Molecular weight characterization of virgin and explanted polyester arterial prostheses.
The macromolecular properties of 17 virgin commercial arterial prostheses and a series of explanted prostheses, both manufactured from poly(ethylene terephthalate) (PET) yarns, have been studied by gel permeation chromatography (GPC) and by differential scanning calorimetry (DSC). Only small differences were found between the average molecular weights and the degree of crystallinity of the unused reference grafts. A broadening of the DSC curves was observed for the prostheses containing texturized yarns compared with those made solely from flat, untexturized yarns. This broadening may be due to greater heterogeneity of the crystal sizes caused by the texturizing process and to the use of two or more different yarns with dissimilar thermal histories in the same prosthesis. Average molecular weights of the explant series were significantly lower than those of the corresponding reference grafts but almost time independent. The polydispersity index and the degree of crystallinity of the explants remained constant as a function of time. These results are discussed in regard to others available in the literature.
Effect of infections on the degradation of polyethylene terephthalate implants.
The macrokinetics of degradation of polyethylene terephthalate (PET) protheses removed from patients were investigated. Two types of protheses were analysed in dependance on polymer environment: 15 patients were characterized as normal, with post-operation periods of 1-10 years and 7 patients were operated at different times after implantation having a bacterial environment around the implants. The tensile strengths, surface morphology and molecular mass of these samples were compared. The macrokinetics of the PET degradation have been described. The presence of bacteria characterized by acid pH accelerates the loss of tensile strength and molecular mass in the PET corresponding to the mechanism of the polymer matrix destruction. The protheses not subjected to infection have been degraded on the surface. The experimental values of the rate constant may be used for lifetime prediction of the polymer implants in the human body under different conditions.
Regional strategies for the minerals industries of the states of the SADCC
The SADCC has been in existence for eleven years but little progress has been made in regional coordination of the minerals sector even though this sector is the most important exporter of the region. There is however scope for minerals development at the regional level.