## 1 Introduction  
Over the last 60 years, implantable electronic systems and devices have undergone a significant transformation, becoming a valuable biomedical tool for monitoring, measuring and soliciting physiological responses _in vivo_ using wireless communication. The invention and subsequent advancement of these devices have relied heavily on the growing knowledge regarding various aspects of the human neuro-motor system, and the development of electronics technologies capable of interfacing with living tissues and organs at micro- and nano-scale. Increased _in vivo_ stability, miniaturization and lower energy requirement of modern electronics led to a multitude of miniature wireless electronic devices, such as sensors, intelligent gastric and cardiac pacemakers, cochlear implant, implantable cardioverter defibrillators, and deep brain, nerve, and bone simulators being implanted in patients worldwide [1; 2; 3; 4]. Figure 1 shows several examples of electronic devices for _in vivo_ applications. According to [PERSON] _et al._ over 25 million US citizens were reliant on implantable medical devices for life-critical functions [5], with the number of implantable cardioverter defibrillator implants increasing tenfold between 1990 and 2002 [6]. Advances in semiconductor technology, particular in the area of micro-electro-mechanical systems (MEMS) and microfluidic lab-on-chip biomedical systems have allowed for the development of units for rapid diagnostics, and precisely controlled pulsatile, rapid or sustained delivery of drugs and biomolecules and complex therapeutics [7; 8; 9; 10; 11]. These systems have also been used for the development of tissue engineering platforms and in regenerative medicine applications, particularly where muscular and nervous tissues are concerned [12; 13]. In addition to enhancing the survival rate and the quality of life of patients globally, implantable electronic systems have contributed significantly to our appreciation of the biological processes taking place within the human body, including the complex mechanisms of neural communication and control, and greatly enhanced our understanding of how these are affected by various diseases and treatments. _Ex vivo_, MEMS and dielectric elastomer actuators (DEAs) have been used to investigate the manner in which biological cells modulate their behavior, express genes, proliferate or differentiate in response to mechanical and electrical stimuli, knowledge which is essential for adequate tissue engineering design [14; 15; 16]. In addition to playing a profound role in the advancement of restorative medicine and biomedical sciences, implantable information and communication technologies drive notable changes in the social and cultural attitudes of people towards technology [17]. There, implantation is viewed beyond the medical context as a means to enhance the abilities and experiences of healthy individuals. In spite of substantial innovations in the fabrication and application of implantable biomedical electronic systems since the first implantable heart pacemaker of 1958, the modern implants are still faced with a number of challenges [18; 19; 20]. In terms of device production, there is a strong trend to produce devices with ever diminishing size and weight in order to make them compatible with normal human activities and enhance comfort for the host. Implants that weigh less than 2% of the patient's body weight are typically required [18]. When used, batteries, whether single-use or rechargeable, significantly contribute to the overall weight and size of the device. Single-use, non-rechargeable batteries, such as those used to support pulse generation in cardiac pacemakers and deep brain stimulators, have a predetermined lifetime, at the end of which they have to be surgically replaced, at high cost to the patient and the healthcare system.