An interdisciplinary research team from Northwestern University, Evanston, IL, the University of Illinois, Urbana-Champaign, and the University of Arizona, Tucson, has developed a flexible medical implant that harvests energy from the beating heart, which, they say, could be used to power pacemakers, defibrillators, and heart-rate monitors naturally and reliably and reduce or eliminate the need for batteries.

The implant contains a flexible piezoelectric film and a tiny rechargeable battery. (Credit: John Rogers, University of Illinois)

The team developed and demonstrated a device that converts mechanical energy from the natural motions of the heart, lung, and diaphragm into enough electrical energy to charge a pacemaker or battery for other practical uses.

They designed the device so that its piezoelectric material (where a voltage develops across the material when it is pressed or bent) could capture the maximum amount of energy. The piezoelectric material was encapsulated lead zirconate titanate (PZT), a ceramic commonly used for sensors but not often used in biomedical devices. When you press the material, it generates an electrical signal. In this case, the mechanical beating of the heart or breathing motion of the diaphragm causes the pressing.

Thin ribbons of PZT are surrounded by flexible, biocompatible plastic, with a rechargeable battery and a rectifier integrated into the system. The entire package is approximately 2.2 centimeters by 2.5 centimeters.

In animal studies, the device was attached to the hearts, lungs, and diaphragms of living animal models, and the mechanical motion of the internal organs produced enough energy to charge a 3.8-volt battery.

The Northwestern team developed theoretical models that establish design rules and capture key behaviors of the device. They plan to optimize different design layouts of the stretchable mechanical energy harvester to facilitate its easy use on animal models.