Bubble-Templated Design of Superelastic Cellulose Foam as a Durable Ionotropic Sensor

Introduction of superelasticity and electric conductivity into ecofriendly and biocompatible cellulose-based foams is highly in pursuit for applications in wearable sensors, artificial skin, and soft robotics. Nevertheless, producing superelastic materials with electric conductivity often fails due to the mechanical brittleness and dielectric feature. Herein, we designed a novel type of regenerated cellulose foam with electric conductivity, superelasticity, and negative Poisson's ratio by combining an air bubble template and ionic liquid modification process. The pore size and density could be controlled between 60 and 750 μm and 74.4 and 125.5 mg cm–3, respectively, by tuning the vacuum degree during the regeneration process. With the presence of cellular microstructures and ionic liquid, this regenerated cellulose foam could reach a high compression strain of up to 90% with a negligible plastic deformation and showed superflexible mechanical performance (tensile yield strain of ∼25%, torsion to 720°, and bending to 180°), together with stable ionotropic conductivity. Both the superelasticity and conductivity could be maintained even after more than 103 cycles of periodic compression. Thus, this novel type of regenerated cellulose foam would be capable of serving as elastic biomaterials and promise applications in many flexible devices.