Azita Emami talks about eventually having microscale devices that are roaming our bodies and either diagnosing problems or fixing things. Emami is the Andrew and Peggy Cherng Professor of Electrical Engineering and Medical Engineering and Heritage Medical Research Institute Investigator. He co-led the research along with Assistant Professor of Chemical Engineering and Heritage Medical Research Institute Investigator Mikhail Shapiro. "Before now, one of the challenges was that it was hard to tell where they are in the body." A paper describing the new device appears in the September issue of the journal Nature Biomedical Engineering).
Device borrows from MRI
The new silicon-chip device is called ATOMS, which is short for addressable transmitters operated as magnetic spins. It borrows from the principles of magnetic resonance imaging (MRI), in which the location of atoms in a patient’s body is determined using magnetic fields. The microdevices would also be located in the body using magnetic fields—but rather than relying on the body’s atoms, the chips contain a set of integrated sensors, resonators, and wireless transmission technology that would allow them to mimic the magnetic resonance properties of atoms.
"A key principle of MRI is that a magnetic field gradient causes atoms at two different locations to resonate at two different frequencies, making it easy to tell where they are," explains Shapiro. "We wanted to embody this elegant principle in a compact integrated circuit. The ATOMS devices also resonate at different frequencies depending on where they are in a magnetic field."
"We wanted to make this chip very small with low power consumption, and that comes with a lot of engineering challenges," adds Emami. "We had to carefully balance the size of the device with how much power it consumes and how well its location can be pinpointed."
Miniature robotic wardens of our bodies
Though the devices are still preliminary, they could one day serve as miniature robotic wardens of our bodies, monitoring a patient’s gastrointestinal tract, blood, or brain. The devices could measure factors that indicate the health of a patient—such as pH, temperature, pressure, sugar concentrations—and relay that information to doctors. Or, the devices could even be instructed to release drugs.
Shapiro elaborates: "You could have dozens of microscale devices traveling around the body taking measurements or intervening in disease. These devices can all be identical, but the ATOMS devices would allow you to know where they all are and talk to all of them at once. Shapiro compares it to the 1966 sci-fi movie Fantastic Voyage, in which a submarine and its crew are shrunk to microscopic size and injected into the bloodstream of a patient to heal him from the inside—but, as Shapiro says, "instead of sending a single submarine, you could send a flotilla."
Keeping power low was challenge
"This chip is totally unique: there are no other chips that operate on these principles," says Manuel Monge, a student in Emami’s lab and a Rosen Bioengineering Center Scholar at Caltech during the development of the device and lead author of the paper published about ATOMS. "Integrating all of the components together in a very small device while keeping the power low was a big task." Monge did this research as part of his PhD thesis, which was recently honored with the Charles Wilts Prize by Caltech’s Department of Electrical Engineering.
The final prototype chip, which was tested and proven to work in mice, has a surface area of 1.4 square millimeters, 250 times smaller than a penny. It contains a magnetic field sensor, integrated antennas, a wireless powering device, and a circuit that adjusts its radio frequency signal based on the magnetic field strength to wirelessly relay the chip’s location. "In conventional MRI, all of these features are intrinsically found in atoms," says Monge. "We had to create an architecture that functionally mimics them for our chip."