Ultra-stretchable, tough, and self-healing polyurethane with tunable microphase separation for flexible wearable electronics

The development of flexible wearable materials that combine high toughness, stretchability, and compatibility with the modulus of human skin remains a significant challenge, due to inherent trade-offs between strength and elongation. These materials must demonstrate mechanical durability and resistance to environmental factors such as moisture and sweat. Herein, we present a polyurethane elastomer (HTPB-PU) that is ultra-stretchable, tough, thermodynamically stable, self-healing, biocompatible, and transparent, specifically designed for flexible wearable electronics. The elastomer incorporates a hydrophobic soft segment and varying concentrations of disulfide bonds to enable tunable microphase separation. This approach leads to the uniform distribution of hardphase aggregates, resulting in exceptional properties, including a tensile elongation of 2180 %, a toughness of 42.8 MJ m-3, and a Young's modulus of 110 kPa, allowing it to support objects weighing 16,666 times its own weight below it. Additionally, the material exhibits self-healing at 36 degrees C and retains stability over 300 cycles at 150 % strain, even after 30 days of immersion in water and synthetic perspiration. Moreover, a stretch sensor capable of detecting physiological signals, including pulse and throat vibrations, was developed by integrating the material with liquid metal, demonstrating its potential for health monitoring and intelligent wearables.