Soft Power: Stretchable and Ultra-Flexible Energy Sources for Wearable and Implantable Devices

Abstract

The development of ultra-compliant power sources is prerequisite to the realization of imperceptible biomedical systems destined to be worn or implanted in the human body. This chapter assesses the viability of conformal piezo and triboelectric, thermoelectric, and photovoltaic technologies as power sources for biomedical applications. It begins by identifying the amount of energy available to each of these modes of power conversion and then gives a brief overview on the methods of fabricating stretchable electronic devices using deterministic structures, random composites, or molecularly stretchable electronic materials. It then provides a detailed description of innovations in “soft power,” where the mentioned design techniques have been employed to develop mechanically compliant power scavengers amenable to integration with stretchable medical devices. The chapter concludes with an analysis of system level power requirements and application specific compatibility, the result of which identifies piezoelectrics and triboelectrics as well suited for intermittent and implantable devices, such as low-power pacemakers for piezoelectrics or higher power wearables and neural stimulators for triboelectrics. Thermoelectrics are highly compatible with epidermal and wearable applications, and can be used as a consistent source of power for tattoo chemical or heat sensors, and photovoltaics can generate large amounts of power in full sun, for high power applications like cochlear implants, or less energy in diffuse or ambient light, for powering hearing aids.