By Rideeta Raquib ‘19

Electronic implants are usually powered by batteries. Rechargeable batteries, which are rare, require continuous charging and primary batteries require implant replacements if they are completely used up. Thus, lead researcher Dr. Lukas Bereuter, and his research team at the University of Bern in Switzerland investigated whether sunlight could serve as an alternative source of energy to power medical implants.

Models of implantable pacemakers powered by solar cells have been previously proposed, but the output and the extent of light exposure have not been assessed. Bereuter and his team developed a wearable device that collects the output of solar cells. The device contained several components, such as optical filters, a maximum power point tracker (MPPT, 7), and solar cells. The optical filters were built to filter ambient light and mimic human skin. This light radiates the solar cells that are connected to the MPPT. The MPPT maximizes solar cell output, which is measured by the current. Additionally, a microcontroller is utilized to control analog-to-digital converters and store the data into a memory card.

After the device was assembled, the researchers proceeded to carry out the validation study with 32 volunteers over six months. Each participant was required to wear the device during a duration of one week per season (summer, autumn, and winter). The date when each participant had to wear the measurement tool was randomly assigned. The experiment was conducted throughout different seasons because the exposure and angle of the sun varies during the various seasons thus effecting the duration that the implant can be powered.

The mean power per month was lower during the winter as predicted by the researchers. It was found that the optical filters cut light at wavelengths lower the 550 nanometers, but the skin still permits light at that range, thus the optical filters underestimate the amount of light that passes through. The overall mean power indicated that solar cells are compilable in powering pacemakers and extend implant lifespan. Overall, there were several factors, such as climate, that impacted the overall output of solar cells employed to power implants and pacemakers. Regardless, this study validates that solar cells are a plausible alternative to rechargeable or primary batteries.

References:

1. Bereuter, et. Al, Energy harvesting by subcutaneous solar cells: a long-term study on achievable energy output. Annals of Biomedical Engineering (2017). doi: 10.1007/s10439-016-1774-4.
2. Image retrieved from: http://www.upsbatterycenter.com/blog/wp-content/uploads/2014/11/A-More-Efficient-Solar-Cell.jpg