Colloidal synthesis of metallodielectric Janus matchsticks.

We present a gram-scale synthesis of metallodielectric Janus matchsticks, which feature a gold-coated silica sphere and a silica rod. SiO2 Janus matchsticks are synthesized in one batch by growing amine-functionalized SiO2 spheres at the end of SiO2 rods. Gold deposition on the spheres produces Au-SiO2 Janus matchsticks with an aspect ratio controlled by the rod length. The metallodielectric Janus matchsticks, produced by scalable colloidal synthesis, hold great potential as functional colloidal materials.

Color-Changing Paints Enabled by Photoresponsive Combinations of Bio-Inspired Colorants and Semiconductors.

Modern paints and coatings are designed for a variety of applications, ranging from fine art to extraterrestrial thermal control. These systems can be engineered to provide lasting color, but there are a limited number of materials that can undergo transient changes in their visual appearance in response to external stimuli without requirements for advanced fabrication strategies. The authors describe color-changing paint formulations that leverage the redox-dependent absorption profile of xanthommatin, a small-molecule colorant found throughout biology, and the electronic properties of titanium dioxide, a ubiquitous whitening agent in commercial coatings. This combination yields reversible photoreduction upon exposure to sunlight, shifting from the oxidized (yellow) form of xanthommatin, to the reduced (red) state. The extent of photoreduction is dependent on the loading density and size of titanium dioxide particles, generating changes in hue angle as large as 77% upon irradiation. These coatings can be blended with non-responsive supplemental colorants to expand the accessible color palette, and irradiated through masks to create transient, disappearing artwork. These formulations demonstrate energy-efficient photochromism using a simple combination of a redox-active dye and metal oxide semiconductor, highlighting the utility of these materials for the development of optically dynamic light-harvesting materials.

Design and Characterization of Model Systems that Promote and Disrupt Transparency of Vertebrate Crystallins In Vitro.

Positioned within the eye, the lens supports vision by transmitting and focusing light onto the retina. As an adaptive glassy material, the lens is constituted primarily by densely-packed, polydisperse crystallin proteins that organize to resist aggregation and crystallization at high volume fractions, yet the details of how crystallins coordinate with one another to template and maintain this transparent microstructure remain unclear. The role of individual crystallin subtypes (α, ß, and γ) and paired subtype compositions, including how they experience and resist crowding-induced turbidity in solution, is explored using combinations of spectrophotometry, hard-sphere simulations, and surface pressure measurements. After assaying crystallin combinations, ß-crystallins emerged as a principal component in all mixtures that enabled dense fluid-like packing and short-range order necessary for transparency. These findings helped inform the design of lens-like hydrogel systems, which are used to monitor and manipulate the loss of transparency under different crowding conditions. When taken together, the findings illustrate the design and characterization of adaptive materials made from lens proteins that can be used to better understand mechanisms regulating transparency.

Design and Production of Customizable and Highly Aligned Fibrillar Collagen Scaffolds.

The ability to fabricate anisotropic collagenous materials rapidly and reproducibly has remained elusive despite decades of research. Balancing the natural propensity of monomeric collagen (COL) to spontaneously polymerize in vitro with the mild processing conditions needed to maintain its native substructure upon polymerization introduces challenges that are not easily amenable with off-the-shelf instrumentation. To overcome these challenges, we have designed a platform that simultaneously aligns type I COL fibrils under mild shear flow and builds up the material through layer-by-layer assembly. We explored the mechanisms propagating fibril alignment, targeting experimental variables such as shear rate, viscosity, and time. Coarse-grained molecular dynamics simulations were also employed to help understand how initial reaction conditions including chain length, indicative of initial polymerization, and chain density, indicative of concentration, in the reaction environment impact fibril growth and alignment. When taken together, the mechanistic insights gleaned from these studies inspired the design, iteration, fabrication, and then customization of the fibrous collagenous materials, illustrating a platform material that can be readily adapted to future tissue engineering applications.

Manipulating polydispersity of lens ß-crystallins using divalent cations demonstrates evidence of calcium regulation.

