Bernard Durand

A poly(L-lactic acid) nanofibre mesh scaffold for endothelial cells on vascular prostheses.

The absence of neoendothelium covering the intimal surface of small-diameter PET vascular prostheses is known to be one cause of failure following implantation in humans. Protein coatings currently used to seal porous textile structures have not shown evidence of in vivo neoendothelium formation. In this study, we covered the inner wall of textile prostheses with a biodegradable synthetic scaffold made of poly(l-lactic) acid (PLLA) nanofibres obtained by an air-spinning process we developed that produces nanofibres by stretching a solution of polymer with a high-speed compressed air jet. The air spinning was designed to process a scaffold that would support good endothelial cell proliferation. Our innovative process enabled us to very rapidly cover textile samples with PLLA nanofibres to determine the influence of air pressure, polymer solution flow rate and polymer concentration on fibre quality. High air pressure was shown to induce a significant number of ruptures. High polymer flow rate stimulated the formation of polymer droplets, and the fibre diameter mean increased for the 4% and 7% polymer concentrations. The adherence and proliferation of bovine aortic endothelial cells was assessed to compare prosthesis samples with or without the PLLA nanofibre scaffold and PET film. The PLLA nanofibres displayed a significantly better proliferation rate, and enabled endothelial cells to proliferate in the monolayer. Our novel approach therefore opens the door to the development of partially degradable textile prostheses with a blood/textile interface that supports endothelial cell proliferation.

Molten salt synthesis of the lead titanate PbTiO3, investigation of the reactivity of various titanium and lead salts with molten alkali-metal nitrites

The reactivity of titanium salts (the oxychloride, the oxysulfate and the potassium fluorotitanate) and lead salts (the chloride, the nitrate and the sulfate) is investigated first separately, then simultaneously. A molten salt synthesis procedure of the lead titanate PbTiO3 is deduced from the results.

Frequency dependence of conductivity in superionic conducting chalcogenide glasses

A good understanding of phenomena related to ionic transport in glasses is still lacking. The most recent models proposed to describe microscopic processes of ion motion in glasses are based upon the observed dependence of conductivity of frequency. This dependence is generally described by the so called ‘universal’ law: σac = σsdc + Aωs In this work, electrical conductivity measurements on superionically conducting chalogenide glasses of the Ag2S-GeS2-AgI family were performed from the microwave region (6 GHz) down to audiofrequencies (1 KHz) in the temperature range (200–300 K). In this case, the observed dependence of conductivity on frequency cannot be described by the universal law but rather by a more complex law of type: σ(ω)=σdc + Aωs + Bωst where 0 < s < 1, s′ ⩾ 1. Parameters A and B are thermally activated. Whereas parameter B is weakly thermally activated, activation energy of A, Eac, can be related to dc activation energy of Edc = (1 − s)Edc′.

Hydrothermal synthesis of porous zircon in basic fluorinated medium

Abstract The hydrothermal synthesis of zircon was performed under autogenous pressure, from inorganic precursors in aqueous fluorinated basic medium. The powders obtained were characterized by an abnormal broadness of all XRD peaks except for the (200) and (220) peaks. Their morphology was strongly dependent upon the concentration [F − ] of fluoride ions in the synthesis gel. At high [F − ], ellipsoidal agglomerates were produced; the powders exhibited a specific surface area of about 200xa0m 2 xa0g −1 ; the frame of the agglomerates was not destroyed by annealing at 800°C for 72xa0h, and 50% of the surface area was maintained. At low [F − ], layered platelets were formed.

Molten alkali metal oxonitrates, a liquid state for nanosized perovskite phase elaboration

Alkali metal nitrates or nitrites have rather low melting points and provide a powerful liquid medium for the precipitation of metal oxides from their common salts. Oxonitrate anions are Lux-Flood bases; the basicity can be chosen between nitrate or nitrite depending on the acidity of the metal cation or the kind of oxide desired. Once the experimental conditions are determined, generally by using TGA, one can obtain phases such as BaTiO n 3 n, PbTiO n 3 n or LaMnO n 3 n quickly and reproducibly. Elementary particles, single crystals about 100 nm in size, form rather soft aggregates of approximately 2 µm. The purity is suitable for most applications.

