(J-385) Surface EMG and Stretchable Bio-electronics

Electromyography (EMG) is a crucial technique for assessing muscle function and diagnosing neuromuscular disorders. Traditional EMG approaches involve invasive, rigid microneedle electrodes or surface EMG with inflexible electrodes that struggle to adapt well to the skin's surface. In this study, we present a groundbreaking, large-area, high-density surface EMG (HD-sEMG) electrode array created from intrinsically stretchable materials, which overcomes the limitations of conventional methods. Our pioneering device features a conductive composite, dubbed "Solution WG," substantially enhancing conformability, user-friendliness, comfort, and adaptability to a variety of skin morphologies. The development of this stretchable HD-sEMG electrode array was fueled by the need for improved EMG techniques that can accommodate diverse skin topographies and age groups, making biomedical technologies more inclusive and accessible. 

The materials used in the fabrication of the sEMG array biosensor included an aqueous dispersion of PEDOT: PSS, a waterborne polyurethane (WPU) dispersion, 1-Ethyl-3-methylimidazolium coordinated with ethyl sulfate (EMIM:ES), glycerol, ammonia hydroxide solution, and Tegaderm™. 

To prepare the composite material, the ionic liquid (EMIM:ES) was diluted with deionized water and added dropwise to the PEDOT: PSS dispersion. After stirring for 12 hours, a 0.15 wt% ammonia solution was added, followed by the WPU dispersion. The mixture was then stirred for over 2 hours, and glycerol was added to obtain "Solution WG."

After preparing Solution WG, it was drop-casted onto a glass slide and left to dry overnight. The electrode array pattern was then laser-cut onto the glass slide with the dried Solution WG. The resulting array was transferred onto a Tegaderm™ substrate using transfer printing. The electrodes were improved for conductivity and adhesion through plasma etching, and the device was encapsulated with a second layer of Tegaderm™ that was laser-patterned to expose the electrode pads for skin contact. 

To fabricate Solution WGP arrays, a gel-like solution of PEDOT: PSS and glycerol in a 1:1 ratio was drop-casted onto the exposed electrode areas to improve the contact interface with the skin's topographical features. Finally, the encapsulated EMG array was thermally annealed on a hot plate at 60℃ for 15 minutes before being applied to the skin.

Our HD-sEMG electrode array demonstrated a significant improvement over traditional rigid electronics in terms of electrode impedance, signal-to-noise ratio, and EMG signal amplitude across all tested skin morphologies. Moreover, this versatile technology not only enables the generation of sEMG maps over extensive body areas but also facilitates controlling robotic prosthetics and interacting with 3D arm models in virtual reality environments. Our findings represent a major advancement in EMG research and applications, addressing current limitations and offering substantial benefits for both clinical and research purposes. The stretchable HD-sEMG electrode array has the potential to transform the field by enabling noninvasive muscle activity measurements across diverse populations, thereby fostering greater inclusivity and accessibility in the development of advanced human-machine interfaces.

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