In a study, the researchers report the design of a flexible gas sensor implant that can monitor various forms of nitric oxide (NO) and nitrogen dioxide (NO2) in the body. Monitoring these types of gases is important because they can play a beneficial – but sometimes harmful - role in human health, according to Huanyu "Larry" Cheng from Pennsylvania State University’s Department of Engineering Science and Mechanics.
Nitric oxide widens blood vessels to enhance blood flow, allowing oxygen and nutrients to circulate through the body. Exposure to nitrogen dioxide from the environment is linked to the progression of conditions such as chronic obstructive pulmonary disease, said Cheng. Nitric oxide is highly reactive and can be transformed into nitrogen dioxide when exposed to oxygen.
According to Cheng, current devices used outside of the body to monitor gas levels are bulky and potentially not as accurate as implantable devices that could need removal in another surgical procedure.
"Let's say you have a cardiac surgical operation, the monitor outside of the body might not be sufficient to detect the gas," Cheng said in a statement. "It might be much more beneficial to monitor the gas levels from the heart surface, or from those 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 gas levels. In this case, the researchers made the device's conductors out of magnesium, and for the functional materials, they used silicon, which is also highly sensitive to nitric oxide.
The body can safely absorb all of the materials used in the device. An added benefit of the design is that the materials dissolve at a slow enough pace that would allow the sensors to function in the body during a patient's recovery.
"Silicon is unique - it's the building block for modern electronics and people consider it to be super-stable," said Cheng. "Silicon has been shown to be biodegradable, as well. It can dissolve in a really slow manner, at about one to two nanometres a day, depending on the environment."
According to the researchers, 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 the Roar supercomputer at Penn State to create computer simulations that can calculate extremely small changes caused by slight changes of shape, or deformations, of the material.
"We base the measurement on resistance, which can change based on the gas absorption, but it can also be changed due to the deformation," said Cheng. "So, if we deform the sensor on the skin surface, that will cause a large force and a large change in resistance and we would have no idea whether the gas' performance is from the deformation, or the exposed environment."
The researchers said future work could look at designing integrated systems that could monitor other bodily functions for healthy aging and various disease applications.
The team's findings are published in NPG Asia Materials.