A Prosthesis is a device that is used to overcome surgically some deficiency in the body, perhaps caused by the necessary surgical removal of diseased tissue. This implies that the prosthetic device must perform the function for the rest of the life of the patient. Reinforcement in contrast may be temporary or permanent depending on need and the ability of the relevant tissue to regenerate . The most common prostheses are made from synthetic fibers specially Teflon and polyester. (5)
The implantable material must meet mechanical requirements for the particular application biocompatibility for examples requires that the biotextiles must interact, with the host in a controlled and predictable way. In addition to these blood cells cause formation of destructive blood clothe. Important application of textiles as implant is vascular wall,( artery and vein) The Vasculature consists of arteries, arterioles capillaries, venues and veins . Arteries carry blood away from the heart to all parts of the body, (38) where arteries are made up of layers of smooth. Muscle fibers and elastic membrane tissue. Arterioles carry blood into capillary tissues ,(39) capillaries , the smallest vessels , through which exchange take place between the blood and the tissues, whereas veins carry blood back to the heart .(40)Vasculars grafts based on permeable. Textile structures are now a widely accepted technology. The performance of the graft is largely dependent on the ability to allow controlled blood to flow through its thickness . yet predicting this flow rate is still not widely understood
Vascular grafts have only been a practical reality for about 30 years , surgical techniques and prosthetic technology have been developed rapidly and allowed life and limb saving surgical interventions that many people take for granted , consider that there was no successful surgical for replacement of the aortic aneurysm until synthetic grafts became available.(41) Artificial veins or arteries are used to replace segments of the natural cardiovascular system that are blocked or weakened . Grafts are inserted to bypass the blockages and restore circulation .(4)
Types of vascular grafts
Vascular grafts maybe biologic or synthetic.
There are three categories of biologic grafts which are autologous grafts ,Allografts and heterografts
Autologous grafts (tissues taken from one part of the body and moved to another part )
Allografts or homografts are tissue from one person transplanted into another . (42)
Heterografts are tissues from another species that are transplanted into a human .(43)
Synthetic vascular grafts are produced from polyester or polytetrafluoroethylene (Teflon) with either woven or knitted structures, as parallel, tapered and bifurcated tubes. The grafts normally incorporate a coloured line along the length of the graft to assist the surgeon in avoiding introducing twist into the graft as it is implanted.
The ideal graft
The ideal graft should last a life time and permit blood passage without clotting or infection .(44) The rate should be as close 100% as possible and it should show more compliance . The vessel that is used in replacing.(45) The grafts should be easy to manufacture and store impervious to blood leakage to prevent excessive blood loss and the development of perigraft hematoma , which can interfere with healing and promote infection .(46) Porosity may be essential for fabrics and other biological grafts
prostheses are crimped as an attempt to resist kinking . The crimps effectively reduce the diameter by about 10% , since the wall of the prostheses is stiff , there will be an impedance at both ends of an insert and in consequence – loss of pulsatile energy .The difficulty is that it is not possible to control or measure accurately all the variables that affect the success of this process , despite all problems, large bore prostheses are very successful when used in appropriate circumstances. There is a reason for this success that is probably the velocity of flow is high and only a very small preparation of the blood flowing through the tube ever comes into contact with the wall
Success of prostheses may be claimed on the basis of complication that can be attributed to the prostheses itself and continues to allow blood flow (this does not necessarily mean good function)