into the surrounding tissues. Metals face corrosion related problems, and ceramic coatings on metallic implants degrade over time during lengthy applications. Ceramic/ceramic composites enjoy superiority due to similarity to bone minerals, exhibiting biocompatibility and a readiness to be shaped. The biological activity of bioceramics has to be considered under various in vitro and in vivo studies. Performance needs must be considered in accordance with the particular site of implantation. Processing Technically, ceramics are composed of raw materials such as powders and natural or synthetic chemical additives, favouring either compaction (hot, cold or isostatic), setting (hydraulic or chemical), or accelerating sintering processes. According to the formulation and shaping process used, bioceramics can vary in density and porosity as cements, ceramic depositions, or ceramic composites. Porosity is often desired in bioceramics including bioglasses. Towards improving the performance of transplanted porous bioceramics, numerous processing techniques are available for the control of porosity, pore size distribution and pore alignment. For crystalline materials, grain size and crystalline defects provide further pathways to enhance biodegradation and osseointegration, which are key for effective bone graft and bone transplant materials. This can be achieved by the inclusion of grain refining dopants and by imparting defects in the crystalline structure through various physical means. A developing material processing technique based on the biomimetic processes aims to imitate natural and biological processes and offer the possibility of making bioceramics at ambient temperature rather than through conventional or hydrothermal processes [GRO 96]. The prospect of using these relatively low processing temperatures opens up possibilities for mineral organic combinations with improved biological properties through the addition of proteins and biologically active molecules (growth factors, antibiotics, anti-tumor agents, etc.). However, these materials have poor mechanical properties which can be improved, partially, by combining them with bonding proteins. Commercial usage Common bioactive materials available commercially for clinical use include 45S5 bioactive glass, A/W bioactive glass ceramic, dense synthetic HA, and bioactive composites such as a polyethylene–HA mixture. All these materials form an interfacial bond with adjacent tissue. High-purity alumina bioceramics are currently commercially available from various producers. U.K. manufacturer Morgan Advanced Ceramics (MAC) began manufacturing orthopaedic devices in 1985 and quickly became a recognised supplier of ceramic femoral heads for hip replacements. MAC Bioceramics has the longest clinical history for alumina ceramic materials, manufacturing HIP Vitox® alumina since 1985. Some calcium-deficient phosphates with an apatite structure were thus commercialised as "tricalcium phosphate" even though