A typical pacemaker could be powered by solar cells as small as 3.6 square centimeters, which could be implanted under the skin, thereby avoiding the need for periodic battery replacements.
Medical implants such as pacemakers can greatly extend a patient's life, but they also require periodic surgeries to replace the battery. However, new research by a team in Switzerland has found that not only could these battery replacements be avoided by using small solar cells implanted under the patient's skin, but that the solar cells could also generate plenty of electricity for the medical implants even in the middle of winter.
Although powering medical implants with solar cells has been proposed by various research groups, and prototypes have been built, the question of whether or not enough electricity could actually be generated year-round by subcutaneous solar cells has remained unanswered. But the findings of the Swiss research team, recently published in the journal Annals of Biomedical Engineering, suggest that it is indeed possible to power pacemakers and other low-power medical implants with solar energy, and could be done with cells measuring as small as 3.6 square centimeters.
"Electronic implants are usually battery powered, rarely with a rechargeable battery—which requires repeated recharging—or with a primary battery, which requires an implant replacement when the battery is depleted. In fact, implant replacements due to battery depletion are common and account for approximately 25% of implantations of cardiac pacemakers, which represent the majority of electronic implants. These re-interventions cause costs and expose the patient to a risk of complications. Moreover, it may be a stressful intervention for the patient. Finally, the size of an electronic implant is mainly governed by the battery volume, i.e. it could be designed smaller if not equipped with primary batteries." - Energy Harvesting by Subcutaneous Solar Cells: A Long-Term Study on Achievable Energy Output
The team built wearable solar measurement devices that would allow them to continuously monitor the output of the solar cells as they were worn by volunteers over a six month period, throughout the summer, autumn and winter. To mimic the effect on the solar output of being covered by the patient's skin, the solar cells on the devices were also covered, but with optical filters that would simulate that coverage, which gave researchers the "first real-life validation data of energy harvesting by subcutaneous solar cells."
According to the research results, the small monocrystalline solar cells (22% efficiency) used in the study were able to generate "much more" than the typical 5 to 10 microwatts that typical cardiac pacemakers use, as even the lowest power output measured by the devices was an average of 12 microwatts.
As solar cells only generate electricity when exposed to sunlight, a battery (or "accumulator" as the research paper calls it) would still be required for round-the-clock operation of a medical implant, but because regular charging would happen via ambient sunlight, the battery for a solar-powered pacemaker could be much smaller than current options, which also means that the pacemaker itself could be much smaller in size.
"The overall mean power obtained is enough to completely power for example a pacemaker or at least extend the lifespan of any other active implant. By using energy-harvesting devices such as solar cells to power an implant, device replacements may be avoided and the device size may be reduced dramatically." - Lukas Bereuter, lead author of the study
The team concluded its research paper by stating that "with a few assumptions," the results of the study "can be scaled and applied to any other mobile, solar powered application on humans."
The full study can be accessed at the Annals of Biomedical Engineering.