Self charging pacemakers to harvest heart's own energy

by R. Colin Johnson
Contributing Editor, MEMS Investor Journal

Applications are years away yet, but Georgia Institute of Technology researchers have demonstrated that piezoelectric nanowires can harvest energy from repetitive motions inside the body -- even the beating of your heart. Future applications could include powering implants -- such as pacemakers -- that today require periodic surgeries just to change their batteries.

The research team, led by Georgia Tech professor Zhong Lin Wang, capitalized on their prior work fabricating nanowires from zinc oxide. Piezoelectric materials like zinc oxide respond to physical deformation with a weak electrical current. When fabricated into nanowires, bending produces a small current, which unfortunately is a current that alternates in direction depending of which way the wire is being bent. Wang's previously crafted a method of harvesting that current by virtue of the gating effect of a Schottky contact at the interface between the nanowire and the metal electrode connected to its end -- called by the researchers a single-wire generator (SWG).

The single-wire generator used for this in vivo demonstration produced about 50 milliVolts at 500 picoAmps -- enough, when ganged together, to keep a small battery charged. The researchers implanted a nanowire about 1 micron in diameter and 50-to-100 microns in length and attached it to a rat's diaphragm (the large muscle below the lungs that flexes up and down as the animal breathes) as well as to its heart.

The nanowire was bonded to a flexible polyimide substrate then encased in a polymer to protect its electrodes from the rat's bodily fluids. The researchers were able to confirm that the nanowire behaved as a charge pump, generating a usable current with each breath. They were also able to confirm that even the rat’s heartbeat could drive the single-wire generator, opening the possibility of self-charging pacemakers which harvest the heart's own energy to charge a pacemaker battery which in turn keeps the heart beat regular.

So far, the researchers’ studies have confirmed that zinc oxide is a biocompatible material suitable for implanting in the human body, but significant testing remains to confirm the suitability of this material for medical uses in humans.