Biomaterials are defined as substances or combinations of substances, other than drugs, synthetic or natural in origin, which can be used for any period of time, as a whole or as a part of a system which treats, augments, or replaces any tissue, organ or function of the body. There are in general terms two types of biomaterials, those which are 'inert', accepting that this is not strictly possible in the way this is understood in chemistry, and those which are 'bioactive'. In both cases there must be a degree of acceptance by the body, expressed as the biocompatibility of the material, a very complex concept involving biochemical, cellular, and mechanical interactions between the implanted material and the living tissues. In most cases there is a response to the implanted biomaterial from the organism and the control of this is one of the major areas of research.
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