Gerd E Schroeder-Turk

Nature offers a remarkable diversity of nanomaterials that have extraordinary functional and structural properties. Intrinsic to nature is the impressive ability to form complex ordered nanomaterials via self-organization. One particularly intriguing nanostructure is the gyroid, a network-like structure exhibiting high symmetry and complex topology. Although its existence in cells and tissues across many biological kingdoms is well documented, how and why it forms remains elusive and uncovering these formation mechanisms will undoubtedly inform bioinspired designs. A beautiful example is the smooth single gyroid that is found in the wing scales of several butterflies, where it behaves as a photonic crystal generating a vibrant green color. Here, we report that the gyroid structures of the Emerald-patched Cattleheart, Parides sesostris, develop as woven fibrillar structures, in contrast to the commonly held assumption that they form as smooth constructs. Ultramicroscopy of pupal tissue reveals that the gyroid geometry consists of helical weavings of fibers, akin to hyperbolic line patterns decorating the gyroid. Interestingly, despite their fibrillar nature, electron diffraction reveals the absence of crystalline order within this material. Similar fibrillar structures are also observed in the mature wing scales of P. sesostris specimens with surgically altered pupal development, leading to a blue coloration. Our findings not only introduce a variation of the gyroid in biology but also have significant implications for our understanding of its formation in nature.

Nature provides many astonishing examples of visual deception, from fish that resemble leaves to spiders and butterfly pupae that look like bird droppings or moth larvae that bear a striking resemblance to the head and neck of a tree snake.1,2 Most types of camouflage rely on preventing object detection, but this strategy of resemblance, known as masquerade, operates by fooling the viewer into misidentifying the animal as an inedible or unprofitable object rather than as predator or prey.3 As masquerade hinders object identification, the masquerader must have coloration that recreates the visual features of the object being mimicked. Here, we report a leaf-mimicking nocturnal moth, Eudocima aurantia (Noctuidae), that mimics not only leaf coloration but also a leaf’s surface highlights and appearance. The three-dimensional (3D) leaf-like appearance, which is accentuated by the apparent presence of a 3D midrib, is achieved with a featureless planar wing featuring uniformly oriented scales that combine structural and pigmentary coloration. Remarkably, these specialized nanostructures occur in those regions of the wing surface that correspond to the convex parts of a leaf. These structures and pigments combine scattering, absorption, and additive color mixing to produce a leaf-like brown coloration. E. aurantia has exploited the inherent mirror-like properties of thin-film reflectors to produce directional reflections that are usually associated with highlights on smooth, curved surfaces. Specular reflections provide a strong indicator of surface curvature to visual systems,4 suggesting that 3D shape mimicry is an integral part of the visual deception.

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.

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 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.

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.

Nature provides a rich source of information for the design of novel materials; yet there remain significant challenges in the design and manufacture of materials that replicate the form, function, and sustainability of biological solutions. Here, we identify key challenges and promising approaches to the development of materials informed by biology. These challenges fall into two main areas; the first relates to harnessing biological information for materials innovation, including key differences between biological and synthetic materials, and the relationship between structure and function. We propose an approach to materials innovation that capitalizes on biodiversity, together with high-throughput characterization of biological material architectures and properties, linked to environmental and ecological context. The second area relates to the design and manufacture of bioinformed materials, including the physical scale of material architectures and manufacturing scale up. We suggest ways to address these challenges and promising prospects for a bioinformed approach to materials innovation.

This study focuses on enhancing sustainability through energy-efficient methods in producing hierarchically structured porous carbons. A novel approach, utilizing an ultrasonic spray nozzle-quartz tube reactor (USN-QTR), is introduced for fabricating carbon beads with customizable ultra-, super-, and mesopores. This study showcases noteworthy results from subjecting spherical char particles to activation processes involving carbon dioxide, a mixture of carbon dioxide and micron-sized water droplets, and highly concentrated supercritical steam at a temperature of 1173 K for durations of 3 and 5 h. Through pulse-field gradient nuclear magnetic resonance measurements, it was noted that carbon beads produced using USN-generated highly concentrated supercritical steam displayed remarkably elevated intrabead self-diffusivity of n-hexane. Inductively coupled plasma-optical emission spectroscopy demonstrates superior gold recovery kinetics from cyanide solutions compared to that from an industrial benchmark. The energy expenditure for USN-generated steam, producing carbon beads with an apparent surface area of 2691 m2/g, is estimated at 97 J per 1 m2 of carbon. This contrasts with the traditional steam generation method requiring approximately the energy of 190 J/m2 for activated carbon with an SBET of 2130 m2/g, making the USN-assisted activation method a more environmentally friendly and sustainable option with nearly half the energy consumption.