Structure, function, and self-assembly of single network gyroid (I4132) photonic crystals in butterfly wing scales

Thermotropic "Plumber's Nightmare"-A Tight Liquid Organic Double Framework

Gyroid, double diamond and the body-centred "Plumber's nightmare" are the three most common bicontinuous cubic phases in lyotropic liquid crystals and block copolymers. While the first two are also present in solvent-free thermotropics, the latter had never been found. Containing six-fold junctions, it was unlikely to form in the more common phases with rod-like cores normal to the network columns, where a maximum of four branches can join at a junction. The solution has therefore been sought in side-branched mesogens that lie in axial bundles joined at their ends by flexible "hinges". But for the tightly packed double framework, geometric models predicted that the side-chains should be very short. The true Plumber's nightmare reported here, using fluorescent dithienofluorenone rod-like mesogen, has been achieved with, indeed, no side chains at all, but with 6 flexible end-chains. Such molecules normally form columnar phases, but the key to converting a complex helical column-forming mesogen into a framework-forming one was the addition of just one methyl group to each pendant chain. A geometry-based explanation is given.

Design and study of additively manufactured Three periodic minimal surface (TPMS) structured porous titanium interbody cage

Objective

TPMS porous structures have adjustable stiffness, a smooth surface, and highly connected pores, which help avoid stress concentration within the dot-matrix structure and promote cell adhesion and proliferation. A cervical interbody cage based on this type of porous structure was designed and fabricated, and its mechanical properties and biocompatibility were evaluated.

Methods

TPMS porous structures have adjustable stiffness, a smooth surface, and highly connected pores, which help avoid stress concentration within the dot-matrix structure and promote cell adhesion and proliferation. A cervical interbody cage based on this type of porous structure was designed and fabricated, and its mechanical properties and biocompatibility were evaluated.

Results

The volume fraction of the 3D-printed TC4-based Tubular-G structure was linearly related to compressive strength. Adjusting the volume fraction resulted in a Tubular-G structure with a modulus and yield strength similar to human bone, without stress concentration within the structure. The designed and fabricated TC4-based Tubular-G porous cervical interbody cage demonstrated excellent anti-sagging properties and biocompatibility.

Conclusions

The volume fraction of the 3D-printed TC4-based Tubular-G structure was linearly related to compressive strength. Adjusting the volume fraction resulted in a Tubular-G structure with a modulus and yield strength similar to human bone, without stress concentration within the structure. The designed and fabricated TC4-based Tubular-G porous cervical interbody cage demonstrated excellent anti-sagging properties and biocompatibility.

Elucidating nanostructural organization and photonic properties of butterfly wing scales using hyperspectral microscopy

Biophotonic nanostructures in butterfly wing scales remain fascinating examples of biological functional materials, with intriguing open questions with regard to formation and evolutionary function. One particularly interesting butterfly species, Erora opisena (Lycaenidae: Theclinae), develops wing scales that contain three-dimensional photonic crystals that closely resemble a single gyroid geometry. Unlike most other gyroid-forming butterflies, E. opisena develops discrete gyroid crystallites with a pronounced size gradient hinting at a developmental sequence frozen in time. Here, we present a novel application of a hyperspectral (wavelength-resolved) microscopy technique to investigate the ultrastructural organization of these gyroid crystallites in dry, adult wing scales. We show that reflectance corresponds to crystallite size, where larger crystallites reflect green wavelengths more intensely; this relationship could be used to infer size from the optical signal. We further successfully resolve the red-shifted reflectance signal from wing scales immersed in refractive index liquids with varying refractive index, including values similar to water or cytosol. Such photonic crystals with lower refractive index contrast may be similar to the hypothesized nanostructural forms in the developing butterfly scales. The ability to resolve these fainter signals hints at the potential of this facile light microscopy method for in vivo analysis of nanostructure formation in developing butterflies.

A Versatile Synthesis Platform Based on Polymer Cubosomes for a Library of Highly Ordered Nanoporous Metal Oxides Particles

Polymer cubosomes (PCs) have well-defined inverse bicontinuous cubic mesophases formed by amphiphilic block copolymer bilayers. The open hydrophilic channels, large periods, and robust physical properties of PCs are advantageous to many host-guest interactions and yet not fully exploited, especially in the fields of functional nanomaterials. Here, the self-assembly of poly(ethylene oxide)-block-polystyrene block copolymers is systematically investigated and a series of robust PCs is developed via a cosolvent method. Ordered nanoporous metal oxide particles are obtained by selectively filling the hydrophilic channels of PCs via an impregnation strategy, followed by a two-step thermal treatment. Based on this versatile PC platform, the general synthesis of a library of ordered porous particles with different pore structures3 ¯ $\bar{3}$ 3 ¯ $\bar{3}$ , tunable large pore size (18-78 nm), high specific surface areas (up to 123.3 m2 g-1 for WO3) and diverse framework compositions, such as transition and non-transition metal oxides, rare earth chloride oxides, perovskite, pyrochlore, and high-entropy metal oxides is demonstrated. As typical materials obtained via this method, ordered porous WO3 particles have the advantages of open continuous structure and semiconducting properties, thus showing superior gas sensing performances toward hydrogen sulfide.

Local Structural Features Elucidate Crystallization of Complex Structures

Complex crystal structures are composed of multiple local environments, and how this type of order emerges spontaneously during crystal growth has yet to be fully understood. We study crystal growth across various structures and along different crystallization pathways, using self-assembly simulations of identical particles that interact via multiwell isotropic pair potentials. We apply an unsupervised machine learning method to features from bond-orientational order metrics to identify different local motifs present during a given structure's crystallization process. In this manner, we distinguish different crystallographic sites in highly complex structures. Tailoring this order parameter to structures of varying complexity and coordination number, we study the emergence of local order along a multistep crystal growth pathway─from a low-density fluid to a high-density, supercooled amorphous liquid droplet and to a bulk crystal. We find a consistent under-coordination of the liquid relative to the average coordination number in the bulk crystal. We use our order parameter to analyze the geometrically frustrated growth of a Frank-Kasper phase and discover how structural defects compete with the formation of crystallographic sites that are more high-coordinated than the liquid environments. The method presented here for classifying order on a particle-by-particle level has broad applicability to future studies of structural self-assembly and crystal growth, and they can aid in the design of building blocks and for targeting pathways of formation of soft-matter structures.

