Multi-functional 3D printed hydrogel electrodes for brain-computer interfaces and wearable sensing

In this study, a 3D printing-based polyvinyl alcohol (PVA)/κ-carrageenan (κ-CA)/ carbon nanotubes (CNTs) hydrogel composite (referred to as PCC) was developed for the fabrication of flexible electrodes, targeting applications in brain-computer interfaces (BCIs) and wearable strain sensors. The hydrogel composite exhibited excellent mechanical properties, including a tensile strength of 633 kPa, an elastic modulus of 243 kPa, and a maximum tensile strain of 283 %. In BCI tests, the PCC hydrogel electrode achieved a scalp contact impedance of 76.08 kΩ across five channels, with signal quality comparable to wet electrodes (3.06 μV at 13 Hz stimulation) and significantly higher than dry electrodes (2.16 μV). The decoding accuracy for the PCC hydrogel electrode was 78.2 % with a 1.25 s window length, comparable to the wet electrode, and the information transfer rate (ITR) reached 71.3 bits/min. Furthermore, the hydrogel demonstrated excellent strain sensing performance, with a gauge factor (GF) of 2.7 in the 0-75 % strain range and fast self-recovery, making it a promising material for dynamic wearable sensing devices. This work highlights the successful integration of material optimization and structural design, offering a new approach for development of next-generation flexible bioelectronic devices.