Synthesis and properties of macroporous SiC ceramics synthesized by 3D printing and chemical vapor infiltration/deposition

Open porosity cellular SiC-based ceramics have a great potential for energy conversion, e.g. as solar receivers. In spite of their tolerance to damage, structural applications at high temperature remain limited due to high production costs or inappropriate properties. The objective of this work was to investigate an original route for the manufacturing of porous SiC ceramics based on 3D printing and chemical vapor infiltration/deposition (CVI/CVD). After binder jetting 3D-printing, the green α-SiC porous structures were reinforced by CVI/CVD of SiC using CH3SiCl3/H2. The multiscale structure of the SiC porous specimens was carefully examined as well as the elemental and phase content at the microscale. The oxidation and thermal shock resistance of the porous SiC structures and model specimens were also studied, as well as the thermal and mechanical properties. The pure and dense CVI/CVD-SiC coating considerably improves the mechanical strength, oxidation resistance and thermal diffusivity of the material

A detailed clinical and molecular survey of subjects with nonsyndromic USH2A retinopathy reveals an allelic hierarchy of disease-causing variants.

Defects in USH2A cause both isolated retinal disease and Usher syndrome (ie, retinal disease and deafness). To gain insights into isolated/nonsyndromic USH2A retinopathy, we screened USH2A in 186 probands with recessive retinal disease and no hearing complaint in childhood (discovery cohort) and in 84 probands with recessive retinal disease (replication cohort). Detailed phenotyping, including retinal imaging and audiological assessment, was performed in individuals with two likely disease-causing USH2A variants. Further genetic testing, including screening for a deep-intronic disease-causing variant and large deletions/duplications, was performed in those with one likely disease-causing change. Overall, 23 of 186 probands (discovery cohort) were found to harbour two likely disease-causing variants in USH2A. Some of these variants were predominantly associated with nonsyndromic retinal degeneration ('retinal disease-specific'); these included the common c.2276 G>T, p.(Cys759Phe) mutation and five additional variants: c.2802 T>G, p.(Cys934Trp); c.10073 G>A, p.(Cys3358Tyr); c.11156 G>A, p.(Arg3719His); c.12295-3 T>A; and c.12575 G>A, p.(Arg4192His). An allelic hierarchy was observed in the discovery cohort and confirmed in the replication cohort. In nonsyndromic USH2A disease, retinopathy was consistent with retinitis pigmentosa and the audiological phenotype was variable. USH2A retinopathy is a common cause of nonsyndromic recessive retinal degeneration and has a different mutational spectrum to that observed in Usher syndrome. The following model is proposed: the presence of at least one 'retinal disease-specific' USH2A allele in a patient with USH2A-related disease results in the preservation of normal hearing. Careful genotype-phenotype studies such as this will become increasingly important, especially now that high-throughput sequencing is widely used in the clinical setting.European Journal of Human Genetics advance online publication, 4 February 2015; doi:10.1038/ejhg.2014.283

Combined genetic approaches yield a 48% diagnostic rate in a large cohort of French hearing-impaired patients

International audienceHearing loss is the most common sensory disorder and because of its high genetic heterogeneity, implementation of Massively Parallel Sequencing (MPS) in diagnostic laboratories is greatly improving the possibilities of offering optimal care to patients. We present the results of a two-year period of molecular diagnosis that included 207 French families referred for non-syndromic hearing loss. Our multi-step strategy involved (i) DFNB1 locus analysis, (ii) MPS of 74 genes, and (iii) additional approaches including Copy Number Variations, in silico analyses, minigene studies coupled when appropriate with complete gene sequencing, and a specific assay for STRC. This comprehensive screening yielded an overall diagnostic rate of 48%, equally distributed between DFNB1 (24%) and the other genes (24%). Pathogenic genotypes were identified in 19 different genes, with a high prevalence of GJB2, STRC, MYO15A, OTOF, TMC1, MYO7A and USH2A. Involvement of an Usher gene was reported in 16% of the genotyped cohort. Four de novo variants were identified. This study highlights the need to develop several molecular approaches for efficient molecular diagnosis of hearing loss, as this is crucial for genetic counselling, audiological rehabilitation and the detection of syndromic forms

