Study On The Processing Of Knit-structural Artificial Tracheal Stent And Its Properties

Stenosis, complete obstruction or other defects of trachea may occur due to trauma, tumors, granulomatous disease, and long-term endotracheal intubation. The usual clinical practice is to connect the two ends together in surgical operation after cutting off a length of pathological trachea. A tracheal prosthesis has to be implanted to the site of injury to keep the trachea continuous and flowing smoothly as the length of pathological trachea exceeds 50mm-60mm. Over the past years, great efforts have been made to develop new surgical methods and techniques for tracheal reconstruction; but due to various reasons, the research work up-to-date in this field is still far from satisfaction.Being an important achievement and development resulted from interpenetration of various sciences and technologies at the end of 20th century, tissue engineering is a perfect combination of polymeric material science, biology and engineering science which offers biological substitutes necessary for the impair of tissues and improvements of their functions. Thanks to the use of medical stents, much progress has been made in the structures relevant to cardiothoracic surgery including trachea.After selection and evaluation of the constituent biological materials, a knit structured composite artificial tracheal stent fabric with adequate radial strength was fabricated from poly(glycolide-lactide)(PGLA) multi-filament and polypropylene (PP) filament, the developed artificial trachea was composed of three different layers with the stent in the middle, the Collagen(Col)/Hydroxyapatite(HA) composite on the outer layer and the PU membrane on the inner surface. This tracheal prosthesis is characterized by composite structure and possesses excellent biocompatibility and bioactive properties.Before the stent fabric knitting process, the author first studied plating technology both theoretically and experimentally. Due to circular knitting machines of different diameters, the yarn feeding locus is different during knitting; for small diameter circular knitting machine, there is few knitting system, thus the central angle subtended by each knitting system is comparatively bigger. The yarn extending from feederto the knocking-over needle will wrap the cylinder, so the yarn feeding locus and the corresponding equation between big diameter and small diameter circular knitting machine is different.In this paper the yarn feeding locus equation were obtained and corresponding drawings were made from the calculation results with Matlab language. It proved that the yarn feeding locus is quite different when plate knitting on small diameter and big diameter circular knitting machine. In addition, the influences of yarn properties on plated fabric quality were also studied.Investigations into the knittability of PGLA and PP filament on a small-diameter circular knitting machine were conducted and the optimized knitting parameters for producing tubular stent fabric were obtained. Factors affecting the covering relationship of plating stitch were analyzed and plate-structured tubular fabrics with PGLA on the technical front and PP on the technical back were knitted. Preferable coating procedure, coating solution concentration were also studied; finally a two-step fabrication method was adopted and a series of knit structured composite artificial tracheal stent samples were made.Tensile tests were carried out in the wale and course directions of composite specimens to examine their stress-strain curve, initial elastic modulus and ultimate strength; Radial compressive tests of various composite stent were also carried out in a specially designed Radial Strength Tester. It is found that by altering fiber volume content, properties of constituent yarns and radius of the composite stent, its radial strength can be further improved.Basic information about the radial strength decreasing process of two types of knitted stent was obtained through simulation in vitro biodegradation tests. Animal tests were performed in mongrel dogs, the results shows that knitted artificia...