Dry-printed electrodes for transcutaneous electrical stimulation of innervated muscles: Towards wearable and closed-loop stimulation.

BACKGROUND

While transcutaneous electrical stimulation is an established clinical technique, applied in clinical settings, the need for precise electrode placement, limited long-term stability, and user inconvenience hinders widespread adoption in wearable and home-based applications. To address these issues, soft screen-printed electrode arrays, previously validated for biopotential recording and bioimpedance applications, were evaluated in two new contexts: (1) Systematic comparison against gel electrodes for stimulation in the neck region, and (2) Real-time closed-loop facial stimulation in healthy subjects.

METHODS

Contact impedance was measured and modeled for both printed (dry) and conventional gel electrodes. Accessory nerve stimulation efficacy was evaluated in 12 healthy subjects using surface electromyography and mechanical movement recorded with an inertial measurement unit.

RESULTS

Despite higher contact impedance, dry electrodes achieved comparable activation thresholds and perceived discomfort to gel electrodes. Finite element modeling confirmed a similar electric field distribution for both electrodes. In addition to validating their effectiveness for transcutaneous stimulation of innervated muscles, we demonstrated the feasibility of closed-loop facial recording and stimulation using dry electrodes in one subject as proof-of-concept.

CONCLUSIONS

Our results pave the way for wearable neuromodulation systems for clinical and home use, particularly in restoring facial symmetry for individuals with neuromuscular impairments. Broader validation with larger sample sizes and testing in patients with denervated muscles will be necessary for clinical translation.