Living jewels: iterative evolution of iridescent blue leaves from helicoidal cell walls

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.

Nonaffinity of Liquid Networks and Bicontinuous Mesophases

Amphiphiles self-assemble into a variety of bicontinuous mesophases whose equilibrium structures take the form of high-symmetry cubic networks. Here, we show that the symmetry-breaking distortions in these systems give rise to anomalously large, nonaffine collective deformations, which we argue to be a generic consequence of "mass equilibration" within deformed networks. We propose and study a minimal "liquid network" model of bicontinuous networks, in which acubic distortions are modeled by the relaxation of residually stressed mechanical networks with constant-tension bonds. We show that nonaffinity is strongly dependent on the valency of the network as well as the degree of strain-softening or strain-stiffening tension in the bonds. Taking diblock copolymer melts as a model system, liquid network theory captures quantitative features of two bicontinuous phases based on comparison with self-consistent field theory predictions and direct experimental characterization of acubic distortions, which are likely to be pronounced in soft amphiphilic systems more generally.

The actin cytoskeleton plays multiple roles in structural colour formation in butterfly wing scales

Vivid structural colours in butterflies are caused by photonic nanostructures scattering light. Structural colours evolved for numerous biological signalling functions and have important technological applications. Optically, such structures are well understood, however insight into their development in vivo remains scarce. We show that actin is intimately involved in structural colour formation in butterfly wing scales. Using comparisons between iridescent (structurally coloured) and non-iridescent scales in adult and developing H. sara, we show that iridescent scales have more densely packed actin bundles leading to an increased density of reflective ridges. Super-resolution microscopy across three distantly related butterfly species reveals that actin is repeatedly re-arranged during scale development and crucially when the optical nanostructures are forming. Furthermore, actin perturbation experiments at these later developmental stages resulted in near total loss of structural colour in H. sara. Overall, this shows that actin plays a vital and direct templating role during structural colour formation in butterfly scales, providing ridge patterning mechanisms that are likely universal across lepidoptera.

Collective Spin-Wave Dynamics in Gyroid Ferromagnetic Nanostructures

Expanding upon the burgeoning discipline of magnonics, this research elucidates the intricate dynamics of spin waves (SWs) within three-dimensional nanoenvironments. It marks a shift from traditionally used planar systems to exploration of magnetization configurations and the resulting dynamics within 3D nanostructures. This study deploys micromagnetic simulations alongside ferromagnetic resonance measurements to scrutinize magnetic gyroids, periodic chiral configurations composed of chiral triple junctions with a period in nanoscale. Our findings uncover distinctive attributes intrinsic to the gyroid network, most notably the localization of collective SW excitations and the sensitivity of the gyroid's ferromagnetic response to the orientation of the static magnetic field, a correlation closely tied to the crystallographic alignment of the structure. Furthermore, we show that for the ferromagnetic resonance, multidomain gyroid films can be treated as a magnonic material with effective magnetization scaled by its filling factor. The implications of our research carry the potential for practical uses such as an effective, metamaterial-like substitute for ferromagnetic parts and lay the groundwork for radio frequency filters. The growing areas of 3D magnonics and spintronics present exciting opportunities to investigate and utilize gyroid nanostructures for signal processing purposes.

Limits of economy and fidelity for programmable assembly of size-controlled triply periodic polyhedra

We propose and investigate an extension of the Caspar-Klug symmetry principles for viral capsid assembly to the programmable assembly of size-controlled triply periodic polyhedra, discrete variants of the Primitive, Diamond, and Gyroid cubic minimal surfaces. Inspired by a recent class of programmable DNA origami colloids, we demonstrate that the economy of design in these crystalline assemblies-in terms of the growth of the number of distinct particle species required with the increased size-scale (e.g., periodicity)-is comparable to viral shells. We further test the role of geometric specificity in these assemblies via dynamical assembly simulations, which show that conditions for simultaneously efficient and high-fidelity assembly require an intermediate degree of flexibility of local angles and lengths in programmed assembly. Off-target misassembly occurs via incorporation of a variant of disclination defects, generalized to the case of hyperbolic crystals. The possibility of these topological defects is a direct consequence of the very same symmetry principles that underlie the economical design, exposing a basic tradeoff between design economy and fidelity of programmable, size controlled assembly.

Construction of the single-diamond-structured titania scaffold-Recreation of the holy grail photonic structure

As one of the most stunning biological nanostructures, the single-diamond (SD) surface discovered in beetles and weevils exoskeletons possesses the widest complete photonic bandgap known to date and is renowned as the "holy grail" of photonic materials. However, the synthesis of SD is difficult due to its thermodynamical instability compared to the energetically favoured bicontinuous double diamond and other easily formed lattices; thus, the artificial fabrication of SD has long been a formidable challenge. Herein, we report a bottom-up approach to fabricate SD titania networks via a one-pot cooperative assembly scenario employing the diblock copolymer poly(ethylene oxide)-block-polystyrene as a soft template and titanium diisopropoxide bis(acetylacetonate) as an inorganic precursor in a mixed solvent, in which the SD scaffold was obtained by kinetically controlled nucleation and growth in the skeletal channels of the diamond minimal surface formed by the polymer matrix. Electron crystallography investigations revealed the formation of tetrahedrally connected SD frameworks with the space group Fd [Formula: see text] m in a polycrystalline anatase form. A photonic bandgap calculation showed that the resulting SD structure has a wide and complete bandgap. This work solves the complex synthetic enigmas and offers a frontier in hyperbolic surfaces, biorelevant materials, next-generation optical devices, etc.

