Progress a heartbeat away


A type of battery has been invented that uses muscle contractions to generate enough electricity to power pacemakers and other devices, Aoife Hardesty investigates

Pacemakers, cochlear implants and internal defibrillators are just a few of the implanted devices that people have come to rely on to maintain their health and quality of life.

Other such devices that act upon the nervous system disorders, such as Parkinson’s disease and epilepsy, also work to significantly diminish, through the use of deep brain stimulators and neural stimulators respectively, the symptoms associated with these diseases.

All of these devices (and many more) require surgery to be implanted inside the body, and subsequently more surgery just to replace the batteries powering these devices.

Would it ever be possible for implanted devices to continue functioning normally in human bodies until death? The answer is looking like a resounding yes, and not just by creating and building longer life batteries.

A type of battery-like device has been created that is powered by muscle contractions, dubbed a mechanical energy harvester. We’ve all heard that ‘energy cannot be created or destroyed’, so by using the natural vibration energy generated when muscles contract, the harvester can store and use the bodies natural power.

Dr John Rogers, of the University of Illinois, and his colleagues have built the harvester and recently tested it in animals. The harvester is based on the piezoelectric effect. This effect results in particular materials becoming electrically charged when under pressure.

For the harvester, a material called lead zirconate titanate (PZT) was used in its crystallised form. The PZT was made into an ultra-thin, flexible ribbon and was then sandwiched between two layers of silicone.

Dr Rogers has done work on silicone in the past, and he and his team have found that by splitting the silicone until it is several times thinner than the width of a human hair, the silicone loses its rigidity and becomes flexible and bendy. The overall flexibility of the harvester allows it to move with the movements of the body organs rather than against them.

Within our bodies, movement is constantly taking place. In the recent experiments performed on cows, sheep and pigs, the harvester was stitched onto the surface of the continually moving heart, diaphragm and lungs.

The idea of using our own natural, bodily functions to power implants is not a novel one. A wave of research has cropped up dedicated to harnessing the energy within our bodies.

While other scientists looked into using glucose breakdown and fluctuations in body temperature, Dr Rogers and his team focused their efforts on harnessing the power of movement from muscle contractions.

What really makes this breakthrough stand apart from other previous experiments is that the harvester was here shown to work on organs of cows, sheep and pigs, organs that are comparable in size to those of humans. What has been demonstrated means that it is possible that the harvester will work in the human body.

In the experiment, the harvester was able to release enough energy that would power a pacemaker. The silicone coating also appeared to be biologically compatible with the animal’s organs. The harvester has been shown to last for half a day, but in order for it to be a better alternative to current battery powered implants, it must be able to last for at least ten years.

Although the results of this experiment are promising, they may not be a true reflection of the harvester’s ability to work in normal, everyday situations. The conditions in which the harvester was tested were very controlled, the animals were under heavy anaesthetic and their chest cavities remained open.

It is unknown how the harvester will function when the entire body is moving. It is possible that friction could occur from other bodily organs and that this friction could interfere with the performance of the harvester.

It is also possible that in high stress situations, when the heart is under pressure and contracting at high rates, too much electrical energy could be generated that could cause the implant to be overloaded with power and stop working.

To examine these concerns and others, further testing on the harvester is required. The team have received permission for a long-term project for the harvester to be inserted into animals. The harvester’s activity would be regularly monitored, allowing the researchers to assess the functionality of the device, and see if it would be a viable long term option.

If successful in these tests, the harvester may advance to human trials. The harvester could be used with implants to keep the battery fully charged and operational or it could be used as a replacement for batteries to directly power the implant.

The end goal is that with devices such as the mechanical energy harvester, patients with battery-powered implants will never require subsequent invasive surgery for battery replacement, thus improving the patients’ quality of life to no end.