Morphological, physical and chemical evaluation of the Vascugraft arterial prosthesis: comparison of a novel polyurethane device with other microporous structures.

In this study the morphology, physical properties, surface chemical characteristics and microstructure of the Vascugraft arterial prosthesis have been investigated. This is a novel microporous polyurethane device, recently developed by the company Braun-Melsungen AG in Germany for use as a small calibre arterial substitute. This comparative study included two other synthetic grafts: the Mitrathane prosthesis, a hydrophilic prototype polyetherurethane urea graft with closed internal pores, and the commercially successful expanded polytetrafluoroethylene reinforced Goretex prosthesis with an open microporous structure. The Vascugraft prosthesis contains a network of fused microfibres of varying thickness and orientation which provide open and communicating pores similar in size to those in the Goretex material. In addition, they extend from one side of the graft wall to the other. As well as having superior longitudinal and radial compliance to the reinforced Goretex device, the Vascugraft prosthesis has more than adequate bursting and suture retention strengths. Through the use of contact angle measurements, electron spectroscopy for chemical analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry and molecular weight analysis by size exclusion chromatography, the surface of the Vascugraft prosthesis has been shown to be uniquely hydrophobic, as well as containing carbonate groups within an aliphatic polyesterurethane polymer. In addition, variations in micro-phase separation structure of hard and soft segment domains between different sizes and batches of product are marginal. Because of the interesting physical and chemical properties, it is recommended that in vitro biocompatibility and biostability studies be undertaken prior to using the prosthesis in animal or clinical trials.

Hydrophobic and fibrillar microporous polyetherurethane urea prosthesis: an ESCA study on the internal and external surfaces of explanted grafts.

The ESCA study gives a good qualitative and quantitative elemental analysis of internal and external surfaces of foreign materials. Microporous hydrophobic Mitrathane (a polyetherurethane urea) grafts were implanted as blood conduits in dogs for up to 6 months. Surface analysis of explanted grafts demonstrated the presence of different contaminants: sodium, chlorine, silicon, in patent grafts, i.e. those implanted for 1 month and less. The sulphur probably comes from the presence of proteins on the surface of the polymer and the high level of nitrogen is also protein-related. At 6 month implantation, the grafts were occluded and a decrease of proteins on the surface was observed. The values of N/C and O/C ratios are also reported. For the virgin material, these ratios correspond to the quantity of hard and soft segments; but, for the explanted grafts, these parameters are also influenced by the presence of proteins due to the Versaclean washing which did not wash away all the proteins on the surface of the polymer. The SEM photographs showed a certain degradation of polyurethane after 6 month of implantation. However, by ESCA study, it is difficult to compare the surface of virgin and explanted grafts because it is masked by the presence of proteins.