Dry Electrodes for Surface Electromyography Based on Architectured Titanium Thin Films

Abstract

Electrodes of silver/silver chloride (Ag/AgCl) are dominant in clinical settings for surface electromyography (sEMG) recordings. These electrodes need a conductive electrolyte gel to ensure proper performance, which dries during long-term measurements inhibiting the immediate electrode’s reuse and is often linked to skin irritation episodes. To overcome these drawbacks, a new type of dry electrodes based on architectured titanium (Ti) thin films were proposed in this work. The architectured microstructures were zigzags, obtained with different sputtering incidence angles (α), which have been shown to directly influence the films’ porosity and electrical conductivity. The electrodes were prepared using thermoplastic polyurethane (TPU) and stainless-steel (SS) substrates, and their performance was tested in male volunteers (athletes) by recording electromyography (EMG) signals, preceded by electrode-skin impedance measurements. In general, the results showed that both SS and TPU dry electrodes can be used for sEMG recordings. While SS electrodes almost match the signal quality parameters of reference electrodes of Ag/AgCl, the performance of electrodes based on TPU functionalized with a Ti thin film still requires further improvements. Noteworthy was the clear increase of the signal to noise ratios when the thin films’ microstructure evolved from normal growth towards zigzag microstructures, meaning that further tailoring of the thin film microstructure is a possible route to achieve optimized performances. Finally, the developed dry electrodes are reusable and allow for multiple EMG recordings without being replaced.

EMG Characterization and Processing in Production Engineering

“…Both types of electrodes can achieve equivalent signal quality [ 13 ], which makes dry electrodes more suitable for industrial applications. Novel types of dry electrodes based on architecture titanium thin films [ 14 ] or flexible hydrographic printed dry electrodes [ 15 ], that may be attached to the body similar to a tattoo, offer an alternative to conventional wet Ag/AgCl electrodes with improved biocompatibility, usability, and long-term wearability. Recently, conductive hydrogels electrodes have been developed to capture biosignals, such as EMG or ECG (ElectroCardoGram), accurately [ 16 ].…”

Me-Doped Ti–Me Intermetallic Thin Films Used for Dry Biopotential Electrodes: A Comparative Case Study

“…Moreover, the use of soft, flexible substrate materials fosters the adaptivity of the electrode to the body shape, increasing the long-term wearing comfort and improving the electrode-skin contact, especially during body motion [3,[12][13][14]. Dry electrodes are thus user-friendly solutions offering improved applicability without the need for hydrogels or other types of wet electrolytes [3,[12][13][14][15][16][17].…”

“…Production cost, complexity, and reproducibility as well as constraints in electrode shape, mechanical characteristics, and durability have limited these materials to prototypes thus far. Coated elastomers have been suggested primarily with Ag [24], Ag/AgCl [11,13,16,25], gold (Au) [26], and titanium (Ti) [17,27,28]. While silverbased coatings are known to provide excellent electrochemical and thus bioelectric signal characteristics, their biocompatibility in long-term repetitive applications remains an often discussed and questioned limitation [29].…”

“…The use of biocompatible thin films enables the activation and functionalization of non-conductive surfaces. When deposited on mechanically flexible polymers, the thin film provides highly conductive pathways for biosignals without compromising the polymer's elastic modulus, while improving the surface mechanical resistance [17,32]. However, a systematic comparison of Ti-based thin film compositions used for bioelectric signal acquisition is missing to date, since existing literature focuses on individual metal combinations only and lacks assessment of cross-system differences.…”

EMG Measurement with Textile-Based Electrodes in Different Electrode Sizes and Clothing Pressures for Smart Clothing Design Optimization

“…At the same time, the rapid development of textile electrodes is producing sensor-embedded clothing that is like conventional clothing without deteriorating the wearer’s comfort [ 14 , 15 ]. In the current study, electrodes made of both carbon and silver layers were assessed in considering that they satisfy several requirements that Rodrigues et al indicated in their study on titanium thin film-based electrodes: high corrosion, wear resistance, good mechanical ductility, chemical and thermal stability, and with high bio-compatibility [ 16 ]. In addition, a conductive sheet can be deposited over fabric with a heat press in a single step and electrodes and interconnector (electrical wire) can be produced at once.…”