Photo: Profusa, Inc.
A new sensor that detects blood oxygen levels gives an accurate reading more than four years after it’s been implanted into a person’s body.
The results represent a significant step forward in the development of precision medicine techniques that promise to help tailor medicine to an individual’s needs.
The “biosensor” — dubbed the Lumee Oxygen Platform — overcomes the “foreign body response,” an issue that’s plagued other implantable sensors. This is when the body’s own immune system attacks implants, causing a hard collagen capsule to form around them and inflammation that renders them useless after a matter of days.
“We call our sensors tissue-integrating sensors,” said Natalie Wisniewski, PhD, chief technology officer at Profusa, the company responsible for developing the sensor. “The sensors are soft and tissue-like. They are highly porous, and the tissue is able to grow in and throughout the sensor, rather than the sensor becoming isolated [because it is encased in collagen], like a conventional sensor.”
How to hide from the immune system
The way it works: The biosensor is implanted into the skin just 8 millimeters below its surface.
The device is seeded with a molecule that lights up in the presence of oxygen. A patch worn on the skin above the sensor picks up on the light. The oxygen level detected is then given out via a reader attached by wire to the patch.
Researchers tested the sensor after 4 1/2 years in one participant. They found no decrease in the sensor’s ability to give an accurate blood oxygen level reading.
The results were presented today at the 255th National Meeting and Exposition of the American Chemical Society.
So, what sets the Profusa biosensor apart? According to Wisniewski, its success lies in its structure.
The biosensor is designed with space in mind, despite being just 5 millimeters by 50 microns in size: It’s 60 percent porous “empty” space. This porous space is structured so material can flow through it. It’s also made of flexible material that better mimics human tissue.
This is a marked contrast to other commercially available sensors, says Wisniewski. These tend to be made of plastic or metal and are rigid, clearly marking them out to the body’s immune system as foreign, and thus, a target for the immune system. As a result, they quickly become encapsulated in collagen, dulling their abilities.
A ‘holy grail’ for biosensors?
Biosensors are nothing new. If you or someone you know has diabetes, you’re probably very familiar with glucose sensors, which give the user a picture of their blood sugar levels.
The first implantable glucose sensor approved for use in the United States is the FreeStyle Libre Flash Glucose Monitoring System. It can be worn for up to 10 days. While sensors such as this one do offer the user more continuous monitoring of their blood glucose levels than the “finger prick” test, they’re still highly limited by that 10-day shelf life.
“It is the holy grail to get an actual device that can be implanted and functional for extended periods,” said Mark Schoenfisch, PhD, a professor of chemistry at the University of North Carolina at Chapel Hill.
Schoenfisch’s lab is working on adapting implantable glucose sensors that are already on the market to try and overcome the foreign body response. Schoenfisch is also a part of Clinical Sensors Inc., a company that’s working on a biosensor that could be implanted and work for up to a month or longer.
There a couple of caveats to Profusa’s results. The light-emitting molecule in the biosensors can wear out over time, says Wisniewski. This means that the four-year life span reported may not be assured.
Also, because the biosensor uses light to transmit the oxygen level to the skin patch, it wouldn’t work if it was implanted into deeper tissue or a person’s organs.
And although Wisniewski believes that the biosensor will one day be adapted to monitor glucose and other chemicals in the blood, the team at Profusa hasn’t yet managed to do this.
“How you measure oxygen and how you measure glucose is a little bit different,” explained Schoenfisch. “So, they would need to demonstrate [the same results] with glucose next.”
“There’s probably a reason why they have done this with oxygen first, and not glucose,” he added.
So, while a similarly long-lasting biosensor for diabetes and other conditions may be some years away, the Lumee Oxygen Platform is on track to get U.S. Food and Drug Administration approval for use in the next year, Wisniewski says. It’s already been approved for use in Europe. Currently, there are clinical trials on-going for people with peripheral artery disease, which causes not enough blood oxygen to flow to the limbs.
To get there, explains Wisniewski, Profusa is trying to refine the biosensor’s design to use Bluetooth to transmit oxygen readings wirelessly to a handheld device, like a cell phone. That would enable the biosensor to be used easily in the home.
Profusa is also forging ahead with trying to rejig the technology for monitoring other chemicals, such as glucose.
Looking to the future, Wisniewski says that these kinds of biosensors may be able to give anyone — whether they’re a patient or just someone interested in monitoring their health — more information to make conscious healthcare choices that exactly fit their individual needs.
“I’m really excited to see what future impact this technology can have,” said Wisniewski.