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

Structural colours in the frond of Microsorum thailandicum.

Blue and near-ultraviolet structural colours have often been reported in understorey plants living in deep shade. While this intense blue coloration is very catchy to the eye of a human observer, there are cases in which structural colours can be hidden either by the scattered light interacting with pigments or because they are found in unexpected positions in the plants. Here, we show that the fronds of Microsorum thailandicum produce structural coloration on both the adaxial and abaxial epidermal surface. While cellulose helicoidal structures are responsible for this coloration in both epidermal layers, the reflected colours are consistently different: an intense blue reflection is found in the adaxial epidermis while red-shifted and less intense colours are observed in the abaxial epidermis, possibly suggesting photo-adaptation of the plant to the light environment. By comparing the optical properties of the fern with its anatomy we computed the theoretical reflection accounting for the presence of disorder in the cellulose helicoidal architecture.This work was supported by the European Research Council [ERC-2014-STG H2020 639088], the BBSRC David Phillips Fellowship [BB/K014617/1], the EPSRC [EP/N016920/1], and the European Commission, Marie Curie Fellowship [LODIS 701455]

Structural colours in the frond of Microsorum thailandicum

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The Potential of Antimicrobials to Induce Thrombocytopenia in Critically Ill Patients: Data from a Randomized Controlled Trial

<div><p>Background</p><p>Antimicrobial-induced thrombocytopenia is frequently described in the literature among critically ill patients. Several antimicrobials have been implicated, although experimental evidence to demonstrate causality is limited. We report, using a randomized trial, the potential of antimicrobials to induce thrombocytopenia.</p> <p>Methods</p><p>Randomized trial allocated patients to antimicrobial treatment according to standard- of-care (SOC group) or drug-escalation in case of procalcitonin increases (high-exposure group). Patients were followed until death or day 28. Thrombocytopenia defined as absolute (platelet count ≤100x109/L) or relative (≥20% decrease in platelet count). Analyses were performed in the two randomized groups and as a merged cohort. </p> <p>Results</p><p>Of the 1147 patients with platelet data available, 18% had absolute thrombocytopenia within the first 24 hours after admission to intensive care unit and additional 17% developed this complication during follow-up; 57% developed relative thrombocytopenia during follow-up. Absolute and relative thrombocytopenia day 1-4 was associated with increased mortality (HR: 1.67 [95% CI: 1.30 to 2.14]; 1.71 [95% CI: 1.30 to 2.30], P<0.0001, respectively). Patients in the high-exposure group received more antimicrobials including piperacillin/tazobactam, meropenem and ciprofloxacin compared with the SOC group, whereas cefuroxime was used more frequently in the SOC group (p<0.05). Risk of absolute and relative thrombocytopenia (RR: 0.9 [0.7-1.3], p=0.7439; 1.2 [1.0-1.4], p=0.06; respectively), as well as absolute platelet count (daily difference, high-exposure vs. SOC -1.7 [-3.8-0.5], p=0.14) was comparable between groups. In observational analyses, use of ciprofloxacin and piperacillin/tazobactam predicted risk of relative thrombocytopenia (vs. cefuroxime, RR: 2.08 [1.48-2.92]; 1.44 [1.10-1.89], respectively), however only ciprofloxacin were associated with a reduction in absolute platelet count (p=0.0005). </p> <p>Conclusion</p><p>High exposure to broad-spectrum antimicrobials does not result in a reduction in thrombocytopenia in critically ill patients. However, single use of ciprofloxacin, and less so piperacillin/tazobactam, may contribute to a lower platelet count.</p> <p>Trial Registration</p><p><a href="http://clinicaltrials.gov" target="_blank">ClinicalTrials.gov</a> NCT00271752 <a href="http://clinicaltrials.gov/ct2/show/nct00271752" target="_blank">http://clinicaltrials.gov/ct2/show/NCT00271752</a></p> </div

Estimated change in daily platelet count.

<div><p>Mixed model adjusted for the following time fixed variables: randomisation group, age, gender, BMI, severe sepsis/septic shock at ICU admission, APACHE II score, surgical vs. medical patients. </p> <p>Time-updated use of antimicrobials was included in the model.</p> <p>Ciprofloxacin, Piperacillin/tazobactam (pip/tazo) (used alone or in combinations not including cefuroxime) and none (no antimicrobials) compared to people receiving cefuroxime (used alone or in combinations non including the antibiotic in question).</p></div

Use of frequent prescribed antimicrobials in the PASS study and occurrence of absolute and relative thrombocytopenia among the two randomized groups.

<div><p>Unadjusted analysis displaying the use of antimicrobials and occurrence of thrombocytopenia among the two randomized groups displayed as relative rate ratio (RR) during 28 day follow-up.</p> <p>Absolute (one platelet count < 100 x 109/L) or relative (>=20 % decrease in platelet count from ICU admission) thrombocytopenia.</p> <p>RR-Ratio >1.0 indicates that the high-ex. group have a relatively higher risk of occurrence of the asses variable and RR-Ratio <1.0 indicates relatively higher risk of patients in the SOC group of occurrence of the asses variable. RR-ratio=0 indicates no difference between the two groups. </p></div