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.
Failure of Dacron prostheses caused by structural defect.
Intrinsic prosthetic failure is quite uncommon since the advent of Dacron prostheses. Only 24 cases of arterial prosthetic failure have been described in the literature. Our experience consists of two additional failures of knitted Dacron prostheses. The first patient developed aortojejunal fistula due to a defect of the aortic prosthesis 6 years after resection and replacement of an abdominal aortic aneurysm. The analysis of the graft revealed a defect in the form of a dropped stitch, which caused a weak spot where the prosthesis was able to be torn apart longitudinally. The second patient had femoropopliteal bypass and 6 years later developed degeneration with aneurysmal formation of the entire length of the prosthesis. Optical microscopy of this prosthesis exhibited mostly transverse failures which were coincident with valleys of the corrugated prosthesis. This was indicative of a defect that rendered the corrugation root too weak to withstand normal arterial pressures. This presentation emphasizes the seldom and serious complication of prosthetic failure due to defect of the prosthetic material. Details of scanning electron microscopy of the prosthesis, clinical presentation, angiography, and pathological findings with treatment also are discussed.
Application of 2μm Tm Laser on Biomedicine
Continuous wave Thulium laser emits at wavelength of 2.0 mm, which is well suited for tissue ablationand thermally stimulating cutaneous nerves due to its high absorption by water. 2 mm laser can be transmitted suffi-ciently by common quartz fibers and it is safe for eyes. A brief introduction of principle of 2 mm CW Tm Laser is giv-en, analyzing the photothermal modeling of thulium laser-tissue interaction, comparing 2 mm CW Tm Laser with tradi-tional laser.