Highly Flexible, Stretchable, and Compressible Lignin-Based Hydrogel Sensors with Frost Resistance for Advanced Bionic Hand Control

Bio-based hydrogels, valued for their flexibility, tunable mechanical properties, and biocompatibility, are promising materials for wearable skins and sensing devices in bionic hand control systems. Lignin, a biopolymer rich in functional groups, can be modified into UV-curable monomers, enabling the development of 3D-printed hydrogels via photopolymerization. However, the inherent rigidity of lignin's aromatic rings, coupled with covalent cross-linking between lignin and other monomers, often limits the hydrogel's stretchability (poor strain) and compressibility. Additional challenges, including poor moisture retention and freeze resistance, further hinder their wider application. In this study, a lignin-based hydrogel is developed with high flexibility, tensile strain (≥350%), compressive strain (≈95%), and fatigue resistance (up to 10 000 cycles under 50% strain, and 200–800 cycles under 95% compressive strain), which is achieved by incorporating glycerol and lithium chloride to facilitate dynamic hydrogen and lithium ion bonds, while accordingly reducing covalent cross-linking sites between monomers. The enhanced moisture retention and freeze resistance of hydrogels allow effective sensing performance at −40±1 °C. Afterward, using 3D printing technology, wearable tensile strain sensors and ripple-shaped 3 × 3 Matrix hydrogel pressure sensors are fabricated, which demonstrated uniform stress distribution and improved performance in controlling complex bionic hand movements, underscoring their application in advancing human–machine interfaces.