Designing biomimetic substrates and electrodes for bioelectronic devices with the necessary mechanical, electrical, and biological properties is critical considering the potential mismatch between soft tissue and rigid electronics, where incompatibility leads to decreased device performance, delamination, inflammation, and discomfort. There is an unmet engineering and clinical need for epidermal bioelectronics that are bioinert, can emulate host tissue mechanical properties, demonstrate low bulk resistivity, and are flexible and scalable. To address this shortcoming, this work describes innovations pertaining to the development of a hydrophilic, biocompatible nanocomposite comprised of carbon black (CB), polyvinyl alcohol (PVA), and glycerol for neuro-muscular and rehabilitative applications. We find that this materials platform (herein referred to as CB-AFTIDerm), comprised of 3 wt% PVA and 5 wt% glycerol, demonstrated superior biocompatibility (cytotoxic grade of 0), high flexibility (maximum of 140% stretchability and as low as 1% ∆R/R