A slightly macabre idea: how a dead spider can be recycled into a robot gripper. “It has a bit of a Frankenstein factor to it.”
A dead spider hangs from the end of the syringe. The syringe moves down towards a block. Just above, the lifeless spider legs suddenly stretch out. Then they curl around the block. As the syringe moves back up, the block is wedged between the legs of the dead spider.
It’s a strange and slightly creepy image. Still, it’s serious science. With this experiment, researchers from Rice University in Houston, Texas show how to ‘reuse’ a dead spider as a mechanical grip. It works surprisingly well, researcher Daniel Preston said in an email.
By using dead spiders, researchers avoid difficult tasks such as designing and making small, soft grippers. Why would you try to build something so complex yourself when nature offers ready-to-use grippers that are so beautifully put together that it is impossible to imitate them?
With this research, which was published in the scientific journal Advanced ScienceRice researchers are taking the first steps in a new field they call necrorobotics.
The idea for the eight-legged, lifeless vulture arose when the researchers were setting up their new laboratory. “We found a dead, coiled spider in the hallway,” writes researcher Faye Yap. ‘Out of curiosity we looked up why the legs always curl up after death.’
It turned out that spiders only have flexor muscles with which they pull their legs inward. This is in contrast to many other animals, which move through a combination of flexor and extensor muscles. Spiders use hydraulic pressure to extend their legs. They push the hemolymph body fluid from their cephalothorax, the head fused with the thorax, to the legs they want to stretch. The legs are automatically contracted again by the flexor muscles when the pressure decreases. Living spiders can control each leg separately via valves in their cephalothorax.
Hollow needle and superglue
Turning a dead spider into a necrobotic grip turned out to be surprisingly easy. Yap simply inserted a hollow needle into the spider’s cephalothorax and secured it with superglue. She then connected the needle to a hand syringe.
The killed wolf spiders that the researchers used for their experiment were able to lift objects of various shapes and with more than 1.3 times the spider’s body weight. They demonstrated this by lifting foam cubes and another dead spider with the spider grip. It also managed to cut an electric line. Each necrobot grip was tested by opening and closing it a thousand times. After about seven hundred times, wear started to occur, probably because the biological material was drying out.
The next step is to allow the spider’s legs to move independently of each other, the researchers report. In addition, they want to apply a thin coating to prevent the body from drying out. This should extend the life of the gripper.
More than a creepy trick
According to the researchers, the necrobotic grip is more than a creepy trick. It is difficult to make such small artificial grippers. They could be used to move small objects. In addition, they are biodegradable. ‘Another application is to catch small insects without damaging them. The gripper is inherently flexible and camouflaged,’ says Yap.
“It has a Frankenstein factor to it,” says researcher Bas Overvelde of the Amsterdam research institute Amolf and Eindhoven University of Technology. ‘But it’s an interesting concept. Deforming something with fluid or air pressure is not new to soft robotics. The use of a dead spider instead of an artificial grip is new.’
Overvelde sees the experiment primarily as a source of inspiration. He doesn’t think dead spiders will be much used as grips. “You’re going to run into problems. Spiders, for example, are not all the same size, and you can already see wear and tear. A live spider has no problem with that. They show how beautiful nature is and how difficult it is to imitate, even if one has the inanimate mechanics.’