Self-assembled cellulose nanocrystal: Expanding structural color materials into next-generation functional...

Cellulose nanocrystal (CNC), derived from renewable biomass, have emerged as a versatile class of nanomaterials with intrinsic chirality, high aspect ratio, and excellent mechanical and optical properties. Their ability to self-assemble into long-range ordered structures endows them with unique photonic and multifunctional characteristics, offering broad opportunities for sustainable advanced materials. In recent years, CNC-based self-assembled systems have moved beyond traditional applications in visual sensing coatings or packaging toward frontier technologies. This review surveys recent advances in which CNC self-assembly is coupled to electronic/ionic conductive skins, electrochromic chiroptical devices, additive manufacturing, structurally colored passive daytime radiative cooling (PDRC), smart photonic textiles and photothermal composites for anti-icing and energy conversion. For each application we compare representative performance metrics, summarize enabling strategies (surface modification, compatibilizers, hierarchical layering, and in-line fixation), and identify key bottlenecks-notably environmental stability, scalable processing, interface compatibilization, and life-cycle sustainability. Finally, we propose concrete directions (mechanistic multiscale modelling, standardized benchmarks, rational interfacial design, and application-level prototyping) to accelerate translation of CNC-based photonic systems into practical sustainable devices.