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 Ca²⁺/Zn²⁺ ion exchange is reported. The high content of Ca²⁺ ions leads to the formation of a rigid hydrogel (Gel‐H‐Ca²⁺) with a great compressive strength (≈2.2 MPa) through coordination cross‐linking network, while Zn²⁺ ions give the cellulose (Sol‐L‐Zn²⁺) a fluid state by eliminating the cellulose intermolecular connections, making it possible to obtain injectable and healable hydrogels. Gel‐H‐Ca²⁺ 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.