Composite material in the sea urchin Cidaris rugosa: ordered and disordered micrometre-scale bicontinuous geometries

The sponge-like biomineralized calcite materials found in echinoderm skeletons are of interest in terms of both structure formation and biological function. Despite their crystalline atomic structure, they exhibit curved interfaces that have been related to known triply periodic minimal surfaces. Here, we investigate the endoskeleton of the sea urchin Cidaris rugosa that has long been known to form a microstructure related to the Primitive surface. Using X-ray tomography, we find that the endoskeleton is organized as a composite material consisting of domains of bicontinuous microstructures with different structural properties. We describe, for the first time, the co-occurrence of ordered single Primitive and single Diamond structures and of a disordered structure within a single skeletal plate. We show that these structures can be distinguished by structural properties including solid volume fraction, trabeculae width and, to a lesser extent, interface area and mean curvature. In doing so, we present a robust method that extracts interface areas and curvature integrals from voxelized datasets using the Steiner polynomial for parallel body volumes. We discuss these very large-scale bicontinuous structures in the context of their function, formation and evolution.

Direct-ink-write cross-linkable bottlebrush block copolymers for on-the-fly control of structural color

Additive manufacturing capable of controlling and dynamically modulating structures down to the nanoscopic scale remains challenging. By marrying additive manufacturing with self-assembly, we develop a UV (ultra-violet)-assisted direct ink write approach for on-the-fly modulation of structural color by programming the assembly kinetics through photo-cross-linking. We design a photo-cross-linkable bottlebrush block copolymer solution as a printing ink that exhibits vibrant structural color (i.e., photonic properties) due to the nanoscopic lamellar structures formed post extrusion. By dynamically modulating UV-light irradiance during printing, we can program the color of the printed material to access a broad spectrum of visible light with a single ink while also creating color gradients not previously possible. We unveil the mechanism of this approach using a combination of coarse-grained simulations, rheological measurements, and structural characterizations. Central to the assembly mechanism is the matching of the cross-linking timescale with the assembly timescale, which leads to kinetic trapping of the assembly process that evolves structural color from blue to red driven by solvent evaporation. This strategy of integrating cross-linking chemistry and out-of-equilibrium processing opens an avenue for spatiotemporal control of self-assembled nanostructures during additive manufacturing.

Coarse-Grained Molecular Simulation of Bolapolyphiles with a Multident Lateral Chain: Formation and Structural Analysis of Cubic Network Phases

Bolapolyphiles constitute a versatile class of materials with a demonstrated potential to form a wide variety of complex ordered mesophases. In particular, cubic network phases (like the gyroid, primitive, and diamond phases) have been a target of many studies for their ability to create percolating 3D nanosized channels. In this study, molecular simulations are used to explore the phase behavior of bolapolyphiles containing a rigid rodlike core, associating hydrophilic core ends and a hydrophobic side chain with a multident architecture, i.e., where the branching pattern can vary from bident (two branches) to hexadent (six branches). Upon network phase formation, its skeleton is made up of "nodes" populated by the core ends and "struts" populated by the cores. It is shown that, by varying the side chain length, branching pattern, and attachment point to the core, one can alter the crowding around the cores and hence tune the nodal size and nodal valence (i.e., number of connecting struts) which lead to different types of network morphologies. For example, for a fixed total side chain length, having more branches generates a stronger crowding around the molecular core, driving them to form bundlelike domains with curvier interfaces that result in thinner struts. Also, attaching the lateral chain closer to one core end breaks the symmetry between the environments around the two core ends, leading to networks with bimodal nodal sizes. Importantly, since the characterization of (ordered or partially ordered) network phases is challenging given the potential incompatibilities between the simulation box size with the structure's space group periodic symmetry and the effect of morphological defects, a detailed framework is presented to analyze and fully characterize the unit cell parameters and structure factor of such systems.

A meta-analysis of butterfly structural colors: their color range, distribution and biological production

Butterfly scales are among the richest natural sources of optical nanostructures, which produce structural color and iridescence. Several recurring nanostructure types have been described, such as ridge multilayers, gyroids and lower lamina thin films. While the optical mechanisms of these nanostructure classes are known, their phylogenetic distributions and functional ranges have not been described in detail. In this Review, we examine a century of research on the biological production of structural colors, including their evolution, development and genetic regulation. We have also created a database of more than 300 optical nanostructures in butterflies and conducted a meta-analysis of the color range, abundance and phylogenetic distribution of each nanostructure class. Butterfly structural colors are ubiquitous in short wavelengths but extremely rare in long wavelengths, especially red. In particular, blue wavelengths (around 450 nm) occur in more clades and are produced by more kinds of nanostructures than other hues. Nanostructure categories differ in prevalence, phylogenetic distribution, color range and brightness. For example, lamina thin films are the least bright; perforated lumen multilayers occur most often but are almost entirely restricted to the family Lycaenidae; and 3D photonic crystals, including gyroids, have the narrowest wavelength range (from about 450 to 550 nm). We discuss the implications of these patterns in terms of nanostructure evolution, physical constraint and relationships to pigmentary color. Finally, we highlight opportunities for future research, such as analyses of subadult and Hesperid structural colors and the identification of genes that directly build the nanostructures, with relevance for biomimetic engineering.

Machine learning-enabled constrained multi-objective design of architected materials

Architected materials that consist of multiple subelements arranged in particular orders can demonstrate a much broader range of properties than their constituent materials. However, the rational design of these materials generally relies on experts' prior knowledge and requires painstaking effort. Here, we present a data-efficient method for the high-dimensional multi-property optimization of 3D-printed architected materials utilizing a machine learning (ML) cycle consisting of the finite element method (FEM) and 3D neural networks. Specifically, we apply our method to orthopedic implant design. Compared to uniform designs, our experience-free method designs microscale heterogeneous architectures with a biocompatible elastic modulus and higher strength. Furthermore, inspired by the knowledge learned from the neural networks, we develop machine-human synergy, adapting the ML-designed architecture to fix a macroscale, irregularly shaped animal bone defect. Such adaptation exhibits 20% higher experimental load-bearing capacity than the uniform design. Thus, our method provides a data-efficient paradigm for the fast and intelligent design of architected materials with tailored mechanical, physical, and chemical properties.

