Novel heart valve prosthesis with self-endothelialization potential made of modified polyhedral oligomeric silsesquioxane-nanocomposite material

In the cardiovascular system, the endothelial layer provides a natural antithrombogenic surface on the inner portion of the heart and associated vessels. For a synthetic material therefore, the ability to attract and retain endothelial or endothelial progenitor cells (EPCs), ultimately creating a single endothelial layer on its surface, is of prime importance. The authors have developed a nanocomposite polymer, based on a combination of polyhedral oligomeric silsesquioxane nanoparticles and polycarbonate urea urethane (POSS-PCU), which is biocompatible and has been used in human for the world's first synthetic trachea, tear duct, and bypass graft. In this study, the authors modified the surface of this casted nanocomposite by grafting fibronectin derived bioactive peptides [glycine-arginine-glycine-aspartic acid-glycine (GRGDG) and lauric acid conjugated GRGDG (GRGDG-LA)] to enhance the endothelialization for using heart valves leaflets from circulating EPCs. Human peripheral blood mononuclear cells were separated using Ficoll-Paque centrifugation, with harvested EPCs purified using CD34 microbead labeling and magnetic-activated cell sorting. Cells were seeded onto 96 well plates coated with POSS-PCU, GRGDG/GRGDG-LA modified POSS-PCU and PCU polymers, for a period of 21 days. Cells were studied under light, confocal, and scanning electron microscope (SEM). Fluorescence-activated cell sorting was used to analyze cell surface markers. Cell attachment and proliferation was observed in all POSS-PCU samples, significantly higher than the activity seen within the control PCU polymers (p < 0.05). Microscopic examination revealed clonal expansion and morphological changes in cells seeded on POSS-PCU. The cells expressed increasing levels of mature endothelial cell markers over time with a concurrent reduction in hematopoietic stem cell marker expression. SEM showed a mixed population of morphologically differentiated endothelial cells and EPCs. These results support the use of heart valve made with the POSS-PCU polymer and demonstrate that suitable chemical modification of this nanocomposite could increase self-endothelialization potential and reduce associated thrombotic events

MÖSSBAUER CHARACTERIZATION OF IRON (II)-IRON (III) METALLORGANIC COMPOUNDS WITH POLYMERICLIGAND (P4VP)

Les spectres Mössbauer de Fe(III)-P4VP, Fe(II)-P4VP, et Fe(CO)4-Py ont été obtenus à la température ambiante. Les spectres à 4 raies correspondent à l'existence de deux types de fer. Le déplacement isomérique et l'effet quadrupolaire indiquent la présence simultanée d'états haut-spin et bas-spin pour les composés P4VP. Les composés Fe(III) sont un mélange d'états électroniques 6A1 (S = 5/2) et 2T2(S = 1/2), alors que dans les composés Fe(II) on trouve les états 1A1 (S = 0) et 5T2 (S = 2). A la température ambiante l'équilibre se déplace vers les états haut-spin. La structure typique du complexe pyridinique semble être une pyramide trigonale.Mössbauer spectra of Fe(III)-P4VP, Fe(II)-P4VP and Fe(CO)4-Py were measured at room temperature. The complexes show a 4-line spectrum corresponding to two different iron forms. The isomershift and quadrupole splitting values point out the presence of both high and low spin iron for P4VP compounds. The Fe(III) compounds are a mixture of 6A1 (S = 5/2) and 2T2 (S = 1/2) iron electronic states, while in the Fe(II) compounds states 1A1 (S = 0) and 5T2 (S = 2) are present. At room temperature the equilibria are shifted towards higher spin states. A trigonal bipyramid seems to be the typical structure of the pyridinic complex

MÖSSBAUER EFFECT STUDY OF THE Sn0.9Ge0.1Te SYSTEM

La corrélation entre les paramètres Mössbauer et l'apparition de modes mous dans le spectre de phonons, liés à la présence d'une transition de phase dans les matériaux ferroélectriques, est rediscutée à la lumière des désaccords observés dans la littérature pour le système Sn0·9Ge0·1Te. Dans ce travail on n'observe pas de variation anormale en fonction de la température entre 80 et 300K pour la fraction sans recul et pour la conductivité électrique, mais seulement pour Γ l'expérimental.The relation between the Mössbauer parameters and the appearance of soft modes in the phonon spectrum related with the phase transition for ferroelectric materials is rediscussed in the light of the discrepancies existing in the literature about the Sn0·9Ge0·1Te system. In the present work no anomalous temperature dependence of the recoil-free fraction and also of the electrical conductivity is observed between 80 and 300 K, but only in linewidth

EXPERIMENTAL EVIDENCE OF THE INFLUENCE OF THE CATION SITE OCCUPANCY AND OF ITS EVALUATION WITH THE TEMPERATURE ON THE MAGNETIC PROPERTIES OF SOFT FERRITES PREPARED BY WET METHODS

Les ferrites de Mn-Zn préparées par voie humide montrent une haute réactivité : les échantillons pressés atteignent une densité presque théorique à des températures inférieures à celles généralement nécessaires pour fritter les poudres préparées par les techniques céramiques classiques. Elles montrent aussi une occupation des sites cationiques très différente qui évolue avec la température, atteignant celle des ferrites céramiques. Les spectres Mössbauer sur MnFe2O4, préparé lui aussi par voie humide, confirment cette évolution qui conduit le moment magnétique mesuré à 0 K à passer de 0,11 à 4,50 µB lorsque la température augmente de 25 à 1 350 °C. Les variations thermiques de l'aimantation dues à l'augmentation du contenu de Zn pour les échantillons tels que varient de manière différente de celles des échantillons frittés à 1 350 °C et trempés à l'eau. Les valeurs des moments magnétiques inférieures à celles prévues par la théorie normale du ferrimagnétisme de Néel sont expliquées assez bien par une certaine évidence phénoménologique d'un effet Yafet-Kittel.Mn-Zn ferrite prepared by wet methods show high reactivity : pressed samples reach almost theoretical density at temperatures lower than those usually required for sintering powders prepared by common ceramic techniques. They also show a largely different cation site occupancy which evolves with temperature approaching that of ceramic ferrites. Mössbauer spectra on MnFe2O4 also prepared by wet methods confirm such evolution which causes the magnetic moment at 0 K to shift from 4.11 to 4.60 µB as the temperature increases from 25 to 1 350 °C. The temperature dependence of magnetization with increasing Zn content for as prepared samples varies in a different way from that of samples annealed at 1 350 °C and quenched in water. The values of magnetic moments lower than those expected by the normal Neel theory of ferrimagnetism are explained rather well by a certain phenomenological evidence of a Yafet-Kittel effect