gap always exists between the material performance generation of new molecules along with the release during in-vivo animal tests and clinical situations, of substances from a multitude of cells. The plasma because of the difference in individual reactions proteins (including coagulation and complement proteins), the blood cells deposited on the material between one animal and another and humans. Likewise, sophisticated in-vitro and in-vivo models surface or circulating in the blood stream and their are being developed to study living body responses. released substances take part in the dynamic process of fibrinolysis and thrombus formation. Progress has been achieved in culturing mammalian cells, particularly human cells, which has lead to new in-vitro models to study cell-biomaterial Tissue response interactions. These techniques are discussed in the other chapters of this volume. Materials implanted in tissues always generate a response. The major tissue response in the extra BIOLOGICAL MODIFICATION vascular system is an inflammatory process, which may be induced chemically or physically. Many Surfaces of polymeric biomaterials may be modified proteins and cells are involved in this very complex by using a variety of biological entities (e.g.
