Flexible, conductive, and anisotropic thermoplastic polyurethane/polydopamine/MXene foam for piezoresistive sensors and motion monitoring

It is a challenge to manufacture pressure sensing materials with flexibility, high sensitivity, wide detection range for the development of intelligent electronic products. Herein, a pressure sensor based on thermoplastic polyurethane (TPU)/polydopamine (PDA)/MXene conductive composite foam (TPMF) was prepared by a combination of directional freezing and dip-coating methods. The compressive strength of anisotropic TPU foam (TF) in the vertical direction is increased by 48.1% compared with isotropic foam. Besides, the conductive foam (0.25 S/ m) with an MXene content of 3.45 wt% exhibits low density (105.5 mg/cm(3)), high porosity (91.2%) and good resistance response behavior. The sensor based on TPMF exhibits excellent flexibility, fast response times (similar to 40 ms), and good durability over 5000 cycles. Furthermore, the composite foam has excellent recognition ability for different compressive strain amplitudes (up to 80%) and a wide stress range (10 Pa-122.5 kPa), as well as a high gauge factor (GF) up to 2.36 in the strain range of 2.5%-20%. The sensor has shown application potential in many fields, including voice recognition, health monitoring, motion monitoring, and artificial electronic skin.