Hydroxyapatite 3D-printed scaffolds with Gyroid-Triply periodic minimal surface porous structure: Fabrication and an in vivo pilot study in sheep

Bone repair is a major challenge in regenerative medicine, e.g. for large defects. There is a need for bioactive, highly percolating bone substitutes favoring bone ingrowth and tissue healing. Here, a modern 3D printing approach (VAT photopolymerization) was exploited to fabricate hydroxyapatite (HA) scaffolds with a Gyroid-"Triply periodic minimal surface" (TPMS) porous structure (65% porosity, 90.5% HA densification) inspired from trabecular bone. Percolation and absorption capacities were analyzed in gaseous and liquid conditions. Mechanical properties relevant to guided bone regeneration in non-load bearing sites, as for maxillofacial contour reconstruction, were evidenced from 3-point bending tests and macrospherical indentation. Scaffolds were implanted in a clinically-relevant large animal model (sheep femur), over 6 months, enabling thorough analyses at short (4 weeks) and long (26 weeks) time points. In vivo performances were systematically compared to the bovine bone-derived Bio-OssⓇ standard. The local tissue response was examined thoroughly by semi-quantitative histopathology. Results demonstrated the absence of toxicity. Bone healing was assessed by bone dynamics analysis through epifluorescence using various fluorochromes and quantitative histomorphometry. Performant bone regeneration was evidenced with similar overall performances to the control, although the Gyroid biomaterial slightly outperformed Bio-OssⓇ at early healing time in terms of osteointegration and appositional mineralization. This work is considered a pilot study on the in vivo evaluation of TPMS-based 3D porous scaffolds in a large animal model, for an extended period of time, and in comparison to a clinical standard. Our results confirm the relevance of such scaffolds for bone regeneration in view of clinical practice. STATEMENT OF SIGNIFICANCE: Bone repair, e.g. for large bone defects or patients with defective vascularization is still a major challenge. Highly percolating TPMS porous structures have recently emerged, but no in vivo data were reported on a large animal model of clinical relevance and comparing to an international standard. Here, we fabricated TPMS scaffolds of HA, determined their chemical, percolation and mechanical features, and ran an in-depth pilot study in the sheep with a systematic comparison to the Bio-OssⓇ reference. Our results clearly show the high bone-forming capability of such scaffolds, with outcomes even better than Bio-OssⓇ at short implantation time. This preclinical work provides quantitative data validating the relevance of such TMPS porous scaffolds for bone regeneration in view of clinical evaluation.

Hierarchical morphogenesis of swallowtail butterfly wing scale nanostructures

The study of color patterns in the animal integument is a fundamental question in biology, with many lepidopteran species being exemplary models in this endeavor due to their relative simplicity and elegance. While significant advances have been made in unraveling the cellular and molecular basis of lepidopteran pigmentary coloration, the morphogenesis of wing scale nanostructures involved in structural color production is not well understood. Contemporary research on this topic largely focuses on a few nymphalid model taxa (e.g., Bicyclus, Heliconius), despite an overwhelming diversity in the hierarchical nanostructural organization of lepidopteran wing scales. Here, we present a time-resolved, comparative developmental study of hierarchical scale nanostructures in Parides eurimedes and five other papilionid species. Our results uphold the putative conserved role of F-actin bundles in acting as spacers between developing ridges, as previously documented in several nymphalid species. Interestingly, while ridges are developing in P. eurimedes, plasma membrane manifests irregular mesh-like crossribs characteristic of Papilionidae, which delineate the accretion of cuticle into rows of planar disks in between ridges. Once the ridges have grown, disintegrating F-actin bundles appear to reorganize into a network that supports the invagination of plasma membrane underlying the disks, subsequently forming an extruded honeycomb lattice. Our results uncover a previously undocumented role for F-actin in the morphogenesis of complex wing scale nanostructures, likely specific to Papilionidae.

Chirality in Light-Matter Interaction

The scientific effort to control the interaction between light and matter has grown exponentially in the last 2 decades. This growth has been aided by the development of scientific and technological tools enabling the manipulation of light at deeply sub-wavelength scales, unlocking a large variety of novel phenomena spanning traditionally distant research areas. Here, the role of chirality in light-matter interactions is reviewed by providing a broad overview of its properties, materials, and applications. A perspective on future developments is highlighted, including the growing role of machine learning in designing advanced chiroptical materials to enhance and control light-matter interactions across several scales.

High-resolution three-dimensional structural determination of unstained double-gyroid block copolymers through scanning transmission electron microscopy

Block copolymer-based multicomponent materials have garnered considerable attention because of tunable properties due to their various constituents. The use of electron tomography through transmission electron microscopy (TEM) for the three-dimensional (3D) imaging of stained block copolymers is an established approach for investigating structure-property relationships. Recently, scanning transmission electron microscopy (STEM) with an annular dark-field (ADF) detector has emerged as a method for the 3D structural analysis of unstained block copolymers. However, because of a lack of electron contrast, only a few low-resolution 3D reconstructions were reported for light elements. Herein, we report the first 3D structural analysis of a 200-nm-thick film composed of unstained double-gyroid block copolymers-polystyrene-b-poly(2-vinylpyridine) (PS-P2VP)-at a resolution of 8.6 nm through spherical aberration Cs-corrected STEM. At this resolution, P2VP molecules can be distinguished from PS molecules in z-contrast 3D reconstructions obtained both experimentally and theoretically. The 3D reconstructions revealed structural differences between stained and unstained specimens.

Reactive Bimetallic Nanostructures Based on Triply Periodic Minimal Surfaces: A Molecular Dynamics Study toward the Limits of Performance

A variety of intermetallic compounds possesses high enthalpies of formation. These compounds may be formed from reactive compacts or nanostructures comprised of unreacted precursor metals. These precursor structures support self-propagating high temperature synthesis (SHS) reactions which afford very high specific energy densities and rates, with excellent spatial control and a variety of useful applications. The present work compares the reactivity of notional bimetallic nanostructures based on well-known triply periodic minimal surfaces (TPMSes) with the popular reactive nanolaminate (RNL) modality for the Ni/Al system, using a molecular dynamics approach. TPMS-derived nanostructures were found to have lower ignition energies and faster reaction rates than RNLs of comparable periodicity, while the maximum achievable temperature of ignitions was found to be modulated by a complex interplay of factors including reaction rate and specific metal/metal interface density. Nanostructure reactivity and thermochemistry is also affected by effective diffusion dimensionality and recalescent precipitation of intermetallic crystallites. The TPMS-derived reactive nanostructures presented herein anticipate plausible advances in nanofabrication technology.

