Bioinspired bright noniridescent photonic melanin supraballs

Structural Color Enhancement through Synchronizing Natural Convection and Marangoni Flow in Pendant Drops

Structural color, renowned for its enduring vibrancy, has been extensively developed and applied in the fields of display and anticounterfeiting. However, its limitations in brightness and saturation hinder further application in these areas. Herein, we propose a pendant evaporation self-assembly method to address these challenges simultaneously. By leveraging natural convection and Marangoni flow synchronization, the self-assembly process enhances the dynamics and duration of colloidal nanoparticles, thereby enhancing the orderliness of colloidal photonic crystals. On average, this technique boosts the brightness of structural color by 20% and its saturation by 35%. Moreover, pendant evaporation self-assembly is simple and convenient to operate, making it suitable for industrial production. We anticipate that its adoption will remarkably advance the industrialization of structural color, facilitating its engineering applications across various fields, such as display technology and anticounterfeiting identification.

pH-Responsive, Wide Color Gamut Dynamic Color Display Enabled by PDMAEMA Brush-Based Fabry-Perot Resonant Cavity

Dynamic color-changing materials have attracted broad interest due to their widespread applications in visual sensing, dynamic color display, anticounterfeiting, and image encryption/decryption. In this work, we demonstrate a novel pH-responsive dynamic color-changing material based on a metal-insulator-metal (MIM) Fabry-Perot (FP) cavity with a pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) brush layer as the responsive insulating layer. The pH-responsive PDMAEMA brush undergoes protonation at a low pH value (pH < 6), which induces different swelling degrees in response to pH and thus refractive index and thickness change of the insulator layer of the MIM FP cavity. This leads to significant optical property changes in transmission and a distinguishable color change spanning the whole visible region by adjusting the pH value of the external environment. Due to the reversible conformational change of the PDMAEMA and the formation of covalent bonds between the PDMAEMA molecular chain and the Ag substrate, the MIM FP cavity exhibits stable performance and good reproducibility. This pH-responsive MIM FP cavity establishes a new way to modulate transmission color in the full visible region and exhibits a broad prospect of applications in dynamic color display, real-time environment monitoring, and information encryption and decryption.

Interactions of Melanin with Electromagnetic Radiation: From Fundamentals to Applications

Melanin, especially integumentary melanin, interacts in numerous ways with electromagnetic radiation, leading to a set of critical functions, including radiation protection, UV-protection, pigmentary and structural color productions, and thermoregulation. By harnessing these functions, melanin and melanin-like materials can be widely applied to diverse applications with extraordinary performance. Here we provide a unified overview of the melanin family (all melanin and melanin-like materials) and their interactions with the complete electromagnetic radiation spectrum (X-ray, Gamma-ray, UV, visible, near-infrared), which until now has been absent from the literature and is needed to establish a solid fundamental base to facilitate their future investigation and development. We begin by discussing the chemistries and morphologies of both natural and artificial melanin, then the fundamentals of melanin-radiation interactions, and finally the exciting new developments in high-performance melanin-based functional materials that exploit these interactions. This Review provides both a comprehensive overview and a discussion of future perspectives for each subfield of melanin that will help direct the future development of melanin from both fundamental and applied perspectives.

Influence of Sphericity on Surface Termination of Icosahedral Colloidal Clusters

Colloids self-organize into icosahedral clusters composed of a Mackay core and an anti-Mackay shell under spherical confinement to minimize the free energy. This study explores the variation of surface arrangements of colloids in icosahedral clusters, focusing on the determining factors behind the surface arrangement. To efficiently assemble particles in emulsion droplets, droplet-to-droplet osmotic extraction from particle-laden droplets to salt-containing droplets is used, where the droplets are microfluidically prepared to guarantee a high size uniformity. The icosahedral clusters are optimally produced during a 24-h consolidation period at a 0.04 m salt concentration. The findings reveal an increase in the number of particle layers from 10 to 15 in the icosahedral clusters as the average number of particles increases from 3300 to 11 000. Intriguingly, the number of layers in the anti-Mackay shells, or surface termination, appears to more strongly depend on the sphericity of the clusters than on the deviation in the particle count from an ideal icosahedral cluster. This result suggests that the sphericity of the outermost layer, formed by the late-stage rearrangement of particles to form an anti-Mackay shell near the droplet interface, may play a pivotal role in determining the surface morphology to accommodate a spherical interface.

Quaternary Ammonium Assisted Synthesis of Melanin-like Poly(l-DOPA) Nanoparticles with a Boosted Photothermal Effect

Poly(levodopa) nanoparticles (P(l-DOPA) NPs) are another kind of melanin mimetic besides well-established polydopamine nanoparticles (PDA NPs). Due to the presence of carboxyl groups, the oxidative polymerization of l-DOPA to obtain particles was not as efficient as that of dopamine. Several established methods toward P(l-DOPA) NP fabrication do not combine convenience, morphological regularity, size controllability, low cost, and adaptability to metal-free application scenarios. In this work, P(l-DOPA) NPs were successfully prepared in hot water with the assistant of organic quaternary ammonium, due to the extra physical cross-linking mediated by cations. The employed physical interactions could also be affected by quaternary ammonium structure (i.e., number of cation heads, length of alkyl chain) to achieve different polymerization acceleration effects. The obtained P(l-DOPA) NPs retained superior photothermal properties and outperformed PDA-based melanin materials. Furthermore, P(l-DOPA) NPs were used in photothermal tumor therapy and showed better efficacy. This study offers new insights into the synthesis of melanin-like materials, as well as new understanding of the interaction between quaternary ammonium and bioinspired polyphenolic materials.

