Caractérisation d'un substitut osseux reconstruit en bioréacteur : Rôle du support dans le comportement mécanique.

Introduction : L’ingénierie tissulaire implique une coopération étroite entre trois acteurs : les cellules, les sollicitations qu’elles perçoivent et le support de culture. Les caractéristiques mécaniques et biologiques du tissu reconstruit in vitro doivent être évaluées pour connaître son comportement in vivo face aux stimuli rencontrés après implantation. Nous proposons d'élaborer un substitut osseux destiné à une reconstruction maxillo-faciale. En particulier, nous visons à identifier la relation existant entre structure du matériau, conditions de culture et propriétés biomécaniques du tissu osseux obtenu. Matériels et Méthodes : Pour le matériau, nous utilisons des granules de phosphate de calcium de différentes tailles (milli, micro et nanométrique) et formes (sphérique et ellipsoïdale) ainsi qu'un support fibreux. Des ostéoblastes humains sont cultivés dans un bioréacteur parallélépipédique (Mabio-International®) sur une couche de biomatériau. Après 4 semaines de culture, le tissu obtenu est caractérisé mécaniquement (Bose Biodynamic®) par des mesures de force et déformation en traction-compression anisotrope, puis biologiquement (viabilité par Live/Dead® et différenciation par test de la phosphatase alcaline). Des essais de traction sont conduits sous microscope électronique à balayage pour identifier les mécanismes et seuils d'endommagement en fonction du support. Résultats : Quel que soit le support, un feuillet biohybride osseux manipulable constitué de cellules viables est formé. Cependant, les caractéristiques mécaniques diffèrent selon le matériau (taille et forme des granules, présence ou non d'un support fibreux), permettant d'obtenir des substituts ayant un comportement macroscopique plus ou moins en adéquation avec les propriétés requises pour des manipulations chirurgicales. Conclusion : La caractérisation mécanique et biologique des différents substituts osseux biohybrides s'avère indispensable pour formaliser le cahier des charges des cliniciens. Les retours d’expérience d’implantation sur petit animal s’ajouteront aux données recueillies lors des tests de traction-compression afin de sélectionner les conditions de culture et supports optimaux

Caractérisation biologique et mécanique d'un subsitut osseux biohybride et développement de scaffolds par électrospinning : vers un pansement vivant pour la reconstruction maxillo-faciale

An hybrid bone substitute, based on a specific biomaterial (scaffold) and living cells, was studied, developed with a tissue engineered method and characterized. It should meet the expectations of the maxillofacial surgery : a standard process which could fit with the complex geometries of each patient’s bone mass loss, a flexible shape with an easy handling, a prevascularization and a sufficient mechanical cohesion. A sheet-like shape was thus designed and developed in a specific flat cell culture chamber, with a monolayer of calcium phosphate granules as a scaffold. After both biological and mechanical full characterizations with a cell line, the process was adapted to a coculture of human primary cells (stem and endothelial cells). Relevant differentiation and prevascularization were highlighted but the mechanical cohesion could be noticed as too low to ensure an easy handling during the surgery. The last part of this thesis project was thus the set-up of a device for electrospun polymer fibers in order to use them as a new scaffold. The production of these materials was efficiently performed for several polymers. The differentiation potential for bone and tendon lineages was studied and compared to other scaffolds from national and international collaborations. The application of mechanical solicitations to the substitutes during cellculture was also studied.Un substitut osseux hybride, composé d’un biomatériau support (scaffold) et de cellules vivantes, a été étudié, développé par la méthode d’ingénierie tissulaire et caractérisé. Il devait répondre aux attentes spécifiques de la chirurgie maxillofaciale : un protocole standard pouvant s’adapter aux géométries complexes des défauts osseux de chaque patient, une forme souple et manipulable, une pré-vascularisation et une cohésion mécanique suffisante. Une forme de feuillet fin et plat a ainsi été définie et développée au sein d’une chambre de culture parallélépipédique spécifique, en utilisant une monocouche de granules de phosphate de calcium comme support. Après une caractérisation biologique et mécanique complète à partir d’une lignée cellulaire, le procédé a été validé puis transposé à une coculture de cellules primaires humaines (cellules souches et endothéliales). La bonne différenciation et la pré-vascularisation ont été constatées mais le maintien mécanique pouvait être considéré comme insuffisant pour assurer une manipulation en cours d’opération chirurgicale. La dernière partie de ce travail de thèse a donc consisté dans la mise en place d’un montage de production de fibres électrospinnées et leur utilisation comme nouveau support de culture. La formation de ces matériaux a été rendue opérationnelle de façon optimale pour différents polymères. Leur potentiel en tant que scaffold favorisant la différenciation en os ou en tendon a été vérifié et comparé à d’autres matériaux fibreux obtenus dans le cadre de collaborations nationales et internationales. La faisabilité de l’application de sollicitations mécaniques aux substituts en cours de culture a également été étudiée

Prediction of photophysical properties of pyrimidine chromophores using Taguchi method