Quasi-Static Mechanical Response of Density-Graded Polyurea Elastomeric Foams

Density gradation of foam structures has been investigated and found to be a practical approach to improve the mechanical efficacy of protective padding in several applications based on nature-based evidence of effectiveness. This research aims to disclose a discrete gradation approach without adhesives by relying on the properties of the frothed foam slurry to bond and penetrate through previously cured foam sheets naturally. As confirmed by electron microscopy observations, bilayer- and trilayer-graded elastomeric polyurea foam sheets were fabricated, resulting in seamless interfaces. The mechanical performance of seamless, graded foam samples was compared with monolayer, mono-density benchmark foam, considered the industry standard for impact mitigation. All foam samples were submitted to compressive loading at a quasi-static rate, reporting key performance indicators (KPIs) such as specific energy absorption, efficiency, and ideality. Polyurea foams, irrespective of gradation and interface type, outperformed benchmark foam in several KPIs despite the drastic difference in the effective or average density. The average compressive stress-strain curves were fitted into empirical constitutive models to reveal critical insights into the elastic, plateau, and densification behaviors of the tested foam configuration. The novelty of these outcomes includes (1) a fabrication approach to adhesive-free density-graded foam structures, (2) implementation of a diverse set of KPIs to assess the mechanical efficacy of foams, and (3) elucidation of the superiority of polyurea foam-based lightweight protective paddings. Future research will focus on assessing the dynamic performance of these graded foam structures under impact loading conditions at a wide range of velocities.

A Devonian crinoid with a diamond microlattice

Owing to their remarkable physical properties, cellular structures, such as triply periodic minimal surfaces (TPMS), have multidisciplinary and multifunctional applications. Although these structures are observed in nature, examples of TPMS with large length scales in living organisms are exceedingly rare. Recently, microstructure reminiscent of the diamond-type TPMS was documented in the skeleton of the modern knobby starfish Protoreaster nodosus. Here we report a similar microlattice in a 385 Myr old crinoid Haplocrinites, which pushes back the origins of this highly ordered microstructure in echinoderms into the Devonian. Despite the low Mg2+/Ca2+ ratio of the 'calcite' Devonian sea, the skeleton of these crinoids has high-Mg content, which indicates strong biological control over biomineralogy. We suggest that such an optimization of trabecular arrangement additionally enriched in magnesium, which enhances the mechanical properties, might have evolved in these crinoids in response to increased predation pressure during the Middle Palaeozoic Marine Revolution. This discovery illustrates the remarkable ability of echinoderms, through the process of evolutionary optimization, to form a lightweight, stiff and damage-tolerant skeleton, which serves as an inspiration for biomimetic materials.

Active control of equilibrium, near-equilibrium, and far-from-equilibrium colloidal systems

The development of top-down active control over bottom-up colloidal assembly processes has the potential to produce materials, surfaces, and objects with applications in a wide range of fields spanning from computing to materials science to biomedical engineering. In this review, we summarize recent progress in the field using a taxonomy based on how active control is used to guide assembly. We find there are three distinct scenarios: (1) navigating kinetic pathways to reach a desirable equilibrium state, (2) the creation of a desirable metastable, kinetically trapped, or kinetically arrested state, and (3) the creation of a desirable far-from-equilibrium state through continuous energy input. We review seminal works within this framework, provide a summary of important application areas, and present a brief introduction to the fundamental concepts of control theory that are necessary for the soft materials community to understand this literature. In addition, we outline current and potential future applications of actively-controlled colloidal systems, and we highlight important open questions and future directions.

Curvature in Biological Systems: Its Quantification, Emergence, and Implications across the Scales

Surface curvature both emerges from, and influences the behavior of, living objects at length scales ranging from cell membranes to single cells to tissues and organs. The relevance of surface curvature in biology is supported by numerous experimental and theoretical investigations in recent years. In this review, first, a brief introduction to the key ideas of surface curvature in the context of biological systems is given and the challenges that arise when measuring surface curvature are discussed. Giving an overview of the emergence of curvature in biological systems, its significance at different length scales becomes apparent. On the other hand, summarizing current findings also shows that both single cells and entire cell sheets, tissues or organisms respond to curvature by modulating their shape and their migration behavior. Finally, the interplay between the distribution of morphogens or micro-organisms and the emergence of curvature across length scales is addressed with examples demonstrating these key mechanistic principles of morphogenesis. Overall, this review highlights that curved interfaces are not merely a passive by-product of the chemical, biological, and mechanical processes but that curvature acts also as a signal that co-determines these processes.

Shape Morphing by Topological Patterns and Profiles in Laser-Cut Liquid Crystal Elastomer Kirigami

Programming shape changes in soft materials requires precise control of the directionality and magnitude of their mechanical response. Among ordered soft materials, liquid crystal elastomers (LCEs) exhibit remarkable and programmable shape shifting when their molecular order changes. In this work, we synthesized, remotely programmed, and modeled reversible and complex morphing in monolithic LCE kirigami encoded with predesigned topological patterns in its microstructure. We obtained a rich variety of out-of-plane shape transformations, including auxetic structures and undulating morphologies, by combining different topological microstructures and kirigami geometries. The spatiotemporal shape-shifting behaviors are well recapitulated by elastodynamics simulations, revealing that the complex shape changes arise from integrating the custom-cut geometry with local director profiles defined by topological defects inscribed in the material. Different functionalities, such as a bioinspired fluttering butterfly, a flower bud, dual-rotation light mills, and dual-mode locomotion, are further realized. Our proposed LCE kirigami with topological patterns opens opportunities for the future development of multifunctional devices for soft robotics, flexible electronics, and biomedicine.