SLC12A2 variants cause a neurodevelopmental disorder or cochleovestibular defect

The SLC12 gene family consists of SLC12A1–SLC12A9, encoding electroneutral cation-coupled chloride co-transporters. SCL12A2 has been shown to play a role in corticogenesis and therefore represents a strong candidate neurodevelopmental disorder gene. Through trio exome sequencing we identified de novo mutations in SLC12A2 in six children with neurodevelopmental disorders. All had developmental delay or intellectual disability ranging from mild to severe. Two had sensorineural deafness. We also identified SLC12A2 variants in three individuals with non-syndromic bilateral sensorineural hearing loss and vestibular areflexia. The SLC12A2 de novo mutation rate was demonstrated to be significantly elevated in the deciphering developmental disorders cohort. All tested variants were shown to reduce co-transporter function in Xenopus laevis oocytes. Analysis of SLC12A2 expression in foetal brain at 16–18 weeks post-conception revealed high expression in radial glial cells, compatible with a role in neurogenesis. Gene co-expression analysis in cells robustly expressing SLC12A2 at 16–18 weeks post-conception identified a transcriptomic programme associated with active neurogenesis. We identify SLC12A2 de novo mutations as the cause of a novel neurodevelopmental disorder and bilateral non-syndromic sensorineural hearing loss and provide further data supporting a role for this gene in human neurodevelopment

Analysis of the Ush2a Gene in Medaka Fish (Oryzias latipes)

Patients suffering from Usher syndrome (USH) exhibit sensorineural hearing loss, retinitis pigmentosa (RP) and, in some cases, vestibular dysfunction. USH is the most common genetic disorder affecting hearing and vision and is included in a group of hereditary pathologies associated with defects in ciliary function known as ciliopathies. This syndrome is clinically classified into three types: USH1, USH2 and USH3. USH2 accounts for well over one-half of all Usher cases and mutations in the USH2A gene are responsible for the majority of USH2 cases, but also for atypical Usher syndrome and recessive non-syndromic RP. Because medaka fish (Oryzias latypes) is an attractive model organism for genetic-based studies in biomedical research, we investigated the expression and function of the USH2A ortholog in this teleost species. Ol-Ush2a encodes a protein of 5.445 aa codons, containing the same motif arrangement as the human USH2A. Ol-Ush2a is expressed during early stages of medaka fish development and persists into adulthood. Temporal Ol-Ush2a expression analysis using whole mount in situ hybridization (WMISH) on embryos at different embryonic stages showed restricted expression to otoliths and retina, suggesting that Ol-Ush2a might play a conserved role in the development and/or maintenance of retinal photoreceptors and cochlear hair cells. Knockdown of Ol-Ush2a in medaka fish caused embryonic developmental defects (small eyes and heads, otolith malformations and shortened bodies with curved tails) resulting in late embryo lethality. These embryonic defects, observed in our study and in other ciliary disorders, are associated with defective cell movement specifically implicated in left-right (LR) axis determination and planar cell polarity (PCP)

A Genetic Basis for Mechanosensory Traits in Humans

Hearing and touch are genetically related, and people with excellent hearing are more likely to have a fine sense of touch and vice versa

A nitric oxide synthase activity is involved in the modulation of acetylcholine release in Aplysia ganglion neurons : a histological, voltammetric and electrophysiological study

International audienc

Opposite effects of nitric oxide on identified inhibitory and exitatory cholinergic synapses of Aplysia californica

