A somewhat 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. While the syringe moves up again, the block is wedged between the legs of the dead spider.
It is a strange and somewhat sinister 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 grab. It works surprisingly well, researcher Daniel Preston said in an email.
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By using dead spiders, the 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?
coiled spider
With this research, which was published in the scientific journal Advanced Sciencethe Rice scientists are taking the first steps in a new field they call necrorobotics.
The idea for the eight-legged, inanimate gripper came about when the researchers were setting up their new lab. “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 stretch 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 automatically contract again by the flexor muscles when the pressure drops. Live spiders can control each leg separately via valves in their cephalothorax.
Hollow needle and superglue
Turning a dead spider into a necrobotic grab turned out to be surprisingly easy. Yap simply stuck a hollow needle into the spider’s cephalothorax and secured it with superglue. She then connected the needle to a hand syringe.
The euthanized wolf spiders that the researchers used for their experiment were able to lift objects of different 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 grab. They also managed to disconnect an electrical wire. Each necrobotic grab was tested by opening and closing it a thousand times. After about seven hundred times, wear started to appear, 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. That should extend the life of the grab.
More than a creepy trick
According to the researchers, the necrobotic grab 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 catching small insects without damaging them. The gripper is by nature 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 liquid or air pressure is not new in soft robotics. The use of a dead spider instead of an artificial grab is new.’
Overvelde sees the experiment primarily as a source of inspiration. He doesn’t think dead spiders will be widely used as grabs. “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 living spider has no problem with that. They show how beautiful nature is and how difficult to imitate, even if you have the inanimate mechanics.’