Introducing Drexel's new swim team

For the past decade, researchers from Drexel University, Phildelphia, PA, have been studying microrobots in biomedical applications, ultimately hoping to develop a robotic chain capable of traveling inside the human body, and then decoupling to deliver medicine or targeted treatment once they reach their destination. Their latest results are published in the most recent issue of the journal Nature Scientific Reports.

These researchers—led by MinJun Kim, PhD, professor, College of Engineering—have discovered how to use these microrobots as “microswimmers”—comprised of multiple chains of microscopic magnetic beads that are capable of swimming in a microfluidic environment. Dr. Kim and team are now able to magnetically link and unlink, bead by bead, the microswimmers while they are swimming. They also discovered how to individually control the smaller, decoupled robots in a magnetic field. Both of these findings may one day be used to carry out targeted, intravenous microrobot drug delivery, surgery, and cancer treatments.

"We believe microswimmer robots could one day be used to carry out medical procedures and deliver more direct treatments to affected areas inside the body," said lead study author U Kei Cheang, PhD, a postdoctoral research fellow in Drexel's College of Engineering. "They can be highly effective for these jobs because they're able to navigate in many different biological environments, such as the blood stream and the microenvironment inside a tumor."

To move, these robot chains spin in conjunction and in proportion to a rotating external magnetic field. The faster the field rotates, the faster the robots spin, and the faster they move. Researchers also found that they can divide the robots into shorter segments using this dynamic propulsion system.

"To disassemble the microswimmer, we simply increased the rotation frequency," said Cheang. "For a 7-bead microswimmer, we showed that by upping the frequency 10 to 15 cycles the hydrodynamic stress on the swimmer physically deformed it by creating a twisting effect, which leads to disassembly into a 3-bead and 4-bead swimmer."

Once the robot is de-coupled into smaller bots, the magnetic field can be adjusted to make the individual, smaller robots move in different directions. To reconnect them, the field can again be manipulated to reunite them magnetically. Cheang and colleagues have discovered the optimal rotation rates and angle of approach with which to do this.

A key finding from this study is that longer chains swim faster than shorter ones, which Cheng et al. proved by starting out with a 3-bead swimmer and gradually assembling longer and longer swimmers. The longest chain, 13 beads long, reaches a speed of 17.85 microns/second.

Drexel University researchers are working in tandem with researchers from 10 institutions around the world to develop this technology to perform minimally invasive vascular surgery.

"For applications of drug delivery and minimally invasive surgery, future work remains to demonstrate the different assembled configurations can achieve navigation through various in vivo environments, and can be constructed to accomplish different tasks during operative procedures," the authors write. "But we believe that the mechanistic insight into the assembly process we discussed in this research will greatly aid future efforts at developing configurations capable of achieving these crucial abilities."

Watch the video from Drexel University here: https://www.youtube.com/watch?v=t4AyM52m0s0&feature=youtu.be