Hierarchical Multiscale Hydrogels with Identical Compositions Yet Disparate Properties via Tunable Phase Separation.

Natural gels are constrained by a limited number of building blocks, yet based on time and space organization, they perform diverse functions. In contrast, the properties of synthetic hydrogels are frequently tuned through substantial changes in their chemical make‐up, causing complex interplay between composition, structure, and properties. This work fabricates a series of hydrogels with identical compositions but disparate properties by selectively quenching the depth and path of a water vapor‐induced phase separation process. These hydrogels are solely comprised of short alkyl side‐modified polyvinyl alcohol at the same volume fraction, but they exhibit hierarchical differences across multiple length scales, including porous morphology (≈µm), hydrophobic clusters (≈10 nm), and molecular packing (subnm). The hierarchical discrepancy is explicitly related to the striking contrast in terms of turbidity, permeability, stretchability, and viscoelasticity, thus advancing the understanding of the relationship between multiscale structures and properties without interference from chemical formulations. In addition, the hydrogels exhibit excellent biocompatibility, acid‐aided degradability, in situ healability, and underwater malleability. This work exploits a design principle to imitate the hierarchically specific tenet in nature, that is, the spatiotemporal organization of a single type of polymer via kinetic arrest of network‐forming phase separation, rather than modulation of the chemical make‐ups. [ABSTRACT FROM AUTHOR]