Can you imagine that solar cells just below your skin might provide enough energy to keep your cardiac pacemaker going?
Overcoming the need for batteries
Electronic medical implants like cardiac pacemakers are powered by batteries. Once they are depleted after a couple of years, they need to be replaced which involves surgery and puts the patient at risk of complications. A quarter of all implantation procedures are replacements and also invoke considerable costs for the health care system. The need for batteries and their replacement procedures might be overcome if a solar cell just below the skin could power such implants.
Sunlight is a reliable, ubiquitous energy source and can be converted into electrical energy by photovoltaic elements, i.e. solar cells. Making use of the fact that near-infrared light penetrates human skin rather well and is largely independent from skin pigmentation permits the idea of having solar cells below our skin.
In their project team, Professor Hildegard Tanner and PD Dr. Andreas Häberlin combine their knowledge in cardiology and biomedical engineering with the skill set of Prof. Thomas Niederhauser in electrical and biomedical engineering to build and validate a working prototype of a batteryless solar pacemaker. Based on theoretical calculations, a subcutaneously implanted solar cell of 1 cm2 may deliver enough energy to power a pacemaker for 24 hours if exposed to full sunlight for a few minutes per day [1]. These estimates have been confirmed in an experimental setting [2], but many challenges remain: First, a long-term validation needs to show that the pacemaker also works during intermittent periods of darkness (nighttime or winter). Second, the solar cell will ideally be miniaturized to increase patient comfort and contain some capacity for energy storage. Using the virtually unlimited energy supply of sunlight would overcome the common issue of battery replacement for active implants.
Since many physicians do not know that it is possible to build batteryless devices, there is very little demand on the industry to develop and commercialize such devices. Once a real-life device will be able to harvest solar energy, the odds are high that this technology will find its way into the medtech industry.
[1] M.V. Tholl, H.G. Akarçay, H. Tanner, T. Niederhauser, A. Zurbuchen, M. Frenz, A. Haeberlin. Subdermal solar energy harvesting – A new way to power autonomous electric implants. Applied Energy, Volume 269, 2020, 114948. DOI: 10.1016/j.apenergy.2020.114948
[2] L. Bereuter, S. Williner, F. Pianezzi, B. Bissig, S. Buecheler, J. Burger, R. Vogel, A. Zurbuchen, A. Haeberlin. Energy Harvesting by Subcutaneous Solar Cells: A Long-Term Study on Achievable Energy Output. Ann Biomed Eng. 2017;45(5):1172-1180. DOI: 10.1007/s10439-016-1774-4
