**1. Introduction**

The human body is an incredibly complex organism that exhibits an impressive resilience to external influences, such as infecting bacteria and inhaled particles. This, however, proves to be a difficult problem to overcome when designing and implementing implantable devices for medical therapy, as the body is supremely primed to resist any artificial intervention. One of the critical parameters to consider is the mechanical compatibility of the implanted device with the tissue of interest. Additionally, the footprint of the device should ideally be as minimal as possible to decrease tissue damage and to minimize encapsulation responses. Until recently, however, it has proven difficult to integrate naturally inflexible solid state circuits with flexible components due to connection complexities and pitch limitations. In addition, material and fabrication limitations have prevented the implementation of thin-film cables, radiofrequency coils, and neural stimulation electrode arrays in implantable devices.

Here, after a brief review of the literature, we discuss novel flexible technologies being developed for biomedical applications, and especially for high density functional neural stimulation and recording. The distinctive parameters of a unique material, namely the semicrystalline thermoplastic parylene C, that make it particularly well-suited as a biocom‐ patible substrate for thin-film biomedical circuits are discussed, explaining the reasoning for its use in a novel paradigm as a substrate and not just as a coating. In addition, we discuss a new packaging scheme that has been developed to enable high lead count interconnects using microfabrication equipment for alignment and patterning, and demonstrate a complete parylene-based stimulation microsystem combining radiofrequency coils with solid state circuits and electrodes in a parylene substrate. This integration of solid state circuits with flexible, biocompatible components gives rejuvenated hope for a new generation of neural

© 2013 Rodger et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Rodger et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

prosthetics aimed to provide eyesight to the blind and limb movement to para- and quadri‐ plegic patients through spinal cord stimulation. These technologies can also enable integration of solid state devices with novel bioMEMS sensors in such a manner that devices previously only conceived of are now possible.
