Biodegradable, implantable pressure sensors

A biodegradable pressure sensor could be used by doctors to monitor chronic lung disease, brain swelling, and other medical conditions before dissolving safely in a patient’s body.Thanh Duc Nguyen

Sensors help health care providers and patients monitor health conditions and ensure that they can make informed decisions about treatment. Sensor that are implanted in the body, however, require surgery to remove. This risks additional damage to the tissue.

Pressure sensors are often implanted into soft tissues and organs. These sensors can detect the buildup of pressure in tissues, such as swelling in the brain, eyes, or other organs. Biodegradable pressure sensors could both monitor health conditions and alleviate the need for invasive surgeries to remove the devices.

To develop a biodegradable, implantable pressure sensor, a team led by Dr. Thanh Duc Nguyen at the University of Connecticut used poly-_L-lactic acid (PLLA), a biodegradable polymer that’s commonly used in FDA-approved medical implants. PLLA was recently found to exhibit a characteristic called piezoelectricity when processed a certain way. Piezoelectricity is the ability to produce electricity when compressed, twisted, or otherwise subjected to mechanical force. The research was supported in part by NIH’s National Institute of Biomedical Imaging and Bioengineering (NIBIB). Results appeared online in Proceedings of the National Academy of Sciences on January 16, 2018.

The researchers designed a pressure sensor made of two layers of PLLA that they processed and tested for its piezoelectrical properties. They placed the processed PLLA in between molybdenum (Mo) or magnesium (Mg), which function as electrodes, and surrounded the device with polyactic acid (PLA). Each of these components are currently used in medical devices. The sensor measures only 5 mm by 5 mm and is 200µm thick.

After developing their device, the team tested it by implanting it at the bottom of the diaphragm in the abdomen of a mouse. The sensor had to be hardwired to an amplifier outside the body to detect the electrical currents. The animals’ diaphragm contractions and breathing patterns could be detected for four days, even as the sensor began to biodegrade.

The researchers also tested the sensor’s biocompatibility by implanting it into the backs of mice and measuring the immune response. The mice showed only mild immune responses with minimal inflammation. The immune responses went back to normal by four weeks.

“We are very excited because this is the first time these biocompatible materials have been used in this way,” Nguyen says.

There are many potential applications for a biodegradable pressure sensor. The team hopes the sensors could become a useful alternative to current devices that measure pressure in the eyes, abdomen, arteries, or brain. In the future, they hope to make a fully implantable, biodegradable system with a wireless transmitter.

—Tianna Hicklin, Ph.D.