Fine Optimization of Colloidal Photonic Crystal Structural Color for Physically Unclonable Multiplex Encryption and Anti-Counterfeiting

Robust anti-counterfeiting techniques aim for easy identification while remaining difficult to forge, especially for high-value items such as currency and passports. However, many existing anti-counterfeiting techniques rely on deterministic processes, resulting in loopholes for duplication and counterfeiting. Therefore, achieving high-level encryption and easy authentication through conventional anti-counterfeiting techniques has remained a significant challenge. To address this, this work proposes a solution that combined fluorescence and structural colors, creating a physically unclonable multiplex encryption system (PUMES). In this study, the physicochemical properties of colloidal photonic inks are systematically adjusted to construct a comprehensive printing phase diagram, revealing the printable region. Furthermore, the brightness and color saturation of inkjet-printed colloidal photonic crystal structural colors are optimized by controlling the substrate's hydrophobicity, printed droplet volume, and the addition of noble metals. Finally, fluorescence is incorporated to build PUMES, including macroscopic fluorescence and structural color patterns, as well as microscopic physically unclonable fluorescence patterns. The PUMES with intrinsic randomness and high encoding capacity are authenticated by a deep learning algorithm, which proved to be reliable and efficient under various observation conditions. This approach can provide easy identification and formidable resistance against counterfeiting, making it highly promising for the next-generation anti-counterfeiting of currency and passports.

Characterizing the Microparticles Deposition Structure and its Photonic Nature in Surfactant-Laden Evaporating Colloidal Sessile Droplets

This work presents a simple method to create photonic microstructures via the natural evaporation of surfactant-laden colloidal sessile droplets on a flat substrate. In the absence of dissolved surfactant, the evaporating colloidal droplet forms a well-known coffee ring deposition. In contrast, the presence of surfactant leads to the formation of multiple ring structures due to the repetitive pinning-depinning behavior of the droplet contact line (CL). It is found that the multiring structure shows vibrant iridescent structural colors while the coffee ring lacks a photonic nature. This difference in the structural color for the presence and absence of the surfactant is found to be dependent on the arrangement of the particles in the deposition structure. The particle arrangement in the multirings is monolayered and well-ordered. The ordering of the particles is strongly influenced by the particle dynamics, contact angle (CA), and CL dynamics of the evaporating colloidal solution droplet. Furthermore, the iridescent nature of the multiring deposition is demonstrated and explained. The dependence of the multiring deposition structure on the concentration of the dissolved surfactant and the suspended particles is also studied. The findings demonstrate that an intermediate surfactant concentration is desirable for the formation of a multiring structure. Further, the pinning-depinning CL dynamics that causes the formation of the multiring deposition structure is discussed. Finally, we demonstrate the applicability of the approach to smaller droplet volumes.

Eumelanin-like Poly(levodopa) Nanoscavengers for Inflammation Disease Therapy

In the current years, polydopamine nanoparticles (PDA NPs) have been extensively investigated as an eumelanin mimic. However, unlike natural eumelanin, PDA NPs contain no 5,6-dihydroxyindole-2-carboxylic acid (DHICA)-derived units and may be limited in certain intrinsic properties; superior eumelanin-like nanomaterials are still actively being sought. Levodopa (l-DOPA) is a natural eumelanin precursor and expected to convert into DHICA and further remain within the final product through covalent or physical interactions. Herein, poly(levodopa) nanoparticles [P(l-DOPA) NPs] were synthesized with the assistance of zinc oxide as a supplement to synthetic eumelanin. This study found that P(l-DOPA) NPs had ∼90% DHICA-derived subunits on their surface and exhibited superior antioxidant activity compared to PDA NPs due to their looser polymeric microstructure. Benefitting from a stronger ROS scavenging ability, P(l-DOPA) NPs outperformed PDA NPs in treating cellular oxidative stress and acute inflammation. This research opens up new possibilities for the development and application of novel melanin-like materials.

Sustainable Cellulose-Derived Organic Photonic Gels with Tunable and Dynamic Structural Color

Structural color is a fascinating optical phenomenon arising from intricate light-matter interactions. Biological structural colors from natural polymers are invaluable in biomimetic design and sustainable construction. Here, we report a renewable, abundant, and biodegradable cellulose-derived organic gel that generates stable cholesteric liquid crystal structures with vivid structural colors. We construct the chromatic gel using a 68 wt % hydroxypropyl cellulose (HPC) matrix, incorporating distinct polyethylene glycol (PEG) guest molecules. The PEGs contain peculiar end groups with tailored polarity, allowing for precise positioning on the HPC helical backbone through electrostatic repulsion between the PEG and HPC chains. This preserves the HPC's chiral nematic phase without being disrupted. We demonstrate that the PEGs' polarity tunes the HPC gel's reflective color. Additionally, gels with variable polarities are highly sensitive to temperature, pressure, and stretching, resulting in rapid, continuous, and reversible color changes. These exceptional dynamic traits establish the chiral nematic gel as an outstanding candidate for next-generation applications across displays, wearables, flexible electronics, health monitoring, and multifunctional sensors.

A Mesostructure Multivariant-Assembly Reinforced Ultratough Biomimicking Superglue

The imitation of mussels and oysters to create high-performance adhesives is a cutting-edge field. The introduction of inorganic fillers is shown to significantly alter the adhesive's properties, yet the potential of mesoporous materials as fillers in adhesives is overlooked. In this study, the first report on the utilization of mesoporous materials in a biomimetic adhesive system is presented. Incorporating mesoporous silica nanoparticles (MSN) profoundly enhances the adhesion of pyrogallol (PG)-polyethylene imine (PEI) adhesive. As the MSN concentration increases, the adhesion strength to glass substrates undergoes an impressive fivefold improvement, reaching an outstanding 2.5 mPa. The adhesive forms an exceptionally strong bond, to the extent that the glass substrate fractures before joint failure. The comprehensive tests involving various polyphenols, polymers, and fillers reveal an intriguing phenomenon-the molecular structure of polyphenols significantly influences adhesive strength. Steric hindrance emerges as a crucial factor, regulating the balance between π-cation and charge interactions, which significantly impacts the multicomponent assembly of polyphenol-PEI-MSN and, consequently, adhesive strength. This groundbreaking research opens new avenues for the development of novel biomimetic materials.

Multicomponent structural color membrane based on soft lithography array for high-sensitive Raman detection

Inspired by ordered photonic crystals and structural color materials in nature, we successfully prepared hydroxypropyl cellulose (HPC) photonic films with ordered surface arrays by double-imprint soft lithography. Then we introduced another important material of the cellulose family, cellulose nanocrystals (CNC), which has liquid crystal nature and birefringent properties of the particles, into the system to realize the single-point shrinkage of the film array and the control of structural color. Through multi-component doping and concentration control, we further optimized the multi-scale structure of the materials, and obtained HPC/CNCs composite photonic films with excellent properties in color, stability and flexibility, whose elastic modulus and tensile properties are significantly higher than those of single-component. Further loading of SiO2@PDA enhances the color saturation and realizes the in-situ reduction of metal ions on the film surface. This plasma film can track a variety of substances with high sensitivity and long-term stability, showing potential application prospects in the field of surface-enhanced Raman scattering (SERS), which provides a potential possibility for chiral structures to be used in the field of biosensor detection and circularly polarized luminescence.

