IN-VIVO PERFORMANCE OF THE POLYESTERURETHANE VASCUGRAFT(R) PROSTHESISIMPLANTED AS A THORACOABDOMINAL BYPASS IN DOGS - AN EXPLORATORY-STUDY

Among the various prototype vascular prostheses that have been develop ed over recent years as small vessel substitutes, the Vascugraft(R) po lyurethane device produced by Braun-Melsungen AG has a number of attra ctive features. As well as having high mechanical compliance similar t o that of the arterial tree, it has been manufactured from a specially synthesized poly(ester urethane) with improved biostability and its m icrofibrous structure provides a highly porous wall with open communic ating pores. With a view to evaluating the in vivo biofunctionality an d biostability of this prosthesis in the dog, 10 mm diameter grafts we re implanted as thoraco-abdominal bypasses for prescheduled periods of 1 month and 12 months, and their performance monitored in terms of gr oss morphology, histology and the measurement of the chemical and phys ical properties of the explanted and cleaned specimens. Both grafts we re patent at retrieval. Each had a smooth and glistening flow surface without organized mural thrombi and showed the development of a thin c ollagenous internal capsule with the presence of endothelial-like cell s. Both grafts were well encapsulated externally and revealed a small distal bend or kink which is frequently observed by any thoraco-abdomi nal bypass in dogs. The fresh explanted prostheses were cleaned by a n ew enzyme treatment which provided specimens for microscopic, mechanic al and thermal analyses, as well as studies of the surface and bulk ch emistry. By comparing the results from the explanted and cleaned mater ial with those of the virgin prosthesis, we have observed some deterio ration in the integrity of the microfibrous structure, some loss in me chanical performance, marginal changes in molecular weight, and an app arent microphase separation of the hard and soft segment domains at a depth of a few mu m. While the biofunctionality of a 10 mm calibre dev ice has been demonstrated, additional in vive studies are recommended to assess the biofunctionality at different diameters and the biostabi lity over longer periods of implantation.