“The ultimate goal is to improve patients’ quality of life,” says Thanh Nguyen, Assistant Professor of Mechanical Engineering at the University of Connecticut. To that end, he’s worked with colleagues to develop a biodegradable piezoelectric sensor that measures vital physiological pressures (1). The 5 mm by 5 mm sensor, only 200 μm thick, is made of flexible biocompatible materials, some of which generate electrical energy through deformation. But why do we need a device that meets such specifications? “Many traumatic injuries, and diseases lead to the buildup of dangerous internal pressures.” Nguyen says. “Monitoring them is tremendously important to provide timely intervention. The available sensors to monitor those pressures, however, are often bulky and non-degradable, requiring invasive removal surgery. We think a sensor based only on commonly used medical materials that can “self-vanish” after finishing its measurement task would be very significant.”
Piezoelectric devices offer several advantages over existing bioelectronic sensors. “First, [our device] is very biocompatible because it is based on a common medical material (PLLA) that has been used for FDA-approved surgical sutures, bone scaffolds, and drug delivery devices. Second, it self-emits electrical signals when subjected to force, potentially avoiding the use of a battery in conventional implanted medical sensors. And finally, the sensors could use that self-emitting signal to produce useful electrical stimulation for tissue healing and growth,” says Nguyen. Applications for the sensor could range from measuring diaphragm and transpulmonary pressures to monitoring intraocular and intracranial pressures in glaucoma and hydrocephalus, respectively. But if the sensor is degradable, how long is it able to provide useful readings? Nguyen’s laboratory implanted several of the devices into mice, then tested and confirmed the viability of the sensors for up to 16 days – for context, that’s four times longer than the typical length of time for monitoring intracranial pressure. They also put the device through an accelerated degradation process (at 74ºC) and found that the sensor completely broke down after 56 days. If necessary, though, its lifetime can be reduced or extended by altering the thickness of the device and the molecular weight of the materials used. Indeed, further development aims to create a biodegradable sensor that gives the user robust control over its lifetime.
Nguyen is hopeful for the overall future of body-bound sensors, but points out a few essentials: “Implanted sensors would have to be multifunctional, small, flexible, wireless, self-powered, and especially biocompatible, in the sense that all byproducts from the degradation process should be safe for long-term use inside the body.”
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References
- EJ Curry et al. “Biodegradable piezoelectric force sensor”, Proc Natl Acad Sci USA, [Epub ahead of print] (2018). PMID: 29339509.
