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Biosensors get under our skin, emerging skin implantable sensors

Biosensors, that is sensors that can detect parameters in a living being, are becoming more and more effective in several respects: detecting more and more parameters, becoming more and more sensitive, being able to co-exist for long period of time with the hosting organism to the point of becoming an integral part of that organism, making transfer of detected parameters more and more seamless.

 

“While fitness trackers and other wearables provide insights into our heart rate, respiration and other physical measures, they don’t provide information on the most important aspect of our health: our body’s chemistry,” explained Natalie Wisniewski, Ph.D. “Based on our ongoing studies, tissue-integrated sensor technology has the potential to enable wearables to live up to the promise of personalized medicine, revolutionizing the management of health in wellness and disease.” Dr. Wisniewski, who leads the team of biosensor developers, is the chief technology officer and co-founder of Profusa Inc., a San Francisco Bay Area-based life science company.

 

So far the main issue of embedding a sensor in the body was the adverse reaction of the body to the foreign invader, leading to inflammation and scarring (foreign body response). Conventional sensors, such as those found in continuous glucose monitors, have a sensing electrode wire that penetrates the skin to measure a target chemical in the fluid that surrounds cells. But because the body “sees” the electrode as foreign material, it needs to be removed and replaced within several days at a different location to avoid the effects of inflammation and scar tissue that eventually prevents the electrode from functioning accurately.

 

But today scientists have developed tiny biosensors that become one with the body have overcome this barrier. They have become capable of continuous, long-term monitoring of body chemistry by streaming data to a mobile phone and to the cloud for personal and medical use.

 

One such example has been a skin implantable sensor developed by Profusa, a US company whose mission is to make human body chemistry easily accessible to improve health and wellness. Rather than being isolated from the body, the biosensors work fully integrated within the body’s tissue — without any metal device or electronics, thereby overcoming the body’s attempts to reject it.

 

The biosensors are made with a tissue-like hydrogel, similar to a contact lens. They have the form of tiny fibres, 5mm long and 0.5mm thick, and can be embedded under skin with a single injection . The fibres, at micro level, have the structure of a scaffold letting body cells to integrate with them. The gel is infused with chemicals. They contain photosensitive molecules that change the light absorption depending on the presence of certain molecules, like oxygen, glucose… These photosensitive molecules are the actual sensing part. The strip starts to glow with fluorescent light, which can be picked up by the detector.

 

By illuminating the skin with infrared light, that penetrates the skin, the photosensitive molecules emit specific light wavelengths, proportional to the molecules detected in the body, that are captured by a detector on the skin. Both the emission of the infrared beam and detection of the sensor emitted wavelengths are actuated by a device touching the skin over the sensor that connects via Bluetooth with a smartphone where data are encrypted and stored. The data is relayed to a smart phone for an encrypted personal record and historical tracking. Data can be shared securely via digital networks with healthcare providers.

 

“These sensors make it possible to detect, in ‘real time’ and over long periods of time, changes in the body’s chemistry,” Jared Adams, chief of communications for the Defense Advanced Research Projects Agency (DARPA), told Insider in a email.

 

An example of application is the use of these sensors to monitor the level of oxygen in case of wounds to check the healing progress (the presence of oxygen is a major indicator of the healing process). In this case the sensors are injected at the time the surgeon cleans the wound and sutures it. Another example is monitoring the oxygen in chronic limb ischemia (often a side effect of diabetes). The data are sent by the smartphone to the Lumee Oxygen Platform approved for medical use in Europe.

 

By embedding different molecules in the sensor fibres it is possible to detect a variety of molecules. An example is the detection of lactate, a molecule that is produced by muscles under stressful activity. Monitoring the lactate presence, and its quantity, can provide valuable information for athletes training leading to personal adaptation of the training program based on biochemical data.

 

Although it was developed with COVID-19 in mind, it is not sophisticated enough to differentiate that disease from others.  Its makers said that the alerts would need to be paired with other methods of identifying COVID-19 to give a conclusive diagnosis. The sensor itself cannot tell if the infection is COVID-19 or another pathogen. But once it starts signaling that something is off, “now you can look under the hood,” Hepburn said.

 

This latter application may result in a subtle human augmentation: that athlete, or just you and me, using embedded sensors to monitor their biochemical activity/metabolism can finely tune their activity to decrease fatigue and increase, over time, their performance.

 

Hwang said that Profusa is currently seeking FDA approval for the sensor that can monitor oxygen. It has been tested to detect the flu, and is being developed to check the oxygenation of tissues after plaque buildup in arteries. The sensor is also being tweaked to monitor glucose levels in real time, which could provide new avenues for diabetes

 

The US military’s  DARPA agency is backing development of a sensor meant to be injected under the skin to monitor for COVID-19. According to the agency the sensor continuously monitors vital signs and can flag an infection up to two days before symptoms appear. The agency is exploring whether the sensor could be given members of the US military. Hepburn says the sensor could also be useful, for instance, in a combat setting to detect if a soldier was exposed to harmful chemical, biological, radiological, or nuclear agents.

 

“The Navy might have deep sea divers, where one of the things that’s important to keep track of is how is their body reacting to the increased pressure and the oxygenation level. On the other hand, pilots that fly in very high altitude use pressurized suits, and when those suits potentially fail, you’re already in a very high altitude, low oxygen environment,” Hwang said.

 

 

 

References and Resources also include:

https://cmte.ieee.org/futuredirections/2018/05/30/sensors-get-under-our-skin/

https://www.businessinsider.com/military-sensor-skin-covid-darpa-19-2021-4

 

About Rajesh Uppal

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