Vascular prostheses -

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About Vascular Prostheses

Background
Vascular grafts are used to replace, bypass or maintain function of damaged, occluded or diseased blood vessels in small, medium and large diameters. This can be achieved through harvesting of blood vessels from the patient's own body (autogenous grafts) or through the use of manufactured prostheses (artificial grafts). Vascular prostheses are manufactured from synthetic, biological or biosynthetic materials. Most of these prosthesis materials are available for use in peripheral bypass and for arteriovenous (AV) access, however, there are limitations specific to each alternative.

The performance of vascular prostheses is measured, amongst other parameters, by the length of time they remain open. This is called patency. The autogenous grafts, represented by veins and arteries, continue to be the mainstay of vascular bypass procedures for long-term performance. The artificial prostheses are deployed when autogenous vessels are unavailable or insufficient for small diameter requirements. There are numerous pharmacological adjuvants included at the time of implantation and subsequently to maintain function of the artificial vascular grafts.

Synthetic prostheses are usually made from PTFE or polyester (Dacron). Biological prostheses may be either allografts or xenografts. Allografts are blood vessels from humans e.g. cadaveric blood vessel grafts, removed varicose veins or human umbilical vein grafts (HUVG). Xenografts are of animal origin e.g. blood vessels such as the bovine carotid artery and bovine mammary artery.

Dacron prostheses
Dacron grafts are made from knitted or woven polyester. They originally required pre-clotting before implantation but are now often produced with a resorbable coating to avoid this. Dacron is very susceptible to infections and bacteria can adhere to the polyester. Dacron grafts sometimes have a silver additive as an anti-bacterial agent. The resorbable coating is designed to be replaced by host tissue in order to ‘heal’ the graft. The continued growth of the host tissue into the vessel reduces the available lumen of the graft. Dacron grafts are mainly used for larger vessels and some above-knee bypasses.

PTFE prostheses
PTFE prostheses [PTFE=polytetrafluoroethylene, e-PTFE = expanded PTFE] are the most commonly used prostheses for peripheral bypass and AV access. e-PTFE is a porous material and requires tissue ingrowth to heal the graft but this process eventually contributes to occlusion of the lumen. e-PTFE also bleeds through suture line needle holes during implantation and ‘seeps’ after implantation which may cause seromas that can be a site for infection. Puncturing a PTFE graft for AV access creates a hole in the graft that often takes a long time to stop bleeding.

Pure biological prostheses
Pure biological prostheses can come from a range of different sources, e.g. human umbilical veins or bovine veins, arteries or even ureters. These prostheses are by-products from other processes and consequently recovered in less than perfect conditions from abattoirs and hospitals. They have in common that they normally have good bio- and haemocompatibility but since they consist of dead tissue with low levels of collagen available for cross-linking they often exhibit poor durability and strength. Attempts have been made to overcome this by reinforcing them with a loose supporting polyester mesh. Very few of these products are available on the market.

Biosynthetic prostheses
Biosynthetic prostheses are made by integrating a biological component that gives good bio- and haemocompatibility with a synthetic component that gives strength and durability. Due to the composite construction, biosynthetic prostheses demonstrate good short- and long-term patency as well as resistance to infections and a low rate of aneurysm formation.

Read more about the features of biosynthetic prostheses

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