Powering a Pacemaker from Within: a Light-Harvesting Implant May Eliminate Battery-Replacement Surgery
A pacemaker battery must be replaced every 5 to 15 years. Researchers at GIST in Korea have developed a novel photonic wireless system to power medical implants—no surgery required.
Extraordinary advances in technology have paved the way for life-saving medical devices like the pacemaker. Unfortunately, like all standalone electrical devices, the functionality of medical implants are limited by a finite battery life. Modern pacemakers need their batteries replaced roughly every 5 to 15 years, calling for complicated and sometimes risky surgeries.
Graphic of a pacemaker in the human body. Image used courtesy of Mt. Nittany Health
To address this issue, there have been a slew of researchers investigating numerous methods of energy harvesting in the body that could lead to infinite battery life for medical implants.
One well-studied method of biological energy harvesting is thermal energy harvesting. Thermoelectric generators work using the Seebeck Effect: temperature deltas between two dissimilar metals produce an electrical potential.
Working principle of Seebeck Effect driving thermoelectric generation. Image used courtesy of Science ABC
The concept here is that the fat in the human body provides good thermal insulation. Hence, the fatty areas of the body, like the abdomen, may provide ideal locations for thermoelectric harvesting.
One of the issues with this technology is that TEGs are inefficient and the temperature differentials in the body are not optimal. Based on an average 100 μW (at 1 V) power requirement of medical implants, researchers at Berkley believe that successful use of this technology would require high aspect ratio thermoelectric elements in high-density arrays.
Kinetic Energy Harvesting
Another form of biological energy harvesting is the harvesting of kinetic energy. Most forms of kinetic energy harvesting are concerned with the piezoelectric effect or its derivatives like the triboelectric effect. In this way, researchers look to convert mechanical energy in the body into electrical energy.
Energy harvester on a pig’s heart. Image used courtesy of Jyoti Madhusoodanan
This has been viewed as a promising technology since the body is rife with mechanical energy from sources including heartbeats, the movement of the diaphragm while breathing, or the vibrations of the body from activities such as walking.
The Biological Issues With Energy Harvesting
One of the main hurdles in harvesting the body’s own energy to power implants is dealing with the law of conservation of energy. Most of the energy produced internally, be it heat or a heartbeat, is meant to be used for that singular task, not to be utilized elsewhere.
For example, the body produces heat to maintain homeostasis. By taking that heat and producing electricity with it, a thermal energy-harvesting device may prevent the heat from fulfilling its original function. This in turn would cause the body to work harder to produce more heat, wasting biological energy overall.
Furthermore, both methods mentioned above require invasive surgery to implant the harvesters in the body. This is exactly what patients are looking to avoid by considering these energy harvesting devices to start with.
Photonic Energy Harvesting: A Non-Invasive Solution?
In the hopes of powering medical implants without wasting biological energy, researchers at GIST in Korea have looked to photonics.
Living tissue has the property of translucency, meaning that light can pass through it. To exploit this property, researchers have proposed an “active photonic power transfer method." The method consists of a skin-attachable micro-LED source and a photovoltaic capturer, which would be embedded on to the implants.
Graphic showing the light penetration into skin. Image used courtesy of nist.gov
Theoretically, a battery could power the light source outside of the body, and through photonics, transfer the battery’s energy to the medical implant. In this way, individuals would be able to recharge their medical implants without consuming biological energy and without the need for any invasive surgeries.
What’s to Come for Medical Implants?
Tests have already been done on mice with this technology from GIST. The results showed that the technology successfully recharged an implant and was easy to use under many environmental conditions.
This is one of the more promising technologies to be proposed for medical implant energy harvesting and looks to have a bright future. In the long term, we may see the day where medical implants won't require replacement—at least because of a low battery.