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.
Late fiber deterioration in Dacron arterial grafts.
The occurrence of late fiber deterioration was examined in 493 Dacron arterial prostheses. Grafts implanted were of four types: 137 Meadox Wesolowski Weavenit (WN), 71 Golaski Microknit (MK), 70 USCI Sauvage(Tm) external velour non-crimped (EVNC), and 215 USCI Sauvage external velour random-crimped (EVRC). Prostheses had been implanted for three to 15.3 years; no defects were detected prior to three years. Deterioration occurred in 15 of 493 grafts (mean incidence: 3%). Between 4.9% and 5.8% of patients had graft deterioration-nearly the same incidence in all four types of grafts. Deterioration consisted of thinning and breakage of yarn filaments, causing development of holes and, in some cases, graft dilatation. Dilatation did not always precede filament breakage. Broken filament ends were either tapered or square-ended, suggesting that modes of breakage. Tensile strength tests howed that fibers sometimes weakened nonuniformly within a specimen. Fiber breakage was associated with crimp ridges. The findings suggest that manufacturing variations probably reduce fiber resistance to mechanical fatigue. Other contributing factors may include storage conditions, sterilization methods, handling, and the degradative effects of tissue fluids and enzymes.
Tridirectional X‐Ray Patterns of Oriented Film at Wide and Small Angles
Drawn, oriented film of polyethylene terephthalate was studied by means of an x‐ray diffraction technique in which the x‐ray beam was directed in three mutually perpendicular directions: (1) through the film, (2) and (3) in the plane of the film, parallel and normal to the direction of draw. Patterns were obtained in each of these directions for the diffractions occurring at both small and large angles. This combination of patterns provides a picture of the film's polymer texture with these parameters: size, orientation, and arrangement of crystallites; extent of amorphous material; shape of microvoids. In this film the crystallites have planar orientation and are 45 A wide in the plane. A long period of 125 A exists in the direction of draw and is comprised of 75‐A crystallite length and 50‐A amorphous material. There is evidence that the film is composed of lamellae about 60 A thick; these lamellae are stacked in a staggered arrangement such that the crystallites in one lamella are adjacent to the amorp...