Dual-Graded Microstructure Engineering for Flexible Piezoresistive Sensors with High Sensitivity and Broad Linear Range in Physiological Monitoring.

Flexible piezoresistive sensors that offer both high sensitivity and a broad linear detection range are highly desirable for wearable health monitoring, as they facilitate simplified circuit design and enable accurate detection of subtle physiological signals. However, existing sensors typically encounter an intrinsic trade-off between sensitivity and linearity, primarily due to structural stiffening under increasing pressure. Here, a flexible piezoresistive pressure sensor featuring dual-graded microstructures (DGM) is reported, formed by embedding multi-walled carbon nanotubes (MWCNTs) into a thermoplastic polyurethane matrix. Leveraging the synergistic effects of progressive structural deformation and MWCNTs-induced tunneling conduction, the sensor achieves a high sensitivity of 69.8 kPa⁻¹ and a broad linear sensing range up to 300 kPa (R ≈ 0.998). The sensor also exhibits rapid response-relaxation time (totaling 5 ms), stable high-frequency detection up to 200 Hz, and good stability over 5 000 repeated loading cycles. Demonstrations in physiological monitoring confirm the sensor's capability to precisely capture detailed radial pulse waveforms, respiratory rhythms, and subtle heartbeat-induced vibrations. Both a scalable, cost-effective structural fabrication and good overall sensing performance establish the DGM-based sensor as a promising candidate for advanced wearable healthcare monitoring devices.