Artificial blood vessels

Artificial blood vessels are tubes made from synthetic (chemically produced) materials to restore blood circulation. During World War I (1914-1918) French-American surgeon Alexis Carrel (1873-1944) perfected a procedure for sewing the ends of blood vessels together. This achievement that won him the 1912 Nobel Prize in medicine. Carrel also made artificial blood vessels with tubes of glass and aluminum.

The most successful artificial blood vessels in use today come from surgical techniques developed in the 1940s and 1950s. To replace damaged or diseased arteries or veins, surgeons initially transplanted arteries or veins from donors, but these transplants frequently failed. In some cases the donor arteries were rejected by the recipient, while in other cases the vessels developed arteriosclerosis ("hardening of the arteries"). Transplanting vessels from the patient's own body was problematic because two surgeries were required, one to harvest the needed vessel and a second to tranplant it. Furthermore, many patients with circulation problems had no suitable vessels that could be transplanted.

To overcome these problems, researchers began to experiment with synthetic blood vessel materials such as polyethylene (a soft and waxy plastic) and siliconized rubber (rubber formed with silicone). These synthetic fabrics showed the most promise.

Synthetic Materials Outperform Natural Ones

A porous material called vinyon, which had been tried on dogs, was first used by A. B. Voorhees on humans in 1953. A variety of synthetic fabrics were subsequently used in experiments; of these, the plastic Teflon and synthetic fiber Dacron proved to work best. Blood vessels made from these synthetics are not rejected by the body's immune system, and the materials are easily available and extremely durable.

While large Dacron blood vessels work very well, small ones have a tendency to become blocked by clots. Researchers are working on ways to make the interior walls of these small synthetic vessels smoother, thus preventing clot formation.

Hybrid Vessels

In the early 1980s chemist Donald Lyman of the University of Utah (Salt Lake City) synthesized a polymer (a plastic formed by long chains of carbon molecules) that had two advantages. Due to a high attraction for albumin (the protein in blood serum), Lyman's polymer reduced clot formation. The polymer also exhibited more elasticity (stretchiness), thereby reducing strain at the site where the natural and artificial vessels were surgically joined. Research Industries of Salt Lake City began testing Lyman's vessels on humans in 1988.

Surgeon David Annis of the University of Liverpool (England) produced a similar flexible, smooth-walled plastic vessel and also began human trials in the late 1980s. In 1990 Organogenesis (a bio-research company) of Cambridge, Massachusetts, began animal testing of its living blood vessel equivalent, which is a hybrid (specialized combination) of natural and artificial materials. This artificial vessel features a smooth inner layer grown in the laboratory from human cadaver (dead body) artery cells and tubules strengthened with Dacron mesh. Another approach worked out by Stuart Williams at Jefferson Medical College, Philadelphia, Pennsylvania, uses cells from the patient's own inner blood vessel lining to grow a lining on the inside of Dacron synthetic vessels.