Induced Circular Dichroism and Circularly Polarized Luminescence for Block Copolymers with Chiral Communications

Many sophisticated chiral materials are found in living organisms, giving specific functions and required complexity. Owing to the remarkable optical properties of chiral materials, they have drawn significant attention for the development of synthetic materials to give optical activities for appealing applications. In contrast to a top-down approach, the bottom-up approach from self-assembled systems with chiral host-achiral guest and achiral guest-chiral host for induced circular dichroism and induced circularly polarized luminescence has greatly emerged because of its cost-effective advantage with easy fabrication for mesoscale assembly. Self-assembled hierarchical textures with chiral sense indeed give significant amplification of the dissymmetry factors of absorption and luminescence (g_abs and g_lum ), resulting from the formation of well-ordered superstructures and phases with the building of chromophores and luminophores. By taking advantage of the microphase separation of block copolymers via self-assembly, a variety of well-defined chiral nanostructures can be formed as tertiary superstructures that can be further extended to quaternary phases in bulk or thin film. In this article, a conceptual perspective is presented to utilize the self-assembly of chiral block copolymers with chiral communications, giving quaternary phases with well-ordered textures at the nanoscale for significant enhancement of dissymmetry factors.

Polyphenol-Functionalized Cubosomes as Thrombolytic Drug Carriers

The safe administration of thrombolytic agents is a challenge for the treatment of acute thrombosis. Lipid-based nanoparticle drug delivery technologies present opportunities to overcome the existing clinical limitations and deliver thrombolytic therapy with enhanced therapeutic outcomes and safety. Herein, lipid cubosomes are examined as nanocarriers for the encapsulation of thrombolytic drugs. The lipid cubosomes are loaded with the thrombolytic drug urokinase-type plasminogen activator (uPA) and coated with a low-fouling peptide that is incorporated within a metal-phenolic network (MPN). The peptide-containing MPN (pep-MPN) coating inhibits the direct contact of uPA with the surrounding environment, as assessed by an in vitro plasminogen activation assay and an ex vivo whole blood clot degradation assay. The pep-MPN-coated cubosomes prepared with 22 wt% peptide demonstrate a cell membrane-dependent thrombolytic activity, which is attributed to their fusogenic lipid behavior. Moreover, compared with the uncoated lipid cubosomes, the uPA-loaded pep-MPN-coated cubosomes demonstrate significantly reduced nonspecific cell association (<10% of the uncoated cubosomes) in the whole blood assay, a prolonged circulating half-life, and reduced splenic uPA accumulation in mice. These studies confirm the preserved bioactivity and cell membrane-dependent release of uPA within pep-MPN-coated lipid cubosomes, highlighting their potential as a delivery vehicle for thrombolytic drugs.

Polymorphic self-assembly of helical tubules is kinetically controlled

In contrast to most self-assembling synthetic materials, which undergo unbounded growth, many biological self-assembly processes are self-limited. That is, the assembled structures have one or more finite dimensions that are much larger than the size scale of the individual monomers. In many such cases, the finite dimension is selected by a preferred curvature of the monomers, which leads to self-closure of the assembly. In this article, we study an example class of self-closing assemblies: cylindrical tubules that assemble from triangular monomers. By combining kinetic Monte Carlo simulations, free energy calculations, and simple theoretical models, we show that a range of programmable size scales can be targeted by controlling the intricate balance between the preferred curvature of the monomers and their interaction strengths. However, their assembly is kinetically controlled-the tubule morphology is essentially fixed shortly after closure, resulting in a distribution of tubule widths that is significantly broader than the equilibrium distribution. We develop a simple kinetic model based on this observation and the underlying free-energy landscape of assembling tubules that quantitatively describes the distributions. Our results are consistent with recent experimental observations of tubule assembly from triangular DNA origami monomers. The modeling framework elucidates design principles for assembling self-limited structures from synthetic components, such as artificial microtubules that have a desired width and chirality.

High-Throughput Generation of 3D Graphene Metamaterials and Property Quantification Using Machine Learning

3D graphene assemblies are proposed as solutions to meet the goal toward efficient utilization of 2D graphene sheets, showing excellent performances in applications such as mechanical support, energy storage, and electrochemical catalysis. However, given the diversity and complexity of possible graphene 3D structures, there does not yet exist a systematic approach that can generate target 3D shapes and also, evaluate their performance. Here high-throughput data generation is combined with artificial intelligence approaches to realize rapid structure formation and property quantification of 3D graphene foams with mathematically controlled topologies, driven by molecular dynamics simulations. More than 4000 different foam structures are created, which feature diverse topologies that contain potential pathways for small molecules and auxetic structures with negative Poisson's ratio. Empowered by machine learning (ML) algorithms including graph neural networks, not only global properties such as elastic moduli, but also local behaviors such as atomic stress can be predicted and optimized based on their atomic structure, bypassing expensive atomistic simulations. The key findings of the research reported in this paper include a high-throughput virtual framework of generating diverse 3D graphene assemblies with mechanical performances quantification, and highly efficient methods of evaluating physical properties based on ML.

3D Tomographic Analysis of the Order-Disorder Interplay in the Pachyrhynchus congestus mirabilis Weevil

The bright colors of Pachyrhynchus weevils originate from complex dielectric nanostructures within their elytral scales. In contrast to previous work exhibiting highly ordered single-network diamond-type photonic crystals, here, it is shown by combining optical microscopy and spectroscopy measurements with 3D focused ion beam (FIB) tomography that the blue scales of P. congestus mirabilis differ from that of an ordered diamond structure. Through the use of FIB tomography on elytral scales filled with platinum (Pt) by electron beam-assisted deposition, it is revealed that the red scales of this weevil possess a periodic diamond structure, while the network morphology of the blue scales exhibit diamond morphology only on the single scattering unit level with disorder on longer length scales. Full wave simulations performed on the reconstructed volumes indicate that this local order is sufficient to open a partial photonic bandgap even at low dielectric constant contrast between chitin and air in the absence of long-range or translational order. The observation of disordered and ordered photonic crystals within a single organism opens up interesting questions on the cellular origin of coloration and studies on bio-inspired replication of angle-independent colors.