International audienc

Numérisation d'électrodes poreuses en or par analyse FIB-SEM

Le développement de batteries bio-enzymatiques et de bio-capteurs est un domaine extrêmement prometteur car ces objets allient l'utilisation d'énergies alternatives à une miniaturisation poussée. Les applications sont nombreuses en tant que microsystèmes comme : capteurs électroanalytiques, alimentation électrique pour dispositifs actifs ou passifs implantables dans le corps humain (pompes, valves, actuateurs, …). Ces biocomposants peuvent être fabriqués à partir de milieux à porosité contrôlée au sein desquels les réactions rédox hétérogènes prennent place pour assurer la conversion d'énergie chimique en énergie électrique ou réciproquement. L'idéal est de combiner une grande surface développée par unité de volume à une bonne accessibilité des espèces chimiques arrivantes et partantes, mais ces deux prérequis sont antagonistes. Cette question d'optimisation n'a pour l'instant pas été abordée de façon systématique et rationnalisée. Le projet « MOMA : Modeling of porous electrodes for an Optimized MAterial design » consiste à utiliser une méthode de type "bottom-up" (micro-macro) pour optimiser le design d'électrodes poreuses en or destinées à équiper des bio-systèmes. L'objectif est ici d'élucider la dépendance des caractéristiques de l'électrode vis-à-vis de sa microstructure, dépendance ensuite exploitée pour optimiser l'architecture porale. On propose pour cela une approche dite de « matériau virtuel », basée sur une caractérisation fine des éléments structuraux et morphologiques des électrodes, permettant ensuite de générer des domaines de calcul adéquats pour la simulation du transfert et des réactions électrochimiques. Le travail commence par une préparation des milieux poreux par une méthode de réplication d'empilements réguliers de nano-billes de silice, donnant une structure de type « opale inverse » ; ensuite, une acquisition d'images est faite sur ces milieux pour alimenter les calculs. Comme les tailles de pores sont entre 10 et 100 nm, le faisceau d'ions focalisé couplé à la microscopie électronique à balayage (FIB-SEM) semble la méthode la plus adaptée [1]. L'application de cette méthode a été concluante pour l'étude d'une électrode poreuse de pile à combustible avec des pores allant de 5 à 200 nm [2]. Une étape de traitement d'images [3] et de reconstruction 3D avec des logiciels spécifiques permettra de caractériser en détails le réseau poral d'or. Avant de s'intéresser à la numérisation des électrodes, voyons comment ces dernières sont élaborées : (i) Tout d'abord, un film de silice (billes de 1 µm de diamètre) est déposé sur un substrat en or (cylindre plein de diamètre 250 µm et de longueur 4 cm) par la technique Langmuir-Blodgett (LB) [4]. (ii) Ensuite, un dépôt d'or est réalisé par technique électrochimique (électrodéposition) sur les billes de silice [5]. (iii) Afin d'obtenir une structure uniquement formée d'or (fil support + réseau poral), les électrodes sont trempées pendant 5 min dans de l'acide fluorhydrique (HF). Cette technique permet d'éliminer toute trace de silice. Le premier objectif de ce travail est de reconstituer en 3D le réseau poral d'or. Un instrument d'imagerie par faisceaux d'ions focalisés (FIB) utilise un faisceau d'ions finement localisé pour modifier et numériser en images (MEB) l'échantillon choisi. Pour un volume d'échantillon donné, l'objectif est donc de réaliser le maximum de coupes pour pouvoir accroitre la qualité de la reconstruction 3D. Le volume analysé est ici de l'ordre de 15 000 µm 3 (cube de 25 µm de côté). 600 coupes successives ont été faites avec un pas de 25 nm, pour une durée totale d'acquisition de 14 h. Après obtention des différentes coupes, un travail d'analyse d'images a été réalisé pour reconstruire en 3D le réseau poral. Pour ce faire, on distingue plusieurs étapes : (i) Les séries d'images obtenues nécessitent un réalignement en raison de l'angle entre les colonnes FIB et MEB (52°), des problèmes de dérive rencontrés lors de l'acquisition (perte de focalisation, problèmes environnementaux…), et d'une résolution différente dans le plan et la profondeur de l'image [6]. (ii) La seconde étape consiste à segmenter (binariser en noir et blanc) les images MEB. Cette étape est délicate du fait de la profondeur de champs visible sur chaque image MEB. Pour ce faire, deux différentes méthodes peuvent être envisagées : (a) Une segmentation dite manuelle où pour chaque image, on vient manuellement recouvrir chaque pore d'un cercle noir (Fig. 1.a). Ce travail est très fastidieux, mais après 35 h de travail (nécessaires pour segmenter 300 images), les résultats sont quasi parfaits après seuillage par image-J (Fig. 1.b). (b) Une segmentation dite automatique où on utilise un logiciel gratuit et disponible en ligne (Ilastik

Digitizing gold porous electrodes using FIB-SEM analysis

This project is dedicated to a bottom-up approach to optimize the design of porous electrode materials devoted to biofuel cells and biosensors. These devices operate on the basis of complex enzymatic electrochemical redox reactions coupled to mass transfer of substrates (glucose and O2) and electron transfer within the pores of the structure and from/to the pore surfaces. The advantage of using porous materials for these devices lies in the very large internal surface area (where electron exchange takes place) to overall material volume ratio, yielding much larger current densities than on a bare solid electrode of the same size. Some very interesting techniques, based on templating silica beads on gold substrate with a Langmuir-Blodgett deposition 1 step followed by electroplating of gold 2 and beads dissolution have been elaborated to synthetize porous materials made of pure gold having a typical spherical pore size of the order of the micrometer. The objective of the project is to model the porous structure of the electrode. First, a determination of the geometrical characteristics can be achieved through image acquisition and analysis. The structure not only contains a gradient of hollow spherical pore radii, but also some degree of disorder due to local arrangement defects; the radii of the windows separating the pores is also locally variable. Since pore window dimensions are around 100 nm, Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM 3) (Fig. 1) has been performed to obtain a 3D reconstruction of the porous medium. Segmentation and binarization of images were made both manually and automatically using Fiji and Python. More than 600 SEM (SE) images (25 nm between 2 images) yield a 3D image of a part of the electrode (Fig. 2). The shape of the connections between spheres, the distances between spheres and the sphere diameters have been analysed