Multimodal wearable sensor based on PVA/CNT composite film with water-induced self-healing for strain, temperature and humidity sensing

A multimodal wearable sensor based on polyvinyl alcohol/citric acid/glycerin/carbon nanotube (PVA/CI/GL/CNT) composite films was developed in this study. Curing at 70 °C and composition optimization (CI: 2 wt% and GL: 10 wt%) produced films with 330% elongation and a wear rate of 1.79 × 10 -8 mm 3 /N·mm. X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) analyses confirmed that ester crosslinking between CI and PVA disrupted the crystalline ordering, improved the thermal stability, and supported the high flexibility of the composites. The sensor detected strain (1–100%, response time: 120 ms), temperature (15–70 °C, sensitivity: ∼0.016 per °C), and humidity (20–90%) on a single platform. The strain and temperature responses operated through distinct mechanisms, namely the geometric separation of CNT contact points and the thermal activation of charge carriers, with limited cross-sensitivity. Peel-off tests confirmed substrate-dependent adhesion, with latex peel strength (0.19 N/cm) within the clinically preferred range for painless skin removal. Cytotoxicity evaluation confirmed cell viability above 90% at concentrations up to 500 ppm. The asymmetric surface structure enabled stable skin attachment without the use of additional adhesives. The joint motion detection, respiration monitoring, and touch detection were verified. Water-induced self-healing restored the sensing and mechanical functions after five cutting-healing cycles (retention >99.6%) through PVA chain re-dissolution and reconstruction of the CNT percolation networks.