From Free-Standing to Textile Electrodes: Carbonaceous Biocompatible Material for Wearable Sensing.

Wearable electronics have been on the rise for personal monitoring in healthcare and sports, allowing real-time tracking. However, developing flexible, conductive, biocompatible, and suitable for continuous, long-term use (bio)electrodes remains a challenge. In this sense, carbon materials offer a promising solution due to their excellent electrical conductivity, mechanical strength, and natural biocompatibility. Moreover, they are cost-effective, modifiable, and align well with environmentally friendly practices. This work presents a simple and sustainable fabrication method for custom-formulated carbon black-chitosan (CB-CH) ink, enhanced with multi-walled carbon nanotubes (MWCNTs). The formulation avoids toxic chemicals, high energy input, and lengthy processing, supporting a greener approach. The resulting ink enables the fabrication of free-standing and textile-based electrodes with high conductivity, mechanical durability, and application-dependent biocompatibility, supporting extended use for CB-CH and short- to medium-term wearable applications (≤24 h) when MWCNTs are incorporated. Their performance was validated through real-time monitoring of electrophysiological signals such as electrocardiograms and electromyograms, showing signal quality comparable to conventional silver electrodes while overcoming gel dehydration and skin irritation. Overall, this work offers a scalable, cost-effective, and eco-friendly pathway for producing multifunctional electrodes, paving the way for next-generation wearable sensing platforms in clinical diagnostics, rehabilitation therapies, and athletic performance monitoring.