Radial Compliance Study Of Woven Vascular Grafts

As one of the earliest used commercial products, woven vascular grafts have been widely used in research and clinical use. But one serious disadvantage of them is that the radial compliance cannot match with that of native arteries. Studies showed that compliance mismatch gave rise to various transplant complications, especially in the anastomosis. Compliance mismatch may cause thrombus arising, lumen thickening, arteriosclerosis forming, leading eventually to the failure of grafts transplant. Radial compliance demonstrates the radial deformation behavior responding to the pulse pressures. It can be calculated from the diameter-pressure relations and can also be showed from the strain-stress curves since radial compliance is reciprocal to tensile modulus. Compliance mismatch between woven vascular grafts and native arteries contains two aspects:the value and the deformation behaviour of radial compliance. The truth is that the compliance of woven vascular grafts is much lower than that of native arteries. Moreover, woven vascular grafts do not possess the diameter-pressure variation similar to native arteries. While native arteries deform easily under low pressures and hard to deform under high pressures, woven vascular grafts do not have similar deformation variation responding to the pulse pressures. Previous studies showed that bilayer structure is promising to overcome compliance mismatch. When bilayer structure grafts are stretched in radial direction, the inner tubular fabric will extend until it contacts with the outer one. After that both tubular fabrics extend together. So the bilayer structure grafts will show lower modulus under low pressures while higher modulus under higher pressures.In order to improve and control the compliance of bilayer woven grafts, this work makes experiments on different factors which may influence the physical dimension and mechanical properties of woven tubular fabrics. Design and fabrication of bilayer tubular fabrics with different diameters and materials of each layer were made. Firstly, since weft tension is a factor that influences the woven tubular fabrics’ properties, this work modifies the existing shuttle structure to obtain uniform and controllable weft tensions during weaving. Secondly, this work uses three kinds of yarns (PET、PTT、PU) as wefts to fabricate single tubular fabrics which are different in weft tension and fabric weave. Analysis of influence of different factors to physical dimension and mechanical properties are made. Thirdly, the work includes the design and fabrication of bilayer tubular fabrics to study the influence of difference in diameter and material between the inner and outer layers.Results showed that, the diameter difference between the two tubes provides grafts with transition from low to high modulus.The modulus can be controlled by the choose of inner and outer tubes’ material: if their materials are the same, after-transition modulus is twice as much as before-transition; if the outer tube is of PET, and the inner is of PU, the ratio can be as much as twenty. The position of transition in tensile curves can be influenced by diameter difference. By designing different warp counts of two tubes, as well as applying various weft tension, the transition position can be controlled.