Peculiar Pangolin Bot Is a Pill-Size Prototype

A tiny robot version of the scaly mammal known as the pangolin may one day perform medical procedures inside the body, a new study finds.

Scientists are increasingly exploring how miniature robots might find use in medicine—for instance, to carry drugs, genes, or cells into the body. Soft robots especially hold the promise of accessing hard-to-reach areas in a safe, minimally invasive way.

Aiming for an alternative to powering these machines using bulky cables or batteries, researchers are investigating untethered versions of these robots that receive their energy remotely, such as via light or ultrasound. Magnetic fields have shown promise for this application because of the way they can penetrate human tissues in a safe manner.

Researchers in Germany have developed a small robot that can deliver drugs to specific locations in a patient’s (in this case) digestive tract and then be unfolded via externally applied magnetic fields. Inspiration for this ‘bot came courtesy of the pangolin, a scaly mammal whose armor covers and fiercely protects the animal’s body while still providing it a wide range of motion. Max Planck Institute for Intelligent Systems

The clinical uses for miniature, untethered magnetic robots are still limited because the devices mainly rely just on mechanical interactions with the body, instead of also using, say, heat. Magnetic fields can also remotely supply energy to robots for heating. However, magnetic fields are best at heating rigid metallic parts, and such components generally take away the advantage of having a soft body.

Now scientists have developed a tiny magnetic robot that combines hard and soft by drawing inspiration from the pangolin. The animal, which resembles a walking pine cone, is the only mammal completely covered in hard scales. However, the pangolin is still capable of flexible motion—it can arrange its scales so that they overlap, letting it curl up into a ball in case of danger.

“I’ve always read about how scientists were inspired by nature, but I’ve never imagined that I myself too would be.”
—Ren Hao Soon, Max Planck Institute for Intelligent Systems, Stuttgart

In the beginning, “I focused on fishes and armadillos as I was more familiar with them,” recalls study lead author Ren Hao Soon, a roboticist at the Max Planck Institute for Intelligent Systems in Stuttgart, Germany. “However, they were not ideal. Individual fish scales were interconnected, which reduced their mechanical deformation. On the other hand, while the armadillo design provided the necessary mechanical compliance, they were not able to provide the necessary heating performance—to enhance the heating performance, a larger volume of material, such as metal scales, needed to be incorporated on the robot.”

While watching YouTube videos on fish and armadillos, Soon says he “stumbled serendipitously on the pangolin, which served our purposes ideally. It was a very exciting moment for me when I thought about it, personally speaking. I’ve always read about how scientists were inspired by nature, but I’ve never imagined that I myself too would be.”

The new robot is a small flat rectangle 1 centimeter by 2 cm by 200 micrometers in size. It consists of aluminum scales on top of a flexible body made of silicone rubber mixed with magnetic microparticles and the liquid alloy eutectic gallium-indium.

In experiments, the scientists used high-frequency magnetic fields to heat the robot to more than 70 °C in less than 30 seconds. They applied these magnetic fields remotely, from a distance of more than 5 cm.

“We challenge the ‘fully soft’ assumption in soft robots. Up till now, there was an inherent assumption that robots used for biomedical applications had to be fully soft.”
—Ren Hao Soon, Max Planck Institute for Intelligent Systems, Stuttgart

When the researchers used low-frequency magnetic fields, they could roll up the robot and move it back and forth. Once curled up, it could transport cargo such as medicine, releasing its contents when heated. For instance, researchers dipped a 50-µm-thick scale and an 80-µm-thick scale in beeswax and then attached a blue cargo packet and a green cargo packet, respectively, to them. When heated magnetically, the thinner packet reached the melting temperature of beeswax 1 second faster than the thicker packet, letting the robot release the blue cargo but not the green one.

“We challenge the ‘fully soft’ assumption in soft robots,” Soon says. “Up till now, there was an inherent assumption that robots used for biomedical applications had to be fully soft. While the compliance of soft materials might make it safer, it greatly restricted the functionalities of these robots—hard materials might have desirable material properties that a fully soft system can utilize.”

The researchers showed that they could roll up this robot so it could fit into a pill to be swallowed for deployment in hard-to-reach areas. In experiments with the robot in pig stomachs from a slaughterhouse, the researchers found it could stop bleeding, and they suggest it could also help treat ulcers, polyps, and tumors, and also target other areas of the gut.

A small robot developed by German researchers provides the prospect of selective deployment of cargos (e.g. medicines) depending on the strength and location of an externally applied magnetic field. Here a simulation is pictured in which a blue-colored cargo is deployed while other portions of the bot remain undeployed.Max Planck Institute for Intelligent Systems

“Minimally invasive surgical devices can reach almost all of the gastrointestinal tract with the endoscope and colonoscope,” Soon says. “However, a large part of the gastrointestinal tract, namely the small intestine, still remains out of reach to these devices, because it is too tortuous to reach with these devices. Untethered robots hence have the opportunity to complement or even supersede existing therapies for diseases in the small intestine.”

The scientists now hope to work with clinicians “to identify a real medical need for which such robots might be useful in,” Soon says.

The scientists detailed their findings 20 June in the journal Nature Communications.