We’ve likely all killed a spider or two in the past, but what if that arachnid’s corpse could be repurposed into something useful? Well, researchers at Rice University in Texas think it can and are pioneering the field of “necrobotics” by injecting dead spiders with air to use them to grasp small objects.
When Rice University assistant professor of mechanical engineering Daniel Preston was setting up his lab, he and graduate student Faye Yap wondered why a dead spider in the corner of the room had its legs curled up. It turns out that spiders extend their legs using hydraulic pressure, which comes from fluid pumped into their legs from a central cavity, which means that when they die, their legs permanently retract. Preston and Yap wondered if they could hack that hydraulic process by injecting air into a dead spider’s legs to force them open. They found that they could, and their study on this macabre opportunity to make a biological gripper was published in Advanced Science on Monday.
“[Spiders] actually only have flexing muscles,” Yap said in a video call, meaning that spiders can pull their legs in, but have no muscles to extend them. “The way they extend their legs is using hydraulic pressure.”
This pressure comes from the spider’s prosoma—the spider’s cephalothorax, where its legs attach to its body—which sends fluid to the arachnid’s legs, allowing it to walk—individual legs are controlled by the opening and closing of valves in the spider’s anatomy. Preston, Yap, and colleagues found that if they carefully inserted a syringe into the prosoma of a dead spider, they could mimic the hydraulic pressure with air, extending and retracting all of the spider’s legs at once. This meant that the spider could be used as a gripper. But why attempt something so disturbing?
“We’re interested in using them for things like sample collection,” Preston said. “They have an intrinsic compliance due to this hydraulic or pneumatic actuation that we’re able to apply, and that helps protect fragile samples or even other living bugs, for example, if we wanted to collect those in the field.”
The properties of the repurposed arachnid are incredibly promising: The team found that a spider gripper could last upwards of 1,000 open/close cycles, and could be used to lift 130% of its own body weight.
The researchers mainly used wolf spiders for the work in this particular manuscript, but they believe that other spider species could be used as well. Interestingly, Yap says that the group found that spiders with larger body mass—such as the Goliath spider—were only able to lift objects that were 1/10th their body weight, while smaller spiders—like jumping spiders—might be able to lift as much as two times their body weight.
As for how those outside the lab reacted to the project, Preston says most were supportive and even excited when they saw how effective the gripper was. Others, though, weren’t too happy about having spiders around.
“One of the employees that works in our front office really doesn’t like spiders. So we had to give a call to the front office whenever we had another delivery coming in for us to use for the project and just kind of give them a heads up,” said Preston with a chuckle. The team ordered their spiders from a biological supply company, but, unfortunately, some of them did not come deceased. Yap elaborated: “Sometimes they are inanimate, but sometimes we do have to euthanize them. So we do look up the most humane way to kill them from literature.”
While the project might seem bizarre, Preston believes it fits right within his lab’s research scope of studying soft robotics. “We look at anything at the intersection of energy, materials and fluids,” he says. “Soft robotics typically applies nontraditional materials, things that are not the typical hard plastics metals but instead things like hydrogels and elastomers and unique actuation modes like magnetism and light.” Preston and Yap are very interested in using this as a jumping-off point for other research on necrobotic grippers, like figuring out how to open and close individual legs.
While researchers across the globe are working on bio-inspired robotics, Preston, Yap, and the rest of the team cut to the chase and used biology itself, plucked from the floor of their lab. This creative, nature-inspired work is clearly mad science at its best.