Structural color from pigment-loaded nanostructures

Color can originate from wavelength-dependence in the absorption of pigments or the scattering of nanostructures. While synthetic colors are dominated by the former, vivid structural colors found in nature have inspired much research on the latter. However, many of the most vibrant colors in nature involve the interactions of structure and pigment. Here, we demonstrate that pigment can be exploited to efficiently create bright structural color at wavelengths outside its absorption band. We created pigment-enhanced Bragg reflectors by sequentially spin-coating layers of poly-vinyl alcohol (PVA) and polystyrene (PS) loaded with β-carotene (BC). With only 10 double layers, we achieved a peak reflectance over 0.8 at 550 nm and normal incidence. A pigment-free multilayer made of the same materials would require 25 double layers to achieve the same reflectance. Further, pigment loading suppressed the Bragg reflector's characteristic iridescence. Using numerical simulations, we further show that similar pigment loadings could significantly expand the gamut of non-iridescent colors addressable by photonic glasses.

DNA-Condensed Plasmonic Supraballs Transparent to Molecules

DNA nanotechnology offers an unrivaled programmability of plasmonic nanoassemblies based on encodable Watson-Crick basepairing. However, it is very challenging to build rigidified three-dimensional supracolloidal assemblies with strong electromagnetic coupling and a self-confined exterior shape. We herein report an alternative strategy based on a DNA condensation reaction to make such structures. Using DNA-grafted gold nanoparticles as building blocks and metal ions with suitable phosphate affinities as abiological DNA-bonding agents, a seedless growth of spheroidal supraparticles is realized via metal-ion-induced DNA condensation. Some governing rules are disclosed in this process, including kinetic and thermodynamic effects stemming from electrostatic and coordinative forces with different interaction ranges. The supraballs are tailorable by adjusting the volumetric ratio between DNA grafts and gold cores and by overgrowing extra gold layers toward tunable plasmon coupling. Various appealing and highly desirable properties are achieved for the resulting metaballs, including (i) chemical reversibility and fixation ability, (ii) stability against denaturant, salt, and molecular adsorbates, (iii) enriched and continuously tunable plasmonic hotspots, (iv) permeability to small guest molecules and antifoulingness against protein contaminates, and (v) Raman-enhancing and photocatalytic activities. Innovative applications are thus foreseeable for this emerging class of meta-assemblies in contrast to what is achieved by DNA-basepaired ones.

Influence of Core Type and Shell Thickness on Avian-Inspired Structural Colors Produced from Melanin Nanoparticle Assemblies

Hollow melanosomes found in iridescent bird feathers, including violet-backed starlings and wild turkeys, enable the generation of diverse structural colors. It has been postulated that the high refractive index (RI) contrast between melanin (1.74) and air (1.0) results in brighter and more saturated colors. This has led to several studies that have synthesized hollow synthetic melanin nanoparticles and fabricated colloidal nanostructures to produce synthetic structural colors. However, these studies use hollow nanoparticles with thin shells (<20 nm), even though shell thicknesses as high as 100 nm have been observed in natural melanosomes. Here, we combine experimental and computational approaches to examine the influence of the varying polydopamine (PDA, synthetic melanin) shell thickness (0-100 nm) and core material on structural colors. Experimentally, a concomitant change in overall particle size and RI contrast makes it difficult to interpret the effect of a hollow or solid core on color. Thus, we utilize finite-difference time-domain (FDTD) simulations to uncover the effect of shell thickness and core on structural colors. Our FDTD results highlight that hollow particles with thin shells have substantially higher saturation than same-sized solid and core-shell particles. These results would benefit a wide range of applications including paints, coatings, and cosmetics.

Exploiting the Potential of Magnetic Nanoparticles for Rapid Diagnosis Tests (RDTs): Nanoparticle-Antibody Conjugates and Color Development Strategies

Magnetic nanoparticles (MNPs) have emerged as a promising material in disease diagnostics due to their potential to enhance detection sensitivity, facilitate concentration and purification of target substances in diverse samples, and enable favorable color-based detection. In this study, antibody-conjugated MNPs were successfully synthesized and validated through two appropriate methods: the measurement of MNPs' size and the use of phosphatase methods. Additionally, three methods were suggested and implemented for developing color in MNPs-based immunoassay, including the formation of MNP aggregations, utilization of MNPs' peroxidase-like activity, and synthesis of dually-conjugated MNPs with both enzyme and antibody. In particular, color development utilizing nanoparticle aggregations was demonstrated to result in a more yellowish color as virus concentration increased, while the peroxidase activity of MNPs exhibited a proportional increase in color intensity as the MNP concentration increased. This observation suggests the potential applicability of quantitative analysis using these methods. Furthermore, effective concentration and purification of target substances were demonstrated through the collection of MNPs using an external magnetic field, irrespective of factors such as antibody conjugation, dispersion medium, or virus binding. Finally, based on the key findings of this study, a design proposal for MNPs-based immunoassay is presented. Overall, MNPs-based immunoassays hold significant potential for advancing disease diagnostics.

