One-dimensional hierarchically structured strain sensor with high sensitivity, stretchability and durability for physiological monitoring

Developing strain sensors with metal film as sensing material is effective route in monitoring human physiological signals. However, most of them exhibit narrow stretchable range, poor detection limit and durability due to the rigidity and low ductility of metal. Here, a wrapping strategy is proposed to fabricate the strain sensor, which employs hydrogel layer to coat conductive Ni film on rubber band to form one-dimensional hierarchical structure. Impressively, the strain sensor achieves a low sensing strain of 0.005%, high stretchability of 352% and ultimate strength of 1870 kPa. Fast response time (0.32 s), high gauge factor (GF=33) and low electrical hysteresis are other characteristics of the sensor. It also presents excellent durability and frost-resistance, in which the electrical signals (ΔR/R0) still keep exceedingly steady after 10000 and 1000 cycles at 25°C and -30°C, respectively. As expect, it is sensitive in detecting breathing, pulse wave, facial expression, speech and joint bending signals in real time. This work provides a significant research idea to exploit highly durable and stretchable strain sensors for physiological monitoring.