Biomaterials science examines the mechanical, physical and chemical properties of materials as well as the complex host responses to introduced bulk material, material surface and biomaterial applications. Biomaterials science has been officially defined as “the study and knowledge of the interactions between living and non-living materials”, and biomaterial as “a material intended to interface with biological systems to evaluate, treat, augment or replace any tissue, organ or function of the body” (Williams et al. 1992).
The development of modern biomaterials is related to the development of modern medicine and new materials. Stainless steel and cobalt chromium alloys were the first materials successfully used inside the body for fracture fixation. In the early 1960s, Sir John Charnley made the first attempt to link together a stainless steel hip prosthesis and high-density polyethylene with metachrylate bone cement. This can be considered the beginning of modern orthopedics, in which the development of better materials plays a central role. In the late 1960s, the excellence of titanium was discovered in medicine (Branemark et al. 1969). At that time, some materials began to be classified as “biomaterials”. Various materials (polymers, ceramics, composites and metals with improved properties) and applications (orthopedics, vascular and heart surgery, etc.) have been developed since then. Today, there are a great number of different professions dealing with the problems associated with biomaterials, and the cross-scientific approach is essential.
There are international organizations which give recommendations and standards for the manufacturing and testing of biomaterials (ISO= International Standards Organization, ASTM= American Society for Testing and Materials). There are also national organizations that supervise biomaterial applications in human use. One of the best known and most demanding control organizations is FDA (Food and Drug Administration of USA) (Brown et al. 1996). It must be pointed that FDA does not regulate the materials used in medical devices, but rather the devices themselves. The biocompatibility of the material is a central factor in devices intended for use inside the body. Biocompatibility has been officially defined as “the ability of a material to perform with an appropriate host response in a specific application” (Williams et al. 1992). There are two main factors that determine the biocompatibility of a material: the host reactions induced by the material and the degradation of the material in the body environment. When evaluating the biocompatibility of the nickel-titanium shape memory metal alloy, both of these must be considered.