D-A Structured High-Performance Photothermal/Photodynamic Thionin-Synthetic Melanin Nanoparticles for Rapid Bactericidal and Wound Healing Effects

Synthesized melanin nanoparticles (SMNPs) are used as advanced photothermal materials. However, their internal structures are complex and disordered, and tuning the photothermal performance of nanoparticles is still a hot spot of concern. This article presents thionin (Th)-doped SMNPs, namely Th-SMNPs, which are the first SMNPs formed using the one-pot polymerization of Th with Levodopa. Th can undergo Michael addition and Schiff base reaction between indole dihydroxy/indolequinone and their oligomers to form donor-acceptor pairs in the structure to modulate the photothermal performance of SMNPs. Structural and spectroscopic analyses and density functional theory simulations further confirm the existence of the donor-acceptor structure. Th-SMNPs exhibit excellent total photothermal efficiency (34.49%) in the near-infrared region (808 nm), which is a 60% improvement compared to SMNPs. This allows Th-SMNPs to exhibit excellent photothermal performance at low power 808 nm laser irradiation. Meanwhile, Th not only enhances the photothermal properties of SMNPs, but also imparts photodynamic effects to SMNPs. Th-SMNPs can produce 1 O2 under 660 nm laser irradiation. A dual-function photothermal and photodynamic textile named Th-SMNPs@cotton is constructed based on Th-SMNPs, which can act as a rapid photothermal/photodynamic sterilization and is promising for wound healing treatment of bacterial infections under low-power dual laser irradiation.

Mechanism of structural colors in binary mixtures of nanoparticle-based supraballs

Inspired by structural colors in avian species, various synthetic strategies have been developed to produce noniridescent, saturated colors using nanoparticle assemblies. Nanoparticle mixtures varying in particle chemistry and size have additional emergent properties that affect the color produced. For complex multicomponent systems, understanding the assembled structure and a robust optical modeling tool can empower scientists to identify structure-color relationships and fabricate designer materials with tailored color. Here, we demonstrate how we can reconstruct the assembled structure from small-angle scattering measurements using the computational reverse-engineering analysis for scattering experiments method and use the reconstructed structure in finite-difference time-domain calculations to predict color. We successfully, quantitatively predict experimentally observed color in mixtures containing strongly absorbing nanoparticles and demonstrate the influence of a single layer of segregated nanoparticles on color produced. The versatile computational approach that we present is useful for engineering synthetic materials with desired colors without laborious trial-and-error experiments.

Bioinspired multiple-degrees-of-freedom responsive metasurface by high-entropy-alloy ribbons with hierarchical nanostructures for electromagnetic wave absorption

The compound eyes of the dragonfly, Pantala flavescens Fabricius, are covered by micro-scaled ocelli capable of sensing polarized light, an attractive property for radar stealth and counterreconnaissance. In this work, we fabricated biomimetic electromagnetic wave absorption materials (EAMs) by analyzing the covert information identifications of biological systems and focusing on the design of metastructures and microstructures. Several bionic metasurfaces with anisotropic double-V meta atoms made up of (FeCoNiSi_8.9Al_8.9)C_0.2 high-entropy-alloy (HEA) ribbons for multiple-degrees-of-freedom recognition and broadband absorption are presented. The covert phase, amplitude, and angular momentum of electromagnetic waves were controlled and recognized as information by manipulating the rotation angle θ of meta atoms. A vortex wave with a topological charge of 1 was generated to recognize linearly polarization and left- and right-handed circular polarization. In addition, the polarization conversion enhanced absorption. The hierarchical nanostructures of HEA ribbons give rise to suitable electromagnetic loss and a superior impedance match. Finally, inspired by the structure of compound eyes, the designed multilayer metamaterials realized effective absorption (reflection loss (RL) ≤  - 10 dB) within the 4.5-18 GHz regime under 2.8 mm thickness. These materials provide evidence for a new way for integrated EAMs and metamaterials.

Electromagnetic response of corrugated multilayer systems inspired by the Dione vanillae butterfly scales

Inspired by the microstructures in the wing scales of the butterfly Dione vanillae, we investigate the optical response of two multilayer structures, which include one or two corrugated interfaces. The reflectance is calculated using the C-method and is compared with that of a planar multilayer. We perform a detailed analysis of the influence of each geometric parameter and study the angular response, which is important for structures exhibiting iridescence. The results of this study aim to contribute to the design of multilayer structures with predetermined optical responses.

Nanostructure-free crescent-shaped microparticles as full-color reflective pigments

Structural colors provide a promising visualization with high color saturation, iridescent characteristics, and fade resistance. However, pragmatic uses are frequently impeded by complex manufacturing processes for sophisticated nanostructures. Here, we report a facile emulsion-templating strategy to produce crescent-shaped microparticles as structural color pigments. The micro-crescents exhibit brilliant colors under directional light originating from total internal reflections and optical interferences in the absence of periodic nanostructures while being transparent under ambient light. The colors are finely tunable by adjusting the size of the micro-crescents, which can be further mixed to enrich the variety. Importantly, the pre-defined convex surface secures high stability of colors and enables structural coloration on target surfaces through direct deposition as inks. We anticipate this class of nanostructure-free structural colorants is pragmatic as invisible inks in particular for anti-counterfeiting patches and color cosmetics with distinctive impressions due to low-cost, scalable manufacturing, unique optical properties, and versatility.

Biomimetic pheomelanin to unravel the electronic, molecular and supramolecular structure of the natural product

A robust route to synthetic pheomelanin gives insight into the electronic, molecular and supramolecular structure of the natural product, further advancing our understanding of this important subfamily of melanin.

Photonic Lignin with Tunable and Stimuli-Responsive Structural Color

Due to the growing sustainability and health requirements, structural color materials fabricated with functional natural polymers have attracted increasing attention in advanced optical and biomedical fields. Lignin has many attractive features such as great biocompatibility, ultraviolet resistance, antioxidant property, and thermostability, making it a promising natural resource to be fabricated as functional structural color materials. However, to date, the utilization of lignin as the building block for structural color materials is still a challenge due to its disordered structure. Herein, we present a strategy to transform disordered lignin into ordered "photonic lignin", in which monodisperse lignin colloidal spheres are prepared via solvent/antisolvent self-assembly, and then the periodic structure is constructed by centrifugal effect. The photonic lignin exhibits structural colors that are tunable by modulating the diameter of lignin colloidal spheres. We further demonstrate the application of photonic lignin as a natural polymer-based coating that shows bright, angle-independent, and stimuli-responsive structural colors. Moreover, the cytotoxicity assay indicates the excellent biocompatibility of photonic lignin with human skin, blood vessels, digestive systems, and other tissues, which demonstrates the great potential of photonic lignin in the applications such as implanted/wearable optical devices, advanced cosmetics, and smart food packaging.