Textile for heart valve prostheses: fabric long-term durability testing.

The rapid developments and success in percutaneous vascular surgery over the last two decades with the now common stent grafts implantation, make the noninvasive surgery technique today attractive even for heart valve replacement. Less traumatic for the patient and also less time consuming, percutaneous heart valve replacement is however at its beginning and restricted to end of life patients. The noninvasive procedure expects from the heart valve prosthesis material to be resistant and adapted to folding requirements of the implantation process (catheter). Polyester fabric could be a suited material for heart valve implanted percutaneously. Highly flexible and resistant, polyester fabric proved to be well adapted to the dynamic behavior of a valve and polyester (Dacron) is also widely used for vascular grafts implantation and shows good biocompatibility and durability. However, today theres no data available on long-term durability of fabric used as heart valve material. The purpose of this work is to study the long term behavior of a microdenier polyester fabric construction under combined in vitro flexure and tension fatigue stress. In the novel in vitro testing technique presented, a fabric specimen was subjected to combined flexural and tensile fatigue generated by fluid flow under physiological pressure conditions. The results obtained show how flexural properties change with fatigue time, which reflects directly on the suitability of a fabric in such devices. It was also observed that these fabric structural changes directly influence the in vitro behavior of the textile heart valve prosthesis.

Molten salt synthesis and characterization of non-doped hafnia

The reactivity of hafnium tetrachloride towards the molten NaNO n 3 n–KNO n 3 n medium is analyzed by thermogravimetry and XRD. After an investigation of the influence of various reaction parameters, an optimized synthesis procedure of the monoclinic variety of hafnia is proposed. The obtained powders are characterized.

High actuation properties of shape memory polymer composite actuator

The shape memory polymers (SMPs) possess two shapes: permanent shape and temporary shape. This property leads to replacement of shape memory alloys by SMPs in various applications. In this work, two properties, namely structure activeness and the shape memory property of ?controlled behavior composite material (CBCM)? plate and its comparison with the conventional symmetrical composite plate (SYM), are studied. The SMPC plates (CBCM and SYM) are manufactured using epoxy resin with a thermal glass transition temperature (Tg) of 130??C. The shape memory properties of these composites are investigated (under three-point bending test) and compared by deforming them to the same displacement. Three types of recoveries are conducted: unconstrained recovery, constrained recovery, and partial recovery under load. It is found that by coupling the structure activeness (due to its asymmetry) and its shape memory property, higher activated displacement is obtained during the unconstrained recovery. Also, at a lower recovery temperature (90??C) than the fixing temperature, a recovery close to 100% is obtained for CBCM, whereas for SYM it is only 25%. During constrained recovery, CBCM produces five times larger recovery force than SYM. In addition, higher actuation properties are demonstrated by calculating recovered work and recovery percentages during partial recovery under load.

A new hydrothermal fluoro-zircon

A zircon exhibiting original properties was synthesized under autogenous pressure at 150°C for a few tens of hours. Silicon vacancies in the form of tetrahedral nests [F n n n n(OH) n 4–n n] were identified by coupling 1 nH NMR CRAMPS and thermogravimetry. A Rietveld refinement of the structure was performed. The mechanism of the hydrothermal synthesis involves heterocondensation reactions between the Si(OH) n 4 n species and a fluoro-zirconium complex rich in fluorine. Annealing of this fluoro-zircon above 500°C produces, according to the heating profile, either monoclinic or tetragonal zirconia with a plate-like morphology having an acicular network texture.

A novel preparation of calcia fully stabilised zirconia from molten alkali-metal nitrate

A novel preparation of cubic calcia stabilised zirconia (CaO–ZrO2) which employs the coprecipitation of the constituents from zirconium oxychloride (ZrO1.22Cl1.56) and calcium nitrate [Ca(NO3)2] with eutectic lithium nitrate-potassium nitrate (LiNO3–KNO3) at around 600 °C is described. The optimisation and advantages of the preparation are discussed.