Fundamental study on small-diameter vascular graft incorporated with new design concepts of mechanical compatibility and tissue morphogenesis.

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In order to minimize compliance mismatch between native artery and arterial graft prosthesis over the entire pressure regions, we proposed a coaxial double tubular artificial graft, which consists of an enhanced compliant inner tube and a less compliant outer tube, both of wihch were fabricated using well-controlled multiply micropored segmented polyurethane (SPU) films. Double tubular grafts were coaxially assembled by inserting the inner tube into the outer tube.Firstly, the pressure-diameter (P-D) relationship of canine common carotid arteries, which exhibited a "J" curve, was determined as a targeted artery. Two determinant variables, the pressure-induced distensibility of each tube and the intertubular space distance, were defined and formulated in several models of coaxial double tubular SPU grafts, which had various intertubular space distances, micropore densities and wall thicknesses. Tire distensibility of the inner tube determined the distensibility in the low-pressure regio … More ns, which was adjusted using wall thickness and microporosity. Thinner films with higher porosities resulted in a high pressure-induced distensibility. On the other hand, a low pressure-induced distensibility in the high-pressure regions was realized using an outer tube with a thicker wall and lower microporosity. The transition point from low- to high-pressure regions was determined by the intertubuiar distance using the theoretical values. On the basis of these results, we presented a prototype model of a coaxial double tubular graft that exhibited well-matched compliance with canine carotid artery.The graft was coaxially assembled by inserting the high-compliant inner tube (coated with photoreactive gelatin mixed with heparin) into the less-compliant outer tube (coated with photoreactive hydrophilic polymer). Twenty-eight coaxial double-tubular compliant grafts were implanted into the canine common carotid arteries up to 12 months in end-to end fashion. The overall patency rate was 85.7% (24 / 27). and neither rupture nor aneurysmal formation was observed. The neoarterial wall was reconslructed form the anastomoses into the luminal surface and into the imer-tubular space of the double-tubular graft, mainly with the myofibroblasts and inflammatory cells in the early stage and collagen-rich extracellular matrices in the late stage of implantation. Adhesion was prevented on the surface of the outer tube with the hydrophilic polymer coating. Although the "J" curve of the implanted prototype model was preserved at 1 month-implantation, the tissue ingrowth, the tissue-adhesion and the biodegradation of the SPU films were clarified to affect the mechanical property of the implanted coaxial double-tubular graft in the late stage. Less