One of the biggest hurdles facing the developers of biological implants is coming up with a power source to keep the implanted devices ticking. We've seen various technologies that could be used instead of traditional batteries (which require the patient to go under the knife so they can be replaced) such as wireless transmission of power from outside the body, biological fuel cells that generate electricity from a person's blood sugar, and piezoelectric devices that generate electricity from body movements or the beating of the heart. Now researchers have developed a device that could be used to generate electricity from a patient's breathing.
The device created by researchers at the University of Wisconsin-Madison relies on the piezoelectric effect - whereby an electrical charge accumulates in certain materials in response to mechanical stress. But instead of relying on body movements to create the mechanical stress, the UW-Madison team's device uses low speed airflow like that caused by normal human respiration to cause the vibration of a plastic microbelt engineered from a piezoelectric material called polyvinylidene fluoride (PVDF).
"Basically, we are harvesting mechanical energy from biological systems. The airflow of normal human respiration is typically below about two meters per second," says Materials Science and Engineering Assistant Professor Xudong Wang who created the device along with postdoctoral researcher Chengliang Sun and graduate student Jian Shi. "We calculated that if we could make this material thin enough, small vibrations could produce a microwatt of electrical energy that could be useful for sensors or other devices implanted in the face," said Wang.
To thin the PVDF material to micrometer scale while preserving its piezoelectric properties, Wang's team used an ion-etching process. Wang believes that, with improvements, the thickness of the material, which is biocompatible, can be controlled down to the submicron level and lead to the development of a practical micro-scale device that could harvest energy from the airflow in a person's nose.
Tests conducted by the team saw the device reach power levels in the millivolt range, but reached up to 6 volts with maximum airflow speeds. Wang and the UW-Madison team now plan to look for ways to improve the efficiency of the device. The team's research appears in the September issue of Energy and Environmental Science.