Some readers will remember the 1970s television show “The Six Million Dollar Man,” whose hero, Col. Steve Austin, had amazing powers of strength, agility, hearing and sight because of having been rebuilt with artificial parts after an accident.

Prostheses are devices used to replace a missing body part or to enhance the performance of an existing part. One of the earliest known examples is a wooden toe found on a 3,000-year-old Egyptian mummy. After eyeglasses, false teeth were perhaps the most common early prosthetic devices, writes Stephanie Pain in the June 16 issue of New Scientist. She says that the first artificial teeth were carved from bone and ivory but these soon decay. Human teeth became in demand for dentures, and scavengers prowled the battlefields of Europe, extracting teeth from dead soldiers to sell to denturists. This practice began to decline in 1837 when porcelain was invented.

Today, writes Joon Bu Park in his book “Biomaterials,” if the patient’s tooth cannot be used, a high-strength ceramic crown is fixed to a post, which screws into a sleeve implanted in the jawbone. But teeth are the exception to the general rule that prosthetic devices down through the years were made from nonbiological materials.

Mitch Jacoby, in the Feb. 5 issue of Chemical & Engineering News, says that more than 10 million Americans carry a major implanted medical device and that the worldwide market for artificial devices exceeds $50 billion annually. These include such diverse materials as stainless steel and chromium alloys used for hip replacements and bone fractures, Teflon and Dacron blood vessels, ceramic bone cement, and silicone polymers in contact lenses. In his book, Park illustrates an amazing variety of prostheses, including intricate hip, knee, elbow and finger joints.

No prosthetic device has gained more notoriety than the total artificial heart. Kevin Murray and Don Olsen cover TAHs in a chapter of the book titled “Biomaterials Science: An Introduction to Materials in Medicine,” where they list TAH research up through 1985. The longest survival was 619 days using a so-called Jarvik heart. TAHs will likely be used as a desperation measure for the foreseeable future but related devices, such as the implanted defibrillator or pacemaker, are becoming routine.

Yet there are problems associated with the huge artificial prosthetic market, says Jacoby. For one, medical device designers have a restricted number of materials to choose from, such as metals, plastics, ceramics and composites. Also these often cause a mild foreign-body response at the implant site and, unless designed as a permanent implant, a second operation is required to remove them. Jacoby quotes Joachim Kohn, a chemistry professor at Rutgers University, as saying a new generation of materials is needed that are biodegradable with the products absorbed into the body, that do not cause an antibody response, and, ideally, can speed up the body’s repair.

One of the first materials to fit the criteria, says Jacoby, was an organic acid called PGA that was used as a suture in the 1970s. PGA degrades quickly in a water environment with the products absorbed by the body. Since those early days, great strides have been made in biopolymers. Robert Langer, a biomedical engineer at MIT, has produced a polymer which he shaped to resemble a rib cage and placed around the heart of a child born with severe chest deformities. The cage was seeded with cartilage cells and, over time, new cartilage built a protective shield around the heart while the artificial rib cage was gradually absorbed by the body.

Much of today’s research is focusing on materials that can work in conjunction with the body to facilitate the healing process rather than simply function as a replacement part. Robert Service, in the Sept. 1, 2000, issue of Science, reports on a plastic that can be injected into a fracture where it forms a porous matrix. If seeded with bone cells, new bone grows as the matrix gradually breaks down and is excreted. One day this may play a vital role in the 450,000 surgical bone grafts performed in the United States annually.

A somewhat similar process takes place in a breast reconstruction method described by Marina Murphy in the May 26 issue of New Scientist. A biodegradable scaffold is implanted in the breast and fitted with a “vascular loop” that generates blood vessels to supply breast cells induced to migrate to the area. The result is a “blob of tissue” that maintains the breast structure as the scaffold disappears. The only problem is the danger of cancer cells migrating to the scaffold if the original breast tissue was lost to disease.

Finally a futuristic prosthetic device operated by brain waves may one day make communication possible for people locked in paralyzed bodies by accident, stroke or disease. A team of German researchers reported in the March 25, 1999, issue of Nature that patients can be trained to use brainwave patterns called slow cortical potentials of the electroencephalogram to control an electronic spelling device. They explain that the alphabet, divided into two columns, is shown on a computer screen. The patient operates the computer by electrodes attached to the scalp and chooses one column or the other by means of the EEG brain responses. The column is then divided and the process repeated until a single letter is chosen. A person can select about two letters per minute by this method but even this is a major advance for people who are completely paralyzed. The first general use model is at least a decade away.

Clair Wood taught chemistry and physics at Eastern Maine Technical College for more than 10 years.