More than 430,000 Americans with heart disease require coronary artery bypass surgery each year, and up to 200,000 suffer from critical limb ischemia, or clogged arteries in the leg--one of the major causes of amputation. In the 1940s and 1950s, techniques were developed to surgically transplant blood vessels by grafting sections of arteries or veins to replace diseased or damaged portions of other vessels. These transplants were frequently unsuccessful--donor arteries often were rejected by the recipient or quickly developed arteriosclerosis, while transplanting vessels from the patient's own body required two surgeries and many patients had no suitable vessels for transplantation.
To overcome these problems, researchers began to experiment with synthetic blood vessel materials. During World War I, French-born surgeon Alexis Carrel had tried using tubes of glass and aluminum, and later attempts were made with polyethylene and siliconized rubber. Results from all these experiments indicated that synthetic fabric was most likely to be successful. A porous material called vinyon was tried on dogs, and A. B. Voorhees used this for the first time on humans in 1953. Many other synthetic fabrics were subsequently experimented with; Teflon (Gortex is an example of a Teflon-based fabric) and Dacron proved to be best. Blood vessels made from these synthetics are not rejected by the body's immune system, and they 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 so clots won't form. Chemist Donald Lyman of the University of Utah synthesized a polymer in the early 1980s that had both a high affinity for albumin, which reduced clot formation in synthetic blood vessels, and elasticity, which reduced strain at the juncture of the natural and artificial vessels. Research Industries of Salt Lake City began testing Lyman's vessels on humans in 1988. Surgeon David Annis of the University of Liverpool produced a similar flexible, smooth-walled plastic vessel and also began human trials in the late 1980s. In 1990 Organogenesis of Cambridge, Massachusetts, began animal testing of its living blood vessel equivalent which featured a smooth inner layer grown in the laboratory from human cadaver artery cells and tubules strengthened with Dacron mesh. Another approach worked out by Stuart Williams at Jefferson Medical College, Philadelphia, uses cells from the patient's own inner blood vessel lining to grow a lining on the inside of Dacron synthetic vessels.
In 1997, Jeffrey Isner in Boston announced successful gene therapy for generating new blood vessels. Injecting a growth-factor- producing DNA into a patient's leg muscles instructs existing vessel cells to create new blood vessels which bypass the clogged vessel. In 1998, Thomas-Joseph Stegmann of Germany announced a similar development through protein therapy by genetic engineering of human growth factor FGF-I which, when injected near a blocked vessel in the heart, created a new vascular system. On a three- month follow-up of patients in his clinical trial, no blockages had formed in the new vessels. Also in 1998, Nicholas L'Heureux and his team in San Diego succesfully engineered human tissue without synthetic scaffolding, creating an entirely new replacement blood vessel from human cells able to withstand 20 times the normal human blood pressure.
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