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Structural color is an optical phenomenon resulting from light interacting with nanostructured materials. Although structural color (SC) is widespread in the tree of life, the underlying genetics and genomics are not well understood. Here, we collected and sequenced a set of 87 structurally colored bacterial isolates and 30 related strains lacking SC. Optical analysis of colonies indicated that diverse bacteria from at least two different phyla (Bacteroidetes and Proteobacteria) can create two-dimensional packing of cells capable of producing SC. A pan-genome-wide association approach was used to identify genes associated with SC. The biosynthesis of uroporphyrin and pterins, as well as carbohydrate utilization and metabolism, was found to be involved. Using this information, we constructed a classifier to predict SC directly from bacterial genome sequences and validated it by cultivating and scoring 100 strains that were not part of the training set. We predicted that SCr is widely distributed within gram-negative bacteria. Analysis of over 13,000 assembled metagenomes suggested that SC is nearly absent from most habitats associated with multicellular organisms except macroalgae and is abundant in marine waters and surface/air interfaces. This work provides a large-scale ecogenomics view of SC in bacteria and identifies microbial pathways and evolutionary relationships that underlie this optical phenomenon. [ABSTRACT FROM AUTHOR]

Background and Aims Structural colour is responsible for the remarkable metallic blue colour seen in the leaves of several plants. Species belonging to only ten genera have been investigated to date, revealing four photonic structures responsible for structurally coloured leaves. One of these is the helicoidal cell wall, known to create structural colour in the leaf cells of five taxa. Here we investigate a broad selection of land plants to understand the phylogenetic distribution of this photonic structure in leaves. Methods We identified helicoidal structures in the leaf epidermal cells of 19 species using transmission electron microscopy. Pitch measurements of the helicoids were compared with the reflectance spectra of circularly polarized light from the cells to confirm the structure–colour relationship. Results By incorporating species examined with a polarizing filter, our results increase the number of taxa with photonic helicoidal cell walls to species belonging to at least 35 genera. These include 19 monocot genera, from the orders Asparagales (Orchidaceae) and Poales (Cyperaceae, Eriocaulaceae, Rapateaceae) and 16 fern genera, from the orders Marattiales (Marattiaceae), Schizaeales (Anemiaceae) and Polypodiales (Blechnaceae, Dryopteridaceae, Lomariopsidaceae, Polypodiaceae, Pteridaceae, Tectariaceae). Conclusions Our investigation adds considerably to the recorded diversity of plants with structurally coloured leaves. The iterative evolution of photonic helicoidal walls has resulted in a broad phylogenetic distribution, centred on ferns and monocots. We speculate that the primary function of the helicoidal wall is to provide strength and support, so structural colour could have evolved as a potentially beneficial chance function of this structure. [ABSTRACT FROM AUTHOR]

Rapid progress in algal biotechnology has triggered a growing interest in hydrogel-encapsulated microalgal cultivation, especially for the engineering of functional photosynthetic materials and biomass production. An overlooked characteristic of gel-encapsulated cultures is the emergence of cell aggregates, which are the result of the mechanical confinement of the cells. Such aggregates have a dramatic effect on the light management of gel-encapsulated photobioreactors and hence strongly affect the photosynthetic outcome. To evaluate such an effect, we experimentally studied the optical response of hydrogels containing algal aggregates and developed optical simulations to study the resultant light intensity profiles. The simulations are validated experimentally via transmittance measurements using an integrating sphere and aggregate volume analysis with confocal microscopy. Specifically, the heterogeneous distribution of cell aggregates in a hydrogel matrix can increase light penetration while alleviating photoinhibition more effectively than in a flat biofilm. Finally, we demonstrate that light harvesting efficiency can be further enhanced with the introduction of scattering particles within the hydrogel matrix, leading to a fourfold increase in biomass growth. Our study, therefore, highlights a strategy for the design of spatially efficient photosynthetic living materials that have important implications for the engineering of future algal cultivation systems. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNCs) are naturally sourced elongated nanocolloids that form cholesteric phases in water and apolar solvents. It is well accepted that CNCs are made of bundles of crystalline microfibrils clustered side-by-side, and there is growing evidence that each individual microfibril is twisted. Yet, the origin of the chiral interactions between CNCs remains unclear. In this work, CNCs are described with a simple model of chiral hard splinters, enabling the prediction of the pitch using density functional theory and Monte Carlo simulations. The predicted pitch P compares well with experimental observations in cotton-based CNC dispersions in apolar solvents using surfactants but also with qualitative trends caused by fractionation or tip sonication in aqueous suspensions. These results suggest that the bundle shape induces an entropy-driven chiral interaction between CNCs, which is the missing link in explaining how chirality is transferred from the molecular scale of cellulose chains to the cholesteric order. [ABSTRACT FROM AUTHOR]

