Fabrication of microporous thermoplastic polyurethane for use as small-diameter vascular graft material. I. Phase-inversion method.

Fabrication conditions of microporous thermoplastic polyurethane to be used in small-diameter vascular grafts are studied. Porosity variations due to various factors such as concentration of PU solution, composition of coagulation bath, effect of coagulant temperature, and effect of dissolved air in PU solution are discussed. The liquid-liquid phase-inversion process used for preparation of PU films and the mechanism for the formation of microporous films are discussed. Surface and cross-section morphologies of PU films are studied with the use of scanning electron microscopy (SEM), and porosity value and mechanical strength of PU films are also determined. SEM photomicrographs show that PU films prepared in an alcoholic coagulant have uniform porous structure compared to films prepared in water coagulant. Increasing the polymer concentration and coagulant temperature (>23 degrees C) decreases the macrovoid formation, as seen in cross sections of PU films. This enhances the tensile modulus of PU films. By using this process adjustment may be made on the morphology and compliance, as they are important factors in design and fabrication of small-diameter vascular grafts.