Sensors that monitor a patient’s condition during and after medical procedures can be expensive, uncomfortable, and even dangerous. Now, an international team of researchers has designed a highly sensitive flexible gas sensor that can be implanted in the body — and, after it’s no longer needed, safely biodegrade into materials that are absorbed by the body.

In a study, Penn State researchers reported they designed a flexible and implantable sensor that can monitor various forms of nitric oxide (NO) and nitrogen dioxide (NO2) gas in the body. Monitoring these types of gases is important because they can play either a beneficial, or sometimes harmful, role in human health.

Nitric oxide, for example, which is produced naturally in the human body, plays an important role in health because it relaxes or widens blood vessels to enhance blood flow, allowing oxygen and nutrients to circulate through the body. On the other hand, exposure to nitrogen dioxide from the environment is linked to the progression of conditions such as chronic obstructive pulmonary disease. Nitric oxide is highly reactive and can be transformed into nitrogen dioxide when exposed to oxygen.

The team added a twist to their sensor design by making it from materials that are not just implantable, flexible, and stretchable, but also biodegradable. While current devices are used outside of the body to monitor gas levels, Cheng said they are bulky and potentially not as accurate as an implantable device. Implantable devices, however, need to be removed, which could mean another operation. The researchers investigated a design that does not need to be removed.

“Let’s say you have a cardiac surgical operation; the monitor outside of the body might not be sufficient to detect the gas,” said Professor Huanyu “Larry”Cheng. “It might be much more beneficial to monitor the gas levels from the heart surface, or from internal organs. This gas sensor is implantable, and biodegradable, as well, which is another research direction we’ve been working on. If the patient fully recovers from a surgical operation, they don’t need the device any longer, which makes biodegradable devices useful.”

According to the researchers, all of the components are biodegradable in water or in bodily fluids but remain functional enough to capture the information on the gas levels. In this case, the researchers made the device’s electrical conductors out of magnesium, and for the functional materials, they used silicon, which is also highly sensitive to nitric oxide. Silicon is unique — it’s the building block for modern electronics, is considered to be super-stable, and is biodegradable. It can dissolve in a really slow manner, at about one to two nanometers a day, depending on the environment. Not only can the body can safely absorb all of the materials used in the device, but they dissolve at a slow enough pace that would allow the sensors to function in the body during a patient’s recovery period.

The sensor was tested in humid conditions and aqueous solutions to show that it could stably perform in the harsh conditions of the body. The team used computational resources of ICDS’s Roar supercomputer to create the computer simulations that can calculate extremely small changes caused by slight changes of shape, or deformations, of the material. They based their measurement on resistance, which can change based on the gas absorption.

The researchers say future work could look at designing integrated systems that could monitor other bodily functions for healthy aging and various disease applications.

For more information, contact Matt Swayne at This email address is being protected from spambots. You need JavaScript enabled to view it..


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This article first appeared in the March, 2021 issue of Sensor Technology Magazine.

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