, and they work just as well when a surface is wet or dry.
There is, however, still much work to be done to see if they can ever be used in a medical or industrial setting. One of the main problems at the moment is finding a way in which the pressure created by the vacuum can be released, while another is simply the fact that while they retain their stickiness underwater, it is still not actually as good as other current products.
2