The Beat Goes On

With the proliferation of portable and wearable electronics, we are finding ourselves with more and more devices to recharge, seemingly by the day. Keeping track of all the chargers, and remembering when to plug in each device is a pain, not to mention the fact that these gadgets are more or less out of service while recharging. For reasons such as these, developers and researchers have increasingly turned their attention to energy harvesting techniques, which offer the promise of capturing otherwise wasted mechanical energy and turning it into electrical energy that can keep our electronics powered up without the inconvenience and downtime associated with traditional charging methods.

Keeping tabs of our smartphones, smartwatches, tablets, and everything else that we rely on daily fully charged is a hassle, but that is nothing compared to implantable electronic devices. Consider the leadless pacemaker, for example. While leadless pacemakers can be implanted in the heart in a relatively noninvasive manner by threading it up through a vein in the leg, their batteries do not last forever — typical battery life is about 6 to 15 years. When the battery starts to run down, there is no way to recharge it, and aside from a highly-invasive and risky surgery, there is no way to remove the battery or replace the device.

As such, surgeons typically simply implant a new pacemaker alongside the existing one to take over the job. However, this is impractical when an individual needs several new devices throughout the course of their life. A better solution may be on the horizon, however. Researchers at the University of Washington have come up with a very clever plan to harvest energy from heartbeats to keep the pacemaker’s battery charged. Preliminary studies have shown that this method has the potential to extend the battery life of leadless pacemakers.

To harvest energy, biocompatible piezoelectric materials were embedded within the housing of a leadless pacemaker. Pressure fluctuations in the right ventricle, where the pacemaker is installed, create motion within the piezoelectric materials, which in turn produces electricity. This electricity is used to recharge the pacemaker’s battery and extend its useful lifespan. The entire device is similar in size to existing commercial leadless pacemakers — about a third of the size of one AAA battery.

The prototype was placed in a pulsatile cardiac pressure simulator where it was subjected to right ventricular systolic and diastolic pressures at a rate of one heartbeat per second. With pressures alternating between 0 and 40 mmHg, the energy harvester was found to be capable of generating almost 11% of the energy needed to power the pacemaker through the next beat.

While these results are very encouraging, the efficiency of the energy harvesting system will need to be improved for real-world use, which is something the researchers are presently working on. That energy will be needed for more than just stimulating heartbeats — a real pacemaker also expends energy in monitoring the heart, which was not accounted for in this study. Much work also stands ahead of the team in confirming that the device works safely and reliably in humans, as well, so it will be some time yet before this technology could potentially find its way into real medical devices.