Microscopic Drug-Delivering Robot Operates In Eye
Robots have been trying to invade our bodies for years. Now they’ve found a way to get in our eyes and–if we’re lucky–we won’t even know about it.
Bradley Nelson is a Professor of Robotics and Intelligent Systems at ETH-Zürich and is the founder of the Institute of Robotics and Intelligent Systems where he leads the Multi-Scale Robotics Lab. Dr. Nelson and his team have created a robot that, once injected into the eye, can be moved forwards, backwards, and turned in place–all by remote control. If they can shrink their micrometer-scale robot enough to fit into a 23 gauge needle it could be injected into the eye with little or no anesthetic.
The MagMite, as it’s called, is driven by magnetic propulsion. At the center of 8 overlapping magnetic fields (and their magnets) the MagMite’s movements are the net result of changes in the strengths of the magnetic fields. It has a mass of 30-50 µg and, measuring 300 µm x 300 µm x 70 µm, the microbot (a nanobot, of course, would have dimensions in the hundreds of nanometers) is comparable in size to the blood vessels in the human retina having diameters of approximately 150 µm. This is important as Dr. Nelson hopes MagMite will one day be used to treat retinal vein occlusion, a common cause of glaucoma or macular edema. The spatial resolution afforded by the MagMite would allow physicians to deliver drugs in a precise, site-specific manner. People with age-related macular degeneration, the most common cause of blindness among older people, would also benefit. Age-related macular degeneration is often treated with injections directly into the eye. But this leads to rapid diffusion of the drug and the need for regular injections. MagMite could remain in the eye for months, dispensing the drug in a time-release fashion.
So far it’s only been tested in synthetic eyes or eyes dissected from animals (the demonstration in the clip below is in a pig eye). Plans are in the works for human trials. Any takers? Try not to look at the needle headed right for your eye. Remember, it probably won’t hurt.
The magnetic control system developed by Dr. Nelson’s group is a major improvement over robotic propulsions systems of the past. A common strategy for designing medical robots has been to give it a kind of motor with the idea of enabling them to swim their way to targets in the body such as a tumor where they could deliver local chemotherapy. As we’ve pointed out before these mechanical approaches have several drawbacks including tissue damage caused by moving parts and the possibility of the motor getting snagged. These robots would also require nano-sized batteries which simply don’t exist yet. The ideal situation would be a robot that doesn’t require internal propulsion or power. That’s what Dr. Nelson has in his MagMites. We can conceive of letting them course through the bloodstream, passively going with the flow, until they near their target where the magnets could then be turned on and guide it the rest of the way.
The MagMite is a major achievement, but there are some additional major advances that need to be developed before anything like the scenario I described above becomes a reality. For one, the robot has to be seen. Dr. Nelson’s group chose to develop their MagMite in the eye because they can watch it from the outside-in (I’m certain it was experimental feasibility rather than a desire to treat eye conditions that drove their test target–but I digress). But even the eye presented difficulties. The various types of tissues that make up the eye scatter light differently. It was a major challenge for the team to tweak the optics so they could properly monitor the MagMite’s movements. Good luck trying to reach that lung tumor. For that to happen, the MagMite technology will probably have to be merged with that of carbon nanotube transmitters that would transmit the robot’s precise location. Again, this technology is a ways off yet.
But Dr. Nelson’s proof of principle is indeed a beautiful display of technological finesse. To manipulate 8 magnetic fields with such a soft touch as to precisely control a micrometer-sized robot is mastery. The MagMite’s speed tops out at 12.5 mm/s or 42 times the robot’s body length per second. At such speeds the robot can produce enough force to push objects of comparable size. It’s easy to get excited about the prospects of using MagMites for noninvasive surgery, at least in the eye where small changes in structure lead to big changes in vision. And the magnetic power required to move it is 2 mT, about 50 times the average magnetic field of the Earth and a thousand times less power than a typical MRI magnet.
At this point, the MagMite is really just a small magnet, not much of a robot at all. But that’ll change soon when Dr. Nelson enables it with drug delivery capabilities. At hundreds of microns the MagMite is not the ideal vehicle for drug delivery. Nanobots, with dimensions in the hundreds of nanometers, would be able to go where MagMite cannot (nanoparticles small enough to pass through cell membranes are already being created in labs). The dream application, of course, is to unleash trillions of robots into the body that would deliver drugs to specific sites, including specific organelles inside of cells. And yes, again, this technology is quite a ways off. But with Dr. Nelson’s demonstration, it was brought that much closer.
[image credits: NewScientist, Institute of Robotics and Intelligent Systems]