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Polymer Science and Engineering: The Shifting Research Frontiers
found in tendons, cartilage, blood vessels, skin, and bone. Elastin, an elastic substance found in ligaments and in the walls of blood vessels, is also a protein. Other polymers such as polysaccharides are also important. They make up chains of sugar units present as a major constituent in all connective tissue. Ribonucleic acid (RNA) molecules also carry information and can serve protein-like functions. Thus informational, chemical, mechanical, and other properties of living systems find their origin in the molecular structure of their component polymers.
Medicine, as a biological science, therefore must be dependent on the nature of polymers. Bandages and dressings are dominated by polymers in modern practice. Molds and impressions of teeth, dentures and denture bases, adhesives, and fillings are polymer based. Sutures, which were made of cat gut for over 2,000 years, are now made of synthetic polymers. Hard and soft lenses required after cataract surgery, artificial corneas, and other ocular materials are all polymers. Orthopedic implants, artificial organs, heart valves, vascular grafts, hernia mesh, and artificial arms, legs, hands, and feet all depend critically on polymeric materials. Similarly, catheters, syringes, diapers, blood bags, and many other trappings of modern medicine depend heavily on polymeric materials. Most of these items arrive in sterile form, packaged in polymers.
Significant quantities of polymers are used in medical devices, consumable medical products, and the packaging for medical products. The most common products are devices such as catheters and intravenous lines, nearly 100 million of which are used annually in the United States. Because medical products use functional rather than structural polymers and their value is not related to the volume they occupy, medical products should be quantified on the basis of number of functional units rather than in terms of pounds of polymers.
Polymers are natural allies of medicine because living tissue is composed substantially of polymers. As our understanding of the processes of life advances, and our ability to tailor synthetic polymer structures to specific chores matures, the power of medicine will grow dramatically. The opportunities for collaborative programs involving materials scientists and medical researchers and practitioners are unlimited. Few, if any, areas of research offer more obvious benefits to society.
Medical devices generally entail intimate contact with living tissue. Organisms are extremely sensitive to the presence of foreign substances and are aggressive in repelling an invading object or agent. To date, empirical means have provided considerable progress in finding materials that are less offensive to living organisms. Polyesters, polyamides, polyethylene, polycarbonate, polyurethanes, silicones, fluorocarbons, and other familiar polymers have been employed successfully in medical applications. Establishing the factors controlling the biocompatibility of these materials is a difficult process that has been only partially defined. Materials experimentation in medical applications has always called for courage as well as technical know-how, but in this litigious era the problems are amplified. Even so, progress continues on a broad front.