High‐index dielectric nanostructures offer strong magnetic and electric resonances in the visible range and low optical losses, stimulating research interest in their use for light manipulation technologies. Lithographic fabrication of dielectric nanostructures, while providing precise control over the pattern dimensions, limits the scalability of this approach for practical applications due to an inefficient fabrication process and limited production quantity. Here, the colloidal synthesis of high‐index chiral dielectric nanostructures with a broom‐like geometry made from trigonal Se is demonstrated. The anisotropic morphology and crystal structure of Se nanobrooms enable both linearly and circularly polarized scattering, as well as spectrum variation along the particle axis, which is, to the authors' knowledge, the first observation of such behavior from dielectric colloidal nanostructures. To show the versatility of the highly scattering Se NB suspensions, 2D and 3D printing of Se NB inks are demonstrated as a proof of concept. This approach provides a way to manipulate light using aqueous dispersions of high‐index dielectric nanostructures, unlocking their potential to fit in various morphologies and dimensions in 2D and 3D for broad applications. [ABSTRACT FROM AUTHOR]

A fundamental question regarding light scattering is how whiteness, generated from multiple scattering, can be obtained from thin layers of materials. This challenge arises from the phenomenon of optical crowding, whereby, for scatterers packed with filling fractions higher than ~30%, reflectance is drastically reduced due to near-field coupling between the scatterers. Here we show that the extreme birefringence of isoxanthopterin nanospheres overcomes optical crowding effects, enabling multiple scattering and brilliant whiteness from ultra-thin chromatophore cells in shrimp. Strikingly, numerical simulations reveal that birefringence, originating from the spherulitic arrangement of isoxanthopterin molecules, enables intense broadband scattering almost up to the maximal packing for random spheres. This reduces the thickness of material required to produce brilliant whiteness, resulting in a photonic system that is more efficient than other biogenic or biomimetic white materials which operate in the lower refractive index medium of air. These results highlight the importance of birefringence as a structural variable to enhance the performance of such materials and could contribute to the design of biologically inspired replacements for artificial scatterers like titanium dioxide. The strong birefringence of liquid crystalline nanospheres in the body of the Pacific cleaner shrimp enables brilliant whiteness by overcoming undesirable optical crowding effects. [ABSTRACT FROM AUTHOR]

Hydroxypropyl cellulose (HPC) is a widely commercialized cellulose derivative. While it is typically used as a binder or stabilizer for foods and pharmaceuticals, it can also form a cholesteric liquid crystal in aqueous solution. Moreover, at high HPC concentrations this lyotropic and thermotropic mesophase is known to reflect structural color. However, it remains a challenge to retain this vibrant coloration into the solid state. Herein, by combining the emulsification of a HPC mesophase with drying at elevated temperature, solid microparticles are produced that can reflect color across the visible spectrum, from blue to green and red. This method provides a facile and scalable pathway to fabricate structurally colored, edible pigments, which can displace existing synthetic additives used in a wide range of foods and cosmetics. [ABSTRACT FROM AUTHOR]

Summary: Structural color is poorly known in plants relative to animals. In fruits, only a handful of cases have been described, including in Viburnum tinus where the blue color results from a disordered multilayered reflector made of lipid droplets. Here, we examine the broader evolutionary context of fruit structural color across the genus Viburnum.We obtained fresh and herbarium fruit material from 30 Viburnum species spanning the phylogeny and used transmission electron microscopy, optical simulations, and ancestral state reconstruction to identify the presence/absence of photonic structures in each species, understand the mechanism producing structural color in newly identified species, relate the development of cell wall structure to reflectance in Viburnum dentatum, and describe the evolution of cell wall architecture across Viburnum.We identify at least two (possibly three) origins of blue fruit color in Viburnum in species which produce large photonic structures made of lipid droplets embedded in the cell wall and which reflect blue light.Examining the full spectrum of mechanisms producing color in pl, including structural color as well as pigments, will yield further insights into the diversity, ecology, and evolution of fruit color. [ABSTRACT FROM AUTHOR]

