Biomaterials are deϐined as “materials intended to interface with biological systems to evaluate, treat, augment, or replace any tissue, organ or function of the body” [139]. The range of applications is vast and includes things such as joint and limb replacements, artiϐicial arteries, and skin, contact lenses, and dentures. This increasing demand arises from an ageing population with higher quality of life expectations. The use of artiϐicial biomaterials for the treatment of diseased tissues traces back to more than 2000 years ago, when heavy metals such as gold were extensively used in dentistry [111]. Other early examples of biomaterials include wooden teeth, but generally, the ϐirst generation of biomaterials developed before 1960 had low success rates due to a poor osseointegration. An entirely new ϐield of research was initiated in the 1952 [121]. Professor Per-Ingvar Brånemark’s serendipitous discovery

of osseointegration occurred during vital microscopy studies in rabbits. He and his team found that titanium oculars placed into the femurs of rabbits could not be removed from the bone after a period of healing. The ϐirst practical application of osseointegration was the implantation of new titanium roots in an edentulous patient in 1965. Brånemark implant methods and materials are one of the most signiϐicant scientiϐic breakthroughs in dentistry since the late 1970s. Table 3.1 gives examples of material properties and their relevance to biomaterials [5, 15, 16]. In general, the physical properties play an important role only in the case of special functional applications such as heart pacemaker electrodes. Good chemical and biological properties are a prerequisite for application as a biomaterial as mentioned above. The most important mechanical properties for highly loaded implants such as hip endoprostheses are fatigue strength and Young’s modulus, which leads to the deϐinition of the biofunctionality BF as the ratio of the fatigue strength σf to Young’s modulus E [5]:

BF = σf/E (3.1) Biomedical materials can be divided roughly into three main types governed by the tissue response: (i) inert (more strictly, nearly inert) materials illicit no or minimal tissue response, (ii) active materials encourage bonding to surrounding tissue with, (iii) degradable, or resorbable materials are incorporated into the surrounding tissue, or may even dissolve completely over a period of time. Metals are typically inert, ceramics may be inert, active or resorbable and polymers may be inert or resorbable. Table 3.2 provided some examples of biomaterials. A comparison of the biofunctionality of various alloys shows the exceptional properties of titanium and titanium alloys due to their low Young’s modulus (Fig. 3.1).