Permeability versus porosity in microporous small-diameter vascular graft made by a "spraying, phase-inversion technology"

Porosity is a key feature in synthetic small-diameter vascular graft (SDVGs) design and development. To manufacture porous SDVGs we used a novel technology called spraying, phase-inversion (SPI) which raises the question of how to evaluate the porosity of these grafts. Stiff grafts made of Dacron and PTFE are traditionally evaluated by water permeability (WP). However, grafts made by SPI feature a filamentous, sponge-like structure and therefore the relationship between WP and porosity is not known. To investigate this issue WP was evaluated by measuring the volume of de-gassed water filtering through the graft wall, at 120mmHg of pressure, in one minute. SEM digitized slow-scan imaging was used to estimate the percentage of luminal and external surface open area. By an image analysis system a grey value threshold was applied to discriminate open from closed area and to calculate their surface ratio. Preliminary data indicate a direct correlation between WP and percentage of open area.