A biodegradable pressure sensor, with the potential to assist doctors to monitor swelling of the brain, chronic lung disease, and other medical conditions before getting dissolved in a patient’s body without any harm, has been developed by UConn engineers.
The UConn study has been published in the latest online issue of the Proceedings of the National Academy of Sciences.
The flexible, small sensor is made of medically safe materials that have been hitherto approved by the U.S. Food and Drug Administration for application in bone grafts, surgical sutures and medical implants. It has been designed as a substitute for prevalent implantable pressure sensors that include possibly toxic components.
Such sensors have to be eliminated from the body after use, putting patients through an additional invasive procedure, increasing their recovery time and increasing the risk of infection.
According to the team, as the UConn sensor releases a small electrical charge upon applying pressure against it, the device can also be applied to provide electrical stimulation for regeneration of tissues. Other prospective applications include observing patients suffering from heart disease, glaucoma and bladder cancer.
“We are very excited because this is the first time these biocompatible materials have been used in this way,” stated Thanh Duc Nguyen, senior author of the paper and an assistant professor of mechanical and biomedical engineering in the Institute of Regenerative Engineering at UConn Health and the Institute of Materials Science at the Storrs campus.
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.
Thanh Duc Nguyen, Senior Author
A prototype sensor created by the lab comprised of a thin polymer film with a length of 5 mm, width of 5 mm and thickness of 200 mm. The sensor was fixed in the abdomen of a mouse to observe its respiratory rate. It provided dependable readings of contractions in the diaphragm of the mouse for 4 days before eventually getting disintegrated into its individual organic components.
In order to ensure that the sensor was also medically safe, the scientists fixed it at the back of a mouse and observed for a response from the immune system of the mouse. The outcomes indicated only minor inflammation following the insertion of the sensor and the adjacent tissue turned normal after a period of 4 weeks.
One of the challenging tasks of the study was to make the biodegradable material to generate an electrical charge upon being squeezed or subjected to pressure, a procedure called the piezoelectric effect. In the normal state, the medically safe polymer utilized to develop the sensor (a product called Poly(L-lactide) or PLLA) is neutral and does not release an electrical charge under pressure.
Eli Curry, the lead author of the paper and a graduate student in Nguyen’s lab, offered the study’s significant advancement when he triumphantly converted the PLLA into a piezoelectric material by cautiously heating, stretching and cutting the material at the optimum angle such that its internal molecular structure was modified and it embraced piezoelectric characteristics. Then, Curry linked the sensor to electronic circuits for investigating the force-sensing capabilities of the material.
Upon being assembled, the UConn sensor includes two piezoelectric PLLA film layers interceded between tiny molybdenum electrodes and then enclosed with layers of polylactic acid or PLA, a biodegradable material often used for making tissue scaffolds and bone screws. Molybdenum is used for making hip implants and cardiovascular stents.
The piezoelectric PLLA film transmits a small electrical charge even if a very minute pressure is applied on it. Such small electrical signals can be captured and conveyed to another device so that a doctor can review it.
To carry out a proof-of-concept investigation of the innovative sensor, the researchers hardwired an implanted sensor to a signal amplifier located outside the body of a mouse. Then, the amplifier conveyed the improved electrical signals to an oscilloscope at which the readings of the sensor can be easily observed.
According to the research team, the readings of the sensor at the time of investigation were equal to those of prevalent commercial devices and equally reliable. The innovative sensor has the ability to capture a broad array of physiological pressures, for example, those observed behind the eye, in the brain, and in the abdomen.
The sensitivity of the sensor can be tuned by altering the number of PLLA layers used and also other aspects.
Nguyen’s team has been testing various ways to increase the functional lifetime of the sensor. The eventual aim of the lab is to create a sensor system that is entirely biodegradable inside the human body.
However, till then, the innovative sensor can be used in its existing form to assist patients in eliminating the need for invasive removal surgery, stated the scientists.
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. 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.
Thanh Duc Nguyen, Senior Author
Nguyen’s research team has filed for a patent for the innovative sensor, and the patent application is pending.
Kai Ke, Kinga Wrobel, Albert Miller III, and Avi Patel from the Nguyen Research Group; Dr Cato Laurencin, Dr Qian Wu, Lixia Yue, Kevin Lo, Insoo Kim, Chia-Ling Kuo, and Jianling Feng from UConn Health; and Professor Horea Ilies and Meysam Chorsi from UConn’s Computational Design Lab are the other authors of the study. Prashant Purohit, associate professor at the University of Pennsylvannia, also contributed to the study.
A National Institutes of Health grant (1R21EBO24787) and funding from UConn’s Academic Plan supported the study.