Highly sensitive, reliable and flexible piezoresistive pressure sensors featuring polyurethane sponge coated with MXene sheets.

Flexible pressure sensors still face a great challenge to combine fast frequency response, wide pressure range, multiple detection modes, satisfactory mechanical and environmental stability, and simple fabrication process into a sensor. Herein, flexible piezoresistive pressure sensors are fabricated by treating the backbone of polyurethane (PU) sponge with chitosan (CS) to obtain positively charged CS@PU sponge, followed by dip-coating of negatively charged Ti3C2Tx MXene sheets. The resulting MXene@CS@PU sponge-based sensor provides a versatile sensing platform with potentials for detecting both small and large pressure signals. Due to the highly compressive resilience of the PU sponge and its polar interaction with the MXene sheets, the MXene@CS@PU sensor has high compressibility and stable piezoresistive response for compressive strains of up to 85% with a stress of 245.7 kPa, and it also exhibits a satisfactory reproducibility for 5000 compression-release cycles. Even after washing in water for 1 h, the sensor still shows good performances. With a rapid response time of only 19 ms and a low detection limit of 30 μN corresponding to a pressure of 9 Pa, the MXene sponge sensor is promising for detecting human physiological signals and insect movements. In addition to the contact mode detection, the sponge sensor could detect voices and human breaths by a non-contact detection mode.