Swim or Crawl, Microscopic Bots Do It All

Science fiction has often imagined medical doctors that could shrink themselves down to a microscopic size so that they could venture inside their patients’ bodies to diagnose and treat diseases in a way that would otherwise be impossible. Shrink rays are still the stuff of fantasy, but Cornell University researchers have found a way to shrink robots to tiny proportions just the same. And by tiny, I mean really tiny — as in smaller than many species of bacteria. At just two to five microns in size, these robots are small enough to theoretically travel through a person’s bloodstream, or deep into other tissues.

Creating microscopic robots was about more than just bragging rights for the team. They were engineered primarily to manipulate light diffraction, which is how light bends when passing through small openings. This enables high-resolution imaging — via tuning or focusing of light — directly within tiny environments like tissues or microscopic structures. But to make it possible, the robots needed to be similar in size to the wavelength of visible light. At that size, they can function as diffractive optical elements.

Do the Locomotion

That is all well and good, but going from a tiny light diffractor to a system that can assist with high-resolution imaging deep within biological tissues is a giant leap. The robots would need to be capable of locomotion to support such an application. And of course a bacteria-sized robot cannot be made to move, right? As it turns out, they can. The team came up with an interesting mechanism that makes it possible for them to walk and swim.

The robots move using a magnetically driven pinching motion, allowing them to inchworm forward on solid surfaces or swim through fluids. This movement is achieved by incorporating nanometer-scale magnets into their structure, each designed with distinct shapes — long and thin or short and stubby. By applying a large magnetic field, all the magnets align in one direction. Smaller magnetic fields selectively flip only the short, stubby magnets, creating controlled mechanical deformations. These deformations generate the forward propulsion needed for the robots to crawl or swim.

I have feelings too, you know

This same magnetically driven pinching motion also enables the robots to act as highly compliant springs, which can be used to measure force. When they push against a structure, the resistance causes the robot to deform slightly, altering the diffraction pattern of light interacting with it. This change in the diffraction pattern is measured to determine the magnitude of the force applied. This innovative approach allows the robots to perform precise force measurements at microscopic scales, making them valuable for studying interactions in delicate structures like DNA or other cellular components.

Future developments may ultimately enable the robots to carry out complex tasks like targeted drug delivery or in-situ sensing in challenging environments. The researchers also plan to explore how swarms of these robots can work collaboratively, opening up new possibilities in material science, nanomanufacturing, and environmental monitoring at unprecedented scales.