International audienceThis paper presents the photophysical properties of a series of pyrimidine chromophores. The influence of three parameters has been studied: the nature of the electron-donating group and of the π-conjugated linker as well as the substituted position of the pyrimidine core (2, 4 and 6 position). Taguchi design of experiment combined with analysis of variance methodologies have been employed. This approach has permitted to highlight the main factor affecting the absorption and emission wavelengths of the studied compounds. Absorption maxima of this family of compounds can be predicted with relatively good precision (±18 nm). The emission maxima can be also predicted, however the precision is lower (±39 nm). Taguchi methodology has been also employed with these families of compounds to optimize the intramolecular charge transfer estimated by emission solvatochromy

Validation and scalability of homemade polycaprolactone macrobeads grafted with thermo-responsive poly(N-isopropylacrylamide) for mesenchymal stem cell expansion and harvesting

In this study, polycaprolactone (PCL) macrobeads were prepared by an oil-in-water (o/w) emulsion solvent evaporation method with poly(vinyl alcohol) (PVA) as an emulsifier and conjugated to poly(N-isopropylacrylamide) (PNIPAAm) to be used as cell carriers with noninvasive cell detachment properties (thermo-response). Following previous studies with PCL-PNIPAAm carriers, our objectives were to confirm the successful conjugation on homemade macrobeads and to show the advantages of homemade production over commercial beads to control morphological, biological, and fluidization properties. The effects of PCL concentration on the droplet formation and of flow rate and PVA concentration on the size of the beads were demonstrated. The size of the beads, all spherical, ranged from 0.5 to 3.7 mm with four bead categories based on production parameters. The morphology and size of the beads were observed by scanning electron microscopy to show surface roughness enhancing cell attachment and proliferation compared to commercial beads. The functionalization steps with PNIPAAm were then characterized and confirmed by Fourier transform infrared spectroscopy​​​​​​, scanning electron microscopy, and energy dispersion spectroscopy. PNIPAAm-grafted macrobeads allowed mesenchymal stem cells (MSCs) to spread and grow for up to 21 days. By reducing the temperature to 25°C, the MSCs were successfully detached from the PCL-PNIPAAm beads as observed with fluorescence microscopy. Furthermore, we validated the scalability potential of both macrobeads production and conjugation with PCL, to produce easily kilograms of thermo-responsive macrocarriers in a lab environment. This could help moving such approaches towards clinically and industrially relevant processes were cell expansion is needed at very large scale

Electroanalysis at discrete arrays of gold nanowire electrodes

The development of reliable nanosensors offers a number of potential advantages in nanoscale analytical science. A hybrid electron beam-photolithography process was used to fabricate robust and reliable electrochemical nanowire array devices, with highly reproducible critical dimensions, 100 ± 6 nm. Nanowire electrode arrays were designed to permit diffusional independence at each nanowire element in an array thereby maximising limiting currents for optimised electrochemical nanosensing. The electrochemical behaviour of discrete nanowire electrode arrays was investigated using cyclic voltammetry in ferrocenemonocarboxylic acid. Single nanowire devices yielded highly reproducible steady-state sigmoidal waveforms, with typical currents of 179 ± 16 pA. Higher steady-state currents were achieved at nanowire arrays, up to ∼1.2 nA for arrays consisting of six nanowire elements. At low and intermediate scan rates, sigmoidal waveforms were observed for nanowire arrays indicating very fast mass transport. However, voltammetric behaviour consistent with semi-infinite linear diffusion was observed at higher scan rates confirming the presence of overlapping diffusion profiles between neighbouring nanowires within an array. The existence of diffusion overlap between neighbouring nanowire elements was further demonstrated by deviation of measured steady-state currents from estimates, becoming more pronounced with increasing numbers on nanowire elements in the array. Finally capacitive charging of the electrodes was explored, and were found to exhibit very low capacitance typically ∼31 ± 3 nF cm−2 per device, three orders of magnitude less than that reported for conventional microelectrodes (∼20 μF cm−2)

Fabrication and mechanical testing of a new sandwich structure with carbon fiber network core

The aim is the fabrication and mechanical testing of sandwich structures including a new core material known as fiber network sandwich materials. As fabrication norms for such a material do not exist as such, so the primary goal is to reproduce successfully fiber network sandwich specimens. Enhanced vibration testing diagnoses the quality of the fabrication process. These sandwich materials possess low structural strength as proved by the static tests (compression, bending), but the vibration test results give high damping values, making the material suitable for vibro-acoustic applications where structural strength is of secondary importance e.g., internal panelling of a helicopter

Crumpling a Thin Sheet

Crumpled sheets have a surprisingly large resistance to further compression. We have studied the crumpling of thin sheets of Mylar under different loading conditions. When placed under a fixed compressive force, the size of a crumpled material decreases logarithmically in time for periods up to three weeks. We also find hysteretic behavior when measuring the compression as a function of applied force. By using a pre-treating protocol, we control this hysteresis and find reproducible scaling behavior for the size of the crumpled material as a function of the applied force.Comment: revtex 4 pages, 6 eps figures submitted to Phys Rev. let

(S)-2-(1H-Imidazol-1-yl)-3-phenyl­propanol

In the title compound, C12H14N2O, the middle C atom in the propanol chain is a chiral center and possesses an S absolute configuration, according to the synthesis. In the crystal structure, inter­molecular O—H⋯N hydrogen bonds link the mol­ecules into a chain along the b axis