Wearable and self-healable textile-based strain sensors to monitor human muscular activities

In this study, a textile-based wearable strain sensor is fabricated to monitor human muscular activities with high sensitivity and large working range. To achieve electrical conductivity, a gum-like sticky polyvinyl acetate-co-vinyl laurate polymer (commercial name: VINNAPASS) is mixed with 50 wt % of carbon nanofiber (CNFs) using ethyl acetate as co-solvent. The VINNAPASS/CNFs-based ink is spray coated onto a stretchable polyethylene terephthalate fabric (commercial name: Lycra) and subsequently covered and stabilized with polydimethylsiloxane protective layer. Another reference sensor is also prepared using thermoplastic polyurethane (TPU) with equal concentration of CNFs. The strain sensor made with VINNAPASS demonstrated sheet resistance, maximum elongation at break, gauge factor (GF) and working range of 32.27 +/- 1.60 Omega/square, 230 +/- 6%, 67.12, >170% as compared to 48.44 +/- 2.33 Omega/square, 122 +/- 7%, 39.97 and similar to 100% for the sensor made with TPU, respectively. Moreover, the VINAPASS-based strain sensor displayed complete self-healing and >90% reversible electrical properties on damage, while the TPU-based sensor was not healable. Finally, the VINNAPASS-based sensor is used to monitor folding-unfolding of human finger and wrist as well as bicep muscle contraction and relaxation, and is envisioned for monitoring human muscular motions during physical activities and exercising.