Electrical signal coupled with mechanochromic feedback: Stretchable dual-mode piezoelectric sensor for cross-validated biomechanical monitoring

The rapid development of flexible electronics offers new opportunities for wearable sensors, among which piezoelectric materials are attractive due to their ability to generate electrical signals without external power. However, traditional piezoelectric sensors face challenges, including single-mode signals, low sensitivity under dynamic strain, and mechanical mismatch with soft tissues. Herein, we address these limitations through the primary innovation of a stretchable dual-mode sensor that uniquely integrates a high-performance piezoelectric composite of polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE) and gallium‑indium eutectic liquid metal (EGaIn) with a mechanochromic visualization layer. Through the combined action of electrospinning, annealing, and liquid metal addition, the β -phase crystallization increased significantly from 36.4 % to 80.0 %, improving the piezoelectric performance. By integrating a mechanochromic liquid crystal elastomer layer, the sensor provides dual-mode feedback: electrical signals serve as data for quantitative analysis, while the corresponding color changes offer intuitive, real-time visual feedback. The latter can also be quantified via its G/B ratio, thereby enabling robust complementarity and cross-validation. The sensor's excellent performance makes it an ideal choice for applications such as voice recognition, gait analysis, and joint rehabilitation monitoring. This work establishes a platform for developing intelligent systems that combine machine-readable precision with human-interpretable feedback, catering to advanced medical and wearable devices.