This review presents the recent progress in mimicking the shiny and iridescent structural colours found in nature.

Cellulose nanocrystals (CNCs) form chiral nematic phases in aqueous suspensions that can be preserved upon evaporation of water. The resulting films show an intense directional coloration determined by their microstructure. Here, microreflection experiments correlated with analysis of the helicoidal nanostructure of the films reveal that the iridescent colors and the ordering of the individual nematic layers are strongly dependent on the polydispersity of the size distribution of the CNCs. We show how this affects the self-assembly process, and hence multidomain color formation in such bioinspired structural films.

The self‐assembly process of photonic structures made of cellulose nanocrystals is studied in detail by locally monitoring and controlling water evaporation. Three different stages during the evaporation process are identified. Spectroscopy quantifies the amount of disorder in the fabricated samples. Control of this process enables the selection of a range of different colors starting from the same suspension, providing a facile, sustainable route for the manufacture of structural color.

Cellulose is a natural linear biopolymer, which constitutes through the assembly of cellulose nanofibrils in a hierarchical order. Nanocelluloses in particular show great promise as a cost-effective advanced material for biomedical applications because of their biocompatibility, biodegradability, and low cytotoxicity. Moreover, with their chemical functionality they can be easily modified to yield useful products. While nature uses the hierarchical nanostructure of the cellulose as the load-bearing constituent in plants, a significant amount of research has been directed toward the fabrication of advanced cellulosic materials with various nanostructures and functional properties. Such nanocelluloses are widely applied in medical implants, tissue engineering, drug delivery, wound healing, diagnostics, and other medical applications with real examples in this field. There are also emerging fields being developed to use nanocelluloses and their composites in more novel ways in biomedical applications such as 3D printing and magnetically responsive materials. In this mini-review, recent advances in the design and fabrication of nanocellulose-based materials and composites are presented with a special emphasis on their suitability for material requirements for biomedical applications as well as the new directions and challenges that the materials might face in the future.

By a simple two-step procedure, large photonic strain sensors using a biocompatible cellulose derivative are fabricated. Transient color shifts of the sensors are explained by a theoretical model that consideres the deformation of cholesteric domains, which is in agreement with the experimental results. The extremely simple fabrication method is suitable for both miniaturization and large-sale manufacture, taking advantage of inexpensive and sustainable materials.