Biomaterials are materials that are used or that have been designed for use in medical devices or in contact with the body. Traditionally, they consist of metallic, ceramic, or synthetic polymeric materials, but more recent developments in biomaterials design have attempted to incorporate materials derived from or inspired by biological materials (e.g., silk and collagen). Often, the use of biomaterials focuses on the augmentation, replacement, or restoration of diseased or damaged tissues and organs. The prevalence of biomaterials within society is most evident within medical and dental offices, pharmacies, and hospitals. However, the influence of biomaterials has reached into many households with examples ranging from increasingly common news media coverage of medical breakthroughs to the availability of custom color noncorrective contact lenses.
The evolving character of the discipline of biomaterials is evidenced by how the term biomaterial has been defined. In 1974, the Clemson Advisory Board, in response to a request by the World Health Organization (WHO), stated that a biomaterial is a ''systemically pharmacologically inert substance designed for implantation within or incorporation with living tissue'' (1). Dr. Jonathan Black further modified this definition to state that a biomaterial is ''any pharmacologically inert material, viable or nonviable, natural product or manmade, that is part of or is capable of interacting in a beneficial way with a living organism'' (1).
An National Institute of Health (NIH) consensus definition appeared in 1983 and defined biomaterials as ''any substance (other than a drug) or combination of substances, synthetic or natural in origin, which can be used for any period of time, as a whole or as a part of a system that treats, augments, or replaces any tissue, organ, or function of the body'' (2). Thus, relatively newer definitions of the term biomaterial recognize that more modern medical and diagnostic devices will rely increasingly upon direct biological interaction between biological molecules, cells, and tissues and the materials from which these devices are manufactured.
HISTORY OF BIOMATERIALS
Compared with the much larger field of materials science, the field of biomaterials is relatively new. Although there exist recorded cases of glass eyes and metallic or wooden dental implants (some of which can be dated back to ancient Egypt), the modern age of biomaterials could not have existed without the adoption of aseptic surgical techniques pioneered by Sir Joseph Lister in the midnineteenth century and indeed, did not fully emerge as an industry or discipline until after the development of synthetic polymers just prior to, during, and following World War II. Prior to World War II, implanted biomaterials consisted primarily of metals (e.g., steel, used in pins and plates for bone fixation, joint replacements, and the covering of bone defects). In the late 1940s, Harold Ridley observed that shards of poly(methyl methacrylate) (PMMA), from airplane cockpit windshields, embedded within the eyes of World War II aviators did not provoke much of an inflammatory response (3). This observation led not only to the development of PMMA intraocular lenses