“It happens to be the case that the spider, after it's deceased, is the perfect architecture for small scale, naturally derived grippers,” said Daniel Preston of Rice’s George R. Brown School of Engineering.
It's the first step in a new area of research the engineers have dubbed necrobotics. We use all kinds of interesting new materials like hydrogels and elastomers that can be actuated by things like chemical reactions, pneumatics and light,” said Preston, whose lab specialises in soft robotic systems using non-traditional materials. “We even have some recent work on textiles and wearables.
“This area of soft robotics is a lot of fun because we get to use previously untapped types of actuation and materials,” Preston said. “The spider falls into this line of inquiry. It’s something that hasn't been used before but has a lot of potential.”
Preston's team used wolf spiders which, in testing, were able to lift more than 130 per cent of their own body weight. The grippers were used to manipulate a circuit board, move objects, and lift another spider.
The researchers noted smaller spiders can carry heavier loads in comparison to their size. Conversely, the larger the spider, the smaller the load it can carry in comparison to its own body weight. Future research will likely involve testing this concept with spiders smaller than the wolf spider, Preston said.
The project began in 2019, said lead author Faye Yap. “We were moving stuff around in the lab and we noticed a curled up spider at the edge of the hallway,” she said. “We were really curious as to why spiders curl up after they die.”
A quick search found the answer: “Spiders do not have antagonistic muscle pairs, like biceps and triceps in humans,” Yap said. “They only have flexor muscles, which allow their legs to curl in, and they extend them outward by hydraulic pressure. When they die, they lose the ability to actively pressurize their bodies. That’s why they curl up.
“At the time, we were thinking, ‘Oh, this is super interesting.’ We wanted to find a way to leverage this mechanism,” she said.
Spiders are unlike mammals because their movement system uses hydraulics, rather than muscles. A chamber near the head contracts to send blood to the limbs, forcing them to extend.
Internal valves in the spiders’ hydraulic chamber, or prosoma, allow them to control each leg individually, and that will also be the subject of future research, Preston said. “The dead spider isn’t controlling these valves,” he said. “They’re all open. That worked out in our favour in this study, because it allowed us to control all the legs at the same time.”
To tap into the prosoma, Yap used a needle, which she attached with a dab of superglue. That was connected to a handheld syringe, which delivered a minute amount of air to activate the legs.
The lab ran one ex-spider through 1,000 open-close cycles to see how well its limbs held up, and found it to be fairly robust. “It starts to experience some wear and tear as we get close to 1,000 cycles,” Preston said. “We think that’s related to issues with dehydration of the joints. We think we can overcome that by applying polymeric coatings.”
So, what makes this a useful experiment rather than a grotesque crime against nature?
Preston said a few necrobotic applications have occurred to him. “There are a lot of pick-and-place tasks we could look into, repetitive tasks like sorting or moving objects around at these small scales, and maybe even things like assembly of microelectronics,” he said.
“Another application could be deploying it to capture smaller insects in nature, because it’s inherently camouflaged,” Yap added.
“Also, the spiders themselves are biodegradable,” Preston said. “So we're not introducing a big waste stream, which can be a problem with more traditional components.”
The stuff of nightmares? Maybe not – Preston and Yap insist this doesn't quite count as reanimation. “Despite looking like it might have come back to life, we’re certain that it’s inanimate, and we’re using it in this case strictly as a material derived from a once-living spider,” Preston said. “It’s providing us with something really useful.”
Want the best engineering stories delivered straight to your inbox? The Professional Engineering newsletter gives you vital updates on the most cutting-edge engineering and exciting new job opportunities. To sign up, click here.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.