Use PTT Fibers To Improve Radial Compliance Of Woven Vascular Prosthesis

In the past 30 years, the design and manufacture of vascular prostheses have been a big challenge in this field. Development of successful small diameter arterial grafts (less than 6 mm) is still the challenge in modern vascular surgery. A major cause for poor performance and no long-term patency of such small diameter prostheses has been shown to be the lack of radial compliance. Radial compliance is the structural property of a tube that expresses a dimensional change in response to a change in intraluminal pressure. All prostheses in general have lower compliance than those of host arteries and woven PET prostheses, in particular, have the lowest compliance and do not have the pressure-diameter change property of arteries at all. At the lower pressure, the wall of arteries deforms easier while it shows small deformation under higher pressure, and the slope of the pressure-diameter curve has obvious turning point which is from lower to higher. The mismatch in compliance plays an important role in the transplant complications, especially in the anastomosis. Mismatch in compliance at the end-to-end anastomosis of a compliant small diameter artery and rigid prostheses increases the probability of thrombus and causes intimal hyperplasia, the formation of atherosclerosis in the end of blood vessels and ultimately prosthesis failure. The study of compliance especially for woven vascular prostheses is almost none, although it is the urgent problem currently.In order to improve compliance of woven vascular prostheses, the material, weave and structure are considered.This study uses poly(trimethylene terephthalate) (PTT) filament yarns which is the same family with PET filaments, featuring lower elastic tensile modulus and good elastic recovery to increase the compliance of woven vascular prosthesis. The tests of mechanical properties of PTT filaments shows that PTT filaments have better mechanical properties used to weave vascular prostheses which could satisfy the need as the biomaterial used for woven vascular prosthesis. Vascular prostheses with PTT filaments as weft yarns show larger compliance compared to PET samples,The influence of weave parameters on the elastic modulus and compliance is analyzed using samples with different parameters. The models of elastic modulus and compliance related to weave parameters are built using least square method. The yarn thickness, Young’s modulus, weave floating length and fabric counts have influence on the tensile properties. The strongest determinant factor that will influence compliance and Young’s modulus of woven tubular prosthesis is yarn properties.According to the structure and mechanical properties of arteries, the bi-layer woven vascular prosthesis is designed to match the compliance property of vascular. PTT filament yarns are used as the circumferential yarns in the inner layer to increase the distensibility of the inner prosthesis wall and polyester (PET) filaments form the outer layer to provide a stronger prosthesis wall. From the surface of the bi-layer woven vascular prosthesis, it can be seen that there is an obvious circumferential difference of the two layers in filling direction. Every two connected points, the outer layer is crimping which can be seen exactly and the surface of inner layer is even and plain. With the stitched weave, the crimp of outer layer is along the filling direction to create the circumferential difference.The compliance of bi-layer samples is almost equal to that of PTT samples before the pressure of 120 mmHg. In the higher pressure zone, the compliance of bi-layer samples is lower than PTT samples and higher than PET samples. Therefore, the compliance of bi-layer samples shows good responsiveness with the change of pressure.Due to the first use of PTT filaments instead of PET filaments as weft yarns to improve compliance of woven vascular prosthesis, the biostability and biocompatibility of PTT materials should be studied. The biostability experiments were done in the NaOH solution, PBS neutral buffer and enzymatic papain solution. The accelerated degradation test shows that the weight loss of PTT fibers is lower than that of PET samples. SEM photographs show that there are pits on the surface, and with the progress of degradation the frequency and depth of pits are all increased. There are fewer pits on the surface of PTT fibers. The diameter of PTT fiber decreased less than that of PET fibers, and compared to the diameter of controlled samples, it increased. After 9 weeks degradation in PBS and papain enzyme solution, the properties of samples have little change. The tensile property test shows that the tensile modulus of samples is decreased after degradation in all conditions, which is related to the decrease of crystallinity and conform change of trimethylene glycol conformers during degradation. Therefore, PTT fibers are more stable in alkaline solution, but less stable in PBS neutral buffer and enzymatic papain environments compared to PET fibers. With the increase of temperature, the more evidence of degradation such as weight loss, pits on the surface could be seen. The factors have the same effect on the properties of PTT and PET fibers. The MTT assay was used to investigate the cell compatibility of PTT. The study shows that Human Dermal Fibroblast cells could grow on the PTT materials and there is no obvious difference compared to cells on PET materials.The fatigue property of PTT vascular prosthesis which is one of the most important properties also should be analyzed. The accelerated fatigue test shows that the changes of the properties, such as fabric densities, tubular diameter and porosity all show the evidence of fatigue. Form SEM photographs the damage on the surface of yarns could be seen. The more fatigue cycles, the more evidence of fatigue could be seen. In addition, samples with PET filaments as circumferential yarns fatigue more easily and faster than the PTT counterparts. Therefore, PTT could be a better candidate for woven vascular prostheses in terms of fatigue properties than PET.