New Microchip Technology to be Used to Track Miniature Medical Devices

Highlights :

• The function of miniature wireless medical devices such as biosensors and drug-delivery systems depends critically on their location inside the body.
• Currently, localizing and communicating with such devices using existing electromagnetic, acoustic and imaging-based methods is limited by physical tissue properties or performance of imaging modality.
• ATOMS is a new technology involving a silicon integrated circuit that uses the principles of nuclear magnetic resonance to accurately detect the location of microdevices.

A prototype miniature medical device, unique in nature, because its location can be precisely identified within the body (something that proved challenging before) has been developed by researchers at Caltech have developed. This technology could ultimately be used in "smart pills" to diagnose and treat diseases. "The dream is that we will have microscale devices that are roaming our bodies and either diagnosing problems or fixing things," says Azita Emami, the Andrew and Peggy Cherng Professor of Electrical Engineering and Medical Engineering and Heritage Medical Research Institute Investigator, who 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."

The research appears in the September issue of the journal Nature Biomedical Engineering. The lead author is Manuel Monge, who was a doctoral student in Emami's lab and a Rosen Bioengineering Center Scholar at Caltech.

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ATOMS - addressable transmitters operated as magnetic spins

The miniature medical devices are silicon-chip devices called addressable transmitters operated as magnetic spins (ATOMS) that use principles of magnetic resonance imaging (MRI), in which the location of atoms in a patient's body is determined using magnetic fields. While the microdevices would also be located in the body using magnetic fields, 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 instead of relying on the body's 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," says 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."

The invention of ATOMS was serendipitous and happened one day when Shapiro and Emami were discussing their respective fields. Shapiro engineers cells for MRI and other medical imaging techniques and Emami creates microchips for medical sensing and performing actions in the body; they chanced upon the idea that combining MRI technology in creating microdevices could potentially resolve the long-standing challenge of locating microdevices in the body.

"This chip is totally unique: there are no other chips that operate on these principles," says Monge, who was enlisted to help realize the idea in the form of a silicon chip. "Integrating all of the components together in a very small device while keeping the power low was a big task."

The device consists of a magnetic field sensor,, 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.

The operation of the device consists of three phases:

• The magnetic phase which senses, processes and stores the applied magnetic field at each of their locations.
• The excitation phase that starts when the radiofrequency or RF pulse is applied. At this point, the frequency of the RF pulse f0 is acquired, and the devices start oscillating at the same frequency.
• The transmission phase during which each device emits a signal with a shifted frequency proportional to the measured magnetic field.

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Advantages of ATOMS

The final prototype chip was tested and proven in mice and had the advantages of having

• A very small surface area of 1.4 square millimeters
• Low power consumption

The above two things had to be balanced correctly so that the chip’s location can be determined precisely.

"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," says Shapiro.

In ATOMS, the features that are intrinsically found in atoms in the human body had to be recreated.

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Functions of ATOMS

Although the research is still at a preliminary stage, miniature robotic devices canto

• Monitor a patient's gastrointestinal tract, blood, or brain
• Measure factors such as pH, temperature, pressure, sugar concentrations - that indicate the health of a patient
• Relay health information to doctors
• Be instructed to release drugs

Future Plans for ATOMS

Now that the chip can relay its location in the body, the next research addition to its function is make it 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."

Reference:

1. Manuel Monge, Audrey Lee-Gosselin, Mikhail G. Shapiro & Azita Emami. Localization of microscale devices in vivo using addressable transmitters operated as magnetic spins. Nature Biomedical Engineering 1, 736–744 (2017) doi:10.1038/s41551-017-0129-2

Source-Medindia