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. 2023 Oct 8;23(19):8321.
doi: 10.3390/s23198321.

Enhancing the Longevity and Functionality of Ti-Ag Dry Electrodes for Remote Biomedical Applications: A Comprehensive Study

Daniel Carvalho  1 , Sandra Marques  1 , Giorgia Siqueira  1 , Armando Ferreira  1   2 , João Santos  3 , Dulce Geraldo  3 , Cidália R Castro  4 , Ana V Machado  5 , Filipe Vaz  1   2 , Cláudia Lopes  1   2
Affiliations

Enhancing the Longevity and Functionality of Ti-Ag Dry Electrodes for Remote Biomedical Applications: A Comprehensive Study

Daniel Carvalho et al. Sensors (Basel). .

Abstract

This study aims to evaluate the lifespan of Ti-Ag dry electrodes prepared using flexible polytetrafluoroethylene (PTFE) substrates. Following previous studies, the electrodes were designed to be integrated into wearables for remote electromyography (EMG) monitoring and electrical stimulation (FES) therapy. Four types of Ti-Ag electrodes were prepared by DC magnetron sputtering, using a pure-Ti target doped with a growing number of Ag pellets. After extensive characterization of their chemical composition and (micro)structural evolution, the Ti-Ag electrodes were immersed in an artificial sweat solution (standard ISO-3160-2) at 37 °C with constant stirring. Results revealed that all the Ti-Ag electrodes maintained their integrity and functionality for 24 h. Although there was a notable increase in electrical resistivity beyond this timeframe, the acquisition and transmission of (bio)signals remained viable for electrodes with Ag/Ti ratios below 0.23. However, electrodes with higher Ag content (Ag/Ti = 0.31) became insulators after 7 days of immersion due to excessive Ag release into the sweat solution. This study concludes that higher Ag/Ti atomic ratios result in heightened corrosion processes on the electrode's surface, consequently diminishing their lifespan despite the advantages of incorporating Ag into their composition. This research highlights the critical importance of evaluating electrode longevity, especially in remote biomedical applications like smart wearables, where electrode performance over time is crucial for reliable and sustained monitoring and stimulation.

Keywords: Ti-Ag thin films; biopotential; degradation; dry electrodes; lifespan; voltammetry.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Diffractograms of the thin films studied.
Figure 2
Figure 2
Cross-sectional images (ai–aiv) and top-view images (bi–biv) of the Ti-Ag thin films produced with different Ag/Ti ratios.
Figure 3
Figure 3
Optical defects observed on the surface of an electrode with an Ag/Ti ratio of 0.31. (a) Image recorded by the optical microscope. (b) Image created by the MATLAB algorithm, marking the defects (black lines).
Figure 4
Figure 4
The percentage of surface defects on the electrodes after varying immersion durations in an artificial sweat solution.
Figure 5
Figure 5
FTIR spectra of the electrodes before and after immersion in artificial sweat solution and of PTFE.
Figure 6
Figure 6
Variation of Ti-Ag electrodes’ electrical resistivity after immersion in artificial sweat for different times.
Figure 7
Figure 7
Anodic stripping voltammograms of the different electrodes immersed in the sweat solution for 240 h, using the square-wave voltammetry technique with a deposition time of 120 s, a potential of −0.9 V, an equilibrium time of 5 s, and stirring at 300 rpm with a GCE electrode.
Figure 8
Figure 8
Concentration of Ag released into the artificial sweat solution after immersion. The values represent the average of the replicates over time.
See this image and copyright information in PMC

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