Color-changing organogel stretches 46 times its size and self-heals

Summary

Self-repairing organogels exhibit ratiometric mechano-fluorescence: orange emission (603 nm) in the relaxed state, blue (451 nm) after stretching. Credit: Adv. Funct. Mater. (2025): e19737. DOI: 10.1002/adfm.202519737 Scientists from Taiwan have developed a new material that can stretch up to 4,600% of its original length before breaking. Even if it does break, gently pressing the pieces together at room temperature allows it to heal, fully restoring its shape and stretchability within 10 minutes. The sticky and stretchy polyurethane (PU) organogels were designed by combining covalently linked cellulose nanocrystals (CNCs) and modified mechanically interlocked molecules (MIMs) that act as artificial molecular muscles. The muscles make the gel sensitive to external forces such as stretching or heat, where its color changes from orange to blue based on whether the material is at rest or stimulated. Thanks to these unique properties, the gels hold great promise for next-generation technologies—from flexible electronic skins and soft robots to anti-counterfeiting solutions. The findings are published in Advanced Functional Materials. Credit: Advanced Functional Materials (2025). DOI: 10.1002/adfm.202519737 MIMs, such as rotaxanes and daisy chains, are promising because their molecular motion enhances toughness and flexibility. MIMs have also opened up the world of mechanochromic materials—substances that fluoresce or change colors in response to a stimulus. These materials contain molecular switches called mechanophores, which respond to force by breaking and reforming chemical bonds, leading to small but dramatic structural shifts. Studies show that even small amounts of MIMs can greatly enhance the stretchability and toughness of polymers. While mechanophores are commonly used for temperature and force sensing, incorporating them into self-healing systems has proven challenging. To address this, the researchers experimented with a range of compositions to develop nove...