It’s not the big electromagnet in an MRI that makes implanted hardware problematic, it’s the pulsing current in the smaller gradient coils — the ones used to generate the position dependent signals. Sylvain Martel, an engineer at the École Polytechnique in Montreal, realized that if those coils can move things in the body, then they can just as well move drug-laden special delivery vehicles or other micromachines. In a recent open source paper he demonstrated successful targeting of a drug to specific points in the hepatic artery of a rabbit.
Lacking any hardware modifications, the typical MRI machine found at any major hospital would suffice to position objects in say, the carotid artery, provided the objects are at least 1.5 mm in size. To generate enough force to position doxorubicin-infused, graphite coated FeCo (Iron-Colbalt) nanoparticles embedded in a 50 micron biodegradeable matrix, Sylvain built custom gradient coils that he could swap into a standard MRI machine. Adding a few modifications to the software for steering control, he was able to achieve sustained localized drug release over the course of several days.
Amidst the many other targeted delivery strategies still lacking the specificity to make them a reality, these achievements are potentially game-changing. Sylvain has already taken the next step in arterial positioning beyond just one or two major bifurcation points, and has now added some control provisions directly to the delivery vehicle itself. Rather than starting from scratch, he has been able to modify naturally occurring magnetotactic bacteria known as MC-1, which use an organelle known as a magnetosome to sense and respond to fields. Bacterial-hybrid devices need not require full blown MRI machines as they are typically responsive to fields many orders of magnitude smaller.
Equally incredible wireless magnetic manipulation strategies are simultaneously under development to deliver clot-busting drugs, for example, within the blood vessels of the retina. The “Octomag,” with five degrees of freedom, represents a radical departure from standard orthogonal control as would be delivered by MRI-style systems. Scaled up to human dimension, this kind of a system would operate at field strengths of only 0 .1 Telsa compared to the several Tesla of modern MRI. While still in its infancy, magnetic targeting to the inner space is shaping up to be a fantastic voyage for medicine.
Article in International Journal of Advanced Robotic Systems: Combining Pulsed and DC Gradients in a Clinical MRI-Based Microrobotic Platform to Guide Therapeutic Magnetic Agents in the Vascular Network