The idea of using solar cells placed under the skin to recharge implanted electronic medical devices continuously is viable. Swiss researchers have done the calculations and found that a solar cell with a surface area of only 3.6 square centimeters is all that is required to produce enough power to power a typical pacemaker during winter and summer.

This is the first study that provides real life data on the potential of using solar cells to power devices such as deep brain stimulators and pacemakers. Lead author Lukas Bereuter of Bern University Hospital and the University of Bern in Switzerland, believes that wearing power-generating solar cells under the skin will one day eliminate the discomfort of having to endure procedures to change the batteries of such life saving devices continuously.

Currently, most electronic implants are battery powered and their size is determined by the battery capacity required for an extended lifespan. The batteries must either be changed or recharged when the power in them runs out. This means that patients have to undergo implant replacement procedures in most cases. Not only is this stressful and costly, but there is also the risk of medical complications. The size of a device is also determined by it having to use primary batteries.

Recently, various research groups have presented prototypes of small electronic solar cells that can be used to recharge medical devices and is carried under the skin. The light from the sun that penetrates the skin surface is converted into energy by these solar cells.

Bereuter and his colleagues developed specially designed solar measurement devices to determine the real life feasibility of such rechargeable energy generators. These devices are able to measure the output power being generated. The cells were small enough to be implanted if required, having a surface are of only 3.6 square centimeters. To test ten devices, each was covered by optical filters to simulate properties of the skin. It was then determined how these properties influence how well the sun penetrates the skin. Thirty-two volunteers in Switzerland wore the filtered devices on their arms for one week each during summer, autumn and winter.

It was found that the tiny cells always generated much more power than the 5 to 10 microwatts that a typical cardiac pacemaker uses, irrespective of the season. Twelve microwatts was generated on average by the participant with the lowest power output.

Bereuter explained that a pacemaker could be completely powered, or the lifespan of any other active implant could be extended by the overall mean power obtained. He added that device size may be reduced dramatically and device replacements may be avoided if energy-harvesting devices such as solar cells were to be used to power an implant.

Bereuter also believes that the results of this study can be applied to any other solar powered, mobile application on humans, if it is scaled up. Before this can be done however, aspects such as the efficiency and catchment area of a solar cell and the thickness of a patient’s skin needs to be considered.

The full study was published in the journal Annals of Biomedical Engineering.

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