3D printed topologically engineered cellulose nanofiber/carbon nanotube scaffolds for highly sensitive humidity sensing

Humidity sensors have attracted considerable attention for their wide applications in industrial fields and daily life, yet the fabrication of high-performance sensors still remains challenging. In this study, we developed a highly sensitive humidity sensor based on a topologically engineered cellulose nanofiber/carbon nanotube (CNF/CNT) composite scaffold fabricated by 3D printing combined with freeze-drying. The hierarchical porous architecture, featuring millimeter-sized topological architectures generated by 3D printing and micrometer-sized pores introduced by freeze-drying, provides abundant active interfaces for water molecule adsorption and enables tailored conductive topology toward the percolation threshold. Enabled by this rational topological design, the optimized scaffold sensor exhibits a high humidity sensitivity of 526.4% (ΔR/R 0 , sampling time: 5 min) at 95% relative humidity (RH), with a wide operating humidity range from 11% to 95% RH and excellent long-term stability over two months. Compared to previously reported cellulose/CNT-based humidity sensors, our 3D printed scaffold sensor demonstrates one of the highest sensitivities. Furthermore, the sensor shows promising potential in practical applications including human respiration monitoring, voice recognition, and non-contact fingertip humidity detection. This work provides a scalable and controllable strategy for designing topologically engineered, high-performance humidity sensors using sustainable cellulose-based materials.