Daytime radiative cooling (DRC) materials offer a sustainable approach to thermal management by exploiting net positive heat transfer to deep space. While such materials typically have a white or mirror‐like appearance to maximize solar reflection, extending the palette of available colors is required to promote their real‐world utilization. However, the incorporation of conventional absorption‐based colorants inevitably leads to solar heating, which counteracts any radiative cooling effect. In this work, efficient sub‐ambient DRC (Day: −4 °C, Night: −11 °C) from a vibrant, structurally colored film prepared from naturally derived cellulose nanocrystals (CNCs), is instead demonstrated. Arising from the underlying photonic nanostructure, the film selectively reflects visible light resulting in intense, fade‐resistant coloration, while maintaining a low solar absorption (≈3%). Additionally, a high emission within the mid‐infrared atmospheric window (>90%) allows for significant radiative heat loss. By coating such CNC films onto a highly scattering, porous ethylcellulose (EC) base layer, any sunlight that penetrates the CNC layer is backscattered by the EC layer below, achieving broadband solar reflection and vibrant structural color simultaneously. Finally, scalable manufacturing using a commercially relevant roll‐to‐roll process validates the potential to produce such colored radiative cooling materials at a large scale from a low‐cost and sustainable feedstock. [ABSTRACT FROM AUTHOR]

The coral‐algal symbiosis is the biological engine that drives one of the most spectacular structures on Earth: the coral reef. Here, living coral microhabitats are engineered using 3D bioprinting, as biomimetic model system of the coral‐algal symbiosis. Various bioinks for the encapsulation of coral photosymbiotic microalgae (Breviolum psygmophilum) are developed and coral mass transfer phenomena are mimicked by 3D bioprinting coral tissue and skeleton microscale features. At the tissue–seawater interface, the biomimetic coral polyp and connective tissue structures successfully replicate the natural build‐up of the O2 diffusive boundary layer. Inside the bioprinted construct, coral‐like microscale gastric cavities are engineered using a multi‐material bioprinting process. Underneath the tissue, the constructs mimic the porous architecture of the coral aragonite skeleton at the micrometer scale, which can be manipulated to assess the effects of skeletal architecture on stress‐related hydrogen peroxide (H2O2) production. The bioprinted living coral microhabitats replicate the diffusion‐related phenomena that underlie the functioning and breakdown of the coral‐algal symbiosis and can be exploited for the additive manufacturing of synthetic designer corals. [ABSTRACT FROM AUTHOR]

Biodegradable photonic microspheres with structural colors are promising substitutes to polluting microbeads and toxic dyes. Here, amphiphilic polyester‐block‐poly(ethylene glycol) bottlebrush block copolymers (BBCPs) with polylactic acid or poly(ϵ‐caprolactone) as the hydrophobic block are synthesized and used to fabricate eco‐friendly photonic pigments. Molecular parameters of BBCPs, including rigidity and symmetry, are precisely tailored by variation of side chain lengths, which enables effective manipulation of interfacial tension (γ). Organized spontaneous emulsion mechanism is enabled only when γ falls in a suitable range (10.6–14.3 mN m−1), producing ordered water‐in‐oil‐in‐water multiple emulsions and ordered porous structures. Consequently, highly saturated and tunable structural colors are observed due to coherent light scattering from the porous structures. Such photonic materials are nontoxic as confirmed by careful safety tests using aquatic model organisms. [ABSTRACT FROM AUTHOR]

To unlock the widespread use of block copolymers as photonic pigments, there is an urgent need to consider their environmental impact (cf. microplastic pollution). Here we show how an inverse photonic glass architecture can enable the use of biocompatible bottlebrush block copolymers (BBCPs), which otherwise lack the refractive index contrast needed for a strong photonic response. A library of photonic pigments is produced from poly(norbornene‐graft‐polycaprolactone)‐block‐poly(norbornene‐graft‐polyethylene glycol), with the color tuned via either the BBCP molecular weight or the processing temperature upon microparticle fabrication. The structure–optic relationship between the 3D porous morphology of the microparticles and their complex optical response is revealed by both an analytical scattering model and 3D finite‐difference time domain (FDTD) simulations. Combined, this allows for strategies to enhance the color purity to be proposed and realized with our biocompatible BBCP system. [ABSTRACT FROM AUTHOR]

