Necrobiotics: Researchers are turning dead spiders' legs into robotic grippers
Shortly after Daniel Preston, assistant professor of mechanical engineering, established his lab in Rice’s Department of Mechanical Engineering in 2019, he and mechanical engineering graduate student Faye Yap had their Eureka moment.
"We were moving stuff around in the lab, and we noticed a curled-up spider at the edge of the hallway," Yap said in a statement. "We were really curious as to why spiders curl up after they die."
The researchers figured that "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.
Years later, the engineers reveal how to repurpose deceased spiders as mechanical grippers that can blend into natural environments while picking up objects, like other insects, that outweigh them.
An open-access study in Advanced Science outlined the process by which Preston and lead author Yap harnessed a spider’s physiology in the first step toward a novel area of research they call "necrobotics."
Spiders employ hydraulics to move their limbs
"It happens to be the case that the spider after it’s deceased is the perfect architecture for small scale, naturally derived grippers," said Preston.
The subject was naturally interesting to Preston as his lab specializes in soft robotic systems that often use nontraditional materials, as opposed to hard plastics, metals, and electronics. "The spider falls into this line of inquiry. It’s something that hasn't been used before but has a lot of potential," he said.
Spiders use hydraulics to move their limbs, as opposed to other mammals that synchronize opposing muscles. They have what's called a prosoma chamber which contracts, sending inner body fluid into their legs, making them extend. Preston's lab chose wolf spiders for their service, and testing revealed that they were able to lift more than 130 percent of their own body weight, and sometimes much more.
They had the grippers manipulate a circuit board, move objects and even lift another spider.
The team inserted a needle into the spider's prosoma chamber and created a seal around the tip of the needle with a glob of superglue. Squeezing a minute amount of air through the syringe was enough to activate the spider's legs, thereby activating the legs almost instantly.
Internal valves in the spiders’ hydraulic chamber 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 favor in this study because it allowed us to control all the legs at the same time."
The researchers also noted that smaller spiders can carry heavier loads in comparison to their size. 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.
More than a cool stunt
So, how useful is this technology?
"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 an assembly of microelectronics," said Preston.
"Another application could be deploying it to capture smaller insects in nature because it’s inherently camouflaged," Yap added.
As the spiders are biodegradable, the engineers are certain of not introducing a big waste stream, "which can be a problem with more traditional components".
Preston and Yap are aware the experiments may sound like nightmares and may border on bringing the spider back to life.
"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."
Designs perfected through evolution have informed bioinspired animal-like robots that mimic the locomotion of cheetahs and the compliance of jellyfish; biohybrid robots go a step further by incorporating living materials directly into engineered systems. Bioinspiration and bio-hybridization have led to new, exciting research, but humans have relied on biotic materials—non-living materials derived from living organisms—since their early ancestors wore animal hides as clothing and used bones for tools. In this work, an inanimate spider is repurposed as a ready-to-use actuator requiring only a single facile fabrication step, initiating the area of “necrobotics” in which biotic materials are used as robotic components. The unique walking mechanism of spiders—relying on hydraulic pressure rather than antagonistic muscle pairs to extend their legs—results in a necrobotic gripper that naturally resides in its closed state and can be opened by applying pressure. The necrobotic gripper is capable of grasping objects with irregular geometries and up to 130% of its own mass. Furthermore, the gripper can serve as a handheld device and innately camouflages in outdoor environments. Necrobotics can be further extended to incorporate biotic materials derived from other creatures with similar hydraulic mechanisms for locomotion and articulation.