Block copolymer self-assembly for nanophotonics

The ability to control and modulate the interaction of light with matter is crucial to achieve desired optical properties including reflection, transmission, and selective polarization. Photonic materials rely upon precise control over the composition and morphology to establish periodic interactions with light on the wavelength and sub-wavelength length scales. Supramolecular assembly provides a natural solution allowing the encoding of a desired 3D architecture into the chemical building blocks and assembly conditions. The compatibility with solution processing and low-overhead manufacturing is a significant advantage over more complex approaches such as lithography or colloidal assembly. Here we review recent advances on photonic architectures derived from block copolymers and highlight the influence and complexity of processing pathways. Notable examples that have emerged from this unique synthesis platform include Bragg reflectors, antireflective coatings, and chiral metamaterials. We further predict expanded photonic capabilities and limits of these approaches in light of future developments of the field

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

Optical memory based on ultrafast wavelength switching in a bistable microlaser

We propose an optical memory cell based on ultrafast wavelength switching in coupled-cavity microlasers, featuring bistability between modes separated by several nanometers. A numerical implementation is demonstrated by simulating a two-dimensional photonic crystal microlaser. Switching times of less than 10 ps, switching energy around 15--30 fJ and on-off contrast of more than 40 dB are achieved. Theoretical guidelines for optimizing the performance of the memory cell in terms of switching time and energy are drawn.Comment: to appear in Optics Letter

The influence of pigmentation patterning on bumblebee foraging from flowers of <em>Antirrhinum majus</em>

Patterns of pigmentation overlying the petal vasculature are common in flowering plants,and have been postulated to play a role in pollinator attraction. Previous studies report that such venation patterning is significantly more attractiveto bee foragers in the field than ivory or white flowers without veins. To dissect the ways in which venation patterning of pigment can influence bumblebee behaviour we investigated the response of flower-naïve individuals of Bombus terrestris to veined, ivory and red near-isogenic lines of Antirrhinum majus. We find that red venation shifts flower colour slightly, although the ivory background is the dominant colour. Bees were readily able to discriminate between ivory and veined flowers under differential conditioning, but showed no innate preference when presented with a free choice of rewarding ivory and veined flowers. In contrast, both ivory and veined flowers were selected significantly more often than were red flowers. We conclude that advantages conferred by venation patterning might stem from bees learning of their use as nectar guides, rather than from any innate preference for striped flowers. </p

Flexible Photonic Cellulose Nanocrystal Films.

The fabrication of self-assembled cellulose nanocrystal (CNC) films of tunable photonic and mechanical properties using a facile, green approach is demonstrated. The combination of tunable flexibility and iridescence can dramatically expand CNC coating and film barrier capabilities for paints and coating applications, sustainable consumer packaging products, as well as effective templates for photonic and optoelectronic materials and structures.CelluForce Inc., Biotechnology and Biological Sciences Research Council (David Phillips fellowship (Grant ID: BB/K014617/1, 76933), European Research Council (Grant ID: ERC-2014-STG H2020 639088), Engineering and Physical Sciences Research Council (Grant ID: 1525292

Optical properties of gyroid structured materials: from photonic crystals to metamaterials

This is the accepted manuscript. The final version is available from Wiley at http://onlinelibrary.wiley.com/doi/10.1002/adom.201400333/abstract.The gyroid is a continuous and triply periodic cubic morphology which possesses a constant mean curvature surface across a range of volumetric fill fractions. Found in a variety of natural and synthetic systems which form through self-assembly, from butterfly wing scales to block copolymers, the gyroid also exhibits an inherent chirality not observed in any other similar morphologies. These unique geometrical properties impart to gyroid structured materials a host of interesting optical properties. Depending on the length scale on which the constituent materials are organised, these properties arise from starkly different physical mechanisms (such as a complete photonic band gap for photonic crystals and a greatly depressed plasma frequency for optical metamaterials). This article reviews the theoretical predictions and experimental observations of the optical properties of two fundamental classes of gyroid structured materials: photonic crystals (wavelength scale) and metamaterials (subwavelength scale).This work was supported by the EPSRC through the Cambridge NanoDTC EP/G037221/1, EP/G060649/1, EP/L027151/1, and ERC LINASS 320503

