Colloquium: Mechanical formalisms for tissue dynamics

The understanding of morphogenesis in living organisms has been renewed by tremendous progressin experimental techniques that provide access to cell-scale, quantitative information both on theshapes of cells within tissues and on the genes being expressed. This information suggests that ourunderstanding of the respective contributions of gene expression and mechanics, and of their crucialentanglement, will soon leap forward. Biomechanics increasingly benefits from models, which assistthe design and interpretation of experiments, point out the main ingredients and assumptions, andultimately lead to predictions. The newly accessible local information thus calls for a reflectionon how to select suitable classes of mechanical models. We review both mechanical ingredientssuggested by the current knowledge of tissue behaviour, and modelling methods that can helpgenerate a rheological diagram or a constitutive equation. We distinguish cell scale ("intra-cell")and tissue scale ("inter-cell") contributions. We recall the mathematical framework developpedfor continuum materials and explain how to transform a constitutive equation into a set of partialdifferential equations amenable to numerical resolution. We show that when plastic behaviour isrelevant, the dissipation function formalism appears appropriate to generate constitutive equations;its variational nature facilitates numerical implementation, and we discuss adaptations needed in thecase of large deformations. The present article gathers theoretical methods that can readily enhancethe significance of the data to be extracted from recent or future high throughput biomechanicalexperiments.Comment: 33 pages, 20 figures. This version (26 Sept. 2015) contains a few corrections to the published version, all in Appendix D.2 devoted to large deformation

Chemical Analysis of Multicellular Tumour Spheroids

This research received support from the QNano Project http://www.qnano-ri.eu which is financed by the European Community Research Infrastructures under the FP7 Capacities Programme (grant no. INFRA-2010-262163), and its partner Trinity College Dublin.Conventional two dimensional (2D) monolayer cell culture has been considered the ‘gold standard’ technique for in vitro cellular experiments. However, the need for a model that better mimics the three dimensional (3D) architecture of tissue in vivo has led to the development of Multicellular Tumour Spheroids (MTS) as a 3D tissue culture model. To some extent MTS mimic the environment of in vivo tumours where, for example, oxygen and nutrient gradients develop, protein expression changes and cells form a spherical structure with regions of proliferation, senescence and necrosis. This review focuses on the development of techniques for chemical analysis of MTS as a tool for understanding in vivo tumours and a platform for more effective drug and therapy discovery. While traditional monolayer techniques can be translated to 3D models, these often fail to provide the desired spatial resolution and z-penetration for live cell imaging. More recently developed techniques for overcoming these problems will be discussed with particular reference to advances in instrument technology for achieving the increased spatial resolution and imaging depth required.Publisher PDFPeer reviewe

Corrosion of ceramic matrix composites

EditorialInternational audienc

PROTECTION AGAINST OXIDATION OF C/SiC COMPOSITES BY CHEMICAL VAPOUR DEPOSITION OF TITANIUM DIBORIDE : DEPOSITION KINETICS AND OXIDATION BEHAVIOUR OF FILMS PREPARED FROM TiCl4/BCl3/H2 MIXTURES

TiB2 coatings were deposited by hydrogen reduction of TiCl4 and BCl3. The objective was to correlate process variables with thermodynamic equilibrium calculations, deposition kinetics, coating structure and properties. Particular emphasis was given to obtaining deposits having appropriate oxidation resistance to protect C/SiC composites. Films, obtained at moderate temperature (800°C), acted as self-healing external barriers below the microcracking temperature of the outer SiC coating used as primary oxygen protection

DEFECT DETECTION IN ENGINEERING CERAMICS USING DIFFERENT NON DESTRUCTIVE TESTING TECHNIQUES

L'emploi des céramiques pour applications mécaniques à haute température et longue durée de vie nécessite des moyens de contrôle non destructif très performants. A cause des caractéristiques particulières de ces matériaux et de la faible taille des défauts recherchés, les techniques mises en oeuvre font l'objet d'un choix rigoureux. Leur application au contrôle industriel est discutée.The use of ceramics for high temperature and long lifetime applications require very sensitive non-destructive testing techniques. Due to the particular characteristics of these materials, and to the very small size of the flaws to be detected, they must be selected very strictly. Their application to industrial control is discussed

Protection against oxidation of C/SiC composites: oxidation behaviour of CVD TiB2 coated substrates

Titanium diboride coatings (20 or 30 µm thick), deposited by hydrogen reduction of TiCl4 and BC13, are protecting C/SiC substrates against oxidation up to 1100 °C. The oxidation of TiB2 leads to the formation of a protective low viscosity B2O3 glass filling the cracks of the primary CVD-SiC oxygen barrier. Above this temperature, the rapid consumption of the B2O3 glass by vaporization limits the duration of the protection system. A comprehensive description of the oxidation mechanism, based on a complementary experimental study of B2O3 evaporation, is presented

A comparative study of O2/SiH4 and N2O/SiH4 mixtures for SiO2 deposition in a microwave afterglow

Silicon dioxide films have been deposited in a microwave afterglow from N2O/SiH4 and O2/SiH4 mixtures. The effect of the pressure and of the substrate to silane injector distance is investigated, and leads to conclude that the growth mechanism is diffusion limited. In complement to previous studies, the composition of films, obtained at several temperatures and oxidant flow rates, is detennined. The gas nature has a low influence on stoichiometry (O/Si∼2 whatever the conditions are) but has an effect on the impurity content. Indeed, when N2O is used, nitrogen is incorporated but, at high temperature, the hydrogen content of the films is lower than for those made from O2. The impurities are thought to come from uneasily desorbed byproducts

Remote Microwave Plasma Enhanced Chemical Vapour Deposition of SiO2 Films : Oxygen Plasma Diagnostic

Silicon oxide is deposited by remote microwave plasma enhanced chemical vapour deposition (RMPECVD). The silica films are produced by exciting oxygen in a microwave discharge while a mixture of 5% of silane diluted in argon is introduced downstream. In the afterglow, double Langmuir probe measurements and rotational temperatures deduced from optical emission spectroscopy (OES), show that the electron energy is transferred to the gas when the pressure increases (19 - 26 Pa). Therefore the electronic temperature decreases from 22000 to 11000 K and the gas temperature increases from 400 to 500 K. Moreover the microwave power (180 - 480 W) has an influence on the deposition rate and on the quality of SiO2 coatings (density and etch rate in an HF solution). This effect can be correlated with the increase in the electron density (0.7.1010 to 3.7.1010 cm-3) and of the gas temperature (400 to 460 K)