Complex photonic structures in nature: from order to disorder

Structural colours arise from the interaction of visible light with nano-structured materials. The occurrence of such structures in nature has been known for over a century, but it is only in the last few decades that the study of natural photonic structures has fully matured due to the advances in imagining techniques and computational modelling. Even though a plethora of different colour-producing architectures in a variety of species has been investigated, a few significant questions are still open: how do these structures develop in living organisms? Does disorder play a functional role in biological photonics? If so, is it possible to say that the optical response of natural disordered photonics has been optimised under evolutionary pressure? And, finally, can we exploit the well-adapted photonic design principles that we observe in Nature to fabricate functional materials with optimised scattering response? In my thesis I try to answer the questions above: I microscopically investigate $\textit{in vivo}$ the growth of a cuticular multilayer, one of the most common colour-producing strategies in nature, in the green beetles $\textit{Gastrophysa viridula}$ showing how the interplay between different materials varies during the various life stages of the beetles; I further investigate two types of disordered photonic structures and their biological role, the random array of spherical air inclusions in the eggshells of the honeyguide $\textit{Prodotiscus regulus}$, a species under unique evolutionary pressure to produce blue eggs, and the anisotropic chitinous network of fibres in the white beetle $\textit{Cyphochilus}$, the whitest low-refractive index material; finally, inspired by these natural designs, I fabricate and study light transport in biocompatible highly-scattering materials.European Research Council grant awarded to Dr Silvia Vignolin

Disordered Cellulose-based Nanostructures for Enhanced Light-scattering

Cellulose is the most abundant bio-polymer on earth. Cellulose fibres, such as the one extracted form cotton or woodpulp, have been used by humankind for hundreds of years to make textiles and paper. Here we show how, by engineering light matter-interaction, we can optimise light scattering using exclusively cellulose nanocrystals. The produced material is sustainable, biocompatible and, when compared to ordinary microfibre-based paper, it shows enhanced scattering strength (x4) yielding a transport mean free path as low as 3.5 um in the visible light range. The experimental results are in a good agreement with the theoretical predictions obtained with a diffusive model for light propagation

Living Light 2018: Conference Report

Living Light is a biennial conference focused on all aspects of light–matter interaction in biological organisms with a broad, interdisciplinary outlook. The 2018 edition was held at the Møller Centre in Cambridge, UK, from April 11th to April 14th, 2018. Living Light’s main goal is to bring together researchers from different backgrounds (e.g., biologists, physicists and engineers) in order to discuss the current state of the field and sparkle new collaborations and new interdisciplinary projects. With over 90 national and international attendees, the 2018 edition of the conference was strongly multidisciplinary: oral and poster presentations encompassed a wide range of topics ranging from the evolution and development of structural colors in living organisms and their genetic manipulation to the study of fossil photonic structures.S.V. thanks the Biotechnology and Biological Sciences Research Council (BBSRC) David Phillips fellowship (BB/K014617/1), the European Research Council (ERC-2014-STG H2020 639088), and the European Commission (Marie Curie Fellowship Looking Through Disorder (LODIS), 701455) for financial support. B.D.W. was financially supported through the National Center of Competence in Research Bio-Inspired Materials and the Ambizione program of the Swiss National Science Foundation (168223)

Efficacy of "Cognitive Multisensory Rehabilitation" on fatigue in stroke subjects: designing a study protocol.

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Clathrin-dependent and independent endocytic pathways in tobacco protoplasts revealed by labelling with charged nanogold

Positively charged nanogold was used as a probe to trace the internalization of plasma membrane (PM) domains carrying negatively charged residues at an ultrastructural level. The probe revealed distinct endocytic pathways within tobacco protoplasts and allowed the morphology of the organelles involved in endocytosis to be characterized in great detail. Putative early endosomes with a tubulo-vesicular structure, similar to that observed in animal cells, are described and a new compartment, characterized by interconnected vesicles, was identified as a late endosome using the Arabidopsis anti-syntaxin family Syp-21 antibody. Endocytosis dissection using Brefeldin A (BFA), pulse chase, temperature- and energy-dependent experiments combined with quantitative analysis of nanogold particles in different compartments, suggested that recycling to the PM predominated with respect to degradation. Further experiments using ikarugamycin (IKA), an inhibitor of clathrin-dependent endocytosis, and negatively charged nanogold confirmed that distinct endocytic pathways coexist in tobacco protoplast

