Sustainable and flexible 3D piezoresistive pressure sensor derived from natural coconut-kapok composite fibers

Conventional flexible pressure sensors generally suffer from the trade-off between high sensitivity and broad detection range, non-degradable petroleum-based polymer substrates as well as complex and high-cost manufacturing processes. Herein, a flexible three-dimensional (3D) piezoresistive pressure sensor was developed with cheap natural thick coconut fibers and thin kapok fibers as skeleton substrate anchored by crosslinked carboxymethyl chitosan and reduced graphene oxide as conductive substance. Thanks to the rational combination of the two natural fibers with different diameters, the sensor achieved a high sensitivity up to 7.80 kPa⁻¹, a wide pressure detection range from 0 to 130 kPa and exceptional sensing stability over 3000 loading-unloading cycles. Benefiting from the all-natural fiber substrate and dynamic crosslinked network formed by imine bonds, the sensor was completely degraded in soil under natural conditions within 90 days, exhibiting remarkable environmental friendliness. Additionally, the sensor was successfully applied for accurately monitoring not only large joint motions but also subtle human physiological signals such as swallowing, vocal cord vibration and pulse beating. The preparation method in this work is facile and low-cost, and the as-prepared sensor exhibits excellent sensing performances and biodegradability, which will greatly boost the sustainable development and practical application of flexible electronics.