Your heart expends half a joule of energy every time it beats. That’s the same amount of juice you’d need to lift an apple 1.6 feet off the ground.
Before every contraction, the potential energy trapped in chemical bonds within cardiac muscle cells is released and converted into the mechanical power of the heartbeat. But, like all energy, that which is harnessed to power the heart is never destroyed; it just changes form as it radiates away from the organ as heat and vibrations of surrounding tissue and fluid.
Now, a science team has announced a breakthrough in harvesting the energy released from the movement of the beating heart, the breathing lung and the flexing diaphragm. They’ve developed a superthin device that can be attached to an organ to generate electricity from its movements.
The tiny device is already within the range of generating enough electricity to power a pacemaker on its own, says John Rogers, a coauthor of the study that was published on Jan. 20 in the Proceedings of the National Academy of Sciences.
“The thing about cardiac pacemakers is that they are currently battery-operated and have a limited lifespan,” says Rogers, a University of Illinois at Urbana-Champaign materials science and engineering professor. “When the battery runs out, you need to have surgery to replace it. Power is always a challenge.”
The innovation is a flexible piezoelectric layer sandwiched between biocompatible plastic. Rogers says the whole system is about as stiff as the plastic used to make food wrappers.
When the piezoelectric material flexes due to contraction and relaxation of the organ to which it is affixed, it generates electrical energy from the movement. Because organ movements occur as pulses, the team had to include energy storage in their creation so that electricity could be delivered continually. They accomplished this by building in a tiny chip-scale, commercially available battery into the device.
The team found through testing that their system could deliver 0.2 microwatts per square centimeter of stable electricity over 20 million cycles. Voltage and current outputs, they write, were three to five orders of magnitude higher than previous experiments. These results, the team concluded, demonstrate that their system could power implants like pacemakers with or without batteries.
“Our ultimate goal is to replace the battery of an implant altogether,” Rogers tells Txchnologist, “but even extending the life of the implant’s own battery is useful.”
They grew rat smooth muscle cells on their prototypes to determine that the materials were not toxic. They then affixed it to beating sheep and cow hearts to see if it would operate as they had hoped and determine the best positions to place it.
Their system converts mechanical to electrical energy at about two percent efficiency, a number that Rogers says is based on the need not to interfere with the target organ’s natural operation.
The authors see huge potentials in their device, both inside and outside the human body.
“Cardiac and lung motions, in particular, serve as inexhaustible sources of energy during the lifespan of a patient,” they write. “In addition to uses on internal organs, the same types of systems can be implemented in skin-mounted configurations for health/wellness monitors or nonbiomedical devices. The potential to eliminate batteries or, at least, the need to replace them frequently represents a source of motivation for continued work in these and related directions.”