Daytime Sub-Ambient Radiative Cooling with Vivid Structural Colors Mediated by Coupled Nanocavities

Daytime radiative cooling is a promising passive cooling technology for combating global warming. Existing daytime radiative coolers usually show whitish colors due to their high broadband solar reflectivity, which is not suitable for aesthetic demands and effective display. It is challenging to produce high-cooling performance materials with vivid colors because colors are often produced by the absorption of visible light, decreasing net cooling power. In this work, we design a series of colorful multilayered radiative coolers (CMRCs) consisting of an optimized selective emitter for cooling and coupled nanocavities for structural coloration, which can successfully delicately balance the trade-off between the chromaticity and cooling performance. By judiciously designing the geometric parameters and manipulating the coupling effect inside the coupled nanocavities, our coolers show sub-ambient cooling performance and a larger color gamut (occupying 17.7% sRGB area) than reported ones. We further fabricate CMRCs and demonstrate that they have temperature drops of 3.4-4.4 °C on average based on outdoor experiments. These CMRCs are promising in thermal management of electronic/optoelectronic devices and outdoor facilities.

Spray-Dried Photonic Balls with a Disordered/Ordered Hybrid Structure for Shear-Stress Indication

Optical microscale shear-stress indicator particles are of interest for the in situ recording of localized forces, e.g., during 3D printing or smart skins in robotic applications. Recently developed particle systems are based on optical responses enabled by integrated organic dyes. They thus suffer from potential chemical instability and cross-sensitivities toward humidity or temperature. These drawbacks can be circumvented using photonic balls as shear-stress indicator particles, which employ structural color as the element to record forces. Here, such photonic balls are prepared from silica and iron oxide nanoparticles via the scalable and fast spray-drying technique. Process parameters to create photonic balls with a disordered core and an ordered particle structure toward the exterior of the supraparticles are reported. This hybrid disordered-ordered structure is responsible for a color loss of the indicator particles during shear-stress application because of irreversible structural destruction. By adjusting the primary silica particle sizes, nearly all colors of the visible spectrum can be achieved and the sensitivity of the response to shear stress can be adjusted.

Hydrophobic Melanin via Post-Synthetic Modification for Controlled Self-Assembly

Allomelanin is a class of nitrogen-free melanin mostly found in fungi and, like all naturally occurring melanins, is hydrophilic. Herein, we develop a facile method to modify synthetic hydrophilic allomelanin to yield hydrophobic derivatives through post-synthetic modifications. Amine-functionalized molecules of various kinds can be conjugated to allomelanin nanoparticles under mild conditions with high loading efficiencies. Hydrophobicity is conferred by introducing amine-terminated alkyl groups with different chain lengths. We demonstrate that the resulting hydrophobic allomelanin nanoparticles undergo air/water interfacial self-assembly in a controlled fashion, which enables the generation of large-scale and uniform structural colors. This work provides an efficient and tunable surface chemistry modification strategy to broaden the scope of synthetic melanin structure and function beyond the known diversity found in nature.

Continuous resin refilling and hydrogen bond synergistically assisted 3D structural color printing

3D photonic crystals (PCs) have attracted extensive attention due to their unique optical properties. However, fabricating 3D PCs structure by 3D printing colloidal particles is limited by control of assembly under a fast-printing speed. Here, we employ continuous digital light processing (DLP) 3D printing strategy with hydrogen bonds assisted colloidal inks for fabricating well-assembled 3D PCs structures. Stable dispersion of colloidal particles inside UV-curable system induced by hydrogen bonding and suction force induced by continuous curing manner cooperatively realize the simultaneous macroscopic printing and microscopic particle assembly, which endows volumetric color property. Structural color can be well regulated by controlling the particle diameter and printing speed, through which various complex 3D structures with desired structural color distribution and optical light-guide properties are acquired. This 3D color construction approach shows great potential in customized jewelry accessories, decoration and optical device preparation, and will innovate the development of structural color.

Deconvoluting the Optical Response of Biocompatible Photonic Pigments

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.

Deconvoluting the Optical Response of Biocompatible Photonic Pigments

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.

Inkjet Printing of Structurally Colored Self-Assembled Colloidal Aggregates

Structurally colored materials offer increased stability, high biocompatibility, and a large variety of colors, which can hardly be reached simultaneously using conventional chemical pigments. However, for practical applications, such as inkjet printing, it is vital to compartmentalize these materials in small building blocks (with sizes ideally below 5 μm) and create "ready-to-use" inks. The latter can be achieved by using photonic balls (PB): spherical aggregates of nanoparticles. Here, we demonstrate, for the first time, how photonic ball dispersions can be used as inkjet printing inks. We use solvent drying techniques to manufacture structurally colored colloidal aggregates. The as-fabricated photonic balls are dispersed in pentanol to form ink. A custom-made inkjet printing platform equipped with an industrial printhead and recirculation fluidic system is used to print complex structurally colored patterns. We increase color purity and suppress multiple scattering by introducing carbon black as a broadband light absorber.

Biomimetic Chiral Photonic Materials with Tunable Metallic Colorations Prepared from Chiral Melanin-like Nanorods for UV Shielding, Humidity Sensing, and Cosmetics

Many biological species combine the helical organization of cellulose or chitin microfibrils with broadband light absorption of black melanin to produce brilliant structural colors with metallic and glossy effects and other diverse functions. In this work, based on core-shell CNC@PDA chiral nanorods consisting of cellulose nanocrystals (CNCs) as the core and melanin-like polydopamine (PDA) as the shell that can form well-defined chiral liquid crystal phases, we report chiral photonic materials that closely mimic the unique coloration mechanisms and functionalities mastered by several biological species. The photonic films formed by such single CNC@PDA nanorods have brilliant iridescent structural colors originating from selective reflection of circularly polarized lights by the helical organization of CNC@PDAs across the films. Furthermore, the colors of such films have background-independent brightness, high visibility, and metallic effects that arise from the light absorption of the PDA component. Especially, the color ranges and metallic effects of the films can be conveniently tuned by varying the thickness of the PDA shell. In addition, the UV absorption and hygroscopic properties of PDA endow these CNC@PDA films with efficient broadband UV shielding and sensitive humidity-induced dynamic color changes. Due to the mussel-like superior adhesion of PDA, CNC@PDA-based photonic coatings can be formed conformably onto diverse kinds of substrates. A shiny eye shadow with viewing angle-dependent colorful patterns was used to demonstrate the potential applications. With combinations of multiple unique properties in one photonic material fabricated from a single building block, these CNC@PDA-based films are expected to have potential applications in cosmetics, UV protection, anticounterfeiting, chiral reflectors, etc.