Bio-inspired Highly Scattering Networks via Polymer Phase Separation

A common strategy to optimize whiteness in living organisms consists in using three-dimensional random networks with dense and polydisperse scattering elements constituted by relatively low-refractive index materials. Inspired by these natural architectures, we developed a fast and scalable method to produce highly scattering porous polymer films via phase separation. By varying the molecular weight of the polymer, we modified the morphology of the porous films and therefore tuned their scattering properties. The achieved transport mean free paths are in the micrometer range, improving the scattering strength of analogous low-refractive index systems, e.g. standard white paper, by an order of magnitude. The produced porous films show a broadband reflectivity of approximately 75 % whilst only 4 m thick. In addition, the films are flexible and can be readily index-matched with water (i.e. they become transparent when wet), allowing for various applications such as coatings with tunable transmittance and responsive paints

Photonics in Nature: From Order to Disorder

The most vibrant and striking colours in living organisms are often caused by a combination of pigments and nano-scale transparent architectures, which interact with light to produce so-called structural colours. These colours are the result of light interfering with the nanoscale structures that are present in the materials. Such colour-producing structures are not perfect, and irregularities in the arrangements (disorder) are present in many organisms. However, disorder in natural structures is not detrimental but functional, as it allows a broader range of optical effects. This chapter reviews and attempts to classify structurally coloured organisms, highlighting the influence that disorder has on their visual appearance. It also showcases how photonic systems, such as the blue Morpho butterfly and the white Cyphochilus beetle, are capable of obtaining optical properties (long-distance visibility and whiteness, respectively) where disorder seems to be highly optimized, indicating that disorder is important for obtaining complex visual effects in natural systems. The chapter first introduces the mathematical concepts required for analysing disordered systems, such as the Fourier transform and the structure factor. Then, ordered and disordered natural photonic systems are reviewed. This is followed by examples of completely disordered structures responsible of white appearances. Finally, we review the possibilities of hierarchical organisation and pixelated surfaces to widen the range of optical appearances

Evaluation of concentration of heavy metals in animal rearing system

Animal manure is one of the diffusion routes of heavy metals and metalloids into the environment, where the soil can accumulate them. Heavy metals and metalloids can then be released into groundwater sources, be absorbed by crops, and enter the food chain with negative effects for human and animal health. The aim of this study was to evaluate the concentration of heavy metals and mineral nutrients from modern animal rearing systems in order to develop effective strategies to increase the sustainability. Samples of feed (n\ubc24: n\ubc16 from swine, n\ubc8 from cattle), faeces (n\ubc120: n\ubc80 from swine, n\ubc40 from cattle) and water (n\ubc8), were collected from eight typical intensive swine and cattle farms located in northern Italy. All samples were analysed for the humidity and the principal components. The samples were also dried, mineralised, and analysed by ICP-MS to detect the following elements: Na, Mg, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Cd, and Pb. The swine diets represented the highest amounts of Zn and Cu, with an average concentration for the finishing and weaning phases of Zn: 1737.9 \ub1 301.3; 821.7 \ub1 301.3; Cu: 133.8 \ub1 11.6; 160.1 \ub1 11.6 mg/kg as fed, respectively. The faecal content reflected the heavy metal composition from feed. The average content of cattle diets of Zn and Cu did not result higher than the maximum permitted levels. We observed that the swine manure represented the sources of Zn and Cu output into the environment. The Zn and Cu content should be monitored strictly in line with agroecology principles

Hereditary Character of Photonics Structure in Pachyrhynchus sarcitis Weevils: Color Changes via One Generation Hybridization

Pachyrhynchus sarcitis weevils are flightless weevils characterized by colored patches of scales on their dark elytra. The vivid colors of such patches result from the reflection of differently oriented three-dimensional photonic crystals within their scales. Our results show that hybrid P. sarcitis, the first filial generation of two P. sarcitis populations from Lanyu Island (Taiwan) and Babuyan Island (Philippines), mixes the color of its ancestors by tuning the photonic structure in its scales. A careful spectroscopical and anatomical analysis of the weevils in the phylogeny reveals the hereditary characteristics of the photonic crystals within their scales in terms of lattice constant, orientation and domain size. Monitoring how structural coloration is inherited by offspring highlights the versatility of photonic structures to completely redesign the optical response of living organisms. Such finding shed light onto the evolution and development mechanisms of structural coloration in Pachyrhynchus weevils and provides inspiration for the design of visual appearance in artificial photonic materials.NanoBio-ICMG platform (FR 2607) Cambridge Trus