There is a steadily increasing importance of implants used as substitutions for body functions which have been impaired due to disease, natural abrasion or accident. With the present state of the art, the limitations for the application of surgical substitutions are due to insufficient properties of biomaterials with regard to specific applications as well as to deficiencies in design and function of the implants used. The basis for the improvement and new development of implants is therefore a functionally adequate design in which the specific properties of the material are taken into account with regard to the individual requirements of the implantation site. For orthopedic implants, materials have to be developed which are to a large extent corrosion and degradation resistant, and withstand high mechanical stress. For implants in the cardiovascular system, compatibility with blood is most significant. Present research in this field is concentrated on efforts to improve the thromboresistivity of conventional polymers by different kinds of surface treatments. One possibility is to influence actively the electrochemical interactions between material and blood components, e.g. by the use of redox catalysts.