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Matériaux tubulaires biomimétiques en collagène : des mécanismes d'auto-assemblages aux applications in vitro
No full textBiological tissues are composed of a precise assembly of cells held together by a complex structure, the extra-cellular matrix (ECM). It is composed of proteins such as laminin, elastin, and in particular type I collagen. Since collagen is the building block of tissues, in the present work we focused on the underlying mechanisms that trigger type I collagen self-assembly as well as processing features that modulate its interaction with cells, to provide keys for the fabrication of biomimetic materials. First, we introduce the structural and functional similarities of the ECM of tubular tissues, including circulatory system, urinary and gastrointestinal tracts, trachea and esophagus. We propose a common simplified hierarchical model for the tissues mentioned above, based on a dual layer tissue constituted by the inner endothelial layer, and the outer muscular layer. The current existing strategies that aim to replicate these layers with a biomimetic approach are described, and in particular those that use type I collagen as a building block. In vivo, the supramolecular assembly of type I collagen molecules into fibrils underpins the formation of the ECM, a central aspect of tissue morphogenesis and remodeling. This process occurs in a narrow set of physicochemical conditions (temperature, concentration, and osmotic force) that are defined by the cells’ physiology and by the composition of the extracellular environment. The current paradigm in collagen-based biomimetic materials states that reproducing, in vitro, the same physicochemical conditions found in vivo, holds the key to mimic the architecture — and the function — of biological tissues. We investigated these conditions, based on scattering, rheological, and thermodynamic experiments combined to electron microscopy, and describe for the first time the organization of collagen as a function of temperature and concentration in state diagrams, both in solution and post-fibrillogenesis. In addition, we exemplify how these state diagrams can be powerful tools to tailor the fabrication processes of biomimetic collagenous materials. Most elaboration strategies found in the literature do not use collagen at a concentration range found in native tissues, estimated between 100 to 200 mg.mL-1. Additionally, collagen is often cross-linked by physical or chemical reactions, which does not reproduce the native assembly of fibrils, and hence the cellular microenvironment. This emphasizes the lack of biomimetic features in current in vitro models and tissue grafts, while such features are crucial in defining material-cell interactions. We unveil in this work how texture, collagen concentration, and the characteristics of the fibrillar network influence the cellular fate. Dense collagen substrates with concentrations ranging from 40 to 900 mg.mL-1, fibrillated according to two different routes, were seeded with endothelial cells. The adhesion and proliferation kinetics correlate with the mechanical and textural gradients resulting from the concentrations and fibrillogenesis pathways, which can be modulated to facilitate graft biointegration. Finally, we gather this knowledge to elaborate biomimetic tubular collagen materials. The application of collagen-based materials in tissue engineering requires a precise control over the proteins’ assembly mechanisms in vitro to mimic the architecture of native tissues. By combining ice templating to topotactic fibrillogenesis routes, we tuned the various structural scales of the hydrogel to reach the biomimetic features of native tubular tissues. The double control over both the porosity (geometry and size) and the collagen ultrastructure provided by our approach yields mechanical and biological properties in the range of tubular tissues.Les tissus biologiques sont composés d'un assemblage précis de cellules qui sont maintenues ensemble par une structure complexe, la matrice extra-cellulaire (MEC). Celle-ci est composée de protéines, majoritairement le collagène de type I, ainsi que de laminine et d'élastine. Le collagène étant l'élément constitutif des tissus, pour ce travail de recherche nous nous sommes concentrés sur la compréhension des phénomènes d'auto-assemblage du collagène, ainsi qu’aux paramètres procédés qui modulent les interactions collagène-cellules. Ces éléments nous ont permis de définir une gamme de paramètres pour la mise au point de matériaux biomimétiques. Nous introduisons en premier lieu les similitudes structurelles et fonctionnelles de la MEC des tissus tubulaires, comprenant le système circulatoire, les voies urinaires et gastro-intestinales, la trachée et l’œsophage. La structure de ces tissus peut être modélisée par un modèle commun, constitué de deux couches superposées : une couche endothéliale interne et une couche musculaire externe. A partir de ce modèle, nous avons recensé les stratégies développées pour répliquer ces couches via une approche biomimétique, notamment celles basées sur du collagène. In vivo, l'assemblage supramoléculaire des molécules de collagène en fibrilles est à la base de la formation de la MEC, un aspect central de la morphogenèse et du