Electronic skin using cellulose nanofiber/hollow polypyrrole microspheres with good sensitivity and vapor permeability

Electronic skin, as an intelligent material capable of simulating human skin functions, plays a crucial role in long-term stable health monitoring, human–computer interaction, and medical devices. However, to achieve the application of highly functional electronic skin, there remains a challenge in fabricating pressure sensors that simultaneously possess flexibility, vapor permeability, and exhibit excellent sensing capabilities. Herein, we prepared a dispersion of 2,2,6,6-tetramethylpiperidinyl-1-oxy oxidized cellulose nanofiber (TOCN) and hollow polypyrrole (hPPy) microspheres prepared through the template method. The hydrogel films were obtained by a simple blending approach and Ca²⁺ crosslinking followed by drying. The resulting TOCN/hPPy hydrogel films exhibited good mechanical properties, exceptional flexibility, and reliable vapor permeability. Notably, the developed piezoresistive pressure sensor demonstrated a sensitivity of 2.08 kPa⁻¹, along with a fast response time (90 ms) and recovery time (150 ms). Furthermore, the sensor exhibited a low detection limit of 7.8 Pa, excellent stability at high pressures, and long-term cycling stability of up to 12,500 cycles.