Well-Ordered Nanonetwork Metamaterials from Block Copolymer Templated Syntheses

ConspectusThrough the morphological evolution to give highly optimized complex architectures at different length scales, fine-tuned textures for specific functions in living organisms can be achieved in nature such as a bone core with very complicated porous architecture to attain a significant structural efficiency attributed to delicately structured ligaments and density gradients. As inspired by nature, materials with periodic network structures (i.e., well-defined porous textures) in the nanoscale are appealing and promising for innovative properties. Biomimicking from nature, organic and/or inorganic nanonetworks can be synthetically fabricated, giving broadness and effectiveness when tuning the desired properties. Metamaterials are materials whose effective properties do not result from the bulk behavior of the constituent materials but rather mainly from their deliberate structuring. The performances of fabricating metamaterials will depend on the control of size, shape, order, and orientation of the forming textures. One of the appealing textures for the deliberate structuring is network architecture. Network materials possess self-supporting frameworks, open-cell character, high porosity, and large specific surface area, giving specific functions and complexity for diverse applications. As demonstrated by recent studies, exceptional mechanical performances such as negative thermal expansion, negative Poisson's ratio, and twisting under uniaxial forces can be achieved by the effect of the deliberate structuring with nanonetwork textures. In contrast to a top-down approach, a bottom-up approach is cost-effective, and also it can overcome the size limitation to reach nanoscale fabrication. It can be foreseen that network metamaterials with a feature size of tens of nanometers (referred as nanonetwork metamaterials) may provide new comprehension of the structure and property relationships for various materials. The self-assembly of block copolymers (BCPs) is one of the most used methods to build up well-ordered nanostructured phases from a bottom-up approach with precise control of size, shape, and orientation in the thin films for realistic applications. In this account, we summarize recent advancements in the fabrication of nanohybrids and nanoporous materials with well-ordered nanonetwork textures even with controlled helicity by combining block copolymer self-assembly and templated syntheses for mechanical and optical applications with superior properties beyond nature as metamaterials as well as chiral metamaterials with new properties for chiroptic applications such as chiral plasmonics, beam splitter, and negative refraction. The description of the fundamental facets of a nonconventional structure-property relationship with the characters of metamaterials and the state-of-the-art methodologies to fabricate nanonetworks using block copolymer self-assembly will stimulate research activities for the development of nanonetwork metamaterials with exceptional individual and multifunctional properties for futuristic devices.

Polarization-dependent reflection of I-WP minimal-surface-based photonic crystal

Brilliantly colored butterflies and weevils are known to utilize photonic crystals for their coloration. Interestingly, the morphology of such crystals made of cuticle is based on triply periodic minimal surfaces such as gyroid and diamond surfaces. Recently, a different minimal-surface-based photonic crystal, the I-WP surface, was discovered inside the scale of a longhorn beetle. The letter I is derived from expressing the body center symmetry and WP is derived from a wrapped package. It was reported that the brilliant green color is produced by the photonic band gap existing along the [110] direction of this crystal. In this study, the polarization dependence of the reflection from this photonic crystal was investigated. A peculiar reflectance spectrum with two peaks was observed under the crossed polarizers. This characteristic is theoretically reproduced by calculating the reflectance from a finite-sized photonic crystal, and the spectral shape is explained based on the symmetry of the electromagnetic modes. In addition, inspired by this longhorn beetle, a photonic crystal structure consisting of colloidal particles is proposed, which has a similar polarization effect.

Moth wings as sound absorber metasurface

In noise control applications, a perfect metasurface absorber would have the desirable traits of not only mitigating unwanted sound, but also being much thinner than the wavelengths of interest. Such deep-subwavelength performance is difficult to achieve technologically, yet moth wings, as natural metamaterials, offer functionality as efficient sound absorbers through the action of the numerous resonant scales that decorate their wing membrane. Here, we quantify the potential for moth wings to act as a sound-absorbing metasurface coating for acoustically reflective substrates. Moth wings were found to be efficient sound absorbers, reducing reflection from an acoustically hard surface by up to 87% at the lowest frequency tested (20 kHz), despite a thickness to wavelength ratio of up to 1/50. Remarkably, after the removal of the scales from the dorsal surface the wing's orientation on the surface changed its absorptive performance: absorption remains high when the bald wing membrane faces the sound but breaks down almost completely in the reverse orientation. Numerical simulations confirm the strong influence of the air gap below the wing membrane but only when it is adorned with scales. The finding that moth wings act as deep-subwavelength sound-absorbing metasurfaces opens the door to bioinspired, high-performance sound mitigation solutions.

Medial packing and elastic asymmetry stabilize the double-gyroid in block copolymers

Triply-periodic networks are among the most complex and functionally valuable self-assembled morphologies, yet they form in nearly every class of biological and synthetic soft matter building blocks. In contrast to simpler assembly motifs – spheres, cylinders, layers – networks require molecules to occupy variable local environments, confounding attempts to understand their formation. Here, we examine the double-gyroid network phase by using a geometric formulation of the strong stretching theory of block copolymer melts, a prototypical soft self-assembly system. The theory establishes the direct link between molecular packing, assembly thermodynamics and the medial map, a generic measure of the geometric center of complex shapes. We show that “medial packing” is essential for stability of double-gyroid in strongly-segregated melts, reconciling a long-standing contradiction between infinite- and finite-segregation theories. Additionally, we find a previously unrecognized non-monotonic dependence of network stability on the relative entropic elastic stiffness of matrix-forming to tubular-network forming blocks. The composition window of stable double-gyroid widens for both large and small elastic asymmetry, contradicting intuitive notions that packing frustration is localized to the tubular domains. This study demonstrates the utility of optimized medial tessellations for understanding soft-molecular assembly and packing frustration via an approach that is readily generalizable far beyond gyroids in neat block copolymers.

Double-gyroid networks assemble in diverse soft materials, yet the molecular packing that underlies their complex structure remains obscure. Here, authors advance a theory that resolves a long-standing puzzle about their formation in block copolymers.

Bioinspired Polypeptide Photonic Films with Tunable Structural Color

We report a new synthetic strategy of combining N-carboxyanhydride (NCA) chemistry and photonic crystals for the fabrication of polypeptide structural color films. Driven by surface-initiated ring-opening polymerization, the di-NCA derivative of l-cystine (Cys) is introduced to replicate the functionalized colloidal crystal templates and construct freestanding P(Cys) films with tunable structural color. Furthermore, the feasibility of preparing patterned polypeptide photonic films is demonstrated via template microfabrication. Because of the incorporation of l-glutamate (Glu) components, the P(Cys-co-Glu) co-polypeptide films are endowed with a visual color responsiveness toward pH changes. Additionally, the polypeptide photonic films show on-demand degradability. Given the large family of amino acid building blocks, this powerful and versatile approach paves the way for chemical derivatization of multifunctional peptide-based optical platforms.

