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Bubble-Based Microrobots for the Delivery of Therapeutic Drugs

At the University of Colorado Boulder, an engineering group has developed a new class of small and self-propelled robots that has the potential to zip via liquid at unbelievable speeds and might one day even provide prescription drugs to hard-to-reach places within the human body.

Medical “microrobots” could one day deliver prescription drugs throughout the human body. Image Credit: Shields Lab

The scientists explain their mini healthcare providers in a study reported in the journal Small.

Imagine if microrobots could perform certain tasks in the body, such as non-invasive surgeries. 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.

Jin Lee, Study Lead Author and Postdoctoral Researcher, Department of Chemical and Biological Engineering, University of Colorado Boulder

Lee and his collaborators are not there yet, but the new study is a big step ahead for tiny robots.

The microrobots created by the group are small. Each one is just a width of 20 μm, several times smaller compared to the width of a human hair. They are also rapid, having the ability to travel at speeds of around 3 mm per second, or approximately 9,000 times their length per minute.

That is several times faster than a cheetah in relative terms.  In the new study performed, the group deployed fleets of such machines to transport doses of dexamethasone, a general steroid medication, to the bladders of lab mice.

The outcomes recommend that microrobots might be a beneficial tool for treating bladder diseases and other illnesses in people.

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,” stated C. Wyatt Shields, a co-author of the new study and assistant professor of chemical and biological engineering.

Fantastic Voyage

If that sounds like something torn from science fiction, that is because it is. In the classic film Fantastic Voyage, a group of adventurers travels through a shrunken-down submarine into the body of a man in a coma.

The movie was released in 1966. Today, we are living in an era of micrometer—and nanometer—scale robots.

Jin Lee, Study Lead Author and Postdoctoral Researcher, Department of Chemical and Biological Engineering, University of Colorado Boulder

Lee imagines that, just like in the movie, microrobots could swirl through a person’s bloodstream, looking for targeted areas to treat several ailments.

The group makes its microrobots out of materials known as biocompatible polymers using a technology that is similar to 3D printing. The machines appear a bit like small rockets and come complete with three small fins.

Each of the robots also carries a small bubble of trapped air. If one exposes the machines to an acoustic field, like the kind utilized in ultrasound, the bubbles will start to vibrate in a wild manner, thereby pushing water away and shooting the robots forward.

Co-authors include Nick Bottenus, Assistant Professor of mechanical engineering; Ankur Gupta, Assistant Professor of chemical and biological engineering; and engineering graduate students Ritu Raj, Cooper Thome, Nicole Day, and Payton Martinez.

To take their microrobots for a test drive, the scientists set their sights on a common issue for humans: bladder disease.

Bringing Relief

Interstitial cystitis, also called painful bladder syndrome, impacts millions of Americans and, as its name suggests, can lead to severe pelvic pain. Treating the disease could be equally uneasy. Frequently, patients visit a clinic several times over a period of weeks where a doctor injects a rough solution of dexamethasone into the bladder with the help of a catheter.

Lee hopes that microrobots might be able to offer some relief.

In laboratory experiments, the scientists fabricated schools of microrobots encapsulating high concentrations of dexamethasone.

They then introduced thousands of those bots into the bladders of laboratory mice. The outcome was a real-life Fantastic Voyage.

After reaching the bladder walls, the machines slowly liberated their dexamethasone over the course of around two days. Such a steady flow of medicine could enable patients to receive more drugs over a longer period, stated Lee, enhancing outcomes for patients.

Lee added that the team has to perform a lot of work before microrobots could travel via real human bodies. For a start, the group wishes to make the machines completely biodegradable so that they can ultimately dissolve in the body.

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.

Jin Lee, Study Lead Author and Postdoctoral Researcher, Department of Chemical and Biological Engineering, University of Colorado Boulder

A robotic Fantastic Voyage

A “microrobot” seen under a microscope as it's being printed, then moving in the presence of an acoustic field, like the kind used in ultrasounds. The robot moves in a looping pattern because one of its three fins is shorter than the others. Image Credit: Shields Lab

Journal Reference

Lee, J.G., et al. (2023) Bubble-Based Microrobots with Rapid Circular Motions for Epithelial Pinning and Drug Delivery. Small.


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