Hierarchical Crack Engineering-Enabled High-Linearity and Ultrasensitive Strain Sensors

Growing imperative for intelligent transformation of electro-ionic actuators in soft robotics has necessitated self-perception for accurately mapping their nonlinear dynamic responses. Despite the promise of integrating crack-based strain sensors for such a purpose, significant challenges remain in controlling crack propagation to prevent the induction of through-cracks, resulting in lower sensitivity, linearity, and poor detection limits. Herein, we propose a hierarchical crack-based synergistic enhancement structure by incorporating conductive poly(pyrrole)-coated polystyrene nanospheres and Ti₃C₂T_<i>x</i> MXene to induce cross-long sensing cracks via point-to-plane contacts, along with silver nanowires for positively engineering networked microcracks for linearity tuning. The prepared microstrain sensor achieves high linearity (GF = 152.4, <i>R</i>² = 0.99) regulation within ∼6% strain range, ultralow detection limit of 0.02%, and ultrafast response/recovery time of 31 ms/32 ms under 0.2%. Notably, state-of-the-art sensing performance by detecting minimal strain changes down to one millionth, i.e., ∼1 microstrain, has been demonstrated by voiceprint recognition, while maintaining superior dynamic measurement capability and long-term stability for mechanical vibrations up to 100 Hz with a response time of 5 ms. Moreover, the introduction of an adhesive and cross-linking layer facilitates robust bonding between the actuator and sensing structure, enabling real-time tracking of the actuation strain without structural interference by a resistance change resolution of 0.01%, providing significant insights for empowering soft robotics with integrated perception and intelligence.