Pachyrhynchus Weevils Use 3D Photonic Crystals with Varying Degrees of Order to Create Diverse and Brilliant Displays

The brilliant appearance of Easter Egg weevils, genus Pachyrhynchus (Coleoptera, Curculionidae), originates from complex dielectric nanostructures within their elytral scales and elytra. Previous work, investigating singular members of the Pachyrhynchus showed the presence of either quasi-ordered or ordered 3D photonic crystals based on the single diamond ( Fd3¯m ) symmetry in their scales. However, little is known about the diversity of the structural coloration mechanisms within the family. Here, the optical properties within Pachyrhynchus are investigated by systematically identifying their spectral and structural characteristics. Four principal traits that vary their appearance are identified and the evolutionary history of these traits to identify ecological trends are reconstructed. The results indicate that the coloration mechanisms across the Easter Egg weevils are diverse and highly plastic across closely related species with features appearing at multiple independent times across their phylogeny. This work lays a foundation for a better understanding of the various forms of quasi-ordered and ordered diamond photonic crystal within arthropods.

Supramolecular meso-Trick: Ambidextrous Mirror Symmetry Breaking in a Liquid Crystalline Network with Tetragonal Symmetry

Bicontinuous and multicontinuous network phases are among nature's most complex structures in soft matter systems. Here, a chiral bicontinuous tetragonal phase is reported as a new stable liquid crystalline intermediate phase at the transition between two cubic phases, the achiral double gyroid and the chiral triple network cubic phase with an I23 space group, both formed by dynamic networks of helices. The mirror symmetry of the double gyroid, representing a meso-structure of two enantiomorphic networks, is broken at the transition to this tetragonal phase by retaining uniform helicity only along one network while losing it along the other one. This leads to a conglomerate of enantiomorphic tetragonal space groups, P4₁2₁2 and P4₃2₁2. Phase structures and chirality were analyzed by small-angle X-ray scattering (SAXS), grazing-incidence small-angle X-ray scattering (GISAXS), resonant soft X-ray scattering (RSoXS) at the carbon K-edge, and model-dependent SAXS/RSoXS simulation. Our findings not only lead to a new bicontinuous network-type three-dimensional mesophase but also reveal a mechanism of mirror symmetry breaking in soft matter by partial meso-structure racemization at the transition from enantiophilic to enantiophobic interhelical self-assembly.

Replicating the Cynandra opis Butterfly's Structural Color for Bioinspired Bigrating Color Filters

Multilayer grating structures, such as those found on the wings of the butterfly Cynandra opis, are able to interact with light to generate structural coloration. When illuminated and viewed at defined angles, such structural color is characterized by exceptional purity and brightness. To provide further insight into the mechanism of structural coloration, two-photon laser lithography is used to fabricate bioinspired bigrating nanostructures, whose optical properties may be controlled by variation of the height and period of the grating features. Through the use of both spectral measurements and finite-element method simulations, herein specific feature dimensions are identified that due to the combined effects of multilayer interference and diffraction generate excellent spectral characteristics and high color purity over the entire visible range. Additionally, it is demonstrated that variation of feature period and/or height plays a central role in controlling both hue and purity. Importantly, such tuneable bigrating structures are of significant utility in color filtering applications.

A bioinspired, electroactive colorable and additive manufactured photonic artificial muscle

Structural coloration in biomimetic nanostructures has remarkable application potential in vivid display devices, but their color change effect is still insufficiently competitive towards biology. Inspired by the feather color change of a hummingbird, a new methodology for coloration is proposed. A structure-colorable flexural artificial muscle (FlexAM) is developed by integrating a view-angle dependent photonic diffraction grating pattern and voltage-actuated dielectric elastomers as an electroactive entity via laminated object additive manufacturing. A multi-physics model is developed which guides the FlexAM to harness the view-angle dependence for the new coloration strategy. The electro-mechanochromic performances are experimentally characterized to verify the prediction of the multi-physics model. An ultrafast coloration in the FlexAM with an advancing figure-of-merit at a color-shift rate of 2.814 nm ms^-1 is realized, in addition to an excellent fatigue resistance up to 10 000 cycles. A photonic display with arrayed FlexAM elements is designed, which can be used to display numbers and letters. The current research offers an advanced artificial muscle towards active photonic and visible strain sensing.

Single Gyroid Self-Assembled by Linear BABAB Pentablock Copolymer

Although the double-gyroid (DG) structure has been commonly formed from the self-assembly of block copolymers, the single-gyroid (SG) structure is rarely reported. Moreover, the SG structure even shows better performance than DG in some optical applications. How to prepare the SG structure has become an attractive but challenging topic. We speculate that the SG structure can be stabilized by the synergistic effect of released packing frustration and stretched bridging block in AB-type block copolymers. Accordingly, we propose the minimum conditions for the design of architecture that enables the two mechanisms simultaneously. Following these conditions, a simple linear BABAB pentablock copolymer is successfully devised. SCFT calculations confirm that the SG phase can be stabilized by tailoring the architecture. Our work is hopeful to promote relevant experimental studies for engineering the unusual SG structure.

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.

Stretchable Soft Composites with Strain-Induced Architectured Color

Colors enable interaction and communication between living species in a myriad of biological and artificial environments. While living organisms feature low-power mechanisms to dynamically control color in soft tissues, man-made color-changing devices remain predominantly rigid and energy intensive. Here, architectured composites that display striking color changes when stretched in selective directions under ambient light with minimum power input are reported. The orientation-dependent color change results from the rotation of reflective coated platelets that are embedded in a soft polymer matrix and pre-aligned in a well-defined architecture. The light reflected by the platelets generates structural color defined by the oxide coating on the platelet surface. By magnetically programming the initial orientation and spatial distribution of selected platelets within the soft matrix, composites with strain-modulated color-changing effects that cannot be achieved using state-of-the-art technologies are created. The proposed concept of strain-induced architectured color can be harnessed to develop low-power smart stretchable displays, tactile synthetic skins, and autonomous soft robotic devices that undergo fast and reversible color changes through the mechano-optic coupling programmed within their soft composite architecture.