When Fei Yap, a graduate student in mechanical engineering, saw a dead spider curled up in the hallway, it made her think about whether it could be used as a robotic item.
Turning dead spiders into mechanical handles might be some people’s idea of a terrifying scenario, but it could have tangible benefits. Spider legs can grip large, delicate and irregular objects firmly and softly without breaking them.
So, in collaboration with mechanical engineer Daniel Preston, Yap and colleagues at Rice University have discovered a way to make a dead wolf spider’s legs open and cling to objects.
They called this new type of robot “microbes”.
Oddly enough, spiders’ legs don’t have muscles to stretch, but instead move their legs by means of hydraulic pressure – they have what’s called a prosoma chamber, or cephalothorax, which contracts, sending internal body fluids into their legs, causing them to stretch.
So, the team inserted a needle into the spider’s prosoma chamber and made a seal around the tip of the needle with a ball of superglue. Squeezing a small puff of air through the syringe was enough to activate the spider’s legs, achieving full range of motion in less than one second.
“We took the spider, and we put the needle in it without knowing what was going to happen,” Yap says in a video on the Rice University website.
“We had an appreciation for where we wanted to put the needle. And when we did, it worked, the first time, right away. I don’t even know how to describe it, that moment.”
The team was able to make the dead spider grab a small ball and used this experiment to determine the peak grip strength of 0.35 millinewton.
Next, they demonstrated using a dead spider to pick up delicate objects and electronics, including making this grunt clutch remove a wire attached to an electrical jumper and then move a block of polyurethane foam.
They also showed that a spider can bear the weight of another spider of roughly the same size.
Since spiders stretch their legs by applying hydraulic pressure from their thoracic head, when they die, the hydraulic system does not work anymore. The flexor muscles of the spider’s legs go into mortuary stiffness, but since the muscles work only in one direction, the spider curls upwards.
While most components of human-made robots are very complex to manufacture, spiders are indeed complex (unfortunately for arachnophobia) available in abundance.
“The concept of pseudonymology proposed in this work takes advantage of unique designs created by nature that can be complex or even impossible to artificially replicate,” the researchers say in their paper.
Spiders are also biodegradable, so using them as robotic parts will reduce the amount of waste in the robots.
“One of the applications where we can see this used is micromanipulation, and that could include things like microelectronic devices,” Preston says in the video.
One drawback of a dead spider’s clutch is that it begins to experience some wear after a couple of days or after 1,000 open and close cycles.
“We think this is related to issues with dry joints,” Preston explains. “We think we can overcome that by applying polymeric coatings.”
The researchers experimented with coating wolf spiders with beeswax and found that their mass drop was 17 times less than that of an uncoated spider over 10 days, which means it retains more water and its hydraulic system may operate for longer.
This study was published in advanced sciences.
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