Mathematical Modeling of Uniaxial Mechanical Properties of Collagen Gel Scaffolds for Vascular Tissue Engineering

Article ID 859416Small diameter tissue - engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and-or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control systemtheory. Second,models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed:Mooney - Rivlin inspired and Hammerstein models. Theresults suggest that Mooney - Rivlin andHammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3 per cent and .75.8 per cent, resp.). When Akaike criterion is used, the best is the Mooney - Rivlin inspired model

Mathematical modeling of uniaxial mechanical properties of collagen gel scaffolds for vascular tissue engineering

Small diameter tissue-engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and/or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control system theory. Second, models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed: Mooney-Rivlin inspired and Hammerstein models. The results suggest that Mooney-Rivlin and Hammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3% and 75.8%, resp.). When Akaike criterion is used, the best is the Mooney-Rivlin inspired model.Facultad de Ciencias ExactasInstituto de Física de Líquidos y Sistemas Biológico

Técnicas de ultrasonido : Una herramienta potencial para la ingeniería de tejidos

El objetivo de este trabajo es desarrollar dos montajes experimentales para la evaluación de las propiedades acústicas de hidrogeles de colágeno y para estudiar su correlación con las propiedades mecánicas. El primero permite estimar la velocidad del sonido, atenuación e impedancia acústica de las muestras manejando la temperatura. En el segundo, la configuración anterior se combina con un ensayo mecánico de compresión, lo que permite interrogar al mismo tiempo, tanto propiedades acústicas como mecánicas de la muestra. Se observan las propiedades acústicas y mecánicas de los geles de colágeno preparados de acuerdo a diferentes condiciones experimentales: pH y la concentración de colágeno. La variación de estos parámetros permite modificar las condiciones mecánicas de la matriz.Facultad de Ingenierí

Integrase-directed recovery of functional genes from genomic libraries

Large population sizes, rapid growth and 3.8 billion years of evolution firmly establish microorganisms as a major source of the planet's biological and genetic diversity. However, up to 99% of the microorganisms in a given environment cannot be cultured. Culture-independent methods that directly access the genetic potential of an environmental sample can unveil new proteins with diverse functions, but the sequencing of random DNA can generate enormous amounts of extraneous data. Integrons are recombination systems that accumulate open reading frames (gene cassettes), many of which code for functional proteins with enormous adaptive potential. Some integrons harbor hundreds of gene cassettes and evidence suggests that the gene cassette pool may be limitless in size. Accessing this genetic pool has been hampered since sequence-based techniques, such as hybridization or PCR, often recover only partial genes or a small subset of those present in the sample. Here, a three-plasmid genetic strategy for the sequence-independent recovery of gene cassettes from genomic libraries is described and its use by retrieving functional gene cassettes from the chromosomal integron of Vibrio vulnificus ATCC 27562 is demonstrated. By manipulating the natural activity of integrons, we can gain access to the caches of functional genes amassed by these structures

Novel Insights into Pituitary Tumorigenesis: Genetic and Epigenetic Mechanisms.

Substantial advances have been made recently in the pathobiology of pituitary tumors. Similar to many other endocrine tumors, over the last few years we have recognized the role of germline and somatic mutations in a number of syndromic or nonsyndromic conditions with pituitary tumor predisposition. These include the identification of novel germline variants in patients with familial or simplex pituitary tumors and establishment of novel somatic variants identified through next generation sequencing. Advanced techniques have allowed the exploration of epigenetic mechanisms mediated through DNA methylation, histone modifications and noncoding RNAs, such as microRNA, long noncoding RNAs and circular RNAs. These mechanisms can influence tumor formation, growth, and invasion. While genetic and epigenetic mechanisms often disrupt similar pathways, such as cell cycle regulation, in pituitary tumors there is little overlap between genes altered by germline, somatic, and epigenetic mechanisms. The interplay between these complex mechanisms driving tumorigenesis are best studied in the emerging multiomics studies. Here, we summarize insights from the recent developments in the regulation of pituitary tumorigenesis

Maires de la Gironde de la Révolution

À l’occasion du bicentenaire de la Révolution française et de la loi municipale de décembre 1789 instituant les communes et les maires, le CESURB-Histoire a lancé une enquête sur “les maires du Sud-Ouest depuis la Révolution". Cet ouvrage présente les résultats d’une première étape de la recherche, consacrée aux chefs-lieux de cantons du département de la Gironde et à la période 1790-1824. L’enquête menée selon la méthode de la prosopographie a poursuivi un triple objectif : dresser le portrait type des hommes qui ont exercé le pouvoir municipal ; mesurer pour les élites locales les continuités et les ruptures au cours d’une époque troublée, entre la Révolution et la Restauration ; tenter d'apprécier l’originalité des maires de Gironde dans l’ensemble national La synthèse montre l'absence de changement brutal magré la diversité des régimes politiques et des modes de recrutement. Les évolutions les plus sensibles sont liées aux renouvellements les plus forts, en 1792 et en 1824. L’originalité des maires girondins se manifeste surtout pour la période révolutionnaire

Parlementaires en Aquitaine occidentale : étude comparée de deux fins de siècles

À l'occasion d'une journée d'études consacrée aux « élites », notre intérêt pour l'histoire politique et notre participation à l'enquête menée depuis quelques années par le Centre d'Histoire du xixe siècle des Universités de Paris I et Paris IV, sous la direction des professeurs J.-M. Mayeur et A. Corbin, nous conduisent à présenter quelques réflexions sur une partie des élites politiques, les parlementaires d'Aquitaine occidentale, c'est-à-dire des cinq départements de l'actuelle région Aqui..

A pterosaur from the Toarcian (Early Jurassic) of the Ardennes (northeastern France) [Un ptérosaure dans le Toarcien (Jurassique inférieur) des Ardennes (NE de la France)]

A pterosaur tibia-fibula is described from Toarcian shales ("Marne de Flize") near the city of Charleville-Mézières (Ardennes, northeastern France). The morphology of this element, especially the reduced fibula partially fused to the tibia, suggests that it belongs to the rhamphorhynchid Dorygnathus, which is well represented in the Toarcian Posidonienschiefer of Germany and has also been reported from the Toarcian of Nancy (eastern France)

Un ptérosaure dans le Toarcien (Jurassique inférieur) des Ardennes (NE de la France)

Un tibia-fibula de ptérosaure est décrit en provenance de schistes argileux toarciens ("Marne de Flize") à proximité de la ville de Charleville-Mézières (Ardennes, NE de la France). La morphologie de cet élément, en particulier la fibula réduite partiellement fusionnée au tibia, suggère qu'il appartient au rhamphorhynchidé Dorygnathus, bien représenté dans les Posidonienschiefer d'Allemagne et aussi signalé dans le Toarcien de Nancy (Est de la France).A pterosaur tibia-fibula is described from Toarcian shales ("Marne de Flize") near the city of Charleville-Mézières (Ardennes, northeastern France). The morphology of this element, especially the reduced fibula partially fused to the tibia, suggests that it belongs to the rhamphorhynchid Dorygnathus, which is well represented in the Toarcian Posidonienschiefer of Germany and has also been reported from the Toarcian of Nancy (eastern France)