Do you remember the Saturday morning PBS show, The Magic School Bus?
In one of my favorite episodes the student Ralphie gets sick, and all his classmates are very worried about him. So the magic school bus shrinks down and enters a cut in Ralphie’s skin, embarking on a journey through Ralphie’s blood stream to find out what is making him sick.
Recently, a group of biomedical engineers at Stanford created a device reminiscent of the magic school bus that can be directed through the blood stream for drug delivery, diagnostics, or minimally invasive procedures, such as attacking blood clots or removing plaques from arteries. Electrical engineer Ada Poon from Standford is developing a new class of tiny, self-propelled medical devices that could be injected or implanted into the human body (watch a video here). These devices are controlled wirelessly using a radio transmitter that is outside the body to send radio waves through the body to the internal device, which detects these signals using a tiny antenna of coiled wire.
For many years scientists had been working to create these tiny implantable devices using low-frequency radio waves to penetrate the body. However, in order to generate enough power for the device, these low frequency waves required antennas a few centimeters in diameter, making them far too large to swim through the blood stream.
It was previously thought that high-frequency radio waves would dissipate too quickly in the human body. Dr. Poon used computer simulations to predict how radio waves of various frequencies would travel through the tissues of the body. She revisited previously-held assumptions about how high frequency radio waves interact with a variety of tissues like muscle, bone, and fat. In doing so, she discovered that the optimal frequency radio waves for wireless powering devices within the human body was actually about 100 times higher than previously thought. The ability to use a higher frequency radio wave meant that the antenna could now be 100 times smaller but still deliver the same amount of power to the device, allowing for the creation of devices small enough to travel through the blood stream… And the magic school bus becomes a reality!
These devices could move through the blood stream by two different mechanisms. One way they can maneuver is by driving electrical current through the fluid, creating directional force that moves the device forward at a rate of up to half a centimeter per second. The second type of movement involves the current switching back and forth through a wire loop, resulting in a motion similar to that a kayaker uses when paddling. So maybe it’s a little more like a kayak than a bus?
While a lot of testing and experiments will need to be done before these can be used in medical applications, it seems likely that one day these devices might be filling the spot of the magic school bus and helping Ralphie figure out what makes him sick.