Implants Send Real-Time Health Data to Patients’ Cellphones

Small and soft, these sensors are designed to track body chemistry for months to years when inserted under the skin. (Profusa Inc.)

(CN) – A new family of small, implantable sensors that could help triage wounded soldiers, indicate effective exercises for an individual athlete, and provide an early warning of a developing health issue moves personalized medicine one step closer to becoming a reality, according to a new study.

The report, which will be presented Monday at the 255th National Meeting & Exposition of the American Chemical Society (ACS), focuses on a device that researchers are now marketing in Europe and hope to get approved in the United States.

“Other implantable sensors currently on the market have a significant drawback,” said lead author Natalie Wisniewski, the chief technology officer and co-founder of Profusa Inc., a San Francisco Bay Area-based life-science company. “They often provoke a ‘foreign body’ immune response that coats the sensor with inflammatory cells or scar tissue.”

That coating can isolate the device from capillaries and prevent it from accurately sensing chemical changes, leaving it ineffective after a few weeks or months.

The team resolved this issue by tricking the body so that it cannot identify the sensors as foreign objects. The devices are smaller than a grain of rice and are comprised of a hydrogel scaffold that is as flexible as a contact lens. They also ensured that their sensor does not have any flat surfaces, which inform cells that an object is not natural, said Wisniewski.

Those features allow cells and capillaries to grow into the device’s porous structure without triggering the typical immune response. Wisniewski announced Monday that, after more than four years, the first sensors the team implanted in human volunteers are still working.

The proprietary hydrogel is a formulation based on poly(2-hydroxyethyl methacrylate), a polymer used to create soft contact lenses. The team added dye molecules that respond to the concentration of an analyte in the blood to the hydrogel scaffold. The type of dye molecule determines the analyte – such as carbon dioxide, oxygen, glucose or lactate – that a specific sensor can recognize.

A small detector, held against the skin or stuck to it as a patch, emits near-infrared light through the skin, leading the dye molecules to shine more or less brightly depending on the concentration of the analyte.

While human eyes cannot perceive this fluorescent light it can be seen by the detector, which then wirelessly communicates the measurement to a computer or cellphone to document the adjustment in brightness as the analyte concentration varies over time.

Profusa is seeking to get the sensors approved by the U.S. Food & Drug Administration. In the meantime, the company’s first product has been green-lighted for marketing in Europe and has been shown to document tissue-oxygen levels in patients getting treated for peripheral artery disease, which restricts the flow of oxygenated blood in legs and arms, leading to amputation in some cases. The disease affects millions of people worldwide.

The company is also launching a clinical trial with the University of California, San Francisco to use the devices to monitor oxygen levels in patients with chronic foot wounds. The trial is sponsored by the National Heart, Lung and Blood Institute.

In addition, the team is working on sensors for other analytes, such as glucose, which will expand the possible applications of the devices. Profusa is also trying to perfect sensors that can track additional analytes that doctors typically evaluate using standard blood tests. The idea is to inject a single sensor that detects multiple body chemistries simultaneously.

“The sensors would provide a continuous record of your analytes relative to your personal baseline,” Wisniewski said. “Then if something goes off kilter, it’s flagged early, before you feel symptoms, so you can get to the doctor in time for treatment.”

The U.S. military is also interested in the sensors and has provided support since the company was created, Wisniewski said. They hope the sensors can be used to evaluate the health of soldiers during deployment or to determine which wounded service members to treat first on the battlefield.

Wisniewski on Monday reported preliminary results showing that monitoring the rise and fall of oxygen levels around muscle with these devices creates an “oxygen signature” that may reveal a person’s fitness level. This could allow the military to determine the ideal training program for a given soldier or to help athletes determine the most effective exercises for improving their performance.

The research was funded by the Defense Advanced Research Projects Agency and the U.S. National Institutes of Health.


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