A group of Drexel University researchers used a rotating magnetic field to show how multiple chains of microscopic, magnetic bead-based robots can link up to reach impressive speeds swimming through a liquid. Their research is the latest step toward using the so-called “microswimmers” for targeted intravenous drug delivery, surgery, and cancer treatment from inside the body. The mechanical engineering team, led by MinJun Kim, Ph.D., a professor in Drexel’s College of Engineering, magnetically linked and unlinked the beads while they were swimming, and individually controlled the smaller decoupled robots in a magnetic field (see figure).
“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 U Kei Cheang, Ph.D., 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.”
One of their central findings is that longer chains can swim faster than shorter ones. This was determined by starting with a three-bead swimmer and progressively assembling longer ones. The longest chain examined by the group, 13 beads in length, reached a speed of 17.85 microns/second.
Drexel engineers’ ultimate goal is to produce a robotic chain that can travel inside the body, then decouple to deliver their medicinal payload or targeted treatment. Using that approach, a versatile robot can do multiple tasks while being controlled with a single magnetic field. The robot chains move by spinning, like a long screw-like propeller, in step with a rotating, external magnetic field.
So the faster the field rotates, the more the robots spin and the faster they move. This dynamic propulsion system is also the key to getting them to divide into shorter segments. At a certain rate of rotation, the robotic chain will split into two smaller chains that can move independently of each other.
“To disassemble the microswimmer, we simply increased the rotation frequency,” Cheang said. “For a seven-bead micro - swimmer, we showed that by upping the frequency 10-15 cycles the hydrodynamic stress on the swimmer physically deformed it by creating a twisting effect, which leads to disassembly into a three-bead and four-bead swimmer.”
Once they’re separated, the field can be adjusted to manipulate the three- and four-bead robots to move in different directions. Because the beads are magnetized, they can eventually be reconnected by tweaking the field to bring them back into contact on the side with the corresponding magnetic charge. The team also determined optimal rotation rates and angle of approach to facilitate re-linking the microswimmer chains.
Currently, Drexel is partnering with ten institutions of research and medicine from around the world to develop this technology for performing minimally invasive surgery on blocked arteries. Watch the microscopic robots in action at https://youtu.be/t4AyM52m0s0 .
For more information, visit http://drexel.edu/ucomm/news-media/newsroom/ .