Crystallins comprise the protein-rich tissue of the eye lens. Of the three most common vertebrate subtypes, ß-crystallins exhibit the widest degree of polydispersity due to their complex multimerization properties in situ. While polydispersity enables precise packing densities across the concentration gradient of the lens for vision, it is unclear why there is such a high degree of structural complexity within the ß-crystallin subtype and what the role of this feature is in the lens. To investigate this, we first characterized ß-crystallin polydispersity and then established a method to dynamically disrupt it in a process that is dependent on isoform composition and the presence of divalent cationic salts (CaCl2 or MgCl2). We used size-exclusion chromatography together with dynamic light scattering and mass spectrometry to show how high concentrations of divalent cations dissociate ß-crystallin oligomers, reduce polydispersity, and shift the overall protein surface charge-properties that can be reversed when salts are removed. While the direct, physiological relevance of these divalent cations in the lens is still under investigation, our results support that specific isoforms of ß-crystallin modulate polydispersity through multiple chemical equilibria and that this native state is disrupted by cation binding. This dynamic process may be essential to facilitating the molecular packing and optical function of the lens.

Probing the alignment-dependent mechanical behaviors and time-evolutional aligning process of collagen scaffolds.

Efficiently manipulating and reproducing collagen (COL) alignment in vitro remains challenging because many of the fundamental mechanisms underlying and guiding the alignment process are not known. We reconcile experiments and coarse-grained molecular dynamics simulations to investigate the mechanical behaviors of a growing COL scaffold and assay how changes in fiber alignment and various cross-linking densities impact their alignment dynamics under shear flow. We find higher cross-link densities and alignment levels significantly enhance the apparent tensile/shear moduli and strength of a bulk COL system, suggesting potential measures to facilitate the design of stronger COL based materials. Since fibril alignment plays a key factor in scaffold mechanics, we next investigate the molecular mechanism behind fibril alignment with Couette flow by computationally investigating the effects of COL's structural properties such as chain lengths, number of chains, tethering conditions, and initial COL conformations on the COL's final alignment level. Our computations suggest that longer chain lengths, more chains, greater amounts of tethering, and initial anisotropic COL conformations benefit the final alignment, but the effect of chain lengths may be more dominant over other factors. These results provide important parameters for consideration in manufacturing COL-based scaffolds where alignment and cross-linking are necessary for regulating performance.

Evaluation of Biologically Inspired Ammonium Xanthommatin as a Multifunctional Cosmetic Ingredient.

We describe the investigation of an organic natural product, ammonium xanthommatin (Xanthochrome), in a series of studies designed to not only assess its impact on endocrine receptor function in vitro but also interrogate its mutagenic potential using bacterial reverse mutation assays. As a multifunctional raw material, ammonium xanthommatin functions as an antioxidant with a broad absorption profile spanning the UV through the visible spectrum, making it an interesting target for cosmetic applications. In solution, ammonium xanthommatin contributes to <30% inhibition of hormonal activities, indicating that it is not an endocrine disruptor. Furthermore, the compound does not cause gene mutations in the bacterial strains used, indicating that it is nonmutagenic. Applications are also described, highlighting xanthommatin's ability to boost the UVA and UVB absorptive properties of traditional chemical UV filters by >50% across all filters tested. In addition to these features, xanthommatin exhibited no phototoxic hazards in vitro when irradiated with UVA and visible light, demonstrating its utility as a multifunctional cosmetic ingredient. Although these findings encourage the use of xanthommatin in cosmetics, they represent only the beginning of the complete in vitro and in vivo data package needed to support safety and efficacy claims for future applications in skin health.

Wearable Light Sensors Based on Unique Features of a Natural Biochrome.

Overexposure to complete solar radiation (combined ultraviolet, visible, and infrared) is correlated with several harmful biological consequences including hyperpigmentation, skin cancer, eye damage, and immune suppression. With limited effective therapeutic options available for these conditions, significant efforts have been directed toward promoting preventative habits. Recently, wearable solar radiometers have emerged as practical tools for managing personal exposure to sunlight. However, designing simple and inexpensive sensors that can measure energy across multiple spectral regions without incorporating electronic components remains challenging, largely due to inherent spectral limitations of photoresponsive indicators. In this work, we report the design, fabrication, and characterization of wearable radiation sensors that leverage an unexpected feature of a natural biochrome, xanthommatin-its innate sensitivity to both ultraviolet and visible through near-infrared radiation. We found that xanthommatin-based sensors undergo a visible shift from yellow to red in the presence of complete sunlight. This color change is driven by intrinsic photoreduction of the molecule, which we investigated using computational modeling and supplemented by radiation-driven formation of complementary reducing agents. These sensors are responsive to dermatologically relevant doses of erythemally weighted radiation, as well as cumulative doses of high-energy ultraviolet radiation used for germicidal sterilization. We incorporated these miniature sensors into pressure-activated microfluidic systems to illustrate on-demand activation of a wearable and mountable form factor. When taken together, our findings encompass an important advancement toward accessible, quantitative measurements of UVC and complete solar radiation for a variety of use cases.

