Tissue Engineering Of Prosthetic Vascular Grafts PDF Download

The demand for small-diameter blood vessel substitutes has been increasing due to a shortage of autograft vessels and problems with thrombosis and intimal hyperplasia with synthetic grafts. To design a feasible vascular graft, biocompatibility and comparable mechanical behaviors to natural tissues are two essential requirements. In this study, various types of small-diameter vascular grafts made of natural silk fibroin and synthetic polymers, including thermoplastic polyurethane (TPU) and poly-L-lactide (PLLA), by braiding and electrospinning techniques will be introduced. Market-available degummed silk fibroin yarns were incorporated in a braiding and coating process with a lab-extracted fibroin solution to produce vascular grafts with adjustable mechanical properties. By altering the braiding and winding patterns and the type of yarn, braided fibroin tubes were able to reach artery-like mechanical performance. Natural silk fibroin possesses the characteristics of biocompatibility, low- or non-immunogenicity, relatively slow proteolytic degradation, robust mechanical properties, and low thrombogenicity that make it a promising material for vascular engineering. Two types of customized collectors have been developed for the electrospinning process to fabricate vascular grafts that mimic the structure of elastic layers and collagen fibers in natural blood vessels. The materials used here were blends of natural fibroin and synthetic polymers at different ratios to leverage their bioactivity and tunable mechanical properties. The first type of collector was a striated collector with grooves and ridges that created the continuous aligned-random fibrous sheet for producing tubular grafts with alternating aligned- and randomly-oriented layers. The other collector was an assembled rotating collector for generating grafts with circumferentially-aligned wavy fibers due to the dynamic "jumping rope" collecting process. Electrospun fibers were collected by a mandrel with changeable diameters during and after the electrospinning process to generate a continuous wavy-flat alternating structure in the circumferential direction. Small-diameter vascular grafts fabricated in this study exhibited similar mechanical behaviors to natural blood vessels. Vascular cell culture tests verified the ability of lab-extracted fibroin in promoting cell activities and the feasibility of commodity-grade degummed silk yarns in medical applications after sufficient cleaning. Cell responses on fibroin/TPU electrospun grafts also presented positive results with high cell viability, adhesion, and migration