Effect of fabric s
Effect of fabric structure on its properties
The vascular prostheses are formed by woven , knitted Gore- tex ,complex weave and nonwoven – knit. Procedures are designed to provide an open lattice structures through which fibrous connective tissues can grow. (22) Grafts usually have a tube shape, the most widely used fibers are polyester and expand PTFE . Polyester vascular grafts can be woven , knitted , braided or extruded.
The surgeon in avoiding introducing twist into the grafts as it implanted , woven constructions were made as a double cloth on narrow fabric loom to give a circular shape. Mostly plain weave is used with yarns between 50-150 denier. The most important property of a graft is its porosity , woven graft structure are typically less porous than knitted structures which diminishes blood leakage through the interstices ,(4) besides that woven grafts are strong and stiff, this stiffness makes it harder to handle because it does not conform to the tissue and is harder for the surgeon to suture .(43)
The woven double – velour differs from smooth walled structure in that, the employment of an addition set of textured yarns . The velour graft is softer to handle, moreover, The velour components allow reduction in fabric tightness without diversely effecting permeability, and it provides better attachment to surrounding tissues .(99) Woven fabrics offer the greatest strength , making them more suitable for high stresses . Typical water permeability of woven grafts are 50-500cc /cm2/min.knitted prostheses are usually made of single jersey structure on weft knitting whereas Rachel structure is used in warp knitting .Velour structure has a rougher inner surface to encourage better adhesion of the thrombus layer. The roughened surface may be obtained by raising a nap, by knitting a looped pile or by using textured filament yarns . Knitted structures are too porous to be used in the machine state so they get compacted by chemical swelling agents or thermal processing . (5) Typical water permeability of knitted grafts is 1.000-2.000 cc/cm/min in order to prevent leakage , knitted grafts with internal and external velour surface have been developed , Warp knit grafts and warp knit graft dilated less than the weft knit graft