Bio-inspired, bimetal ZIF-derived hollow carbon/MXene microstructure aim for superior microwave absorption

Electromagnetic pollution has become an increasingly important problem which has drawbacks to both the accurate operation of the electronic facilities and the safety of human beings. To alleviate and eliminate electromagnetic irradiation, it is inevitable to design microwave absorption materials with desirable absorption intensity and broad effective frequency bandwidth. The combination of carbon-based materials and magnetic materials is an adoptable strategy to perform remarkable microwave absorption performance, while the microstructure should not be ignored. Inspired by the electromagnetic response behaviors of the microstructure from the leafhopper, the hetero-microstructure with hollow void is constructed by adopting bimetal ZIF as the precursor, followed by an interfacial tailoring strategy through electrostatic assembling and calcinating process, which enhances the microwave absorption performance by integrating the merits between the components and the micro-structure. The minimum value of reflection loss achieved -76.40 dB at 7.50 GHz under filler loading of 20% with the thickness of 2.92 mm. Besides, the effective absorption bandwidth could be tailored from 3.55 to 18 GHz among different thicknesses as required. The bio-inspired strategy is validated as a promising method, exhibiting great potential in the designing of the next-generation microwave absorber.

Spatiotemporal Control of Melanin Synthesis in Liquid Droplets

Melanins are natural biopolymers that have remarkable properties including UV-protection, coloration, and antioxidant activity. Their biosynthesis is regulated both spatially and temporally and involves supramolecular templating and compartmentalization of enzymes and reactants within specialized organelles called melanosomes. In contrast, the laboratory-based bulk synthesis of melanin by tyrosine or dopamine oxidation is a poorly controlled process, resulting in materials with undefined properties. Inspired by the pigment's biosynthesis, we developed a methodology to spatiotemporally regulate melanin formation in liquid droplets. The spatial control is achieved by sequestration of the reaction in dextran-rich droplets of a polyethylene glycol/dextran aqueous two-phase system, where the use of a photocleavable protected tyrosine provides a temporal control over its enzymatic oxidation-polymerization. We show that the liquid droplets allow for confined local reactivity as they serve as reaction centers for melanin synthesis and compartmentalize the melanin product. This methodology opens tremendous opportunities for applications in skincare and biomedicine.

Coloration in Supraparticles Assembled from Polyhedral Metal-Organic Framework Particles

Supraparticles are spherical colloidal crystals prepared by confined self‐assembly processes. A particularly appealing property of these microscale structures is the structural color arising from interference of light with their building blocks. Here, we assemble supraparticles with high structural order that exhibit coloration from uniform, polyhedral metal–organic framework (MOF) particles. We analyse the structural coloration as a function of the size of these anisotropic building blocks and their internal structure. We attribute the angle‐dependent coloration of the MOF supraparticles to the presence of ordered, onion‐like layers at the outermost regions. Surprisingly, even though different shapes of the MOF particles have different propensities to form these onion layers, all supraparticle dispersions show well‐visible macroscopic coloration, indicating that local ordering is sufficient to generate interference effects.

Rapid Assembly of Magnetoplasmonic Photonic Arrays for Brilliant, Noniridescent, and Stimuli-Responsive Structural Colors

There are usually trade-offs between maximizing the color saturation and brightness and minimizing the angle-dependent effect in structural colors. Here, a magnetic field-induced assembly for the rapid formation of scalable, uniform amorphous photonic arrays (APAs) featuring unique structural colors is demonstrated. The magnetic field plays a fundamental role in photonic film formation, making this assembly technology versatile for developing structural color patterns on arbitrary substrates. The synergistic combination of surface plasmonic resonance of the Ag core and broadband light absorption of high refractive index (RI) Fe₃ O₄ shell in hybrid magnetoplasmonic nanoparticles (MagPlas NPs) enables breaking the trade-offs to produce brilliant, noniridescent structural colors with high tunability and responsiveness. These features enable the fabrication of various types of highly sensitive and reliable colorimetric sensors for naked-eye detection without sophisticated instruments. Furthermore, large-scale structural color patterns are effortlessly achieved, demonstrating the high potential of the present approach for full-spectrum displays, active coatings, and rewritable papers.

Iridescent coating of graphene oxide on various substrates

Two-dimensional nanomaterials have been incorporated into coating layers for exceptional properties in mechanic toughness, electronics, thermology and optics. Graphene oxide (GO), however, was greatly hindered by its strong adsorption within visible wavelength and hereby the intrinsic dark color at the solid state. Herein, we found a unique aqueous mixture of GO containing sodium dodecyl sulfate and l-ascorbic acid. It enabled to produce iridescent coating layers with tunable thickness of 0.3-50 μm on both hydrophilic and hydrophobic substrates (e.g., glass, aluminum foil, polytetrafluoroethylene), through brushing, liquid-casting, dipping and writing. Their iridescence could be further tuned by incorporating MXene nanosheets. And their mechanical properties could be enhanced by certain synthetic polymers (e.g., polyvinyl alcohol and polyethylene glycol). Their sensitivity to heat, laser and water also benefited to pattern the coating layers. Furthermore, by controlling laser intensity, the domain color could be changed (e.g., green to blue). Thus, this study may pave a new pathway of producing iridescent coatings of graphene oxide in a large scale for practical applications.

Self-Assembly of Upconversion Nanoparticles Based Materials and Their Emerging Applications

In the past few decades, significant progress of the conventional upconversion nanoparticles (UCNPs) based nanoplatform has been achieved in many fields, and with the development of nanoscience and nanotechnology, more and more complex situations need a UCNPs based nanoplatform having multifunctions for specific multimodal or multiplexed applications. Through self-assembly, different UCNPs or UCNPs with other materials could be combined together within an entity. It is more like an ideal UCNPs nanoplatform, a unique system with the properties defined by its individual components as well as by the morphology of the composite. Various designs can show their different desired properties depending on the application situation. This review provides a complete summary on the optimization of the synthesis method for the recently designed UCNPs assemblies and summarizes various applications, including dual-modality cell imaging, molecular delivery, detection, and programmed control therapy. The challenges and limitations the UCNPs assembly faces and the potential solutions in this field are also presented.

