Image: A biodegradable piezoelectric pressure sensor can monitor a wide range of medical conditions before dissolving safely (Photo courtesy of Thanh Duc Nguyen /UConn).
A new study describes how a biodegradable pressure sensor can monitor chronic lung disease, brain swelling, and other medical conditions before dissolving harmlessly in the body.
Under development at the University of Connecticut (UConn; Storrs, USA), the new sensor is made of two layers of piezoelectric poly-D,L-lactide (PDLLA) polymer film sandwiched between miniature molybdenum electrodes, and then encapsulated in layers of polylactic (PLA). The piezoelectric PLLA film emits a small electrical charge when pressure is applied to it, allowing it to precisely measure pressures between 0–18 kPa, and maintain reliable performance levels for a period of up to four days in an aqueous environment.
In a proof of concept study, the researchers implanted the PLLA piezoelectric sensor in the abdominal cavity of a mouse in order to monitor the pressure of diaphragmatic contraction and respiratory rate. The implanted sensor was hardwired to an external signal amplifier, which transmitted the enhanced electrical signals to an oscilloscope. After four days, the sensor broke down into its individual organic components. Immune response was confined to minor inflammation in the surrounding tissues, which returned to normal after four weeks. The study was published on January 16, 2018, in Proceedings of the National Academy of Sciences (PNAS).
“We are very excited because this is the first time these biocompatible materials have been used in this way,” said senior author Thanh Duc Nguyen, PhD, of the UConn Institute of Materials Science. “Medical sensors are often implanted directly into soft tissues and organs. Taking them out can cause additional damage. We knew that if we could develop a sensor that didn't require surgery to take it out, that would be really significant.”
“There are many applications for this sensor. Let's say the sensor is implanted in the brain; we can use biodegradable wires and put the accompanying non-degradable electronics far away from the delicate brain tissue, such as under the skin behind the ear, similar to a cochlear implant,” concluded Dr. Nguyen. “Then it would just require a minor treatment to remove the electronics, without worrying about the sensor being in direct contact with soft brain tissue.”
Piezoelectricity, discovered in 1880 by French physicists Jacques and Pierre Curie, is a reversible effect in crystals that describes the internal generation of an electrical charge resulting from a mechanical force. For example, lead zirconate titanate crystals will generate measurable piezoelectricity when their static structure is deformed by about 0.1% of the original dimension. Conversely, those same crystals will change about 0.1% of their static dimension when an external electric field is applied to the material. The inverse piezoelectric effect is used in the production of ultrasonic sound waves.
University of Connecticut