In Situ Growth of MXene (Ti3C2TX) Self-reducing Platinum Particles on Carbon Nanotube Yarns for Skin-Fitting Flexible Strain Sensors

The rapid development of smart wearable technology has driven innovation in the field of flexible strain sensors. Carbon nanotube (CNT) fibers have emerged as promising candidates for the fabrication of flexible strain sensors due to their exceptional flexibility, remarkably high specific surface area, outstanding mechanical properties, and excellent electrical conductivity. However, interstitial voids between CNT bundles constitute structural defects that impair both load-bearing capacity and electron transport efficiency. This limitation can be effectively mitigated by incorporating metal nanoparticles, which not only fill these voids but also enhance composite performance through their intrinsic low electrical resistance and exceptional chemical inertness. In this study, MXene was utilized as a reducing agent to directly reduce platinum particles from chloroplatinic acid and autonomously grow into the voids of carbon nanotube yarns without the need for additional reducing agents. This modification strategy resulted in substantial enhancements in both mechanical and electrical properties: The tensile strength of platinum-modified CNT yarns increased from 121.2 to 137.27 MPa (13.3% increase), while electrical conductivity demonstrated an 85.3% improvement from 6.18×10 4 S/m to 11.45×10 4 S/m. The prepared flexible and stretchable strain sensors exhibit a resistive change of 380%, a tensile strain range of 0–30%, a GF sensitivity of 23.8, a fast response time of 0.6 s, a recovery time of 0.8 s, and dynamic sensing stability under varying conditions. Significantly, the sensor enables multi-channel synchronous monitoring of biomechanical signals at major human joints, establishing a new design framework for CNT yarn-based elastic strain sensors.