Conductivity Enhancement and Strain Gauge Optimization for Accurate and Stable Flexible Wearable Motion Sensors

Flexible wearable sensors are widely used in health monitoring and sports training, but their accuracy and stability are often limited by poor conductivity and unsuitable strain gauge design. Conductive hydrogels offer softness and biocompatibility, yet PEDOT:PSS-based systems typically suffer from unstable signals and limited long-term reliability. Enhancing conductivity and aligning the strain gauge orientation with muscle motion are crucial to improving performance. This study developed a dual-network poly-(vinyl alcohol) (PVA)/poly-(acrylic acid) (PAA) hydrogel containing dimethyl sulfoxide (DMSO)-modified poly-(3,4-ethylenedioxythiophene):poly-(styrenesulfonate) (PEDOT:PSS) for wearable motion sensing. DMSO was introduced as a secondary dopant, and FTIR, resistivity measurements, and DMA evaluated its effect. Two sensor designs, a biaxial strain gauge and a strain rosette, were fabricated using laser cutting and casting, and applied to shoulder joint monitoring during bench press and shoulder press training. Long-term stability was assessed using dynamic error control charts over 21 days. The results showed that DMSO reduced resistivity by up to 80% at 15 wt % and improved stability at 5 wt %. Motion tests confirmed that the biaxial gauge outperformed the rosette in multiplane monitoring with mean errors below 6°. Stability analysis further revealed that 5 wt % DMSO samples maintained reproducibility for 21 days, while untreated samples degraded after 14 days. These findings confirm that DMSO-enhanced hydrogels and biaxial strain gauge design provide accurate, stable, and practical wearable sensors.