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Biodegradable Sensor for monitoring nitric oxide (NO) and nitrogen dioxide (NO2) in human body

Biological Sensors that monitor the condition of a patient during and after medical procedures can be costly, uncomfortable, and even hazardous. Now, an international research team has developed a versatile gas sensor that can be inserted into the body and safely biodegraded into materials that are absorbed by the body when it is no longer necessary. 

This research appear in NPG Asia Materials under title "Biodegradable, flexible silicon nanomembrane-based NOx gas sensor system with record-high performance for transient environmental monitors and medical implants,". The researchers announced that a versatile and implantable sensor was created that can track the body's different forms of nitric oxide (NO) and nitrogen dioxide (NO2) gas.

Unprecedented possibilities for medical implants, environmental sensors and other applications are provided by a novel transient electronics technology which is capable of fully dissolving or decomposing under some conditions after a period of service. Here, we identify a biodegradable, versatile electronic device based on silicon that detects NO species with a record-breaking sensitivity of 136 Rs (5 ppm, NO2) and 100-fold selectivity over other rapid response (~30 s) and recovery (~60 s) substances for NO species,' the investigators wrote.

The exceptional characteristics depend primarily not only on materials, measurements, and layouts of design, but also on temperatures and electrical operations. In a mechanically pliable configuration, large-scale sensor arrays exhibit negligible performance deterioration under different modes of applied loads, consistent with mechanical modelling.

In vitro evaluations show the capability and stability for biomedical applications of integrated NOx devices in extreme wet environments.

According to Huanyu 'Larry' Cheng, PhD, the Dorothy Quiggle professor of career growth in the Department of Engineering Science and Mechanics at Penn State and an affiliate of the Institute for Computational and Data Sciences (ICDS), monitoring these types of gases is important because they can play either a beneficial or often harmful role in human health.

For example, nitric oxide, which is created naturally in the human body, plays an important role in health because it relaxes or widens blood vessels to increase blood flow, enabling the body to circulate oxygen and nutrients. Nitrogen dioxide emission from the atmosphere, on the other hand, is related to the development of conditions such as chronic obstructive pulmonary disease, said Cheng, who is also associated with the Institute of Materials Science. Nitric oxide is highly reactive and can, when exposed to oxygen, be converted into nitrogen dioxide.

The team developed its sensor from materials that, Cheng continued, are not only implantable, versatile and stretchable, but also biodegradable. Although current devices are used to track gas levels outside of the body, Cheng said they are voluminous and potentially not as precise as an implantable device.

However, implantable devices, which may involve another procedure, need to be removed. A feature that doesn't need to be eliminated was investigated by the researchers.

"Let 's assume that you have heart surgery, the monitor outside the body may not be adequate to detect the gas," Cheng said. Monitoring gas levels from the heart surface or from those internal organs may be even more useful. This gas sensor is implantable, and also biodegradable, which is another path we have been working on in science. They no longer need the system after the patient completely recovers from surgery, which makes biodegradable devices useful.

All the components are biodegradable in water or in body fluids, according to the researchers, but remain sufficiently functional to collect information on gas levels. In this case , the researchers made the conductors of the device out of magnesium and used silicon, which is also very sensitive to nitric oxide, for the functional materials.

The body, the team noted, will safely absorb all of the materials used in the system. An added advantage of the design is that the materials dissolve at a sufficiently slow rate that would allow the sensors to work in the body during the recovery period of a patient, they said.

"Silicon is unusual. "It is the building block for modern electronics and it is considered to be super-stable by people," Cheng explained. "It has been shown that silicon is also biodegradable. Depending on the environment, it will dissolve in a very slow way, at around one to two nanometers per day.

According to the researchers, in humid environments and aqueous solutions, the sensor was checked to prove that it could work stably in the body's harsh conditions.

The team used the ICDS Roar supercomputer's computing power to construct computer simulations that can quantify extremely small changes induced by minor shape changes or material deformations.

"We base the calculation on resistance, which can vary depending on the absorption of gas, but can also be altered because of deformation," Cheng said. "So, if we deform the sensor on the surface of the skin, that will cause a large force and a large resistance shift and we will have no idea whether the output of the gas is due to the deformation or the environment exposed."

The researchers suggest that future studies should look at developing integrated systems for safe ageing and different disease applications that could track other body functions.

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