Scientists have developed piezoelectric nanogenerators that are able to stretch as well as flex, enabling greater functionality for self-powered implanted medical devices such as pacemakers.
While it is possible to construct devices on a nano-scale from high performance piezoelectric ceramics PZT, which can be printed onto substrates to produce energy from functions such as walking, this only requires the material to be flexible.
However the high performance PZT ribbons, which can offer 80 percent transfer of mechanical energy to electrical energy, are very brittle when stretched meaning that it has not been possible to implement in many potential areas.
“PZT is among the most efficient piezoelectric materials known, but it is an extremely brittle material, with a Young’s Modulus half that of steel,” McAlpine of Princeton University told Nanowerk.
Scientists at Princeton and the University of Pennsylvania have now developed a method of integrating piezoelectric ribbons into silicon rubber, having arranged the ribbons into a wavy shape which allows the material to withstand considerably more strain.
To achieve these results silicone rubber is prestretched, with PTZ nanoribbons printed on before the strain is released, causing the ribbons to buckle in a predetermined manner.
With the ribbons formed into wavy shapes it was found that the combined materials could withstand strains which were larger than the flat equivalent.
Essentially this means that devices will be capable of working in conjunction with, for example, a patient’s lungs or heart, being able to stretch with the organ as it functions, providing power to any implanted medical devices.
“Pacemakers are currently run off of batteries, which means that surgery is required every few years to replace the battery,” said McAlpine.
“The lungs operate in a mode similar to a balloon expanding and contracting i.e., in a stretching operation mode. Our biocompatible energy harvesting materials have now been shown to generate power in such stretching modes.”
While we should not, er, hold our breath for such devices to reach the market any time soon, with researchers currently working on scaling up the technology from just a few ribbons to entire wafers scales, it appears that the wavy PZT method offers a tangible high-power way to go battery free.
“A bonus feature was that the strain imparted to the ribbons actually led to an increased piezoelectric response due to an effect known as the flexoelectric effect,” says McAlpine.