Medical nanobots have long been a dream of science fiction: minute devices that can roam the bloodstream and the organs looking for, and even treating, disease and other conditions. As The Engineer has reported, the first steps towards these technologies are being taken around the world, with targeted drug delivery systems that bind to specific sites and release specifically-targeted medicines. Other research has looked at smart pills – devices that can carry cameras or other miniaturised technology inside the body to help clinicians treat patients. One problem with such devices is tracking their location once they are ingested. Researchers from Caltech have now borrowed a technique for magnetic resonance imaging to help tackle this problem.
The team, led by electrical engineer Azita Emami and chemical engineer Mikhail Shapiro, has developed a technique known as ATOMS (addressable transmitters operated as magnetic spins) which allows smart pills — also known as capsule endoscopes — to be located in the body using magnetic fields. The technique uses silicon chips that contain a set of integrated sensors, resonators and wireless transmission technology that 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," said 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."
Emami and Shapiro enlisted the help of Manuel Monge, a bioengineer and former doctoral student in Emami lab now working at Elon Musk-founded neurotechnology company Neuralink, to design a chip that would embody their idea. Monge is lead author on a paper in Nature Biomedical Engineering describing the research.
The chip Monge designed has a surface area of 1.4 mm² and contains a magnetic field sensor, integrated antennas, a wireless powering device, and a circuit that adjusts its radio frequency signal based on a magnetic field strength the sensor detects to wirelessly relay the chip's location.
"This chip is totally unique: there are no other chips that operate on these principles," said Monge. "Integrating all of the components together in a very small device while keeping the power low was a big task." The paper describes successful tests on the device inside mice.
The researchers stress that this device is only preliminary. Shapiro envisages further steps that would incorporate sensors into small pills that could detect pH, temperature, pressure and blood sugar concentrations, and relay these to doctors or use them to trigger and control the release of drugs.
"You could have dozens of microscale devices travelling around the body taking measurements or intervening in disease," he said. 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. Referring back to science fiction, in particular the 1960s film Fantastic Voyage, where a miniaturised submarine was used to find and dissolve a life-threatening blood clot, Shapiro added "instead of sending a single submarine, you could send a flotilla."
But for now, the team has a more modest target in its sights. Its next goal is a device that cannot only be detected, but can simultaneously relay and sense body states. "We want to build a device that can go through the gastrointestinal tract and not only tell us where it is but communicate information about the various parts of the body and how they are doing," Monge said.