Three years experience with experimental implantation of fibrous polyurethane microvascular prostheses in the rat aorta

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Abstract
The results of a 3‐year study in which a series of 355 implantations of 1‐cm‐long fibrous polyurethane microvascular prostheses into the infrarenal aorta of the rat (group A) were evaluated with respect to patency and formation, structure, and fate of the neo‐intima. Rats were sacrificed at various intervals from 1 day to 2 years in order to obtain a time‐related impression of the reendothelialization and stability of the neo‐intima. A second series of 51 implants was done with prostheses 10 cm in length, placed in a 1.5‐cm loop in the abdominal aorta (group B). An overall patency rate of 92.7% was achieved in group A. Initially, eight technical failures caused early thrombosis of the prostheses. Sixteen prostheses became infected and subsequently occluded. The overall patency in group B was 52.9%, due to kinking from adhesion formation and normal growth of the rat. In both the long and short prostheses, a continuous multilayered neo‐intima developed, growing from the aortic stumps into the prosthesis from both sides. According to the growth rate of 0.3 mm/day, a 1‐cm prosthesis was reendothelialized after ± 20 days and a 10‐cm prosthesis after ± 9 months. Once developed, the neo‐intima, consisting of myofibroblasts and smooth muscle cells covered with a flat endothelium, remained stable and continuous, throughout the observation period. The neo‐intima was firmly anchored onto the prosthetic wall by means of cellular protrusions extending between the polyurethane fibres. The significance of rapid healing of an implanted prosthesis is emphasized with respect to preventing (late) hematogenous, endogenous infection of the prosthesis. It is concluded that in this type of fibrous polyurethane prosthesis, a new lining is rapidly developed and will remain stable and permanent for a long period of time. Further investigations, using other species, are strongly recommended, with a goal of clinical application of this type of prosthesis.