Summary: The majority of plant colours are produced by anthocyanin and carotenoid pigments, but colouration obtained by nanostructured materials (i.e. structural colours) is increasingly reported in plants. Here, we identify a multilayer photonic structure in the fruits of Lantana strigocamara and compare it with a similar structure in Viburnum tinus fruits.We used a combination of transmission electron microscopy (EM), serial EM tomography, scanning force microscopy and optical simulations to characterise the photonic structure in L. strigocamara. We also examine the development of the structure during maturation.We found that the structural colour derives from a disordered, multilayered reflector consisting of lipid droplets of c.105 nm that form a plate‐like structure in 3D. This structure begins to form early in development and reflects blue wavelengths of light with increasing intensity over time as the structure develops. The materials used are likely to be lipid polymers.Lantana strigocamara is the second origin of a lipid‐based photonic structure, convergently evolved with the structure in Viburnum tinus. Chemical differences between the lipids in L. strigocamara and those of V. tinus suggest a distinct evolutionary trajectory with implications for the signalling function of structural colours in fruits. [ABSTRACT FROM AUTHOR]

Diverse forms of nanoscale architecture generate structural colour and perform signalling functions within and between species. Structural colour is the result of the interference of light from approximately regular periodic structures; some structural disorder is, however, inevitable in biological organisms. Is this disorder functional and subject to evolutionary selection, or is it simply an unavoidable outcome of biological developmental processes? Here we show that disordered nanostructures enable flowers to produce visual signals that are salient to bees. These disordered nanostructures (identified in most major lineages of angiosperms) have distinct anatomies but convergent optical properties; they all produce angle-dependent scattered light, predominantly at short wavelengths (ultraviolet and blue). We manufactured artificial flowers with nanoscale structures that possessed tailored levels of disorder in order to investigate how foraging bumblebees respond to this optical effect. We conclude that floral nanostructures have evolved, on multiple independent occasions, an effective degree of relative spatial disorder that generates a photonic signature that is highly salient to insect pollinators., Author(s): Edwige Moyroud [1]; Tobias Wenzel [2]; Rox Middleton [3]; Paula J. Rudall [4]; Hannah Banks [4]; Alison Reed [1]; Greg Mellers [1]; Patrick Killoran [1]; M. Murphy Westwood [1]; [...]

Block‐copolymer self‐assembly has proven to be an effective route for the fabrication of photonic films and, more recently, photonic pigments. However, despite extensive research on this topic over the past two decades, the palette of monomers and polymers employed to produce such structurally colored materials has remained surprisingly limited. In this Scientific Perspective, the commonly used block‐copolymer systems reported in the literature are summarized (considering both linear and brush architectures) and their use is rationalized from the point of view of both their historical development and physicochemical constraints. Finally, the current challenges facing the field are discussed and promising new areas of research are highlighted to inspire the community to pursue new directions. [ABSTRACT FROM AUTHOR]

Additive manufacturing is becoming increasingly important as a flexible technique for a wide range of products, with applications in the transportation, health, and food sectors. However, to develop additional functionality it is important to simultaneously control structuring across multiple length scales. In 3D printing, this can be achieved by employing inks with intrinsic hierarchical order. Liquid crystalline systems represent such a class of self‐organizing materials; however, to date they are only used to create filaments with nematic alignment along the extrusion direction. In this study, cholesteric hydroxypropyl cellulose (HPC) is combined with in situ photo‐crosslinking to produce filaments with an internal helicoidal nanoarchitecture, enabling the direct ink writing of solid, volumetric objects with structural color. The iridescent color can be tuned across the visible spectrum by exploiting either the lyotropic or thermotropic behavior of HPC during the crosslinking step, allowing objects with different colors to be printed from the same feedstock. Furthermore, by examining the microstructure after extrusion, the role of shear within the nozzle is revealed and a mechanism proposed based on rheological measurements simulating the nozzle extrusion. Finally, by using only a sustainable biopolymer and water, a pathway toward environmentally friendly 3D printing is revealed. [ABSTRACT FROM AUTHOR]