remodelage des tissus. Ce processus se produit dans une gamme restreinte de conditions physico-chimiques (température, concentration et force osmotique) définies par la physiologie des cellules et la composition de l’environnement extracellulaire. Le paradigme actuel des matériaux biomimétiques à base de collagène stipule que la reproduction, in vitro, des conditions physico-chimiques trouvées in vivo, est la clé pour imiter l'architecture et la fonction des tissus biologiques. En étudiant ces conditions, nous avons décrit pour la première fois l'organisation du collagène en fonction de la température et de la concentration, sur la base d'expériences de diffusion RX, de rhéologie et de thermodynamique combinées à de la microscopie électronique et à lumière polarisée. Ces résultats nous ont permis de tracer des diagrammes d'état, à la fois en solution et post-fibrillogenèse, qui constituent de puissants outils pour le design d’expériences ciblant la fabrication de matériaux biomimétiques en collagène. La plupart des méthodes décrites dans la littérature utilisent du collagène à des concentrations bien inférieures à celles des tissus natifs, estimées entre 100 et 200 mg.mL-1, et rarement avec une structure fibrillaire native. Cela souligne le manque d’implants et de modèles in vitro biomimétiques, malgré l’importance de cet aspect dans la régulation des interactions matériau-cellule. Dans ce travail, nous démontrons comment la texture, la concentration en collagène et les caractéristiques du réseau fibrillaire influencent le devenir cellulaire. Les cinétiques d'adhésion et de prolifération corrèlent avec les gradients mécaniques et de texture résultant des paramètres de fabrication, ce sur une large gamme de concentrations et avec l’utilisation de deux voies d’auto-assemblage. Dans le cas d’une application en clinique, ces paramètres peuvent ainsi être modulés pour faciliter la biointégration du greffon. Enfin, la conjugaison de ces connaissances nous a permis d’élaborer des matériaux tubulaires en collagène qui sont, d’un point de vue structurel et compositionnel, très proches des tissus natifs. En combinant l’ice-templating à la fibrillogenèse topotactique, les différentes échelles structurelles de l'hydrogel présentent à la fois une couche interne lisse - qui permet l’endothélialisation - et une structure externe poreuse - qui permet la colonisation cellulaire. Le double contrôle de la porosité (géométrie et taille) et de l'ultrastructure du collagène apporté par notre approche, permet d’aboutir à des propriétés mécaniques et biologiques dans la gamme des tissus [...]
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Matériaux tubulaires biomimétiques en collagène : des mécanismes d'auto-assemblages aux applications in vitro
No full textLes tissus biologiques sont composés d'un assemblage précis de cellules qui sont maintenues ensemble par une structure complexe, la matrice extra-cellulaire (MEC). Celle-ci est composée de protéines, majoritairement le collagène de type I, ainsi que de laminine et d'élastine. Le collagène étant l'élément constitutif des tissus, pour ce travail de recherche nous nous sommes concentrés sur la compréhension des phénomènes d'auto-assemblage du collagène, ainsi qu’aux paramètres procédés qui modulent les interactions collagène-cellules. Ces éléments nous ont permis de définir une gamme de paramètres pour la mise au point de matériaux biomimétiques. Nous introduisons en premier lieu les similitudes structurelles et fonctionnelles de la MEC des tissus tubulaires, comprenant le système circulatoire, les voies urinaires et gastro-intestinales, la trachée et l’œsophage. La structure de ces tissus peut être modélisée par un modèle commun, constitué de deux couches superposées : une couche endothéliale interne et une couche musculaire externe. A partir de ce modèle, nous avons recensé les stratégies développées pour répliquer ces couches via une approche biomimétique, notamment celles basées sur du collagène. In vivo, l'assemblage supramoléculaire des molécules de collagène en fibrilles est à la base de la formation de la MEC, un aspect central de la morphogenèse et du remodelage des tissus. Ce processus se produit dans une gamme restreinte de conditions physico-chimiques (température, concentration et force osmotique) définies par la physiologie des cellules et la composition de l’environnement extracellulaire. Le paradigme actuel des matériaux biomimétiques à base de collagène stipule que la reproduction, in vitro, des conditions physico-chimiques trouvées in vivo, est la clé pour imiter l'architecture et la fonction des tissus biologiques. En étudiant ces conditions, nous avons décrit pour la première fois l'organisation du collagène en fonction de la température et de la concentration, sur la base d'expériences de diffusion RX, de rhéologie et de thermodynamique combinées à de la microscopie électronique et à lumière polarisée. Ces résultats nous ont permis de tracer des diagrammes d'état, à la fois en solution et post-fibrillogenèse, qui constituent de puissants outils pour le design d’expériences ciblant la fabrication de matériaux biomimétiques en collagène. La plupart des méthodes décrites dans la littérature utilisent du collagène à des concentrations bien inférieures à celles des tissus natifs, estimées