Abstract
This PhD thesis addresses the design, fabrication, characterization, and validation of a prototype for non invasive assessment of blood volume changes in arteries and veins, aimed at peripheral arterial disease monitoring. The research focuses on the electrical and electromechanical performance of reusable printed electrodes based on silver (Ag) and Ag coated with multilayer PEDOT:PSS for impedance plethysmography (IPG), benchmarked against conventional solid gel electrodes. Overall, the results support the feasibility of reusable PEDOT:PSS based dry electrodes as a practical alternative to solid gel electrodes for distal IPG monitoring, particularly in wearable and long term applications where reusability, comfort, and system integration are prioritized over maximal signal to noise performance. The first part of this research work, summarized in Chapter 3, focuses on the fabrication of dry electrodes using screen printing techniques on thermoplastic polyurethane (TPU) substrates, combining silver based conductive inks with multilayer PEDOT:PSS coatings to enhance electrical performance and mechanical compliance. A tetrapolar electrode configuration with a dedicated encapsulation region was implemented to physically separate the active sensing area from the interconnection zone. The fabrication process was optimized through controlled printing, curing, and encapsulation steps to ensure surface uniformity, mechanical robustness, and compatibility with textile integration. The second part of this research, summarized in Chapter 4, addresses the morphological characterization of the dry electrodes. Surface topography was investigated using confocal laser microscopy, combining line roughness and areal surface roughness analyses to capture both local directional features and global surface characteristics. The results demonstrate a progressive evolution of surface morphology as a function of the number of PEDOT:PSS layers. Both line and areal analyses revealed an initial amplification of roughness features after the first polymer deposition, followed by a gradual reduction in average roughness amplitudes and spatial variability as the layer number increased. Quantitatively, the system with three PEDOT:PSS layers exhibited the lowest average roughness values. These findings indicate that multilayer PEDOT:PSS deposition promotes a more homo geneous and controlled surface topography while preserving sufficient surface complexity for functional interfacial performance, highlighting the Ag + 3L PEDOT:PSS configuration as the most favorable morphological compromise. In Section 4.2, electromechanical testing revealed that pristine Ag electrodes exhibited minimal resistance variation under single elongation events but developed pronounced resistance drift and hysteresis under cyclic loading, indicating progressive degradation of the conductive network. In contrast, Ag/PEDOT:PSS hybrid electrodes demonstrated improved stability under repeated deformation, with the electromechanical response strongly dependent on the number of polymer layers. Among the tested configurations, the Ag electrode with three PEDOT:PSS layers maintained normalized resistance variations within ±1 over 100 cycles at elongations up to 4.5%, exhibiting reduced hysteresis and enhanced recovery after unloading. In Subsection 4.4.3, impedance plethysmography signals were analyzed in 10 healthy subjects using both Bluesensor standard electrodes and Ag+3L PEDOT:PSS, evaluated over two temporal windows (5–10 min and 15–20 min). For each subject electrode window combination, temporal and morphological pulse metrics were extracted, including Peak Amplitude (PA) and ECG/IPG delay (PT). Analyses were performed at the subject level by averaging both windows to avoid pseudo replication. Ag+3L PEDOT:PSS yielded systematically higher and more dispersed PT values compared to Bluesensor standard electrodes (dry: 207.00 ± 14.93 ms; wet: 187.13 ± 9.07 ms). Finally, in Subsection 4.4.3.3, the quality of the electrode was quantitatively evaluated using the high frequency signal to noise ratio, SNRHF, in two cohorts: a healthy group (10 subjects) and a non healthy group (5 subjects), considering both Bluesensor standard and Ag+3L PEDOT:PSS. In the healthy cohort, Bluesensor standard electrodes consistently achieved higher mean SNRHF values and lower variability than Ag+3L PEDOT:PSS (lower average SNRHF), indicating supe rior signal quality and greater intersubject stability. These differences were further accentuated in the non healthy cohort, where Bluesensor standard electrodes maintained moderate SNRHF levels with relatively controlled variability, whereas Ag+3L PEDOT:PSS were strongly affected by intersubject differences and, in some cases, presented very low or negative SNRHF values.