Robot-assisted kidney transplantation with regional hypothermia using grafts with Multiple Vessels After Extracorporeal Vascular Reconstruction: results from the European Association of Urology Robotic Urology Section Working Group

Background: Kidney transplantation using grafts with multiple vessels (GMVs) is technically demanding and may be associated with increased risk of complications or suboptimal graft function. To date, no studies have reported on robot-assisted kidney transplantation (RAKT) using GMVs. Objective: To report our experience with RAKT using GMVs from living donors, focusing on technical feasibility and early postoperative outcomes. Design, setting, and participants: We reviewed the multi-institutional, prospectively collected European Association of Urology (EAU) Robotic Urology Section (ERUS)-RAKT database to select consecutive patients undergoing RAKT from living donors using GMVs between July 2015 and January 2018. Patients undergoing RAKT using grafts with single vessels (GSVs) served as controls. In case of GMVs, ex vivo vascular reconstruction techniques were performed during bench surgery according to the case-specific anatomy. Intervention: RAKT with regional hypothermia. Outcome measurements and statistical analysis: Intraoperative outcomes and early (30 d) postoperative complications and functional results were the main study endpoints. Multivariable logistic regression analysis evaluated potential predictors of suboptimal renal function at 1 mo. Results and limitations: Overall, 148 RAKTs were performed during the study period. Of these, 21/148 (14.2%) used GMVs; in all cases, single arterial and venous anastomoses could be performed after vascular reconstruction. Median anastomoses and rewarming times did not differ significantly between the GMV and GSV groups. Total and cold ischemia times were significantly higher in the GMV cohort (112 vs 88 min, p = 0.004 and 50 vs 34 min, p = 0.003, respectively). Overall complication rate and early functional outcomes were similar among the two groups. No major intra-or postoperative complications were recorded in the GMV cohort. At multivariable analysis, use of GMVs was not significantly associated with suboptimal renal function at 1 mo. Small sample size and short follow-up represent the main study limitations. Conclusions: RAKT using GMVs from living donors is technically feasible and achieved favorable perioperative and short-term functional outcomes. Larger studies with longer follow-up are needed to confirm our findings. Patient summary: In this study, we evaluated for the first time in literature the results of RAKT from living donors using kidneys with multiple arteries and veins. We found that, in experienced centers, RAKT using kidneys with multiple vessels is feasible and achieves optimal results in terms of postoperative kidney function with a low number of postoperative complications. (C) 2018 European Association of Urology. Published by Elsevier B.V. All rights reserved

Ultrafast nonlinear response of gold gyroid three-dimensional metamaterials

We explore the nonlinear optical response of 3D gyroidal metamaterials, which show >10-fold enhancements compared to all other metallic nanomaterials as well as bulk gold. A simple analytical model for this metamaterial response shows how the reflectivity spectrum scales with the metal fill fraction and the refractive index of the material that the metallic nanostructure is embedded in. The ultrafast response arising from the interconnected 3D nanostructure can be separated into electronic and lattice contributions with strong spectral dependences on the dielectric filling of the gyroids, which invert the sign of the nonlinear transient reflectivity changes. These metamaterials thus provide a wide variety of tuneable nonlinear optical properties, which can be utilised for frequency mixing, optical switching, phase modulators, novel emitters, and enhanced sensing.This is the author's accepted manuscript. The final version is available from APS in Physical Review Applied at http://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.2.044002#fulltext#fulltext

Structural colour from helicoidal cell-wall architecture in fruits of Margaritaria nobilis

The bright and intense blue-green coloration of the fruits of Margaritaria nobilis (Phyllanthaceae) was investigated using polarization-resolved spectroscopy and transmission electron microscopy. Optical measurements of freshly collected fruits revealed a strong circularly polarized reflection of the fruit that originates from a cellulose helicoidal cell wall structure in the pericarp cells. Hyperspectral microscopy was used to capture the iridescent effect at the single-cell level.Leverhulme Trust (F/09-741/G)United States. Air Force Office of Scientific Research (award number FA9550-10-1-0020)Adolphe Merkle FoundationSwiss National Science Foundation (National Centre of Competence in Research Bio-Inspired Materials)Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC David Phillips fellowship (BB/K014617/1)