Tunable Assembly of Organic-Inorganic Molecules into Hierarchical Superstructures as Ligase Mimics for Enhancing Tumor Photothermal Therapy

The assembly of molecules into hierarchical superstructures is ubiquitous in the construction of novel geometrically complex hierarchical superstructures, attracting great attention. Herein, a metal-ligand cross-linking strategy is developed for the fabrication of ferric ion-dopamine coordination hierarchical superstructures. A range of superstructures with highly complex morphologies, such as flower-like, octopus-like, and hedgehog-like superstructures, are synthesized. The mechanism for formation of hierarchical superstructures involves the pre-cross-linking of ferric ion with dopamine molecules, the fabrication of iron-dopamine precursors aggregated into the spherical aggregates, the nanoscale aggregates sintering and ordering themselves upon equilibration, the nanodots polymerizing into nanorods, and finally the nanorods self-assembling into hierarchical superstructures. In-depth research illustrates that as the permittivity (ξ) of the reaction system increases, the resulting hierarchical superstructures tend to converge into spherical shape. As a proof of concept, the 0D nanospheres, 1D nanorods, and 3D hierarchical superstructures are fabricated through adjusting system permittivity. The hierarchical superstructure is utilized as peroxidase-like ligase mimics to enhance the effect of tumor photothermal treatment. Further in vitro and in vivo assays demonstrate that the hierarchical superstructure can effectively ablate tumor cells. This work opens new horizons in hierarchical superstructures with complex architectures, and has great potential in nanozymology, biomedical science, and catalysis.

Structural Color Spectral Response of Dense Structures of Discoidal Particles Generated by Evaporative Assembly

Structural color─optical response due to light diffraction or scattering from submicrometer-scale structures─is a promising means for sustainable coloration. To expand the functionality of structural color, we introduce discoidal shape anisotropy into colloidal particles and characterize how structural color reflection can be engineered. Uniaxial compression of spheres is used to prepare discoids with varying shape anisotropy and particle size. Discoids are assembled into thin films by evaporation. We find that structural color of assembled films displays components due to diffuse backscattering and multilayer reflection. As discoids become more anisotropic, the assembled structure is more disordered. The multilayer reflection is suppressed─peak height becomes smaller and peak width broader; thus, the color is predominantly from diffuse backscattering. Finally, the discoid structural color can be tuned by varying particle size and has low dependence on viewing angle. We corroborate our results by comparing experimental microstructures and measured reflection spectra with Monte Carlo simulations and calculated spectra by finite-difference time-domain simulation. Our findings demonstrate that the two tunable geometries of discoids─size and aspect ratio─generate different effects on spectral response and therefore can function as independent design parameters that expand possibilities for producing noniridescent structural color.

Co-Assembly of Colloids and Eumelanin Nanoparticles in Droplets for Structural Pigments with High Saturation

Colloidal crystals have been used to develop structural colors. However, incoherent scattering causes the colors to turn whitish, reducing the color saturation. To overcome the problem, light-absorbing additives have been incorporated. Although various additives have been used, most of them are not compatible with a direct co-assembly with common colloids in aqueous suspensions. Here, the authors suggest eumelanin nanoparticles as a new additive to enhance the color chroma. Eumelanin nanoparticles are synthesized to have diameters of several nanometers by oxidative polymerization of precursors in basic solutions. The nanoparticles carry negative charges and do not weaken the electrostatic repulsion among same-charged polystyrene particles when they are added to aqueous suspensions. To prove the effectiveness of eumelanin as a saturation enhancer, the authors produce photonic balls through direct co-assembly of polystyrene and eumelanin using water-in-oil emulsion droplets, while varying the weight ratio of eumelanin to polystyrene. The high crystallinity of colloidal crystals is preserved for the ratio up to at least 1/50 as the eumelanin does not perturb the crystallization. The eumelanin effectively suppresses incoherent scattering while maintaining the strength of structural resonance at an optimum ratio, improving color chroma without compromising brightness.

Multicolor Photonic Pigments for Rotation-Asymmetric Mechanochromic Devices

Photonic crystals are extensively explored to replace inorganic pigments and organic dyes as coloring elements in printing, painting, sensing, and anti-counterfeiting due to their brilliant structural colors, chemical stability, and environmental friendliness. However, most existing photonic-crystal-based pigments can only display monochromatic colors once made, and generating multicolors has to start with designing different building blocks. Here, a novel photonic pigment featuring highly tunable structural colors in the entire visible spectrum, made by the magnetic assembly of monodisperse nanorods into body-centered-tetragonal photonic crystals, is reported. Their prominent magnetic and crystal anisotropy makes it efficient to generate multicolors using one photonic pigment by magnetically controlling the crystal orientation. Further, the combination of angle-dependent diffraction and magnetic orientation control enables the design of rotation-asymmetric photonic films that display distinct patterns and encrypted information in response to rotation. The efficient multicolor generation through precise orientational control makes this novel photonic pigment promising in developing high-performance structural-colored materials and optical devices.

Enhancing the Refractive Index of Polymers with a Plant-Based Pigment

Polymers are essential components of many nanostructured materials. However, the refractive indices of common polymers fall in a relatively narrow range between 1.4 and 1.6. Here, it is demonstrated that loading commercially-available polymers with large concentrations of a plant-based pigment can effectively enhance their refractive index. For polystyrene (PS) loaded with 67 w/w% β-carotene (BC), a peak value of 2.2 near the absorption edge at 531 nm is achieved, while maintaining values above 1.75 across longer wavelengths of the visible spectrum. Despite high pigment loadings, this blend maintains the thermoforming ability of PS, and BC remains molecularly dispersed. Similar results are demonstrated for the plant-derived polymer ethyl cellulose (EC). Since the refractive index enhancement is intimately connected to the introduction of strong absorption, it is best suited to applications where light travels short distances through the material, such as reflectors and nanophotonic systems. Enhanced reflectance from films is experimentally demonstrated, as large as sevenfold for EC at selected wavelengths. Theoretical calculations highlight that this simple strategy can significantly increase light scattering by nanoparticles and enhance the performance of Bragg reflectors.

