A “PHASE” Strategy for Preparing Flexible Piezoelectric Polylactic Acid Double Network Hydrogel Sensors

Abstract Traditional piezoelectric polylactic acid (PLA) preparation relies on mechanical stretching under solid‐state conditions or electrospinning under liquid‐state conditions. However, thermal stretching requires high energy consumption, while electrospinning is inefficient and susceptible to environmental factors. Gels represent an intermediate state between solid and liquid, thermodynamically reducing energy required for polymer chain orientation while kinetically allowing sufficient time for fixed polymer chains. This work innovatively proposes the preparation of piezoelectric PLA hydrogel sensors via the “PHASE” strategy, integrating “Pre‐stretching of the organo‐Hydrogel”, “Annealing”, and “Solvent Exchanging”. Oriented structures are obtained through pre‐stretching and fixed via solvent exchange, inducing β‐phase formation. Annealing is performed to enhance crystallinity, further improving mechanical properties. In the double network hydrogel constructed from hydroxyethyl acrylate, acrylonitrile and PLA, PLA serves as a reinforcing phase for mechanical properties and a functional phase for piezoelectric response. The prepared hydrogels exhibit a tensile strength of 6.27 MPa and a fracture energy of 46.27 kJ m ⁻² . The hydrogels are fabricated into piezoelectric sensors, demonstrating excellent frequency‐domain responsiveness. Additionally, the sensors exhibit freezing resistance, maintaining flexibility and piezoelectric properties at −20 °C. The “PHASE” strategy provides an innovative approach for preparing flexible piezoelectric PLA hydrogel sensors, demonstrating potential for human‐machine interaction applications.