entre 100 et 200 mg.mL-1, et rarement avec une structure fibrillaire native. Cela souligne le manque d’implants et de modèles in vitro biomimétiques, malgré l’importance de cet aspect dans la régulation des interactions matériau-cellule. Dans ce travail, nous démontrons comment la texture, la concentration en collagène et les caractéristiques du réseau fibrillaire influencent le devenir cellulaire. Les cinétiques d'adhésion et de prolifération corrèlent avec les gradients mécaniques et de texture résultant des paramètres de fabrication, ce sur une large gamme de concentrations et avec l’utilisation de deux voies d’auto-assemblage. Dans le cas d’une application en clinique, ces paramètres peuvent ainsi être modulés pour faciliter la biointégration du greffon. Enfin, la conjugaison de ces connaissances nous a permis d’élaborer des matériaux tubulaires en collagène qui sont, d’un point de vue structurel et compositionnel, très proches des tissus natifs. En combinant l’ice-templating à la fibrillogenèse topotactique, les différentes échelles structurelles de l'hydrogel présentent à la fois une couche interne lisse - qui permet l’endothélialisation - et une structure externe poreuse - qui permet la colonisation cellulaire. Le double contrôle de la porosité (géométrie et taille) et de l'ultrastructure du collagène apporté par notre approche, permet d’aboutir à des propriétés mécaniques et biologiques dans la gamme des tissus [...].Biological tissues are composed of a precise assembly of cells held together by a complex structure, the extra-cellular matrix (ECM). It is composed of proteins such as laminin, elastin, and in particular type I collagen. Since collagen is the building block of tissues, in the present work we focused on the underlying mechanisms that trigger type I collagen self-assembly as well as processing features that modulate its interaction with cells, to provide keys for the fabrication of biomimetic materials. First, we introduce the structural and functional similarities of the ECM of tubular tissues, including circulatory system, urinary and gastrointestinal tracts, trachea and esophagus. We propose a common simplified hierarchical model for the tissues mentioned above, based on a dual layer tissue constituted by the inner endothelial layer, and the outer muscular layer. The current existing strategies that aim to replicate these layers with a biomimetic approach are described, and in particular those that use type I collagen as a building block. In vivo, the supramolecular assembly of type I collagen molecules into fibrils underpins the formation of the ECM, a central aspect of tissue morphogenesis and remodeling. This process occurs in a narrow set of physicochemical conditions (temperature, concentration, and osmotic force) that are defined by the cells’ physiology and by the composition of the extracellular environment. The current paradigm in collagen-based biomimetic materials states that reproducing, in vitro, the same physicochemical conditions found in vivo, holds the key to mimic the architecture — and the function — of biological tissues. We investigated these conditions, based on scattering, rheological, and thermodynamic experiments combined to electron microscopy, and describe for the first time the organization of collagen as a function of temperature and concentration in state diagrams, both in solution and post-fibrillogenesis. In addition, we exemplify how these state diagrams can be powerful tools to tailor the fabrication processes of biomimetic collagenous materials. Most elaboration strategies found in the literature do not use collagen at a concentration range found in native tissues, estimated between 100 to 200 mg.mL-1. Additionally, collagen is often cross-linked by physical or chemical reactions, which does not reproduce the native assembly of fibrils, and hence the cellular microenvironment. This emphasizes the lack of biomimetic features in current in vitro models and tissue grafts, while such features are crucial in defining material-cell interactions. We unveil in this work how texture, collagen concentration, and the characteristics of the fibrillar network influence the cellular fate. Dense collagen substrates with concentrations ranging from 40 to 900 mg.mL-1, fibrillated according to two different routes, were seeded with endothelial cells. The adhesion and proliferation kinetics correlate with the mechanical and textural gradients resulting from the concentrations and fibrillogenesis pathways, which can be modulated to facilitate graft biointegration. Finally, we gather this knowledge to elaborate biomimetic tubular collagen materials. The application of collagen-based materials in tissue engineering requires a precise control over the proteins’ assembly mechanisms in vitro to mimic the architecture of native tissues. By combining ice templating to topotactic fibrillogenesis routes, we tuned the various structural scales of the hydrogel to reach the biomimetic features of native tubular tissues. The double control over both the porosity (geometry and size) and the collagen ultrastructure provided by our approach yields mechanical and biological properties in the range of tubular tissues
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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