Rice University mechanical engineers are showing how to repurpose deceased spiders as mechanical grippers that can blend into natural environments while picking up objects, like other insects, that outweigh them.
“It happens to be the case that the spider, after it’s deceased, is the perfect architecture for small scale, naturally derived grippers,” said Assistant Professor Daniel Preston of Rice’s George R. Brown School of Engineering.
An open-access study in Advanced Science outlines the process by which Preston and lead author Faye Yap harnessed a spider’s physiology in a first step toward a novel area of research they call “necrobotics.”
Preston’s lab specializes in soft robotic systems that often use nontraditional materials, as opposed to hard plastics, metals and electronics. “We use all kinds of interesting new materials like hydrogels and elastomers that can be actuated by things like chemical reactions, pneumatics and light,” he said. “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.”
Unlike people and other mammals that move their limbs by synchronizing opposing muscles, spiders use hydraulics. A chamber near their heads contracts to send blood to limbs, forcing them to extend. When the pressure is relieved, the legs contract.
The cadavers Preston’s lab pressed into service were wolf spiders, and testing showed they were reliably 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.
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 favor in this study, because it allowed us to control all the legs at the same time.”
Setting up a spider gripper was fairly simple. Yap tapped into the prosoma chamber with a needle, attaching it with a dab of superglue. The other end of the needle was connected to one of the lab’s test rigs or a handheld syringe, which delivered a minute amount of air to activate the legs almost instantly.
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.”
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.