Self-Regulating Hydrogel with Reversible Optical Activity in Its Gel-to-Gel Transformation.

This study reports a supramolecular gel system capable of dynamic gel-to-gel transformations and reversible inversion of optical activity between superhelical and single-helical structures without passing through a sol phase. Inspired by collagen-like adaptability, the system utilizes 4-pyridinylboronic acid and guanosine as building blocks. Hierarchical assembly is achieved through pH-responsive boronic ester formation and guanosine-mediated G-quadruplex stacking, enabling transitions between superhelices and single helices with opposite optical activity. The system employs three regulatory pathways: bidirectional pH modulation, monotonic pH increase, and monotonic pH decrease, demonstrating programmable and reversible control over chirality, morphology, and mechanical properties. In the autonomous pH regulation, we have created an out-of-equilibrium hydrogel system with controlled switching of optical activity. Unlike traditional gel-sol-gel systems, this gel maintains macroscopic stability during transformations. Our remarkable finding bridges the gap between static supramolecular assemblies and dynamic soft materials, offering a platform for designing functional, biomimetic systems. The combination of hierarchical organization, dynamic chirality control, and robust programmability positions this gel for applications in adaptive optics, responsive biomaterials, and programmable soft matter.