Cellulose nanocrystals-strengthened, anti-drying, and anti-freezing hydrogels for human motion sensing and 3D printing

Recently, stretchable hydrogels have been widely applied in flexible wearable devices. However, their stability, sensitivity, and mechanical properties still remain significant shortcomings. In this work, a double-network and conductive hydrogel formed by sodium alginate and poly(vinyl alcohol) in a glycerol-water system is developed. The network consists of poly(vinyl alcohol) and sodium alginate with rod-like cellulose nanocrystals as a supporting structure, which provides enhanced mechanical properties such as high tensile strength (2.4 MPa), high toughness (4.61 MJ/m 3 ), high compressive strength (7.83 MPa), as well as excellent fatigue resistance. On one hand, due to the incorporation of salt, the hydrogels are endowed with good electrical conductivity. On the other hand, since the hydrogels exhibit the ability to sense pressure and strain, it is considered to be a sensor that can be used to monitor various movements of human bodies. It is worth mentioning that the addition of glycerol provides the hydrogels good anti-freezing properties, and the hydrogels have an operating temperature tolerance as low as −25 °C, which allows the hydrogels to work well even in winter. In addition, the hydrogel solution has good injectability, gelling rate controllability, and biocompatibility, which makes it a good candidate in 3D printing. In summary, the hydrogel developed in this study has good application scenarios for applications such as electronic skin, flexible wearable devices, strain sensors, and 3D-printed scaffolds.