Synergistic Microcrack Engineering and Auxetic Metamaterials for Enhanced Sensitivity in Stretchable Strain Sensors

Abstract Piezoresistive strain sensors are promising candidates for stretchable wearable devices. Although elastomer‐based composite piezoresistive strain sensors offer a broad sensing range, achieving high sensitivity remains a challenge. Herein, a method is proposed to enhance sensor sensitivity by forming microcracks compatible with the behavior of auxetic metamaterials through biaxial pre‐stretching. By applying biaxial pre‐stretching to simply fabricated multi‐walled carbon nanotubes/Ecoflex composite strain sensors, large cracks are formed, resulting in a 56% increase in gauge factor, from 15.3 ± 2.1 to 23.8 ± 2.5, compared to uniaxially pre‐stretched sensors. Circular auxetic metamaterials with an effective Poisson's ratio ranging from −0.485 to 0.385, depending on the radius of the inner circle, are designed and integrated into the biaxially pre‐stretched strain sensor. The cracks formed through biaxial pre‐stretching exhibit significant resistance changes even in response to movements perpendicular to the stretching direction induced by the auxetic metamaterial. This led to a 136% increase in gauge factor, from 23.8 ± 2.5 to 56.2 ± 8.9, with the sensor maintaining high stability over 20000 cycles. The crack formation strategy introduced through biaxial pre‐stretching extends beyond the scope of this study, offering a guideline for designing cracks optimized for auxetic metamaterial integration in crack‐based piezoresistive strain sensors.