Batteries for wearable and implantable biomedical devices: a comprehensive review

Wearable and implantable medical devices have been strongly contributing to the progress of the health care system through the continuous monitoring and treatment of the patient. These devices can facilitate the detection of symptoms, diagnosis of illnesses and remote monitoring of the patient, becoming a key factor in the development of an innovative type of health care, the so called “telemedicine”. This medical equipment must guarantee high safety, excellent biocompatibility and biodegradability to avoid undesired accidents (i.e. release of toxic substances, fires, explosions) that can severely hurt the patient, so a careful choice of materials is necessary to minimize this risk. Most of these devices require a power source that should satisfy the same requirements of safety, biocompatibility and biodegradability but also provide sufficient power for a long period of time. In this context, batteries are the most common power sources for biomedical devices and the development of more efficient electrochemical cells has contributed to the production of more advanced medical devices with innovative features. This review discusses the most important batteries employed in wearable and implantable biomedical devices starting from the early technologies, such as nickel-cadmium and zinc-mercury batteries, to the widespread lithium batteries currently employed in modern medical equipment. Moreover, the paper also provides a focus on the new post-lithium batteries under development with superior electrochemical performance and higher safety and sustainability with respect to lithium ones, which could become the future power sources for a new generation of smart medical devices.