Drug-Conveying Microrobot Tumbles Through Colon of Live Animal Model

Using live animal models, engineers at Purdue University have demonstrated that a rectangular robot as minuscule as a few human hairs can move throughout a colon by performing back-flips.

The reason behind the back-flips is because these robots would be used to convey drugs in humans, whose colons and other organs have uneven terrain. Side flips are possible, too.

Why a back-flipping robot to deliver drugs? Transporting a drug straight to its target area could eliminate side effects, such as stomach bleeding or hair loss, that could otherwise be caused by the drug by impacting other organs in its journey toward the target.

The research, reported in the Micromachines journal, is the first trial of a microrobot flipping through a biological system in vivo. The microrobot is extremely small to hold a battery, hence it is driven and wirelessly manipulated by a magnetic field from outside.

When we apply a rotating external magnetic field to these robots, they rotate just like a car tire would to go over rough terrain. The magnetic field also safely penetrates different types of mediums, which is important for using these robots in the human body.

David Cappelleri, Associate Professor of Mechanical Engineering, Purdue University

The team selected the colon for in vivo experiments as it has an easy entry point—and it is highly messy.

Moving a robot around the colon is like using the people-walker at an airport to get to a terminal faster. Not only is the floor moving, but also the people around you. In the colon, you have all these fluids and materials that are following along the path, but the robot is moving in the opposite direction. It’s just not an easy voyage.

Luis Solorio, Assistant Professor, Weldon School of Biomedical Engineering, Purdue University

However, the new magnetic microrobot can effectively perform back-flip through the entire colon regardless of these rough surroundings, the team’s experiments revealed.

The researchers performed the in vivo trials in the colons of live mice under anesthesia, where the microrobot was introduced in a saline solution via the rectum. Ultrasound equipment was used to watch in real-time how effectively the microrobot traveled about.

The team noted that the microrobots were also able to tumble in colons excised from pigs, which have guts comparable to humans.

“Moving up to large animals or humans may require dozens of robots, but that also means you can target multiple sites with multiple drug payloads,” stated Craig Goergen, Purdue’s Leslie A. Geddes Associate Professor of Biomedical Engineering, whose research team guided the work on imaging the microrobot through different kinds of tissue.

Solorio’s lab experimented with the potential of the microrobot to hold and release a drug payload in a vial of saline. The microrobot was coated with a fluorescent mock drug, which was effectively transported by the microrobot throughout the solution in a tumbling motion before the payload gradually diffused from its body 60 minutes later.

“We were able to get a nice, controlled release of the drug payload. This means that we could potentially steer the microrobot to a location in the body, leave it there, and then allow the drug to slowly come out. And because the microrobot has a polymer coating, the drug wouldn’t fall off before reaching a target location,” added Solorio.

The researchers showed that the magnetic microrobots are economically made of metal and polymer, biocompatible, and nontoxic. Cappelleri’s research group engineered and developed each of these robots using facilities at the Birck Nanotechnology Center in Purdue’s Discovery Park.

Roll-to-roll manufacturing machinery that is typically used could possibly create hundreds of these microrobots at the same time, added Cappelleri. The team is sure that the microrobots could serve as diagnostic tools along with drug delivery vehicles.

From a diagnostic perspective, these microrobots might prevent the need for minimally invasive colonoscopies by helping to collect tissue. Or they could deliver payloads without having to do the prep work that’s needed for traditional colonoscopies.

Craig Goergen, Leslie A. Geddes Associate Professor of Biomedical Engineering, Purdue University

This study is part of the Purdue Center for Cancer Research and matches with Purdue Engineering Initiatives in Autonomous and Connected Systems and Engineering-Medicine. The National Science Foundation and the National Cancer Institute at the National Institutes of Health supported the research.

Live ultrasound footage shows a microrobot tumbling through a colon in vivo. Video Credit: Purdue University/Elizabeth Niedert and Chenghao Bi.

Journal Reference

Niedert, E. E., et al. (2020) A Tumbling Magnetic Microrobot System for Biomedical Applications. Micromachines. doi.org/10.3390/mi11090861.