Artificial organs are materials or devices designed either for implantation in or use outside the body, to replace functions that have been lost through disease or injury to major organs. Artificial organs may be used to take over the full-time functions of organs or as a bridge to a transplant. Artificial organs include such permanent devices as tubes made of various synthetic materials to replace diseased arteries and metal replacements for diseased or injured hip sockets or other joints, and the heart-lung machine, which takes over the function of those two organs during open heart surgery.
When organ failure is irreversible, the best long-term solution (if possible) is organ transplantation. However, demand for organ transplants far exceeds available donor organs, and patients may die while waiting for a transplant. A device such as the artificial kidney, a machine that is connected externally to filter wastes from the blood of patients who have impaired kidney function, can be a temporary measure until a suitable donor kidney is found. The artificial kidney can also function as a long-term replacement, as in cases of chronic uremia. The device consists of a semipermeable membrane package into which the patient's blood flows in a continuous circuit from and to blood vessels in the arm or leg. The membrane filters wastes from the blood to a circulating fluid that flows outside the membrane compartment and is discarded. The process, called "hemodialysis," is undergone three or more times each week, for four to six hours per treatment. There are approximately 500,000 people worldwide who are sustained by maintenance dialysis.
The hemodialysis techniques were quickly adapted to the heart-lung machine, which removes carbon dioxide and adds oxygen to blood circulating outside the body. This machine provides surgeons with the time needed for complex heart surgery. The technology of the heart-lung machine has been adapted to create an "artificial lung," which for periods of up to several days is able to sustain patients with acute lung disorders who are likely to recover.
This type of treatment has become a mainstay of treatment for premature infants with underdeveloped lungs.
Artificial heart valves and cardiac pacemakers have been implanted in many people with heart disease. Permanent artificial heart transplants were tried beginning in 1982 but have been discontinued because of lack of success. Artificial hearts are still used temporarily as a bridge until a human heart becomes available for transplant. Research teams continue to refine artificial heart designs for eventual human use.
Among the other artificial organs available are the artificial larynx, or "voice box," an electrically powered device used externally, and the cochlear implant, an electrode or electrodes implanted in the cochlea of the inner ear of some profoundly deaf adults and children with undamaged auditory nerves (see hearing aid). Artificial skin made of animal protein fiber and silicon has been developed for burn victims, and blood substitutes have had limited use in patients who cannot accept natural blood. Artificial bladders and ureters can replace bladders lost to cancer.
Research continues in bioartificial organs, in which a synthetic membrane encloses functioning human or animal cells, permitting a naturally functioning organ to do its job, yet protecting it from rejection by the body. Experiments are focusing on replacing the liver, the insulin-producing cells in the pancreas, and the adrenal cells in Parkinson disease patients and on stimulating nerve cell regrowth.