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

## TL;DR

This paper presents a new hydrogel-based wearable sensor with improved conductivity and design for accurate motion tracking.

## Contribution

A DMSO-modified hydrogel and biaxial strain gauge design that enhances conductivity and stability for wearable motion sensors.

## Key findings

- DMSO reduced hydrogel resistivity by up to 80% at 15 wt % and improved stability at 5 wt %.
- The biaxial strain gauge outperformed the rosette design with mean errors below 6° in motion tests.
- 5 wt % DMSO samples maintained reproducibility for 21 days, while untreated samples degraded after 14 days.

## Abstract

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.