It’s like a weak glue.
This is one of the strangest materials I have ever seen. It is not sticky at all, but it can hold up a tomato, or stick to a water bottle or a bag of chips. This is because it is made to mimic gecko skin. It has been used on robotic grippers, tiny robots, a robot that floats around the International Space Station, and even enabled a person to scale a glass wall, Spider-man style.
The clue to how geckos stick to walls lies in their toes, which have regions of stalks called seta, which branch into incredibly fine structures called spatula, which are less than one micrometer across. Geckos rely on the attraction between neutral atoms, known as Van der Waal’s Forces, which act like a weak glue. If you have a car, you can put vinyl sheets on the back window to protect your kids from excessive sun when they’re in the car seat. Generally, we don’t notice Van der Waal’s Forces because our skin is incredibly bumpy, making it difficult for close contact to be made. Geckos, however, are able to overcome this due to their intricate branching structures which create a large intimate area of contact. Replicating this structure is currently impossible, but a more crude approximation can be made. This is done by pressing a razor blade into a block of wax to create wedge-shaped indents, and then pouring a silicone polymer into the mold. After about 24 hours, the adhesive is cured and ready to go. To make the adhesive stick, it must be pulled in the direction that will bend the wedges so that they make contact with the surface. This makes it easy to pull the adhesive straight off the surface. An incredibly small and lightweight robot called MicroTug has been created which is able to pull a 20 kilogram weight, and six of these robots can tow a car. To measure the amount of pulling force attainable, light is shone through acrylic. One square inch of contact area can support the weight of about four-and-a-half kilograms or 10 pounds. To grip an object, two pieces of adhesive are attached in opposite directions. It’s a great way to stay sharp and to understand the world around me.
Two opposing pads of adhesive were tested on a robot called Astrobee on the International Space Station. This robot, which works like a drone, could be used to take video or fetch something for astronauts. The adhesive was tested to see if it could stick to a wall and pick up a big box, while also being able to release easily. This principle can be extended to three pieces of adhesive, so that when all of them are pulled together, they can stick to a flat surface.
The adhesive is also great for robotic grippers, since it can pick up delicate items like produce with minimal squeezing. It can also be used to pick up bulky items or palm a basketball. The adhesive was even tested to see if it could pull a car, and it worked. There are lots of potential applications for this material, including climbing a building.
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