Search

The authors attempt to describe a comprehensive study of physical ageing in vivo on the properties of explanted prostheses. Infrared spectroscopy (FTIR) technique has been used to compare the molecular conformation of various polyethylene terephthalate (PET) yarns extracted from the different areas of the prostheses (with different lifetimes) collected after ageing. The FTIR found results showed an increased PET crystallinity related to the development of microcrystallites in the amorphous areas of PET chains. Nevertheless, these small crystallites are not perfectly orientated according to the fiber axis. In addition, we can deduced that the ruptures in macromolecular chain can occur in the diethylene glycol groups existing in the zones amorphous and can be induced the crystallization process. [ABSTRACT FROM AUTHOR]

The Fourier transform infrared (FTIR) spectrum of polyethylene terephthalate (PET) fibers extracted from vascular prostheses was used to illustrate the mechanisms of structure degradation. A quantitative model for fitting infrared spectra of PET samples over the region from 3200 to 3600 cm−1 has been evaluated. Examination of a series spectrum of PET vascular prostheses collected after aging showed significant chemical differences in comparison with the virgin prosthesis. Analysis of these spectrums showed an increase of the end group concentrations for the explants. We used a complementary technique, the chemical titration method, in order to validate (FTIR) results. A considerable loss of macromolecular weight was observed, which is related to the formation of the smaller molecules that may proceed by random scission. Even if the time clearly influences the level of degradation, the results highlight other mechanisms of degradation that are probably related to human metabolism. [ABSTRACT FROM PUBLISHER]

Woven and knitted cardiovascular prostheses are tubular structures made of polyester filaments. They present particular mechanical properties linked to the wavy form of their walls, allowing them to be used in curved configurations. Pulsatile blood flows have been studied in bent textile prosthesis. The results obtained showed velocity peaks involving high-shear stress zones and turbulence phenomenon inside the graft. The flow velocity distribution near a prosthetic surface is strongly influenced by the crimping morphology. A local flow analysis is imperative in understanding pathologies implying hemodynamic factors and in optimizing the prosthesis design. [ABSTRACT FROM AUTHOR]

There are five members of the RFX family of transcription factors in mammals. While RFX5 plays a well-defined role in the immune system, the functions of RFX1 to RFX4 remain largely unknown. We have generated mice with a deletion of the Rfx3 gene. RFX3-deficient mice exhibit frequent left-right (LR) asymmetry defects leading to a high rate of embryonic lethality and situs inversus in surviving adults. In vertebrates, specification of the LR body axis is controlled by monocilia in the embryonic node, and defects in nodal cilia consequently result in abnormal LR patterning. Consistent with this, Rfx3 is expressed in ciliated cells of the node and RFX3-deficient mice exhibit a pronounced defect in nodal cilia. In contrast to the case for wild-type embryos, for which we document for the first time a twofold increase in the length of nodal cilia during development, the cilia are present but remain markedly stunted in mutant embryos. Finally, we show that RFX3 regulates the expression of D21ic, the mouse orthologue of a Caenorhabditis elegans gene that is implicated in intraflagellar transport, a process required for the assembly and maintenance of cilia. In conclusion, RFX3 is essential for the differentiation of nodal monocilia and hence for LR body axis determination. [ABSTRACT FROM AUTHOR]

The authors have studied three polyethylene terephthalate filaments from the same manufacturer. The results of the dyeing process depend on the filaments' characteristics. Dyeing modifies the macromolecular organization according to the manufacturing process. To understand the dyeing influence, each filament is subjected to a heat treatment that reproduces the effect of dyeing. The organizational molecular modifications are determined by x-ray diffraction and viscoelasticimeter measurements. The study shows that drawing and shearing align macromolecules, affecting the crystallinity. The crystallinity of a trilobal filament and of a microfilament are almost identical whatever the heat treatment. The less significant drawing of a circular filament provides a more amorphous and more sensitive filaments for heat treatment. Super-drawing induces the existence of macromolecular segments of a great mobility. Moreover, a heterogeneity of the organization is detected at the glass transition point. [ABSTRACT FROM AUTHOR]

The article describes a concept of heart valve prosthesis, based on the use of textile material. The goal of the work is to make a fabric prosthesis by using woven yarns made up of polyester. The method for prothesis manufacturing is described. Fabric prosthesis shows encouraging behavior in vitro such as good flexibility, reduced permeability with adapted fabric parameters.

The article examines the nature of morphological changes induced by ageing on polyethylene terephthalate fibers extracted from explanted prostheses. The method for testing a commercial Warp-knitted prosthesis is described. It was found that the implantation involves a transformation of the original crystalline structure as shown by the modulate differential scanning calorimetry scans of yarns extracted from different prostheses.

The article reports on the development of a device that is able to follow the total constraint in the textile structure, the field of deformation of a face and the thermal losses generated in the filaments by friction and deformation in vascular textile prostheses (VTP). The construction of the device on a classical dynamometer is described. Load-elongation curves provide a general knowledge of the mechanical properties of the prostheses.

Focuses on a study which utilized mechanical analysis to predict rupture sites on vascular prostheses. Materials and methods; Results; Discussion and conclusion.

Presents information on a study which examined the deformation and degradation mechanisms of expanded polytetrafluoroethylene materials. Materials and methods; Results; Discussion and conclusion.