Influence of Surfactant-Mediated Interparticle Contacts on the Mechanical Stability of Supraparticles

Colloidal supraparticles are micron-scale spherical assemblies of uniform primary particles, which exhibit emergent properties of a colloidal crystal, yet exist as a dispersible powder. A prerequisite to utilize these emergent functionalities is that the supraparticles maintain their mechanical integrity upon the mechanical impacts that are likely to occur during processing. Understanding how the internal structure relates to the resultant mechanical properties of a supraparticle is therefore of general interest. Here, we take the example of supraparticles templated from water/fluorinated oil emulsions in droplet-based microfluidics and explore the effect of surfactants on their mechanical properties. Stable emulsions can be generated by nonionic block copolymers consisting of a hydrophilic and fluorophilic block and anionic fluorosurfactants widely available under the brand name Krytox. The supraparticles formed in the presence of both types of surfactants appear structurally similar, but differ greatly in their mechanical properties. While the nonionic surfactant induces superior mechanical stability and ductile fracture behavior, the anionic Krytox surfactant leads to weak supraparticles with brittle fracture. We complement this macroscopic picture with Brillouin light spectroscopy that is very sensitive to the interparticle contacts for subnanometer-thick adsorbed layers atop of the nanoparticle. While the anionic Krytox does not significantly affect the interparticle bonds, the amphiphilic nonionic surfactant drastically strengthens these bonds to the point that individual particle vibrations are not resolved in the experimental spectrum. Our results demonstrate that seemingly subtle changes in the physicochemical properties of supraparticles can drastically impact the resultant mechanical properties.

Mechanics of colloidal supraparticles under compression

Colloidal supraparticles are finite, spherical assemblies of many primary particles. To take advantage of their emergent functionalities, such supraparticles must retain their structural integrity. Here, we investigate their size-dependent mechanical properties via nanoindentation. We find that the deformation resistance inversely scales with the primary particle diameter, while the work of deformation is dependent on the supraparticle diameter. We adopt the Griffith theory to such particulate systems to provide a predictive scaling to relate the fracture stress to the geometry of supraparticles. The interplay between primary particle material and cohesive interparticle forces dictates the mechanical properties of supraparticles. We find that enhanced stability, associated with ductile fracture, can be achieved if supraparticles are engineered to dissipate more energy via deformation of primary particles than breaking of interparticle bonds. Our work provides a coherent framework to analyze, predict, and design the mechanical properties of colloidal supraparticles.

Melanin-based structural coloration of birds and its biomimetic applications

Melanin has been a widely researched pigment by scientists for decades as it is undoubtedly the most ubiquitous and ancient pigment found in nature. Melanin plays very significant roles in structural plumage colors in birds: it has visible light-absorbing capabilities, and nanoscale structures can be formed by self-assembling melanin granules. Herein, we review recent progress on melanin-based structural coloration research. We hope that this review will provide current understanding of melanin's structural and optical properties, natural coloration mechanisms, and biomimetic methods to implement artificial melanin-based structural colors.

Rayleigh method adapted for the study of the optical response of natural photonic structures

To study the electromagnetic response of natural structures that exhibit interesting optical properties, we developed a computational tool to solve the problem of electromagnetic scattering by a rough interface between two isotropic media, based on the Rayleigh method. The key aspect of the developed formalism is its capability of introducing the interface profile within the code by means of a digitalized image of the structure, which can be either obtained from an electron microscopy image or simply by design according to the complexity of the scattering surface. As application examples, we show the results obtained for surfaces taken directly from microscopy images of two different biological species. This approach constitutes a fundamental step in order to model the electromagnetic response of natural photonic structures.

Nanocapsules with excellent biocompatibility and stability in protein solutions

Silica nanocapsules (SiO₂NCs) are usually prepared with cationic surfactants that are not cytocompatible. Dialysis can be used to remove surfactants but leads to instability of the SiO₂NCs when they are in the presence of proteins or biological media. Herein, SiO₂NCs stabilized with a reactive surfactant are synthesized to prevent leaching upon dialysis. The SiO₂NCs show superior stability and biocompatibility compared with SiO₂NCs prepared with conventional surfactants. The SiO₂NCs can be used in self-healing materials, smart agriculture and biomedical applications.

Investigating the trade-off between color saturation and angle-independence in photonic glasses

Photonic glasses-isotropic structures with short-range correlations-can produce structural colors with little angle-dependence, making them an alternative to dyes in applications such as cosmetics, coatings, and displays. However, the low angle-dependence is often accompanied by low color saturation. To investigate how the short-range correlations affect the trade-off between saturation and angle-independence, we vary the structure factor and use a Monte Carlo model of multiple scattering to investigate the resulting optical properties. We use structure factors derived from analytical models and calculated from simulations of disordered sphere packings. We show that the trade-off is controlled by the first peak of the structure factor. It is possible to break the trade-off by tuning the width of this peak and controlling the sample thickness. Practically, this result shows that the protocol used to pack particles into a photonic glass is important to the optical properties.

Rapid Responsive Mechanochromic Photonic Pigments with Alternating Glassy-Rubbery Concentric Lamellar Nanostructures

Photonic pigment particles prepared via self-assembly have been suffering from their poor mechanical performances; i.e., they can easily be damaged and lose structural color under a compression force. This greatly limits their uses as mechanochromic pigments. Here, a nanoscale concentric lamellar structure of alternating glassy-rubbery microdomains is successfully created within photonic microparticles through a confined self-assembly and photo-cross-linking strategy. The glassy domain is composed of polystyrene, and cross-linked bottlebrush polydimethylsiloxane served as the supersoft elastic domain. The obtained photonic structure not only shows large deformation and visible color changes under a loaded compression force but also rapidly recovers to its original state in less than 1 s (∼0.16 s) upon unloading. Continuously loading-unloading micro compression test indicates that no obvious damage can be identified after 250 cycles, indicating the high durability of the pigments against deformation. These pigments with different reflected colors are simply obtained using bottlebrush block copolymer formulations with tunable weight percentages of polymer additives. The mechanical robust photonic pigments may be useful in many important applications.