Challenges limiting powering and communication of implantable medical devices

Abstract

Cardiovascular disease (CVD) is the leading cause of death worldwide. Among various CVDs, the death rate from coronary heart disease (CHD) is remarkably high, which was responsible for 9.43 million death in the UK in 2016. CHD develops as a consequence of coronary artery disease (CAD), caused by atherosclerosis. Atherosclerosis is an inflammatory disease that is characterised by the formation of atherosclerotic lesions in the arterial wall. Coronary revascularisation is the optimal treatment to restore blood flow to affected areas via a semi-invasive procedure called percutaneous coronary intervention (PCI). To overcome the impact caused by CVD and improve the quality of life of patients an innovative smart stent is being developed by Dr. Mercer’s research group. Their goal is both aid the diagnose and is hoped will provide treatment for diseases such as atherosclerosis and in-stent restenosis. Powering this smart stent is one the major challenges, thus various implantable wireless devices have been critically evaluated here with the goal of appraising the best approach to power an implanted stent. Furthermore, integrating an antenna into the smart stent for the purpose of powering and data transmitting is also a significant challenge. Hence, different wireless power transfer techniques based on electromagnetic (EM), ultrasound, and solar, are investigated in section (3). Each approach has their own advantages and disadvantages which limit the powering choice to be used for implantable devices. For example, the near-field based on EM induction method requires two coils that sit in close proximity, which makes it unsuitable to power deep-tissue implantable devices. The far field EM requires an antenna to link implantable device to magnetic sources and possibility of antenna deformation causes variation in resonant frequency making this approach impractical for CVD micro-implants. Solar based wireless power transfer approach is also analysed for implantable devices. This approach is constrained due to the lack of light source penetrating the body tissues. Hence, solar powering cannot be used for direct cardiovascular devices. Power transfer using ultrasound waves was also investigated but it also loses its signal strength as it travels deeper into the body, hence, it delivers low power and loses data accuracy quickly. Recently, a new technique based on mid-field EM is developed by Stanford university to power deep-tissue micro-implants wirelessly. This technique combines the near and far-field methodologies to enable specific signal frequency selection which makes it feasible for deep-tissue implantation. After analysing/investigating all the techniques in the literature, it is concluded that mid-field powering technique is the optimal approach so far. Hence, it can be used to power implantable medical devices implanted deep in tissue wirelessly providing a safe exposure to EM radiations/waves much below the threshold of human safety.