Stretchable, adhesive, antifreezing and 3D printable double-network hydrogel for flexible strain sensors

As a new flexible strain sensing material, hydrogels have broad application prospects in the fields of wearable electronic devices, human health monitoring devices and robot aided devices. Therefore, multiple excellent properties of hydrogels were taken into account simultaneously in this work. Double-network (DN) strategy of combining hardness and flexibility was adopted, and the plant materials were adhibited (nanocellulose and proline). The mechanical properties of hydrogels could be significantly improved by combining nanocellulose with conductive ions (stress of 0.293 MPa and strain of 2587%). The excellent antifreezing properties (the conductivity was 0.087 S m-1 at -20 degrees C) and adhesiveness of hydrogels were endowed with the zwitterionic proline, which was significantly accumulated in plants under low temperature stress. The prepared multifunctional hydrogel was suitable for 3D printing, which provided a new approach for producing complex geometry. Multifunctional hydrogel could be used as a flexible strain sensor to detect human movements, including limb bending, facial expression and vocal vibration because of its outstanding strain sensing characteristics. Hence, we expect it to be an ideal candidate material to flexible electronic detection equipments for human motion detection or machine motion feedback in the future.