Introduction: Vascular grafts are implanted daily, whether it is as leg or coronary bypasses or as arteriovenous shunts. Autologous blood vessels are the gold standard but have limited availability while synthetic materials are prone to thrombosis, intimal hyperplasia and infections. To overcome these limitations, our team produced a biological Tissue-Engineered Vascular Graft (TEVG) woven from yarn of Cell-Assembled Extracellular Matrix (CAM). This textile-based approach is very versatile because it gives fine control over the geometrical and mechanical properties of the TEVG. The goal of this study is to establish how changes in production parameters (e.g.: yarn count, yarn density, etc.) affect the properties of the TEVG (e.g.: mechanical properties, wall thickness, surface waviness, etc.).
Methodology: CAM sheets were produced by sheep dermal fibroblasts seeded in 225 cm2 flasks and cultured in DMEM/F-12 with 10% FBS and 0.5 mM Na L-ascorbate. Threads were cut with a custom motorized device composed of rolling blades spaced at the desired width (5 mm). Woven grafts were assembled on a circular loom and composed of a series of longitudinal threads, called “warp”, and a circumferential one that spiraled along the length of the vessel, the “weft”. The latter was made of two threads twisted together at 5 revolution/cm. The effects of yarn thickness and warp count (number of longitudinal threads) were tested. The influence of weft thread production parameters and its tension during weaving were also studied. Transmural permeability, suture retention strength, compliance and burst pressure were evaluated. Geometrical properties including TEVG inner diameter, wall thickness and graft lumen surface profile were assessed macroscopically and by X-ray microtomography. For each condition, n=3 TEVGs were woven.
Results: A lower yarn thickness decreased wall thickness and suture retention strength. A lower warp count had the same effect on wall thickness, while the compliance increased linearly with a decrease in warp count. In addition, the surface profile, which may have an impact on cellular infiltration and blood compatibility, was influenced by both parameters. Narrower weft ribbons decreased weft diameter which resulted in thinner walls and TEVGs with lower strength. Finally, a lower tension in the weft during weaving resulted in a significantly higher compliance while burst pressure was decreased.
Conclusion: We have demonstrated the influence of a number of parameters on the geometric and mechanical properties of a TEVG woven from CAM yarn. Investigation of the influence of weft twist is underway to improve our control over the properties of the TEVG, focusing on increasing its compliance. These results are helping to build a toolbox that will allow the production of the TEVG with the most relevant properties for implantations as an arteriovenous graft in sheep.