Ordered-Disorder Transition Induced Stretchable Collagen Ionic Gels Toward Flexible Sensors.

Natural structural proteins such as collagen offer exceptional biocompatibility and mechanical versatility, making them promising candidates for wearable and implantable sensing applications. However, achieving integrated high stretchability, stable electrical performance, and long-term durability in protein-based sensing materials remains a critical challenge. Conventional modification strategies are largely confined to molecular-scale adjustments, which often fail to simultaneously address these functional demands. This study introduces a fundamentally different approach by leveraging Hofmeister-ion engineering to directly regulate the aggregation structure of tropocollagen, which enables a structural transformation from long-range order to entropy-driven disorder. Unlike previous methods that rely on chemical crosslinking or exogenous additives, our strategy selectively disrupts collagen's supramolecular order while preserving its triple-helical integrity, resulting in a highly stretchable and conductive ionic gel with exceptional elasticity (fracture strain 560.00%, elastic range 300.53%, resilience 97.36%), durable ionic conductivity (0.56 S m-1), and reliable sensing performance over 1500 tensile cycles. By establishing a new paradigm of mesoscale disordering, this work not only deepens the understanding of ion-modulated hierarchical assembly but also provides a versatile, biocompatible platform for next-generation flexible electronics, soft robotics, and implantable sensing systems.