Microrobots Eyed for Use Inside the Human Body

One of the modern promises of robotic-enhanced medicine is that one day, legions of tiny robots will perform procedures inside the human body with little human intervention or surgical intrusion. Researchers at University of Colorado Boulder (CU Boulder) are a step closer to this goal with the development of microrobots that can self-propel through liquid at high speeds, they said. One day, scientists hope these machines can be used to deliver targeted medications to hard-to-reach places in the body.

“Imagine if microrobots could perform certain tasks in the body, such as non-invasive surgeries,” said Jin Lee, a postdoctoral researcher in the CU Boulder Department of Chemical and Biological Engineering. “Instead of cutting into the patient, we can simply introduce the robots to the body through a pill or an injection, and they would perform the procedure themselves.”

That's the promise of the bots, which measure only 20 micrometers wide—or several times smaller than the width of a human hair—and are capable of traveling at speeds of about 3 millimeters per second. This is roughly 9,000 times their own length per minute—or, in relative terms, multiple times faster than the fastest-moving known animal, the cheetah.

Specifically, the researchers used fleets of the machines to transport doses of dexamethasone, a common steroid medication, to the bladders of lab mice, they said. This demonstrates that they could be useful for treating not just bladder diseases but also other illnesses in human patients.

“Microscale robots have garnered a lot of excitement in scientific circles, but what makes them interesting to us is that we can design them to perform useful tasks in the body,” said C. Wyatt Shields, assistant professor of chemical and biological engineering, who led the research.

How Microrobots Work

Researchers developed the microrobots—which look similar to small rockets outfitted with three tiny fins—out of biocompatible polymers using a technology similar to 3D printing. They reported on the design and development of the robots in a paper in the journal, Small.

In addition to the fins, the robots also each carry a small bubble of trapped air, similar to what happens when someone submerges a glass upside-down in water, the researchers explain. This added feature means that if the robots are exposed to an acoustic field—such as the kind used in ultrasound—the bubbles will begin to vibrate wildly, they said. This pushes water in an aquatic environment away, shooting the robots forward for movement.

To test the machines, the team focused their tests on treating bladder disease—or, more specifically, interstitial cystitis, also known as painful bladder syndrome, which affects millions of people in the United States.

The affliction can cause severe pelvic pain—however, its treatment also can be equally uncomfortable, the researchers said. That's because it typically requires patients to report to a clinic several times over a period of weeks so a doctor can inject a harsh solution of dexamethasone into the bladder through a catheter. 

Using the microrobots to deliver these treatments, then, can spare patients this invasive and painful treatment, the researchers said. To prove this, they fabricated schools of microrobots encapsulating high concentrations of dexamethasone, and then introduced thousands of those bots into the bladders of lab mice.

Results, Further Research, and Application

The result showed success, with the microrobots dispersing through the organs before sticking onto the bladder walls, which would make them difficult for a patient to expel through urination, the researchers said. They then slowly released their respective doses of dexamethasone over the course of about two days.

Releasing this type of steady flow of medicine could allow patients to receive more drugs over a longer span of time, Lee said, which can improve outcomes for patients. However, there is much work to be done before the microrobots can perform this similar medical task inside human bodies, he said.

To start with, the research team wants to make the machines fully biodegradable so that they would eventually dissolve in the body—something they will proceed with as they continue to develop the microrobots in the future, Lee said.

“If we can make these particles work in the bladder, then we can achieve a more-sustained drug release, and maybe patients wouldn’t have to come into the clinic as often," he explained.