New Delhi: In the Harry Potter books, dark wizards used magic to reanimate corpses to do their bidding. Meanwhile, in the real world, a team of scientists from the US is using dead wolf spiders to grasp objects by puffing air into their limbs, causing them to spread out and then curl inwards, much like the claw machines found in gaming arcades. 

While this novel area of research — termed ‘necrobotics’ — may seem bizarre to some, according to the team of scientists from Rice University, Texas, the ‘grippers’ they have created can blend into natural environments and pick up objects that even outweigh them. Their findings, which have been peer-reviewed, were published in a study in the journal Advanced Science on 25 July.

According to the study, unlike human beings and other mammals that move their limbs by syncronising opposing muscles, spiders use hydraulics. A chamber located near their heads contracts to send blood to their limbs, which forces them to extend. When the pressure is relieved, the limbs contract. The team put this natural architecture to use to create a small-scale robot or ‘necrobot’.

“It happens to be the case that the spider, after its death, has the perfect architecture to build small-scale, naturally-derived grippers,” said Daniel Preston, one of the researchers, in a statement.

He added that this area of research in soft robotics is a lot of fun because scientists get to use previously untapped types of actuation and materials. The team showed that the bodies of wolf spiders could lift at least 130 per cent of their body weight. They used the grippers to manipulate a circuit board, move objects, and even lift other spiders. One another observation made by the researchers was that smaller spiders could carry heavier loads in comparison to their size. 

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The project began in 2019 when a dead, curled-up spider kindled the curiosity of the scientists. They then embarked on research to understand why spiders curl up after they die, and found that spiders do not have antagonistic muscle pairs like biceps and triceps in humans. In an antagonistic muscle pair, as one muscle contracts, the other muscle relaxes or lengthens.

Spiders only have flexor muscles, which decrease the angle between the bones on two sides of a joint. The flexor muscles allow the spider’s legs to curl inwards. To extend them outward, spiders use hydraulic pressure, which is created by the flowing fluids. The internal valves present in the spider’s hydraulic chamber or prosoma allow them to control each leg individually.

When they die, spiders lose the ability to actively pressurise their bodies, which causes their limbs to curl up. After witnessing this, the team wanted to leverage the mechanism for their research. To set up the spider gripper, the scientists inserted a needle into the prosoma chamber, sealing the same with glue. The other end of the needle was connected to a hand-held syringe. A puff of air sent through the syringe activated the dead spider’s legs.

The scientists ran one spider cadaver through 1,000 open-close cycles to see how well the limbs held up, and found it to be fairly robust. “It (spider cadaver) started experiencing wear and tear as we got closer to 1,000 cycles. We think it is related to the issues with dehydration of the joints. We think we can overcome that by applying polymeric coatings,” Preston said in the statement.

According to the team, ‘necrobotics’ can be useful in various applications. “We can look into the areas of pick-and-place tasks, repetitive tasks like sorting or moving objects around at these small scales, and maybe even things like assembling microelectronics,” Preston said. It could also be deployed to capture smaller insects, as the gripper is inherently camouflaged, according to the team.

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