Architecting bioinspired nanocrystalline domains for ultimate robust and transparent cellulose photonic hydrogels

Biomimetic spider silk achieves remarkable functionalities through hierarchical architectures with highly oriented crystalline domains, offering potential across multiple disciplines. However, achieving uniform alignment and spatial control of nanocrystalline domains remains a critical challenge, limiting the realization of structure-derived optical and mechanical functionalities in bioinspired systems. Here, we develop an ultrastrong, transparent photonic hydrogel composed of cellulose nanocrystals (CNCs), wherein a programmable five-stage stretching-pause process enables precise alignment of CNC domains without sacrificing their intrinsic chirality-unattainable in conventional flexible polymers. This strategy facilitates uniform nanocrystal reorientation (orientation factor = 0.91) and transforms the porous network into aligned nanofibril bundles, yielding optical transparency (>90%) with anisotropic polarization responses, superior mechanical strength (61.6 MPa), toughness (251.8 MJ·m^-3), and fatigue resistance (226.7 kJ·m^-2). The flexible hydrogel resists creasing and serves as a sustainable scattering polarizer for programmable polarized displays and secure information encryption, providing a versatile platform for advanced optical and electronic applications.