Cellulose Hydrogels by Reversible Ion‐Exchange as Flexible Pressure Sensors

Abstract Inspired by biological camouflage strategy according to the surrounding environment, a facile method to fabricate state‐switchable cellulose hydrogels (fluid, brittle, and rigid hydrogel) driven by Ca 2+ /Zn 2+ ion exchange is reported. The high content of Ca 2+ ions leads to the formation of a rigid hydrogel (Gel‐H‐Ca 2+ ) with a great compressive strength (≈2.2 MPa) through coordination cross‐linking network, while Zn 2+ ions give the cellulose (Sol‐L‐Zn 2+ ) a fluid state by eliminating the cellulose intermolecular connections, making it possible to obtain injectable and healable hydrogels. Gel‐H‐Ca 2+ is highly oriented and anisotropic, and such flexible hydrogel can effectively monitor slight bending and pressure changes of fingers. This cellulose hydrogel will be a promising candidate for bionic and multifunctional sensors.