Barriers and Promises of the Developing Pigment Organelle Field.

Many colors and patterns in nature are regulated by the packaging and processing of intracellular pigment-containing organelles within cells. Spanning both molecular and tissue-level spatial scales with chemical and physical (structural) elements of coloration, pigment organelles represent an important but largely understudied feature of every biological system capable of coloration. Although vertebrate melanosomes have historically been the best-known and most studied pigment organelle, recent reports suggest a surge in studies focusing on other pigment organelles producing a variety of non-melanic pigments, optic crystals and structural colors through their geometric arrangement. In this issue, we showcase the importance of these integrative and comparative studies and discuss their results which aid in our understanding of organelle form and function in their native environment. Specifically, we highlight how pigment organelles can be studied at different scales of organization, across multiple species in biology, and with an interdisciplinary approach to better understand the biological and chemical mechanisms underlying color. This type of comparative approach provides evidence for a common origin and identity of membrane-bound pigment organelles not only in vertebrates, as was originally postulated 40 years ago, but in all animals. This indicates that we have much to gain by studying a variety of pigment organelles, as the specific biological context may provide important and unique insights into various aspects of its life. We conclude by highlighting some barriers to this research and discussing strategies to overcome them through a discussion of future directions for pigment organelle research.

Compositional Similarities that Link the Eyes and Skin of Cephalopods: Implications in Optical Sensing and Signaling during Camouflage.

Cephalopods, including squid, octopus, and cuttlefish, can rapidly camouflage in different underwater environments by employing multiple optical effects including light scattering, absorption, reflection, and refraction. They can do so with exquisite control and within a fraction of a second-two features that indicate distributed, intra-dermal sensory, and signaling components. However, the fundamental biochemical, electrical, and mechanical controls that regulate color and color change, from discrete elements to interconnected modules, are still not fully understood despite decades of research in this space. This perspective highlights key advancements in the biochemical analysis of cephalopod skin and discusses compositional connections between cephalopod ocular lenses and skin with features that may also facilitate signal transduction during camouflage.

Biomimetic Colorants and Coatings Designed with Cephalopod-Inspired Nanocomposites.

Brilliant and dynamic colors in nature have stimulated the design of dyes and pigments with broad applications ranging from electronic displays to apparel. Inspired by the nanostructured pigment granules present in cephalopod chromatophore organs, we describe the design and fabrication of biohybrid colorants containing the cephalopod-specific pigment, xanthommatin (Xa), encased within silica-based nanostructures. We employed a biomimetic approach to encapsulate Xa with amine-terminated polyamidoamine (PAMAM) dendrimer templates, which helped stabilize the pigment during encapsulation. Depending on the concentration of Xa used in the reaction, the resultant biohybrid nanomaterials generated a range of neutral colors of differing hues. When applied as coatings, these colorants can be triggered to change color from yellow/gold to red in the presence of a chemical reducing agent, as we leverage the natural redox-dependent color change of Xa. Altogether, these capabilities demonstrated the ability to process biochromes like Xa as nanomaterials that can be applied as coatings with a tunable and dynamic range.

A Role for Monosaccharides in Nucleation Inhibition and Transport of Collagen.

