Ultrathin Temporary Tattoo Electrodes Enable Prolonged Skin-Conformable EMG Sensing for Hip Exoskeleton Control.

Area of Science:

• Biomedical Engineering
• Wearable Technology
• Robotics

Background:

• Conventional gel electrodes for surface electromyography (sEMG) are bulky and have limited gel lifetime, hindering integration with wearable robots.
• There is a need for comfortable, long-lasting electrodes for seamless integration with wearable robotic systems.

Purpose of the Study:

• To compare the signal quality of ultrathin, skin-conformal temporary tattoo electrodes with traditional gel electrodes for sEMG.
• To evaluate the day-long usability and signal stability of tattoo electrodes integrated with a hip exoskeleton.
• To assess the potential of tattoo electrodes for real-time control of wearable robots.

Main Methods:

• Five healthy participants walked on a treadmill using a powered hip exoskeleton equipped with either gel or tattoo electrodes.
• sEMG signals were recorded from tibialis anterior, gastrocnemius medialis, rectus femoris, and biceps femoris muscles.
• Signal quality was assessed by comparing normalized sEMG envelopes to biological activation profiles using root mean square error (RMSE) and Pearson's correlation coefficient (ρ).
• Tattoo electrode signal quality was re-evaluated after eight hours of continuous wear to assess long-term stability.

Main Results:

• Tattoo electrodes demonstrated signal quality comparable to gel electrodes across all tested muscles, with no significant differences in RMSE or ρ.
• No significant degradation in signal quality was observed for tattoo electrodes after eight hours of wear.
• Tattoo electrodes reliably drove hip-extension assistance in real-time, demonstrating their potential for closed-loop control.

Conclusions:

• Ultrathin, skin-conformal temporary tattoo electrodes are a viable alternative to conventional gel electrodes for sEMG in wearable robotics.
• Tattoo electrodes offer comparable signal fidelity, improved comfort, and day-long usability, facilitating seamless integration with wearable robots.
• These findings support the use of tattoo electrodes for advanced EMG-based control in wearable robotic applications.