Microchips Designed for Tracking Bodily Functions

The Atoms chip placed on a U.S. penny (Shapiro and Emami Labs/Caltech)

13 September 2017. Engineering researchers designed a tiny chip device that identifies precise locations inside the body, a key feature for ingestible medical devices. A team from California Institute of Technology in Pasadena describes the microchips in yesterday’s issue of the journal Nature Biomedical Engineering.

The Caltech researchers, led by chemical engineering professor Mikhail Shapiro and electrical engineering professor Azita Emami, seek to advance miniaturized wireless medical technology for diagnostics and drug delivery. For many of these ingestible devices to operate effectively, however, they need to give their precise locations, a task made difficult by human tissue interfering with and distorting signals sent by the devices when inside the body.

Shapiro, Emami, and colleagues created tiny radio frequency transmitters that take features of magnetic resonance imaging, or MRI, scans to give their locations based on positions inside a magnetic field. As explained by Shapiro in a Caltech statement, atoms at different locations resonate or reflect at different frequencies with MRI, due to variations in the magnetic field, making it easier to identify their location. “We wanted to embody this elegant principle in a compact integrated circuit.”

And the circuit had to be compact. Emami notes that the chip needed to be both small and use little power. “We had to carefully balance the size of the device with how much power it consumes and how well its location can be pinpointed.”

The actual devices, designed by doctoral candidate and first author Manuel Monge, are called transmitters operated as magnetic spins or Atoms, and include sensors, resonators, and wireless transmitters. The prototype chip used in lab and animal tests measures 1.4 millimeters square, about 1/250th the size of an American penny. Monge used standard CMOS — complementary metal-oxide-semiconductor — processes to fabricate the chip.

In proof-of-concept tests, the researchers implanted the Atoms device under the skin of an anesthetized lab mouse, moving the chip to four different locations. The mouse was then exposed to a magnetic field, with a signal receiver nearby to measure and track the chip’s location, and the captured signals plotted on a chart. The chart shows four peaks identifying the locations of the chip in the mouse, within 500 micrometers of the true location in all cases.

Further development of the chip is needed to extend its capabilities to three-dimensional location tracking — the tests reported on two-dimensional locations — as well as extending the range of the chips’ signals. The authors foresee the chips used in devices for tracking blood chemistry, such as pH or sugar concentrations, as well as temperature and pressure measurements in real time. The devices could also help release medications at precise locations in the body instead of systemic drugs that could trigger adverse side effects.

In addition, the chips are small enough for many devices to be used simultaneously. “You could have dozens of microscale devices traveling around the body taking measurements or intervening in disease,” adds Shapiro. “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.”

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