Background: Collagenous tissues are composed of precisely oriented, tightly packed collagen fibril bundles to confer the maximal strength within the smallest volume. While this compact form benefits mobility, it consequentially restricts vascularity and cell density to a minimally viable level in some regions. These tissues reside in a homeostatic state with an unstable equilibrium, where perturbations to structure or molecular milieu cause descension into a long-term compromised state. Several studies have shown that glycosaminoglycans are key molecules required for healthy tissue maintenance. Our long-term goal is to determine if glycosaminoglycans serve a critical function of stabilizing soluble monomeric collagen in the interstitial fluid that bathes tissue for immediate availability in tissue development and repair in vivo. Materials and Methods: To test glycosaminoglycan and collagen interactions at the most fundamental level, we have explored the effect of the monosaccharides that populate the glycosaminoglycans of the extracellular matrix on collagen assembly kinetics, pre-established matrix stability, and collagen incorporation into a preassembled matrix. Results: Results showed that monosaccharides increased the threshold concentration required for spontaneous polymerization by at least three orders of magnitude. When the monosaccharides were introduced to a pre-existing collagen network, fibrillar dissociation was undetectable. Fluorescent-labeling studies illustrated that in the presence of the saccharide solution, soluble collagen maintains the functional capacity to integrate into a pre-existing network. Conclusion: This work demonstrates a feasible role for glycosaminoglycans in supporting tissue remodeling and highlights the potential importance of age-related deterioration of glycosaminoglycan biosynthesis in reference to the homeostasis of collagen-based tissues.

A bioinspired, photostable UV-filter that protects mammalian cells against UV-induced cellular damage.

While commercially available suncare products are effective at absorbing ultraviolet (UV)-light, recent studies indicate systemic toxicities associated with many traditional chemical and physical UV-filters. We demonstrate the application of xanthommatin, a biochrome present in arthropods and cephalopods, as an alternative chemical UV-filter that is cytocompatible while maintaining its photostability and photoprotective properties.

Dynamic pigmentary and structural coloration within cephalopod chromatophore organs.

Chromatophore organs in cephalopod skin are known to produce ultra-fast changes in appearance for camouflage and communication. Light-scattering pigment granules within chromatocytes have been presumed to be the sole source of coloration in these complex organs. We report the discovery of structural coloration emanating in precise register with expanded pigmented chromatocytes. Concurrently, using an annotated squid chromatophore proteome together with microscopy, we identify a likely biochemical component of this reflective coloration as reflectin proteins distributed in sheath cells that envelop each chromatocyte. Additionally, within the chromatocytes, where the pigment resides in nanostructured granules, we find the lens protein Ω- crystallin interfacing tightly with pigment molecules. These findings offer fresh perspectives on the intricate biophotonic interplay between pigmentary and structural coloration elements tightly co-located within the same dynamic flexible organ - a feature that may help inspire the development of new classes of engineered materials that change color and pattern.

Xanthommatin-Based Electrochromic Displays Inspired by Nature.

Color is a signature visual feature in nature; however, the ability to trigger color change in the presence of different environmental stimuli is unique to only a handful of species in the animal kingdom. We exploit the natural color-changing properties of the predominant pigment in arthropods and cephalopods-xanthommatin (Xa)-and describe its utility as a new broad-spectrum electrochromic material. To accomplish this goal, we explored the spectroelectrochemical properties of Xa adsorbed to an indium-doped tin oxide-coated substrate chemically modified with poly(3,4-ethylene dioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS). We identified a synergistic role between PEDOT:PSS and Xa that contributed to its absorption profile, which could be modulated across multiple cycles. By varying the ratio of the two electroactive components, we also altered the perceived visible color of Xa-based devices, which cycled from different shades of red to yellow under reducing and oxidizing potentials, respectively. Together, our data illustrate the utility of Xa-based devices as new broad-spectrum electrochromic materials.

Rapid, High Affinity Binding by a Fluorescein Templated Copolymer Combining Covalent, Hydrophobic, and Acid⁻Base Noncovalent Crosslinks.

A new type of biomimetic templated copolymer has been prepared by reverse addition fragmentation chain transfer polymerization (RAFT) in dioxane. The initial formulation includes the template fluorescein, N-isopropylacrylamide (NIPAM, 84 mol %), methacrylic acid (MAA, 5-mol %), 4-vinylpyridine (4-VP, 9 mmol %), and N,N′-methylenebis(acrylamide) (MBA, 2 mol %). PolyNIPAM is a thermosensitive polymer that comes out of aqueous solution above its lower critical solution temperature forming hydrophobic ‘crosslinks’. MAA and 4-VP interact in dioxane forming acid⁻base crosslinks. The excess 4-VP serves as a recognition monomer organizing around the template fluorescein to form a binding site that is held in place by the noncovalent and covalent crosslinks. The MBA is a covalent crosslinker. The RAFT agent in the resulting copolylmer was reduced to a thiol and attached to gold nanoparticles. The gold nanoparticle bound copolymer binds fluorescein completely in less than two seconds with an affinity constant greater than 108 M−1. A reference copolymer prepared with the same monomers by the same procedure binds fluorescein much more weakly.

