Biodegradable
sensor could help doctors monitor serious health conditions
University of
Connecticut
 |
| This biodegradable piezoelectric pressure sensor developed by the University of Connecticut's Nguyen Research Group could be used by doctors to monitor chronic lung disease, brain swelling, and other medical conditions before dissolving safely in a patient's body. Credit: Thanh Duc Nguyen |
UConn engineers have
created a biodegradable pressure sensor that could help doctors monitor chronic
lung disease, swelling of the brain, and other medical conditions before
dissolving harmlessly in a patient's body.
The UConn research is
featured in the current online issue of the Proceedings of the National
Academy of Sciences.
The small, flexible
sensor is made of medically safe materials already approved by the U.S. Food
and Drug Administration for use in surgical sutures, bone grafts, and medical
implants.
It is designed to replace existing implantable pressure sensors that
have potentially toxic components.
Those sensors must be
removed after use, subjecting patients to an additional invasive procedure,
extending their recovery time, and increasing the risk of infection.
Because the UConn
sensor emits a small electrical charge when pressure is applied against it, the
device also could be used to provide electrical stimulation for tissue
regeneration, researchers say.
Other potential applications include monitoring
patients with glaucoma, heart disease, and bladder cancer.
"We are very excited because this is the first time these biocompatible materials have been used in this way," says Thanh Duc Nguyen, the paper's senior author 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," Nguyen notes.
"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."
A prototype sensor
made by the lab consisted of a thin polymer film five millimeters long, five
millimeters wide, and 200 micrometers thick. The sensor was implanted in the
abdomen of a mouse in order to monitor the mouse's respiratory rate.
It emitted
reliable readings of contractions in the mouse's diaphragm for four days before
breaking down into its individual organic components.
To make sure the
sensor was also medically safe, the researchers implanted it in the back of a
mouse and then watched for a response from the mouse's immune system. The
results showed only minor inflammation after the sensor was inserted, and the
surrounding tissue returned to normal after four weeks.
One of the project's
biggest challenges was getting the biodegradable material to produce an
electrical charge when it was subjected to pressure or squeezed, a process
known as the piezoelectric effect. In its usual state, the medically safe
polymer used for the sensor -- a product known as Poly(L-lactide) or PLLA -- is
neutral and doesn't emit an electrical charge under pressure.
Eli Curry, a graduate
student in Nguyen's lab and the paper's lead author, provided the project's key
breakthrough when he successfully transformed the PLLA into a piezoelectric
material by carefully heating it, stretching it, and cutting it at just the
right angle so that its internal molecular structure was altered and it adopted
piezoelectric properties.
Curry then connected the sensor to electronic
circuits so the material's force-sensing capabilities could be tested.
When put together, the
UConn sensor is made of two layers of piezoelectric PLLA film sandwiched
between tiny molybdenum electrodes and then encapsulated with layers of
polylactic acid or PLA, a biodegradable product commonly used for bone screws
and tissue scaffolds. Molybdenum is used for cardiovascular stents and hip
implants.
The piezoelectric PLLA
film emits a small electrical charge when even the most minute pressure is
applied against it. Those small electrical signals can be captured and
transmitted to another device for review by a doctor.
As part of their proof
of concept test for the new sensor, the research team hardwired an implanted
sensor to a signal amplifier placed outside of a mouse's body. The amplifier
then transmitted the enhanced electrical signals to an oscilloscope where the
sensor's readings could be easily viewed.
The sensor's readings
during testing were equal to those of existing commercial devices and just as
reliable, the researchers say.
The new sensor is capable of capturing a wide
range of physiological pressures, such as those found in the brain, behind the
eye, and in the abdomen. The sensor's sensitivity can be adjusted by changing
the number of layers of PLLA used and other factors.
Nguyen's group is
investigating ways to extend the sensor's functional lifetime. The lab's
ultimate goal is to develop a sensor system that is completely biodegradable
within the human body.
But until then, the
new sensor can be used in its current form to help patients avoid invasive
removal surgery, the researchers say.
"There are many
applications for this sensor," says Nguyen. "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."
Nguyen's research
group has filed for a patent for the new sensor. The patent application is
pending.
