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A battery-free magnetic implant paired with a miniaturized wearable device could one day be used to wirelessly monitor health, early studies suggest.

Chipless implants were able to measure glucose levels, the viscosity of cerebrospinal fluid and intracranial pressure in preclinical experiments conducted in rats.

The implants wirelessly communicated with the wearable device through a magnetic field, researchers report in the journal Science Advances.

The system opens up the possibility of continuous health monitoring without needing transcutaneous wires, integrated circuit chips, or bulky readout equipment, thereby reducing infections, improving biocompatibility, and aiding portability.

“Our miniaturized system presents exciting possibilities for advancing health monitoring,” said lead investigator Mengdi Han, PhD, an assistant professor in the department of biomedical engineering at Peking University.

“By inserting a tiny magnetic implant into the body, it can provide a rich set of real-time data related to your health status. We aim to use such magnetic implants to enhance the way we monitor and manage health.”

The implant includes a micro-magnet to generate an alternate magnetic field during vibration, a soft, elastomeric membrane to improve the vibration amplitude, and surface coatings to selectively absorb targeted biochemicals.

The wearable device establishes a bidirectional interaction with the implant through the magnetic field.

This removes the need for commercial chips, batteries, or coils in the implant and it does not require bulky readout equipment, thereby keeping size to a minimum.

“Unlike traditional methods, the wearable device has the capability to initiate a damped vibration in the magnetic implants, subsequently capturing their ensuing vibration motions wirelessly,” explained Zhongyi Nie, a PhD student in Han’s lab.

“These motions serve as precise indicators of the biophysical conditions surrounding the implants and the concentration of specific biochemicals, depending on surface modifications.”

For example, to achieve wireless sensing of glucose levels, the team used chemical modifications on the surface of the micro-magnet to enable specific adsorption of glucose.

The implants incorporate soft materials to generate vibration amplitudes two orders of magnitude larger than those of conventional micro-electro-mechanical, with vibration frequencies that can be tailored.

This allows measurements in an unshielded environment and offers the possibility of multiplexed sensing using different frequency bands.

The vibrational features of the magnetic implants after surface modification reflect both the surrounding physical conditions and also information on the concentration of a specific chemical.

A deep learning model correlates the time- and frequency-domain data with physical and chemical parameters so measurement is insensitive to the relative positions of the magnetic implant and wearable device.

The researchers believe the wireless sensing system could also be used for measuring blood pressure and viscosity of the cardiovascular system, contact force in dentistry and orthopedics, and pressure in the abdominal region, as well as the distribution and concentration of proteins, peptides, small molecules, and cells within the body.

“Monitoring of these conditions outside of hospital settings is useful for the diagnosis, treatment, and management of a variety of acute and chronic diseases, such as traumatic injuries, heart failure, diabetes, cancer, liver cirrhosis, ascites, and others,” they say.

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