Production-scale fibronectin nanofibers promote wound closure and tissue repair in a dermal mouse model.

Wounds in the fetus can heal without scarring. Consequently, biomaterials that attempt to recapitulate the biophysical and biochemical properties of fetal skin have emerged as promising pro-regenerative strategies. The extracellular matrix (ECM) protein fibronectin (Fn) in particular is believed to play a crucial role in directing this regenerative phenotype. Accordingly, Fn has been implicated in numerous wound healing studies, yet remains untested in its fibrillar conformation as found in fetal skin. Here, we show that high extensional (∼1.2 ×105 s-1) and shear (∼3 ×105 s-1) strain rates in rotary jet spinning (RJS) can drive high throughput Fn fibrillogenesis (∼10 mL/min), thus producing nanofiber scaffolds that are used to effectively enhance wound healing. When tested on a full-thickness wound mouse model, Fn nanofiber dressings not only accelerated wound closure, but also significantly improved tissue restoration, recovering dermal and epidermal structures as well as skin appendages and adipose tissue. Together, these results suggest that bioprotein nanofiber fabrication via RJS could set a new paradigm for enhancing wound healing and may thus find use in a variety of regenerative medicine applications.

Fabrication of Millimeter-Long Carbon Tubular Nanostructures Using the Self-Rolling Process Inherent in Elastic Protein Layers.

Millimeter-long conducting fibers can be fabricated from carbon nanomaterials via a simple method involving the release of a prestrained protein layer. This study shows how a self-rolling process initiated by polymerization of a micropatterned layer of fibronectin (FN) results in the production of carbon nanomaterial-based microtubular fibers. The process begins with deposition of carbon nanotube (CNT) or graphene oxide (GO) particles on the FN layer. Before polymerization, particles are discrete and nonconducting, but after polymerization the carbon materials become entangled to form an interconnected conducting network clad by FN. Selective removal of FN using high-temperature combustion yields freestanding CNT or reduced GO microtubular fibers. The properties of these fibers are characterized using atomic force microscopy and Raman spectroscopy. The data suggest that this method may provide a ready route to rapid design and fabrication of aligned biohybrid nanomaterials potentially useful for future electronic applications.

Color Richness in Cephalopod Chromatophores Originating from High Refractive Index Biomolecules.

Cephalopods are arguably one of the most photonically sophisticated marine animals, as they can rapidly adapt their dermal color and texture to their surroundings using both structural and pigmentary coloration. Their chromatophore organs facilitate this process, but the molecular mechanism potentiating color change is not well understood. We hypothesize that the pigments, which are localized within nanostructured granules in the chromatophore, enhance the scattering of light within the dermal tissue. To test this, we extracted the phenoxazone-based pigments from the chromatophore and extrapolated their complex refractive index (RI) from experimentally determined real and approximated imaginary portions of the RI. Mie theory was used to calculate the absorbance and scattering cross sections (cm2/particle) across a broad diameter range at λ = 589 nm. We observed that the pigments were more likely to scatter attenuated light than absorb it and that these characteristics may contribute to the color richness of cephalopods.

A Method for Extracting Pigments from Squid Doryteuthis pealeii.

Cephalopods can undergo rapid and adaptive changes in dermal coloration for sensing, communication, defense, and reproduction purposes. These capabilities are supported in part by the areal expansion and retraction of pigmented organs known as chromatophores. While it is known that the chromatophores contain a tethered network of pigmented granules, their structure-function properties have not been fully detailed. We describe a method for isolating the nanostructured granules in squid Doryteuthis pealeii chromatophores and demonstrate how their associated pigments can be extracted in acidic solvents. To accomplish this, the chromatophore containing dermal layer is first manually isolated using a superficial dissection, and the pigment granules are removed using sonication, centrifugation, and washing cycles. Pigments confined within the purified granules are then extracted via acidic methanol solutions, leaving nanostructures with smaller diameters that are void of visible color. This extraction procedure produces a 58% yield of soluble pigments isolated from granules. Using this method, the composition of the chromatophore pigments can be determined and used to provide insight into the mechanism of adaptive coloration in cephalopods.