Transient Piezoresistive Strain Sensors Based on Elastic Biopolymer Thin Films

Natural polymers are known for their “green” characteristics with high biodegradability and biocompatibility and thus have great potential for the development of transient sensors. In this paper, flexible and stretchable transient piezoresistive sensors were developed based on natural polymer blends of starch and cellulose. When starch, water-soluble sodium carboxymethyl cellulose, and plasticizer glycerol were combined, highly stretchable polymer thin films were created and subsequently used as substrates to develop degradable piezoresistive strain sensors. The resultant sensors exhibit a gauge factor of 3.9, fast response (response time of 0.38 s), great durability, a failure strain up to 180%, and low hysteresis (∼15%) when exposed to 20% cyclic tensile strain. The sensors have demonstrated abilities to detect respiration rate and human joint bending (such as the bending of wrist, finger, and neck joints). More significantly, it was shown that the sensor can be dissolved in hot water (95 °C), indicating that it is “green” and can be easily disposed of. It is thus expected that it offers sustainable options to develop transient electronics with potential applications in health and sports monitoring and human–machine interfaces.