3D-printed cellulose hydrogel keeps wearable sensors working at -13°F after 168 hours

Wearable sensors could become more reliable in freezing conditions with a new cellulose-based hydrogel that continued detecting movement after being exposed to -13°F for seven days. Researchers developed the flexible material from cotton pulp cellulose, turning an abundant renewable material into an electrically conductive hydrogel. The approach is designed to address a basic problem with conventional hydrogel sensors: water inside them can freeze, making the material stiff and reducing its ability to carry ionic signals. The team used a mixture of zinc chloride and lithium bromide salts to dissolve the cellulose. The combination disrupted the tightly packed crystalline structure of cellulose while protecting the resulting molecular chains from damage. The dissolved material was then formed into a transparent hydrogel called HZ0.3L0.7-C3. The resulting material combined electrical conductivity with mechanical strength and resistance to freezing. Researchers measured an ionic conductivity of 4.48 S/m and a compressive stress of up to 2.48 MPa. Tests between -112°F and 68°F showed no exothermic peaks associated with water crystallization, indicating that ice formation was suppressed in the hydrogel. Cold-proofed wearable sensing The researchers then subjected the optimized material to a longer cold test. After remaining at -13°F for 168 hours, the hydrogel continued producing repeatable electrical signals when exposed to movements such as finger bending and fingertip pressing. That performance is important for wearable electronics that could operate outdoors, in refrigerated environments, or in other applications where conventional water-rich hydrogels can lose flexibility and conductivity. The material also showed shear-thinning behavior, meaning it could flow under pressure and then retain its shape after being printed. This allowed the researchers to use it as a 3D-printing material and produce structures including five-pointed stars and maple leaves. For use directly on the body, the team added a polydopamine coating to improve skin compatibility. Sensors made from the hydrogel could be attached to fingers, wrists, elbows and the throat to detect movement and pressure. From skin sensors robotics The wearable sensor responded in about 100 milliseconds and recovered in roughly 300 milliseconds. It also maintained stable performance through 500 compression cycles at 30 percent strain. The researchers demonstrated the material in a data-glove system that detected hand movements and translated them into corresponding movements on a robotic model in real time. This points to possible uses in human-machine interfaces where sensors must remain flexible while handling repeated deformation. The cellulose base also gives the material a renewable component, while the salt-based formulation provides the ions needed for electrical signal transmission without relying on conventional conductive polymers. The researchers say the work could provide a route to customizable wearable sensors that remain functional in low-temperature environments. However, the material is still at the research and prototype stage, and further testing would be needed before commercial deployment. The study is published in the Journal of Bioresources and Bioproducts.Get the latest in engineering, tech, space & science - delivered daily to your inbox.With over a decade-long career in journalism, Neetika Walter has worked with The Economic Times, ANI, and Hindustan Times, covering politics, business, technology, and the clean energy sector. Passionate about contemporary culture, books, poetry, and storytelling, she brings depth and insight to her writing. When she isn’t chasing stories, she’s likely lost in a book or enjoying the company of her dogs.